Region-level seismic risk assessments have estimated the economic and life-safety impact of a large magnitude earthquake in the US New Madrid Seismic Zone at over $300 billion dollars and close to 100,000 casualties, respectively. Seismic rehabilitation of structures has been a research priority for the last 2 decades to address safety of older structures. Non-ductile reinforced concrete (RC) frame structures have been a focus of much of this research due to their prevalence in the Central and Eastern US. However, prior research and existing solutions have several limitations. Regarding experimental research, most prior tests fail to capture the interaction of multiple components in a full structural system, or the studies involve reduced scales that do not appropriately replicate critical resistance mechanisms. For existing retrofit solutions, these have been effective in increasing life-safety for occupants but they typically sustain levels of damage that render them irreparable, which fails to address economic impacts. In addition, their construction is typically invasive, which may disrupt building occupants and operations. Thus, this research attempts to address these limitations by proposing a retrofit solution that is reusable, self-centering, and has a minimally invasive construction and installation procedure. The retrofit was tested dynamically in a full-scale system to overcome the limitations of prior, reduced-scale experimental testing research. Experimental and analytical results showed that the SMA bracing device effectively reduced inter-story drifts compared to a non-retrofitted frame. The retrofitted test structure showed minimal damage at demand levels that would have collapsed the original structure. Numerical results indicate that the SMA brace retrofit significantly reduces the probability of exceeding all damage states at given spectral accelerations. Most notably, the probability of exceeding the complete damage state was reduced from 50% (as-built) to less than 2% (SMA brace retrofit) at a 0.78g spectral acceleration. The design and assembly steps for experimental testing suggest that this retrofit can be beneficial in practical applications where disruptions to building occupants are a concern. The retrofit design procedure, its behavior and response to all test loads, a qualitative evaluation of the design method, seismic risk performance assessment, and implications on future research are discussed.
Dr. Reginald DesRoches
Dr. Roberto T. Leon (Virginia Tech)
Dr. C.S. Walter Yang
Dr. David W. Scott
Dr. Richard W. Neu (ME)