Seismic Retrofit of Reinforced Concrete Shear Walls to Ensure Reparability

Many reinforced concrete (RC) buildings built before the adoption of modern seismic codes in high seismic regions need to be retrofitted to perform well in a major earthquake. This study introduces a new retrofit method for code-deficient reinforced concrete shear walls that are vulnerable to non-ductile failure modes due to improper detailing or lack of well-confined boundary elements. The retrofit method combines weakening of shear walls with a base cut and self-centering of the walls with the addition of external unbonded post-tensioned strands. The retrofitted walls are expected to have controlled rocking behavior as opposed to the original walls that undergo shear and flexure and are expected to have minimized damage caused by earthquakes resulting in shorter repair times and lower repair costs. Three-dimensional finite element models of pre- and post-retrofit shear walls under cyclic lateral loading were used to identify working details of the retrofit method. To transfer shear at base and minimize shear slip, shear keys and other non-straight wall base cut shapes were explored. The contribution of shear, flexure, and rocking to the global response were measured and compared for pre- and post-retrofit walls. Results of analysis showed that rocking is the governing behavior for the retrofitted walls and contribution of shear to displacements decreased due to retrofit. Changes in residual displacements, energy dissipation, strength, and secant stiffness due to retrofit were documented.