SR258 Critical properties of mortar for good seismic performance of brick veneer (2011)

The quality of brick veneer construction has improved markedly in recent years, with requirements for the ties to be screw-fixed to the timber framing and with the advent of lighter bricks with vertical penetrations. This is the sixth BRANZ investigation of a series looking into the seismic performance of brick veneer. This study examines the effects of mortar type and the quality. The interaction of the factors that affect brick veneer performances that are relevant to this project are also summarised.

Recent cyclic displacement tests and shake table tests on full-scale buildings have shown that modern single and two-storey brick veneer New Zealand houses, constructed using good mortar, will perform very well under both in-plane and out-of-plane testing. The veneer can be relied on to carry a significant portion of the seismic design load.

In this project, mortar compression strength and the mortar-to-brick bond strength were measured using both mortar taken from building sites and laboratory mixes (but made under site conditions to a desired workability by an experienced masonry tradesman). The strength of a bond between brick tie and mortar was also measured in the laboratory. The laboratory mixes were designed to cover the range of mortar being used on New Zealand sites.

The seismic performance of brick veneer walls constructed using a selected set of the laboratory mixes was determined by shake table testing. By examining which walls gave good performance and which gave unsatisfactory performance, minimum mortar properties to ensure good seismic performance were determined. Good seismic performance was defined as the veneer being able to resist the design level earthquake without any masonry shedding.