Evaluation of Composite Sandwich Bridge Decks with Hybrid FRP-Steel Core

A hybrid concept of composite sandwich panel with hybrid fiber-reinforced polymer (FRP)—steel core was proposed for bridge decks in order to not only improve stiffness and buckling response but also be cost efficient compared to all glass fiber-reinforced polymer (GFRP) decks. 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 was evaluated and compared with the ANSYS finite element predictions. It was found that the presented composite sandwich panel with hybrid FRP-steel core was very efficient for use in bridges. The thickness of the hybrid deck may be decreased by 19% when compared with the all GFRP deck. The failure mode of the proposed hybrid deck was more favorable because of the yielding of the steel tube when compared with that of all GFRP decks.     

Dynamic Response of Three Fiber Reinforced Polymer Composite Bridges

Fiber reinforced polymer (FRP) composite bridge decks are gaining the attention of bridge owners because of their light self-weight, corrosion resistance, and ease of installation. Constructed Facilities Center at West Virginia University working with the Federal Highway Administration and West Virginia Department of Transportation has developed three different FRP decking systems and installed several FRP deck bridges in West Virginia. These FRP bridge decks are lighter in weight than comparable concrete systems and therefore their dynamic performance is equally as important as their static performance. In the current study dynamic tests were performed on three FRP deck bridges, namely, Katy Truss Bridge, Market Street Bridge, and Laurel Lick Bridge, in the state of West Virginia. The dynamic response parameters evaluated for the three bridges include dynamic load allowance (DLA) factors, natural frequencies, damping ratios, and deck accelerations caused by moving test trucks. It was found that the DLA factors for Katy Truss and Market Street bridges are within the AASHTO 1998 LRFD specifications, but the deck accelerations were found to be high for both these bridges. DLA factors for Laurel Lick bridge were found to be as high as 93% against the typical design value of 33%; however absolute deck stress induced by vehicle loads is less than 10% of the deck ultimate stress.     

Design Recommendations for a FRP Bridge Deck Supported on Steel Superstructure

No appropriate provisions from either AASHTO Standard (2002) or AASHTO LRFD (2004) bridge design specifications are available for the design of fiber-reinforced polymer (FRP)-deck-on-steel-superstructure bridges. In this research, a parametric study using the finite-element method (FEM) is conducted to examine two design issues concerning the design of FRP-deck-on-steel-superstructure bridges, namely deck relative deflection and load distribution factor (LDF). Results show that the strip method specified in AASHTO LRFD specification as an approximate method of analysis, can also be applied to FRP decks as a practical method. However, different strip width equations have to be determined by either FEM or experimental methods for different types of FRP decks. In this study, one such equation has been derived for the Strongwell deck. In addition, both FEM results and experimental measurements show that the AASHTO LDF equations for glued laminated timber decks on steel stringers provide good estimations of LDF for FRP-deck-on-steel-superstructure bridges. Finally, it is found that the lever rule can be used as an appropriately conservative design method to predict the LDF of FRP-deck-on-steel-superstructure bridges.     

Performance Comparison of Four Fiber-Reinforced Polymer Deck Panels

In an effort to assess the constructability and performance of bridges with fiber-reinforced polymer (FRP) composite decks, the short-term and long-term responses of a 207 m, five-span bridge retrofitted with four different FRP panel systems were monitored. The overall aspects of the panel systems, connection details, and construction techniques are presented prior to presentation of the observed and measured responses. Key design parameters (impact factors, girder distribution factors, and level of composite action) for FRP and reinforced concrete decks are evaluated. This paper demonstrates that FRP replacement decks are a viable alternative to reinforced concrete decks and identifies the differences in performances of various FRP deck systems. Two of the FRP panel systems were found to perform considerably better than the other deck systems. Issues that may reduce the service life of FRP deck systems are presented and discussed.     

Close Look at Construction Issues and Performance of Four Fiber-Reinforced Polymer Composite Bridge Decks

Four different fiber-reinforced polymer (FRP) panel systems were installed in a 207 m, five-span, three-lane bridge in an effort to assess the constructability, performance, and applicability of bridges with fiber-reinforced polymer composite decks. This paper examines whether four common deck systems are able to realize many of the anticipated benefits of using FRP composites in lieu of conventional reinforced concrete bridge decks. Particular installation issues, connection details, and specific construction techniques for each deck system are described, along with a discussion of the shortcomings in terms of handling, performance, and serviceability. Other factors such as key design parameters (e.g., impact factor and thermal characteristics) and unexpected responses are used to further quantify the performance of four FRP representative deck systems under identical traffic and environmental constraints.     

Designing and Testing of Concrete Bridge Decks Reinforced with Glass FRP Bars

In addition to their high strength and light weight, fiber-reinforced polymer (FRP) composite reinforcing bars offer corrosion resistance, making them a promising alternative to traditional steel reinforcing bars in concrete bridge decks. FRP reinforcement has been used in several bridge decks recently constructed in North America. The Morristown Bridge, which is located in Vermont, United States, is a single span steel girder bridge with integral abutments spanning 43.90 m. The deck is a 230 mm thick concrete continuous slab over girders spaced at 2.36 m. The entire concrete deck slab was reinforced with glass FRP (GFRP) bars in two identical layers at the top and the bottom. The bridge is well instrumented at critical locations for internal temperature and strain data collection with fiber-optic sensors. The bridge was tested for service performance using standard truck loads. The construction procedure and field test results under actual service conditions revealed that GFRP rebar provides very good and promising performance.     

Service Load Effective Compression Flange Width in Fiber Reinforced Polymer Deck Systems Acting Compositely with Steel Stringers

This paper reports on the field study of a steel stringer-fiber reinforced polymer (FRP) deck composite bridge in Pennsylvania. The objective of the study is to assess the effective compression flange width in the FRP deck and floor systems when they act compositely with underlying steel girders at service conditions. The research results reported herein support the notion of employing a design approach, for both interior and exterior girders of a composite floor system, that is philosophically consistent with current practice related to steel girders acting compositely with concrete decking. It appears from the results presented herein that FRP decks and floors acting compositely with underlying steel girders exhibit an effective width that is close to the actual girder spacing for interior beams, and approximately one-half this value for exterior beams.     

Laboratory and Field Performance of Cellular Fiber-Reinforced Polymer Composite Bridge Deck Systems

This paper addresses the laboratory and field performance of multicellular fiber-reinforced polymer (FRP) composite bridge deck systems produced from adhesively bonded pultrusions. Two methods of deck contact loading were examined: a steel patch dimensioned according to the AASHTO Bridge Design Specifications, and a simulated tire patch constructed from an actual truck tire reinforced with silicon rubber. Under these conditions, deck stiffness, strength, and failure characteristics of the cellular FRP decks were examined. The simulated tire loading was shown to develop greater global deflections given the same static load. The failure mode is localized and dominated by transverse bending failure of the composites under the simulated tire loading as opposed to punching shear for the AASHTO recommended patch load. A field testing facility was designed and constructed in which FRP decks were installed, tested, and monitored to study the decks’ in-service field performance. No significant loss of deck capacity was observed after more than one year of field service. However, it was shown that unsupported edges (or free edges) are undesirable due to transitional stiffness from approach to the unsupported deck edge.     

Light-Weight Fiber-Reinforced Polymer Composite Deck Panels for Extreme Applications

Currently within the military there is a need for a universal light-weight bridge deck system capable of supporting extreme loads over a wide temperature range. This research presents the development, testing, and analysis of five different fiber-reinforced polymer (FRP) webbed core deck panels. The performance of the FRP webbed decks are compared with an existing aluminum deck and with a baseline balsa core system, which has previously been tested as part of the development of the composite army bridge for the US Army. The study shows that for one-way bending, the FRP webbed core can exceed the shear strength of the baseline balsa core by a factor of 3.2 at a core’s density, which is 28% lighter than the balsa baseline. In addition, weight savings in excess of 30% are shown for using FRP decking in place of conventional aluminum decking. Based on test results and finite-element analysis, the failure modes of the different FRP webbed cores are discussed and design recommendations for FRP webbed core decks are provided.     

Vehicle-Induced Dynamic Performance of FRP versus Concrete Slab Bridge

In the United States alone, about 30% of the bridges are classified as structurally deficient or functionally obsolete. To alleviate this problem, a great deal of work is being conducted to develop versatile, fully composite bridge systems using fiber-reinforced polymers (FRPs). To reduce the self-weight and also achieve the necessary stiffness, FRP bridge decks often employ hollow sandwich configurations, which may make the dynamic characteristics of FRP bridges significantly different from those of conventional concrete and steel bridges. Due to the geometric complexity of the FRP sandwich panels, dynamic analyses of FRP bridges are very overwhelming and rarely reported. The present study develops an analysis procedure for the vehicle-bridge interaction based on a three-dimensional vehicle-bridge coupled model. The vehicle is idealized as a combination of rigid bodies connected by a series of springs and dampers. A slab FRP bridge, the No-Name Creek Bridge in Kansas, is first modeled using the finite-element method to predict its modal characteristics, then the bridge and vehicle systems are integrated into a vehicle-bridge system based on the deformation compatibility. The bridge response is obtained in the time domain by using an iterative procedure employed at each time step, considering the deck surface roughness as a vertical excitation to the vehicle. The bridge dynamic response and the calculated impact factors are compared between the FRP slab bridge and a corresponding concrete slab bridge. Finally, the applicability of AASHTO impact factors to FRP bridges is discussed.     

FEA of Complex Bridge System with FRP Composite Deck

Innovative fiber-reinforced polymer (FRP) composite highway bridge deck systems are gradually gaining acceptance in replacing damaged/deteriorated concrete and timber decks. FRP bridge decks can be designed to meet the American Association of State Highway and Transportation Officials (AASHTO) HS-25 load requirements. Because a rather complex sub- and superstructure system is used to support the FRP deck, it is important to include the entire system in analyzing the deck behavior and performance. In this paper, we will present a finite-element analysis (FEA) that is able to consider the structural complexity of the entire bridge system and the material complexity of an FRP sandwich deck. The FEA is constructed using a two-step analysis approach. The first step is to analyze the global behavior of the entire bridge under the AASHTO HS-25 loading. The next step is to analyze the local behavior of the FRP deck with appropriate load and boundary conditions determined from the first step. For the latter, a layered FEA module is proposed to compute the internal stresses and deformations of the FRP sandwich deck. This approach produces predictions that are in good agreement with experimental measurements.     

Evaluation of Effective Width and Distribution Factors for GFRP Bridge Decks Supported on Steel Girders

Glass fiber-reinforced polymer (GFRP) bridge deck systems offer an attractive alternative to concrete decks, particularly for bridge rehabilitation projects. Current design practice treats GFRP deck systems in a manner similar to concrete decks, but the results of this study indicate that this approach may lead to nonconservative bridge girder designs. Results from a number of in situ load tests of three steel girder bridges having the same GFRP deck system are used to determine the degree of composite action that may be developed and the transverse distribution of wheel loads that may be assumed for such structures. Results from this work indicate that appropriately conservative design values may be found by assuming no composite action between a GFRP deck and steel girder and using the lever rule to determine transverse load distribution. Additionally, when used to replace an existing concrete deck, the lighter GFRP deck will likely result in lower total stresses in the supporting girders, although, due to the decreased effective width and increased distribution factors, the live-load-induced stress range is likely to be increased. Thus, existing fatigue-prone details may become a concern and require additional attention in design.     

Finite-Element Modeling and Development of Equivalent Properties for FRP Bridge Panels

Fiber-reinforced polymer (FRP) composite materials are increasingly making their way into civil engineering applications. To reduce the self-weight and also achieve the necessary stiffness, sandwich panels are commonly used for FRP bridge decks. However, due to the geometric complexity of the FRP sandwich deck, convenient analysis and design methods for FRP bridge deck have not been developed. The present study aims at developing equivalent properties for a complicated sandwich panel configuration using finite-element modeling techniques. With equivalent properties, the hollowed sandwich panel can be transformed into an equivalent solid orthotropic plate, based on which deflection limits can be evaluated and designed. A procedure for the in-plane axial properties of the sandwich core has first been developed, followed by developing the out-of-plane panel properties for bending behavior of the panel. An application is made in the investigation of the stiffness contribution of wearing surface to the total stiffness of bridges with FRP panels. The wearing surface contribution is not usually accounted for in a typical design of bridges with traditional deck systems.     

Evaluation of Load Distribution Factor by Series Solution for Orthotropic Bridge Decks

In bridge engineering, the three-dimensional behavior of a bridge system is usually reduced to the analysis of a T-beam section, loaded by an equivalent fraction of the applied live load, which is called the live load distribution factor (LDF). The LDF is defined in the both the AASHTO Standard Specifications and the LRFD Specifications primarily for concrete slabs and has inherent applicable limitations. This paper provides explicit formulas using series solutions for LDF of orthotropic bridge decks, applicable to various materials but intended for fiber-reinforced polymer (FRP) decks. The present formulation considers important parameters that represent the response characteristics of the structure that are often omitted or limited in the AASHTO Specifications. A one-term series solution is proposed based on the macroflexibility approach, in which the bridge system is simplified into two major components, deck and stringers. The governing equations for the two components are obtained separately, and the deflections and interaction forces are solved by ensuring displacement compatibility at stringer lines. The LDF is calculated as the ratio of the single stringer interaction force to the summation of total stringer interaction forces. To verify this solution, a finite-element (FE) parametric study is conducted on 66 simply supported concrete slab-on-steel girder bridges. The results from the series solution correlates well with the FE results. It is also illustrated that the series solution can be applied to predict LDF for FRP deck-on-steel girder bridges, by favorable comparisons among the analytical, FE, and testing results for a one-third-scale bridge model. The scale test specimen consists of an FRP sandwich deck attached to steel stringers by a mechanical connector. The series solution is further used to obtain multiple regression functions for the LDF in terms of nondimensional variables, which can be used for simplified design purposes.     

Flexural Lateral Load Distribution Characteristics of Sandwich Plate System Bridges: Parametric Investigation

The sandwich plate system (SPS) is a relatively new bridge deck system that consists of steel face plates bonded to a rigid polyurethane core. The decks are thin, lightweight, and modular in design and can be tailored to numerous applications. This system provides an excellent alternative for the rapid construction and rehabilitation of bridge decks. With any new system, there exists some uncertainty in the design procedures as a result of the limited population for comparison. This paper presents the results of a finite-element parametric investigation of the lateral load distribution characteristics of SPS bridges. The parametric study primarily focuses on the influence of deck thickness on distribution behavior as compared to conventional reinforced concrete decks. Results from the study demonstrate that the inherent flexibility of a thin SPS deck yields larger distribution factors (up to 20%) than a typical reinforced concrete deck, but these distribution factors can still be conservatively estimated with current AASHTO LRFD methods. Additional comparisons indicate that the distribution behavior of SPS bridges can also be estimated with the equations proposed by the NCHRP 12-62 project.     

Sustained-Load and Fatigue Performance of a Hybrid FRP-Concrete Bridge Deck System

The design and construction of bridge systems with long-term durability and low maintenance requirements is a significant challenge for bridge engineers. One possible solution to this challenge could be through the use of new materials, e.g., fiber-reinforced polymer (FRP) composites, with traditional materials that are arranged as an innovative hybrid structural system where the FRP serves as a load-carrying constituent and a protective cover for the concrete. This paper presents the results of an experimental investigation designed to evaluate the performance of a 3/4 scale hybrid FRP-concrete (HFRPC) bridge deck and composite connection under sustained and repeated (fatigue) loading. In addition, following the sustained-load and fatigue portions of the experimental study, destructive testing was performed to determine the first strength-based limit state of the hybrid deck. Results from the sustained-load and fatigue testing suggest that the HFRPC deck system might be a viable alternative to traditional cast-in-place reinforced concrete decks showing no global creep behavior and no degradation in stiffness or composite action between the deck and steel girders after 2 million cycles of dynamic loading with a peak load of 1.26 times the scaled tandem load (TL). Furthermore, the ultimate strength test showed that the deck failed prior to the global superstructure at a load approximately six times the scaled TL.     

Development of an Efficient Connector System for Fiber Reinforced Polymer Bridge Decks to Steel Girders

This paper discusses the development of an innovative and efficient connector to be used with fiber reinforced polymer (FRP) decks supported by steel girders. A summary is provided detailing various proprietary connectors currently employed by FRP deck manufacturers. The paper then describes the development and experimental testing of a clamped shear stud-type connector. Experimental testing was conducted in two phases. The first phase consisted of individual connector testing. In this phase, several variations of the connector are tested and evaluated for strength, damage development, and overall performance. Results of this phase of testing are used to select a final connection design to be used in the second phase of testing, which consisted of testing a scale model bridge that incorporates several of the proposed connectors. The bridge is subjected to static load tests and the resulting reactions and deflections from these tests are compared with comprehensive finite element models of the system.     

Deck-Mounted Steel Post Barrier System

An existing mountable safety barrier system, previously crash tested successfully on a wood bridge deck, was evaluated for use on a fiber reinforced plastic (FRP) bridge deck. In an attempt to avoid expensive full-scale crash testing, components of the existing system were evaluated using worst case conditions on two dynamic bogie crash tests and a series of computer simulations using nonlinear finite-element analysis. Simulation results closely approximated the physical results, with both displaying similar deformation, damage, and force levels. Both testing and simulation demonstrated that the barrier should function sufficiently if used on the FRP deck system. Further, the development of an accurate model makes it possible to evaluate the potential success of the existing system for use on other bridge decks. As an example, a more rigid bridge deck, similar to reinforced concrete, was evaluated. Results showed that due to the stiffer deck, more of the impact energy must be absorbed by the posts and attachment hardware, resulting in significantly more deformation than when used on the flexible FRP deck.     

Connection of Concrete Railing Post and Bridge Deck with Internal FRP Reinforcement

The use of fiber-reinforced polymer (FRP) reinforcement is a practical alternative to conventional steel bars in concrete bridge decks, safety appurtenances, and connections thereof, as it eliminates corrosion of the steel reinforcement. Due to their tailorability and light weight, FRP materials also lend themselves to the development of prefabricated systems that improve constructability and speed of installation. These advantages have been demonstrated in the construction of an off-system bridge, where prefabricated cages of glass FRP bars were used for the open-post railings. This paper presents the results of full-scale static tests on two candidate post–deck connections to assess compliance with strength criteria at the component (connection) level, as mandated by the AASHTO Standard Specifications, which were used to design the bridge. Strength and stiffness until failure are shown to be accurately predictable. Structural adequacy was then studied at the system (post-and-beam) level by numerically modeling the nonlinear response of the railing under equivalent static transverse load, pursuant to well-established structural analysis principles of FRP RC, and consistent with the AASHTO LRFD Bridge Design Specifications. As moment redistribution cannot be accounted for in the analysis and design of indeterminate FRP RC structures, a methodology that imposes equilibrium and compatibility conditions was implemented in lieu of yield line analysis. Transverse strength and failure modes are determined and discussed on the basis of specification mandated requirements.     

Analysis of an Orthotropic Deck Stiffened with a Cement-Based Overlay

Over the past years, with increasing traffic volumes and higher wheel loads, fatigue damage in steel parts of typical orthotropic steel bridge decks has been experienced on heavily trafficked routes. A demand exists to find a durable system to increase the fatigue safety of orthotropic steel bridge decks. A solution might be to enhance the stiffness of the traditional orthotropic bridge deck by using a cement-based overlay. In this paper, an orthotropic steel bridge deck stiffened with a cement-based overlay is analyzed. The analysis is based on nonlinear fracture mechanics, and utilizes the finite-element method. The stiffness of the steel deck reinforced with an overlay depends highly on the composite action. The composite action is closely related to cracking of the overlay and interfacial cracking between the overlay and underlying steel plate (debonding). As an example, a real size structure, the Far? bridges located in Denmark, are analyzed. The steel box girders of the Far? bridges spans 80?m, and have a depth of 3.5?m, and a width of 19.5?m. The focus of the present study is the top part of the steel box girders, which is constructed as an orthotropic deck plate. Numerous factors can influence the cracking behavior of the cement-based overlay system. Both mechanical and environmental loading have to be considered, and effects such as shrinkage, temperature gradients, and traffic loading are taken into account. The performance of four overlay materials are investigated in terms of crack widths. Furthermore, the analysis shows that debonding is initiated for a certain crack width in the overlay. The load level where cracking and debonding is initiated depends on the stress-crack opening relationship of the material.