Journal of Composites for Construction

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.

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.

Collapse of unreinforced masonry (URM) walls is the cause of many casualties during extreme loading events. The objective of this current research was to investigate effective and practical approaches for strengthening URM block walls with openings to resist extreme out-of-plane loads. Five full-scale masonry block walls were constructed. The walls had different opening configurations such as a single center window, one window off center, two windows, a wide window and a door. The walls were tested when subjected to uniformly distributed lateral load up to failure. The walls were then strengthened using carbon fiber-reinforced polymer laminate strips and then retested. The walls were set up in a vertical test frame and were subjected to cyclic out-of-plane distributed pressure using an airbag. Failure of the unstrengthened URM block wall was along the mortar joints. In the strengthened walls, failure occurred in the mortar joints as well as in concrete blocks near the carbon strips. The lateral load carrying capacity of the strengthened walls was found to be significantly higher than that of the unstrengthened walls and had much more ductile performance.

A method to utilize fiber composites for rapid repair of earthquake damaged flared columns was developed. Two 0.4-scale reinforced concrete columns that had been tested to failure in previous research were used. Both columns had been subjected to slow cyclic loads and had failed due to low-cycle fatigue of the longitudinal bars. To repair the columns, the damaged concrete in and around the plastic hinge was removed and the steel bars were straightened. Low-shrinkage, high-strength concrete grout was placed in the column afterward. The broken longitudinal bars were not replaced. Rather, glass and carbon fiber reinforced polymer (FRP) sheets with fibers running in the axial direction of the column were added to provide flexural strength to the columns. Additionally, glass FRP sheets with horizontal fibers were attached on the column to provide confinement and shear strength. Cyclic tests of the repaired columns indicated that the method to restore the strength was effective. Analysis using conventional constitutive relationships led to a close estimate of the lateral load response of the models.

Lateral confinement of reinforced concrete columns can significantly increase their lateral deflection capability and load-carrying capacity. While such retrofits were initially completed using steel jackets, fiber-reinforced polymer (FRP) composites have been used successfully and extensively for seismic and blast upgrades. Numerical modeling of such structures requires the use of a concrete material model that can accurately represent the volumetric behavior of concrete under triaxial stress states, to capture the interaction between concrete expansion and the resulting stress increase in the confining jacket. Test data by Suter and Pinzelli, Karbhari and Gao, and Mirmiran and Shahawy on concrete cylinders and prisms confined by aramid, carbon, and glass FRP sheets are analyzed numerically. The concrete material model used was developed for the study of the effect of blast loading on reinforced concrete structures and was verified and validated for a variety of triaxial stress paths. The numerical analyses closely reproduce the strength enhancements observed in the test specimens for various levels of confinement. The model also confirms the observed inefficiency of low levels of lateral confinement and the superior enhancement provided by circular cross sections as compared to rectangular ones.

Laboratory investigations of the compressive behavior of fiber-reinforced polymer (FRP)-confined concrete columns have generally been carried out using relatively small-scale specimens, and the majority of theoretical models that have been developed so far are based on test data from such specimens. However, the use of small specimens may conceal possible scale effects. In this study, the influence of slenderness ratio and specimen size on axially loaded FRP-confined concrete columns was investigated experimentally, and the results have been compared to theoretical models and experimental results gathered from the published literature. The investigation aims to validate past results obtained from concrete cylinders and to verify existing empirical models as well. Three different specimen diameters and two slenderness (length-to-diameter) ratios, combined with two FRP-confinement materials, were varied as parameters. According to the statistical analysis of the results, it is shown that conventional FRP-confined concrete cylinders can effectively be used to model the axial behavior of short columns. Size effects, however, are clearly evident in very small $(\approx 50\mathrm{mm}$ diameter) specimens. The usefulness of published results involving such small-scale specimens is therefore questionable, as is the validity of theoretical models and strength predictions based on test data from small-diameter specimens.

This paper presents a numerical model for evaluating the behavior of axially loaded rectangular and cylindrical short columns of concrete confined by fiber-reinforced polymer (FRP) composites. The proposed formulation considers, for unconfined and confined compressed concrete, a uniaxial constitutive relation that utilizes the area strain as a parameter of measure of the material secant axial stiffness. For unconfined concrete, the model adopts an explicit relationship between axial strain and lateral strain, while for confined concrete, an implicit relation is considered. For this last case, the model employs a simple iterative-incremental approach that describes the entire stress-strain response of the columns. The behavior of the FRP is considered linear elastic until the rupture. To validate the model, a number of columns were analyzed and the numerical results were compared with experimental values published by other authors. This comparison between experimental and numerical results indicates that the model provides satisfactory predictions of the stress-strain response of the columns.

An analytical model to predict the behavior of concrete confined with fiber reinforced plastic (FRP) composites subjected to axial compressive loads was developed. First, a constitutive model for plain concrete was formulated from past experimental results obtained from triaxial compression tests of concrete, in which concrete specimens were maintained under constant confining stresses. This was an orthotropic constitutive model based on the concept of equivalent uniaxial strain. Subsequently, in the analytical model for FRP confined concrete, the proposed constitutive model for concrete materials was incorporated. The FRP was assumed to be a linear elastic material. Force equilibrium and strain compatibility between the concrete and the FRP as well were satisfied. When the proposed model was applied to FRP confined concrete, the model overestimated the axial stress. To rectify this, a subsequent maximum strength criterion was introduced to control the maximum strength in the postpeak region when confining stress was continuously increased. The proposed analytical model with the addition of the subsequent maximum strength criterion is in good agreement with the experimental results.

In this paper, a conventional test method using a notched three-point bending beam (3PBB) specimen is adapted to characterize Mode I fracture of composite-concrete bonded interfaces, and the interface fracture energy is evaluated based on a fictitious crack model. Two types of fiber fabrics—E-glass and carbon—are used, and a common epoxy resin is applied to bond the composite fabriçs to concrete. Mode I fracture tests of the 3PBB specimens for carbon fiber reinforced polymer (CFRP)- and glass fiber reinforced polymer (GFRP)-concrete bonded interfaces are performed to determine the applied load and load point displacement relationship from which the interface fracture energy is computed. The effects of loading rates, types of fiber fabrics, and curing time on the fracture energy of FRP-concrete bonded interfaces are studied and discussed. It is expected that the proposed experimental method can be used effectively to obtain fracture data for performing delamination studies under various environmental exposures and service loading.

Structural restoration of spliced or damaged wood piles with fiber reinforced polymer (FRP) composite shells requires that shear forces be transferred between the wood core and the encasing composite shells. When a repaired wood pile is loaded, shear stresses develop between the wood pile and the FRP composite shell through the grouting material. Alternatively, shear force transfer can be developed through mechanical connectors. The objective of this study was to characterize the interfaces in wood piles repaired with FRP composite shells and grout materials. Two interfaces were studied: wood pile/grout material and a grout material/innermost FRP composite shell. A set of design parameters that control the response of both interfaces was identified: (1) extent of reduction of cross section of wood pile due to deterioration (necking); (2) type of grout material (cement-based or polyurethane); (3) use of mechanical connectors; and (4) addition of frictional coating on the innermost shell. Push-out tests by compression loading were performed to characterize the interfaces and discriminate the effect of the design parameters. The outcome of the push-out tests was evaluation of the shear stress and force versus slip response and characterization of the failure mechanism. A set of repair systems that represent different combinations of the design parameters was fabricated and the interfaces evaluated. It was found that the combination of cement-based grout and polymer concrete overlay on the innermost shell provided the most efficient shear force-slip response. A simplified piecewise linear model of shear stress versus slip at the wood/grout and grout/FRP composite interfaces with and without mechanical connectors is proposed to synthesize the experimental response.

Many experimental studies have been performed to evaluate the behavior of noncorroding glass fiber reinforced polymer (GFRP) rebars in reinforced concrete (RC) flexural members. Relatively few studies have focused on the behavior of bridge deck overhangs in the event of a barrier wall impact, which subjects this region to a combination of flexure, shear, and axial tension. The objective of this investigation is to evaluate deck overhangs under these forces. Three bridge deck reinforcing schemes were considered in the study: all epoxy-coated steel (ECS), all GFRP, and hybrid made up of a top mat of GFRP rebars and a bottom mat of ECS rebars. Laboratory testing of nine RC specimens was performed. Results showed that all three reinforcing schemes meet the AASHTO requirements.