Partially-restrained steel frame filled by RC infill walls with openings: Tests and numerical simulation

Abstract

To evaluate the influence of door and window openings on the seismic performance of partially restrained (PR) steel frames infilled with reinforced concrete (RC) walls (PSRCW), this study conducted by cyclic loading tests and numerical simulations systematically investigated the effects of opening ratio and opening location. Two 1/3-scale, single-span, two-storey PSRCW specimens with door and window openings were designed and tested, accompanied by the development of 20 finite element models for parametric analysis. Experimental results revealed that the presence of openings interrupted the shear transfer path within the RC infill walls, significantly reducing the lateral load-carrying capacity and initial stiffness of PSRCW structure. Specifically, the door and window openings led to strength reductions of 24.6 % and 29.5 %, and initial stiffness reductions of 77.0 % and 65.0 %, respectively. When the drift ratio exceeded 2 %, the primary energy dissipation mechanism transferred from shear energy dissipation of the RC wall to that of the steel frame. This transition was primarily governed by the bending response of the middle steel beam, resulting in maximum equivalent damping ratios of 0.23 and 0.17 for the door and window specimens, respectively. Compared to the window opening, the door opening caused a more pronounced weakening of the concrete confinement on both sides of the middle beam. It was therefore recommended that PSRCW structures with door openings adopted some effective measures such as web stiffeners, increased the beam section stiffness, or enhanced local confinement from the adjacent RC walls to improve seismic performance. Finite element analysis indicated that the opening ratio was the dominant factor affecting the seismic performance of PSRCW structures with openings. Limiting the opening ratio to within 25 % could moderately release the lateral stiffness of the RC wall, thereby achieving optimal ductility while maintaining sufficient load-bearing capacity. As deformation increased, the shear-resisting mechanism gradually transferred from wall-dominated to frame-dominated mode. When the drift ratio reached about 3 %, the lateral stiffness reduced to only 1/11 of its initial value, with the residual stiffness being almost entirely provided by the surrounding steel frame. Although the opening location produced the limited influence on load capacity, stiffness, and shear distribution, it played a significant role in regulating ductility. The ductility performance followed the hierarchy: top-positioned openings performed better than center-positioned ones, which in turn outperformed eccentric layouts. Therefore, eccentric openings should be carefully considered in design to improve the deformation capacity of the PSRCW structure.