What ductility value should be used when assessing unreinforced masonry buildings

Abstract

There has been much discussion regarding the appropriate values of structural ductility factor, structural performance factor, and equivalent viscous damping coefficient to be used in the assessment of unreinforced masonry (URM) buildings in New Zealand and Australia. The New Zealand Society for Earthquake Engineering 2006 guidelines proposes a ductility factor of 1.0 to be used along with a damping coefficient ratio of 15%. A draft guideline recently developed by researchers from the University of Auckland suggests that a ductility factor of 2.0 and damping ratio of 5% is more suitable. Elsewhere in the world, other researchers have made recommendations regarding these topics. Furthermore, the Canterbury Earthquakes Royal Commission has recently recommended this topic receive further attention. Different alternatives are evaluated by conducting Nonlinear Static (pushover) analyses for a representative URM structure. A comparison is made to previous experimentally and analytically derived equivalents. Following this research, a recommendation is made regarding values which should be used in future design. Results of a simplified plane stress analysis for this building are also presented and compared to the results obtained from the pushover analyses.