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.     

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.     

Evaluating and Proposing Models of Predicting IC Debonding Failure

Debonding failure due to intermediate crack-induced (IC) fracture is one of the most dominant failure modes associated with the fiber-reinforced polymer (FRP) bonding technique. To date, extensive efforts have been paid by many researchers worldwide to study the debonding phenomenon for effective applications of FRP composites and rational design of FRP-strengthened structures. Based on these efforts and various relevant field applications, different models and code provisions have been proposed to predict IC debonding failure. Out of all the existing code provisions and models, five typical ones are investigated in the current paper. A comprehensive comparison among these code provisions and models is carried out in order to evaluate their performance and accuracy. Test results of 200 flexural specimens with IC debonding failures collected from the existing literature are used in the current comparison. The effectiveness and accuracy of each model have been evaluated based on these experimental results. Finally, based on a statistical analysis, a simple and more effective model for predicting the load-carrying capacity of FRP-strengthened flexural members due to IC debonding failure is proposed.     

Mechanical Behavior of Fiber-Reinforced Polymer-Wrapped Concrete Columns—Complicating Effects

The present study focuses on the mechanical response of concrete columns confined with fiber-reinforced polymer composites (FRP). Practical columns often deviate from axisymmetric conditions due to noncircular cross section, geometric imperfections, and loading eccentricities. This paper discusses these complicating effects on the mechanical behavior of columns confined with FRP. Experiments have been carried out to examine the effects of geometric and loading imperfections on columns of various shapes. A model originally developed for axisymmetric situations has been extended to include the complicating effects. An analytical study for the corner radius that avoids concentration of stress is carried out. The theoretical models have been verified with the present and published experimental results.     

Strengthening Masonry Arches with Composite Materials

The aim of this study was to compare the effects of strengthening masonry arches using two different composite materials. To this end, an experimental analysis was carried out on models of arches that were first damaged, then strengthened by applying composite material sheets to the surface of the intrados, and last, subjected to a loading process until the point of collapse. One arch was strengthened with carbon fiber-reinforced polymer, the other with glass fiber-reinforced cement matrix. Results collected during the experimental analysis were significant in assessing the capability to support horizontal load, in increasing the collapse load, stiffness, and ductility, and in assessing the different fracture patterns and collapse modes of the arches strengthened with different fiber-reinforced composites. The comparison will be useful for establishing the physical-mechanical and aesthetic compatibilities between the original construction and the strengthening matrix (polymeric or cementitious), particularly with reference to the safeguarding of historical buildings.     

Verifications of Design Equations of Beams Externally Strengthened with FRP Composites

Based on the test information available in the literature since 1990, a comprehensive database is assembled for an extensive survey of existing studies on the flexural behavior of reinforced concrete beams externally strengthened with fiber-reinforced polymer (FRP) composites. Beam dimensions, material properties (concrete, steel reinforcement, FRP composites, etc.), and corresponding flexural responses such as failure modes, moment capacities, and so on, are collected in this database. The purpose of this database is to verify the design formulas presented in ACI 440.2R-02, Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures. The performance of some other simple strength design models is investigated based on the same database and compared with that of the ACI model, which is found to have the least scattered prediction compared to others. Finally, a modified maximum strain FRP equation is recommended.     

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.     

Impact Response of Externally Strengthened Unreinforced Masonry Walls Using CFRP

Research reported herein investigates the out-of-plane impact resistance of unreinforced masonry (URM) walls strengthened with carbon fiber-reinforced polymer (CFRP) composites, externally applied in sheets to one face of the wall. Two analytical methods based on energy principle and wave propagation theory and a finite-element-based numerical model have been developed, assuming a perfect bond at composite–masonry interface with an equivalent stiffness of the system. Full-scale impact tests are conducted for verification purpose, where three 1.2?m tall URM concrete walls (one unstrengthened and two strengthened with continuous unidirectional and woven CFRP sheets) are vertically tested up to cracking using a pendulum drop-weight impact tester. The test results compare reasonably well with those obtained from the analyses and simulation. It is found that the energy and finite-element methods can provide reasonable estimates for peak impact force and wall deflection, whereas the wave propagation method is rather limited by its applicability. Parametric studies are conducted to examine the effect of impactor mass, velocity, amount of CFRP reinforcement, and property of masonry material using the developed models.     

Glass Fiber Reinforced Polymer Pultruded Members: Constitutive Model and Stability Analysis

The increasingly widespread use of fiber-reinforced polymers as an alternative to conventional materials makes it necessary to formulate theoretical models which adequately evaluate the influence of the anisotropy of such composites on the structural behavior. While the cross section shapes adopted for compressed members are generally the same as in steel structures, the anisotropy which characterizes these polymers may reduce the critical loading threshold due to local buckling phenomena. A procedure to study the buckling of glass fiber reinforced polymer pultruded members by means of an homogenization approach is proposed here. A two-stage buckling model permits the determination of both global and local critical loads as explicit functions of the member geometry and its material behavior. These functions may be used for optimization of the shape of the above-mentioned members. Besides the model shows its reliability as it fits the results of experimental testson members with different slenderness ratios.     

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.     

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.     

Experimental Evaluation of Axial Behavior of Strengthened Circular Reinforced-Concrete Columns

Insufficient or deteriorating reinforced-concrete piers in many existing bridges are required to be strengthened using economical, fast, and efficient methods. Currently, only a few methods can be used to strengthen circular columns. Steel jackets and fiber-reinforced polymer (FRP) composites are the two commonly used methods. In this study, along with these two strengthening methods, concrete jackets reinforced with spiral rebar, welded wire fabric (WWF), and a new steel reinforcement called PCS are investigated under different axial-load applications. Fifteen identical specimens were constructed, strengthened, and tested: one column with no strengthening; three columns strengthened with FRP; two with steel jacketing; and nine with concrete jacketing (two with WWF, three with spiral rebar, and four with the new reinforcement). The bare or unretrofitted specimens had a 152?mm (6?in.) diameter, while the outside diameter of concrete-jacketed specimens was 254?mm (10?in.). Effectiveness of each strengthening method in increasing the stiffness, axial capacity, and displacement ductility was investigated using the experimental data.     

Comparative Study of Models on Confinement of Concrete Cylinders with Fiber-Reinforced Polymer Composites

The use of fiber-reinforced polymer (FRP) composites for strengthening and/or rehabilitation of concrete structures is gaining increasing popularity in the civil engineering community. One of the most attractive applications of FRP materials is their use as confining devices for concrete columns, which may result in remarkable increases of strength and ductility as indicated by numerous published experimental results. Despite a large research effort, a proper analytical tool to predict the behavior of FRP-confined concrete has not yet been established. Most of the available models are empirical in nature and have been calibrated against their own sets of experimental data. On the other hand, the experimental results available in the literature encompass a wide range of values of the significant variables. The objective of this work is a systematic assessment of the performance of the existing models on confinement of concrete columns with FRP materials. The study is conducted in the following steps: the experimental data on confinement of concrete cylinders with FRP available in the technical literature are classified according to the values of the significant variables; the existing empirical and analytical models are reviewed, pointing out their distinct features; the whole set of available experimental results is compared with the whole set of analytical models; and strengths and weaknesses of the various models are analyzed. Finally, a new equation is proposed to evaluate the axial strain at peak stress of FRP-confined concrete cylinders.     

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.     

Retrofitting Precast Bridge Beams with Carbon Fiber-Reinforced Polymer Strips for Shear Capacity

Advancements in fiber-reinforced polymers (FRPs) have made this an attractive material for rehabilitation and strengthening of bridge superstructures. FRP has primarily been used with the intention of increasing the bending strength of bridge members. However, this paper investigates the use of externally placed FRP strips to increase shear capacity of short-span, 5.7?m (19?ft), precast concrete channel beam bridges. A statewide survey revealed that as many as 389 bridges in the state of Arkansas are comprised of these members. Notably, beams within these bridges were designed under provisions that did not require shear reinforcement. In this research, four sections were retrofitted using carbon fiber-reinforced polymer (CFRP) strips and load tested to failure to measure the repair effectiveness. The performance of the retrofitted sections far exceeded that of unretrofitted sections. It was concluded that the addition of the CFRP repair increased the deflection ductility at least 123%. In addition, beams retrofitted with the CFRP strips experienced at least 26% more deflection after the initiation of a shear crack; therefore reducing the risk of a catastrophic failure.     

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 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.     

Accelerated Degradation of Recycled Plastic Piling in Aggressive Soils

Fiber-reinforced polymer composites represent an alternative construction material without many of the performance disadvantages of traditional materials. The use of fiber-reinforced polymer as a pile material can eliminate deterioration problems of conventional piling materials in waterfront environments and aggressive soils. This paper presents the preliminary results of an experimental study conducted to assess the durability of piling made of recycled plastics in aggressive soils for long-term usage in civil infrastructure applications. An accelerated testing protocol permitting prediction of the behavior of plastic piles was developed. Specimens were exposed to solutions with fixed acidic, basic, and neutral pH at elevated temperatures. Compressive strength was used as an index to quantify the degradation of the specimens. An Arrhenius model was used to predict the service life of the product.     

Analytical Model for FRP-Confined Circular Reinforced Concrete Columns

One disadvantage of most available stress–strain models for concrete confined with fiber-reinforced polymer (FRP) composites is that they do not take into consideration the interaction between the internal lateral steel reinforcement and the external FRP sheets. According to most structural concrete design codes, concrete columns must contain minimum amounts of longitudinal and transverse reinforcement. Therefore, concrete columns that have to be retrofitted (and therefore confined) with FRP sheets usually contain lateral steel. Hence, the retrofitted concrete column is under two actions of confinement: the action due to the FRP and that due to the steel ties. This paper presents a new designed-oriented confinement model for the axial and lateral behavior of circular concrete columns confined with steel ties, FRP composites, and both steel ties and FRP composites. Comparison with experimental results of confined concrete stress–strain curves shows good agreement between the test and predicted results.