Shear failure of structural elements such as beams and columns is considered as a brittle failure. Accordingly, the design standards provide conservative equations for determining shear strength to ensure to delay of this abrupt failure. In this regard, the AISC 360 Standard provides equations to determine the shear strength of encased composite members considering the steel contribution, the reinforced concrete contribution, and the strength of the steel section in combination with the transverse reinforcement. The AISC 360 conservatively ignores the combination of the shear strength of steel section and reinforced concrete to determine the shear strength of encased composite members due to insufficient research.
This study investigates the shear behavior of encased composite (EC) columns experimentally and numerically. Short EC columns in which their behavior is governed by shear are tested considering several design variables, including the concrete compressive strength, the steel ratio, the shape of the steel core, the ratio of longitudinal reinforcement, the transverse reinforcement spacing, and the level of the composite action. Failure mode, the crack pattern, the load-displacement response, the nominal shear strength of EC columns, the yield condition of steel core, and the effects of key variables on the shear strength of EC columns are presented and discussed. The results of this study show that the exclusion of steel section or reinforced concrete contribution leads to a significant underestimation of the shear strength of encased composite members. Out of the considered design variables, the transverse reinforcement ratio, concrete compressive strength, and steel core ratio are the most influential variables affecting the shear behavior of EC columns.