Resilient Seismic Retrofit of Non-Ductile Code-deficient Reinforced Concrete Shear Walls

Presented by Sina Basereh, University at Buffalo


Description: This study presents an experimental investigation conducted to evaluate a new seismic retrofit method for reinforced concrete shear walls. One pre-retrofit and one post-retrofit wall were tested under quasi-static cyclic loading. The benchmark pre-retrofit shear wall was a non-ductile, code-deficient RC shear wall resembling pre-1970’s construction practices. The retrofitted wall utilized the concepts of selective weakening (through making a non-straight cut at the base) and self-centering (through adding external unbonded post-tensioning strands). The goal of the retrofit is to shift the failure of shear walls from brittle modes towards ductile modes and to reduce residual displacements for resiliency. The pre-retrofit wall was slender and carried an axial load equal to 6% of its axial capacity. The wall was designed with inadequate boundary element detailing (non-ductile) and insufficient transverse reinforcement in the web (code-deficient). The failure was a flexure/shear one. The retrofitted wall had the following changes compared with the pre-retrofit wall: 1) a cold joint at the wall-foundation interface (base cut) enabled rocking, which left 50% of the vertical reinforcement uncut for energy dissipation. 2) External post-tensioning, equal to 4% of the axial capacity of the wall, was added to enable self-centering. 3) The toes of the wall were confined using external steel plates. Lateral load, lateral displacement, vertical and horizontal reinforcing bar strains, concrete strains, and gap opening were recorded during testing. The pre- and post-retrofit walls were compared in terms of strength, stiffness, energy dissipation, residual displacements, displacement source and failure modes to evaluate the new retrofit method.