Experimental and Analytical Research on Seismic Behavior of Circular‐in‐Square ECC‐Filled High‐Strength Double‐Skin Steel Tubular Columns With Out‐of‐Code <scp><i>B</i></scp>/<scp><i>t</i></scp> Ratios

ABSTRACT By utilizing high‐strength (HS)/performance materials such as HS steel and engineered cementitious composite (ECC) within concrete‐filled double‐skin steel tubes, the further development of a lightweight and HS structural system can be achieved in response to the growing trend of prefabricated buildings. Nonetheless, the seismic safety of HS steel is compromised by various uncertainties such as the elevated width‐to‐thickness ( B / t ) ratio and the risk of fracture or fatigue failure. This study investigates the seismic performance of circular‐in‐square ECC‐filled HS double‐skin steel tubular (EFHDST) columns with B / t ratios exceeding the specified values in T/CCES 7‐2020 through quasistatic testing and analytical research. A typical failure mode observed involves the fracture and buckling of the outer steel tubes, along with the crushing of ECC. The ductility experiences a significant reduction with an increase in the hollow ratio or axial compression ratio. Following this, a finite element analysis was carried out, including a parametric investigation to elucidate the failure mechanism and the impact of geometrical‐physical parameters. It was found that the lower steel yield strength of the inner steel tube can be utilized due to its minimal influence on stiffness and load‐bearing capacity. Moreover, imposing limitations on the high axial compression ratio or hollow ratio is imperative to ensure satisfactory seismic performance. In the domain of EFHDST column analysis, a comprehensive restoring force model has been developed to simulate the seismic response, integrating the tensile properties of ECC into an analytical framework for evaluating the moment‐resisting capacities. This investigative effort into EFHDST columns provides an advanced procedural resource for its practical engineering implementation.