Gapped-Inclined Braces for Seismic Retrofit of Soft-Story Buildings

Abstract

Although soft-story mechanisms are generally undesirable for the seismic response of building structures, they provide potential benefits caused by the isolating effect they produce for the stories located above. In this paper, an approach for enhancing the seismic response of soft-story structures is proposed that takes advantage of the positive aspects of their response while mitigating the negative ones. To this end, an additional gapped-inclined brace (GIB) is introduced to reduce the impact of P-Delta effects on the displacement demands and to increase the deformation capacity of existing columns in soft stories without significantly increasing their lateral resistance. The mechanics of the proposed system are first defined, and theoretical relations and numerical models are then derived to verify the response. The cyclic behavior of a single-degree-of-freedom single-bay RC frame is then investigated numerically to illustrate the effect of the retrofitted system on the global response of a structure. The analytical results indicate that the hysteretic response of the retrofitted system is highly improved in terms of the energy dissipation and the residual deformation while not significantly increasing the overall strength of the structure. Although the equations governing the response of the system are derived for a single story, the concept is primarily intended to be applicable to multistory buildings.