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Structural performance of laminated FRP box girder bridge deck compared to slab on prestressed concrete girder bridge
NRCC-53572 Almansour, H.; Cheung, M.S.
July 2010
A version of this document is published in / Une version de ce document se trouve dans:
The 8th Canada Japan Joint Workshop on Composites, Montreal, Canada, July 26-29, 2010, pp. 1-32
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Structural Performance of Laminated FRP Box Girder Bridge Deck Compared to Slab on Prestressed Concrete Girder Bridge Dr. Husham Almansour Research Officer, Institute for Research in Construction, National Research Council Canada, 1200 Montreal Road, Building M-20, Ottawa, Ontario K1A 0R6, Canada
[email protected] Dr. Moe Cheung Chair Professor and Director, Smart and Sustainable Infrastructure Research Center’ Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China
[email protected]
ABSTRACT A promising advance in the use of advanced composites in civil-structures is the development of a bridge superstructure with all-advanced composite elements. However, one of the critical obstacles to extensive use of advanced composites in construction is the lack of simplified and practical design approaches, specifications or guidelines. In this paper, an iterative performance based multi-scale analysis and design approach for all-advanced composite bridge superstructure is proposed. The bridge superstructure is formed from laminated FRP box girder and chopped FRP top surface layer or “deck slab”. Several laminate designs are examined and the performance of the most efficient material and structural designs of the proposed bridge are compared to a traditional slab on prestressed concrete bridge. The results show that the proposed procedure leads to an efficient use of the materials with higher structural performance and significantly lower superstructure weight. However, further research is needed to investigate manufacturing and construction procedures and long term performance.
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INTRODUCTION Advanced composites shows advantageous properties such as high stiffness and strength to weight ratios, durability, fatigue resistance, etc., which could lead to a significantly wide range of application in civil structures Typical applications of advanced composites (AC) in civil engineering are in strengthening, retrofitting and reinforcing of concrete structures. Advanced composites in such applications are assumed to act as isotropic materials and traditional design approaches of the structures built using traditional construction materials are extended to design AC elements. However, an efficient use of advanced composites that takes into account the anisotropic nature of the material and the need to relate the material micro/macro design to the structural performance of the system is still not sufficiently developed and evaluated. Therefore, one of the obstacles to the extensive use of advanced composites (AC) such as fiber reinforced polymers (FRP) in construction is the lack of simplified and practical design approaches and guidelines. Unlike standard materials, advanced composites are orthotropic or anisotropic, and the structural analysis and design of AC structures requires more complex computations since material properties are coupled with the structural geometry and deformations. For example, while changes in the geometry of AC structures is related to changes in the material stiffness, changes in the material constituents could not lead to obvious changes in the stiffness in a specified direction of the structure. In addition, shear deformations in pultruded FRP composite materials are usually significant and, therefore, modeling of FRP structural components should account for various shear effects. For the applications of AC in bridge superstructures, there is a need to develop a simplified design procedure, which should provide accurate predictions of the bridge behavior and be easily implemented by practicing engineers. In the design of AC structural members, stiffness and strength properties are equally important and depend on the coupled material and geometry of the AC structural system [Mosallam and Bank 1992]. Davalos et al. [1996] presented a comprehensive approach for the analysis and design of pultruded FRP beams in bending. The research was based on Barbero’s [1991] proof that the material architecture of pultruded FRP shapes can be efficiently modeled as a layered system. Salim et al. [1997] presented a comprehensive study on the analysis and design of FRP deck-and-stringer bridge deck. Qiao and Davalos [2000] presented a systematic approach for the analysis and design of all-FRP-deck-stringer bridges. Aref and Parsons [2000] presented an integral FRP bridge structural system. The bridge was manufactured using the filament winding process. Burgueno et al. [2001] tested, at large scale, a system comprised of concrete filled, filament wound, circular carbon/epoxy girders and an Eglass/polyester deck. The development of optimization design procedures has emerged as an essential component primarily to overcome the challenge of high initial construction costs associated with the fiber reinforced polymer (FRP) bridge deck systems. He and Aref [2003] presented a genetic algorithm-based optimization procedure to minimize the weight of FRP web core sandwich bridge deck systems. 2
The objective of this paper is to propose a performance based multi-scale analysis and a design approach for all-advanced composite (AAC) bridge superstructures. The procedure would lead to an efficient use of the materials with highest structural performance. PERFORMANCE BASED ANALYSIS – DESIGN PROCEDURE An iterative analysis and design procedure is proposed in this paper. The procedure includes three phases. In the first phase, a micro design is performed for each independent AC material then a macro level design of the lamina is performed. The second phase includes a macro design of the laminate and then design of the laminated box girder and the top chopped layer. Two checks are following the first two phases, which consist of the material failure criterions and the serviceability and ultimate limit states for the bridge super structure.
Figure 1. Multi scale analysis and design procedure 3
The third phase includes the numerical simulation of the AAC bridge superstructure and verification of the structural performance under static and dynamic loading conditions. Figure 1 shows the proposed procedure. SUPERSTRUCTURE AND DESIGN LOADS The case of an all-advanced-composite bridge formed from laminated FRP box girder and chopped FRP top surface plate is considered in this paper (Figure 2). The bridge deck section consists of a series of inner FRP box cells surrounded by an outer FRP binding box. A filament winding process is to be used in manufacturing this deck section. This would deliver a high-speed and accurate lay-up of fiber reinforcement around a mandrel. In this process the fiber winding angles are machine controlled to form the required stacking sequence specified by the design. Effective transfer of shear through the deck components is achieved by providing large contact areas approaching the full contact between the inner cells and the outer box in addition to the full contact between the top surface of the binding box and the deck top chopped FRP plate or “deck slab”. In addition to its ability to distribute the concentrated load, the chopped FRP plate smoothes stresses when they are transferred to the laminated box girder to minimize punching failure occurrence, local buckling or delamination. The boundary dimensions of the deck section are variable and are defined by the traffic volume and the structural behavior of the bridge. The internal proportions and thicknesses of the section are complex functions of the material properties and the structural analysis. In contrast with the relatively simple stage of selecting a traditional material from a welldefined list, more complicated micro-macro material design process is needed for advanced composite materials. Optimizing the stiffness and strength of the laminated box girder is a complex multi-task process that consists in: (i) specifying laminate structure and thickness; (ii) detailing box-girder cell shape dimensions and then number of cells; (iii) evaluating level of stress concentration at cell corners; and (iv) assessing the interaction between inner cells and outer binding box. The laminated cells, outer box dimensions, laminates thicknesses and lay-up are complex variables all contributing to the stiffness of the overall bridge section. The thickness of the “deck slab” or the top surface plate is designed to withstand thepunching stresses caused by vehicle wheel loads based on the chopped FRP material properties. In AC structures, the geometry of the structural section is coupled with the material properties to account for material anisotropy. More advanced (complicated) failure criteria are required to examine the state of stresses in AC structure and hence, optimize the laminate thickness and constitution (number of laminas and their properties). The Tsai-Hill criterion [Jones 1999] for anisotropic materials is used to check the first ply failure.
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Figure 2. Deck Section of the simply supported advanced composite bridge superstructure sections The bridge has two lanes of 3.75 m each, two shoulders of 2.5 m each (including the barrier wall), and the design traffic speed is 100 km/hr. The traffic load model of the Canadian Highway Bridge Design Code CHBDC [CSA S06-2006] is used. For short span bridges, the truck load rather than the lane loading leads to maximum stresses in the bridge superstructure. Figure 3 shows CL-625-ONT truck and lane loading.
Figure 3. CL-625-ONT truck loads, lane loads and design truck dimensions Two extreme truckload settings are considered: (i) for both opposite traffic directions, the bridge mid-span in the longitudinal direction is at the mid-distance between the truck center of gravity and the closest axel (Figure 4-a); and (ii) in one traffic direction, the second axel of a design truck just passes over one of the bridge support lines (axel 1 is 5
out of the bridge, axels 2, 3, 4 and 5 are on the bridge), while axel 4 of a second design truck is just passing on the same bridge support line (axel 5 is out of the bridge, axels 1, 2, 3 and 4 are on the bridge) in the second traffic direction (Figure 4-b). SUPERSTRUCTURE AND DESIGN LOADS Homogenized materials properties of chopped FRP of the “deck slab” are: (i) modulus of elasticity is 9.32 GPa; (ii) Poisson ratio is 0.276; and (iii) ultimate strength is 139 MPa. The lamina is formed from E-Glass fiber and Vinylester Matrix (GFVM) with material properties shown in Table 1. Table 1. Mechanical properties of the lamina - E-Glass fiber and Vinylester Matrix (GFVM) Longitudinal modulus of elasticity, E1 Transverse modulus of elasticity, E2 In-plane Poisson ratio, υ12 In-plane shear modulus Longitudinal tensile strength Longitudinal compressive strength Transverse tensile strength Transverse compressive strength In-plane shear strength
36.61 GPa 12.83 GPa 0.279 4.013 GPa 1020 MPa 620 MPa 40 MPa 140 MPa 70 MPa
CG Bridge mid‐span CG
Figure 4-a. AC bridge with first extreme CL-625-ONT truck loading
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Bridge support line
Figure 4-b. Advanced composite bridge with second extreme CL-625-ONT truck loading
Lamina
Table 2. Different designs of internal and external laminates Lamina Alignment LAa(1) LAb LAc LAd LAe LAf Deg Deg Deg Deg Deg Deg
LAg Deg
IL(2), OL(3) IL & OL IL & OL IL & OL IL & OL IL & OL IL & OL 1 -10, -10 10 30 45 10 10 10 2 30, 45 -10 -30 -45 30 45 30 3 10, 10 -10 -30 -45 -10 -10 45 4 -30, -45 10 30 45 -30 -45 -10 5 10, 10 -30 -45 -30 6 45, 90 -10 -10 -45 7 45, 90 30 45 -45 8 10, 10 10 10 -30 9 -30,-45 -10 10 10, 10 45 11 30, 45 30 12 -10, -10 10 (4) LTh -a 1.5 4.5 4.5 4.5 2.5 2.5 1.5 LTh-b 2.25 6.75 6.75 6.75 3.37 3.37 2.25 LTh-c 3.0 9.0 9.0 9.0 4.5 4.5 3.0 (1) LA: Laminate Alignment (Deg); (2) IL: Inner Laminate Box; (3) OL: Outer Binding Laminate Box; (4) LTh: Laminate Thickness (mm). Mid surface symmetry plane. Efficient laminate macro design is investigated by examining seven different designs with 4, 8 and 12 laminas, either for the inner boxe or for the outer binding box laminates. Laminate thicknesses for inner and outer boxes are the same for all the studied designs. The lamina thickness is assumed to be constant in every design. Three different laminate 7
thicknesses of 18 mm, m27 mm and 36 mm (same unit as in Table 2) are studied (this is not what I see in Table 2 - ref LTh-a, Lth-b and LTh-c). All the studied laminate designs are shown in Table 2. For all Laminate Alignments (LA), except LAa, the orientation is symmetrical on either side of the laminate mid-surface, and every orientation has its skew-symmetric couple (e.g. +10° and –10°). In laminate designs LAb, LAc and LAd, a single lamina-orientation of ±10° or ±30° or ±45°, respectively, is used. In laminate designs LAe and LAf, two lamina-orientations of ±10° and ±30° or ±10° and ±45°, respectively, are used. In laminate design LAg, three lamina-orientations of ±10° and ±30° and ±45° are used. (it would have been nice to show a schematic of a laminated material with lamina, material orientation and laminate mid-surface symmetry concepts. It would make it easier to follow for non-initiated people), STRUCTURE MODELING AND RESULTS The proposed AAC bridge is modeled using nonlinear anisotropic finite element model. The finite element mesh is refined in the regions where the applied wheel loads result in high stress concentration. Figure 5 shows the mesh for the bridge superstructure. The first flexural natural frequency of the bridge for all cases is ranged between 1.45 Hz to 1.7 Hz. According to CHBDC, this leads to an acceptable static deflection between 0.08 m and 0.11 m. Maximum deflection of the bridge for all laminate design cases are within the acceptable range. The distribution of deformations over the bridge is unsymmetrical; however, it is observed that the divergence from symmetry becomes negligible with LAg and LAa. Figures 6 shows the effect of laminate thickness on the maximum deflection of the bridge deck. Figure 7 shows the effect of laminate thickness on the first vertical natural frequency for different laminate designs. Figure 8 shows the maximum Tsai-Hill Failure Function (THFF) for different laminate thicknesses.
Figure 5. Finite element mesh for the advanced composite bridge
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Comparing the results of single-orientation-angle laminate arrangements (i.e. LAb, LAc, and LAd), it is observed that LAb (±10°) gives minimum lateral displacement and reasonably low deflection, LAc (±30°) gives minimum longitudinal displacement, and LAd (±45°) gives minimum deflection, minimum Tsai Hill Failure Function and the highest flexural natural frequency. For the double-angle-orientation laminate designs resulting from combining ±10° with either ±30° or ±45° (i.e. LAe, and LAf, respectively), it is found that LAe gives lower lateral displacement for all thicknesses, and lower longitudinal displacement only with medium laminate thickness. LAf gives lower deflection, lower Tsai-Hill Failure Function, lower longitudinal displacement for low or high thickness, and higher vertical natural frequencies. On the other hand, the triple-angle-orientation laminate design LAg gives medium deformations, medium flexural natural frequency and high Tsai-Hill Failure Function. After testing many modifications to LAg a more efficient laminate design is developed, LAa, which gives very low lateral displacement, the lowest deflection, the lowest longitudinal displacement, the highest vertical natural frequencies and the second lowest Tsai-Hill Failure Function. Hence, this design is the best among all designs presented in Table 2 from the structural performance point of view. The modifications to LAg that leads to LAa are: (i) giving a priority to one orientation which has the lowest inclination with respect to the bridge direction (i.e. ±10°); (ii) separating the laminas orientations of the inner from the outer laminate by using low to medium orientation angles for the inner laminate (30°, and 45°), and medium to high orientation angles for the outer laminate ( 45°, 90°), in addition to the (10°); (iii) breaking the skew-symmetric rule but keeping the symmetry of the laminas on the mid-surface of the laminates. In LAa, some orientations are switched with each other, keeping the original number of orientations constant, which is 12.
Figure 6. Maximum deflection of the deck top surface of the bridge versus the laminate thickness, under dead loads and traffic loads 9
Figure 7. First vertical flexural natural frequencies versus laminate thickness of the bridge The increase of the laminate thickness results in decreasing the resultant displacement field, increasing natural frequencies and decreasing the Tsai-Hill Failure Function. The rate of decrease of the deflection and Tsai-Hill Failure Function, and the rate of increase of the natural frequencies diminish with further increase of the laminate thickness. STRUCTURAL PERFORMANCE COMPARED TO PRECAST-PRESTRESSED CONCRETE BRIDGE The deflection of the proposed all AC bridge is comparable to the long term deflection of a typical slab on prestressed concrete bridges. The slab on prestressed concrete girder bridge, shown in Figure 9, is designed for the same loading. Its slab thickness is 0.25 m and its concrete compressive strength is ( f c' = 30 MPa). The five prestressed concrete girders of this bridge are standard CPCI-1400 girders with concrete compression strength of ( f c' = 40 MPa). Each girder has a prestressing reinforcement of twenty-eight strands (low relaxation, size designation 13, grade 1860 and diameter 12.7 mm). Eighteen of them are straight and lie at the bottom of the girder. The remaining ten strands are linearly varied from 0.85 m (average height from the girder bottom surface) at both girder ends to 0.15 m over one third of the girder length from each side; while on the middle third, the strands are straight. The maximum static deflection is calculated to be 15.4 mm and the first flexural natural frequency is 3.81 Hz. The maximum deflection limit for this highway bridge superstructure vibration is 20 mm. The final deflection (including creep, shrinkage, etc) is calculated to be 72 mm.
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Figure 8. Tsai-Hill Failure Function for different laminate thicknesses of the bridge
Figure 9. Section of slab on prestressed concrete
The results of AAC bridge analysis show that its deflection is higher than the short term deflection of the slab on prestressed girder bridge but close to the long term deflection of that same bridge. On the other hand, the AAC gives lower flexural natural frequencies than those of the slab on prestressed concrete girder bridge. CONCLUSIONS In this paper, an iterative performance based multi-scale analysis and design approach for all-advanced composite bridge superstructure is proposed. The bridge superstructure is formed from laminated FRP box girder and chopped FRP top surface plate. Several laminate designs are examined and the performance of the most efficient material and structural design of the proposed bridge is compared to a slab on prestressed concrete girder bridge. The results show that the proposed procedure leads to an efficient use of the materials with the highest structural performance. 11
ACKNOWLEDGMENT The authors wish to acknowledge the financial support of Hong Kong Research Grant Council #611908 for the Performance and Dynamic Characteristics of Composite Long-span Cablestayed Bridges
REFERENCES H.H. Almansour, The performance of hybrid long span cable stayed bridges using advanced composites. Ph.D. Thesis, U of Ottawa, 2006. H.H. Almansour, and M.S. Cheung, Finite element modeling of a CFRP composite deck for long span cable-stayed bridge. Proc JCJC-III, Ueda, Nagano, JAPAN, 2003. A.J. Aref, and I.D. Parsons, Design and performance of a modular fiber reinforced plastic bridge. Composites: Part B, 31, 2000, 619-628. E.J. Barbero, Pultruded structural shapes: from the constituents to the structural behavior. SAMPE J., 27(1), 1991, 25-36. R. Burgueno, V.M, Karbhari, F. Seible, R.T. Kolozes, Experimental dynamic characterization of an FRP composite bridge, superstructure assembly. Composite Structures, 54, 2001, 427 – 444. Canadian Standards Association, Canadian Highway Bridge Design Code. CSA S06-06, 2006. J.F. Davalos, H.A. Salim, P. Qiao, R. Lopez-Anido and E.J. Barbero, Analysis and design of pultruded FRP shapes under bending. Composites: Part B, 27B, 1996, 295-305. Y. He and A.J. Aref, An optimization design procedure for fiber reinforced polymer web-core sandwich bridge deck system. Composite Structures, 60, 2003, 183-195. R.M .Jones, Mechanics of composite materials, Second Edition, Taylor & Francis, 1999. A.S. Mosallam and A.S. Bank, Short-term behavior of pultruded fiber-reinforced plastic frame, J. of Struct. Eng., 118(7), 1992, 1937-1944. P. Qiao, J. F. Davalos and B. Brown, A systematic analysis and design approach for single-span FRP deck/stringer bridges. Composites: Part B 31, 2000, 593 – 609. H.A. Salim, J.F. Davalos, P. Qiao, and S.A. Kiger, Analysis and design of fiber reinforced plastic composite deck-and-stringer bridges, Composite Structures, 38(1), 1997, 295-307. 12
