Journal of Composites for Construction

In the field of reinforced-concrete (RC) structures, the use of fiber reinforced plastic rebars (FRP rebars) as an alternative to the steel reinforcements appears very promising, especially if such structures are exposed to corrosive environments. However, a better understanding of the mechanical behavior of FRP reinforcements—in particular bond behavior—is needed in order to use them for practical purposes. For this reason, in the last few years a number of tests on several types of FRP rebars has been conducted in order to evaluate the interaction phenomena between FRP rebars and the concrete matrix and to evidence behavioral differences with respect to the deformed steel rods. In this paper a state-of-the-art report on the bond of FRP bars to concrete is presented. Numerous tests are analyzed to better understand bond mechanisms and the influence of type of fiber, outer surface (shape and type of matrix), and other significant parameters (i.e., confining pressure, bar diameter, compressive concrete strength) on bond performances. Furthermore, some analytical models of bond-slip behavior are examined to assess their adequacy to reproduce the experimental bond behavior. In particular, the investigation focuses on the reliability of the well-known model by Malvar (the first one dedicated to FRP reinforcements) as well as on the model by Eligehausen, Popov, and Bertero, developed for steel reinforcements but successfully applied to FRP ones. In addition, the effectiveness of two analytical formulations proposed by the authors, the first one representing the ascending branch of the bond-slip curve and the second the entire curve, is demonstrated.

The development, the validation, and the implementation of a new seismic retrofit system for reinforced concrete columns are described. The column jacketing system consists of continuous carbon fiber prepreg tows wound in an automated fashion onto existing circular or rectangular concrete columns, with variable jacket thickness along the column height based on experimentally validated design models. Jacket design criteria for various seismic column failure modes are described and detailed examples show their application to retrofits of columns with circular and rectangular column geometry, different reinforcement ratios, and detailing. The carbon jacket designs are validated through large-scale bridge column model tests and are found to be just as effective as steel shell jacketing in providing desired inelastic design deformation capacity levels. Furthermore, it is shown that the retrofit criteria and guidelines are also applicable to other advanced composite jacketing systems with appropriate considerations for differences in mechanical properties of the materials system, installation and curing technology, as well as jacket discontinuities.

Experimental data obtained from strengthened, precracked, reinforced concrete (RC) specimens are presented together with the results of material characterization. Strengthening was attained with the adhesion of carbon fiber-reinforced plastic (CFRP) sheets to the concrete surface. The CFRP was applied as in situ (i.e., working under the beam). Several variables were investigated, including: two CFRP material systems, two concrete surface preparations, two RC cross sections, and the number and location of CFRP plies. For two specimens, the presence of applied load (simulating the total service load) as well as external prestressing during the adhesion of the CFRP reinforcement, were investigated. It is shown that the effect of CFRP strengthening was considerable, but the effect of some of the tested variables was modest. An existing analytical model has been extended to simulate the load-deflection behavior as well as the failure mode of the precracked RC specimens. Different failure mechanisms from ductile to brittle were simulated and verified, adopting the mechanical properties of the constituent materials obtained via standard tests or using a simple test for the concrete-adhesive interface.

Bolted connections are most suitable for civil engineering applications since they are easy to inspect, have low construction costs, are easy to manufacture, and offer reliability compared with bonded joints. However, using advanced composite material members with unidirectional fibers could create a state of high stress concentration around the bolt holes due to their inherent geometric discontinuities. Due to a lack of information and the need for understanding the mechanism of these connections, a comprehensive experimental and analytical investigation was conducted at the University of Manitoba to study and to determine the behavior of bolted connections using glass fiber-reinforced plastic (GFRP) structural members. Based on the test results and observed behavior, a design procedure is introduced that accounts for the material orthotropy, pseudoyielding capability, and other factors that influence the connection behavior. The proposed rational model is capable of predicting the ultimate capacity of the multibolted connection and the failure mode. The generic nature of the proposed design guidelines can be applied to a multitude of composite material systems.