Shake Table Testing of Seismically Restrained Clay-Brick Masonry Parapets

Abstract

Past seismic events, such as the 1994 Northridge earthquake, the 2001 Nis-qually earthquake, and the 2010/2011 Canterbury earthquakes, have repeatedly served as reminders of the hazards posed by unreinforced masonry parapets. Observed failure modes have included several cases where adopted retrofit techniques were inadequate to effectively secure parapets during earthquake-induced shaking. In response, this paper investigates, by means of shake table testing, the dynamic behavior of nine clay-brick masonry parapets with commonly used bracing systems and alternative securing techniques, such as post-tensioning and combined braces and vertical strong-backs. Seismic capacity was improved 6 to 8 times compared to the as-built postcracked condition. The addition of vertical strong-backs further improved the performance of braced parapets, with capacity increased 12 times compared to as-built parapets. Parapet construction and retrofit procedures are presented, followed by a discussion of the developed failure modes as well as the response of the retrofitted parapets.