Steel Hexagonal Honeycomb Core Equivalent Elastic Moduli for Bridge Deck Sandwich Panels

Glass fiber-reinforced polymer (GFRP) materials possess inherently high strength-to-weight ratios, but their effective elastic moduli are low relative to civil engineering (CE) construction materials. While elastic modulus may be comparable to that of some CE materials, the lower shear modulus adversely affects stiffness. As a result, serviceability issues are what govern GFRP deck design in the CE bridge industry. An innovative solution to increase the stiffness of a commercial GFRP reinforced-sinusoidal honeycomb sandwich panel was proposed; this solution would completely replace the GFRP honeycomb core with a hexagonal honeycomb core constructed from commercial steel roof decking. The purpose of this study was to perform small-scale tests to characterize the steel hexagonal honeycomb core equivalent elastic moduli in an effort to simplify the modeling of the core. The steel core equivalent moduli experimental results were compared with theoretical hexagonal honeycomb elastic modulus equations from the literature, demonstrating the applicability of the theoretical equations to the steel honeycomb core. Core equivalent elastic modulus equations were then proposed to model and characterize the steel hexagonal honeycomb as applicable to sandwich panel design. The equivalent honeycomb core will enable an efficient sandwich panel stiffness design technique, both for structural analysis methods (i.e., hand calculations) and finite-element analysis procedures.     

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.     

Effect on Superstructure Stress of Replacing a Composite RC Bridge Deck with a GFRP Deck

Glass fiber-reinforced polymer (GFRP) composite bridge decks behave differently than comparable reinforced concrete (RC) decks. GFRP decks exhibit reduced composite behavior (when designed to behave in a composite manner) and transverse distribution of forces. Both of these effects are shown to counteract the beneficial effects of a lighter deck structure and result in increased internal stresses in the supporting girders. The objective of this paper is to demonstrate through an illustrative example the implications of RC-to-GFRP deck replacement on superstructure stresses. It is also shown that, regardless of superstructure stresses, substructure forces will be uniformly reduced due to the lighter resulting superstructure.     

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.     

Critical Evaluation of Strain Measurements in Glass Fiber-Reinforced Polymer Bridge Decks

An experimental study of principal strains and deflections of glass fiber-reinforced polymer (GFRP) composite bridge deck systems is presented. The experimental results are shown to correlate well with those of an analytical model. While transverse strains and vertical deflections are observed to be consistent, repeatable, and predictable, longitudinal strains exhibit exceptional sensitivity to both strain sensor and applied load location. Large, reversing strain gradients are observed in the longitudinal direction of the bridge deck. GFRP deck system geometry, connectivity, material properties, and manufacturing imperfections coupled with the observed strains suggest that the performance of these structures should be assessed under fatigue loading conditions. Recommendations for accurately assessing longitudinal strain in GFRP bridge decks are made, and a review of existing data is suggested.     

Evaluation of GFRP Honeycomb Beams for the O’Fallon Park Bridge

This paper presents a study on the evaluation of the static performance of a glass fiber-reinforced polymer (GFRP) bridge deck that was installed in O’Fallon Park over Bear Creek west of the City of Denver. The bridge deck has a sandwich panel configuration, consisting of two stiff faces separated by a light-weight honeycomb core. The deck was manufactured using a hand lay-up technique. To assist the preliminary design of the deck, the stiffness and load-carrying capacities of four approximately 330 mm (13 in.) wide GFRP beam specimens were evaluated. The crushing capacity of the panel was also examined by subjecting four 330×305×190?mm?(13×12×7.5?in.) specimens to compression tests. The experimental data were analyzed and compared to results obtained from analytical and finite element models, which have been used to enhance the understanding of the experimental observations. The failure of all four beams was caused by the delamination of the top faces. In spite of the scatter of the tests results, the beams showed good shear strengths at the face-to-core interface as compared to similar panels evaluated in prior studies.     

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.     

Fatigue and Strength Evaluation of Two Glass Fiber-Reinforced Polymer Bridge Decks

The use of glass fiber-reinforced polymer (GFRP) bridge decks is appealing for applications where minimizing dead load is critical. This paper describes fatigue and strength testing of two types of GFRP decks being considered for use in the retrofit of an aging steel arch bridge in Snohomish County, Washington, where a roadway expansion is necessary and it is desirable to minimize the improvements to the arch superstructure. Each test used a setup designed to be as close as practicable to what will be the in situ conditions for the deck, which included a 2% cross slope for drainage. The fatigue testing consisted of a single 116 kN (26 kip) load applied for 2 million cycles, which corresponds to an AASHTO HS-25 truck with a 30% impact factor, and the strength testing consisted of multiple runs of a monotonically applied minimum load of 347 kN (78 kips). Results from the fatigue testing indicated a degradation of the stiffness of both deck types; however, the degradation was limited to less than 12% over the duration of loading. Further, the results showed both deck types accumulated permanent deck displacement during fatigue loading and one deck type used a detail with poor fatigue performance. That detail detrimentally impacted the overall deck performance and caused large permanent deck deformations. It was also found that degradation of composite behavior between the deck and girders occurs during fatigue loading and should be included 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.     

Structural Performance of Hybrid GFRP/Steel Concrete Sandwich Panels

Precast/prestressed concrete sandwich panels consist of two concrete wythes separated by a rigid insulation foam layer and are generally used as walls or slabs in thermal insulation applications. Commonly used connectors between the two wythes, such as steel trusses or concrete stems, penetrate the insulation layer causing a thermal bridge effect, which reduces thermal efficiency. Glass fiber-reinforced polymer (GFRP) composite shell connectors between the two concrete wythes are used in this research as horizontal shear transfer reinforcement. The design criterion is to establish composite action, in which both wythes resist flexural loads as one unit, while maintaining insulation across the two concrete wythes of the panel. The experiments carried out in this research show that hybrid GFRP/steel reinforced sandwich panels can withstand out-of-plane loads while providing resistance to horizontal shear between the two concrete wythes. An analytical method is developed for modeling the horizontal shear transfer enhancement using a shear flow approach. In addition, a truss model is built, which predicts the panel deflections observed in the experiments with reasonable accuracy.     

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.     

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.     

Nondestructive Testing of GFRP Bridge Decks Using Ground Penetrating Radar and Infrared Thermography

As glass fiber-reinforced polymer (GFRP) bridge decks are becoming a feasible alternative to the traditional concrete bridge decks, an innovative methodology to evaluate the in situ conditions are vital to GFRP bridge decks’ full implementation. Ground penetrating radar (GPR) typically performs well in detecting subsurface condition of a structural component with moisture pockets trapped within the material. On the other hand, infrared thermography (IRT) is traditionally known for its ability to detect air pockets within the material. In order to evaluate both nondestructive testing methods’ effectiveness for subsurface condition assessment of GFRP bridge deck, debonds of various sizes were embedded into a GFRP bridge deck module. A 1.5 GHz ground-coupled GPR system and a radiometric infrared camera were used to scan the deck module for condition assessment. Test results showed that both GPR and IRT retained their respective effectiveness in detecting subsurface anomalies. GPR was found to be capable of detecting water-filled defects as small as 5×5?cm2 in plan size, and as thin as 0.15 cm. Furthermore, tests on additional specimens showed that the GPR system offers some promise in detecting bottom flange defects as far down as 10 cm deep. IRT, on the other hand, showed that it is capable of finding both water-filled and air-filled defects within the top layers of the deck with solar heating as main source of heat flux. While test results showed IRT is more sensitive to air-filled defects, water-filled defects can still be detected with a large enough heating mechanism. The experiments showed that a more detailed and accurate assessment can be achieved by combining both GPR and IRT.     

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.     

Filament-Wound Glass Fiber Reinforced Polymer Bridge Deck Modules

The demand for the development of efficient and durable bridge decks is a priority for most of the highway authorities worldwide. This paper summarizes the results of an experimental program designed to study the behavior of an innovative glass fiber reinforced polymer (GFRP) bridge deck recently patented in Canada. The deck consisted of a number of triangular filament wound tubes bonded with epoxy resin. GFRP plates were adhered to the top and bottom of the tubes to create one modular unit. The experimental program, described in this paper, discusses the evolution of two generations of the bridge deck. In the first generation, three prototype specimens were tested to failure, and their performance was analyzed. Based on the behavior observed, a second generation of bridge decks was fabricated and tested. The performance was evaluated based on load capacity, mode of failure, deflection at service load level, and strain behavior. All decks tested exceeded the requirements to support HS30 design truck loads specified by AASHTO with a margin of safety. This paper also presents an analytical model, based on Classical Laminate Theory to predict the load-deflection behavior of the FRP decks up to service load level. In all cases the model predicted the deck behavior very well.     

Structural Characterization of Hybrid Fiber-Reinforced Polymer-Glulam Panels for Bridge Decks

The structural characterization of hybrid fiber-reinforced polymer (FRP)–glued laminated (glulam) panels for bridge deck construction is examined using a combined analytical and experimental approach. The structural system is based on the concept of sandwich construction with strong and stiff FRP composite skins bonded to an inner glulam panel. The FRP composite material was made of E-glass reinforcing fabrics embedded in a vinyl ester resin matrix. The glulam panels were fabricated with bonded eastern hemlock vertical laminations. The FRP reinforcement was applied on the top and bottom faces of the glulam panel by wet layup and compacted using vacuum bagging. An experimental protocol based on a two-span continuous bending test configuration is proposed to characterize the stiffness, ductility, and strength response of FRP-glulam panels under simulated loads. Half-scale FRP-glulam panel prototypes with two different fiber orientations, unidirectional (0°) and angle-ply (±45°), were studied and the structural response correlated with control glulam panels. A simple beam linear model based on laminate analysis and first-order shear deformation theory was proposed to compute stiffness properties and to predict service load deflections. In addition, a beam nonlinear model based on layered moment-curvature numerical analysis was proposed to predict ultimate load and deflections. Correlations between experimental results and the two proposed beam models emphasize the need for complementing both analytical tools to characterize the hybrid panel structural response with a view toward bridge deck design.     

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.     

Theoretical and Experimental Analysis of GFRP Bridge Deck under Temperature Gradient

The temperature difference between the top and bottom of a glass fiber reinforced polymer (GFRP) composite deck, ～ 65°C ( ～ 122°F), is nearly three times that of conventional concrete decks ～ 23°C ( ～ 41°F). Such a large temperature difference is attributed to the relatively lower thermal conductivity of GFRP material. In this study, laboratory tests were conducted on two GFRP bridge deck modules (10.2 and 20.3?cm deep decks) by heating and cooling the top surface of the GFRP deck, while maintaining ambient (room) temperature at the deck bottom. Deflections and strains were recorded on the deck under thermal loads. Theoretical results (using macro approach, Navier-Levy, and FEM) were compared with the laboratory test data. The test data indicated that the GFRP deck exhibited hogging under a positive temperature difference (i.e., Ttop>Tbottom, heating test; Ttop and Tbottom are temperatures at top and bottom of the deck, respectively) and sagging under a negative temperature difference (i.e., Ttop相似文献   

Field Investigation on the First Bridge Deck Slab Reinforced with Glass FRP Bars Constructed in Canada

Recently, there has been a rapid increase in using noncorrosive fiber-reinforced polymers (FRP) reinforcing bars as alternative reinforcement for bridge deck slabs, especially those in harsh environments. A new two-span girder type bridge, Cookshire-Eaton Bridge (located in the municipality of Cookshire, Quebec, Canada), was constructed with a total length of 52.08 m over two equal spans. The deck was a 200-mm-thick concrete slab continuous over four spans of 2.70 m between girders with an overhang of 1.40 m on each side. One full span of the bridge was totally reinforced using glass fiber-reinforced polymer (GFRP) bars, while the other span was reinforced with galvanized steel bars. The bridge deck was well instrumented at critical locations for internal temperature and strain data collection using fiber optic sensors. The bridge was tested for service performance using calibrated truckloads as specified by the Canadian Highway Bridge Design Code. The construction procedure and field test results under actual service conditions revealed that GFRP rebar provides very competitive performance in comparison to steel.     

Static and Fatigue Testing of Hybrid Fiber-Reinforced Polymer-Concrete Bridge Superstructure

This paper presents the experimental results from static and fatigue testing on a scale model of a hybrid fiber-reinforced polymer (FRP)–concrete bridge superstructure. The hybrid superstructure was designed as a simply-supported single span bridge with a span of 18.3 m. Three trapezoidal glass fiber-reinforced polymer (GFRP) box sections are bonded together to make up a one-lane superstructure, and a layer of concrete is placed in the compression side of those sections. This new design was proposed in order to reduce the initial costs and to increase the stiffness of GFRP composite structures. Static test results showed that the bridge model meets the stiffness requirement and has significant reserve strength. The bridge model was also subjected to two million load cycles to investigate its fatigue characteristics. The fatigue testing revealed that the structural system exhibits insignificant stiffness degradation.