A systematic analysis and design approach for single-span FRP deck/stringer bridges

There is a concern with worldwide deterioration of highway bridges, particularly reinforced concrete. The advantages of fiber reinforced plastic (FRP) composites over conventional materials motivate their use in highway bridges for rehabilitation and replacement of structures. In this paper, a systematic approach for analysis and design of all FRP deck/stringer bridges is presented. The analyses of structural components cover: (1) constituent materials and ply properties, (2) laminated panel engineering properties, (3) stringer stiffness properties, and (4) apparent stiffnesses for composite cellular decks and their equivalent orthotropic material properties. To verify the accuracy of orthotropic material properties, an actual deck is experimentally tested and analyzed by a finite element model. For design analysis of FRP deck/stringer bridge systems, an approximate series solution for orthotropic plates, including first-order shear deformation, is applied to develop simplified design equations, which account for load distribution factors under various loading cases. An FRP deck fabricated by bonding side-by-side box beams is transversely attached to FRP wide-flange beams and tested as a deck/stringer bridge system. The bridge systems are tested under static loads for various load conditions, and the experimental results are correlated with those by an approximate series solution and a finite element model. The present simplified design analysis procedures can be used to develop new efficient FRP sections and to design FRP highway bridge decks and deck/stringer systems, as shown by an illustrative design example.     

Evaluation of effective flange width by shear lag model for orthotropic FRP bridge decks

In bridge engineering, the three-dimensional behavior of a bridge system is usually reduced to the analysis of a T-beam section with a reduced width of deck in relation to center-to-center spacing of stringers, over which the longitudinal normal stresses are assumed to be uniformly distributed, which is termed as effective flange width. It is defined in the AASHTO specifications primarily for concrete slabs and has inherent applicable limitations because of its empirical nature. This paper provides an analytical shear lag model for effective flange width for orthotropic bridge decks, applicable to various materials including Fiber-Reinforced Polymer (FRP) and concrete decks. To verify this solution, a Finite Element (FE) parametric study is conducted on 44 simply-supported FRP deck-on-steel girder bridges. The results from the shear lag model correlate well with the FE results. The accuracy of this model is further verified by close correlations with an existing empirical solution. It is also illustrated that the shear lag model, with the introduction of a reduction factor, can be applied to predict effective flange width for FRP deck-on-steel girder bridges with partial composite action, by favorable comparisons between the analytical and testing results for a T-beam section cut from a one-third scaled bridge model, which consists of an FRP sandwich deck attached to steel girders by mechanical connectors.     

Quasi-static and fatigue performance of a cellular FRP bridge deck adhesively bonded to steel girders

This paper describes the quasi-static and fatigue performance of hybrid bridge girders composed of cellular FRP bridge decks and steel girders. The FRP bridge deck is connected adhesively to the steel girders and acts as the top chord of the hybrid section. Compared to a reference steel girder, the stiffness and quasi-static load-carrying capacity of the hybrid girders were considerably increased due to composite action between the FRP decks and the steel girders. Failure due to quasi-static loading occurred in the FRP decks during yielding of the bottom steel flanges. The adhesive bond between the FRP decks and the steel girders showed no signs of damage due to fatigue loading. The results of the investigation showed that the well-established design method for steel–concrete composite girders with shear stud connections can essentially be used for the design of such FRP-steel girders. The principal modifications necessary for design are proposed.     

Flexural behavior of prestressed FRP tubular bridge deck

An experimental and analytical study was undertaken to assess the flexural behavior of a new fiber reinforced polymer (FRP) deck system. The deck consists of a series of pultruted FRP tubes, post-tensioned in between each two stringers. Seven pure compression tests and eleven flexural tests were carried out to investigate the effect of tube size, bonding condition, post-tensioning, and supporting conditions. Finite element modeling of compression and flexural specimens was carried out to determine the effect of tube interface friction, bond and geometry restraints. The study showed feasibility of the new deck system for bridges with closely spaced stringers, where lack of two-way panel action is not a primary concern. Failure modes were also identified for these types of deck systems. Longer span decks generally failed in bending, whereas shorter span decks suffered from local shear failure at the corner of the tubes. Prestressing provided redundancy and reserved strength to the deck system.     

Load and resistance factor design of fiber reinforced polymer composite bridge deck

The majority of our bridges were constructed with conventional civil engineering materials of steel and concrete in a typical slab on girder or truss construction. Reinforced concrete bridge decks have approximately 40% life of the steel girders that support these structures. In order to support the use of alternative materials to replace deteriorating concrete decks, this paper outlines the Load and Resistance Factor Design (LRFD) of Fiber Reinforced Polymer composite (FRP) panel highway bridge deck. The deck would be of a sandwich construction where 152.4 mm × 152.4 mm × 9.5 mm square pultruded glass FRP (GFRP) tubes are joined and sandwiched between two 9.5 mm GFRP plates. The deck would be designed by Allowable Stress Design (ASD) and LRFD to support AASHTO design truckload HL-93. There are currently no US standards and specifications for the design of FRP pultruded shapes including a deck panel therefore international codes and references related to FRP profiles will be examined and AASHTO-LRFD specifications will be used as the basis for the final design. Overall, years of research and laboratory and field tests have proven FRP decks to be a viable alternative to conventional concrete deck. Therefore, conceptualizing the design of FRP bridge decks using basic structural analysis and mechanics would increase awareness and engineering confidence in the use of this innovative material.     

Modeling and characterization of fiber-reinforced plastic honeycomb sandwich panels for highway bridge applications

Fiber-reinforced plastic (FRP) composite decks have been increasingly used in highway bridge applications, both in new construction and rehabilitation and replacement of existing bridge decks. Recent applications have demonstrated that FRP honeycomb panels can be effectively and economically used for highway bridge deck systems. This paper is concerned with design modeling and experimental characterization of a FRP honeycomb panel with sinusoidal core geometry in the plane and extending vertically between face laminates. The analyses of the honeycomb structure and components include: (1) constituent materials and ply properties, (2) face laminates and core wall engineering properties, (3) equivalent core material properties, and (4) apparent stiffness properties for the honeycomb panel and its equivalent orthotropic material properties. A homogenization process is used to obtain the equivalent core material properties for the honeycomb geometry with sinusoidal waves. To verify the accuracy of the analytical solution, several honeycomb sandwich beams with sinusoidal core waves either in the longitudinal or transverse directions are tested in bending. Also, a deck panel is tested under both symmetric and asymmetric patch loading. Finite element (FE) models of the test samples using layered shell elements are further used to correlate results with analytical predictions and experimental values. A brief summary is given of the present and future use of the FRP honeycomb panel for bridge decks. The present simplified analysis procedure can be used in design applications and optimization of efficient honeycomb structures.     

平行双箱梁桥面颤振稳定性试验研究

在建的佛山平胜大桥和设计中的青岛海湾桥红岛航道桥方案分别是具有平行双箱梁的独塔自锚式悬索桥和独塔斜拉桥，对两座桥梁的单、双桥面弹性悬挂节段模型风洞试验结果表明双桥面之间存在不可忽略的气动干扰效应，从而使桥梁在单、双桥面状态时的颤振临界风速不同。以平胜桥主梁节段模型为基础的一系列风洞试验研究表明，平行双箱梁桥面主梁的颤振临界风速与两桥面之间的距离有关系，双桥面的颤振临界风速随两桥面之间距离D值的增大而增加。与单桥面状态相比较，平行双箱梁桥面的颤振导数也有相应的变化，且这种变化和两桥面之间的距离D也有关系。     

Experimental and Numerical Investigations on Multicellular GFRP Bridge Deck Panels

The maintenance, upgrading and replacement of existing bridges have become urgent requirement and a challenging task for the construction sector. Bridge decks made of fibre reinforced polymers (FRP), have been widely adopted both in new construction and replacement of existing bridge decks. This paper reports the studies carried out hand lay-up multicellular glass fibre reinforced polymer. Multicellular bridge deck panels with various cross sectional profiles have been analysed using a general purpose finite element software ANSYS. A cross sectional profile that satisfied the deflection criteria with minimum weight was selected for analysis and fabrication. Six multicellular GFRP composite bridge deck panel of size 1250mm × 333mm × 150mm (l×b×d) were fabricated by hand lay-up process using various materials. The responses have been compared with analytical and numerical solutions and found to be they are in good agreement with each other.     

Structural performance of composite sandwich bridge decks with hybrid GFRP–steel core

This paper presents the static and fatigue performance of composite sandwich bridge decks with hybrid GFRP–steel core. The composite sandwich bridge deck system is comprised of wrapped hybrid core of GFRP grid and multiple steel box cells with upper and lower GFRP facings. Its structural performance under static loading and fatigue loading with a nominal frequency of 5 Hz was evaluated. The responses from laboratory testing were compared with the ANSYS finite element predictions. The failure mode of the proposed composite sandwich bridge deck was more favourable because of the yielding of the steel tube when compared with that of all-GFRP decks. The ultimate failure of the composite sandwich deck panels occurs by shear of the bonded joints between GFRP facings and steel box cells. Results from fatigue load test indicated no loss in stiffness, no signs of de-bonding and no visible signs of deterioration up to 2 million load cycles. The thickness of the composite sandwich deck retaining the similar stiffness may be decreased to some extent when compared with the all-GFRP deck. This paper also presents design of a connection between composite sandwich deck and steel girder.     

Load response due to local and global indeterminacies of FRP-deck bridges

In a cellular FRP deck-on-beam bridge, the deck’s load response is influenced by the cellular frame’s local indeterminacy and by the global indeterminacy due to multiple beams at each support. Thus, the stiffness distributions for both levels of indeterminacy are important. This paper reports concentrated load tests and FE analyses (FEA) of an 8 m long bridge comprising cellular FRP decking bonded to and spanning across three pretensioned concrete beams. Another specimen comprising a rigidly supported, narrow width of decking where only local strains developed under load and which enabled strain measurements near the loads on external and internal surfaces of the deck, is also presented. Loads were applied via steel plates and elastomeric pads. Pressure-sensitive films enabled deduction of pad-to-deck contact zones. The FEA used contact elements at pad–deck interfaces, solid elements for the deck and beams, and included deck material and geometry anisotropies. The bridge’s test data show a 25% asymmetry of the deck’s local longitudinal strains and rapid transverse attenuation of these strains away from the loads. The FE results – including the strain asymmetry when FRP moduli are locally altered – are comparable to the experimental data. This suggests that FEA can reliably represent indeterminacy effects for these complex structures.     

铁路正交异性桥面加劲肋-横隔板局部疲劳受力特性研究

正交异性钢桥面因整体性好、承载力强等优势在铁路大跨度桁梁及箱梁斜拉桥、拱桥等桥型中应用越来越广泛,其疲劳特性与公路桥面具有显著的差异。针对铁路正交异性钢桥面加劲肋与横隔板连接处的疲劳敏感区,通过弹性支撑梁理论及闭口薄壁杆件理论分析其局部受力特征,提出了加劲肋疲劳敏感部位面内疲劳应力的解析公式,分析了解析公式中各疲劳影响因素的影响程度及作用机理。基于甬江特大桥——大跨度铁路斜拉桥的钢箱梁正交异性桥面设计了包含2个U肋及2个V肋的正交异性桥面疲劳试验模型,并进行了560万次疲劳加载。研究结果表明:解析公式与有限元分析、试验测试结果相符良好;试验模型测试结果能准确反映疲劳敏感点的应力情况,解析理论则能够反映疲劳敏感点应力的影响因素与规律;在铁路荷载下,加劲肋与横隔板的焊缝长度和加劲肋腹板倾角的增大能够有效降低加劲肋的疲劳应力幅;在铁路正交异性钢桥面板中面积相近、抗弯刚度相等的V肋比U肋具有更好的抗疲劳工作性能。     

Flexural fatigue analysis of a CFRP form reinforced concrete bridge deck

Concrete bridge decks reinforced with fiber reinforced polymer (FRP) composite panels have recently been used where the FRP panels also serve as the permanent formwork for concrete. Comparing to their short-term behavior, their long-term performance especially under repeated traffic loads (fatigue) has not yet been widely known. This paper presents a fatigue analysis tool developed for a new steel-free concrete bridge deck reinforced with carbon FRP stay-in-place form. The developed model takes into account the cyclic creep of concrete in compression, the reduction in flexural stiffness due to fatigue tensile cracking and the reduction in modulus of rupture under cyclic loading. Comparisons with experimental data show reasonable agreement where a full-size 2-span deck specimen was subjected to millions of fatigue cycles. The parametric study recommends reducing the amount of FRP reinforcement and concrete strength of the current design, and lower loading rate may introduce more stiffness degradation in the system.     

Field performance of an FRP slab bridge

Fiber reinforced polymer (FRP) composite decks are new to bridge applications and hence not much literature exists on their in-service performance. The in-service performance, and impact and dynamic characteristics of the first fiber reinforced polymer composite bridge superstructure built in New York State in late 1998 are documented in this paper. Test data indicate that the superstructure and the shear-key are structurally performing well. The average impact factor was about 0.3. Observed low strains and deflections, compared to those predicted at the design stages, show room for optimization of the deck design to make these more cost-effective in the future. Higher modal damping values were observed and reflect the vibration absorbing capacity of FRPs. Several delaminations were found during visual inspections and the wearing surface was replaced once. For future applicability of FRPs for bridge deck applications, these issues affecting the long-term durability should be resolved.     

Durability simulation of FRP bridge decks subject to weathering

Fiber Reinforced Polymer (FRP) composite panels are particularly attractive as bridge decks due to their high strength, low density, and durability, which are of importance in the bridge industry. Although the short term performance of FRP decks is satisfactory, the long-term performance under weather conditions still awaits future testimony and remains a major concern in their use as primary load bearing members. Since the load capacity and structural stiffness of FRP decks deteriorate over time at different rates, it is necessary to develop robust mechanics models to simulate the long-term performance of FRP deck structures subject to the combined effects of mechanical and environmental loading. To this end, a comprehensive mechanics framework has been developed, taking into account the critical deterioration rates of the FRP constituents. Such deterioration relationships were obtained by calibrating the accelerated laboratory durability test data with the in-service field measurements. Simulation results agree well with the 4-year performance data of a FRP-deck road bridge. Long-term validation data is, however, still needed.     

分离式公铁双层桥面相互气动干扰及对列车走行性的影响

横向风作用下公铁两用双层桥的上、下桥面间存在相互的气动干扰,为研究公铁两用组合桥间隔高度对列车走行性的影响,针对某分离式公铁两用混凝土箱梁桥,采用计算流体动力学（CFD）数值模拟和风-车-桥耦合振动研究的方法,分析了上、下桥面间隔高度对列车气动特性和车辆动力响应的影响。分析结果表明,公铁两用组合桥间隔高度对列车的气动特性和动力响应影响显著,间隔高度减小,列车升力系数和竖向加速度显著增大,轮重减载率也随之增大。公铁两用组合桥的设计应考虑间隔高度对列车的影响,以选择合理的间隔高度。     

Fibre composite bridge decks — an alternative approach

This paper presents initial results of a study into the structural behaviour of a new type of fibre composite bridge deck. The deck, which uses a particulate filled resin core can be produced for costs similar to steel and concrete decks. The manufacturing method is suitable for both small and large-scale production runs and does not require large up front investments. Aspects of the design and method of manufacture are presented together with test results for two different size decks.     

斜拉桥中索-桥耦合非线性振动的理论研究

考虑拉索的垂度、大位移引起的几何非线性及空气动力对系统的影响,将桥面简化为等截面的连续梁,建立了索-桥耦合的非线性振动模型。得到了对不同拉索数值求解的结果,表明当桥面和拉索的振动频率比值在1:1和2:1附近的小区间范围内时,索-桥耦合系统将产生严重的内共振,并呈现拍振的特征,而拉索与桥面耦合的振动特性与索的振动频率、垂度、倾角、风速偏航角、风速大小和阻尼等因素有关,从而为桥梁的设计和计算提供了理论依据。     

曲线梁桥地震响应的简化分析方法

曲线梁桥的平面不规则性引起的弯扭耦合效应,导致了地震响应的复杂性。对弹性支座上的刚性桥面系统建立了具有刚度偏心的简单曲线梁桥模型,给出了自振特性和地震响应的简化计算方法。通过数值模拟比较,系统地分析了各种影响因素及其对曲线梁桥动力响应的影响规律和计算图表,可以在抗震初步设计中参考使用。     

Load Testing of an FRP Bridge Deck on a Truss Bridge

New York State has constructed a fiber reinforced polymer (FRP) bridge deck as an experimental project. The goal of the project was to improve the load rating of a 50-yr old truss bridge located in Wellsburg, New York. The FRP deck weighs approximately 80-percent less than the deteriorated concrete bridge deck it replaced. Reducing the dead load increased the allowable live load capacity of the bridge without significant repair work to the existing superstructure, thus lengthening its service life. Load testing was conducted after installation of the FRP deck to study the conservativeness of the design, ascertain the assumptions made on composite action between the deck and the superstructure, and examine the effectiveness of joints in load transfer. This report describes the testing and discusses the results. The results indicate that the design was conservative. The design assumed no composite action between the deck and the superstructure, and the experimental data confirms that assumption. The study also shows that the joints are only partially-effective in load transfer between panels. Peak strains under the test loads were only a very small fraction of the ultimate strength of the FRP deck.     

A Simplified Nonlinear Model of Vertical Vortex-Induced Force on Box Decks for Predicting Stable Amplitudes of Vortex-Induced Vibrations

Wind-tunnel tests of a large-scale sectional model with synchronous measurements of force and vibration responses were carried out to investigate the nonlinear behaviors of vertical vortex-induced forces (VIFs) on three typical box decks (i.e., fully closed box, centrally slotted box, and semi-closed box). The mechanisms of the onset, development, and self-limiting phenomenon of the vertical vortex-induced vibration (VIV) were also explored by analyzing the energy evolution of different vertical VIF components and their contributions to the vertical VIV responses. The results show that the nonlinear components of the vertical VIF often differ from deck to deck; the most important components of the vertical VIF, governing the stable amplitudes of the vertical VIV responses, are the linear and cubic components of velocity contained in the self-excited aerodynamic damping forces. The former provides a constant negative damping ratio to the vibration system and is thus the essential power driving the development of the VIV amplitude, while the latter provides a positive damping ratio proportional to the square of the vibration velocity and is actually the inherent factor making the VIV amplitude self-limiting. On these bases, a universal simplified nonlinear mathematical model of the vertical VIF on box decks of bridges is presented and verified in this paper; it can be used to predict the stable amplitudes of the vertical VIV of long-span bridges with satisfactory accuracy.