Researching Seismic Risk

A significant earthquake poses the greatest potential for a natural disaster for Canada. A high percentage of the country’s urban infrastructure was constructed prior to the introduction of modern seismic provisions in the mid-1980s and, thus, a large inventory of deficient infrastructure needs to be identified and upgraded. It is essential that Canada’s deficient infrastructure be improved, especially critical urban infrastructure such as hospitals, schools and bridges. These critical facilities and structures must remain operational after a seismic event.

RESEARCHING SEISMIC RISK

The Canadian Seismic Research Network (CSRN) was formed with funding from the federal government (NSERC) and has the overall goal of reducing urban seismic risk in major cities in Canada. The work of the CSRN is focused on the major urban centres that dominate our national seismic risk: Vancouver, Victoria, Montréal, Ottawa, Toronto and Québec City (Please see Figure 1).

The CSRN consists of 26 researchers from eight universities: University of British Columbia, Western University, University of Toronto, University of Ottawa, Carleton University, École Polytechnique de Montréal, McGill University and the University of Sherbrooke. Aside from producing research, the network is also training highly qualified personnel, including more than 150 Masters and PhD students carrying out research on different aspects of earthquake engineering, seismology and risk engineering.

CSRN is collaborating with about 40 research partners from industry and federal, provincial and municipal government agencies. The Institute for Catastrophic Loss Reduction (ICLR) has a major role in the network activities, providing two yearly scholarships for graduate students, collaborating in the research projects and playing a key role on CSRN’s board of directors.

CSRN researchers have made site visits following recent earthquakes in Haiti (Figure 2), New Zealand (Figure 3) and Chile (Please see Figure 4, on Page 45) to study several aspects of the events: the details of the ground motions; the influence of soil conditions on ground motion amplification; damage to structures, including buildings and bridges; and the deficiencies in current and past codes of practice.

GOALS OF THE CSRN

Three interrelated research themes have been developed to achieve the goals of the network.

Theme 1 involves the assessment of seismic hazard, including:

• the development of probable ground motions to help evaluate the structural response of existing structures;

• the subdivision of potential seismic or earthquake-prone areas into zones within key cities such as Vancouver, Victoria, Montreal and Ottawa (a process known as ‘microzonation’); and

• studies of the seismic risk in cities listed above.

Theme 2 involves the development of more sophisticated techniques for the evaluation of seismic vulnerability of existing structures. The vulnerability assessment techniques are being developed for steel, concrete and masonry buildings as well as for bridges.

Theme 3 involves developing innovative techniques for upgrading deficient structures to mitigate damage by improving their seismic performance capabilities.

Microzonation studies

One example of a microzonation study is the preparation of the microzonation mapping of Ottawa, a joint project between the CSRN and the Geological

Survey of Canada. These maps provide valuable site-specific information for the city. Similar microzonation studies are currently being conducted for Vancouver and Montreal.

DEFICIENT STRUCTURES

CSRN researchers are carrying out a number of testing programs involving simulated earthquake loading on components of structures. These experiments include the shake-table testing of a multi-storey concrete shear wall, reversed cyclic loading testing of masonry walls and the testing of steel braced frames. This experimental evidence permits the development of a better understanding of the deficiencies in older structures.

Innovative retrofit techniques

Experimental research is being conducted on the seismic upgrading or retrofit of existing deficient structures using innovative approaches such as the use of carbon fibre wrapping to improve the behaviour of reinforced concrete elements. Researchers are testing the effects of using carbon fibre wrap on masonry walls (Figure 5) and concrete shear walls (Figure 6). This cost-effective retrofit technique provides a means of improving the seismic performance with minimum intervention. It is ideally suited to existing structures that must remain in use.

This retrofit technique resulted in significant improvement of the reversed cyclic loading performance, including an increased strength and improved ability to undergo large deformations without failing in a brittle manner.

Developing retrofit guidelines

CSRN is currently developing Guidelines for the Evaluation and Retrofit of Structures. This document will provide a unified, state-of-the-art methodology for assessing the seismic performance of existing structures. The results of CSRN’s research from the three different themes noted above will form the basis of the retrofit guidelines.