Prediction of shear strength of FRP reinforced concrete beams using fuzzy inference system

The objective of this paper is to develop a more accurate and reliable alternative method using fuzzy inference system (FIS) to predict the shear strength of FRP-reinforced concrete beams. Such an accurate model, which can lead to an economical use of FRP reinforcement, is in high demand since existing design provisions for shear capacity of FRP-RC beams are either very conservative or even inadequate mainly due to two factors. Firstly, the current design codes follow the conventional assumption of superposition of concrete plus stirrup contribution to the shear strength, hence ignoring any interaction between shear resisting mechanisms. Secondly, the current design guidelines simply assume that some modified versions of the shear design equations which are empirically derived for steel-reinforced concrete beams can be easily extended to cover FRP-RC beams although the guidelines vary greatly in the manner they modify the equations. Given very different properties of FRP as compared to those of steel, such an assumption, however, needs to be examined and validated. To relax both of these assumptions, the FIS approach offers an attractive solution because it does not require a priori information. As a result, the proposed FIS model compares favorably with a large data base containing the test results of 197 FRP-RC beams assembled from literature. Moreover, the proposed FIS model outperforms the latest design provisions for shear strength of FRP-RC beams, namely ACI 440-06 and CSA S806-02. Also, a special attention is paid to differentiate between shear-compression mode and shear-tension mode of failure, which are the two common types of shear failure for FRP-RC beams with FRP stirrups. In light of the proposed FIS model, modifications to the shear-compression resistance provided by the considered design guidelines are recommended.