Experimental testing of RC shear wall seismic retrofit using selective weakening, self-centering and Ultra High performance concrete

Traditional retrofit methods often focus on increasing the structure's strength, stiffness, or both. This may increase seismic demand on the structure and could lead to irreparable damage during a seismic event. This paper presents a retrofit method, integrating concepts of selective weakening and self-centering (rocking) to achieve low seismic damage for non-code compliant reinforced concrete shear walls. The proposed method involves converting traditional cast-in-place concrete shear walls into rocking walls, which helps to lower the shear demand, while allowing re-centering. Two large-scale lateral load tests were performed to validate the retrofit concept on a concrete shear wall designed according to pre-1970s standards. The design parameters investigated were amount of energy dissipating reinforcements and confinement enhancement. Two different methods using Ultra High Performance Concrete (UHPC) were investigated to provide additional confinement to boundary elements of older shear walls. Observations from the tests showed minimized damage and enhanced recentering in the retrofitted wall specimens. Use of UHPC in the boundary elements of the retrofitted walls provided additional confinement and reduced damage in the rocking corners.