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Bridge construction and beyond
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Bridge construction and beyond M a u n s e l l Structural Plastics has s p e n t the last t e n years d e v e l o p i n g systems for u s i n g advanced compos i t e s in c o n s t r u c t i o n a p p l i c a t i o n s . S u c c e s s e s i n c l u d e e n c l o s u r e p a n e l s on t h e A19 T e e s Viaduct and the A b e r f e l d y G o l f C o u r s e bridge. Brian R i c h m o n d , m a n a g i n g director o f t h e UK-based c o m p a n y reviews t h e s e projects and l o o k s at further areas w h e r e the ACCS system can be applied.
Plank
3-Way Connector
he Aberfeldy cable stayed bridge is the world's first major bridge in advanced composite materials and i ncorporat es a n u m b e r of i n n o v a t i o n s in s t r u c t u r a l systems, materials and m e t h o d s of construction. Figure 1 shows a view of the 63 m span, 112 m long bridge crossing the River Tay at t he Aberfeldy Golf Club providing access to a new section of t he course. The towers and the deck st ruct ure are fabricated from Maunsell Structural Plastics' Advanced C o m p o s i t e C o n s t r u c t i o n System (ACCS) using the cellular modules shown in Figure 2 which are glass reinforced pultrusion (E-glass/isophthalic resin). The bridge was c om pl et ed in October 1992 and has already proved itself capable of withstanding the
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FIGURE 1:
Aberfeldy composite cable stayed bridge.
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REINFORCED PLASTICS OCTOBER 1993
ToggleConnector
FIGURE 2: Advanced Composite Construction System (ACCS) modules.
e x t r e m e s of both wind and flooding which w e r e e x p e r i e n c e d in t h e following few months. As well as d e m o n s t r a t i n g vibration characteristics u n d e r normal use which were as good as the best comparable conventional structures. The a p p r o a c h chosen was successful in meeting the golf club's s h o r t term and long t e r m financial r e q u i r e m e n t s as well as satisfying the local planning a u th o rity for the following reasons: • the structural form and system chosen was capable of spanning the fast flowing a n d u n p r e d i c t a b l e Tay riv e r w i t h o u t i nt erm edi at e supports; • very high quality factory p ro d u c e d components could be assembled on site using specially developed epox y bonding technology to give structural continuity of the highest quality; • t h e design system opt i m iz e s m a t e r i a l cont ent using a cellular form of structure found in natural fibrous structures; • materials are self coloured to m a tc h the local colours; • c o m p o n e n t s were light e n o u g h to be handl ed for t he rapid and safe construction of t he bridge on site by students with no major plant; and • the materials are largely m a i n t e n a n c e free, relieving t he club of a future cost burden. Additionally, Parafil cable stays which use Kevlar fibres were chosen for their ease of handling on site and long t e rm durability.
0034-3617/93/$6.00 © 1993, Elsevier Science Publishers Ltd.
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c o n s t r u c t i o n field w h e r e s t r u c t u r al p e r f o r m a n c e is a significant ....................... i System (ACC8) • l,mU, i~11 r e q u i r e m e n t . T h e s e are: • h i g h v o l u m e s o f glass fibre relative to resin; • c o n t i n u o u s fibres, e.g. glass 'SldoSifo' Vohicle ~d~lul¢l rovings aligned for m a x i m u m •~ System t efficiency; • high q u a l i t y in t e r m s of all s u l t s , ~ Production Experience, ............. ~.Durability, Resin Toughness factors including g e o m e t r i c acUrr~t Stlto Design Meihod I c u r a c y b o t h overall a n d local; ; FRP Compolitl Matoflals • t h e a r r a n g e m e n t of t h e struct u r a l form of the system to be n e a r t h e o p t i m u m for m a t e r i a l II o","', Ex,."ence 6 Pultruded Composite [. . . . . ~ - ..... content; a n d I SideguardBeams ] AIO Tees / • predictability and repeatability ,.F--i:.; i. I ..... J ~'~ l l i e~, I of s t r e n g t h a n d stiffness of t h e _ _ . _ _ . J " .... I s t r u c t u r a l systems a t all levels, .... • ~ 2$OTo.neso! n i.e. individual walls, s e p a r a t e I I ; ,=s I i System II m o d u l e s a n d c o m p l e t e structures. r_.-_L,_~IE_I~Zi.( Class '0' Resin ............................ The last of t h e above p o i n t s is i Supelc'ell Syllem ~ .... ~ i Houl~ng I p a r t i c u l a r l y i m p o r t a n t in t h e Im i,upm=-] Vadabkl I L. I r e a l m of civil a n d building strucBrutally V__. n ~ln Building I s,~, t u r e s w h e r e t h e s t r u c t u r e s are ................... V system I Enclosure ] very large a n d for a n u m b e r of r e a s o n s t h e d e s i g n is a l m o s t e n t i r e l y b a s e d on c o m p u t e r evaluations. The new a p p r o a c h to Cumbda : d e s i g n d e v e l o p e d by M a u n s e l l ' B' ~ r .~-0,~.v] Muili-nloro Footb~lgo U Major H ghwly B ~ e s i Offshore Sm~=tur~s • B,,;~,__Y i~ has been v a l i d a t e d by e x t e n s i v e t e s t p r o g r a m m e s s o m e of which are d e s c r i b e d below. The above a t t r i b u t e s are essenFIGURE 3: Ten years of M a u n s e l l Structural Plastics. t i a l in o r d e r t o p r o v i d e t h e c o m b i n a t i o n o f h i g h levels o f The c o n s t r u c t i o n m e t h o d used a n d design safety, reliability a n d d u r a b i l i t y over a 100 were fully i n t e g r a t e d in t h e p r o j e c t e d plan- y e a r p e r i o d at relatively low levels of cost as ning so t h a t a t e a m o f six s t u d e n t s c o u l d d e m a n d e d by t h e c o n s t r u c t i o n i n d u s t r y a n d build t h e s t r u c t u r e in t h e i r e i g h t w e e k t h e o w n e r s a n d users o f i n f r a s t r u c t u r e such vacation. I n n o v a t i v e c o n s t r u c t i o n m e t h o d s as bridges. The d e v e l o p m e n t of a m o d u l a r system of w e r e m a d e p o s s i b l e by t h e l i g h t n e s s of materials. Towers w e r e e r e c t e d by pivoting thin walled cellular p u l t r u s i o n s w h i c h m e t t h e m a b o u t t h e i r bases a n d t h e m a i n s p a n t h e s e c r i t e r i a d e p e n d e d o n a s e r i e s of deck was l a u n c h e d over a t e n s i o n e d cable i n n o v a t i o n s w h i c h have r e s u l t e d in a new technology that can provide the most net, using t e m p o r a r y l o n g i t u d i n a l cables. Figure 3 gives a s u m m a r y of t h e p r o c e s s a p p r o p r i a t e s t r u c t u r a l f o r m s for t h e successof d e v e l o p m e n t of new design t e c h n i q u e s , ful a p p l i c a t i o n of fibre r e i n f o r c e d c o m p o s i t e s m a n u f a c t u r i n g technology, t e s t d a t a a n d t h e in this field. F o r e x a m p l e t h e Supercell ACCS over a t e n y e a r p e r i o d t h a t e n a b l e d s t r u c t u r e s w h i c h were used for t h e towers Maunsell to u n d e r t a k e t h e c o m p l e t e Aber- at Aberfeldy closely m i m i c fibrous s t r u c t u r e s feldy bridge p r o j e c t w i t h i n an eight m o n t h f o u n d in n a t u r e w h e r e t h e walls o r p l a t e s p r o g r a m m e . T h i s i n c l u d e d c o n c e p t a n d f o r m i n g t h e m a i n cells a r e t h e m s e l v e s d e t a i l design, c o n s t r u c t i o n s c h e m e s a n d f o r m e d from cellular s u b - s t r u c t u r e s . supervision of c o n s t r u c t i o n . The f u n d a m e n The n e c e s s a r y verification for this develtal n a t u r e o f t h e p r o g r e s s m a d e in t h a t ten o p m e n t in which t h e p u l t r u d e d c o m p o n e n t s y e a r p e r i o d in m a n y a s p e c t s of r e i n f o r c e d are e n t i r e l y b o n d e d by e p o x y a d h e s i v e s c o m p o s i t e s m a d e it possible to satisfy t h e w i t h o u t t h e use of m e c h a n i c a l f a s t e n e r s key c r i t e r i a t h a t a r e n e c e s s a r y in t h e was p r o v i d e d by a m a j o r t e s t p r o g r a m m e . ra
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REINFORCED PLASTICS OCTOBER 1993
ONSTRUCTION
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FIGURE 4: Fabrication of Supercell test beam.
new approaches to design and manufacture were essential. In the field of design this was brought about by the introduction of limit state design principles which identify the limit state at which a structure ceases to fulfil its design function. The aim of limit state design is to achieve acceptable probabilities in t h a t the relevant limit states will not be reached during the intended life of the structure. The assessment of these probabilities sets up a framework within which the uncertainties in test data, loading, stress analysis, etc. can be quantified and understood. The m e t h o d is particularly suited to the design of composite structures and an area where new d a t a is e s s e n t i a l as t h e r e is not extensive experience of design and performance to draw upon as in steel and concrete construction. International and European documents provide a unified approach to the principles which then require to be specially adapted to specific materials and types of project. The importance of using such an approach which can be assessed by independent authorities where public safety is involved c a n n o t be e m p h a s i z e d too strongly where such complex materials are involved. The resulting methods of design are an order of magnitude more complex t h a n s i m i l a r limit s t a t e design m e t h o d s for bridges constructed from conventional materials. One example, t h a t of partial material factors to allow for variability of strength and stiffness, will show some of the added complexity. In assessing each l a m i n a t e configuration 28 different partial material factors are incorporated compared with the three or four necessary for steel or concrete. The vital i m p o r t a n c e of developing a detailed specification for manufacture, test-
Figure 4 shows one of the 18 m long and 2 m wide test beams being fabricated. The beams were designed to carry full highway loading and have performed outstandingly well u n d e r tests which consisted of the application of the full highway load over an eight m o n t h period, ultimate load tests and tests on durability and creep. The success of the programme, which was partly funded by the UK Department of Transport, was partly the result of European industrial collaboration in which material scientists, production engineers, structural engineers and construction engineers have worked as a team. The companies involved u n d e r Maunsell's leadership were DSM Resins, Vetrotex (UK) Ltd, Ciba Polymers Division and CU Bridges. This programme, Aberfeldy and a number of other recent projects have evolved from the interacting process of developing design and manufacturing technology in combination with the applications to projects over the ten y e a r period referred to above. Maunsell recognized ten years ago t h a t a q u a n t u m leap in design, manufacture and fabrication technology was necessary if a d v a n c e d c o m p o s i t e s were to make t h e t r a n s i t i o n from low volume, high p e r f o r m a n c e and high cost markets such as aerospace and defence to the high volume, high performance and low cost construction market. In order to provide a sound basis for FIGURE 5: Bromley bridge. the innovations mentioned above
REINFORCED PLASTICS OCTOBER 1993
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m~mmrl
Pigments and ultraviolet absorbers are specified a n d o t h e r additives such as fillers, flame r e t a r d a n t s u b s t a n c e s a n d low profile additives are permitted as long as performance requirements are achieved. A surface veil is generally specified on exposed profile surfaces. Type approval -- a type approval process is required to be carried out before resin and glass are supplied for manufacture of the finished profiles. This consists FIGURE 6: Bridge enclosures for motorway bridges. of obtaining certificates of conformity for constituent materials ing, assembly and erection of advanced and carrying out of a series of tests on composite bridge structures was recognized pultruded laminate samples to demonstrate at an early stage in the development of the satisfactory performance including CRAG design method. For example, the evaluation and ultrasonic tests. of partial material factors for strength and Pultrusion process - a detailed specificastiffness is dependent on a knowledge of the tion for the manufacturing process. m a x i m u m variation in laminate thickness Physical properties -- requirements for and glass content or position. These toler- physical properties of the finished pultruded ances need to be realistic in relation to the profiles are specified in terms of appearance, manufacture of complete advanced compo- selection of test pieces for destructive tests, site sections and therefore extensive con- mechanical properties, tolerances, quality s u l t a t i o n s were carried o u t w i t h i n t h e control, batch acceptance and proof testing, industry on a international basis as the M i n i m u m r e q u i r e m e n t s a r e given for specifications and design methods have been strength, stiffness, glass content and barcol developed. hardness, all to be established generally by The design-specification-manufacture in- destructive tests on each batch of material. terfaces have been carefully studied at all As for type approval, the current CRAG test stages of the design development and a methods are specified, with strength being performance specification has been evolved defined as failure of the first lamina. based on defined material types and strucThe ACCS was used for the design and tural geometry. A full programme of type erection of the world's first major bridge approval, batch and panel assembly tests is enclosure completed in 1989 in the UK. The specified including tests for fire resistance entire 16 000 sq m of the underside of the and effects of weathering. The main elements steel girders of the A19 Tees Viaduct are of the specification are summarized below. covered by a lightweight structural floor of Laminates and profiles -- fibre layouts for the highly durable interlocking panels which each laminate with requirements for short and long term strength, stiffness, durability and fire resistance to be validated by type approval. Materials (resin, glass, additives a n d surface veil) -- a detailed resin specification is given covering physical properties, storage properties, packaging, labelling, quality control and batch acceptance. It is expected t h a t filled resin will be supplied to the manufacturer and therefore tolerances are specified on filled resin properties for quality assurance purposes covering viscosity, volatile matter, gel time and density. Glass fibre grades a n d relevant British Standards are specified together with a particular specification for specialist mats.
R E I N F O R C E D PLASTICS
O C T O B E R 1993
FIGURE 7: Twostorey office building.
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provided access for maintenance and prevents corrosion of the steelwork. Figure 5 shows the first bridge to be built with a similar system as part of the initial design concept. The bridge for Bromley relief road spans the main line and the Bromley station platforms. Figure 6 shows the concept for bridges currently under construction for the second Severn crossing approach roads. The ACCS has also been used in a number of o t h e r areas w h e r e its p r o p e r t i e s of strength, lightness, durability, fire resistance a n d t h e r m a l i n s u l a t i o n have p a r t i c u l a r advantages, e.g. variable message sign gantries, m a r i n a s , car w a s h h o u s i n g s a n d buildings. Figure 7 shows a two storey office building in which all floors, walls and roof are made from the ACCS system. The technology and systems t h a t have been applied successfully to a range of applications including bridges and buildings have been based on thorough research and development, specially developed design t e c h n i q u e s a n d a u t o m a t e d m e t h o d s of production. The wider application of this technology, whilst still demanding innovation to make the most effective use of the three-dimensional forms t h a t the system can
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REINFORCED PLASTICS OCTOBER 1993
produce, is consequently capable of being undertaken by a natural process of further development for specific requirements. Recent studies into various project areas by Maunsell have shown the viability of such d e v e l o p m e n t s . For highway bridges the a p p r o a c h e s developed for s h o r t e r span bridges can be extended to much longer spans in the range 100 to 350 m. Both bridge enclosures which can bring aerodyn a m i c a d v a n t a g e s to longer spans and structural bridge forms based on Supercells have areas of application in this range. In t h e latter case the use of the structural properties of the glass reinforced modules may r e q u i r e t h e use of o t h e r m a t e r i a l s to complement the ACCS as in the use of Parafil fibre cables on Aberfeldy. Carbon fibre and steel may require consideration in structural modes depending on the type of structural form envisaged. For buildings a wide range of applications have been identified in which the attributes of composite materials and the advantages of a cellular m o d u l a r system with high structural qualities as an in-plane plate element as well as out of plane. Medium h e i g h t multi-storey buildings with good earthquake characteristics have been shown to be viable using the systems already tested. Very high buildings can be considered using, for example, carbon fibre reinforced pultrusions. The combination of durability, fire resistance and light weight produce very import a n t a d v a n t a g e s for offshore s t r u c t u r e s which the modular properties of the ACCS provide in a most effective fashion. Both deck and subsea applications are important areas for the future. In order to ensure t h a t the most effective means of exploitation of the technology are chosen the responsibilities for commercial developments have been focused into a new company. The design of future applications will continue to be u n d e r t a k e n by Maunsell S t r u c t u r a l Plastics as p a r t of Maunsell International, the consulting engineering organization. The development of commercial applications is now the responsibility of Designer Composites Technology Ltd. The viability of fibre reinforced composites in the construction field has been proved b o t h t e c h n i c a l l y a n d in t e r m s of cost effectiveness using the b u i l d i n g blocks provided by the Advanced Composite Construction System combined with innovative designs for each area of application. •
ONSTRUCTION
Bridge construction and beyond M a u n s e l l Structural Plastics has s p e n t the last t e n years d e v e l o p i n g systems for u s i n g advanced compos i t e s in c o n s t r u c t i o n a p p l i c a t i o n s . S u c c e s s e s i n c l u d e e n c l o s u r e p a n e l s on t h e A19 T e e s Viaduct and the A b e r f e l d y G o l f C o u r s e bridge. Brian R i c h m o n d , m a n a g i n g director o f t h e UK-based c o m p a n y reviews t h e s e projects and l o o k s at further areas w h e r e the ACCS system can be applied.
Plank
3-Way Connector
he Aberfeldy cable stayed bridge is the world's first major bridge in advanced composite materials and i ncorporat es a n u m b e r of i n n o v a t i o n s in s t r u c t u r a l systems, materials and m e t h o d s of construction. Figure 1 shows a view of the 63 m span, 112 m long bridge crossing the River Tay at t he Aberfeldy Golf Club providing access to a new section of t he course. The towers and the deck st ruct ure are fabricated from Maunsell Structural Plastics' Advanced C o m p o s i t e C o n s t r u c t i o n System (ACCS) using the cellular modules shown in Figure 2 which are glass reinforced pultrusion (E-glass/isophthalic resin). The bridge was c om pl et ed in October 1992 and has already proved itself capable of withstanding the
T
FIGURE 1:
Aberfeldy composite cable stayed bridge.
{
REINFORCED PLASTICS OCTOBER 1993
ToggleConnector
FIGURE 2: Advanced Composite Construction System (ACCS) modules.
e x t r e m e s of both wind and flooding which w e r e e x p e r i e n c e d in t h e following few months. As well as d e m o n s t r a t i n g vibration characteristics u n d e r normal use which were as good as the best comparable conventional structures. The a p p r o a c h chosen was successful in meeting the golf club's s h o r t term and long t e r m financial r e q u i r e m e n t s as well as satisfying the local planning a u th o rity for the following reasons: • the structural form and system chosen was capable of spanning the fast flowing a n d u n p r e d i c t a b l e Tay riv e r w i t h o u t i nt erm edi at e supports; • very high quality factory p ro d u c e d components could be assembled on site using specially developed epox y bonding technology to give structural continuity of the highest quality; • t h e design system opt i m iz e s m a t e r i a l cont ent using a cellular form of structure found in natural fibrous structures; • materials are self coloured to m a tc h the local colours; • c o m p o n e n t s were light e n o u g h to be handl ed for t he rapid and safe construction of t he bridge on site by students with no major plant; and • the materials are largely m a i n t e n a n c e free, relieving t he club of a future cost burden. Additionally, Parafil cable stays which use Kevlar fibres were chosen for their ease of handling on site and long t e rm durability.
0034-3617/93/$6.00 © 1993, Elsevier Science Publishers Ltd.
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c o n s t r u c t i o n field w h e r e s t r u c t u r al p e r f o r m a n c e is a significant ....................... i System (ACC8) • l,mU, i~11 r e q u i r e m e n t . T h e s e are: • h i g h v o l u m e s o f glass fibre relative to resin; • c o n t i n u o u s fibres, e.g. glass 'SldoSifo' Vohicle ~d~lul¢l rovings aligned for m a x i m u m •~ System t efficiency; • high q u a l i t y in t e r m s of all s u l t s , ~ Production Experience, ............. ~.Durability, Resin Toughness factors including g e o m e t r i c acUrr~t Stlto Design Meihod I c u r a c y b o t h overall a n d local; ; FRP Compolitl Matoflals • t h e a r r a n g e m e n t of t h e struct u r a l form of the system to be n e a r t h e o p t i m u m for m a t e r i a l II o","', Ex,."ence 6 Pultruded Composite [. . . . . ~ - ..... content; a n d I SideguardBeams ] AIO Tees / • predictability and repeatability ,.F--i:.; i. I ..... J ~'~ l l i e~, I of s t r e n g t h a n d stiffness of t h e _ _ . _ _ . J " .... I s t r u c t u r a l systems a t all levels, .... • ~ 2$OTo.neso! n i.e. individual walls, s e p a r a t e I I ; ,=s I i System II m o d u l e s a n d c o m p l e t e structures. r_.-_L,_~IE_I~Zi.( Class '0' Resin ............................ The last of t h e above p o i n t s is i Supelc'ell Syllem ~ .... ~ i Houl~ng I p a r t i c u l a r l y i m p o r t a n t in t h e Im i,upm=-] Vadabkl I L. I r e a l m of civil a n d building strucBrutally V__. n ~ln Building I s,~, t u r e s w h e r e t h e s t r u c t u r e s are ................... V system I Enclosure ] very large a n d for a n u m b e r of r e a s o n s t h e d e s i g n is a l m o s t e n t i r e l y b a s e d on c o m p u t e r evaluations. The new a p p r o a c h to Cumbda : d e s i g n d e v e l o p e d by M a u n s e l l ' B' ~ r .~-0,~.v] Muili-nloro Footb~lgo U Major H ghwly B ~ e s i Offshore Sm~=tur~s • B,,;~,__Y i~ has been v a l i d a t e d by e x t e n s i v e t e s t p r o g r a m m e s s o m e of which are d e s c r i b e d below. The above a t t r i b u t e s are essenFIGURE 3: Ten years of M a u n s e l l Structural Plastics. t i a l in o r d e r t o p r o v i d e t h e c o m b i n a t i o n o f h i g h levels o f The c o n s t r u c t i o n m e t h o d used a n d design safety, reliability a n d d u r a b i l i t y over a 100 were fully i n t e g r a t e d in t h e p r o j e c t e d plan- y e a r p e r i o d at relatively low levels of cost as ning so t h a t a t e a m o f six s t u d e n t s c o u l d d e m a n d e d by t h e c o n s t r u c t i o n i n d u s t r y a n d build t h e s t r u c t u r e in t h e i r e i g h t w e e k t h e o w n e r s a n d users o f i n f r a s t r u c t u r e such vacation. I n n o v a t i v e c o n s t r u c t i o n m e t h o d s as bridges. The d e v e l o p m e n t of a m o d u l a r system of w e r e m a d e p o s s i b l e by t h e l i g h t n e s s of materials. Towers w e r e e r e c t e d by pivoting thin walled cellular p u l t r u s i o n s w h i c h m e t t h e m a b o u t t h e i r bases a n d t h e m a i n s p a n t h e s e c r i t e r i a d e p e n d e d o n a s e r i e s of deck was l a u n c h e d over a t e n s i o n e d cable i n n o v a t i o n s w h i c h have r e s u l t e d in a new technology that can provide the most net, using t e m p o r a r y l o n g i t u d i n a l cables. Figure 3 gives a s u m m a r y of t h e p r o c e s s a p p r o p r i a t e s t r u c t u r a l f o r m s for t h e successof d e v e l o p m e n t of new design t e c h n i q u e s , ful a p p l i c a t i o n of fibre r e i n f o r c e d c o m p o s i t e s m a n u f a c t u r i n g technology, t e s t d a t a a n d t h e in this field. F o r e x a m p l e t h e Supercell ACCS over a t e n y e a r p e r i o d t h a t e n a b l e d s t r u c t u r e s w h i c h were used for t h e towers Maunsell to u n d e r t a k e t h e c o m p l e t e Aber- at Aberfeldy closely m i m i c fibrous s t r u c t u r e s feldy bridge p r o j e c t w i t h i n an eight m o n t h f o u n d in n a t u r e w h e r e t h e walls o r p l a t e s p r o g r a m m e . T h i s i n c l u d e d c o n c e p t a n d f o r m i n g t h e m a i n cells a r e t h e m s e l v e s d e t a i l design, c o n s t r u c t i o n s c h e m e s a n d f o r m e d from cellular s u b - s t r u c t u r e s . supervision of c o n s t r u c t i o n . The f u n d a m e n The n e c e s s a r y verification for this develtal n a t u r e o f t h e p r o g r e s s m a d e in t h a t ten o p m e n t in which t h e p u l t r u d e d c o m p o n e n t s y e a r p e r i o d in m a n y a s p e c t s of r e i n f o r c e d are e n t i r e l y b o n d e d by e p o x y a d h e s i v e s c o m p o s i t e s m a d e it possible to satisfy t h e w i t h o u t t h e use of m e c h a n i c a l f a s t e n e r s key c r i t e r i a t h a t a r e n e c e s s a r y in t h e was p r o v i d e d by a m a j o r t e s t p r o g r a m m e . ra
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REINFORCED PLASTICS OCTOBER 1993
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FIGURE 4: Fabrication of Supercell test beam.
new approaches to design and manufacture were essential. In the field of design this was brought about by the introduction of limit state design principles which identify the limit state at which a structure ceases to fulfil its design function. The aim of limit state design is to achieve acceptable probabilities in t h a t the relevant limit states will not be reached during the intended life of the structure. The assessment of these probabilities sets up a framework within which the uncertainties in test data, loading, stress analysis, etc. can be quantified and understood. The m e t h o d is particularly suited to the design of composite structures and an area where new d a t a is e s s e n t i a l as t h e r e is not extensive experience of design and performance to draw upon as in steel and concrete construction. International and European documents provide a unified approach to the principles which then require to be specially adapted to specific materials and types of project. The importance of using such an approach which can be assessed by independent authorities where public safety is involved c a n n o t be e m p h a s i z e d too strongly where such complex materials are involved. The resulting methods of design are an order of magnitude more complex t h a n s i m i l a r limit s t a t e design m e t h o d s for bridges constructed from conventional materials. One example, t h a t of partial material factors to allow for variability of strength and stiffness, will show some of the added complexity. In assessing each l a m i n a t e configuration 28 different partial material factors are incorporated compared with the three or four necessary for steel or concrete. The vital i m p o r t a n c e of developing a detailed specification for manufacture, test-
Figure 4 shows one of the 18 m long and 2 m wide test beams being fabricated. The beams were designed to carry full highway loading and have performed outstandingly well u n d e r tests which consisted of the application of the full highway load over an eight m o n t h period, ultimate load tests and tests on durability and creep. The success of the programme, which was partly funded by the UK Department of Transport, was partly the result of European industrial collaboration in which material scientists, production engineers, structural engineers and construction engineers have worked as a team. The companies involved u n d e r Maunsell's leadership were DSM Resins, Vetrotex (UK) Ltd, Ciba Polymers Division and CU Bridges. This programme, Aberfeldy and a number of other recent projects have evolved from the interacting process of developing design and manufacturing technology in combination with the applications to projects over the ten y e a r period referred to above. Maunsell recognized ten years ago t h a t a q u a n t u m leap in design, manufacture and fabrication technology was necessary if a d v a n c e d c o m p o s i t e s were to make t h e t r a n s i t i o n from low volume, high p e r f o r m a n c e and high cost markets such as aerospace and defence to the high volume, high performance and low cost construction market. In order to provide a sound basis for FIGURE 5: Bromley bridge. the innovations mentioned above
REINFORCED PLASTICS OCTOBER 1993
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m~mmrl
Pigments and ultraviolet absorbers are specified a n d o t h e r additives such as fillers, flame r e t a r d a n t s u b s t a n c e s a n d low profile additives are permitted as long as performance requirements are achieved. A surface veil is generally specified on exposed profile surfaces. Type approval -- a type approval process is required to be carried out before resin and glass are supplied for manufacture of the finished profiles. This consists FIGURE 6: Bridge enclosures for motorway bridges. of obtaining certificates of conformity for constituent materials ing, assembly and erection of advanced and carrying out of a series of tests on composite bridge structures was recognized pultruded laminate samples to demonstrate at an early stage in the development of the satisfactory performance including CRAG design method. For example, the evaluation and ultrasonic tests. of partial material factors for strength and Pultrusion process - a detailed specificastiffness is dependent on a knowledge of the tion for the manufacturing process. m a x i m u m variation in laminate thickness Physical properties -- requirements for and glass content or position. These toler- physical properties of the finished pultruded ances need to be realistic in relation to the profiles are specified in terms of appearance, manufacture of complete advanced compo- selection of test pieces for destructive tests, site sections and therefore extensive con- mechanical properties, tolerances, quality s u l t a t i o n s were carried o u t w i t h i n t h e control, batch acceptance and proof testing, industry on a international basis as the M i n i m u m r e q u i r e m e n t s a r e given for specifications and design methods have been strength, stiffness, glass content and barcol developed. hardness, all to be established generally by The design-specification-manufacture in- destructive tests on each batch of material. terfaces have been carefully studied at all As for type approval, the current CRAG test stages of the design development and a methods are specified, with strength being performance specification has been evolved defined as failure of the first lamina. based on defined material types and strucThe ACCS was used for the design and tural geometry. A full programme of type erection of the world's first major bridge approval, batch and panel assembly tests is enclosure completed in 1989 in the UK. The specified including tests for fire resistance entire 16 000 sq m of the underside of the and effects of weathering. The main elements steel girders of the A19 Tees Viaduct are of the specification are summarized below. covered by a lightweight structural floor of Laminates and profiles -- fibre layouts for the highly durable interlocking panels which each laminate with requirements for short and long term strength, stiffness, durability and fire resistance to be validated by type approval. Materials (resin, glass, additives a n d surface veil) -- a detailed resin specification is given covering physical properties, storage properties, packaging, labelling, quality control and batch acceptance. It is expected t h a t filled resin will be supplied to the manufacturer and therefore tolerances are specified on filled resin properties for quality assurance purposes covering viscosity, volatile matter, gel time and density. Glass fibre grades a n d relevant British Standards are specified together with a particular specification for specialist mats.
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FIGURE 7: Twostorey office building.
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provided access for maintenance and prevents corrosion of the steelwork. Figure 5 shows the first bridge to be built with a similar system as part of the initial design concept. The bridge for Bromley relief road spans the main line and the Bromley station platforms. Figure 6 shows the concept for bridges currently under construction for the second Severn crossing approach roads. The ACCS has also been used in a number of o t h e r areas w h e r e its p r o p e r t i e s of strength, lightness, durability, fire resistance a n d t h e r m a l i n s u l a t i o n have p a r t i c u l a r advantages, e.g. variable message sign gantries, m a r i n a s , car w a s h h o u s i n g s a n d buildings. Figure 7 shows a two storey office building in which all floors, walls and roof are made from the ACCS system. The technology and systems t h a t have been applied successfully to a range of applications including bridges and buildings have been based on thorough research and development, specially developed design t e c h n i q u e s a n d a u t o m a t e d m e t h o d s of production. The wider application of this technology, whilst still demanding innovation to make the most effective use of the three-dimensional forms t h a t the system can
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REINFORCED PLASTICS OCTOBER 1993
produce, is consequently capable of being undertaken by a natural process of further development for specific requirements. Recent studies into various project areas by Maunsell have shown the viability of such d e v e l o p m e n t s . For highway bridges the a p p r o a c h e s developed for s h o r t e r span bridges can be extended to much longer spans in the range 100 to 350 m. Both bridge enclosures which can bring aerodyn a m i c a d v a n t a g e s to longer spans and structural bridge forms based on Supercells have areas of application in this range. In t h e latter case the use of the structural properties of the glass reinforced modules may r e q u i r e t h e use of o t h e r m a t e r i a l s to complement the ACCS as in the use of Parafil fibre cables on Aberfeldy. Carbon fibre and steel may require consideration in structural modes depending on the type of structural form envisaged. For buildings a wide range of applications have been identified in which the attributes of composite materials and the advantages of a cellular m o d u l a r system with high structural qualities as an in-plane plate element as well as out of plane. Medium h e i g h t multi-storey buildings with good earthquake characteristics have been shown to be viable using the systems already tested. Very high buildings can be considered using, for example, carbon fibre reinforced pultrusions. The combination of durability, fire resistance and light weight produce very import a n t a d v a n t a g e s for offshore s t r u c t u r e s which the modular properties of the ACCS provide in a most effective fashion. Both deck and subsea applications are important areas for the future. In order to ensure t h a t the most effective means of exploitation of the technology are chosen the responsibilities for commercial developments have been focused into a new company. The design of future applications will continue to be u n d e r t a k e n by Maunsell S t r u c t u r a l Plastics as p a r t of Maunsell International, the consulting engineering organization. The development of commercial applications is now the responsibility of Designer Composites Technology Ltd. The viability of fibre reinforced composites in the construction field has been proved b o t h t e c h n i c a l l y a n d in t e r m s of cost effectiveness using the b u i l d i n g blocks provided by the Advanced Composite Construction System combined with innovative designs for each area of application. •