Test and analysis of ECC-NC composite column

The composite column, which consists of an external engineered cementitious composite (ECC) jacket and internal normal concrete, is a promising approach improving seismic performance. However, the cyclic behavior and design methodology have not been investigated extensively. This study experimentally investigates the cyclic performance of the composite column, focusing on variables such as the ECC jacket thickness, axial load ratio, etc. The cracking pattern, hysteretic response, and failure modes are observed and analyzed. The composite column exhibits improving cracking control and damage tolerance capabilities, with peak force and deformability 1.15 and 1.25 times higher than those of the RC column, respectively. Using a thicker ECC jacket may not obviously enhance the bearing capacity and may potentially diminish the ductility. A numerical model was developed and validated, followed by a comprehensive parametric analysis to elucidate the underlying impact mechanisms. A formula for determining the optimal thickness of the ECC jacket is proposed to balance the bearing capacity and ductility of composite columns. Typically, when the compressive strength of ECC is within the range of 2.0 to 3.0 times the concrete, the thickness of the ECC jacket decreases linearly from 0.25 to 0.15 times the side length of the column.