ALTERNATIVE RETROFIT STRATEGIES FOR SEISMIC RISK REDUCTION: STUDYING THE EFFECTIVENESS OF LOW-DAMAGE EXTERNAL EXOSKELETONS

Abstract

Recent earthquakes occurred worldwide have further highlighted the high vulnerability of existing Reinforce Concrete RC buildings built prior the enforcement of modern seismic codes. For this reason, such buildings are generally expected to be 'earthquake prone'. As a result, in recent decades, an unprecedent research effort has been undertaken to develop efficient and cost-effective retrofit strategies able to improve safety, reduce the expected losses related to earthquake damage, and, in general terms, enhance the resilience of the existing building stock and the overall community. More specifically, both local retrofit interventions (e.g., based on the use of Fiber Reinforced Polymers, FRP, concrete or steel jacketing, etc.) as well as global ones (e.g., based on the use of shear walls or external exoskeletons) have been developed. The main outcome of this work is to evaluate the effectiveness and thus support the attractiveness of low-damage exoskeletons when compared to other retrofit strategies. The low-damage technology herein considered is the PREcast Seismic Structural Systems (PRESSS) developed in the 1990's. In a first phase, a pre-1970 RC buildings has been selected as a case study building and assessed in terms of seismic performance considering both non-linear static (pushover) as well as more refined non-linear dynamic methods. Using results, the Safety-Index as well as the Expected Annual Losses (EAL) have been evaluated, and suggestions are provided to improve the simplified procedures currently available for the calculation of the latter index (EAL). Finally, alternative retrofit strategies have been implemented for the seismic retrofit of the as-built configuration, and the push-over based method has been used to calculate the Safety-Index as well as the Expected Annual Losses of the retrofitted configurations. The results of this work confirm the improved performance of low-damage exoskeletons when compared to similar traditional global strategies and even further when compared with local strategies.