Life cycle cost analysis of low ductility r.c. frame buildings retrofitted by modern retrofit techniques

Many reinforced concrete (RC) frame buildings designed before the introduction of modern seismic codes are highly vulnerable to seismic actions due to their reduced ductility capacity. Passive control systems have emerged to be efficient tools for the seismic retrofit of low ductility RC frames and help to reduce economical losses in consequence of seismic events. Since funds to investment for seismic vulnerability reduction may be limited, a risk-based life cycle cost analysis approach is required to evaluate and compare the cost effectiveness of different mitigation strategies. In this paper, several retrofit methods are compared. In particular, superelastic Shape Memory Alloys braces or Buckling Restrained Braces are investigated for their effectiveness in reducing seismic vulnerability and losses. A benchmark two-dimensional reinforced concrete frame with low ductility capacity is considered as a case study. The frame is designed for gravityload only and does not comply with modern seismic code requirements. The retrofit devices are designed in a way to obtain the same base shear capacity for the two retrofitted frames. The study to evaluate the effectiveness of the retrofit is conducted by a probabilistic approach where the seismic record-to-record variability is modeled by using a suite of recorded ground motions, and nonlinear time history analyses are performed to generate samples of the demand. Fragility curves are generated for slight, moderate, extensive and collapse limit states. Finally, the comparison among the different retrofit methods is conducted by performing a Seismic Life Cycle Cost Analysis and by evaluating the loss saving for each method.