Experimental Verification of Load-Bearing Capacity of FRP Bars under Combined Tensile and Shear Forces

Abstract

In recent decades, the number of applications of fiber-reinforced polymer (FRP) reinforcement for concrete has significantly expanded. This fact is mainly due to the FRP reinforcement cost competitiveness, the increasing availability of design provisions, and due to the advantageous physical-mechanical and chemical properties of this composite material, which open up new possibilities for the design and implementation of extremely durable elements. Currently, the most commonly used types of reinforcement bars are those containing glass FRP (GFRP) or basalt FRP fibers, which is mainly the result of their favorable price and high resistance to aggressive environments. The use of composites in construction is wide-ranging: it is possible to apply FRP bars not only in the design and strengthening of concrete structures but also in the installation of shear dowels in concrete pavement, as rock bolts or as anchors for overhanging facade components. In the case of the design of load-bearing elements subjected to a combination of tensile and shear force, it is necessary to quantify their shear resistance and concisely describe the effect of the interaction of the tensile and shear force on the load-bearing capacity of the reinforcing element. This is a broadly addressed area as regards composite laminates and fabrics, but when it comes to FRP bars, there are very few available experimental results. For that reason, this research deals with the experimental testing and quantification of the influence of the interaction of normal and shear force. The behavior of GFRP bars from two different manufacturers, with three different diameters, different surface treatments, and mechanical characteristics, was experimentally verified. The findings are presented, a material failure curve is compiled, and the results are compared with those predicted according to the available relationship for composite laminates and von Mises theory. The presented research was driven foremost by industry demand concerning prestressed fiber-reinforced polymer (FRP) rock bolts. In situations where such bolts are used, the slippage and displacement of parts of rocks can be expected, and consequently, the creation of a shear plane in the prestressed anchor occurs. However, there are no existing methods for determining the load-bearing capacity of such loaded FRP bars. This paper aims to determine the short-term behavior of specimens under the combined action of tensile and shear forces (failure envelope) and to compare their load-bearing capacity with available relationships for steel and composite laminates.