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.     

LRFD Orthotropic Plate Model for Live Load Moment in Filled Grid Decks

Due to the orthogonal elastic properties and significant two-way bending action, orthotropic plate theory may best be used to describe the behavior of concrete filled grid bridge decks. The current AASHTO LRFD specification employs an orthotropic plate model with a single patch load to predict live load moment in concrete filled grid bridge decks, which may not be conservative. This paper presents alternative equations to predict maximum moments, based on classical orthotropic plate theory, which include multiple patch loads, both the LRFD design truck and tandem load cases, and the two most common deck orientations. The predicted moments are verified through finite-element analyses.     

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.     

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.     

Influence of Reinforcement on the Behavior of Concrete Bridge Deck Slabs Reinforced with FRP Bars

This paper presents the results of an experimental study to investigate the role of each layer of reinforcement on the behavior of concrete bridge deck slabs reinforced with fiber-reinforced polymer (FRP) bars. Four full-scale concrete deck slabs of 3,000?mm length by 2,500?mm width and 200?mm depth were constructed and tested in the laboratory. One deck slab was reinforced with top and bottom mats of glass FRP bars. Two deck slabs had only a bottom reinforcement mat with different reinforcement ratios in the longitudinal direction, while the remaining deck slab was constructed with plain concrete without any reinforcement. The deck slabs were supported on two steel girders spaced at 2,000?mm center to center and were tested to failure under a central concentrated load. The three reinforced concrete slabs had very similar behavior and failed in punching shear mode at relatively high load levels, whereas the unreinforced slab behaved differently and failed at a very low load level. The experimental punching capacities of the reinforced slabs were compared to the theoretical predictions provided by ACI 318-05, ACI 440.1R-06, and a model proposed by the writers. The tests on the four deck slabs showed that the bottom transverse reinforcement layer has the major influence on the behavior and capacity of the tested slabs. In addition, the ACI 318-05 design method slightly overestimated the punching shear strength of the tested slabs. The ACI 440.1R-06 design method yielded very conservative predictions whereas the proposed method provided reasonable yet conservative predictions.     

Characterization of a Low-Profile Fiber-Reinforced Polymer Deck System for Moveable Bridges

Moveable bridges in Florida typically use open steel grid decks due to weight limitations. However, these decks present rideability, environmental, and maintenance problems, as they are typically less skid resistant than a solid riding surface, create loud noises, and allow debris to fall through the grids. Replacing open steel grid decks with a lightweight fiber-reinforced polymer (FRP) deck can improve rideability and reduce maintenance costs, simultaneously satisfying the strict weight requirement for such bridges. In this investigation, a new low-profile, pultruded FRP deck system successfully passed the preliminary strength and fatigue tests per AASHTO requirements. Two two-span deck specimens were tested, one with the strong direction of the deck placed perpendicular to the supporting girders, whereas the other had a deck placed with 30° skew. This paper also describes a simplified finite-element approach that simulates the load–deformation behavior of the deck system. The results from the finite-element model showed a good correlation with the deflection and strain values measured from the tests.     

Fatigue Behavior of a Steel-Free FRP–Concrete Modular Bridge Deck System

This paper presents results of an evaluation of the fatigue performance of a novel steel-free fiber-reinforced polymer (FRP)–concrete modular bridge deck system consisting of wet layup FRP–concrete deck panels which serve as both formwork and flexural reinforcement for the steel-free concrete slab cast on top. A two-span continuous deck specimen was subjected to a total of 2.36 million cycles of load simulating an AASHTO HS20 design truck with impact at low and high magnitudes. Quasistatic load tests were conducted both before initiation of fatigue cycling and after predetermined numbers of cycles to evaluate the system response. No significant stiffness degradation was observed during the first 2 million cycles of fatigue service load. A level of degradation was observed during subsequent testing at higher magnitudes of fatigue load. A fairly elastic and stable response was obtained from the system under fatigue service load with little residual displacement. The system satisfied both strength and serviceability limit states with respect to the code requirements for crack width and deflection.     

Fatigue Life Evaluation of Concrete Bridge Deck Slabs Reinforced with Glass FRP Composite Bars

Since bridge deck slabs directly sustain repeated moving wheel loads, they are one of the most bridge elements susceptible to fatigue failure. Recently, glass fiber-reinforced polymer (FRP) composites have been widely used as internal reinforcement for concrete bridge deck slabs as they are less expensive compared to the other kinds of FRPs (carbon and aramid). However, there is still a lack of information on the performance of FRP–reinforced concrete elements subjected to cyclic fatigue loading. This research is designed to investigate the fatigue behavior and fatigue life of concrete bridge deck slabs reinforced with glass FRP bars. A total of five full-scale deck slabs were constructed and tested under concentrated cyclic loading until failure. Different reinforcement types (steel and glass FRP), ratios, and configurations were used. Different schemes of cyclic loading (accelerated variable amplitude fatigue loading) were applied. Results are presented in terms of deflections, strains in concrete and FRP bars, and crack widths at different levels of cyclic loading. The results showed the superior fatigue performance and longer fatigue life of concrete bridge deck slabs reinforced with glass FRP composite bars.     

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.     

Performance Evaluation of Repair Technique for Damaged Fiber-Reinforced Polymer Honeycomb Bridge Deck Panels

All-composite, fiber-reinforced polymer honeycomb (FRPH) sandwich panels are an innovative application of modern composite materials in civil engineering. These panels have become increasingly popular for use as full-depth bridge decks and have been used to span both transversely between steel or concrete girders and longitudinally between abutments. Although several bridges using FRPH panels have been installed in recent years, a method to repair the panels if they are damaged has not been thoroughly investigated. This paper presents the analysis and full-scale evaluation of a 9.75 m (32 ft) long FRPH member that was subjected to severe core-face delamination damage and subsequently repaired. As such, the work presented herein is the first of its kind to be conducted for FRPH bridge members. The damaged member when repaired was shown to have approximately 65% more capacity than a similar undamaged member. The additional capacity was achieved using a single wrapping layer over the face plates and sinusoidal core. This wrapping layer is believed to have prevented a failure (at the resin bond line) between the face plates and core by engaging a shear-friction type clamping force. The contribution of the wrap layer is considered using simple calculations, rigorous finite-element models, and experimental data. Acoustic emission monitoring was used to compare the performance of the damaged and repaired specimens under sustained load.     

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.     

Testing, Analysis, and Evaluation of a GFRP Deck on Steel Girders

North Carolina has recently installed a fiber-reinforced polymer (FRP) deck on steel girders at a site in Union County. The bridge was instrumented with foil strain gauges, strain transducers, and displacement transducers. The bridge was then tested with a simulated MS-22.5 design load. Experimental data confirmed full composite interaction between the girders and the FRP deck panels. The neutral axis was measured to be 383?mm above the bottom flange of the 618-mm-deep girder. It was found that composite action could be estimated within 3% using a transformed section analysis of the deck panels. For two lanes loaded, the maximum live load distribution factor was computed to be 0.75. When looking at the overall performance of the structure, the deck deflected 5?mm, with the allowable stress at least 10 times over the maximum stress measured in the material. The girder deflection of 7?mm was well within the parameters set forth by AASHTO. Simple span deflection equations were found to conservatively model the anticipated deflection of the girders when using the transformed section properties.     

Construction, Inspection, and Maintenance of FRP Deck Panels

Composite materials are clearly having a major impact on how facilities are designed, constructed, and maintained. In order to enhance the application of fiber-reinforced composites in infrastructure renewal, it will be important to understand the constructability, maintainability, operability, and inspection issues related to the use of fiber-reinforced polymer (FRP) structural components. This paper identifies these issues as well as fabrication issues, construction methods, quality, man-hour requirements, cost and productivity issues, and the skill level required to install FRP bridge deck panels. The data required for this research were collected through two questionnaire studies, personal interviews with two manufacturers of FRP bridge deck panels (i.e., Hardcore Composites and Martin Marietta Composites), and candidate projects for FRP bridge deck construction.     

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.     

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.     

Field Testing and Analysis of CRC Deck Girder Bridges

This paper presents findings of field tests and analysis of two conventionally reinforced concrete (CRC) deck girder bridges designed in the 1950s. The bridges are in-service and exhibit diagonal cracks. Stirrup strains in the bridge girders at high shear regions were used to estimate distribution factors for shear. Impact factors based on the field tests are reported. Comparison of field measured responses with AASHTO factors was performed. Three-dimensional elastic finite-element analysis was employed to model the tested bridges and determine distribution factors specifically for shear. Eight-node shell elements were used to model the decks, diaphragms, bent caps, and girders. Beam elements were used to model columns under the bent caps. The analytically predicted distribution factors were compared with the field test data. Finally, the bridge finite-element models were employed to compare load distribution factors for shear computed using procedures in the AASHTO LRFD and Standard Specifications.     

Development and Evaluation of an Adhesively Bonded Panel-to-Panel Joint for a FRP Bridge Deck System

A fiber-reinforced polymer (FRP) composite cellular deck system was used to rehabilitate a historical cast iron thru-truss structure (Hawthorne St. Bridge in Covington, Va.). The most important characteristic of this application is reduction in self-weight, which raises the live load-carrying capacity of the bridge by replacing the existing concrete deck with a FRP deck. This bridge is designed to HL-93 load and has a 22.86?m clear span with a roadway width of 6.71?m. The panel-to-panel connections were accomplished using full width, adhesively (structural urethane adhesive) bonded tongue and groove splices with scarfed edges. To ensure proper construction, serviceability, and strength of the splice, a full-scale two-bay section of the bridge with three adhesively bonded panel-to-panel connections was constructed and tested in the Structures Laboratory at Virginia Tech. Test results showed that no crack initiated in the joints under service load and no significant change in stiffness or strength of the joint occurred after 3,000,000 cycles of fatigue loading. The proposed adhesive bonding technique was installed in the bridge in August 2006.     

Effects of Fabrication Procedures on Fatigue Resistance of Welded Joints in Steel Orthotropic Decks

A common practice for the fabrication of steel orthotropic bridge decks in the United States is to use 80% partial joint penetration (PJP) groove welds between the closed ribs and deck plate. However, it is difficult to eliminate weld melt-through with the thin rib plates. Heat straightening after welding, sometimes combined with precambering, is used to meet the deck plate flatness requirement. To study the effects of both weld melt-through and distortion control measures on the fatigue resistance of the rib-to-deck plate welded joint, six full-scale two-span orthotropic deck specimens were subjected to laboratory testing. Specimens, 10 m long and 3 m wide with four closed ribs, were fabricated with and without weld melt-through and were heat straightened; three specimens were also precambered. To simulate the effect of repetitive truck traffic, each specimen was tested up to 8 million cycles. Test results showed that six cracks initiated from the weld toe outside the rib. Only one crack developed at the weld root inside the rib; this crack initiated from a location transitioning from the 80% PJP to 100% penetration weld. None of the cracks propagated through the deck plate thickness. Precambering was beneficial in fatigue resistance as two effectively precambered specimens did not experience cracking in the PJP welds.     

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.     

Finite-Difference Solution of a Both-End-Fixed Orthotropic Composite Beam under Uniformly Distributed Loading Using Displacement Potential Function Formulation

The elastic solution of an orthotropic composite beam under the influence of uniformly distributed loading is obtained numerically. Two ends of the beam are rigidly fixed, and the fibers are oriented along and perpendicular to the direction of the length of the beam. An efficient finite-difference computational scheme based on displacement potential formulation is used to analyze the present mixed-boundary-value elastic problem. The effect of several important parameters such as beam aspect ratio and fiber orientation on the elastic field are investigated. Solutions are presented mainly in the form of graphs and deformed shapes. Finally, the reliability as well as superiority of the present computational scheme is discussed by comparing the present solution with the corresponding finite-element solutions.