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Performance of Precast Prestressed Steel-Concrete Composite Panels Under Static Loadings to Replace the Timber Transoms for Railway Bridge
Structures 19 (2019) 30–40
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Performance of Precast Prestressed Steel-Concrete Composite Panels Under Static Loadings to Replace the Timber Transoms for Railway Bridge
T
Olivia Mirzaa, , Sukanta Kumer Shillb,c, Jason Johnstona ⁎
a
School of Computing, Engineering & Mathematics, University of Western Sydney, Australia School of Engineering and Information Technology, the University of New South Wales, Canberra, Australia c Department of Civil Engineering, Dhaka University of Engineering & Technology (DUET), Bangladesh b
ARTICLE INFO
ABSTRACT
Keywords: Transoms Prestressed concrete panels Reinforced concrete panels AJAX ONESIDE blind bolts LINDAPTER blind bolts
Timber is widely used as transoms in numerous railway networks all over the world and currently in use on the existing Sydney Harbour bridge railway system. Now-a-days, the timber transoms, in numerous railway networks, are edging towards the end of their design life. Moreover, often these timber transoms are subjected to repeated mechanical loadings, chemical degradation and prolonged environmental exposures. As a result, frequent maintenance and sometimes complete replacement to ensure the functionality of the railway network significantly increases the track maintenance cost. Therefore, the paper aims to presents alternative solutions to replace the timber transoms with other more durable and virtually maintenance free materials that will improve the long-term functionality of the transoms in Sydney Harbour bridge railway system. To achieve the goal of the study, an experimental investigation was carried out on the precast prestressed steel-concrete composite panels using two different connectors like AJAX ONESIDE blind bolts and LINDAPTER blind bolts. The experimental results of precast prestressed steel-concrete composite panels under two-point bending test were also compared with the conventional reinforced concrete. It can be concluded that the prestressed panels performed better and exhibited less cracking, less deflection and higher stiffness compared to the conventionally reinforced concrete panels. Moreover, the prestressed panel with AJAX ONESIDE blind bolt connectors shows slightly higher deflections and lower uncracked stiffness in comparison to the prestressed panel with LINDAPTER blind bolt connectors. Therefore, LINDAPTER blind bolts connectors, are preferable in connecting the bridge stringer steel and the prestressed composite panel, could be a viable solution to replace the existing timber transoms of the Sydney Harbour bridge railway line.
1. Introduction Timber transoms are widely used in numerous railway networks around the world. Transoms are usually used to distribute and transfer the applied railway loadings to the underlying ballast bed or supporting system [1]. Now-a-days, the timber transoms, in numerous railway networks, are edging towards the end of their design life. It is well known that the existing railway tracks of the Sydney Harbour bridge also use hardwood timber transoms. Transoms are often subjected to repeated mechanical loads, prolonged environmental exposures, climate change, chemical degradation and biological degradation by fungus [2,3]. Consequently, the timber transoms usually require frequent maintenance and must be regularly replaced to ensure the functionality of the railway network. Moreover, moisture absorption of the timber transoms that contributes to the corrosion of the top part of the stringer top flange, noting that this location is very difficult to access and inspect. Besides the above issues mentioned,
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the frequency and magnitude of loadings are recently becoming significantly higher compared to the time of initial placement. In light of the above issues, the Sydney Harbour bridge project aims to develop solutions to provide an alternative solid, that are durable and virtually maintenance free to improve the long-term functionality of the transoms [4]. While conventional alternative materials such as steel and concrete have been considered, no other materials are ideal to replace the degraded hardwood timber transoms. The Sydney Harbour bridge project proposes three alternative solutions to replace these timber transoms. The three alternatives are conventionally reinforced concrete panels, prestressed steel-concrete composite panels, and the use of a new material, Wagners Composite Fibre Technology within a panel design. The conventionally reinforced panel was designed by Griffin [5] and fabricated and experimentally tested by Zaher [6]. The prestressed steel-concrete composite panels were designed and partially fabricated by Zaher [6] who was unable to complete the fabrication and
Corresponding author. E-mail address: [email protected] (O. Mirza).
https://doi.org/10.1016/j.istruc.2018.12.001 Received 16 October 2017; Received in revised form 26 November 2018; Accepted 2 December 2018 Available online 04 December 2018 2352-0124/ © 2018 Published by Elsevier Ltd on behalf of Institution of Structural Engineers.
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Fig. 1. Panel specimen size [6].
bridge project, the prestressed panel was required to be 3237 mm long with a width of 600 mm. The panel is supported by the bridge stringers which span 1981 mm measured from the centre of the supports. The prestressed panel design outlines three strand cables with 15.2 mm diameter. A draped tendon profile was used in the prestressed panels rather than straight tendon profile as shown in Fig. 3. It is well known that a prestressed beam or slab with draped tendon profile shows a higher ultimate load, lower deflection, a higher moment resistance and a stiffer response compared to beams with a undraped straight tendon profile [13,14]. Furthermore, the design requires 50 MPa concrete, Bondek II profiled steel sheeting, 4N12 reinforcing bars, and N10 stirrups spaced at 90 mm between the supports and 130 mm centres outside the support. The design of the prestressed panel is shown in Figs. 1 to 3.
testing of the prestressed panels, while the Wagners Composite Fibre Technology panels were investigated by Johnston [7]. In the past, in order to compare the behaviour of reinforced and prestressed concrete under repeated loads, Bate [8] conducted an extensive experimental study on the two types of concrete beams. The author determined that while loading was within the beam's load capacity, the prestressed concrete beam did not crack and slightly deformed under repetition. In comparison, the reinforced concrete beam experienced cracking under the same loading. Kaewunruen & Remennikov [1] conducted static and impact loading experiments on prestressed concrete sleepers to determine its failure mechanism and ultimate capacity. In the static testing, the authors performed a positive bending moment test using a steel plate to disperse loading to mimic the rail seat of a railway system. This allowed the ultimate bending moment capacity of the prestressed concrete sleeper to be calculated while measuring the deflection of the structural member. Moreover, the authors [9] also investigated the residual energy toughness of prestressed concrete sleepers in railway track structures subjected to repeated impact loads. Further, Remennikov et al. [10], presented the background information and focuses on the new limit states design concept for prestressed concrete sleepers. According to Ferdous and Manalo [11], the premature deterioration of traditional railway sleepers has become of great concern over the last two decades and has significantly increased the track maintenance costs. The authors revealed in their review works that fungal decay, end splitting, termites, still sound, sapwood, shelling, rail cut, weathering, spike kill, and knots the principal causes of traditional timber sleeper failure. Moreover, issues with the timber transoms are rotting, splitting and insect attack [3]. Although the higher initial cost, the prestressed concrete sleepers are being popular because of the higher impact resistance and durability compared to timber and steel [2]. Considering the minimum maintenance and long design life of the precast or prefabricated steel-concrete composite panels and to increase the speed of installation and thereby minimise the disruptions to existing railway services, the authors investigated the feasibility of using prestressed steel-concrete composite panels to replace the timber transoms in the Sydney Harbour bridge railway network. Moreover, the paper presents the deflection characteristics, stiffness properties, cracking patterns, load carrying capacity, retrofitting to supporting stringers and horizontal slip occurrences of prestressed steel-concrete composite panels under two points bending test. Finally, a comparison between conventional reinforced concrete panel and the prestressed concrete panel is also discussed in this paper.
2.2. Fabrication of specimen Two prestressed panels were fabricated at the laboratory of the Western Sydney University Kingswood campus. One panel uses AJAX ONESIDE blind bolts to retrofit the panel to the bridge stringer steel while the second panel uses LINDAPTER blind bolts for the connection. The initial fabrication of the prestressed panels prior to concrete pouring included the following work: formwork preparation, installation of Bondek profiled steel sheeting, steel reinforcement placement, the installation of the prestress duct, and installation of strain gauges. Concrete with a characteristic compressive strength of f′c = 50 MPa was used in the study. The panels were cured for 28 days to allow the concrete to reach its characteristic compressive strength. However, after the concrete was allowed to harden for a period of 14 days, the prestress strands were tensioned using a hydraulic jack to achieve a tension value of 174 kN. The prestress ducts were filled with high strength grout to provide the necessary connection between the prestressing strands and the concrete to transfer the prestress effectively. 2.3. Retrofitting Shear connectors were used to retrofit the precast prestressed steelconcrete composite panel to the supporting steel stringers. Two different types of shear connectors were used: AJAX ONESIDE blind bolts, and LINDAPTER blind bolts. The Ajax ONESIDE blind bolting system used in this paper comprises of a circular bolt head, internal folding stepped washer, sleeve, external solid stepped washer and nut. A special installation tool was also required to insert the blind bolt and tighten it. In the study, the ajax ONESIDE blind bolting method was done according to Lee et al. [15], and the LINDAPTER blind bolt shear connectors were used according to Mirza et al. [16]. The AJAX ONESIDE blind bolts and LINDAPTER blind bolts fitted to the steel stringer are shown in Figs. 4 and 5 respectively. During the fabrication of the panels, PVC pipes were placed at the hole locations of the shear connectors. Once the concrete had hardened,
2. Methodology 2.1. Design of prestressed steel-concrete composite panel Prestressed steel-concrete composite panels are designed following the AS3600 [12]. To match the other panels in the Sydney Harbour 31
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Fig. 2. Panel reinforcement details [6].
Fig. 3. Panel chair height [6].
Fig. 4. AJAX ONESIDE blind bolts.
Fig. 5. LINDAPTER blind bolts assembly.
the PVC pipes were removed to provide a void in the concrete at the shear connector locations. The panel was then lifted onto the steel stringers so the shear connectors lined up with the void locations in the concrete. Once in place, these holes were filled with high strength grout to effectively connect the panel to the bridge stringers.
3. Experimental set-up The experimental setup that of the study is similar to the experimental set up that was used by Kaewunruen & Remennikov [1], where the precast prestressed panel was tested under static loading to determine ultimate bending capacity while measuring the deflection of 32
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Fig. 6. Schematic experimental test set-up summary.
Fig. 7. Experimental test set-up of prestressed panel.
Fig. 8. Cracking in the AJAX ONESIDE blind bolt panel (N-side).
the member in response to the loading. The experimental test set-up basically involved four main steps:
Linear potentiometers were placed at either end of the panel to measure the horizontal slip between the concrete and Bondek profiled steel sheeting. Additionally, linear potentiometers were placed underneath the two load locations and at midspan of the panel to measure vertical deflection. Loading on the panel was applied with the help of hydraulic jack of capacity of 1000 kN. Two-line loads to replicate the rails of the Sydney Harbour bridge railway network were placed at a span of 1435 mm as outlined in Fig. 6. The two-line loads were achieved by placing two steel beams with a width of 100 mm on the panel. A
• Connecting the steel beams to the strong floor • Placement of linear potentiometers along the panel • Connecting the strain gauges to the reading system and • Placement of plywood, steel beam, and knife edges over the width of the panel
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Fig. 9. Cracking in the AJAX ONESIDE blind bolt panel (S-side).
and rail, associated with the abnormalities in either a wheel or a rail. The design static wheel load per rail seat for a 40-tone axle load usually varies from 100 kN to 110 kN [17]. In this study, the static loading test on the transom panels was conducted following the AS1085.14 [18]. Load was applied to the panels to determine their structural performance based on load deflection chracteristics. Loading and unloading were applied at a rate of 6 mm/min in accordance to achieve the following magnitudes in the corresponding order:
Table 1 Deflection under applied loadings for AJAX ONESIDE panel. Applied load (kN)
100 150 240 360
Deflection point (mm)
Average (mm)
C
E
D
C
E
D
0.26 0.28 0.28 0.42 0.47 0.43 0.70 0.74 0.79 1.34 1.46 1.51
0.37 0.39 0.38 0.52 0.54 0.59 1.1 1.13 1.1 1.66 1.73 1.73
0.01 0.01 0.02 0.00 0.00 0.01 0.45 0.55 0.6 1.65 1.81 1.86
0.27
0.38
0.01
0.44
0.55
0.00
0.74
1.11
0.53
1.44
1.71
1.77
• Load to 50 kN and check all testing equipment is recording accurately • Load to 100 kN and unload to 50 kN (repeated three times) • Load to 150 kN and unload to 50 kN (repeated three times) • Load to 240 kN and unload to 100 kN (repeated three times) • Load to 360 kN and unload to 100 kN (repeated three times) • Load to failure or 900 kN
plywood plate with similar dimensions was placed between the panel and the steel beam. Once testing began, the spreader beam connected to the hydraulic jack was lowered until contact was made with the knife edge on top of each steel beam. The vertical load was controlled using a load cell connected to the automatic data acquisition system. The experimental test set-up is summarised in Fig. 6, in this figure, point A and B correspond to the horizontal linear potentiometers while points C and E represent the vertical linear potentiometers at the load locations. Point D corresponds to the vertical linear potentiometer at the midspan of the panel. The completed experimental test set-up of one prestressed panel can be observed in Fig. 7.
The final stage of loading is to determine whether the load that causes failure in the panel. The load was increased to a maximum value of 900 kN as the capacity of the hydraulic jack in the laboratory is 1000 kN. The loads 100 kN, 150 kN, 240 kN, and 360 kN correspond to the loads associated with the wheel load of the different rail loading systems. Notably, the 240 kN and 360 kN are the maximum static load per wheel correspond to the 200 LA and 300 LA rail loading system respectively, as outlined in AS5100.2 [19].
3.1. Loading system
During the experimental testing of the AJAX ONESIDE blind bolt panel, when the loading was first increased to 240 kN, cracking noises were heard at a load of approximately 184 kN. Similarly, when the loading was first increased to 360 kN, cracking noises were heard at a
4. Results and discussion 4.1. AJAX ONESIDE blind bolt panel
Railway transoms are often subjected to the static loading and sometimes impact loading condition due to the interactions of wheel
Fig. 10. Load versus deflection curve at midspan for AJAX ONESIDE panel. 34
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Fig. 11. Load versus deflection curve at load points for AJAX ONESIDE panel.
value of 1.77 mm. The highest deflection recorded in the experiment occurred at the maximum load of 900 kN. The deflection at this load at the midspan was 10.31 mm while at points C and E the deflection was 5.38 mm and 5.91 mm respectively. The experimental load versus deflection curve at the midspan for the AJAX ONESIDE panel is shown in Fig. 10. Similarly, the load versus deflection curve for the load point deflections (points C and E) are shown in Fig. 11. The linear potentiometers placed horizontally at points A and B were used to measure the horizontal slip between the concrete and the Bondek profiled steel sheeting. The maximum slip recorded at either end of the panel was 0.53 mm. As this value is minimal, the horizontal slip between the concrete and Bondek profiled steel sheeting can be considered negligible. Using a line of best fit on the load versus deflection curves shown in Figs. 10 and 11 the stiffness of the prestressed panel can be calculated from the gradient of the curves. The stiffness for points C, D, and E of the AJAX ONESIDE panel are summarised in Table 2.
Table 2 Stiffness at points C, E, and D for AJAX ONESIDE panel. Stiffness points
C
E
D
Uncracked stiffness (kN/mm) Cracked stiffness (kN/mm)
326 158
265 146
– 65
load of approximately 330 kN. The cracking noises can be attributed to the expansion of the Bondek profiled steel sheeting and/or minor cracking in the concrete. At the 360 kN load, there was no visible cracking in the prestressed panel. The loading was then increased to cause failure in the panel and allow its ultimate capacity to be determined. As the load was increased above 500 kN, cracking noises was frequently heard until the maximum possible load of 900 kN was reached. The cracking in the AJAX ONESIDE panel on the N and S long sides under the 900 kN load is shown in Figs. 8 and 9. However, there were no visible cracks near the retrofitted, grouted holes above the bridge stringer supports. While some minor cracking occurred on the long sides of the panel, however, the panel did not show any major signs or distress that the panel was near failure. The deflection of the AJAX ONESIDE panel under the load's sensitivity is summarised in Table 1. In Table 1, points C and E correspond to the deflection under the east and west load points respectively while deflection at point D represents the deflection at the midspan of the panel. The three values for each load correspond to the three load cycles for each load, which allow an average to be calculated. The deflections presented in Table 1 are within the permissible deflection limit as required by AS3600 [12]. According to AS3600, a minimum deflection/span ratio of 1/800 for members subjected to vehicular or pedestrian traffic. Considering the effective span of the panel, which is equal to 3237 mm, the maximum allowable deflection 1752 of the panel is 800 = 2.19 mm . All deflection values presented in Table 1 are below the permissible deflection with the maximum deflection occurring at the applied load of 360 kN at the midspan of the panel with a
4.2. LINDAPTER blind bolt panel During the experimental testing of the LINDAPTER blind bolt panel, cracking noises were first heard at a load of approximately 280 kN, when the loading was first increased to 360 kN. At the 360 kN serviceability load, there was no visible cracking in the panel. The loading was then increased to cause failure in the panel and allow its ultimate capacity to be determined. As the load was increased above 500 kN, cracking noises was frequently heard until the maximum possible load of 900 kN was reached. One extremely loud cracking noise was heard when the load increased above 500 kN. The cracking in the LINDAPTER panel on the N and S long sides under the 900 kN load is shown in Figs. 12 and 13. Furthermore, there were no visible cracks near the retrofitted, grouted holes above the bridge stringer supports. While some minor cracking occurred on the long sides of the panel, however, the LINDAPTER panel did also not show any major signs or indications
Fig. 12. Cracking in the LINDAPTER panel (N-side). 35
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Fig. 13. Cracking in the LINDAPTER panel (S-side).
• The linear potentiometers placed horizontally at points A and B
Table 3 Deflection under serviceability loading for LINDAPTER panel. Applied load (kN)
100 150 240 360
Deflection point (mm)
were used to measure the horizontal slip between the concrete and the Bondek profiled steel sheeting. The maximum slip recorded at either end of the prestressed panel was 0.19 mm. In the case of LINDAPTER panel, the horizontal slip between the concrete and Bondek profiled steel sheeting also can be considered negligible. Using the load versus deflection curves shown in Figs. 14 and 15 the stiffness of the panel can be calculated from the gradient of the curves. The stiffness for points C, D and E for the LINDAPTER panel are summarised in Table 4.
Average (mm)
C
E
D
C
E
D
0.26 0.27 0.25 0.34 0.33 0.33 0.55 0.55 0.53 0.89 0.94 0.96
0.3 0.29 0.27 0.43 0.44 0.41 0.63 0.65 0.69 1.27 1.3 1.32
0.47 0.48 0.46 0.66 0.67 0.64 1.02 1.03 1.07 1.91 1.98 2.04
0.26
0.29
0.47
0.33
0.43
0.66
0.54
0.66
1.04
0.93
1.30
1.98
4.3. Comparison between AJAX ONESIDE and LINDAPTER blind bolt panels Both panels exhibited a greater load capacity than the maximum load possible for this experiment under the two-point bending test. Both panels were tested to a maximum load of 900 kN. Under the 900 kN load, both panels did not exhibit any signs of failure; there was only minor cracking on the long sides of both panels. Furthermore, the shear connectors in both panels appear undamaged after the testing had concluded. In both the AJAX ONESIDE and LINDAPTER panels, the horizontal slip was negligible. The deflection under the applied loads for both panels is summarised in Table 5. Table 5 presents the average deflection under each load at points C, E, and D for the AJAX ONESIDE and LINDAPTER panels. Table 5 reveals that the difference between the deflection in the AJAX ONESIDE panel and the LINDAPTER panel is minimal. Therefore, it can be concluded that while the difference in deflection is minimal, the AJAX ONESIDE panel deflected more under serviceability loading than the LINDAPTER panel. All deflections recorded in the experimental testing of the panels are below the permissible limit of 2.19 mm. The deflection of both panels at the maximum load of 900 kN followed a similar pattern. The deflection at the midspan for the AJAX ONESIDE panel was 10.31 mm while the LINDAPTER panel deflected 10.13 mm. At the load points C and E, the AJAX ONESIDE panel
that the panel was near failure. The deflection of the LINDAPTER panel under the applied loads is summarised in Table 3 below. In Table 3, points C and E correspond to the deflection under the east and west load points respectively while deflection at point D represents the deflection at the midspan of the panel. The three values for each load correspond to the three load cycles for each load, which allow an average to be calculated. All deflections presented in Table 3 are below the permissible deflection with the maximum deflection occurring at the applied load of 360 kN at the midspan of the panel with a value of 1.98 mm. The highest deflection recorded in the experiment occurred at the maximum load of 900 kN. The deflection at this load at the midspan was 10.13 mm while at points C and E the deflection was 5.21 mm and 4.94 mm respectively. The experimental load versus deflection curve at the midspan for the LINDAPTER panel is shown in Fig. 14. Similarly, the load versus deflection curve for the load point deflections (points C and E) are shown in Fig. 15.
Fig. 14. Load versus deflection curve at midspan for LINDAPTER panel. 36
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Fig. 15. Load versus deflection curve at load points for LINDAPTER panel. Table 4 Stiffness at points C, E, and D for LINDAPTER panel.
Table 6 Stiffness of both panels.
Stiffness points
C
E
D
Deflection point
Shear connector
Uncracked stiffness (kN/mm) Cracked stiffness (kN/mm)
415 146
360 158
220 75
Uncracked stiffness (kN/mm)
Cracked stiffness (kN/mm)
C
AJAX LINDAPTER AJAX LINDAPTER AJAX LINDAPTER
326 415 265 360 – 220
158 146 146 158 65 75
E
Table 5 Deflection of both panels under applied loads. Deflection point
C E D
Shear connector
AJAX (mm) LINDAPTER (mm) AJAX (mm) LINDAPTER (mm) AJAX (mm) LINDAPTER (mm)
D
Load (kN) 100
150
240
360
0.27 0.26 0.38 0.29 0.01 0.47
0.44 0.33 0.55 0.43 0.00 0.66
0.74 0.54 1.11 0.66 0.53 1.04
1.44 0.93 1.71 1.30 1.77 1.98
LINDAPTER panels are presented in Table 6. The major variation in stiffness occurs in the uncracked stiffness for points C and E, where the LINDAPTER panel exhibits a higher stiffness. However, the variation in the cracked stiffness for both panels is minimal, which reinforces the conclusion that the shear connector has little to no influence on the behaviour of the prestressed panels under applied loading. The results presented above demonstrates that the similarity in behaviour when comparing the two panels. The AJAX ONESIDE panel and the LINDAPTER panel shows similar patterns in cracking, deflection and stiffness. The AJAX ONESIDE panel recorded slightly higher deflections and lower uncracked stiffness in comparison to the LINDAPTER panel. Thus, LINDAPTER blind bolts are the preferred method of connection between the bridge stringer steel and the precast prestressed steel-concrete composite panel. However, as differences in results are minimal, it is likely that the shear connector has a minimal impact on the behaviour of the panel. It is more likely that the slight variations in the results are a consequence of other factors during the fabrication of the specimens. Hence, it is difficult to make a definitive conclusion about the influence of the shear connectors. Furthermore, the panels did not exhibit any signs of failure or damage
deflected 5.38 mm and 5.91 mm respectively compared to the LINDAPTER deflections of 5.21 mm and 4.94 mm respectively. It is evident that the AJAX ONESIDE panel has a higher deflection when compared against the LINDAPTER panel at the 900 kN load, reinforcing the findings from the deflection under the applied loads. The load versus deflection curve at the midspan of panel for both the AJAX ONESIDE and the LINDAPTER panel are shown in Fig. 16. Fig. 16 presents that the AJAX ONESIDE panel has a higher deflection relative to the LINDAPTER panel. However, this difference in deflection is minimal. As the two curves are extremely similar, it can be concluded that the shear connector does not have an impact on the behaviour of the panel. The stiffness of the AJAX ONESIDE and
Fig. 16. Load versus deflection curve at midspan for both panels. 37
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Fig. 17. Cracking in conventionally reinforced panel.
Fig. 18. Cracking in prestressed panel.
Fig. 19. Cracking near retrofitted grouted hole in conventionally reinforced panel [6].
when the load was increased to a maximum load of 900 kN. Consequently, the precast prestressed steel-concrete composite panel design proposed by Zaher [6] is a feasible solution to replace the existing timber transoms currently in use on the Sydney Harbour bridge railway line.
Table 7 Deflection of conventionally reinforced and prestressed panels under applied loads. Deflection point
C
Panel type
Conventional Prestressed
E
Conventional Prestressed
D
Conventional Prestressed
Shear connector
AJAX (mm) LINDAPTER AJAX (mm) LINDAPTER AJAX (mm) LINDAPTER AJAX (mm) LINDAPTER AJAX (mm) LINDAPTER AJAX (mm) LINDAPTER
(mm) (mm) (mm) (mm) (mm) (mm)
Load (kN) 100
150
240
360
0.52 0.38 0.27 0.26 0.51 0.51 0.38 0.29 0.81 0.59 0.01 0.47
1.34 0.56 0.44 0.33 1.11 0.69 0.55 0.43 2.28 0.91 0.00 0.66
2.44 1.86 0.74 0.54 2.21 2.17 1.11 0.66 4.05 3.52 0.53 1.04
3.63 2.89 1.44 0.93 3.60 3.48 1.71 1.30 6.64 5.80 1.77 1.98
4.4. Comparison between precast prestressed panels and conventional reinforced panels Both the conventionally reinforced panels experimentally tested by Zaher [6] and the precast prestressed steel-concrete composite panels presented in this paper exhibit a greater load capacity than the maximum load possible under the two-point bending test. While both types of panels exhibited similar cracking noises, the amount of visible cracking was reduced in the prestressed panels in comparison to the conventionally reinforced panels. This is evident when comparing Figs. 17 and 18. The conventionally reinforced panel in Fig. 17 has more cracking along its long side relative to the prestressed panel shown in Fig. 18 under same loads. This is expected as one of the major 38
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Fig. 20. Load versus deflection curve at midspan for conventionally reinforced and prestressed panels.
The deflection of the two types of panels at the maximum load of 900 kN followed a similar pattern; the prestressed panels recorded a smaller deflection than the conventionally reinforced panels. The deflection for the prestressed panels at the 900 kN load was 10.31 mm and 10.13 mm for the AJAX ONESIDE and LINDAPTER panels respectively. In comparison, the conventionally reinforced panel recorded deflections of 15.20 mm and 13.98 mm for the AJAX ONESIDE and LINDAPTER panels respectively. The deflection at the 900 kN load reinforces the conclusion that the use of prestressed panels reduces deflection relative to conventionally reinforced panels. The load versus deflection graphs at the midspan for the four different panels, the prestressed AJAX ONESIDE panel, the prestressed LINDAPTER panel, the conventionally reinforced AJAX ONESIDE panel, and the conventionally reinforced LINDAPTER panel, are shown in Fig. 20. The conventionally reinforced panels experience significantly higher deflections compared to the prestressed panels. Furthermore, the shear connector affects the deflection for conventionally reinforced panels while the shear connector has minimal influence on the behaviour of the prestressed panels. The stiffness of the prestressed panels and conventionally reinforced panels are presented in Table 8. Table 8 clearly shows that the prestressed panels possess higher stiffness than the conventionally reinforced panels. This pattern is common across all deflection points. The only exception is the initial stiffness of the LINDAPTER conventionally reinforced panel which exhibits a similar stiffness to the prestressed panels. However, the cracked stiffness of this panel is similar to the cracked stiffness of the other conventionally reinforced panel. The comparison between stiffness for point D, the midspan of the panel, is represented by the gradients in the load versus deflection curves in Fig. 20. Therefore, it can be concluded that the prestressed panels exhibit higher stiffness than the conventionally reinforced panel. Overall, the results presented above demonstrate that the prestressed panels are more favourable over the conventionally reinforced panels, regardless of the type of shear connector. While both types of panels do not fail at the maximum possible experimental load of 900 kN, the prestressed panel exhibits less cracking on the long side of the precast panels relative to the conventionally reinforced panels. Furthermore, the prestressed panel significantly reduces deflection of the panel when compared to the conventionally reinforced panel. Additionally, the prestressed panel exhibits the higher stiffness than the conventionally reinforced panel. Consequently, prestressed panels are the preferred choice over conventionally reinforced panels to replace the existing timber transoms currently in use in the Sydney Harbour bridge railway line.
Table 8 Stiffness of prestressed and conventionally reinforced panels. Deflection point
Panel type
Shear connector
Uncracked stiffness (kN/ mm)
Cracked stiffness (kN/ mm)
C
Conventional
AJAX LINDAPTER AJAX LINDAPTER AJAX LINDAPTER AJAX LINDAPTER AJAX LINDAPTER AJAX LINDAPTER
174 290 326 415 219 290 265 360 128 169 – 220
116 123 158 146 105 105 146 158 56 57 65 75
Prestressed E
Conventional Prestressed
D
Conventional Prestressed
benefits of prestressed concrete is the reduction in cracking in concrete. Additionally, cracks formed on the top surface of the panel near the retrofitted holes in the conventionally reinforced panels, which is shown in Fig. 19. Conversely, the prestressed panels did not crack on the top surface. However, in the conventionally reinforced panels and prestressed panels, the horizontal slip is negligible. The deflection under the serviceability loads for the two different panel types are summarised in Table 7. Table 7 presents the average deflection under each serviceability load at points C, E, and D for the AJAX ONESIDE and LINDAPTER conventionally reinforced and prestressed panels. Table 7 reveals that a noticeable variation in deflection between the conventionally reinforced panels and the prestressed panels. At all deflection points, the conventionally reinforced panel records a significantly higher deflection than the prestressed panel. This is evident in the deflection at the midspan, point D, where the minimum deflection in the conventionally reinforced panel occurs in the LINDAPTER panel with a value of 5.80 mm, which is nearly three times greater than the maximum deflection in the prestressed panel that occurs in the LINDAPTER panel with a value of 1.98 mm. Therefore, it can be concluded that the prestressed panel reduces deflection in comparison to the conventionally reinforced panel. This is an expected result as reduced deflection is a further benefit of prestressed concrete. All recorded deflections for the prestressed panel are within the permissible limit of 4.05 mm for concrete member subjected to vehicular or pedestrian traffic. Conversely, the conventionally reinforced panel exceeds the serviceability at the midspan for the 360 kN load, thereby failing the permissible limit of deflection.
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5. Conclusions and further research
investigate the damage derailment. (iii) A finite element analysis of the prestressed panel and its response to applied loading could be validated as a further research. (iv) The durability analysis of the proposed panels might be conducted as a further research.
5.1. Concluding remarks The research presented herein has focused on the response of the precast prestressed steel-concrete composite panel under static loading in a two-point bending experiment. In the study, the panels were designed, fabricated and tested to determine their performance under static loading and the feasibility in replacing the wooden transoms of the Sydney Harbour bridge railway line. Based on the experimental results the following conclusion can be drawn:
References [1] Kaewunruen S, Remennikov AM. Impact capacity of railway prestressed concrete sleepers. Eng Fail Anal 2009;16(5):1520–32. [2] Ferdous W, Manalo A, Van Erp G, Aravinthan T, Kaewunruen S, Remennikov A. Composite railway sleepers–recent developments, challenges and future prospects. Compos Struct 2015;134:158–68. [3] Silva ÉA, Pokropski D, You R, Kaewunruen S. Comparison of structural design methods for railway composites and plastic sleepers and bearers. Aust J Struct Eng 2017;18(3):160–77. [4] Shanmuganathan S, Speers R, Ruodong P, Sriskanthan S. Sydney harbour bridge: replacement rail track support. 2011. [5] Griffin D. Design of precast composite steel-concrete panels for track support: for use on the Sydney Harbour Bridge, School of Computing, Engineering and Mathematics, University of Western Sydney. 2013. [6] Zaher N. Behaviour of modular precast pre-stressed concrete panels for Sydney Harbour Bridge, School of Computing, Engineering and Mathematics, Western Sydney University. 2016. [7] Johnston J. Feasibility design of transom using composite fibre technology for sydney harbour bridge. School of Computing, Engineering and Mathematics, Western Sydney University; 2016. [8] Bate S. A comparison between prestressed-concrete and reinforced-concrete beams under repeated loading. Proc Inst Civ Eng 1963;24(3):331–58. [9] Kaewunruen S, Remennikov A. On the residual energy toughness of prestressed concrete sleepers in railway track structures subjected to repeated impact loads. 2013. [10] Remennikov A, Murray MH, Kaewunruen S. Reliability-based conversion of a structural design code for railway prestressed concrete sleepers. Proc Inst Mech Eng F J Rail Rapid Transit 2012;226(2):155–73. [11] Ferdous W, Manalo A. Failures of mainline railway sleepers and suggested remedies–review of current practice. Eng Fail Anal 2014;44:17–35. [12] AS3600. Concrete structures, Australian standards. 2009. [13] Ibrahim AM. Parametric study of continuous concrete beam prestressed with external tendon. Jordan J Civ Eng 2010;4(3):211–21. [14] Harajli M, Khairallah N, Nassif H. Externally prestressed members: evaluation of second-order effects. J Struct Eng 1999;125(10):1151–61. [15] Lee J, Goldsworthy H, Gad E. Blind bolted T-stub connections to unfilled hollow section columns in low rise structures. J Constr Steel Res 2010;66(8):981–92. [16] Mirza O, Uy B, Patel N. Behaviour and strength of shear connectors utilising blind bolting, steel and composite structures. 2010. p. 791–6. [17] Kaewunruen S, Remennikov AM. Effect of a large asymmetrical wheel burden on flexural response and failure of railway concrete sleepers in track systems. Eng Fail Anal 2008;15(8):1065–75. [18] Standards Australia. Railway track material – part 14: prestressed concrete sleepers. Australian standard: AS1085.14-2003. 2003. [19] AS5100.2. Bridge design - design loads, Australian standards. 2004.
(i) Deflections of both AJAX ONESIDE blind bolt and LINDAPTER blind bolt prestressed panels were below the permissible deflection of 2.19 mm as required by AS3600 for members subjected to vehicular or pedestrian traffic. The recorded maximum deflection under the applied load of 360 kN of either prestressed panel was 1.98 mm, which is approximately half of the permissible deflection limit. (ii) The prestressed panels did not fail under the maximum load of 900 kN. Therefore, the capacity of the prestressed panels was higher than the maximum experimental load of 900 kN. (iii) Cracking noises were frequent throughout the experimental testing. Minor cracks were visible on the long sides of the both panels under 900 kN loading. (iv) Horizontal slip between the concrete and the Bondek profiled steel sheeting was considered negligible. The maximum horizontal slip recorded was 0.53 mm for either panel, which was minimal. (v) The type of shear connectors has minimal effect on the behaviour of the prestressed panels. However, LINDAPTER blind bolts are the preferred method of connection between the bridge stringer steel and the prestressed composite panel. 5.2. Recommendations for further research Further research in the following areas may be considered to enhance the research presented within this paper and reinforce the prestressed panels as a viable solution for the Sydney Harbour bridge project: (i) Further experimental investigation using a higher loading can be done to cause failure in the prestressed panels. (ii) Besides static loads, impact loading need to be considered to
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Structures journal homepage: www.elsevier.com/locate/structures
Performance of Precast Prestressed Steel-Concrete Composite Panels Under Static Loadings to Replace the Timber Transoms for Railway Bridge
T
Olivia Mirzaa, , Sukanta Kumer Shillb,c, Jason Johnstona ⁎
a
School of Computing, Engineering & Mathematics, University of Western Sydney, Australia School of Engineering and Information Technology, the University of New South Wales, Canberra, Australia c Department of Civil Engineering, Dhaka University of Engineering & Technology (DUET), Bangladesh b
ARTICLE INFO
ABSTRACT
Keywords: Transoms Prestressed concrete panels Reinforced concrete panels AJAX ONESIDE blind bolts LINDAPTER blind bolts
Timber is widely used as transoms in numerous railway networks all over the world and currently in use on the existing Sydney Harbour bridge railway system. Now-a-days, the timber transoms, in numerous railway networks, are edging towards the end of their design life. Moreover, often these timber transoms are subjected to repeated mechanical loadings, chemical degradation and prolonged environmental exposures. As a result, frequent maintenance and sometimes complete replacement to ensure the functionality of the railway network significantly increases the track maintenance cost. Therefore, the paper aims to presents alternative solutions to replace the timber transoms with other more durable and virtually maintenance free materials that will improve the long-term functionality of the transoms in Sydney Harbour bridge railway system. To achieve the goal of the study, an experimental investigation was carried out on the precast prestressed steel-concrete composite panels using two different connectors like AJAX ONESIDE blind bolts and LINDAPTER blind bolts. The experimental results of precast prestressed steel-concrete composite panels under two-point bending test were also compared with the conventional reinforced concrete. It can be concluded that the prestressed panels performed better and exhibited less cracking, less deflection and higher stiffness compared to the conventionally reinforced concrete panels. Moreover, the prestressed panel with AJAX ONESIDE blind bolt connectors shows slightly higher deflections and lower uncracked stiffness in comparison to the prestressed panel with LINDAPTER blind bolt connectors. Therefore, LINDAPTER blind bolts connectors, are preferable in connecting the bridge stringer steel and the prestressed composite panel, could be a viable solution to replace the existing timber transoms of the Sydney Harbour bridge railway line.
1. Introduction Timber transoms are widely used in numerous railway networks around the world. Transoms are usually used to distribute and transfer the applied railway loadings to the underlying ballast bed or supporting system [1]. Now-a-days, the timber transoms, in numerous railway networks, are edging towards the end of their design life. It is well known that the existing railway tracks of the Sydney Harbour bridge also use hardwood timber transoms. Transoms are often subjected to repeated mechanical loads, prolonged environmental exposures, climate change, chemical degradation and biological degradation by fungus [2,3]. Consequently, the timber transoms usually require frequent maintenance and must be regularly replaced to ensure the functionality of the railway network. Moreover, moisture absorption of the timber transoms that contributes to the corrosion of the top part of the stringer top flange, noting that this location is very difficult to access and inspect. Besides the above issues mentioned,
⁎
the frequency and magnitude of loadings are recently becoming significantly higher compared to the time of initial placement. In light of the above issues, the Sydney Harbour bridge project aims to develop solutions to provide an alternative solid, that are durable and virtually maintenance free to improve the long-term functionality of the transoms [4]. While conventional alternative materials such as steel and concrete have been considered, no other materials are ideal to replace the degraded hardwood timber transoms. The Sydney Harbour bridge project proposes three alternative solutions to replace these timber transoms. The three alternatives are conventionally reinforced concrete panels, prestressed steel-concrete composite panels, and the use of a new material, Wagners Composite Fibre Technology within a panel design. The conventionally reinforced panel was designed by Griffin [5] and fabricated and experimentally tested by Zaher [6]. The prestressed steel-concrete composite panels were designed and partially fabricated by Zaher [6] who was unable to complete the fabrication and
Corresponding author. E-mail address: [email protected] (O. Mirza).
https://doi.org/10.1016/j.istruc.2018.12.001 Received 16 October 2017; Received in revised form 26 November 2018; Accepted 2 December 2018 Available online 04 December 2018 2352-0124/ © 2018 Published by Elsevier Ltd on behalf of Institution of Structural Engineers.
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Fig. 1. Panel specimen size [6].
bridge project, the prestressed panel was required to be 3237 mm long with a width of 600 mm. The panel is supported by the bridge stringers which span 1981 mm measured from the centre of the supports. The prestressed panel design outlines three strand cables with 15.2 mm diameter. A draped tendon profile was used in the prestressed panels rather than straight tendon profile as shown in Fig. 3. It is well known that a prestressed beam or slab with draped tendon profile shows a higher ultimate load, lower deflection, a higher moment resistance and a stiffer response compared to beams with a undraped straight tendon profile [13,14]. Furthermore, the design requires 50 MPa concrete, Bondek II profiled steel sheeting, 4N12 reinforcing bars, and N10 stirrups spaced at 90 mm between the supports and 130 mm centres outside the support. The design of the prestressed panel is shown in Figs. 1 to 3.
testing of the prestressed panels, while the Wagners Composite Fibre Technology panels were investigated by Johnston [7]. In the past, in order to compare the behaviour of reinforced and prestressed concrete under repeated loads, Bate [8] conducted an extensive experimental study on the two types of concrete beams. The author determined that while loading was within the beam's load capacity, the prestressed concrete beam did not crack and slightly deformed under repetition. In comparison, the reinforced concrete beam experienced cracking under the same loading. Kaewunruen & Remennikov [1] conducted static and impact loading experiments on prestressed concrete sleepers to determine its failure mechanism and ultimate capacity. In the static testing, the authors performed a positive bending moment test using a steel plate to disperse loading to mimic the rail seat of a railway system. This allowed the ultimate bending moment capacity of the prestressed concrete sleeper to be calculated while measuring the deflection of the structural member. Moreover, the authors [9] also investigated the residual energy toughness of prestressed concrete sleepers in railway track structures subjected to repeated impact loads. Further, Remennikov et al. [10], presented the background information and focuses on the new limit states design concept for prestressed concrete sleepers. According to Ferdous and Manalo [11], the premature deterioration of traditional railway sleepers has become of great concern over the last two decades and has significantly increased the track maintenance costs. The authors revealed in their review works that fungal decay, end splitting, termites, still sound, sapwood, shelling, rail cut, weathering, spike kill, and knots the principal causes of traditional timber sleeper failure. Moreover, issues with the timber transoms are rotting, splitting and insect attack [3]. Although the higher initial cost, the prestressed concrete sleepers are being popular because of the higher impact resistance and durability compared to timber and steel [2]. Considering the minimum maintenance and long design life of the precast or prefabricated steel-concrete composite panels and to increase the speed of installation and thereby minimise the disruptions to existing railway services, the authors investigated the feasibility of using prestressed steel-concrete composite panels to replace the timber transoms in the Sydney Harbour bridge railway network. Moreover, the paper presents the deflection characteristics, stiffness properties, cracking patterns, load carrying capacity, retrofitting to supporting stringers and horizontal slip occurrences of prestressed steel-concrete composite panels under two points bending test. Finally, a comparison between conventional reinforced concrete panel and the prestressed concrete panel is also discussed in this paper.
2.2. Fabrication of specimen Two prestressed panels were fabricated at the laboratory of the Western Sydney University Kingswood campus. One panel uses AJAX ONESIDE blind bolts to retrofit the panel to the bridge stringer steel while the second panel uses LINDAPTER blind bolts for the connection. The initial fabrication of the prestressed panels prior to concrete pouring included the following work: formwork preparation, installation of Bondek profiled steel sheeting, steel reinforcement placement, the installation of the prestress duct, and installation of strain gauges. Concrete with a characteristic compressive strength of f′c = 50 MPa was used in the study. The panels were cured for 28 days to allow the concrete to reach its characteristic compressive strength. However, after the concrete was allowed to harden for a period of 14 days, the prestress strands were tensioned using a hydraulic jack to achieve a tension value of 174 kN. The prestress ducts were filled with high strength grout to provide the necessary connection between the prestressing strands and the concrete to transfer the prestress effectively. 2.3. Retrofitting Shear connectors were used to retrofit the precast prestressed steelconcrete composite panel to the supporting steel stringers. Two different types of shear connectors were used: AJAX ONESIDE blind bolts, and LINDAPTER blind bolts. The Ajax ONESIDE blind bolting system used in this paper comprises of a circular bolt head, internal folding stepped washer, sleeve, external solid stepped washer and nut. A special installation tool was also required to insert the blind bolt and tighten it. In the study, the ajax ONESIDE blind bolting method was done according to Lee et al. [15], and the LINDAPTER blind bolt shear connectors were used according to Mirza et al. [16]. The AJAX ONESIDE blind bolts and LINDAPTER blind bolts fitted to the steel stringer are shown in Figs. 4 and 5 respectively. During the fabrication of the panels, PVC pipes were placed at the hole locations of the shear connectors. Once the concrete had hardened,
2. Methodology 2.1. Design of prestressed steel-concrete composite panel Prestressed steel-concrete composite panels are designed following the AS3600 [12]. To match the other panels in the Sydney Harbour 31
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Fig. 2. Panel reinforcement details [6].
Fig. 3. Panel chair height [6].
Fig. 4. AJAX ONESIDE blind bolts.
Fig. 5. LINDAPTER blind bolts assembly.
the PVC pipes were removed to provide a void in the concrete at the shear connector locations. The panel was then lifted onto the steel stringers so the shear connectors lined up with the void locations in the concrete. Once in place, these holes were filled with high strength grout to effectively connect the panel to the bridge stringers.
3. Experimental set-up The experimental setup that of the study is similar to the experimental set up that was used by Kaewunruen & Remennikov [1], where the precast prestressed panel was tested under static loading to determine ultimate bending capacity while measuring the deflection of 32
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Fig. 6. Schematic experimental test set-up summary.
Fig. 7. Experimental test set-up of prestressed panel.
Fig. 8. Cracking in the AJAX ONESIDE blind bolt panel (N-side).
the member in response to the loading. The experimental test set-up basically involved four main steps:
Linear potentiometers were placed at either end of the panel to measure the horizontal slip between the concrete and Bondek profiled steel sheeting. Additionally, linear potentiometers were placed underneath the two load locations and at midspan of the panel to measure vertical deflection. Loading on the panel was applied with the help of hydraulic jack of capacity of 1000 kN. Two-line loads to replicate the rails of the Sydney Harbour bridge railway network were placed at a span of 1435 mm as outlined in Fig. 6. The two-line loads were achieved by placing two steel beams with a width of 100 mm on the panel. A
• Connecting the steel beams to the strong floor • Placement of linear potentiometers along the panel • Connecting the strain gauges to the reading system and • Placement of plywood, steel beam, and knife edges over the width of the panel
33
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Fig. 9. Cracking in the AJAX ONESIDE blind bolt panel (S-side).
and rail, associated with the abnormalities in either a wheel or a rail. The design static wheel load per rail seat for a 40-tone axle load usually varies from 100 kN to 110 kN [17]. In this study, the static loading test on the transom panels was conducted following the AS1085.14 [18]. Load was applied to the panels to determine their structural performance based on load deflection chracteristics. Loading and unloading were applied at a rate of 6 mm/min in accordance to achieve the following magnitudes in the corresponding order:
Table 1 Deflection under applied loadings for AJAX ONESIDE panel. Applied load (kN)
100 150 240 360
Deflection point (mm)
Average (mm)
C
E
D
C
E
D
0.26 0.28 0.28 0.42 0.47 0.43 0.70 0.74 0.79 1.34 1.46 1.51
0.37 0.39 0.38 0.52 0.54 0.59 1.1 1.13 1.1 1.66 1.73 1.73
0.01 0.01 0.02 0.00 0.00 0.01 0.45 0.55 0.6 1.65 1.81 1.86
0.27
0.38
0.01
0.44
0.55
0.00
0.74
1.11
0.53
1.44
1.71
1.77
• Load to 50 kN and check all testing equipment is recording accurately • Load to 100 kN and unload to 50 kN (repeated three times) • Load to 150 kN and unload to 50 kN (repeated three times) • Load to 240 kN and unload to 100 kN (repeated three times) • Load to 360 kN and unload to 100 kN (repeated three times) • Load to failure or 900 kN
plywood plate with similar dimensions was placed between the panel and the steel beam. Once testing began, the spreader beam connected to the hydraulic jack was lowered until contact was made with the knife edge on top of each steel beam. The vertical load was controlled using a load cell connected to the automatic data acquisition system. The experimental test set-up is summarised in Fig. 6, in this figure, point A and B correspond to the horizontal linear potentiometers while points C and E represent the vertical linear potentiometers at the load locations. Point D corresponds to the vertical linear potentiometer at the midspan of the panel. The completed experimental test set-up of one prestressed panel can be observed in Fig. 7.
The final stage of loading is to determine whether the load that causes failure in the panel. The load was increased to a maximum value of 900 kN as the capacity of the hydraulic jack in the laboratory is 1000 kN. The loads 100 kN, 150 kN, 240 kN, and 360 kN correspond to the loads associated with the wheel load of the different rail loading systems. Notably, the 240 kN and 360 kN are the maximum static load per wheel correspond to the 200 LA and 300 LA rail loading system respectively, as outlined in AS5100.2 [19].
3.1. Loading system
During the experimental testing of the AJAX ONESIDE blind bolt panel, when the loading was first increased to 240 kN, cracking noises were heard at a load of approximately 184 kN. Similarly, when the loading was first increased to 360 kN, cracking noises were heard at a
4. Results and discussion 4.1. AJAX ONESIDE blind bolt panel
Railway transoms are often subjected to the static loading and sometimes impact loading condition due to the interactions of wheel
Fig. 10. Load versus deflection curve at midspan for AJAX ONESIDE panel. 34
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Fig. 11. Load versus deflection curve at load points for AJAX ONESIDE panel.
value of 1.77 mm. The highest deflection recorded in the experiment occurred at the maximum load of 900 kN. The deflection at this load at the midspan was 10.31 mm while at points C and E the deflection was 5.38 mm and 5.91 mm respectively. The experimental load versus deflection curve at the midspan for the AJAX ONESIDE panel is shown in Fig. 10. Similarly, the load versus deflection curve for the load point deflections (points C and E) are shown in Fig. 11. The linear potentiometers placed horizontally at points A and B were used to measure the horizontal slip between the concrete and the Bondek profiled steel sheeting. The maximum slip recorded at either end of the panel was 0.53 mm. As this value is minimal, the horizontal slip between the concrete and Bondek profiled steel sheeting can be considered negligible. Using a line of best fit on the load versus deflection curves shown in Figs. 10 and 11 the stiffness of the prestressed panel can be calculated from the gradient of the curves. The stiffness for points C, D, and E of the AJAX ONESIDE panel are summarised in Table 2.
Table 2 Stiffness at points C, E, and D for AJAX ONESIDE panel. Stiffness points
C
E
D
Uncracked stiffness (kN/mm) Cracked stiffness (kN/mm)
326 158
265 146
– 65
load of approximately 330 kN. The cracking noises can be attributed to the expansion of the Bondek profiled steel sheeting and/or minor cracking in the concrete. At the 360 kN load, there was no visible cracking in the prestressed panel. The loading was then increased to cause failure in the panel and allow its ultimate capacity to be determined. As the load was increased above 500 kN, cracking noises was frequently heard until the maximum possible load of 900 kN was reached. The cracking in the AJAX ONESIDE panel on the N and S long sides under the 900 kN load is shown in Figs. 8 and 9. However, there were no visible cracks near the retrofitted, grouted holes above the bridge stringer supports. While some minor cracking occurred on the long sides of the panel, however, the panel did not show any major signs or distress that the panel was near failure. The deflection of the AJAX ONESIDE panel under the load's sensitivity is summarised in Table 1. In Table 1, points C and E correspond to the deflection under the east and west load points respectively while deflection at point D represents the deflection at the midspan of the panel. The three values for each load correspond to the three load cycles for each load, which allow an average to be calculated. The deflections presented in Table 1 are within the permissible deflection limit as required by AS3600 [12]. According to AS3600, a minimum deflection/span ratio of 1/800 for members subjected to vehicular or pedestrian traffic. Considering the effective span of the panel, which is equal to 3237 mm, the maximum allowable deflection 1752 of the panel is 800 = 2.19 mm . All deflection values presented in Table 1 are below the permissible deflection with the maximum deflection occurring at the applied load of 360 kN at the midspan of the panel with a
4.2. LINDAPTER blind bolt panel During the experimental testing of the LINDAPTER blind bolt panel, cracking noises were first heard at a load of approximately 280 kN, when the loading was first increased to 360 kN. At the 360 kN serviceability load, there was no visible cracking in the panel. The loading was then increased to cause failure in the panel and allow its ultimate capacity to be determined. As the load was increased above 500 kN, cracking noises was frequently heard until the maximum possible load of 900 kN was reached. One extremely loud cracking noise was heard when the load increased above 500 kN. The cracking in the LINDAPTER panel on the N and S long sides under the 900 kN load is shown in Figs. 12 and 13. Furthermore, there were no visible cracks near the retrofitted, grouted holes above the bridge stringer supports. While some minor cracking occurred on the long sides of the panel, however, the LINDAPTER panel did also not show any major signs or indications
Fig. 12. Cracking in the LINDAPTER panel (N-side). 35
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Fig. 13. Cracking in the LINDAPTER panel (S-side).
• The linear potentiometers placed horizontally at points A and B
Table 3 Deflection under serviceability loading for LINDAPTER panel. Applied load (kN)
100 150 240 360
Deflection point (mm)
were used to measure the horizontal slip between the concrete and the Bondek profiled steel sheeting. The maximum slip recorded at either end of the prestressed panel was 0.19 mm. In the case of LINDAPTER panel, the horizontal slip between the concrete and Bondek profiled steel sheeting also can be considered negligible. Using the load versus deflection curves shown in Figs. 14 and 15 the stiffness of the panel can be calculated from the gradient of the curves. The stiffness for points C, D and E for the LINDAPTER panel are summarised in Table 4.
Average (mm)
C
E
D
C
E
D
0.26 0.27 0.25 0.34 0.33 0.33 0.55 0.55 0.53 0.89 0.94 0.96
0.3 0.29 0.27 0.43 0.44 0.41 0.63 0.65 0.69 1.27 1.3 1.32
0.47 0.48 0.46 0.66 0.67 0.64 1.02 1.03 1.07 1.91 1.98 2.04
0.26
0.29
0.47
0.33
0.43
0.66
0.54
0.66
1.04
0.93
1.30
1.98
4.3. Comparison between AJAX ONESIDE and LINDAPTER blind bolt panels Both panels exhibited a greater load capacity than the maximum load possible for this experiment under the two-point bending test. Both panels were tested to a maximum load of 900 kN. Under the 900 kN load, both panels did not exhibit any signs of failure; there was only minor cracking on the long sides of both panels. Furthermore, the shear connectors in both panels appear undamaged after the testing had concluded. In both the AJAX ONESIDE and LINDAPTER panels, the horizontal slip was negligible. The deflection under the applied loads for both panels is summarised in Table 5. Table 5 presents the average deflection under each load at points C, E, and D for the AJAX ONESIDE and LINDAPTER panels. Table 5 reveals that the difference between the deflection in the AJAX ONESIDE panel and the LINDAPTER panel is minimal. Therefore, it can be concluded that while the difference in deflection is minimal, the AJAX ONESIDE panel deflected more under serviceability loading than the LINDAPTER panel. All deflections recorded in the experimental testing of the panels are below the permissible limit of 2.19 mm. The deflection of both panels at the maximum load of 900 kN followed a similar pattern. The deflection at the midspan for the AJAX ONESIDE panel was 10.31 mm while the LINDAPTER panel deflected 10.13 mm. At the load points C and E, the AJAX ONESIDE panel
that the panel was near failure. The deflection of the LINDAPTER panel under the applied loads is summarised in Table 3 below. In Table 3, points C and E correspond to the deflection under the east and west load points respectively while deflection at point D represents the deflection at the midspan of the panel. The three values for each load correspond to the three load cycles for each load, which allow an average to be calculated. All deflections presented in Table 3 are below the permissible deflection with the maximum deflection occurring at the applied load of 360 kN at the midspan of the panel with a value of 1.98 mm. The highest deflection recorded in the experiment occurred at the maximum load of 900 kN. The deflection at this load at the midspan was 10.13 mm while at points C and E the deflection was 5.21 mm and 4.94 mm respectively. The experimental load versus deflection curve at the midspan for the LINDAPTER panel is shown in Fig. 14. Similarly, the load versus deflection curve for the load point deflections (points C and E) are shown in Fig. 15.
Fig. 14. Load versus deflection curve at midspan for LINDAPTER panel. 36
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Fig. 15. Load versus deflection curve at load points for LINDAPTER panel. Table 4 Stiffness at points C, E, and D for LINDAPTER panel.
Table 6 Stiffness of both panels.
Stiffness points
C
E
D
Deflection point
Shear connector
Uncracked stiffness (kN/mm) Cracked stiffness (kN/mm)
415 146
360 158
220 75
Uncracked stiffness (kN/mm)
Cracked stiffness (kN/mm)
C
AJAX LINDAPTER AJAX LINDAPTER AJAX LINDAPTER
326 415 265 360 – 220
158 146 146 158 65 75
E
Table 5 Deflection of both panels under applied loads. Deflection point
C E D
Shear connector
AJAX (mm) LINDAPTER (mm) AJAX (mm) LINDAPTER (mm) AJAX (mm) LINDAPTER (mm)
D
Load (kN) 100
150
240
360
0.27 0.26 0.38 0.29 0.01 0.47
0.44 0.33 0.55 0.43 0.00 0.66
0.74 0.54 1.11 0.66 0.53 1.04
1.44 0.93 1.71 1.30 1.77 1.98
LINDAPTER panels are presented in Table 6. The major variation in stiffness occurs in the uncracked stiffness for points C and E, where the LINDAPTER panel exhibits a higher stiffness. However, the variation in the cracked stiffness for both panels is minimal, which reinforces the conclusion that the shear connector has little to no influence on the behaviour of the prestressed panels under applied loading. The results presented above demonstrates that the similarity in behaviour when comparing the two panels. The AJAX ONESIDE panel and the LINDAPTER panel shows similar patterns in cracking, deflection and stiffness. The AJAX ONESIDE panel recorded slightly higher deflections and lower uncracked stiffness in comparison to the LINDAPTER panel. Thus, LINDAPTER blind bolts are the preferred method of connection between the bridge stringer steel and the precast prestressed steel-concrete composite panel. However, as differences in results are minimal, it is likely that the shear connector has a minimal impact on the behaviour of the panel. It is more likely that the slight variations in the results are a consequence of other factors during the fabrication of the specimens. Hence, it is difficult to make a definitive conclusion about the influence of the shear connectors. Furthermore, the panels did not exhibit any signs of failure or damage
deflected 5.38 mm and 5.91 mm respectively compared to the LINDAPTER deflections of 5.21 mm and 4.94 mm respectively. It is evident that the AJAX ONESIDE panel has a higher deflection when compared against the LINDAPTER panel at the 900 kN load, reinforcing the findings from the deflection under the applied loads. The load versus deflection curve at the midspan of panel for both the AJAX ONESIDE and the LINDAPTER panel are shown in Fig. 16. Fig. 16 presents that the AJAX ONESIDE panel has a higher deflection relative to the LINDAPTER panel. However, this difference in deflection is minimal. As the two curves are extremely similar, it can be concluded that the shear connector does not have an impact on the behaviour of the panel. The stiffness of the AJAX ONESIDE and
Fig. 16. Load versus deflection curve at midspan for both panels. 37
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Fig. 17. Cracking in conventionally reinforced panel.
Fig. 18. Cracking in prestressed panel.
Fig. 19. Cracking near retrofitted grouted hole in conventionally reinforced panel [6].
when the load was increased to a maximum load of 900 kN. Consequently, the precast prestressed steel-concrete composite panel design proposed by Zaher [6] is a feasible solution to replace the existing timber transoms currently in use on the Sydney Harbour bridge railway line.
Table 7 Deflection of conventionally reinforced and prestressed panels under applied loads. Deflection point
C
Panel type
Conventional Prestressed
E
Conventional Prestressed
D
Conventional Prestressed
Shear connector
AJAX (mm) LINDAPTER AJAX (mm) LINDAPTER AJAX (mm) LINDAPTER AJAX (mm) LINDAPTER AJAX (mm) LINDAPTER AJAX (mm) LINDAPTER
(mm) (mm) (mm) (mm) (mm) (mm)
Load (kN) 100
150
240
360
0.52 0.38 0.27 0.26 0.51 0.51 0.38 0.29 0.81 0.59 0.01 0.47
1.34 0.56 0.44 0.33 1.11 0.69 0.55 0.43 2.28 0.91 0.00 0.66
2.44 1.86 0.74 0.54 2.21 2.17 1.11 0.66 4.05 3.52 0.53 1.04
3.63 2.89 1.44 0.93 3.60 3.48 1.71 1.30 6.64 5.80 1.77 1.98
4.4. Comparison between precast prestressed panels and conventional reinforced panels Both the conventionally reinforced panels experimentally tested by Zaher [6] and the precast prestressed steel-concrete composite panels presented in this paper exhibit a greater load capacity than the maximum load possible under the two-point bending test. While both types of panels exhibited similar cracking noises, the amount of visible cracking was reduced in the prestressed panels in comparison to the conventionally reinforced panels. This is evident when comparing Figs. 17 and 18. The conventionally reinforced panel in Fig. 17 has more cracking along its long side relative to the prestressed panel shown in Fig. 18 under same loads. This is expected as one of the major 38
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Fig. 20. Load versus deflection curve at midspan for conventionally reinforced and prestressed panels.
The deflection of the two types of panels at the maximum load of 900 kN followed a similar pattern; the prestressed panels recorded a smaller deflection than the conventionally reinforced panels. The deflection for the prestressed panels at the 900 kN load was 10.31 mm and 10.13 mm for the AJAX ONESIDE and LINDAPTER panels respectively. In comparison, the conventionally reinforced panel recorded deflections of 15.20 mm and 13.98 mm for the AJAX ONESIDE and LINDAPTER panels respectively. The deflection at the 900 kN load reinforces the conclusion that the use of prestressed panels reduces deflection relative to conventionally reinforced panels. The load versus deflection graphs at the midspan for the four different panels, the prestressed AJAX ONESIDE panel, the prestressed LINDAPTER panel, the conventionally reinforced AJAX ONESIDE panel, and the conventionally reinforced LINDAPTER panel, are shown in Fig. 20. The conventionally reinforced panels experience significantly higher deflections compared to the prestressed panels. Furthermore, the shear connector affects the deflection for conventionally reinforced panels while the shear connector has minimal influence on the behaviour of the prestressed panels. The stiffness of the prestressed panels and conventionally reinforced panels are presented in Table 8. Table 8 clearly shows that the prestressed panels possess higher stiffness than the conventionally reinforced panels. This pattern is common across all deflection points. The only exception is the initial stiffness of the LINDAPTER conventionally reinforced panel which exhibits a similar stiffness to the prestressed panels. However, the cracked stiffness of this panel is similar to the cracked stiffness of the other conventionally reinforced panel. The comparison between stiffness for point D, the midspan of the panel, is represented by the gradients in the load versus deflection curves in Fig. 20. Therefore, it can be concluded that the prestressed panels exhibit higher stiffness than the conventionally reinforced panel. Overall, the results presented above demonstrate that the prestressed panels are more favourable over the conventionally reinforced panels, regardless of the type of shear connector. While both types of panels do not fail at the maximum possible experimental load of 900 kN, the prestressed panel exhibits less cracking on the long side of the precast panels relative to the conventionally reinforced panels. Furthermore, the prestressed panel significantly reduces deflection of the panel when compared to the conventionally reinforced panel. Additionally, the prestressed panel exhibits the higher stiffness than the conventionally reinforced panel. Consequently, prestressed panels are the preferred choice over conventionally reinforced panels to replace the existing timber transoms currently in use in the Sydney Harbour bridge railway line.
Table 8 Stiffness of prestressed and conventionally reinforced panels. Deflection point
Panel type
Shear connector
Uncracked stiffness (kN/ mm)
Cracked stiffness (kN/ mm)
C
Conventional
AJAX LINDAPTER AJAX LINDAPTER AJAX LINDAPTER AJAX LINDAPTER AJAX LINDAPTER AJAX LINDAPTER
174 290 326 415 219 290 265 360 128 169 – 220
116 123 158 146 105 105 146 158 56 57 65 75
Prestressed E
Conventional Prestressed
D
Conventional Prestressed
benefits of prestressed concrete is the reduction in cracking in concrete. Additionally, cracks formed on the top surface of the panel near the retrofitted holes in the conventionally reinforced panels, which is shown in Fig. 19. Conversely, the prestressed panels did not crack on the top surface. However, in the conventionally reinforced panels and prestressed panels, the horizontal slip is negligible. The deflection under the serviceability loads for the two different panel types are summarised in Table 7. Table 7 presents the average deflection under each serviceability load at points C, E, and D for the AJAX ONESIDE and LINDAPTER conventionally reinforced and prestressed panels. Table 7 reveals that a noticeable variation in deflection between the conventionally reinforced panels and the prestressed panels. At all deflection points, the conventionally reinforced panel records a significantly higher deflection than the prestressed panel. This is evident in the deflection at the midspan, point D, where the minimum deflection in the conventionally reinforced panel occurs in the LINDAPTER panel with a value of 5.80 mm, which is nearly three times greater than the maximum deflection in the prestressed panel that occurs in the LINDAPTER panel with a value of 1.98 mm. Therefore, it can be concluded that the prestressed panel reduces deflection in comparison to the conventionally reinforced panel. This is an expected result as reduced deflection is a further benefit of prestressed concrete. All recorded deflections for the prestressed panel are within the permissible limit of 4.05 mm for concrete member subjected to vehicular or pedestrian traffic. Conversely, the conventionally reinforced panel exceeds the serviceability at the midspan for the 360 kN load, thereby failing the permissible limit of deflection.
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5. Conclusions and further research
investigate the damage derailment. (iii) A finite element analysis of the prestressed panel and its response to applied loading could be validated as a further research. (iv) The durability analysis of the proposed panels might be conducted as a further research.
5.1. Concluding remarks The research presented herein has focused on the response of the precast prestressed steel-concrete composite panel under static loading in a two-point bending experiment. In the study, the panels were designed, fabricated and tested to determine their performance under static loading and the feasibility in replacing the wooden transoms of the Sydney Harbour bridge railway line. Based on the experimental results the following conclusion can be drawn:
References [1] Kaewunruen S, Remennikov AM. Impact capacity of railway prestressed concrete sleepers. Eng Fail Anal 2009;16(5):1520–32. [2] Ferdous W, Manalo A, Van Erp G, Aravinthan T, Kaewunruen S, Remennikov A. Composite railway sleepers–recent developments, challenges and future prospects. Compos Struct 2015;134:158–68. [3] Silva ÉA, Pokropski D, You R, Kaewunruen S. Comparison of structural design methods for railway composites and plastic sleepers and bearers. Aust J Struct Eng 2017;18(3):160–77. [4] Shanmuganathan S, Speers R, Ruodong P, Sriskanthan S. Sydney harbour bridge: replacement rail track support. 2011. [5] Griffin D. Design of precast composite steel-concrete panels for track support: for use on the Sydney Harbour Bridge, School of Computing, Engineering and Mathematics, University of Western Sydney. 2013. [6] Zaher N. Behaviour of modular precast pre-stressed concrete panels for Sydney Harbour Bridge, School of Computing, Engineering and Mathematics, Western Sydney University. 2016. [7] Johnston J. Feasibility design of transom using composite fibre technology for sydney harbour bridge. School of Computing, Engineering and Mathematics, Western Sydney University; 2016. [8] Bate S. A comparison between prestressed-concrete and reinforced-concrete beams under repeated loading. Proc Inst Civ Eng 1963;24(3):331–58. [9] Kaewunruen S, Remennikov A. On the residual energy toughness of prestressed concrete sleepers in railway track structures subjected to repeated impact loads. 2013. [10] Remennikov A, Murray MH, Kaewunruen S. Reliability-based conversion of a structural design code for railway prestressed concrete sleepers. Proc Inst Mech Eng F J Rail Rapid Transit 2012;226(2):155–73. [11] Ferdous W, Manalo A. Failures of mainline railway sleepers and suggested remedies–review of current practice. Eng Fail Anal 2014;44:17–35. [12] AS3600. Concrete structures, Australian standards. 2009. [13] Ibrahim AM. Parametric study of continuous concrete beam prestressed with external tendon. Jordan J Civ Eng 2010;4(3):211–21. [14] Harajli M, Khairallah N, Nassif H. Externally prestressed members: evaluation of second-order effects. J Struct Eng 1999;125(10):1151–61. [15] Lee J, Goldsworthy H, Gad E. Blind bolted T-stub connections to unfilled hollow section columns in low rise structures. J Constr Steel Res 2010;66(8):981–92. [16] Mirza O, Uy B, Patel N. Behaviour and strength of shear connectors utilising blind bolting, steel and composite structures. 2010. p. 791–6. [17] Kaewunruen S, Remennikov AM. Effect of a large asymmetrical wheel burden on flexural response and failure of railway concrete sleepers in track systems. Eng Fail Anal 2008;15(8):1065–75. [18] Standards Australia. Railway track material – part 14: prestressed concrete sleepers. Australian standard: AS1085.14-2003. 2003. [19] AS5100.2. Bridge design - design loads, Australian standards. 2004.
(i) Deflections of both AJAX ONESIDE blind bolt and LINDAPTER blind bolt prestressed panels were below the permissible deflection of 2.19 mm as required by AS3600 for members subjected to vehicular or pedestrian traffic. The recorded maximum deflection under the applied load of 360 kN of either prestressed panel was 1.98 mm, which is approximately half of the permissible deflection limit. (ii) The prestressed panels did not fail under the maximum load of 900 kN. Therefore, the capacity of the prestressed panels was higher than the maximum experimental load of 900 kN. (iii) Cracking noises were frequent throughout the experimental testing. Minor cracks were visible on the long sides of the both panels under 900 kN loading. (iv) Horizontal slip between the concrete and the Bondek profiled steel sheeting was considered negligible. The maximum horizontal slip recorded was 0.53 mm for either panel, which was minimal. (v) The type of shear connectors has minimal effect on the behaviour of the prestressed panels. However, LINDAPTER blind bolts are the preferred method of connection between the bridge stringer steel and the prestressed composite panel. 5.2. Recommendations for further research Further research in the following areas may be considered to enhance the research presented within this paper and reinforce the prestressed panels as a viable solution for the Sydney Harbour bridge project: (i) Further experimental investigation using a higher loading can be done to cause failure in the prestressed panels. (ii) Besides static loads, impact loading need to be considered to
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