Canterbury Earthquake Clearinghouse

You may view more reports and observations on our ”Reports from the field” page at http://eqclearinghouse.org/20100903-christchurch/reports-from-the-field/.

On Saturday, 9/11, I walked the Central Business District of Christchurch using prior reports of severe damage and references to retrofitted buildings as a guide. By the end of the week, 19 previously retrofitted buildings were observed in greater Christchurch and one in Lincoln. The retrofitted portions of these buildings performed quite well in comparison with similar unretrofitted buildings nearby. The retrofits ranged in age with most taking place over the last several decades. Information that may eventually become available could help clarify the criteria to which these buildings were retrofitted. In several cases, retrofits appear to have consisted only of parapet braces and wall anchors to floors and roofs. In addition, several buildings had been partially retrofitted. In some of those buildings, the unstrengthened portions suffered severe damage in sharp contrast with retrofitted portions. Access to the interiors of these buildings were generally not sought, so additional information about the retrofits and their performance from others will hopefully help our understanding. Many of the unretrofitted buildings appeared to have relatively low mortar strength and often unfilled collar joints, so gaining information about the design of retrofits of similar buildings in the vicinity will be an important benchmark of performance for regions of the world with similar strengths, configurations and hazards. A notable variety of techniques were used for retrofitting unreinforced masonry including throughbolts, screen anchors, glass fibre reinforced polymer, and the addition of external steel vertical and horizontal elements. Buckling restrained braced frames and eccentric braced frames were observed in retrofits of institutional buildings. These methods did not exhibit systematic vulnerabilities as a result of this particular sequence of earthquakes.

Many modern and relatively undamaged buildings and their occupants in older commercial districts were also indirectly impacted by the disruption caused by nearby severely damaged buildings. Falling hazards generally tended to stem from unreinforced masonry that experienced failures of unbraced parapets and inadequate between upper walls and roofs.

Glass breakage was prevalent in many midrise commercial and institutional buildings, some from the mid-20th century and newer.

Over 15,000 chimneys have been estimated by the New Zealand Earthquake Commission to have suffered severe damage. In the past, Christchurch has prohibited most uses of chimneys and have encouraged homeowners to replace the use of chimneys for heat with more efficient and less polluting sources. As a result, a significant number of homeowners had removed the tops of chimneys frome their homes prior to the earthquake.

Some wood frame buildings utilize brick masonry walls as fire separations near property lines. Incompatibility of deformations between the more flexible wood frame systems and the more rigid masonry walls caused severe damage in the walls in several buildings.

Many low-rise unreinforced masonry buildings utilized cavity wall construction with wire ties connecting wythes of brick. Severe damage due primarily to out-of-plane response and instability occurred in some of these wall systems.

Severely damaged unreinforced masonry buildings have created challenges for barricading and disruption to keep the public from being exposed to loose elements that could fall, particularly on streets and intersections with busy pedestrian and auto uses.

Reportedly only one fire occurred in the Central Business District of Christchurch when electricity was restored.

Preliminary Report on Bridge Damage from the Darfield (New Zealand) M7.1 earthquake of September 4, 2010 – Draft of 2010-09-13 by by Michel Bruneau, Myrto Anagnostopoulou, and Alessandro Palermo may be viewed here: http://eqclearinghouse.org/20100903-christchurch/reports-from-the-field/preliminary-report-on-bridge-damage-from-the-darfield-new-zealand-m7-1-earthquake-of-september-4-2010-%E2%80%93-draft-of-2010-09-13/