Applications in advanced polymer composite constructions

Chapter 8 APPLICATIONS IN ADVANCED POLYMER COMPOSITE CONSTRUCTIONS

8.1. Introduction The advanced polymer composite material is arguably the newest material to enter the construction industry but its utilization is growing rapidly. It is currently being used in many areas of civil engineering. The most highly developed application to date is the use of advanced composites in repair and upgrading of bridge decks utilizing the plate bonding technique, column wrapping and other support elements to improve their ductility, particularly for seismic resistance. Both epoxy- and vinylester-impregnated glass, aramid and carbon fibre materials are being used in construction after many laboratory tests have been undertaken to justify their utilization and to determine the ductility that can be achieved in older, non-ductile concrete systems. The more exciting application of advanced polymer composites is in the construction of new bridges and bridge deck replacement units. Research conducted throughout the world has resulted in the design of polymer-composite-material highway- and footbridges, polymer composite bridge decks and in polymer composite bridge enclosures. Furthermore, there is demand for piling, poles and highway overhead sign-posts. In piling applications the material has to withstand aggressive corrosive environment particularly in the splash zone in the case of marine piles. Likewise, highway overhead sign structures, poles and bridge columns have to retain their integrity in cold regions where salt is used for de-icing the roads. In addition to upgrading reinforced concrete bridge and building structures, advanced composites are being used in rehabilitation of masonry and brick structural wall systems. For instance, a single layer of carbon fabric overlay (predominately horizontal woven carbon fabric with epoxy resin composite) applied to each side of a structural wall with two layers in the toe region would help to double the inelastic deformation capacity in the critical punch direction. The reasons for the considerable increase in interest and use of advanced composites over the past few years are as follows. (1) Advances in lower-cost FRP manufacturing by pultrusion, resin transfer moulding, filament winding and the semi-automated manufacturing of large components. (2) Reduction in material demand in the high-priced defence industry, expansion of a high-competitive market for these materials in the sporting goods industry and prospects for large-volume use in the civil sector have led to new low-cost materials manufacturing. 221

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Advanced polymer composites and polymers in the civil infrastructure

(3) Development of new structural shapes and geometries which lend themselves to both function and manufacturability. (4) Designs of these new materials in conjunction with conventional structural materials rather than individual component replacement or complete advanced composite design (less expensive) have shown that technical efficiency can be achieved within competitive economic constraints. The following sections will describe and illustrate some buildings and structures that have been constructed using the advanced polymer composite material. It should be mentioned that the examples cited are not exhaustive and that other structural units and systems can be and have been manufactured using advanced polymer composites and polymer materials. These latter examples have been mentioned in particular sections of the book concerned with the material description and the systems which use them. These examples include the geosynthetic structural elements, soil nails and rock bolts. Some examples illustrated in this chapter have also been discussed in Hollaway and Head (2000), and in Hollaway and Spencer (2000).

8.2. New polymer composite building systems The polymer composite material and their various manufacturing methods do lend themselves to the development of building systems and building blocks. An example of a composite building system manufactured from an automated process is the Advanced Composite Construction System (ACCS). a cross-section of which is shown in Fig. 8.1. It was conceived and designed by Maunsell Structural Plastics. The ACCS construction consists of a number of interlocking fibre-reinforced polymer composite Maunsell plank units which can be assembled into a large range of different high performance structures for use in the construction industry. The system is manufactured by the pultrusion technique, discussed in Section 3.2.3, using isophthalic polyester resin and unidirectional, bidirectional and chopped strand-mat glass fibre reinforced for the main structural members. The production and material content of the ACCS plank are optimized to provide highly durable and versatile composites and, in addition, structures can be formed quickly from a small number of standard components. As the material is lightweight, transportation and erection on site is efficient. All site joints, which are adhesively bonded, are made to form a completely integrated monocoque structure. The thermal insulation standards match the very best in Europe and far exceed the new British Building Regulations. The rights to the manufacture of this system has now been passed to Strongwell USA. Fiberline ^ has developed a similar profile. The plank consists of a series of I sections with an integral top plate flange and open bottom flange. The unit is pultruded in one operation and has width and depth dimensions of 500 mm and 40 mm, respectively. The standard length of the panel is 6 m.

' Fiberline Composites A/S, DK-6000 Kolding. Denmark.

Chapter 8. Applications in advanced polymer composite constructions

Phf^k Croxs section

223

Canneciar Cross secfion

2310 Stn Beaffi Cross sectityn Kev m

80x80 mided commior 60S X W voided pkmk

Notes ii) Ail dimensitms are in miilimefre'i mi Aii vf>ids arc 80 x 76 mm Fig. 8.1. Cross-section of ACCS unit.

8.3. Building structures Composites have been used very successfully in specialized market sectors of the building industry where weight and corrosion resistance are important together with others where the architectural possibilities of moulded building panels have been exploited. Resins have been improved to provide good long-term performance and adequate fire resistance. In the past, manufacturing has relied heavily on the hand lay-up techniques with associated conversion costs and this has meant that composite structures have not often been competitive in price with those built using conventional materials. However, conventional building costs are rising fast because of the ever increasing labour costs fuelled by skilled labour shortages and the higher specifications for thermal insulation needed to improve energy efficiency. At the same time automated fabrication techniques for GFRP composite components linked to innovative designs for forming complete building structures from modular systems are offering much more cost effective solutions for complete building structures and ones in which greater architectural freedom of expression is possible. As environmental assessment of building designs develops, it is likely that these structures will be increasingly attractive because

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Advanced polymer composites and polymers in the civil infrastructure

of high insulation levels, low energy requirements during manufacture and the fact that the glass is theoretically recyclable. However, with respect to this latter point, it is more likely that the material would be ground to a coarse powder and used as a filler in a lower-grade composite (see Chapter 3, Section 3.3.15). A two-storey building structure has been developed using ACCS in which the wall and floors are bonded together to form an integral monocoque structure. Vertical ACCS panels in the walls, with suitable openings for doors and windows, form the vertical box carrying members and floors span between them and act as stiffening diaphragms to the vertical box structure. Floors can be ribbed slabs or a beam and slab form if the spans are large. Wall and floor components can be delivered flat-packed and are light enough to be handled by small cranes or robots. Connections are made by bonding and load continuity, between end sections, is achieved by bonded lapping sections, equivalent to bolted splice plates where bolts are replaced with adhesive. ACCS sections, 80 mm thick with a polyurethane foam core, have a thermal insulation U-value of 0.35 W/m^ K. This meets UK requirements for domestic buildings and offices. Buildings can be fitted with double-glazed windows with pultruded GFRP window frames and this then provides a largely integral glass structure with excellent thermal insulation and uniform temperature expansion characteristics. The GFRP overcomes the cold bridge effect and buildings have been found to be comfortable and have low running costs. Sections manufactured from GFRP and isophthalic polyester resins with a polyurethane foam core have been tested in a whole range of fire tests. The high glass content in each pultruded section means that heat is not conducted away from the fire source or through the panel thickness and the cellular configuration of the panels maintains load carrying integrity for long periods of time. Fig. 8.2 shows a prototype building structure of two-storey height using the ACCS; the building was used as site offices at the second Severn crossing. FRP composites have been used in the construction of a 123 m telecom tower in Santis Mountain, Switzerland. Self-supporting GFRP cylinders were used on the outer strengthening of the tower. The client had decided to heat the tower to eliminate any danger of falling ice during the winter season; the tower is located 2500 m above sea level. Large GFRP square panels with middle dome configuration were designed to resist wind pressure on the main structure which was built as a tourist attraction with lookout terraces. Because of the lightweight property of the GFRP the units could be transported to the summit of the mountain by cable-car. The non-magnetic characteristics of GFRP were essential for the functioning of a dish antennae which was installed within these panels. The Isogrid structure is an integrally stiffened structural membrane developed by NASA contractors over three decades ago (Isogrid Design Handbook, 1975). This structural form has since been successfully utilized in a variety of weight-critical applications such as launch vehicle structures (Kim et al., 1993). However, although it offers significant structural performance with relatively little material compared with a shell or sandwich construction, the isogrid is considerably more difficult and expansive to fabricate. The IsoTruss^'^^ grid structure (Jensen, 2000) has evolved from the Isogrid structure. This latter is a three-dimensional grid structure filament wound or continuously processed. The system takes advantage of the highly directional properties

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225

I

Fig. 8.2. Maunsell House Design using the ACCS Planks (photograph by kind permission of Maunsell Structural Plastics, Beckenham, Kent, UK).

of the advanced composite materials to produce an efficient and lightweight grid structure with a high stiffness and strength-to-weight ratio. The helical and longitudinal members which spiral around a central cavity, are repeatedly inter-woven, yielding a highly redundant and stable configuration. During the 1980s, at the University of Surrey, double-layer skeletal structural systems were developed in which the members were manufactured from pultruded tubes, and patented polymer composite nodal joint connections, for these members, were made by the injection moulded process using glass-filled polyester composite. Fig. 8.3 shows an example of this system. Fig. 8.4 illustrates the end cap which is bonded to the pultruded members to form connections at the nodal joints. Goldsworthy and Heil (1998) have introduced a new class of joint for composite structures. The joints have been called 'Snap' joints and are based upon an original fibre-architecture design that pays particular attention to interiaminar requirements for load introduction. The authors state that the current composite structures technology is locked into the past by using joining technology which works well for metals but which fails when considered from the standpoint of benefiting from the structural advantages of composites. By introducing the 'Snap' joint method, the authors are considering composites as artificial w^ood and state that composite designers should not copy the metal technology, as is common practice currently, but should return to the wood technologies. The main reason behind this argument is that bolts and rivets direct the connection forces to specific points thus causing high stress concentrations. Composites,

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Advanced polymer composites and polymers in the civil infrastructure

Fig. 8.3. A double-layer skeletal system manufactured from pultruded GFRP tubes.

unlike metals, have low bearing and interiaminar shear strengths and therefore, stress concentrations threaten the failure of the composite material at joints. The concept of 'Snap' joints for composites has the capability of distributing stress over a wide area of the joint. Consequently, the 'Snap' joint is the first of an entirely new generation of joints for composites, each of which has the ability to satisfy a specific set of design requirements. A 28 m tall transmission tower (Fasteneriess 'Snap' composite transmission tower) was erected in 1994 and extensive tests were undertaken on this structure (Goldsworthy and Associates, Inc., 1994). It is claimed that it completely outperformed the classical steel lattice structure. A small crew of only three people erected the structure within a day. Subsequent to the erection of this structure, four similar structures have been erected and located in coastal areas and have been completely maintenance free. 8.3.1. Applications ofFRP rebars and FRP dowels in concrete Applications of GFRP reinforcement in the UK include post and panel fencing where the material was chosen because it would not cause interference to sensitive electrical equipment. For the same reason, GFRP was used to reinforce the foundations for sensitive equipment in a London hospital. There have been similar applications in hospitals and mihtary installations in the USA, Japan and France. The first concrete footbridge in the UK to use GFRP rebars was constructed at Chalgrove in Oxfordshire. The bridge slab measured 5 m x 1.5 m x 0.30 m and was pre-cast using grade 40 concrete. Vibrating wire strain gauges and thermistors were cast

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227

Fig. 8.4. End caps for the pultruded members of the skeletal structure.

into the concrete and fibre optic sensors fitted to the slab to allow long-term monitoring of the bridge to take place. The bridge was also fitted with GFRP handrails. A number of bridges have been built using FRP rebars. The Oppegard footbridge Oslo, Norway, was built in 1997 on a golf course. It has a span of about 10 m and consists of twin-arched beams, with glass FRP main and shear reinforcement. In the USA, the McKinleyville bridge in West Virginia was completed in 1996 and has a length of 54 m with three continuous spans. Two types of GFRP reinforcing bars were used in its deck. In Canada, a number of beams of the five-span Taylor bridge in Headingly, Manitoba, were reinforced and prestressed with CFRP composite rods. In addition, various FRP materials were used in the deck slab and the safety barrier. Steel dowels currently used for highway pavement joints can cause severe deterioration of concrete due to the expansive forces experienced during oxidation of the steel over

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Advanced polymer composites and polymers in the civil infrastructure

time due to corrosion. A full size test programme was set up at the University of Manitoba, Canada, in 1997 to compare the behaviour of conventionally used epoxy-coated steel dowels with FRP composite dowels. In addition, a long-term field study was initiated at the Bishop Grandin Boulevard in Winnipeg, Manitoba (Eddie et al., 1998). From the laboratory test results it was found that there was no loss in joint effectiveness, indeed, GFRP dowels could have a higher joint effectiveness than ones manufactured from steel. 8.3,2. Prestressing fibre composite tendons A number of bridges have been built worldwide utihzing prestressed FRP tendons for the longitudinal beams and generally using FRP rebars for the unstressed concrete slabs. A total of five road bridges and footbridges have been built in Germany and Austria utilizing glass fibre composite tendons, Polystal (Wolff and Meisseler, 1993). The first highway bridge opened to traffic in 1986 was the Ulenbergstrasse bridge in Dusseldorf. The bridge is 15 m wide and has spans of 21.3 and 25.6 m. The slab was first post-tensioned with 59 Polystal prestressing tendons, each made up from 19 glass reinforced polymer rods of nominal diameter 7.5 mm. These tendons were anchored to a designed block and each tensioned to a working load of 60 kN; four tonnes of glass reinforced polymer prestressing tendons were used. This bridge has been monitored and test loaded periodically since it was opened. In Japan, where a total of ten bridges have been built since 1988 (Tsuji et al., 1993) and (Noritke, 1993), the emphasis has been on the development of carbon and aramid fibre tendons. Carbon fibre has also been used on one bridge in Germany and aramid fibre tendons for a cantilevered road-way in Spain, Casas and Aparicio (1990). One bridge in North America, at South Dakota, has been stressed using glass and carbon fibre composite tendons (Iyer, 1993), and a bridge in Calgary, Canada, has been built using carbon fibre composite strands (Anon, 1993). When glass fibre composite tendons are used as prestressing cables, care must be taken not to over-stress the tendons to a value greater than 25% of their ultimate strength. Stress-corrosion of GFRP tensile composites under low levels of sustained stress can occur.

8.4. Offshore structures Innovative technologies are required to meet the demanding challenges of the offshore oil industry to develop deep oil production. GFRP phenolic gratings provide the weight savings necessary for floating tension leg platforms as well as fire resistance with low smoke and low fume emissions. In this type of environment, weight savings are absolutely necessary as the structure should be as light as possible in order to optimize its weight, the drill pipes and the production equipment. The typical weight of a steel grating is 10-11 Ibf/ft^ (480-530 N/mm^) compared with a phenolic grating which weighs about 3.5 Ibf/ft^ (168.0 N/mm'). In the Gulf of Mexico, Strongwell (formally the Morrison Moulded Fibre Glass Company) have installed a well bay platform entirely from glass fibre reinforced

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229

Fig. 8.5. Walkways on an offshore platform manufactured by Strongwell (by kind permission of Strongwell, Bristol, VA, USA).

polyester which includes structural sections, gratings and walkways. The structure was designed as an access platform and therefore, is not subjected to heavy loadings. One of the main reasons for its use is its superior corrosion resistance thus eliminating maintenance costs. Furthermore, the reduction in weight compared with the more conventional materials was a significant selling point that is likely to lead to an increase on mobiles such as semi-sub and jack-up and drilling rigs. On another offshore project, Strongwell manufactured platforms using phenolic resin and glass fibre. The structural members of the platform were manufactured by the pultrusion process; Fig. 8.5 shows a view of this structure. In addition to the utilization of composites in the Gulf of Mexico, GFRP gratings, walkways and handrails have been installed by Shell Offshore in Brunei, by Total and Elf in Balikpapin and by AMOCO in the North Sea. These are believed to have been in the splash zone areas where the corrosion resistance of composites is seen as a decided advantage over steel walkways which, because of degradation, have to be replaced every three years. Fig. 8.6 shows Fiberline gratings being fitted to the AMOCO oil-rig before

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Advanced polymer composites and polymers in the civil infrastructure

Fig. 8.6. Fibreline grading systems of phenolic resin (by kind permission of Fiberline Composites, A/S Kolding, Denmark).

installation in the North Sea. Fibreline railing and grating systems of phenolic resin were used on the oil-rig for increased fire resistance. The gratings of reinforced polymer provide a low weight, high strength and an easy fit and assembly solution for site.

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Table 8.1 Comparison of dry and submerged weights of reinforced plastics and conventional steel drilling risers (Composites Offshore, 1998) Riser parameters: Riser length (m) Design internal pressure (bar) Internal diameter (mm)

1500 205 500

Water density (kg/m^) Internal fluid density (kg/m^)

1025 2000

Connector dry weight (2 flanges) (kg) Number of jointed sections

1000 78

Parameter

Comparison of buoyancy of composite versus steel risers in 1500 m depth Composite

Material density Wall thickness (mm) Material volume (m^)

1560 26.0 64.0

Steel 7850 15.9 39.0

Dry weight of material (kg) Dry weight of connectors (kg) Total dry weight (kg)

103,115 78,000 181,115

303,440 78,000 381,440

Submerged weight of material (kg) Submerged weight of connectors (kg) Total structural submerged weight (kg)

37,057 67,815 104,872

263,819 67,815 331,634

Throughout the North Sea, numerous pipeHnes run along the sea bed to carry oil and gas product from the production platform to the shore terminals. The pipelines are interlocked at sub-sea manifolds which are complex arrangements of valves and other control devices. To protect these manifolds, large steel frames with steel grating mesh panels are lowered into the sea over them. To reduce the effort needed to lift these frames into position offshore, GFRP gratings are being used to replace the steel ones. As competition for oil increases, oil companies are drilling in deeper water. Current deep-water oil completion and production technology utilizes steel riser systems that are heavy, require expensive tensioning and buoyancy systems and whose designs are often governed by fatigue considerations. Advanced polymer composite marine risers provide advantages over those of steel risers because of their superior mechanical properties for this specific task, including lightweight, fatigue resistance and improved thermal insulation. The overall platform production cost reductions are possible as a result of the lower weight and greater compliance of composite risers and improved system reliability. One of the major advantages of reinforced polymers for offshore designers is the submerged weight of the structural units compared with those of conventional steel. Table 8.1 compares the dry and the submerged weights of reinforced polymers and conventional steel drilling risers operating in 1500 m of water. It is based upon a half

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Advanced polymer composites and polymers in the civil infrastructure

metre internal diameter samples filled with drilling mud; a design requirement of 205 bar internal pressure is assumed. A composite system, comprising of 78 jointed sections of carbon fibre reinforced epoxy tube, would weigh 32% of the weight of steel equivalent in the depth stated; in air it would weigh 50% of that of steel. The submerged weight parameter is important, whether this is for the average mobile rig having only one riser for drilling or for rigs equipped with upto 40 production risers, the savings will be very substantial and will have a major impact on facility design. In addition, composite risers are less likely than steel to require buoyancy augmentation from additional buoyancy modules which are large and costly. Furthermore, where continuous coiled tubing is used for drilling rather than jointing pipes, operating reach with conventional steel pipe is limited to about 7.5 km. but by replacing steel drill pipe with composite material would extend the reach to over 10 km. Reinforced polymer composites also have the potential to replace other steel pipes and tubular members used in the offshore industry. Continuous pipes would probably be manufactured by the filament wound technique using high-grade epoxy resin reinforced glass or carbon fibres where the fibres are aligned to provide high hoop strength. Pipes would be linked with polymer material able to resist attack from hot hydrocarbons under pressure. Alternatively, the polymer composite can be used for liners inside conventional steel pipes. Industry is investigating the use of reinforced thermoplastic pipes for continuous length manufacture. Aramid fibre reinforced polyethylene pipes can be designed to have axial strength capacity; these pipes have already been used for onshore work and are now being investigated for the offshore sector. Fire resistance can be increased by the utilization of phenolic resin and exterior intumescent coatings. In addition to the use of polymer composites for risers, pipes and tubular members, there is a great potential for the use of this material in other offshore systems. The Norwegian Research Institute (SINTEF) considers that upto half of the steel tanks, accumulators and other vessels which are associated with offshore platforms could be substituted by polymer composite structures typically weighing 30% less than steel. This would greatly benefit the designers of deep-water platforms where the need for extra processes and other equipment on the platform deck can represent a very high dead-weight penalty. One area that has not been tapped yet in the offshore constructions is the primary load-bearing structure. Although the potential benefits of employing the polymer composite material for structural use are as great as those which pertain to risers, little investigative work has been undertaken in this area. It is clear that there are several dissuading arguments to the widespread use of composites for primary load-bearing structures for offshore use, these include the higher material and manufacturing costs and their relative lack of track record. The understanding of the short- and long-term durability of composites is not as well known as metals, particularly in an environment in which there are highly regulated safety issues and hence the tendency for designers to use materials that are familiar to them is understandable. Furthermore, the current safety-led regulations tend to be prescriptive, specifying in detail the equipment and technical solutions that are to be used. For example, fire specifications may needlessly

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restrict the use of composites, in-spite of the fact that some composites can outperform metals in a fire situation. However, there are signs that this rigid design approach is changing and that future performance-based regulations should increasingly require the designer to take responsibility by showing that any given composite is suitable for its intended application.

8.5. FRP composite marine piling In the early 1990s FRP composite piling was developed to provide a solution to the deteriorating piers and water front structures which were exposed to the harsh marine operating environments. FRP polymer composites provide an alternative construction material to the more conventional ones without many of their performance disadvantages such as rot, rust and degradation. Furthermore, the increase in number of marine borers, the environmental laws that limit the use of toxic treatments for wood and the banning of the use of traditional maintenance practices of lead-based primers for steels, have resulted in higher costs of replacement of the conventional materials. Polymer composite materials have resistance against aggressive environments as discussed in Chapters 2 and 3, and generally have low long-term maintenance costs and more economical life-cycle costs compared with timbers. Polymer composite materials have been used for marine retaining walls in applications which include docks, harbours, lakes, residual developments, rivers and streams and, in addition, in the heavier engineering applications such as structural piles for piers, docks and wharves. Furthermore, composite piles can be engineered to provide uniform and predictable strength and stiffness for bridge pier protection systems such as fender piles, organized in clusters to protect bridge piers from vessel collisions and floating debris. The pultrusion technique is currently the preferred manufacturing method using glass fibre reinforcement and a premium-grade polyester resin, containing an ultraviolet inhibitor to provide improved lifetime, thus giving the product corrosion resistance and required strength. Creative Pultrusions, Inc. Alum Bank, PA, USA, manufactures FRP composite sheet piles under their trade name SuperLoe™; Fig. 8.7a illustrates typical profiles for their GFRP sheet piles and Fig. 8.7b typical top-cap sections. The piles can be installed using standard piling installation equipment such as an impact hammer, vibrating hammer and water-jet equipment. It is an important requirement for FRP products particularly GFRP that all field-cut edges, drilled holes and abrasions are sealed with resin. The sealing operation of the cut edges prevents fraying of the fibres and prevents moisture getting to the interface between the fibres and the matrix. Hardcore Composites, Newcastle, DE, USA, manufactures large-scale FRP composite structures for the infrastructure including FRP composite piles. These tubular piles are manufactured as a cylindrical shell fabricated from high strength FRP composite material. To provide additional protection against abrasion, the outer surface of the shell of the hybrid pile could be coated with a rubber-toughened acrylic skin. The inner surface of the shell is textured to create a mechanical bond with the filler material, usually concrete. The pile would be filament wound as a hollow shell and then filled with

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Advanced polymer composites and polymers in the civil infrastructure

o 450mm

i-K=

450mm

(a) 265mm 200mm

IT

100mm

150mm

(b) Fig. 8.7. (a) Typical profile for a GFRP sheet pile (after Creative Pultrusions Inc., Alum Bank, PA, USA), (b) Typical top cap to FRP pile (after Creative Pultrusions Inc., Alum Bank, PA. USA).

concrete or other appropriate core material. The piling system then has approximately the same stiffness as a timber pile system but has 4 times the strength and 15 times more energy-absorbent capacity. The GFRP tubular piling is designed to resist tensile, compressive, shear and torsional stresses. The concrete filler carries the compressive load and enhances the bending performance. The resulting pile system then carries bearing and lateral loads whilst providing energy absorbing capacity. If the hybrid pile system is used for mooring applications it can be configured as a single-pile dolphin in v^hich case the pile would be a large-diameter one greater than 600 mm diameter. Alternatively, a cluster of smaller piles can be used. The concrete-filled/GFRP hybrid tubular pile is characterized by lateral load capacity (bending) and by axial load capacity for bearing; the former behaves in a non-linear manner. It is, therefore, necessary to define regions of the load/deflection relationship (namely, the initial tangent modulus, the secant modulus and the tangent modulus), to evaluate the various mechanical properties. The tangent modulus of the hybrid pile can be defined at any (maximum) load on the load/deflection curve; similarly, secant modulus can be computed between any two points on the load/deflection curve. DML Composites, Devonport, UK, has designed and installed GFRP blast wall upgrades on Mobil Beryl B and BP Cleeton platforms and has designed, manufactured

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235

and installed carbon fibre composite structural beams on the Alba North platform. Using composites to upgrade steel structures is appealing to the engineer because the polymers can be cold cured and thus avoid the need for hot working with a consequent closing down of facilities.

8.6. Bridge structures The history of bridge engineering is allied to the development of structural materials. Until Ironbridge was built in England in 1780, timber and stone had been used almost exclusively in bridge construction. The invention of wrought iron and then the development of steel and reinforced concrete changed bridge engineering completely in the 19th century. The 20th century saw many developments in design and construction methods but relatively few fundamental changes in the material used. The spans of bridges and the number of bridge structures have increased dramatically to meet the demands of the rapid growth of the infrastructure, but no new materials have found widespread use in bridges. In the past when a new material, such as wrought iron or steel, was invented a prototype bridge was often built, such as Ironbridge in 1780 and the steel bridge near Vienna in 1828, to demonstrate the capability of the materials. Various forms of fibre reinforced polymer materials have been available for over thirty years and GFRP has been used in prototype bridge structures. However, the materials did not show the immediate and obvious advantages that iron and steel offered over timber and stone in the 19th century, except perhaps, their potential for the construction of extremely long span bridges. As a consequence, fibre reinforced polymers had not been seen as a material likely to make an impact on general bridge engineering until the last ten years when the full implications of corrosion of steel in modem bridges was appreciated. Widespread and serious deterioration of reinforced and prestressed concrete bridges, accelerated by the use of de-icing salts, has affected the infrastructure in Europe, North America and Japan. In addition, increasing labour costs for maintenance work, together with associated traffic disruption has caused engineers to look for more durable bridge materials. Fibre reinforced polymers were seen to have major advantages because of their excellent durability particularly in marine and industrial environments, and it is this characteristic which is currently leading to a significant step forward in their use in bridges. 8.6.1. Composite bridges Prototype bridges constructed entirely from FRP were first conceived in Europe and North America in the late 1970 and the first FRP bridge built in Europe is believed to be the 10 m span bridge constructed at Ginzi, Bulgaria, in 1981/1982. This is shown in Fig. 8.8. The GFRP bridge was constructed using chopped strand mat in a resin matrix and fabricated by the hand lay-up method. The second GFRP bridge to be constructed was the Miyun bridge in Biejing, China, and was completed in October 1982. Over a period of twenty-five years considerable research resource went into the development

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Advanced polymer composites and polymers in the civil infrastructure

Fig. 8.8. The first European polymer composite bridge built at Ginzi, Bulgaria.

of the use of composites and much of the work was undertaken at the Shanghai GFRP Research Institute; the investigations included ageing tests on composite materials. Conventional civil engineering materials for bridge construction are likely to continue to be cheaper, in the near future, than GFRP material but savings in fabrication costs of the latter material may be considerable if highly automated production of advanced polymer composite materials is developed. Thus complete box girder structures could be pultruded in future. Speed of construction, savings in erection costs and in foundation sizes will all contribute to economy. The deck weight is an important part of the overall design of a long span bridge and its form and stiffness are important with respect to aerodynamic stability. There are likely to be significant advantages to be gained in the use of advanced composites in these decks particularly as the trend to increase bridge spans beyond their previous limits will continue into the 21st century. The material characteristics of composites and their successful applications in other areas are sufficiently encouraging to show that there are certain to be important developments in using them in bridge deck structures. Ingenious design with isophthalic polyester/glass fibre composites is creating a revolution in bridge structures. An example of this emerging concept is the world's longest composite bridge spanning the River Tay at the golf club at Aberfeldy, Scotland. The footbridge has a span of 63 m, width 2.12 m and an overall length of 113 m and a design load capacity of 10 kN/m. The polymer composite components which form the deck and towers of the bridge were manufactured from the pultruded ACCS plank. Applying epoxy adhesive on each side of the 0.08 m deep integral grooves connected

Chapter 8. Applications in advanced polymer composite constructions

•'

• "

•

',

. ''••'

,; ; - ' , /

"-

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237

'-''/,-

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Fig. 8.9. Aberfeldy Advance Composite bridge (by kind permission of Maunsell Structural Plastics Ltd., Beckenham, UK).

these components. The components were then brought together and locked by sUding a toggle (dog bone) section into the two grooves, one in each plank. Three planks and four connectors were joined alternately, in a single thickness, to form the 2.12 m wide deck. The cable stays were manufactured from aramid fibres. Fig. 8.9 shows the Aberfeldy advanced composite bridge. The concept and design of the Aberfeldy bridge was undertaken by Maunsell Structural Plastics. A major research programme was undertaken within a LINK programme, sponsored by DTI, EPSRC and industry, in which an extensive test programme was undertaken at the University of Surrey on a full size prototype highway bridge. Fig. 8.1 shows the cross-section of the box beams, which were fabricated from 10 ACCS modules; for 9 months a continuous static test load of 20 tonnes was applied to two beams of 17 m span placed back to back. The canal which joins the rivers Thames and Severn separates Stonehouse and Bonds Mill in Gloucestershire, UK, and in 1994 a link was formed between these two areas by a single bascule lift bridge which was designed and developed by Maunsell Structural Plastics. This bridge is designed to carry full UK highway loading including a 38 tonnes truck. An epoxy bonded multi-celled box beam (Fig. 8.1) with 90 kg/m^ epoxy foam filled into the compressive flange and web cells of the ACCS modules was manufactured and fabricated in a factory and transported to site. Transverse ACCS planks were bonded to the compressive flange of the box beam and were also filled with foam. The running surface of the polymer composite bridge was manufactured from

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Advanced polymer composites and polymers in the civil infrastructure 4

Fig. 8.10. Opening ceremony of the Bonds Mill lift bridge, Gloucestershire (by kind permission of Maunsell Structural Plastics Ltd., Beckenham, UK).

ACME panels (a proprietary system of epoxy-coated panels with grit bonded to the surface); these were bolted to the transverse ACCS planks. Fig. 8.10 shows the opening ceremony. The bridge was required to carry concentrated wheel loads and to resist the large number of load cycles without fatigue damage. To overcome these problems a slow foaming epoxy was developed by CIBA polymers and was used to foam in place the 80 mm X 80 mm x 9 m compressive and web member cells of the ACCS modules. The material provided uniform support to the walls of the cells of the ACCS planks thus allowing transfer of load without high local bending stresses. The effects of the local wheel loads on the section of the box beam were investigated at the University of Surrey through a DTI/EPSRC Link programme. Fig. 8.11 shows the experimental set-up for the wheel load test. A footbridge manufactured from pultrusion sections by Fiberline is shown in Fig. 8.12. It is 15 m long and has a free span of 12 m across a purifying plant in Urmitz near Bonn, Germany. The footbridge weighs 60% less than one fabricated from a similar steel construction; this makes installation easier and reduces transportation and fabrication costs. The bridge requires minimum maintenance and thus secures a longer life span compared to conventional materials. The whole-life cost of the bridge is lower than a construction made from traditional materials. The advantage of the lightweight composite bridge construction is illustrated by two footbridges which have been airlifted into position by helicopter because of the difficulty of transportation in the severe terrain in which they are situated. A bridge,

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Fig. 8.11. Experimental set-up for the Bonds Mill bridge wheel load test at the University of Surrey.

Fig. 8.12. Footbridge manufactured from pultrusions across a purifying plant in Urmitz, Germany (by kind permission of Fiberline Composites A/S Kolding, Denmark).

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Fig. 8.13. A footbridge in a remote area in Wales (kind permission of Maunsell Structural Plastics Ltd.. Beckenham. UK).

designed by Maunsell Structural Plastics, using the Maunsell ACCS was lowered into position in a remote area of Wales and is shown in Fig. 8.13. The 17 m long footbridge weighed only 1 tonne. The other bridge was erected across a river at a ski-resort near St. Moritz, Switzerland, and is shown in Fig. 8.14. The ski-bridge weighing 2.5 tonnes is removed by helicopter each Spring before the glacier melt water washes tonnes of stone and gravel downstream. The bridge was designed by a consortium of the Municipality of Pontresina, ETH Technical University of Zurich and Fiberline Composites, Denmark, who also pultruded and fabricated the bridge.

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Fig. 8.14. A footbridge being lowered into position at the ski-resort at St. Moritz, Switzerland (by kind permission of Fiberline Ltd., Denmark).

Tom's Creek bridge in Blacksbury VA, USA, was the first composite short-span vehicular bridge in the USA. The project upgraded the 17.5 ft x 22 ft (5.33 m x 7.66 m) wide bridge from 10 tonnes to 20 tonnes capacity by replacing corroded steel beams with pultruded composite double-webbed I-beams (8 inches x 6 inches x 3/8 inch with 1/16 inch web thickness and 5/8 inch flange thickness). The entire bridge rehabilitation, including asphalting the decking, was completed in five days. The composite beams were manufactured by the pultrusion technique with a hybrid of carbon and glass fibres in a vinylester polymer. Martin Marietta Composites Inc., USA, designed a polymer composite bridge for Butler County, USA. The Tech 21 (materials technology for the 21st century) bridge was

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manufactured from isopolymer matrix and E-glass fibre and was designed to the American Association of State Highway and Transportation Officials (AASHTO), HS-20 code. The bottom of each section of the bridge has a U-shaped composite box beam or 'hatsection' about 0.60 m high. The U-beam provided the primary support for the bridge load. The bridge deck was a sandwich construction consisting of proprietary box beams between flat composite facing plates. The deck box beams are 150 mm high and have a trapezoidal-shaped cross-section. The centre bridge section is 1.2 m wide and weighs 2270 kg. Each side section is 3.1 m wide and was loaded to the centre section at dovetail joints. The adhesive used during the fabrication of the bridge was a two-part epoxy paste. 8.6.2. Composite bridge decks The bridge deck, generally, requires the maximum maintenance of all elements in a bridge superstructure, this may be the result of the deterioration of the wearing surface to the degradation of the deck system itself. In addition, there may be a need (a) to increase the load ratings and number of lanes on the existing bridge, (b) to accommodate the constantly increasing traffic flow, (c) to upgrade the bridge to conform to new codes. Furthermore, to undertake work on an existing bridge, it is necessary to keep in mind the important consequences relating to the overall economics of time loss and resources, caused by delays and detours of traffic during construction. Consequently, these restraints have provided the impetus for the development of bridge decks utilizing materials that are durable lightweight and easy to install. In addition to the potential savings in life-cycle costs due to increased durability, decks fabricated from composites would be significantly lighter thereby affecting savings in substructure costs. These deck structures can either be used for replacements for existing, but deteriorated or substandard concrete/conventional deck or used as new structural components on conventional or new supporting structural elements. Karbhari and Seible (2000) have suggested that the replacement FRP composite decks have to be designed with three criteria in mind; these are: • stiffness, developed through the combination of a core and face-plates, must fall in the range between that of an equivalent uncracked and a cracked concrete deck • factors of safety must be designed in, through the use of an appropriately factored equivalent energy approach, so as to offset the initial linear response followed by irreversible cracking/delamination/separation of fabric layers in composite decks • processing methods must be such as to enable uniformity at costs comparable with the in-place costs of existing deck systems (Table 8.2). A number of manufacturing processes have been used to fabricate FRP composite bridge decks. These have included the wet lay-up (Miyun bridge in China, Seible et al. (1993), one of the first vehicular demonstration bridges), the resin infusion technique (Chajes et al., 1998), the pultrusion method (Karbhari et al., 1997; Head, 1998; Lopez-Anido et al., 1998), or a combination of these methods. Head was responsible for the fabrication of the Aberfeldy cable stay footbridge in Scotland (Head, 1996), see Section 8.6.1. Goldsworthy and Heil (1998) discuss the use of modular sections that can 'snap' together in the field so as to provide flexibility, whilst standardizing sections, and opportunities for further development.

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Chapter 8. Applications in advanced polymer composite constructions Table 8.2 Generic in-place costs of conventional bridge deck systems (after Karbhari and Seible, 2000) Type of deck

Cast-in-place concrete Precast concrete Prestressed concrete Concrete filled steel grid Half filled grid Open grid Exodermic Steel orthotropic Aluminium orthotropic

Weight

Cost ($/m2)

($/ft-)

(lbs/ft2)

(N/m-)

15-20 15-30 15-25 20-25 20-25 25-30 30-35 60-80 50-60

1.40-1.86 1.40-2.79 1.40-2.32 1.86-2.32 1.86-2.32 2.32-2.79 2.79-3.25 5.57-7.43 4.65-5.57

100 100 90 75 55 25 60 90 35

4788 4788 4309 3591 2633 1197 2873 4309 1676

An example of a composite modular bridge deck construction is the Wickwire Run bridge (FRP modular deck on steel beams) located in Taylor County, West Virginia, USA, and shown in Fig. 8.15. It consists of a FRP composite deck cross-section that is composed of full-depth hexagonal and half-depth trapezoidal components. The wearing surface is a polyester polymer concrete overlay of 1/2 inch (12.7 mm) thick. The glass fibre architecture (fabrics) was designed at the Constructed Facilities Center, West Virginia University and West Virginia Department of Highways, District Four

Fig. 8.15. Wickwire Run bridge located in Taylor County, West Virginia, USA, and manufactured by Creative Pultrusions (by kind permission of Creative Pultrusions Inc., Alum Bank, PA, USA).

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and manufactured by Creative Pultrusions, to provide optimal structural performance for highway bridge loads. The FRP composite deck modules are placed transverse to the traffic direction and are supported by longitudinal steel beams. The FRP composite deck components are joined by a shear key system that provides a safe mechanical interlocking system and an adhesively bonded surface. High performance polyurethane adhesive is used to factory assemble the deck components into long modules upto 8 ft (2.44 m) width before shipping to the bridge site. It is claimed that this FRP composite bridge deck is about five times lighter and six times stronger than the conventional concrete deck. Other features of this FRP composite bridge deck are that it: (a) is well suited for modularization and mass production; (b) possesses good energy absorbing capacity; (c) has enhanced fatigue and corrosion resistance properties; and (d) requires less erection time since it weighs less and uses light equipment. The length and width of the Wickwire Run bridge are 30 ft (9.12 m) and 22 ft (6.69 m), respectively. A 5 X 15 feet 3 inches (1.5 m x 4.5 m) FRP composite bridge deck has been installed at the Troutville Weigh Station on Interstate 81 near Troutville, VA; this bridge is shown in Fig. 8.16. The composite bridge deck utilizes a &' x 3/8" (150 mm x 9.25 mm) pultruded square tube and 3/8" (9.25 mm) plate with a 1/2" (12.5 nmi) thick heavy-duty bonded vinylester and aggregate wear surfaces. The deck is set on 10" (250 mm) steel beams with 7' (2.1 m) clear span between the beams. The bridge deck was installed the first week of November 1999 on the concrete roadway apron leading to

Fig. 8.16. Troutville Weigh Station, Troutville, VA, USA (by kind permission of Strongwell. Bristol, VA, USA).

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the truck weigh scales. Up to 13,000 tractor trailer loads (of over 40,000 Ibf (18,150 kg)) each per day will cross this section of roadway. The bridge deck was installed with strain gauges and a data acquisition terminal to continuously monitor the deflection for at least a year. The ultimate goal is to prove the durability of FRP decks in high stress areas for future infrastructure rehabilitation projects. The project was the final phase of a co-operative effort to develop and test composite bridge decks for use in rehabilitating the infrastructure. As a team Strongwell, Virginia Polytechnic Institute and State University, Virginia Transportation Research Council and the Virginia Department of Transportation were awarded a grant from the Federal Highway Innovative Bridge Programme for the development and testing of this bridge deck. The prototype deck tested some two years earlier was loaded to 20,800 psi (143.42 MPa) for 3 million cycles to meet the AASHTO HS-20 requirements. In Europe an all composite bridge deck has been analyzed and develop by a consortium of industrial firms; the project ASSET consisted of seven partners^. The highway bridge has been designed to carry 40 tonnes vehicle wheel load. Fig. 8.17a shows a section of the deck unit and Fig. 8.17b illustrates the section of the composite profiles. One of the tasks within the project was to design all the vital connection details to achieve a complete decking system. Conventional connecting parts such as parapets, lamp posts, existing main girders, etc., must fit into the system. An ASSET highway bridge to carry 40 tonnes vehicle will be constructed for Oxford County Council in the year 2(X)1. The bridge will be made entirely from GFRP consisting of the deck and main girders; the latter will be constructed from GFRP I-sections. A GFRP composite bridge deck was erected at the Mill Creek, Delaware in 1999 and was manufactured by Hardcore Composites, Delaware, USA, using the SCRIMP process (see Chapter 3, Section 3.2.3); the process met the AASHTO HS-25 load rating and FHWA codes of practice for bridges. Fig. 8.18 shows the Mill Creek bridge. The bridge deck is 17 ft (5.2 m) wide, 39 ft (11.9 m) span and varies from approximately 9 inches (225 mm) to 10 inches (250 mm) in depth. The deck incorporates integrally moulded 6 inches (150 mm) high curbs drainage openings, hardware for attaching guard rails and bolt holes for anchoring the deck to the steel girders. The composite bridge is approximately one-fifth the weight of a traditional steel and concrete bridge structure and was manufactured in a factory off site in 45 days which was estimated to be one half the time a traditional bridge deck construction would have taken. With this type of construction the speed of erection is a major advantage over the traditional steel and wood construction. In addition, the weight savings of the composite deck allowed the existing foundations to be used, thus enabling an extension of their useful life. A typical bridge deck is laid up using dry reinforcement in a one-piece open mould and infusing the entire part with resin applied in one 'shot' by means of a vacuum-assisted process. The mould is treated with mould release oil followed by a red mesh of 0.03125 inches (0.8 mm) thick film generally used for vacuum-assisted resin transfer moulding ^Mouchel (UK), Fiberline (Denmark), Skanska (Sweden), lETCC (Consej Superior de Investigaciones Cientificas (Spain)), and HIM (Netherlands).

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Composite profiles

"

Po^yme^ Modified Concrete

Fig. 8.17. (a) Section of the ASSET deck unit developed by the ASSET consortium (by kind permission of Mouchei, West Byfleet, UK), (b) Section of the ASSET deck composite profile (by kind permission of Mouchel West Byfleet, UK).

(VARTM) and resin infusion. The lower skin of the bridge deck's structural sandwich construction is built up by applying about 10 layers stitch-bonded fabric. The latter is typically E-glass, but in some areas carbon fibre tow is incorporated to add stiffness to the part. The thickness of the outer layer is typically 1/2 inch (12.5 mm) or more, depending upon the bridge. The foam core is laid over the lower face material and in some cases 4 inch (100 mm) to 12 inch (300 nwn) cubes of closed-cell polymer foam (Hardcore uses Polyisocyanurate); these are wrapped in quadraxial or other glassfibrefabric, depending upon the design and location of the cubes in the bridge. If loads do not warrant the expense of quadraxial orientation, a more cost-efficient unidirectional or bidirectional fabric is used. The cubes are positioned to meet the configuration of the bridge. The core is placed to achieve a centre crown with the specific slope for the bridge under construction. An exactly similar lay-up of quadraxial fabric over the core completes an upper skin laminate that mirrors exactly the bottom skin. A top resin distribution mesh is laid over the upper laminate before the entire section is vacuum bagged. Cellular core technology gives designers the ability to detail a composite deck with sufficient shear capacity, transverse web stiffeners and redundant load paths.

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Fig. 8.18. Mill Creek bridge, Delaware, USA (by kind permission of Hardcore Composites).

Hardcore Composites manufactures deck panels with a vacuum infusion technology that simultaneously produces the face and the core material sandwich system. It has been shown, by testing, that the levels of stress resulting from service loads or fatigue is dissipated throughout the core material. Some of the unique features of a Hardcore Composites deck are the ability to vary the face thickness, the core geometry and the fibre architecture. This provides a means to design and fabricate composite decks to carry AASHTO HS-25 loads and transfer those loads to the existing bridge superstructure. Because the depth of section and the face thickness are readily varied, Hardcore Composites can design and fabricate complete bridge structures capable of carrying HS-25 loads whilst maintaining the L/800 deflection criteria. The ability to modify the core allows the inclusion of mechanical fasteners, lifting elements, block-outs and accessories such as drainage scuppers, expansion joints and utility conduits. The ability to design and fabricate three-dimensional core geometry allows the implementation of deck skew, cross slope, deck crown, curbs, gutters, super-elevation and curved beams. It should be mentioned that as SCRIMP is a closed process, emissions of volatile organic compounds are minimal. However, fumes emitted during exotherm cure of epoxy vinylester resin would be collected by a series of charcoal air scrubbers; clean air would be vented to the outside. Charcoal canisters with collected styrene would be sent to a hazardous material facility, where they would be cleaned, recharged and returned for re-use.

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8.7. Composite enclosures and aerodynamic fairings for bridges Bridge structures require regular inspection and maintenance but, the closure of bridges, required to facilitate maintenance, will cause considerable disruption to travellers. Furthermore, the cost of closure will be high; this is particularly so for long span bridges. Stringent standards are increasing costs of maintenance work over or beside busy roads and railways. Many bridges, designed and built over the past 30 years, do not have good access for inspection. In addition, in many North European and North American countries deterioration, caused by de-icing salts, is creating an increasing maintenance workload. The 'Bridge Enclosure' is a suspended floor beneath the girders of steel composite bridges to provide inspection and maintenance access. It is sealed onto the underside of the edge girders to enclose the steelwork and to protect it from further corrosion and ingress of moisture. Research work undertaken at the TRL (McKenzie, 1991, 1993) has shown that once the enclosures are erected and sealed, the rate of corrosion of un-coated steel within the protective environment of the enclosure is 10% of that of painted steel in the open. It should be noted that no dehumidifying equipment is needed to prevent corrosion. The chloride and sulphur pollutants are excluded from the enclosure by the seals and although there could be high humidity with condensation within the enclosure, the water drops onto the enclosure floor, which is erected below the steel girders, where it escapes through small holes. In the future, enclosures will be important for long span bridges. The development of the cable stayed bridge has resulted in an increase in the use of plate girders for long span bridges and a reduction in fabrication costs of steel girders over those of the labour intensive steel box girder bridges. The addition of the fibre polymer composite enclosures around such structures not only enables maintenance costs to be greatly reduced but also allows the shape of the cross-section to be optimized by extending the enclosure into a fairing to give minimum drag consistent with aerodynamic drag. One recent example where the GFRP enclosure is extended into a fairing is the nine structures on the approach road to the second Severn crossing. Fig. 8.19. The high specific strength and good durability property of the composite materials makes them ideal candidates for enclosure floors, in addition, as they are situated on the soffit of the bridge and away from the direct rays of the sun no ultra violet protection is required. Most bridge enclosures which have been erected in the UK have utilized GFRP as the material of construction and the first major installation as a permanent enclosure in the UK was to the A19 Tees Viaduct. This bridge was fitted with the Maunsell 'caretaker' system. This was followed by further retrofitting projects, one at Botley, Oxfordshire (1990) where the hand lay-up GFRP method was used and Nevilles Cross (1990) near Durham where the pultruded GFRP system was fitted to an existing bridge over the main railway line. Two new bridges were built with enclosures, one at Bromley South, London, which is shown in Fig. 8.20, utilizing Maunsell 'caretaker' system; the other was in 1993 at Winterbrook, Fig. 8.21, and was manufactured by the hand lay-up GFRP method. The Bridge Department of Oxfordshire County Council undertook the design of this bridge structure; the enclosure was designed by Mouchel Consulting, West Byfleet, Surrey, UK.

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Fig. 8.19. Bridge enclosure on approach road 2nd Severn Crossing (by kind permission of Maunsell Structural Plastics Ltd., Beckenham, UK).

The SPACES system was conceived by Maunsell Group, London, UK. The structural form, which is being developed and promoted by a partnership of material suppliers, manufacturers, fabricators, bridge designers and constructors, is shown in Fig. 8.22. Key technologies have been combined to form a total structural component and many of the technologies have involved those developed for the offshore industry. The SPACES system consists of a steel space frame acting compositely with a concrete deck slab. It is manufactured predominately under factory conditions where quality and reliability can be achieved more readily than they can be on site. An aesthetic, aerodynamically profiled shell manufactured from polymer composite material encloses the space frame. The former acts as an enclosure and provides permanent protection for the steel work and in addition provides safe access for inspection and maintenance of the superstructure and bearings. The economic success of the SPACES concept is the excellent long-term performance provided by the advanced composite enclosure skin as well as the development of a robotic welder for the joints between cable support decks. The SPACES system is able to accommodate bridge spans between 60 m and long span cable support decks and this enables designers to adopt a 'systems approach' to bridge engineering for the complete range of spans. The polymer composite enclosure is fabricated from the ACCS and has excellent long-term performance properties thus providing good long-term durability and minimal maintenance requirements.

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Fig. 8.20. Bridge enclosure at Bromley South Railway Station, London (by kind permission of Maunsell Structural Plastics Ltd., Beckenham, UK).

8.8. Upgrading structures 8.8.1. Introduction For a variety of reasons, reinforced concrete, steel and cast iron structures may be found to be unsatisfactory. Design strengths of structures may not be achieved in practice because of deficiencies at the design phase; these deficiencies include marginal design/design errors causing inadequate factors of safety, the use of inferior materials, or poor construction workmanship/management. In service, increased safety requirements, a change in use or modernization causing redistribution of stresses, an increase in the management or intensity of the applied loads require to be supported, or an upgrading of design standards may render all or part of a structure inadequate. In addition, the load carrying capacity of a member may be compromised by deterioration of the material as a result of the corrosion of internal reinforcement, in the case of reinforced concrete beams, from carbonization of the concrete or alkali-silica reaction, hostile marine and industrial environments and structural damage. On highway structures, corrosion of the internal reinforcement is exacerbated by the application of de-icing salts. For prestressed concrete beams, strengthening measures may be required to prevent further loss of prestress. These inadequacies may manifest themselves by poor performance under service loading in the form of excessive deflections and material failure, or through inadequate fatigue or ultimate strength. When maintenance or local

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Fig. 8.21. Bridge enclosure at Winterbrook, Oxfordshire (kind permission of Oxford County Council, Bridge Department, Oxfordshire, UK).

repair will not restore a deficient structure to the required standards, there are two possible alternatives; complete or partial demohtion and rebuild, or commencement of a programme of strengthening. The choice between strengthening or demolition depends on many factors, such as material and labour costs, time during which the structure is out of commission and distribution of other facilities. However, the financial benefits of strengthening as opposed to demolition can often be considerable, particularly if a simple, quick strengthening technique is available. In addition, if the structure in question has historical importance, the possibility of demolition may be precluded. ROBUST (Hollaway and Leeming, 1999) provided detailed techniques for plate bonding in the UK and further demonstrated the ability to prestress the CFRP plates on to full size 18 m beams following laboratory development and tests undertaken on 4.5 m beams at the laboratories of the University of Surrey. Chapter 5 of this book discusses the plate bonding techniques, the structural characteristics and the design of the component parts of the system for upgrading a beam in flexure and in shear; it also discusses the technique of wrapping columns. From Chapter 5 it may be concluded that, in general, composites can be applied in three ways as described in Table 8.3, of which the first two are the most widely used. However, it should be noted that although the wet lay-up process affords significant flexibility for work on site and is probably the most commonly used process in the field, there may be significant advantages, both technical

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Fig. 8.22. The spaces system conceived by the Maunsell Group, London, UK (by kind permission of Maunsell Structural Plastics Ltd., Beckenham, UK).

and psychological, in the use of prefabricated and hence, presumably, standardized strips and plates. These plates are adhesively bonded to the concrete substrate. It is important to note that, irrespective of the method of application, the efficacy of the method depends upon the appropriate selection of the composite material based upon stiffness and strength requirements and the efficiency and integrity of the bond between the composite surface and the composite. The latter requirement must also be capable of performing, not only under ambient conditions but also under extremes of temperature (including temperature gradients between the top and bottom surfaces of the concrete), under the resulting stress and strain conditions and in the presence of moisture. Some durability testing of the bond between the composite plate and the concrete are given in Karbhari et al. (1996) and Karbhari and Zhao (1998). The technique of plate bonding is now becoming established and although FRP composite materials are not as well understood as steel and concrete, they have several superior characteristics which are highly desirable in bridge applications. Several design guides, concerned with plate bonding, are being produced throughout the world by Institutions; these have been discussed in Chapter 5, Section 5.12. Theflexuralstrengthening generally takes place on an uneven concrete surface even after the concrete surface preparation of grit blasting and removal of any contaminants. Consequently, the thickness of the adhesive would be between 1 and 2 mm to allow for this unevenness. Ideally, a 'propping' system, under the entire length of the plate, would

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Table 8.3 Methods of appHcation of external composite reinforcement for strengthening (after Karbhari and Seible, 2000) Procedure

Description

Adhesive bonding

Composite strip/panel/plate is prefabricated and then bonded onto the concrete substrate using an adhesive under pressure

Wet lay-up

Resin is applied to the concrete substrate and layers of fabric are then impregnated in place using rollers and/or squeegees (or a preimpregnated wet layer of fabric is squeezed on). The composite and bond are formed at the same time

Slower and needs more set-up Ambient cure effects " Waviness/wrinkling of fibre Non-uniform wet-out and/or compaction

Resin infusion

Reinforcing fabric is placed over the area under consideration and the entire area is encapsulated in a vacuum bag. Resin is infused under vacuum. In a variant the outer layer of fabric in contact with the bag is partially cured prior to placement in order to get a good surface

' Far slower with need for significant set-up ' Dry spots

Time/issues Very quick application Good quality control

be put in place until the adhesive has polymerized, this small pressure would enable a more satisfactory adhesive joint to be formed. The 'propping' system could be effected by vacuum bagging or more simply by a physical prop, always providing access in permitted under the beam. However, in many plate bonding examples propping is not carried out, in these cases the adhesive has sufficient stiction to hold itself in position until the adhesive has polymerized. If it were necessary for the composite to navigate a comer or non-planar section of the concrete system, the pultrusion manufacturing technique could not normally be used in this situation. Although pultruded angles or other more complicated sections can be formed (provided the dies are available), the engineered angles would not necessarily fit the comer of the concrete. In this case a prepreg could be employed and the REPLARK or the RIFT procedures would be used to apply the composite to the surface of the concrete. There are numerous examples of retrofitting or upgrading reinforced concrete beams using CFRP composites which could be cited, only two illustrative reinforced concrete examples will be given here. Fig. 8.23 shows a flexural plate bonding example using the REPLARK process and Fig. 8.24 illustrates another example of plate bonding using the Sika procedure. A principal curved steel beam was strengthened using a Low Temperature Moulding (LTM) advanced polymer composite material, manufactured by ACG, Derbyshire, UK; Taywood Engineering was the specialist subcontractor for this work. The beam is curved in plan to connect two straight members around the comer of the building. The purpose of the strengthening scheme was to restore the flexural and torsional capacity of the beam to above its original uncorroded level so that an anticipated increase in floor loading could be accommodated. The thickness of the composite strengthening layer,

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Fig. 8.23. Flexural plate bonding example (REPLARK wrap) (photograph by kind permission of Sumitomo Corporation (UK). London, UK).

Fig. 8.24. Flexural plate bonding example (Sika) (by kind permission of Sika Ltd., Welwyn Garden City, Herts.. UK).

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Fig. 8.25. Vacuum bag used to apply pressure for compaction of composite material (kind permission of Taywood Engineering, Southall, UK, and ACG, Derbyshire, UK).

which comprised of unidirectional, 0°/90° and ±45° fibre orientation, was 2 mm. The unidirectional fibres were aligned along the direction of the beam's length for flexural strengthening. The 0°/90° fibre directions were used to resist shear and torsional loading, created due to the curvature of the beam. The prepreg composite layers were based upon glass and carbon fibres, using a low temperature curing epoxy resin developed by The Advanced Composite Group, Heanor, Derbyshire. The surface preparation and installation procedure was undertaken as described in Chapter 5, but in addition, the steel beam was kept in a dry condition by placing silica gel packs onto it, with the beam enclosed in polythene. To act as a bonding aid, an ambient-cured epoxy adhesive was painted onto the clean and dry steel surfaces. Fig. 8.25 shows a vacuum bag used to apply pressure for compaction of the composite material and Fig. 8.26 illustrates the final placement of the carbon fibre prepreg layers around the flanges and web of the steel beam. Tickford bridge is the oldest operational cast iron highway bridge in the world. It was designed by Thomas Wilson and built over the River Ouze in the summer of 1810 and is a Scheduled Ancient Monument. Maunsell Beckenham, Kent, UK, was appointed to suggest the most appropriate strengthening strategy and recommended that the 3 tonnes gross weight restriction could be removed and that the full highway loading could be achieved by strengthening the structure with CFRP. The selected system was a carbon fibre prepreg sheet system. In addition, a continuous filament

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Fig. 8.26. Final placement of the CFRP prepreg layers around the flanges and web of the steel beam (kind permission of Taywood Engineering, Southall, UK, and ACG, Derbyshire. UK).

polyester drape veil was installed to provide insulation between the carbon fibre and the cast iron to avoid any possibility of galvanic corrosion. In total 120 m^ of carbon fibre prepreg sheet was applied in upto 14 layers and repainted. The maximum thickness of 10 mm demonstrates that this system of strengthening can be achieved with negligible visible affect to the bridge appearance and the work was completed within 10 weeks. During the ROBUST project (see Section 5.10.1) structural strengthening of reinforced concrete beam were investigated by using prestressed plates. The aim was to either increase the serviceability capacity of the structural strengthening or to extend its ultimate limit state. It is important that the existing structure can accommodate the mounting of additional elements for the ends of the prestressing components. It is necessary to investigate fully the magnitude and form of any local stresses which may be induced into the existing structure as a result of the application of additional prestress. The method of prestressing with external bonded composite plates combines the benefits of excellent plate durability and structural improvement due to the plate tension at the greatest possible distance from the neutral axis of the beam. It has been suggested that prestressing with composite plates is a more economical alterative to conventional prestressing methods used in new construction (Triantafillou and Plevris, 1991). Fig. 8.27 shows the experimental procedure undertaken at the University of Surrey to prestress a 4.5 m long reinforced concrete beam.

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Fig. 8.27. Prestressing technique undertaken on a 4.5 m reinforced concrete beam at University of Surrey.

The first known application of the prestressing technique for flexural upgrading cast iron bridges was utihzed on the Hythe bridge, Oxford, which was constructed in 1874. The objective of strengthening the bridge was to raise the capacity from Group-2 fire engines to 40 tonnes vehicles. The bridge was weak in mid-span bending, but was able to support the full 40 tonnes assessment in shear. The bridge consisted of two spans each of 7.8 m. The structure carries a busy city centre road above a tributary of the River Thames and a means of strengthening was required which did not cause traffic disruption. A feasibility study was carried out and showed theoretically that it was possible to strengthen the structure with either steel plate bonding, unstressed composite plates or stressed composite plates. Each of the three methods involved a degree of uncertainty because they extended past practical previous limits in ways that threatened technical or economical viability. Steel plate bonding and unstressed composite plate bonding both presented significant difficulties, as follows.

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Steel plate bonding • Thickness of 135 mm would have resulted in restricted head room and would have imposed high additional load. • Such thickness would have required several layers and was beyond previous experience. • Difficulties in handling and fixing with drilling into cast iron was not advisable. • Expensive to undertake and final system would require continuing maintenance. Unstressed composite plate bonding • Multiple layers required increasing labour and material costs beyond that normally associated with plate bonding. • Behaviour of such high build multi-layer system is untested. • Peel forces for such a thick system would require strapping, in the absence of representative tests. Stressed composite plate bonding • No system for stressing composites in this situation was available. • Stressing of cast iron could reveal weaknesses. It was eventually concluded that the stressed composite technique offered the most satisfactory solution. The proprietary technique developed by Mouchel Consulting, West Byfleet, UK, requires anchorages at the extremities of the plate to be fixed by bonding, friction or mechanical means or a combination of all methods. End tab plates are bonded to each end of the carbon fibre reinforced composite tendons and provide a means of attaching jacking equipment and anchoring the tendon when extended to the final working strain. The tendons are stressed by hydraulic jack, which reacts against a jacking frame temporarily fixed to the anchorage. The stressed tendon is secured after extension by a shear pin that transfers load from a key way in the end-tab to the anchorage. The tendons are bonded to the beam by epoxy resin in addition to the end anchorages. The anchorage itself is surrounded by a protective casing and fully grouted. Fig. 8.28 shows the prestressing plates in Hythes bridge and Fig. 8.29 is the general view of Hythe bridge. Carbon fibre composites have also been used to strengthen masonry walls for seismic and for wind loading. An office building at Muhlebachstrasse, Zurich was converted from apartments and this required structural alterations, including removal of a load-bearing wall. Redistribution of load together with increased seismic and wind load design was required. The final design required that two existing brick walls should be strengthened and stiffened with carbon fibre/epoxy polymer composites. Sika 'CarboDur' type S1012 plates were applied to the brick wall with Sikadur 30; this is shown in Fig. 8.30. 8.8.2. Plate bonding to improve the shear capacity of the beam Some site work has been undertaken to upgrade beams in shear using composite materials; the pultrusion and the REPLARK techniques for the manufacturing of the

Chapter 8. Applications in advanced polymer composite constructions

Fig. 8.28. Hythe bridge

259

prestressed composite plated cast iron beams (by kind permission of Mouchel Consulting Ltd., West Byfleet, UK).

materials have been used. The installation procedure for the shear plates is similar to that for the flexural plates. One problem of using pultruded plates (which is also a problem with steel plate bonding) is the difficulty of obtaining a sufficient bond length for the composite. It would be necessary to resort to the use of bolts at the end of the plate or possibly to use REPLARK to overiay the pultrusion and extend it to incorporate part wrapping of the column. It is worth mentioning that the pultruded plate would contain ±45° off-axis fibres to resist the external shear and 0° fibres to enable the tensile force from the pultruder to be taken by the uncured composite. Hutchinson et al. (1997) has described tests that were undertaken at the University of Manitoba to investigate the shear strengthening of scaled models of the Maryland bridge which required shear capacity upgrading in order to carry increased truck loads. The bridge had an arrangement of stirrups which caused spalling of the concrete cover followed by straightening of the stirrups and sudden failure. CFRP sheets were effective in reducing the tensile force in the stirrups under the same applied shear load. The CFRP plates were clamped to the web of the Tee beams in order to control the outward force in the stirrups within the shear span. This allowed the stirrups to yield and to contribute to a 27% increase in the ultimate shear capacity. Hutchinson showed that CFRP sheets are more efficient than the horizontal and vertical CFRP sheet combination in reducing the tensile force in the stirrups at the same level of applied shear load. Taljsten (1997) studied the shear force capacity of beams when these had been strengthened by CFRP composites applied to the beams by three different techniques; these were: • hand lay-up system by two different approaches

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Advanced polymer composites and polymers in the civil infrastnictiire

Fig. 8.29. Hythe bridge after plate bonding completed (by kind permission of Mouchel Consulting, West Byfleet, UK).

• prepreg in conjunction with vacuum and heat • vacuum injection. The results of the four point loaded tests showed, in all cases, a very good strengthening effect in shear when the CFRP-composites were bonded to the vertical faces of the concrete beams. The strengthening effect of almost 300% was achieved, although it must be stated that this value is dependent upon the degree to which the beam was reinforced in shear initially. It was possible to reach a value of 100% with an initially completely fractured beam. Generally it was easier to apply the hand lay-up system and Taljsten suggested that although the prepreg and vacuum injection methods gave higher material properties than those of the hand lay-up method, the site application technique seemed to be more controllable for the hand lay-up process. Fig. 8.31 shows a system for providing stirrups for shear upgrading; the bridge beams have been retrofitted withflexuralpultruded plates and pultruded shear stirrups. O'Connor et al. (1999) have discussed the recent advances that New York State has made in reducing the number of bridges that are classified as structurally deficient. The Department of Transport (DOT) has enhanced its inspection programme with the addition of bridge safety assurance assessments that measure the degree of risk related to particular failure modes. In 1998, the DOT initiated an evaluation of FRP composites to determine if these materials could be used to reduce the risk of overload failure. The belief at (NYSDOT) is that FRP has great potential in bridge rehabilitation and that benefits include improved strength, lightweight, easier and faster installation, improved durabihty, long service life and low life-cycle costs.

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261

Fig. 8.30. Brick wall upgrading (by kind permission of Sika Ltd., Welwyn Garden City, Herts, UK).

8.8.3. Wrapping of columns using composites The majority of buildings and bridge piers, which utilize polymer composite confinements, are those in the USA and Japan. The available composite systems include epoxy with either carbon, aramid or glass fibre fabric materials. A column consisting of fibre/polymer and concrete systems can deform much more under severe stress conditions than a conventional material system. In addition, by providing composite confinement to the concrete a much improved ultimate compressive strain is achieved. The two fabrication systems available for site work are the XXsys Technologies procedure and the REPLARK prepreg or equivalent wet lay-up method. Figs. 8.32 and 8.33 illustrate these two procedures respectively.

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Advanced polymer composites and polymers in the civil infrastructure

Fig. 8.31. System for the provision of stirrups for shear upgrading. Pultruded flexural plate bending illustrated (by kind permission of Sika Ltd. Welwyn Garden City, Herts, UK).

Fig. 8.32. XXsys Technologies for polymer composite wrapping of columns (by kind permission of XXsys Technologies, Inc., San Diego, CA, USA).

Chapter 8. Applications in advanced polymer composite constructions

263

Fig. 8.33. The REPLARK prepreg method for polymer composite wrapping of columns (photograph by kind permission of Sumitomo Corporation (UK), London, UK).

The Departmental Standard BD/48/93, the Assessment and Strengthening of Highway Bridge Supports was published in 1993. It sets out criteria to be used in order to determine the adequacy of older bridge supports in dealing with vehicle collision loading. In 1998 a trial to determine the effectiveness and particularly of strengthening bridge supports by wrapping with advanced composite materials was undertaken by the Highway Agency. The Sakawa River Bridge project in Japan is believed to be one of the largest seismic retrofitting projects to date using carbon fibre composites. The bridge consists of 7 m diameter hollow concrete columns varying from 30 to 60 m high. Some parts of the columns where the concrete/steel splice joints are located were jacketed by the utiUzation of the REPLARK process in a carbon fibre wrap; 50,000 m^ of sheet material were used to upgrade eight columns. In a demonstration project in 1997 six columns, supporting a bridge, under a Seattle freeway, were wrapped with multi-layers of carbon composites using the XXsys technique; recently the method has also been used to strengthen an historic arch bridge at the Arroyo Seco near the Rose Bowl stadium, Pasadena. At Sherbrooke University, Canada, a research project demonstrated that E-glass/epoxy wrap can enhance the tolerance of reinforced concrete columns to axial loads by 45%. This led to glass fibre/epoxy wraps being used by the City Council to undertake rehabilitation work on columns, beams and slabs in the car parks of that city.

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The A30 Bible Christian bridge in Cornwall England, was chosen for the trial because it is a fairiy typical Trunk road bridge with substantial supports against Heavy Goods Vehicle (HGV) impact. The structure comprises a four-span reinforced concrete superstructure supported on three piers, each of 800 mm diameter reinforced concrete columns. The prototype designs for the trial were developed to enhance the flexural and shear strength of the piers. Three generic types of wrapping systems with an epoxy matrix were used, one on each column, namely: E-glass fibre, aramid fibre and carbon fibre fabrics. XXsys, DuPont and Hexcel supplied the carbon, aramid and E-glass respectively. Based upon design and methodology procedures the wrapping designs were as follows. DuPont Aramid (Kevlar 49). Ten vertical layers curtailed progressively towards the top of the column, three horizontal layers reducing to two layers at the top of the column lapped by 200 mm. Hexel Epoxy-Glass (Hex-SRIOO). Fifteen vertical layers curtailed progressively towards the top of the column, seven horizontal layers lapped by 150 mm. XXsys Carbon Fibre (RTC). Four continuous vertical layers curtailed progressively towards the top of the column. Two horizontal layers lapped by 300 mm. All wrapping systems terminated at the top of the columns and at the junction with the existing base. The laps of each wrapping system were staggered around the circumference of each colunm. Fig. 8.34 shows the procedure used by Sika for bonding the Hex-3R100 system onto one of the columns. The trial was successful with respect to the quality of installation at cost being much less than for traditional repair methods. As a consequence the Highway Agency UK conmiissioned research at the Transport Research Laboratory (TRL) to study the structural behaviour of wrapped columns. Aramid fibre Kevlar® was chosen for this study as it offers the best overall mechanical impact/energy absorbing characteristics. The results are given in Cuninghame and Sadka (1999). Six half-scale concrete colunms (3 m in length and 400 nun in diameter) were strengthened by the wet lamination technique with layers of UD-fabric of aramid laminated with epoxy resin system of two, three or four layers in the length direction and two layers in the hoop direction. Fig. 8.35 shows the relationships between load and mid-span deflection and compared to the original bending strength of a non-reinforced column, the improvement is good. The predicted failure loads calculated by conventional methods were in good agreement with those obtained from the tests. A confinement model has been introduced by Fam and Rizkalla (2001a) to predict the behaviour of axially loaded concrete confined by FRP tubes. The model is based upon the model of Mander et al. (1988) and is capable of predicting the confined stress-strain response of concrete. The results show that by orientation the fibres as closely as possible to the hoop direction or increasing the shell thickness does increase the maximum strength of confined concrete, but, providing strength and stiffness in the longitudinal direction reduces the confinement effectiveness for the same shell thickness. In addition, if voids are formed in the concrete the confinement efficiency is reduced. Furthermore, ignoring the axial compression stress developed in the shell could highly overestimate the confined strength of concrete.

Chapter 8. Applications in advanced polymer composite constructions 265

266

Advanced polymer composites and polymers in the civil infrastructure 1000 I 3 axial a!nd 2 hoop layers

20 Mid-Span

40 60 deflection mm

Fig. 8.35. Relation between load and niid-span deflections (after Pinzelli, 1999).

Fam and Rizkalla (2001b) investigated the behaviour of partially filled GFRP tubes with concrete under axial compression and a tube-in-tube system with concrete filling the annulus. All tubes were designed to provide strength in both axial and transverse directions and were axially loaded with the concrete core in composite action configuration. It was again verified that if the GFRP tubes are designed to provide strength in both axial and hoop directions, the system is then bi-axially loaded and is less effective in confinement. When the inner GFRP tube maintains the central void, the confinement effectiveness is improved over the randomly voided tube and approaches that of the totally filled tube. The actual degree of confinement is dependent upon the stiffness of the shell. To compensate for the shrinkage effects of the concrete, expansive concrete mixes can be used.

8.9. Vehicle side-guard rails and road-side barriers A side-guard system for commercial vehicles using a GFRP pultruded hollow section with legs at the rear for attachment to the supports was introduced by Maunsell Structural Plastics Ltd. in the mid 1980s. The advantages of this system are lightweight and good durability; the lightweight property would reduce the dead weight of the total vehicle and thus reduce its fuel consumption. The span of these units would be of the order of 3 m. The regulations for side-guards require the beam to be capable of withstanding a force of 2 kN applied transversely to the vehicle at any point in the beam with a permitted deflection of the beam limited to 150 mm. The utilization and installation of roadside barriers has been described by the Roadside Design Guide (1989), as: "Roadside barriers are designed to shield motorists from man-made or natural hazards and to redirect errant vehicles back onto the roadway.

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267

Installation of these devices is warranted when the consequences of a vehicle impacting a barrier are deemed to be less severe than the consequences of the vehicle leaving the highway if the barrier did not exist". The three major categories of barrier systems are outlined below: (1) flexible systems which permit vehicles to travel upto 4 m off the road until tension forces developed in the system are adequate to restrain the vehicle (2) semi-rigid ones which allow upto 1 m deflection before the vehicle is stopped or redirected (3) rigid systems which allow no deflection and simply redirect the vehicle into traffic. The most common system used is the semi-rigid one. In the United States of America the US Federal Highway Administration (FHWA) uses the system described as G4(1S) guard rail. It allows for significant deflection and provides acceptable deceleration rates for vehicle occupants. Research undertaken on the use of polymer composite units manufactured by the pultrusion technique (Svenson et al., 1992; Svenson, 1994) showed that the system is capable of absorbing and hence dissipating sufficient impact energy to make them viable for use in roadside safety structures. This research led to the development of design goals for composite guard rail systems (Svenson et al., 1995). In the early 1990s a limited number of composite E-glass and polyester guard-rails, similar in geometric design to the current steel w-beam guard-rails, were produced by a hand lay-up open-moulding process (McDevitt and Dutta, 1993; Dutta, 1998). Bank and Gentry (2000) have described an on-going research and development project investigating the use of glass/thermosetting polymer composite material guardrails as potential replacements for steel w-beam guard-rails. The test programme investigated a range of potential design schemes and composite manufacturing techniques including pultrusion, moulding and sandwich panel construction. The sections analyzed were standard off-the-shelf pultruded sections produced with vinylester resin and E-glass fibre reinforcement consisting of unidirectional rovings and randomly orientated continuous strand mats at a volume fraction of approximately 40%. Typically, the longitudinal modulus and the tensile strengths were 12-21 GPa and 200-275 MPa respectively. The tensile strengths in the transverse direction ranged from 48 to 70 MPa. Although polymer composite materials with high longitudinal fibre content are essentially linear in longitudinal tension, it has been shown that significant energy can be dissipated through crushing, separation and tearing of the composite materials (Svenson, 1994; Palmer et al., 1998). In addition, the linear elastic behaviour of the materials may result in a shorter length of composite guard-rail being damaged during a given impact event relative to a steel guard rail. The composite guard-rail would, therefore, require less rail replacement after a crash. If the composite guard-rail contained continuous glass reinforcement could act as an internal 'cable' within the composite, and thus would ensure that no rupture of the rail occurs during an impact (Bank and Gentry, 2000).

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8.10. Hybrid FRP/concrete members 8.10.L Introduction The civil engineering industry is constantly striving for ways to improve design and construction technologies to obtain a more economical solution to engineering problems. It has long been recognized that, in the area of construction involving reinforced concrete beams, the region of the beam below the neutral axis is wasteful of material. Concrete is very weak in tension and the sole use of this material in this location is to position the reinforcing steel bars and to protect them from aggressive environments. However, this latter property is not completely fulfilled as the concrete in the tensile zone of the loaded beam will crack and allow aggressive substances to attack the steel, causing gradual degradation. On the other hand advanced structural composites (either glass or carbon fibre in vinylester or epoxy polymer matrix), possess excellent in-service properties, in particular, resistance to aggressive substances. Furthermore, composites with high fibre volume fractions have high specific strength and stiffness and have excellent durability with minimum maintenance requirements over thirty years. Thus advanced continuous fibre reinforced polymer composites and concrete wound appear to be an example in which two very dissimilar materials can be joined to form a composite structure. If the high-compressive strength concrete is placed above, and the high-tensile strength fibre/polymer composite is placed below the neutral axis, a composite beam is formed and the two materials will be used to their best advantage. In the case of composite construction employing steel/concrete structural units, shear connectors take the shear/bond resistance between the two components. For a polymer composite and concrete construction this can be achieved by a number of techniques, namely: • lugs in the vertical faces of the permanent shuttering • horizontal bolts through the concrete and vertical faces of the permanent shuttering • bonding the hardened concrete into the permanent shuttering; this implies forming the concrete separately from the composite unit and then bringing the two units together for bonding; this could be a difficult operation on a large-scale beam but would provide a 100% composite action between the composite and cured concrete • an adhesive injection process between the cured concrete and the permanent shuttering • applying an adhesive, which is water-based, to obtain a bond between the applied adhesive and freshly made concrete. 8.10.2. Duplex composite/concrete beams Recent research developments, in particular, at the University of California, San Diego, University of Surrey, UK, University of Warwick, UK, and EMPA, Switzerland, have focussed upon hybrid systems that combine advanced composites with conventional materials, in particular, concrete. One of the earliest attempts to produce a hybrid FRP/concrete beam element was undertaken by Fardis and Khalili (1981). Concrete was cast into FRP boxes and the mechanical role of the FRP was:

Chapter 8. Applications in advanced polymer composite constructions

(a)

269

(b)

Fig. 8.36. Section of concrete beam where the up-stands are either (a) cast into concrete or (b) cast outside the concrete section.

• to provide partial confinement of the concrete in the compression zone • to carry the tensile force in the tension zone • to carry the shear force in the beam through the two sides of the box. The role of the concrete was to provide compressive strength and rigidity in order to prevent local buckling of the FRP casing. Furthermore, the adhesion between the concrete and the FRP is not necessary provided, the FRP box is closed at both ends and the UD fibres at the soffit of the beam have adequate end anchorage. One beam which had no unidirectional axial tension fibres, was considered to be under-reinforced and failed by fracture of the GFRP cloth in tension. All other beams had directional fibres, were over-reinforced and, when tested, experienced ductile behaviour with the concrete failing in compression. At failure the FRP on the three sides of the box was still intact and provided confinement to the concrete which was severely cracked in tension and shear and crushed at the top of the beam. However, unloading after failure led to almost total recovery of the deflection. Hall and Mottram (1998) presented a hybrid section combining GFRP pultruded sections with concrete, the GFRP sections used were commercially available as floor panels. The sections acted, simultaneously, as tension reinforcement and permanent formwork. Fig. 8.36a shows a section of the GFRP reinforcing system having the Tee up-stands and a continuous base; the Tee up-stands are cast into the concrete. Fig. 8.36b shows sections of the composite beam where the up-stands are situated outside the concrete section and Fig. 36c shows a combination of Fig. 36a and b. The whole floor panel was 500 mm wide and composed of polyester resin matrix reinforced with E-glass fibres including unidirectional rovings and continuous filament mat. As the pultruded panels have smooth surfaces, the study included push-out tests from the concrete, when the surface adjacent to the concrete was coated with a moisture compatible cured adhesive and when the surface was 'as received'. The shear bond strength of the examples was 5.3 and 3.2 MPa, respectively. Triantafillou and Meier (1992), Deskovic and TriantafiUou (1995) and Triantafillou (1995) presented an innovative hybrid box section suited for simply supported span. The new system combined composite materials with a low-cost construction material, namely, concrete which resulted in a new concept for the design of lightweight, corrosion free, excellent damping and fatigue properties. A schematic illustration of the hybrid section is shown in Fig. 8.37. The section consisted of a GFRP pultruded box

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FRF Permanent shuttering Concrete

GFRP

:FRP Fig. 8.37. Hybrid concrete. GFRP/CFRP rectangular section (after Triantafillou and Meier, 1992).

section with an upper layer of concrete in the compression side and a thin layer of CFRP in the tension side. The design involved in casting concrete on the upper side of the GFRP and therefore, a part of the GFRP box section was extended to act as permanent formwork for the wet concrete and shear transfer medium between the concrete and GFRP components. The University of Surrey has also been investigating the above form of construction and has realized that buckling of the webs would be one of the critical mode of failure of the system. An optimization study was performed to compare different configurations as shown in Fig. 8.38. The web diaphragm model was found to be the optimum solution. Furthermore, it was realized that complete composite action was necessary for the beam to act efficiently. Tests showed that the most practical and cost effective way to achieve shear/bond resistance between the composite material and fresh-made concrete was to apply a water-based adhesive. The failure mechanism of a standard system was by concrete crushing and local buckling of the GF'RP permanent shuttering, when under a four point loading situation. This failure mechanism is followed by a shear failure of the GFRP composite in the web. Canning et al. (1999), and Hulatt et al. (2000, 2001) give details of the development of this composite/concrete duplex beam for both a standard rectangular and a Tee beam cross-sections, respectively. Thefinalversions of these beam sections consisted of either a sandwich construction, for the webs below the neutral axis, shown in Fig. 8.39, or hollow box beams with two vertical (webs) skins of polymer composite and web diaphragm stiffeners shown in Fig. 8.40. The inner and outer faces of the sandwich system (Canning et al., 1999) were manufactured from ACG Ltd. Derbyshire material^ as ± 45° glassfibreprepregs and had three and seven layers of composites, respectively. The foam core was made of Airex R63.80 PVC rigid foam and was 12 mm thick. The GFRP face materials of the web's sandwich construction extended into the compressive region to form the permanent shuttering for the concrete. The soffit of the beam was fabricated by wrapping the ±45° GFRP prepreg around the base of the beam; laminates of unidirectional CFRP prepreg'^ were interleaved in four layers between the GFRP ^ GFOIOO (390 g/m- E-glass 2 x 2 twill)/LTM 26-50% fibre volume fraction. -^ HTA 12k 150 g/m^ LTM 26-28 g/m- 60% Vf.

Chapter 8. Applications in advanced polymer composite constructions

271

Concrete FRP composite

GFRP composite

>

CFRP composite

CFRP composite

(a)

(b)

Concrete

Concrete —

Vertical transverse stiffeners in web

+/-45° GFRP composite

-f/-45° GFRP composite interleaved with 0° C m P composite

+/-45° GFRP composite interleaved with 0° CFRP composite (c)

(d)

Horizontal transverse stiffener in web

(e)

(f)

+/-45° GFRP corrugated composite

+/-45° GFRP composite interleaved with 0° CFRP composite

(g) Fig. 8.38. Different configurations for duplex beams.

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Advanced polymer composites and polymers in the civil infrastructure

L8mm 0.9nmi

Total thickness of outer faces = 2.1mm Total thickness of CFRP = 0.6mm

NOT TO SCALE 14mm 3.6mm

0.9mm'

12mifk :)imin 51mm ^^ii22m ' 12mn^ mm m'

0.' 0.9mm

2.1mm 2.1mm Fig. 8.39. Cross-section of rectangular composite/concrete beam (Canning et al., 1999).

u

140

f

Two pUes of +/- 45« GFRP manufactured from XLTM65U prepreg 151.08

4min plywooi plate Eight plies of 0/9(K CFRP from XLTM65U prepreg 80 Fig. 8.40. Cross-section of Tee beam of composite/concrete construction (Hulatt et al., 2000).

laminates. A variety of manufacturing techniques were available; for this project the ACG Ltd. Low-temperature vacuum pressure prepreg moulding was chosen as the most suitable material process.

8.11. Concrete-filled tubular compressive members In Section 5.12.18 of Chapter 5 a discussion was made of the wrapping of RC columns using composites manufactured from the RIFT method or by a wet lay-up

Chapter 8. Applications in advanced polymer composite constmctions

213

technique for upgrading existing structures. For new structural members the concretefilled FRP tube systems utilize the best characteristics of the individual materials. The concrete core supports the FRP tube and prevents premature local buckling failure experienced in hollow tubes, whilst the tube confines the concrete and increases its strength and ductility. In addition, the system simplifies the construction procedures and reduces erection time. The concept of concrete-filled FRP tubes was developed for two different uses. Firstly, to develop non-corrosive piles for marine environments; this has been discussed by Mirmiran and Shahawy (1996) and Parvathaneni et al. (1996). Secondly, to enhance the ductility of the tubes. The second example has been discussed by Seible (1996) and Seible et al. (1998) in terms of bridge columns and piers in seismic zones. This section will discuss the concrete-filled pre-cast FRP and steel tubes. 8.11.1. Concrete-filled steel tubes to act as axial compression members Gardner and Jacobson (1967) noted that Sewell in 1901 was the first recorded engineer to use concrete-filled tubes but he used them only to protect the inside of the tube against rusting. When some of these columns were accidentally overloaded he noticed that the stiffness had increased by 25% over that of the hollow section. Furlong (1967), Gardner and Jacobson (1967), Prion and Boehme (1994) and Kilpatrick and Rangan (1997) have also shown that the steel tube acts as permanent form-work and provides well-distributed reinforcement which is located at the most efficient location. The confined concrete prevents the steel columns from buckling inwards and this forces the local buckling of the column outwards and thus into a higher buckling mode. Consequently, it develops a higher critical buckling load. The steel tubes confine the concrete laterally thus placing the concrete into a tri-axial state of stress. In addition to improving the compressive load characteristics of the column, the ultimate bending strength of the concrete/steel column is increased considerably which in turn will increase the initial flexural stiffness and ductility. As the shear capacity of the concrete-filled steel tubular members is high the tubes will fail predominately in flexure in a ductile manner. When the concrete-filled circular steel tube is loaded in compression, under an axial load applied to both the steel cylinder and the concrete, the steel tube has no confining effect at axial strain levels of less than 0.001. This is because the Poisson ratio of concrete is lower than that of steel; these values are 0.15-0.25 and 0.283 respectively. As the load increases, the lateral expansion of the unconfined concrete increases and approaches that of steel. At this point a radial pressure develops at the steel/concrete interface and confinement is maintained. The confinement level of the concrete is higher if the load is applied to the concrete only. 8.11.2. Concrete-filled FRP tubes to act as axial compression members It is possible to manufacture FRP tubular sections by the filament wound process and to fill these with concrete. The jacket will have a low elastic modulus in the longitudinal

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Advanced polymer composites and polymers in the civil infrastructure

direction, due to being lightly reinforced in this direction and therefore, the concrete will take the majority of the axial load. The FRP jacket will be loaded essentially in the hoop direction and, unlike the steel jacket, the FRP expansion in this direction due to the Poisson ratio effect of the axial load is less than that of the concrete thus providing a significant confinement. This scenario will prevent the tube failing prematurely by local buckling as is the case with steel tubes. Furthermore, the FRP jacket will, in the early stages of loading, expand less than the steel tube in the hoop direction. In addition, the orthotropic structure of the FRP shell allows de-coupling of the two fibre orientations for design optimization. 8.11.3. Composite action between advanced polymer composite and concrete If composite action between the composite jacket and the concrete is required, it can be achieved by the application of an adhesive, by mechanical shear connectors in the form of internal ribs or by an expansive agent applied to the concrete at the time of mixing to produce a high friction with the inside of the jacket. 8.11.4. Comparison between steel and FRP confined concrete Samaan et al. (1998) have compared the stress-strain behaviour of concrete-filled GFRP tubes with those of concrete-filled steel tubes. As steel jackets have a high modulus of elasticity, the confining action commences at a low load level (this assumes that the steel jacket is not loaded axially and that the concrete takes the whole axial load) compared with that of GFRP which is insensitive to small lateral expansion. Consequently, in this latter case, the system will behave similarly to an unconfined concrete situation. As the unconfined strength of the concrete is reached micro-cracking develops in it with high lateral expansion occurring and activation of the hoop strength of the FRP composite. The variable confining pressures will increase consistent with the linear characteristic of the FRP until the jacket reaches its hoop strength and the concrete fails. Fig. 8.41 illustrates the stress-strain response of a GFRP and a steel confined concrete. 8.11.5. Piles manufactured from FRP/concrete members Investigations by Jolly and Lillistone (1998) used the concept of hybrid systems in which filament wound composite tubes, filled with concrete, can be used as hybrid shells for bridge columns. The prefabricated filament wound tubes serve the dual functions of reinforcement and permanent form-work for the concrete. The concrete aids the compression force transfer and stabilizes the thin-walled shell. Between 1994 and 1999 a new piling system was developed for the Rorida, Department of Transport, consisting of concrete-filled GFRP tubes some of which were designed as under-reinforced and some as over-reinforced systems (Shahawy and Mirmiran, 1998; Mirmiran and Shahawy, 1999). The corrosion resistance required a minimum of 0.0155 m^ section for the piles when they were driven into salt water or water containing a high chloride content and wet/dry cycles, regardless of the load

Chapter 8. Applications in advanced polymer composite constructions

275

Steel-confined concrete

0.01

0.02

0.03 Axial

0.04

0.06

strain

Fig. 8.41. Stress-strain response of GFRP-confined concrete versus steel-confined concrete (after Samaan et al., 1998).

level. The reason for encasing the concrete into GFRP was to protect the concrete core and to alleviate the problems of moisture intrusion and permeability. The wall thickness of the FRP tubes was 14 mm and 6.6 mm for the over- and under-reinforced concrete-filled GFRP tubes; this resulted in 18.2% and 7.51% reinforcement ratios respectively. The designers introduced a reinforcement index, which is defined as the ratio [the tensile strength of the tube in the axial direction/the concrete compressive strength] multiplied by [the reinforcement ratio]. The reinforcement indices of the overand under-reinforced sections were 3.39 and 0.19 respectively. Under an increasing bending moment and fixed axial load, these two types of piles exhibit a momentcurvature response that is bi-linear with the transition point between the two slopes corresponding to major cracking in the concrete. The upper slope of the over-reinforced system is considerably larger than the under-reinforced one, although the lower slopes of the graphs for both under- and over-reinforced systems were approximately the same. Shahawy and Mirmiran (1998), manufactured a filament wound tube of ±45° GFRP composite which had axial tensile and compressive strengths of 105 and 230 MPa, respectively. The encapsulated concrete had a compressive strength of 21 MPa. Initially the column was loaded with 1779 kN axial load, then four point bending tests were undertaken over 2.6 m span. At 89 mm deflection the test was stopped and at zero load there was over 50% deflection recovery. The beam was then given a cyclic load and failed at 200 kN m bending; the central deflection was 1/20 of the span. The failure was by fracture of the bottom fibres. From these tests the authors concluded that bond failure between the GFRP casing and the confined concrete was satisfactory; therefore, standard sections can be used. However, it should be noted that a shear transfer mechanism (see Section 8.11.3) is required for beams. In addition, the authors recommended that the

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over-reinforced section should be used due to the higher failure load, lower deformation and greater ductility compared with the under-reinforced system. 8.11.6. Prestressed FRP tubes/concrete members Parvathaneni et al. (1996) introduced a filament wound GFRP tube prestressed in the axial direction in compression and filled with concrete. The object was to replace traditional steel tube piles, which were being corroded, by composite tubes containing concrete, at the Cedar Shore resort marina. Chamberlain in South Dakota, USA. The authors estimated that, depending upon the thickness and diameter of tube, fibre architecture and Poisson's ratio, the ultimate compressive strength of the confined concrete would be 6-8 times that of its unconfined strength. The piles were subjected to bending and tensile stresses. The thickness and diameter of the tubes were 6.35 mm and 318 mm respectively, and were manufactured by the filament wound technique using two different types of mandrels; these were a plastic 'in situ' tube and a collapsible aluminium tube. The 13.72 m long tube was fabricated in three separate segments which were spliced together by short steel tubes, 0.6 m long and matched with the inside diameter of the FRP tubes and filled with concrete. The prestress to the GFRP tubes was applied by means of three Dywedag bars of 35 mm diameter paced inside the tubes. A 35 MPa concrete was then cast inside the tube. The steel bars were de-stressed causing the concrete to be stressed to 31 MPa in compression. On site a conventional diesel driven hammer was used to drive the piles into the ground. The 13.72 m long test pile was instrumented and the maximum dynamic strain in the concrete was recorded as 1360 |x strain in compression and no tensile strains were induced. It was driven 7.62 m into the river bed and under a lateral load of 8.9 kN the lateral deflection was 34 mm.

8.12. FRP composite/concrete beams for short and medium span bridge A concrete-filled composite shell system (CSS) was developed at the University of California, San Diego (Seible et al., 1995) after conducting successful tests on bridge columns retrofitted with thin carbon fibre jackets to provide ductility and shear strength as a seismic retrofit. The (CSS) was constructed by the use of a thin-walled pre-manufactured carbon fibre composite shell with both hoop reinforcement (90° from member axis) and ±10° longitudinal fibre reinforcement manufactured by the filament winding process. A special mandrel enabled the helical ribs on the inside of the carbon shell to be formed in order to provide shear transfer between the lightweight infill concrete and the shell; this is shown in Fig. 8.42. The concept was validated by large-scale flexural tests that featured conventional starter bar connections; it replaced conventional reinforcing steel and the form-work, whilst providing enhanced confinement to the concrete core, increases durability and greatly enhances ease of handling and erection speeds. The experimental programme used a building block approach to characterize the behaviour of the key components as steps towards characterization and ultimate field demonstration

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Fig. 8.42. Helical rib on the inside of the carbon shell (by kind permission of V. Karbhari and F Seible at UCSD).

of the prototype bridge system. The dimensions for the test units (Karbhari et al., 2000), were determined from a design performed on a prototype bridge. These were as follows: • the geometry of the carbon shell was that of a cylindrical tube with an inside diameter of 343 mm and wall thickness of 10 mm • the shell lay-up architecture was 80% longitudinal (±10° helical) and 20% transverse (90*") fibre reinforcement • the average fibre volume fraction was 55% • the longitudinal and transverse modulus of elasticity was 97.8 GPa and 25.7 GPa respectively • the longitudinal and transverse Poisson ratio was 0.18 • the concrete in-fill was a 20.7 MPa lightweight concrete pump mix. The (CSS) column was developed further for use as girders and beams (Burgueno et al., 1998), and in addition, a design was developed for a square or rectangular section thin-walled carbon shell; these shells incorporated large rounded corners, to enable them to exhibit significant confinement effects (see Section 5.12.20). Furthermore, the large radii of curvature are beneficial for the strength development in the carbon fibre composite shell since carbon fibres are sensitive to transverse pressure. The circular section was advantageous in terms of concrete confinement and for filament wound manufacturing techniques but it did have limitations in girder type applications. It is possible to splice the girders where necessary and in a similar way to that used for column and connectors, mild steel reinforcement bars or FRP reinforcing units can be used.

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An extension of the confined concrete columns (circular or rectangular cross-section) has been to develop complete structural systems. Complete bridge systems can be composed of linear segments of carbon shell tubes assembled together by means of longitudinal and off axis joints with appropriate mechanisms depending upon the response required for the structural component. Karbhari et al. (2000) developed an experimental prototype beam and slab bridge system, shown in Fig. 8.43; the main reason for this investigation was to provide the basis for design and analysis of new modular fibre reinforced composite bridge systems. The concrete-filled carbon shell system allowed for new modular bridge components, consisting of prefabricated filament-wound carbon/epoxy thin shells filled on-site with concrete. The shell served the dual function of reinforcement and permanent shuttering for the concrete core. The function of the concrete was to provide compression force transfer, to stabilize the thin shell against buckling and to allow for the anchorage of connection elements. Transverse ribs were provided on the inside surface of the carbon shell, to allow a force transfer between the concrete in-fill and the shell. The concrete-filled carbon shell was then combined with a structural deck system to form the super-structure component. The deck system may consist of either a conventional cast-in-place reinforced concrete slab or an advanced composite modular deck design. The connection between the deck and the carbon fibre shell girder can be accomphshed by conventional dowel technology by embedding shear connectors into the shell system during grouting. The dowels are either cast directly into the RC deck or anchored by polymer concrete-filled sections of the cellular advanced composite deck system, Fig. 8.44 shows a section through the connection. Karbhari et al. (2000) suggest that additional advantages of such structural systems are the lightweight carbon shell system which provides significant advantages in the construction process of structural members. No heavy lifting equipment is required on site to place the shells and no reinforcement cage construction and placement as would be the case for RC construction, as well as, form-work removal are no longer necessary. Burgueno et al. (2001) have undertaken experimental and numerical dynamic characterization of the FRP bridge superstructure assembly. These forced vibration tests in conjunction with the numerical modelling provided the basis for the characterization of the system durability in terms of the structural integrity, damage tolerance and health monitoring. Therefore, the vibration-based modal investigations were used as a health-monitoring and level 1 NDE technique for that bridge system and the clearest indicators of the state of structural condition were the fundamental frequencies and the vibration mode shapes. The Kings Stormwater Channel bridge (Karbhari et al., 1998; Seible et al., 1999) is a demonstration bridge (based upon the design shown in Fig. 8.43), on California State Route 86, near the Salton Sea. The prototype bridge was completed in the sunmier of 2(K)0. It is a short-span beam and slab structure (2 x 10 m long, 2-lane highway bridge) which uses concrete-filled carbonfibre/epoxytubes as the girders and a modular FRP E-glass/vinylester polymer deck system. The structure is composed of six longitudinal girders (10 mm wall thickness and 0.34 m inside diameter) filled on site with hghtweight concrete. Fig. 8.45 shows a photograph of the beam and slab bridge under construction. The girders are connected to the abutment end diaphragm and the centre cap beam by continuing the carbon shell into the reinforced concrete elements and by

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providing a conventional steel reinforcement anchorage. The pier columns, which are situated in a river bed, are conventional reinforced concrete pile extensions encased in a carbon fibre/epoxy composite shell. This construction will allow an evaluation of the environmental durability of the composite. This system is claimed to be one of the most

Fig. 8.45. Kings Stormwater Channel bridge, Salton Sea, CA, USA (by kind permission of V. Karbhari and F Seible at UCSD).

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(T) Hybrid Tubular Girder ®

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efficient structural options in the development of advanced composite deck systems. The modular FRP E-glass deck consists of pultruded trapezoidal elements bonded together and overlaid with continuous face sheets under factory conditions. A typical composite deck weighs 1-1.5 kN/m^, which is 25% of that of a conventional reinforced concrete deck. A second modular system incorporates a new FRP girder system, which is rectangular, and has an anchorage concept for connectors to enable easy assembly of the system. The Hybrid Tube System (HTS) uses hollow E-glass-carbon/vinylester girders, to which the transverse spanning stiffener deck panels are attached, with snap-in shear stirrups connected to a polypropylene fibre reinforced concrete deck. The modular prefabricated bridge system is shown in Fig. 8.46. The girders are fabricated through the pultrusion or wet lay-up process with longitudinal carbon reinforcement in the bottom flange. The tubes are left ungrouted except for the connection regions. An FRP form panel is snap-locked to the pultruded girders, providing a tension tie between girders and the stay-in-place form for the fibre-reinforced arch action type concrete deck. The liner of the tension tie panel is composed of a unidirectional carbon/epoxy laminate with top and bottom face sheets composed of E-glass/vinylester chopped strand mats. To provide stiffness to the panels and thus allow for full construction loads, the transverse FRP laminate is overlaid with lightweight polymer concrete. The I-5/Gilman advanced technology bridge, shown in Fig. 8.47, will provide a link between the east and west parts of the University of California, San Diego campus, which are separated by a ten-lane interstate freeway. The functional requirements are to provide service for two 3.7 m wide lanes of vehicular traffic, two 1.8 m wide lanes

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Fig. 8.47.1-5/Gilman advanced technology bridge to link two separate areas of the campus at University of California, San Diego, USA (by kind permission of V. Karbhari and F. Seible at UCSD).

for bicycles, two 1.5 m wide pedestrian walkways and utility tunnels. The bridge is to be a 137 m long dual plane fan-type cable-stayed bridge supported by a 58 m high A-frame pylon with circular legs, 1.68 m in diameter, filled with normal concrete. The carbon fibre/epoxy shell members of the pylon consist of circular tubes, each with an inside diameter of 1.52 m and wall thickness of 13 mm. The bridge deck design utilizes the composite bridge system discussed above. Two longitudinal carbon fibre/epoxy girders spaced 13.7 m apart and filled and grouted with lightweight concrete forms the superstructure of the bridge. These two beams are joined in the longitudinal direction by hybrid E-glass/carbon fibres/vinylester girders that in turn support a polypropylene fibre reinforced concrete arch deck. The longitudinal carbon fibre/epoxy shell members consist of circular tubes, each with an inside diameter of 914 nmi and a wall thickness of 10 mm. The longitudinal girders are divided into 9.75 m segments and are spliced by means of conventional steel reinforcement. Conventional steel dowels anchored into the concrete of the carbon fibre/epoxy shell (beam) and extended into the fibre reinforced concrete deck achieve the connection between these girders and the slab. The transverse girders are manufactured from the hollow pultruded hybrid rectangular beams, discussed above, and have a depth of 711 mm, a vertical shear wall thickness of 19 mm, a 25 mm and a 76 mm wall thickness at the soffit and at the top anchorage zone, respectively. These hybrid transverse box beams are spaced at 2.4 m along the centre of the bridge length and straddle the longitudinal girders. A limited number of FRP cable stays will be manufactured from carbon fibre/epoxy and aramid fibres and used within the short span but the majority of cable stays will be made from steel; clusters of

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cable stays will be instrumented and monitored. The abutments will be of conventional form. The first FRP composite highway bridge, located in Rexville, New York, was opened in October 1998. This was the country's first such FRP superstructure, on a Federal Highway Administration (FHWA), recognized state highway. It was also the first FRP bridge to employ a high skew angle, integral barrier and deck cross-slopes. A comprehensive test programme, comprising of yearly load tests and finite element analyses is in progress to document its long-term performance. As part of these tests, experimental modal analysis techniques were used to characterize its dynamic properties and to calibrate analytical and theoretical analyses (Alampalli, 2000). 8.13. Observations This new group of very promising materials, namely advanced polymer composite materials, are being applied to, and used increasingly in, the construction industry. This chapter has attempted to show how these materials are utilized in bridges and buildings and in the rehabilitation and strengthening of existing structures. In view of the positive material properties, such as high strength/weight ratio, high resistance to corrosion and the low thermal conductivity, it has undoubtedly the potential to bring about far reaching innovations in bridge and structural engineering. However, the continued use of FRP composite in civil engineering infrastructure applications is dependent, amongst other factors, on the demonstration of their enhanced durability and lower whole life cycle costs as compared to conventional materials. Currently, there is a lack of a comprehensive data base on the long-term response and there is a need to provide cost effective and efficient means of non-destructive evaluation and health monitoring of these systems in thefield.Examples of the techniques for long-term field health-monitoring of structures are: • forced vibration testing in conjunction with analytical modelling provides the basis for system characterization and health monitoring • strain analysis using optical fibres • electronic stain gauges.

8.14. References Alampalli, S. (2000), Modal analysis of a fiber-reinforced polymer composite highway bridge, IMAC, San Antonio, USA. Anon (1993), Carbon fibre strands prestress Calgary span, Eng. News Rec. 18 October, p. 21. Bank, L.C. and Gentry, T.R. (2000), Composite materials for roadside safety structures. In Composites in Transportation Industry, Proc. of the ACUN-2 International Composites Conference, Sydney, Australia, pp. 61-72. Burgueno, R., Davol, A. and Seible, F. (1998), The carbon shell system for modular bridge components, 2nd Int. Conf. Composites in Infrastructure, Tucson, AZ, Jan. 1998. Burgueno, R., Karbhari, V.M., Seible, F. and Kolozs, R.T. (2001), Experimental dynamic characterisation of a FRP composite bridge superstructure assembly, Int. J. Composite Struct., in press. Canning, L., HoUaway, L. and Thorne, A.M. (1999), Manufacture, testing and numerical analysis of an

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innovative polymer composite/concrete structural unit, Proc. Inst. Civ. Eng. Structures and Bldgs, Vol. 134, pp. 231-241. Casas, J.R. and Aparicio, A.C. (1990), A full-scale experiment on a prestressed concrete structure with high strength fibres: the North ring road in Barcelona, FIP-XI Int. Congr, Hamburg, June 1990, paper T15. Chajes, M., Gillespie, J., Mertz, D. and Shenton. H. (1998), Advanced composite bridges in Delaware, Proc. ICCI '98, Vol. 1, Tucson. AZ, 1998, pp. 645-650. Composites Offshore (1998), Composites rise to the challenge of the deep, Reinf. Plast. 42(11), 33. Cuninghame, J. and Sadka, B. (1999), Fibre reinforced strengthening of bridge supports to resist vehicle impact, SAMPE Europe Int. Conf., Paris, 14 April, 1999. Deskovic, N. and Triantafillou, T.C. (1995), Innovative design of FRP combined with concrete: short-term behaviour, J. Struct. Eng. 121(7), 1069-1078. Dutta, RK. (1998), Investigations of plastic composite materials, CRREL Report 98-7, US Army Corps of Engineers. Eddie, D., Rizkalla, S. and Shalaby, A. (1998), Research in Progress Session. October 25-30, Presented at 1998 Fall Convention, American Concrete Institute in Los Angeles, CA. Fam, A.Z. and Rizkalla, S.H. (2001a), Confinement model for axially loaded concrete confined by circular FRP tubes. Struct. J., 98(4), in press. Fam, A.Z. and Rizkalla, S.H. (2001b), Behaviour of axially loaded concrete-filled FRP tubes, Struct. J., 90(3), 1-10. Fardis, M.N. and Khalili, H., (1981), Concrete encased in fibreglass-reinforced plastic, J. Am. Concrete Inst., 78(6), 440-446. Furlong, R.W. (1967), Strength of steel-encased concrete beam columns, Proc. ASCE, Vol. 93, No. ST5, Oct. pp. 113-124. Gardner, N.J. and Jacobson, E.R. (1967), Structural behaviour of concrete filled steel tubes, ACI J., Title No. 64-38, July, pp. 404-416. Goldsworthy and Associates, Inc. (1994), Test Reports for 28 metre Fastenerless Transmission Tower. Goldsworthy, W.B. and Heil, C. (1998), Composite Structures are a Snap, 2nd Int. Conf. Composites in Infrastructure, Vol. 2, Tucson, AZ, pp. 382-396. Hall, J.E. and Mottram, J.T. (1998), Combined FRP reinforcement and permanent formwork for concrete members, J. Compos. Construct., ASCE 2(2), 78-86. Head, P. (1996), High performance structural materials: advanced composites, lABSE Colloquium on Remaining Structural Capacity, Copenhagen. Head, PR. (1998), Advanced composites in civil engineering — a critical overview at this high interest, low use stage of development, Proc. ICCI, Vol. 1, Tucson, AZ, pp. 3-15. HoUaway, L.C. and Head, PR. (2(X)0), Composite materials and structures in civil engineering. In Chapter 6.25 Vol. 6 (M.G. Bader, K.T. Keedward and Yoshihiro Sawada, eds.) of Comprehensive Composite Materials (A. Kelly and C. Zweben, eds. in chief), Elsevier, Amsterdam, pp. 489-527. Hollaway, L.C. and Leeming, M.B. (1999), Strengthening of reinforced concrete structures using externally bonded FRP composites. In Structural and Civil Engineering (L.C. Hollaway and M.B. Leeming, eds.), Woodhead Publishing, Cambridge. Hollaway, L. and Spencer, H. (2000), Modem Developments. In Manual of Bridge Engineering, (M.J. Ryall, G.A.R. Parks and J.E. Harding, eds.), Thomas Telford, London, Ch. 13. Hulatt, J., Hollaway, L. and Thome, A. (20(X)), Characteristics of composite concrete beams. In Bridge Management 4. Inspection, Maintenance, Assessment and Repair (M.J. Ryall, G.A.R. Parke and J.E. Harding, eds.), Thomas Telford, London, pp. 483-491. Hulatt, J., Hollaway, L.C. and Thome, A.M. (2001), Developing the use of advanced composite materials in the construction industry. In Proc. Int. Conf. FRPRC-5, Cambridge, UK, July 2001. Hutchinson, R., Abdelrahman, A. and Rizkalla, S. (1997), Shear strengthening using CFRP sheets for a prestressed concrete highway bridge in Manitoba, Canada. In Recent Advances in Bridge Engineering — Advanced Rehabilitation, Durable Materials, Non-destructive Evaluation and Management (U. Meier and R. Betti, eds.), Proc. Workshop held at EMPA, Dubendorf. pp. 97-104. Isogrid Design Handbook (1975), McDonnell Douglas Aeronautics Company, USA. Iyer, S.L. (1993), Advanced composite demonstration bridge deck. In Fibre Reinforced Plastic Reinforce-

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ment for Concrete Structures (A. Nanni and C.W. Dolan, eds.), SP 138, American Concrete Institute, Detroit, p. 83. Jensen, D.W. (2000), A glimpse into the world of innovative composite IsoTruss™ grid structure, SAMPE J. 36(5), 8-16. Jolly, C.K. and Lillistone, D. (1998), Stress-strain behaviour of confined concrete. Concrete Communication Conference '98, British Cement Association, Crowthoren, Berkshire, pp. 117-135. Karbhari, V.M. and Seible, F. (2000), Fibre reinforced composites — advanced materials for the renewal of civil infrastructure. Appl. Compos. Mater. 7, 95-124. Karbhari, V.M. and Zhao, L. (1998), Issues related to composite plating and environmental exposure effects on composite-concrete interface in external strengthening. Compos. Struct. 40(3/4), 293-304. Karbhari, V.M., Engineer, M. and Eckel, D.A. (1996), On the durability of composite rehabilitation schemes for concrete; use of a peel test, J. Mater. Sci. 32, 147-156. Karbhari, V.M., Seible, R, Hegemier, G. and Zhao, I. (1997), Fibre reinforced composite decks for infrastructure renewal — results and issues, Proc. Int. Composites Expo, Nashville, TN, pp. 3C/1-3C/6. Karbhari, V.M., Seible, F., Burgueno, R., Davol, A., Wemli, M. and Zhao, L. (1998), Structural characterisation of fibre reinforced composite short and medium span bridge systems. In Proc. ECCM-8 Naples, June, pp. 35-42. Karbhari, V.M., Seible, F., Burgueno, R., Davol, A., Wemli, M. and Zhao, L. (2000), Structural characterisation of fiber-reinforced composite short- and medium-span bridge, Appl. Compos. Mater. 7, 151182. Kilpatrick, A.E. and Rangan, B.V. (1997), Tests on high-strength composite concrete columns. Research Report No. 1/97, School of Civil Engineering, Curtin University of Technology, Perth, WA, March. Kim, TD., Koury, J.L., Telford, K.N., Tracy, J.J. and Harvey, A. (1993), Continuous fibre composite Isogrid for launch vehicle application, Proc. 9th Annu. Conf. Composite Materials, Vol. 6, July, p. 106. Lopez-Anido, R., Ganga Rao, H.V.S., Troutman, D. and Williams, D. (1998), Design and construction of short-span bridges with modular FRP composite decks, Proc. ICCI, Vol. 1, Tucson, AZ, pp. 705-714. Mander, J.B. et al. (1988), Theoretical stress-strain model for confined concrete. J. Struct. Eng. 114(8), 1804-1826. McDevitt, C.F. and Dutta, P.K. (1993), New and recycled plastic composites for roadside safety hardware, Plast. Build. Construct. 18(2), 6-12. McKenzie, M. (1991), Corrosion Protection: the environment created by bridge enclosure. Research Report 293, TRRL, 1991. McKenzie, M. (1993), The corrosivity of the environment inside the Tees Bridge Enclosure, Final Year Results, Project Report PR/BR/10/93, TRRL, 1993. Mirmiran, A. and Shahawy, M. (1996), A new concrete-filled hollow FRP composite column. Composite Part B: Engineering, Special Issue on Infrastructure, Vol. 27B(3-4), 263-268. Mirmiran, A. and Shahawy, M. (1999), Comparison of over- and under-reinforced concrete-filled FRP tubes, Proc. 13th ASCE Engineering Mechanics Division Conf., Baltimore, MD, June 13-16. Noritke, K. (1993) Practical applications of aramid FRP rods to prestressed concrete structures. In Fibre Reinforced Plastic Reinforcement for Concrete Structures (A. Nanni and C.W. Dolan, eds.), SP 138, American Concrete Institute, Detroit, p. 853. O'Connor, J., Yannotti, A.P, Alampalli, S. and Khoung Luu (1999), FRP composites for bridge rehabihtation in New York, Proc. 16th Annu. Meet. Int. Bridge Conference, June 14-16, Pittsburgh, PA, pp. 143-147. Palmer, D.W., Bank, L.C. and Gentry, T.R. (1998), Progressive tearing failure of pultruded composite box beams: experimental and simulation. Compos. Sci. Technol. 58(8), 1353-1359. Parvathaneni, H.K., Iyer, S. and Greenwood, M. (1996), Design and construction of test mooring using superstressing. In: Proc. Advanced Composite Materials in Bridges and Structures (ACMBS), Montreal, pp. 313-324. Pinzelli, R. (1999), Kevlar® Aramid fibre for external strengthening and repair of concrete structures. In Proc. Strucmral Faults and Repair 99, Paper B-15 July, London. Prion, H.G.L. and Boehme, J. (1994), Beam-column behaviour of steel tubes filled with high strength concrete, Can. J. Civ. Eng. 21, 207-218. Roadside Design Guide, 1989, AASHTO, Washington, DC.

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Samaan, M., Mirmiran, A. and Shahawy, M. (1998), Model of concrete confined by fiber composites, J. Struct. Eng. Sept., 1025-1032. Seible, F. (1996), Advanced composite materials for bridges in the 21st century. In Proc. First Int. Conf. Composites in Infrastructure (ICCF 96), Tucson, AZ, Jan., pp. 17-30. Seible, F., Sun, Z. and Ma, G. (1993), Glass fibre composite bridges in China, ACTT - 93/01, University of California, San Diego. Seible, F., Burgueno, R., Abdalah, M.G. and Nuismer, R. (1995), Advanced composite carbon shell systems for bridge columns under seismic loads. In Proc. National Seismic Conference on Bridges and Highways, San Diego, CA, Dec. Seible, F, Karbhari, V.M., Burguefio, R. and Seaberg, E. (1998), Modular advanced composite bridge system for short and medium span bridges. In Proc. 5th Int. Conf. Short and Medium Span Bridges, Calgary, AB, July, p. 11. Seible, F, Karbhari, V.M. and Burgueno, R. (1999), Kings Stormwater Channel and I-5/Gilman Bridges, USA, Adv. Mater., Struct. Eng. Int. 4, 250-253. Shahawy, M. and Mirmiran, A. (1998), Hybrid FRP-concrete beam-column. In Proc. 5th Int. Conf. Composites Engineering (ICCE/5), Las Vegas, NV, July, pp. 619-620. Svenson, A.L. (1994), Impact characteristics of glass fibre reinforced composite materials for use in roadside safety barriers. Report FHWA-RD-92-090, FHWA, US. Svenson, A.L., Hargrave, M.W. and Bank, L.C. (1992), Impact performance of glass fibre composite materials for roadside safety structures. In Advanced Composite Materials in Bridges and Structures (K.W. Neale and P. Labossiere, eds.), Proc. 1st International Conference for Advanced Composite Materials in Bridges and Structures, Sherbrooke, Canada, Oct. 6-9, Canadian Society for Civil Engineering, pp. 559-568. Svenson, A.L., Hargrave, M.W., Tabiei, A., Bank, L.C. and Tang, Y. (1995), Design of pultruded beams for optimisation of impact performance, Proc. 50th Annu. SPI Conference, 10-E, pp. 1-7. Taljsten, B. (1997), Strengthening of concrete strucmres for shear with bonded CFRP fabrics. In Proc. US-Canada-Europe Workshop on Recent Advances in Bridge Engineering — Advanced Rehabilitation, Durable Materials, Non-destructive Evaluation and Management (U. Meier and R. Betti. eds.), EMPA, Dubendorf. Triantafillou, T.C. (1995), Composite materials for civil engineering construction, Proc. 1st Israeli Workshop on Composite Materials for Civil Engineering Construction, Haifa, May, pp. 17-20. Triantafillou, T.C. and Meier, U. (1992), Innovative design of FRP combined with concrete, Proc. 1st Int. Conf. Advanced Composite Materials for Bridges and Structures (ACMBS), Sherbrooke, Que., pp. 491-499. Triantafillou, T.C. and Plevris, N. (1991), Post strengthening of RC beams with epoxy bonded fibre composite materials, Proc. Specialty Conference Advanced Composites Materials in Civil Engineering Structures, NV, pp. 245-256. Tsuji, Y, Kanda, M. and Tamura, T. (1993), Applications of FRP materials to prestressed concrete bridges and other structures in Japan, PCI J. July-Aug., 50. Wolff, R. and Meisseler, H.J. (1993), Glass fibre prestressing system. In Alternative Materials for the Reinforcement and Prestressing of Concrete (J.L. Clarke, ed.), Blackie, Glasgow, pp. 127-152.

8.15. Bibliography Departmental Standard BD/48/93. The Assessment and Strengthening of Highway Bridge Supports 1993.