Seismic behaviour and design code provisions for predicting the capacity of ductile slender reinforced masonry shear walls

Ductile slender reinforced masonry shear walls (DSRMSWs) designed and detailed according to modern seismic design provisions, such as those prescribed by the Canadian masonry design code CSA S304-14, are expected to demonstrate ductile performance when subjected to earthquake effects. These walls have shown good energy dissipation characteristics similar to ductile slender reinforced concrete (RC) shear walls and are used as the seismic-force-resisting system (SFRS) for contemporary buildings in Canada and other countries. These walls are usually slender, with clear height-to-thickness (h(u)/t(w)) ratios that can exceed 20, and height-to-length (h(u)/L-w) aspect ratios usually greater than 1.5. Experimental studies have shown that the response of DSRMSWs subjected to in-plane simulated seismic loading is often affected by multiple failure modes. The initial failure mode often transitions into other failure modes that may govern the response of the DSRMSWs at high ductility demand levels. It is essential that designers understand the prominent DSRMSW failure modes and how they interact with one another to ensure the adequate seismic performance of DSRMSWs. Seismic design and detailing provisions for DSRMSWs contained in international design codes aim for a ductile, well-controlled flexure-dominant seismic response and preclude the occurrence of undesirable shear-dominant failure modes. However, the interaction between various failure modes is usually only accounted for implicitly. The capacity predictions for DSRMSWs based on in-plane ductile failure modes vary between different masonry design codes in terms of the methodology, complexity level, and material resistance factors. This paper provides a detailed comparison of the capacity predictions from the following international codes: CSA S304-14 (Canada); TMS 402/602-16 (USA); NZS 4230:2004 (New Zealand); and Eurocodes 6 and 8 - EN 1996-1-1:2005/EN 1998-1:2004 (EU). The assessment focuses on the following six in-plane flexure-dominant failure modes: (i) ductile flexure, (ii) shear-flexure, (iii) sliding, (iv) toe-crushing, (v) rocking/bond-slip, and (vi) lateral instability, observed in a series of eight full-scale, fully-grouted DSRMSW specimens tested under reversed cyclic loading. The specimens were characterized by varying h(u)/L-w and h(u)/t(w) ratios, the amount and distribution of reinforcement, cross-sectional shape, axial stress level, and type of cyclic loading protocol. The results of this study provide a systematic comparison of the DSRMSW capacity predictions from the different international masonry design codes.