Post-Earthquake Reconnaissance of Unreinforced and Retrofitted Masonry Parapets

Abstract

Unrestrained unreinforced clay brick masonry (URM) parapets are freestanding wall elements found atop a large number of vintage URM buildings. Parapets are considered to be one of the most vulnerable nonstructural components that are prone to out-of-plane collapse when subjected to earthquake induced shaking. Using data collected during the earthquake reconnaissance efforts, 959 URM parapets were identify to be in existence in the Christchurch (New Zealand) area prior to 2010, with 60% (580) of them having collapsed during the 2010/2011 Canterbury earthquake sequence. Construction details and observed performance of both as-built and retrofitted parapets were documented. The reported study provides an inventory of observed parapet failure modes and a critical review of commonly encountered parapet retrofits and their respective seismic performance

Shake Table Testing of Seismically Restrained Clay-Brick Masonry Parapets

“…Using the floor height coefficient ðC Hi Þ calculated in accordance with NZS 1170.5 (Standards of New Zealand 2004) the effective PGA necessary to cause failure of the retrofitted parapets was estimated in relation to the number of floors, as shown in Figure 20. Based on Giaretton et al (2016a), the typical building height at the roof line was considered to be:…”

“…Most ordinances and guidelines (e.g., Ministry for Cultural Heritage and Activities 2011, NZSEE 2015) suggest general rules for assessing and securing nonstructural elements but do not provide detailed standardization and recommendations-for example, FEMA 547 (FEMA 2006) for steel-braced parapets. As a result, a mixture of seismic improvement techniques is implemented on existing buildings, which leads to a wide range of seismic performance levels for the secured a) Department of Civil and Environmental Engineering, University of Auckland, Private Bag 92019, Auckland 1010, New Zealand parapets (Giaretton et al 2016a). Concrete bond beams, steel braces connected to the roof structure, steel strips fixed with adhesive anchors or struts at the edge, steel corner connections, vertical steel bars inserted into the parapet, and replacement with lightweight replicas are some of the retrofit techniques identified during inspection of damaged URM buildings after the 2010/2011 Canterbury (New Zealand) earthquakes (Giaretton et al 2016a) (Figure 1).…”

“…As a result, a mixture of seismic improvement techniques is implemented on existing buildings, which leads to a wide range of seismic performance levels for the secured a) Department of Civil and Environmental Engineering, University of Auckland, Private Bag 92019, Auckland 1010, New Zealand parapets (Giaretton et al 2016a). Concrete bond beams, steel braces connected to the roof structure, steel strips fixed with adhesive anchors or struts at the edge, steel corner connections, vertical steel bars inserted into the parapet, and replacement with lightweight replicas are some of the retrofit techniques identified during inspection of damaged URM buildings after the 2010/2011 Canterbury (New Zealand) earthquakes (Giaretton et al 2016a) (Figure 1). A total of 78% (175 of 224) of the secured URM parapets that were inspected post-earthquake had either collapsed or had sustained damage during the earthquake sequence.…”

“…Freestanding cantilevered nonstructural components such as unreinforced masonry (URM) parapets pose a significant falling hazard and, in past earthquakes, have caused numerous injuries and required costly repairs (Klingner et al 1994, Giaretton et al 2016a). Unreinforced masonry parapets typically fail out ofplane because of rocking at the roofline.…”

Parapets, Politics, and Making a Difference: Lessons from Christchurch

“…URM buildings did not fare well in Christchurch (Moon et al 2014). Those of us next to these buildings fared even worse (Giaretton et al 2016).…”