8 September 2011
Quakes Royal Commission Releases Unreinforced Masonry Report
A technical report prepared for the Canterbury Earthquakes Royal Commission in Christchurch about the performance of unreinforced masonry buildings contains recommendations of significance to the whole country.
The report ‘The Performance of Unreinforced Masonry Buildings in the 2010-2011 Canterbury Earthquake Swarm’ was prepared by Associate Professor Jason Ingham of the University of Auckland and Professor Michael Griffith of the University of Adelaide. It is available on the Commission’s website.
Unreinforced masonry is a construction of clay brick, concrete block or natural stone units bound together using lime or cement mortar, without any reinforcing elements such as steel reinforcing bars. Forty people died in the 22 February 2011 earthquake due to the failure of unreinforced masonry buildings in and near the Christchurch CBD.
The report discusses the architectural characteristics and seismic vulnerability of unreinforced masonry buildings in New Zealand, makes observations about the performance of such buildings in the Canterbury earthquakes and available techniques for seismic upgrading. It recommends certain structural elements of all unreinforced masonry buildings be improved to meet the requirements for such structural elements in new buildings and other elements be improved to meet at least 67% of the standard required for new buildings. The authors recommend that there be one national standard instead of policies being set by individual territorial authorities.
To ensure that advice given to the Commission reflects international understandings and best practice, the report will be peer reviewed separately by structural engineer Fred Turner of California's Seismic Safety Commission and Bret (correct spelling) Lizundia of San Francisco-based structural engineering and geotechnical firm Rutherford and Chekene. Both peer reviews will be published on the Commission’s website.
The Commission has requested any evidence or submissions on the issues discussed in the report be provided in electronic form by Friday 14 October 2011. The evidence and submissions will be published on the Commission’s website unless there are compelling reasons not to do so.
The report will be presented at a public hearing to be held at St Teresa Hall in Riccarton, Christchurch commencing Monday 7 November 2011. This hearing is expected to take two weeks and cover:
- Legal requirements for buildings that are “earthquake prone” under section 122 of the Building Act 2004.
- The requirements for existing buildings that are not “earthquake prone” but do not meet current legal and best practice requirements for the design, construction and maintenance of new buildings, including whether, to what extent, and over what period, they should be required to meet those requirements.
- Existing and new methods for the seismic strengthening or “retro-fitting” of existing unreinforced masonry buildings.
- The desirability of immediate action in respect of restraining parapets, chimneys, and other high-hazard elements.
- The respective roles of central and local government in respect of earthquake-prone buildings and their seismic strengthening.
About the Report
The Commission has sent advice about the report to all persons and organisations who have filed expressions of interest in the inquiry, as well as persons and bodies with relevant knowledge about strengthening unreinforced masonry buildings.
The report’s executive summary states the main recommendations are:
• All unreinforced masonry buildings should be improved so that the public is protected from all falling hazards such as chimneys, parapets, gable end walls and out-of-plane wall failures. These parts of unreinforced masonry buildings should be improved to the full design strength required for new buildings in New Zealand. If required, further building improvements should aim for 100% of the requirements for new buildings with lower values negotiable on a case by case basis. However, a minimum of 67% is recommended.
• There should be a single, national policy for unreinforced masonry building maintenance and seismic strengthening rather than multiple regional policies.
• The estimated cost to upgrade all of New Zealand’s approximately 3867 unreinforced masonry buildings to a minimum of 67% of the new building standards requirements is approximately $2 billion. This is slightly more than the estimated value of $1.5 billion for the total unreinforced masonry building stock. A cost effective strategy is needed to direct the limited resources available to tackle this problem.
• Field testing of a limited number of existing unreinforced masonry buildings in the Christchurch CBD or nearby (that have been listed for demolition) would improve the current understanding of the seismic capacity of these buildings as well as offer an opportunity to develop and validate more cost-effective seismic strengthening/retrofit technologies. Such testing would focus on global structural performance characteristics and how loads are transmitted through buildings, and would be undertaken using such techniques as snap back testing to generate lateral loads and deformations that simulate earthquake effects. The performance of structural elements either extracted from such buildings, or tested in place, would also provide important new information.
• In view of the estimated cost to upgrade all unreinforced masonry buildings to a minimum of 67% of the new building standards, it is proposed that first priority be given to ensuring public safety by securing/removing falling hazards as outlined in section 7: Recommendation 3, Stage 1 and Stage 2. The cost to do this is unknown but would be substantially less than the amount to fully upgrade all buildings.
Report Author Contact Details
Associate Professor Jason Ingham
University of Auckland
Phone: +64 9 373 7599 ext 87803
Professor Michael Griffith
University of Adelaide
Phone: +61 8 8303 4316
Royal Commission Media Contact
Senior Communications Advisor
Canterbury Earthquakes Royal Commission
Phone +64 3 7413004 or +64 21 621 656