Experimental study on strengthening interior beam column joints in reinforced concrete structures using wing walls

Early damage to beam‒column joints during an earthquake can cause rapid degradation of structural seismic performance or even collapse of buildings. Installing reinforced concrete (RC) wing walls to one side of the columns of an existing RC frame structure, i.e., enlarging the column cross section, can not only improve the strength of the columns but also strengthen the beam-column joints. Quasistatic cyclic loading tests were conducted to validate the strengthening effectiveness for interior beam‒column joints by wing wall installation methods, and the strengthening mechanism was analyzed. Through theoretical analysis, a mechanical model and a simplified design method for strengthening interior beam-column joints using wing walls were proposed. The method focuses specifically on the contribution of the compressive wing wall to the joint strengthening effect. The test results revealed that for the non-strengthened benchmark specimen, damage was concentrated at the joint region. The strength of the strengthened specimen was largely improved, and an ideal beam-yielding mechanism was formed. A mechanical model and design theory for strengthening interior beam‒column joints was proposed, with which the maximum strengths and failure modes of the specimens with/without strengthening were evaluated. This study reveals that seismically deficient interior beam-column joints, which are subjected to shear forces up to twice those of exterior joints during seismic events, can be effectively strengthened using a wing wall installation method. A novel, simplified design approach is proposed for this strengthening technique, offering improved practicality and efficiency compared to existing methods.