Seismic retrofit of Italian pre-‘70 case-study RC buildings by solving shear failures: code-compliant assessment and economic effort

Abstract

Existing reinforced concrete (RC) buildings designed for gravity loads only (GLD) are widespread worldwide even in seismic prone areas, including Italy, showing a significant vulnerability to shear failures under seismic shaking.

This work focuses on the seismic upgrading of pre-70 GLD buildings, by means of solving tensile shear failures of primary elements. Its technical effectiveness, depending on building height and seismic hazard throughout the Italian country, is also evaluated.

RC GLD moment resisting frames case-study buildings, with the same floorplan, and a number of stories ranging from 2 to 6 are considered. Seismic assessment is performed using nonlinear static analyses, according to the current Italian technical code. Then, strengthening interventions, based on fibre reinforced polymers wrapping for beams/columns and pre-stressed steel strips for beam-column joints, are designed aiming at solving the detected tensile shear failures at Severe Damage Limit State. Post-strengthening seismic capacity is compared with seismic demand throughout the Italian country, finding that 2- and 3-storey buildings can always reach 100% of safety level of a newly designed building. This condition is attained, on average, also for 4- to 6-storey buildings only in sites where the peak ground acceleration demand is lower than 0.15 g. In the other sites, the 60% of the safety level of a newly designed building can be achieved, on average.

Lastly, the economically feasibility of the adopted strengthening strategy is examined through its comparison with the most recent grant opportunities to mitigate seismic risk of buildings funded by Italian government.