Design and evaluation of seismic strengthening techniques for reinforced concrete frames with soft ground story

This paper presents a design procedure and analytical evaluation of two strengthening techniques to improve the seismic performance of the existing non-ductile RC frames with soft-story at the ground story level. The first technique, termed as column retrofit (CR), uses only partial steel jacketing (or caging) to enhance the lateral strength and plastic rotational capacities of the deficient columns at the ground story level. The later technique, termed as full retrofit (FR), considers the aluminum shear links as supplemental energy dissipation devices in addition to the strengthened ground story columns. Steel collector beams and chevron braces are used to transfer the lateral load from the RC frame to these dissipating devices. Performance-based plastic design approach is used to proportion various elements of the strengthening techniques. Nonlinear static and dynamic analyses are carried out to evaluate the performance of the existing and the strengthened frames. The main parameters investigated are (a) interstory drift, (b) residual drift, (c) yield mechanism, (d) energy dissipation, and (e) lateral strength. The FR frame effectively controlled the drift response by avoiding the soft-story collapse because of the significant energy dissipation in the shear links. Moreover, the FR frame achieved the desired yield mechanism without exceeding the design target drift level.