Seismic Strengthening of Unreinforced Masonry Piers with Steel Elements

Abstract

The system of wall piers and spandrels, created by openings, largely controls the inplane lateral resistance of the wall. For the “rocking-critical” masonry wall piers, the overall hysteretic behavior can be significantly improved by installing a steel framing system consisting of vertical and horizontal elements around the wall — without any braces. Vertical elements provide the necessary hold-down forces to stabilize the rocking piers. The stabilized piers “rocked” through a number of cycles of large displacements (up to 2.5%) without crumbling or shattering, displaying a ductile response. The strengthened system has excellent strength, stiffness and ductility, despite the brittleness of the masonry because of considerable load sharing between the existing masonry and the added steel elements. FE analyses predicted the envelope response of the rocking piers accurately. A simple mechanics based model was developed to predict the load-deflection behavior of a stabilized rocking pier which can be used to design the strengthening system more rationally.