Journal of Composites for Construction

Compressive membrane action in bridge deck slabs has been shown to considerably increase the failure loads of such slabs. Thus, the reinforcing requirement can be reduced if a system is configured to ensure development of compressive membrane action. Recent research has shown that the use of transverse prestressing in bridge deck slabs can achieve even greater savings by reducing slab thickness and reinforcing requirements while enhancing serviceability. This paper describes an investigation of a deck slab system totally devoid of steel reinforcement. A one-quarter-scale model of a typical deck slab supported on three steel girders was constructed in the laboratory and transversely prestressed with carbon-fiber-reinforced plastic tendons. Polypropylene-fiber-reinforced concrete was used for temperature and shrinkage crack control. The deck slab panels in the model bridge were tested to failure under simulated concentrated wheel loads. The observed failure mode of all panels was that of punching shear, at loads in excess of the scaled Ontario Highway Bridge Design Code specified design service load. Load-deflection curves and failure loads are presented and compared. The test results show that transverse prestressing enhances, considerably, the punching failure loads of deck slabs. It was also observed that bridge deck slabs totally devoid of any steel reinforcement perform satisfactorily in both strength and deformation.

Bonding composite plates to reinforced concrete beams is an effective technique of repair and retrofit. The ultimate capacity of the strengthened beam is controlled by either compression crushing of concrete, rupture of the plate, local failure of concrete at the plate end due to stress concentration, or debonding of the plate. These failure modes have been considered for developing design guidelines for strengthening reinforced concrete beams using fiber composite plates. The effect of multistep loading of the beam, before and after upgrading, has been included in these guidelines. Limit state design concept has been followed in this paper. Terms, definitions, and notations compatible to design guidelines for ordinary reinforced concrete beams have been used.

The application of carbon fiber composite jackets for the three columns and cap beam of an existing concrete bridge pier was performed in September 1996. The evaluation of the pier in the as-is condition, the rehabilitation objectives, and the composite wrap design are presented. A bilinear stress-strain curve for the confinement model of circular and rectangular concrete sections with fiber-reinforced plastic composite jackets is used for performing pushover analyses. In addition, a comparison is made between analytical results and full-scale experiments. It was found that the shear capacity of the cap beam and columns and the ductility of the pier were improved significantly.

Confinement effectiveness of fiber reinforced plastic (FRP) jackets (shells) in concrete columns depends on several parameters, including concrete strength, types of fibers and resin, fiber volume and fiber orientation in the jacket, jacket thickness, shape of cross section, length-to-diameter (slenderness) ratio of the column, and the interface bond between the core and the jacket. In this paper effects of shape, length, and bond on FRP-confined concrete are studied. Square sections are shown to be less effective in confining concrete than their circular counterparts. Their effectiveness is measured by a modified confinement ratio that is a function of the corner radius and the jacket's hoop strength. Length effect in short columns of up to 5:1 is shown to be similar to ACI provisions for tied columns, i.e., 10% eccentricity and 20% strength reduction in pure compression. While chemical adhesive bond does not change the confinement effectiveness of the jacket, mechanical shear connectors can enhance the load-carrying capacity of the column by providing an effective load distribution mechanism.

The behaviors of simply and continuously supported beams reinforced with fiber reinforced polymer (FRP) materials are presented in this paper. The experimental testing program included seven simple rectangular beams and seven continuous T-section beams. Reinforcing bars and stirrups were made of steel, carbon, or glass fiber reinforced polymer (GFRP). It was concluded that the use of GFRP stirrups increased the shear deformation, and as a result deflection increased. Also, GFRP stirrups changed the failure mode from flexural to shear or flexural-shear, depending on the type of reinforcement bars (FRP or steel). Furthermore, the use of FRP reinforcement in continuous beams increased deformation. This increase remained small and acceptable at the service load level, but significantly increased near failure. While different FRP reinforcement arrangements were found to have the same load capacity as steel reinforcements in conventional beams, failure modes and ductility differed. Failure mode was governed by both the type of reinforcing bars and the type of stirrups. Additionally, the dowel effect influences the load carrying capacity of FRP reinforced continuous beams. A method for evaluating the ductility is presented. The ratio of absorbed energy at failure to the total energy, “energy ratio,” was used as a measure of ductility. Based on this definition, a classification of ductile, semiductile, and brittle behavior is suggested. The theoretical results obtained using the suggested method were substantiated experimentally. The continuous beams experienced higher “energy ratios” than did simple beams.

Fiber reinforced polymer (FRP) materials are continuing to show great promise for use in strengthening reinforced concrete structures. These materials are an excellent option for use as external reinforcing because of their light weight, resistance to corrosion, and high strength. Externally bonded FRP sheets have been used to increase moment capacity of flexural members and to improve confinement in compression members. Investigations into the use of externally bonded FRP sheets for shear strengthening have also been conducted and have been shown to be viable. The objectives of this study were to review the current research on shear strengthening with FRP and propose design algorithms to compute the contribution of FRP to the shear capacity of reinforced concrete flexural members. Methods for computing the shear capacity based on the stress level that causes tensile fracture of the FRP sheet (at times this stress may be less than ultimate due to stress concentrations) and based on delamination of the sheet from the concrete surface are presented. Areas of research that have the potential for further development are also discussed.