Earthquake resisting potential of an innovative HCW system with laser-cut open-to-CHS connections

Abstract

Although conventional reinforced concrete (RC) or hybrid coupled wall (HCW) structures have been used for a number of years as seismic resistant system thanks to their lateral strength, stiffness, and energy dissipation characteristics, some drawbacks such as expensive detailing, costly foundations, heavy superstructure, difficult restoration works etc. have limited their potential from a structural and an economic perspective. To minimize these drawbacks and make further advancement, an innovative HCW system is proposed in this study consisting of a single RC wall coupled with two steel circular hollow section (CHS) columns via steel coupling links. The RC wall carries almost all the horizontal shear force while the overturning moments are partially resisted by an axial compression-tension couple developed by the two CHS columns rather than by the individual flexural action of the wall alone. The primary objective in designing this system is ensuring a "fuse"-like behaviour of the steel coupling links, i.e. concentrating the seismic damage in the coupling links while avoiding any damage in the RC wall as well as in the connections between the links and the primary vertical elements (RC wall and CHS column). Multiple case studies with varying coupling ratios are investigated through nonlinear pushover analyses to verify the above-mentioned design objective. Different configurations are proposed to achieve an efficient link-to-RC wall composite connection, which can ensure the "fuse"-like behaviour of the coupling link. The steel coupling links are connected to a steel profile either partly embedded in the RC wall or passing through it. The connection zone is designed in such a way that the damage always occurs in the steel links (fuses) prior to any damage in the RC wall in general and in the connection zone in particular. Case studies have therefore been designed based on the force demands obtained from the global structure and further examined through detailed pushover analyses to highlight their applicability in the HCW systems. A suitable link-to-CHS column connection is also necessary to ensure the "fuse"-like behaviour of the coupling links. However, the conventional open-to-CHS column connections, with beams (or links) directly welded on the tube, are often prone to severe local distortion of the CHS column surface, premature flange fractures and excessive welding quantity. To avoid such limitations, this paper introduces different types of innovative I-beam-to-CHS-column "passing-through" connections. These connections consist of coupling links connected to an I-beam stub (or vertical and horizontal plates) entering the CHS column through laser-cut slots. Standard design guidelines have been developed in accordance with Eurocode provisions for gravitational and seismic loading scenarios to calculate the ultimate joint resistances. Case studies have therefore been designed based on the global demands and further examined through detailed pushover analyses in order to validate their compatibility to the HCW systems. Based on the design case studies, the primary design objective was achieved in both cases-the global and local perspective. Yielding was attained in the coupling links prior to any damage in the RC wall, CHS columns, and the connections. Encouraging validations are therefore presented regarding the earthquake resistant potential of the HCW system and the applicability of the innovative connections.