Experimental study on seismic performance of reinforced concrete columns with unilateral wing walls

Excessive lateral deformation of frame structures under seismic action leads to overall dynamic instability. This means that the stiffness of the structures need to be increased. Hence, a less wall frame structure is formed by retrofitting reinforced concrete columns with wing walls (RCCWWs) at specific critical positions of the structure. RCCWWs are widely used in multi-storey and high-rise buildings due to the advantages of relatively flexible layout, higher space utilization, sufficient stiffness provided by wing walls. Nevertheless, the failure mechanism and seismic performance of RC columns would be changed by supplementing wing walls. Past studies and current Chinese code have mainly focused on the application of wing walls to the enhancement of stiffness in the elastic stage of the structure, ignoring crucial factors that affecting the plastic behavior of RCCWWs under cyclic loading, including the lengths of the wing walls, the lengths of boundary elements and stirrups ratio of boundary elements. This paper provides a comprehensive experimental study on the seismic behavior of six RCCWWs specimens which constructed and tested under cyclic loading, examining the effects of the three key factors mentioned above. The damage evolution, the failure mechanism and failure characteristics of RCCWWs is revealed. Test results indicated that RC columns and wing walls can operate better in concert. Simultaneously, the asymmetry of the cross-section causes the damage primarily at the wing walls tips firstly, with less damage observed in the RC columns. RCCWW obviously underwent two-stage failure, the wing wall first failed and lost its bearing capacity, then the RC column held the load individually and dissipated energy until it failed. It is found that the length of the wing wall has extraordinarily significant effect on the bearing capacity and energy dissipation capacity. Increasing the wing walls lengths form 500 mm to 700 mm leads to positive and negative bearing capacity improved by 63 %∼74 % and 16 %∼38 %, respectively. And positive and negative energy dissipation capacity improved by 6 %∼37 % and 2 %∼44 %, respectively. Note that the specification limits of lateral drift ratio (1/50) for frame structures in GB50010-2010 are not applicable to less wall frame structures instead, a more stringent criterion (1/120) is necessary. Finally, a method for estimating the bending moment capacity of RCCWWs is proposed.