Four industry documents, discussing retrofit needs for heritage buildings, were recently published by Geoscience Australia. Duratec’s Principal Structural Engineer, Peter Baxendale, was one of the main consultants.
Australia has a large inventory of legacy unreinforced masonry (URM) buildings that pre-date earthquake-resistant structural design practices. They date from the early 1800s and early-to-mid 1900s, long before seismic design regulations were introduced to Australia (1979). As a result, much of our existing URM building stock is expected to be vulnerable in the event of a major earthquake.
URM buildings tend to be earthquake-prone due to a combination of factors, including heavy mass, low tensile strength, potential for existing cracking and limited ability to accommodate deformations (low ductility). Older URM structures often have poor walls-to-floors and walls-to-roof connections, which can compromise the building’s lateral load path and lead to premature failure by the detachment of components, such as parapets, gables, or facades.
Such buildings are also vulnerable under high wind action for similar reasons but also due to inadequate or the total absence of connectivity and/or strength throughout the roof structure to resist uplift loads.
Prior to joining Duratec as Principal Structural Engineer, I acted for the industry reference group that was consulted by the Federal Government’s Geoscience Australia in the publication of three earthquake retrofitting documents. I also co-authored a fourth wind document.
The first earthquake document, Earthquake retrofitting for resilient communities, is aimed at governments and explains the nature of earthquake hazard in Australia, as well as the risk it presents and the vulnerability factors at play. It looks at the effectiveness of retrofitting in reducing the impact of earthquakes and discusses emergency management logistics and recovery needs.
Readers will also find links to resources that can be used to advance local programs for building community resilience. While the focus is on URM structures, the principles can also be applied to other high-risk building types.
The second publication, Resisting the shake, is aimed at asset owners and focuses on the risks earthquakes impose on property and lives. In good news, the document outlines how buildings can be retrofitted to improve their earthquake resilience, both within a sensible budget and without compromising their heritage value. Many state and local governments are seeking to raise awareness of earthquake risk among property owners and are targeting grants schemes to promote cost-shared investment in retrofitting.
The third document, Earthquake retrofit for older masonry buildings, is aimed at design professionals – in particular, those working with property owners who have taken the initiative to address structural deficiencies and engage a skilled construction industry – and provides guidance on undertaking retrofit with due address of heritage considerations. The objective is to achieve cost-effective retrofit measures, while minimising disruption to occupants.
The publication also describes common failure modes and suggests measures that can be employed to preclude these. It also provides links to other resources that can assist in the development of tailored design solutions.
The fourth resource, Wind retrofit for older masonry buildings, contains a suite of typical wind-strengthening details for URM structures, where the building fabric may differ substantially from the types of construction normally encountered in more modern buildings. The document considers a range of wind hazards, including tropical cyclones, using WA for examples of risk evaluation.
The retrofit resources can be found at the Geoscience Australia website at www.ga.gov.au. You can also click on the images above or the links below:
Asset owners: Resisting the shake
About the author
Peter Baxendale is Duratec’s Principal Structural Engineer with 30 years’ experience experience and a passion for the built heritage environment. Peter acted for the industry reference group consulted by the Federal Government’s Geoscience Australia in the publication of its earthquake retrofitting publications, and was co-author of the corresponding wind document.
At Duratec, Peter and the technical team are tackling structural assessment, remediation, conservation and adaptation works across all fabric and building types, including present retrofitting projects to civic and educational structures.