Bracing capacity of partially grouted concrete masonry walls with openings

Technical Abstract

In 1999 an updated version of NZS:4229, the non-specific design code for concrete masonry, was released. The bracing capacity values in this code were derived from wall tests conducted at the University of Auckland, of which only two considered the performance of walls with openings. Furthermore, an important reinforcement detail adopted in testing of these two walls differed from that later specified in NZS 4229:1999. As part of a parallel research project considering the shear strength of concrete masonry walls a third wall, having an opening and reinforcement detailing complying with NZS 4229:1999, was recently tested. This wall did not achieve the bracing capacity prescribed in NZS 4229:1999, and subsequent assessment has indicated that the existing design standard may be unconservative in its treatment of walls with openings.

A parallel issue is the influence which shrinkage control joints have on bracing capacity. NZS 4229:1999 prescribes a procedure to account for shrinkage control joints, but this detail has never been verified through structural testing. Recently, concerns have been expressed regarding the manner in which foundation details were modelled in previous tests, and whether foundation failure may develop in structures designed to NZS 4229:1999, when subjected to an earthquake. Finally, it has become evident that both masonry and other forms of concrete walls typically have a hysteretic form different from that assumed when formulating the design spectra in NZS 4203:1992. These issues will also be addressed in this research programme.