Dynamic behaviour of seismically retrofitted clay brick masonry cavity walls

Abstract

Loadbearing cavity (aka hollow) wall construction is a form of masonry wall construction where two leaves of unreinforced clay brick masonry (URM) are separated by a continuous air cavity and are interconnected using some form of tie system. An informative background to URM cavity walls is presented herein, including historical development, typical construction details, and observed earthquake damage. Shake table experimental testing of five walls that closely mimicked in-situ conditions for the most commonly encountered URM cavity wall arrangements was undertaken and the test methodology and results are presented herein. Mortar strength, retrofit type screws and spacing were the parameters investigated. Cavity walls were tested both in as-built and retrofit condition, considering the application of screw ties in the wall cross section and the combination of both timber strong backs and screw ties as retrofit intervention. During the test, cracking appeared mainly in the top quarter of the wall height, and differential movement of the two wall layers was observed only in as-built, showing the low strength of original ties. The use of screw ties lead to an improvement in seismic capacity of 30% to 60% depending on retrofit tie spacing. The performance of retrofitted walls further increased with the addition of timber strong backs, attaining a PGA two times higher the walls retrofitted using screw ties only.