Seismic Evaluation of a Nonductile Soft-First-Story RC Building Retrofitted with Steel-Braced Frames

AbstractA large number of soft-first-story reinforced concrete (RC) buildings have been significantly damaged or completely collapsed in past earthquakes. In this paper, the seismic performance of a nonductile soft-first-story RC building retrofitted with eccentrically steel-braced frames was evaluated. At first, the results of the previous experimental investigations on the RC frame retrofitted by the steel-braced frame were used to calibrate the analytical results obtained by the open system for earthquake engineering simulation software. The modeling of the flexural behavior of the RC and steel members were accomplished by the well-known fiber model technique. Moreover, the shear and axial failures of the RC members were taken into account. Secondly, the intended building was planned to be retrofitted by five retrofit strategies. Four retrofit strategies are strength type, and one retrofit strategy is strength–ductility type upgrading. Nonlinear static and dynamic analyses were implemented to evaluate the seismic performance of the nonductile soft-first-story building and the retrofitted ones. The results showed that, in the strength-type retrofit, because of lack of required ductility, premature shear and/or axial failures of RC columns are more likely to occur than those failures in nonretrofitted ones. Also, it was found that the variation of the axial and shear forces in the boundary RC columns and the slenderness ratios of the steel braces are the critical factors influencing the seismic responses of the buildings retrofitted using the steel-braced frames.