| A MULTI-DISCIPLINARY APPROACH TO SEISMIC RISK |
| When looking at all the design requirements for new construction, seismic risk is all about the design team.
Owner’s responsibility Life safety is identified as a requirement in the National Building Code of Canada (NBC). Property damage and recovery is a direct relation to the owner end use. Most seismic risk is based on damage and recovery from an owner’s point of view. Consultant’s responsibility
Constructor’s responsibility
The constructors are also responsible for the installation of seismic restraints. |
Damages to the built environment
Most earthquake damage is caused by ground shaking. However, in Canada, falling objects pose the greatest danger. In this country, no house has ever collapsed during a seismic event, but many types of objects may fall and cause damage or injuries. Of prime concern, therefore, is protection from falling objects such as:
- framed pictures;
- light fixtures;
- plaster from ceilings or the upper part of walls; or
- chimneys that may fall outside or through the roof into the house.
Earthquakes have rendered spaces buildings unusable due to extensive damage to their operational and functional components (OFCs). The main cause of casualties and property damage in the event of an earthquake is often the failure of these OFCs. In many cases, losses associated with damage to these components are considerably greater than damage to the structural system.
National codes and guidelines are in place for the seismic design, evaluation, and upgrading of building structures in Canada. Similar documents did not exist for the OFCs of buildings prior to the publication of the first edition of CSA S832, Seismic Risk Reduction of Operational and Functional Components (OFCs) of Buildings. This standard is intended to address the need to reduce the seismic risk of OFCs, thus improving the post-earthquake functionality of buildings.
A well-designed and constructed building is expected to provide safety and comfort to its occupants when it is subjected to building use, occupancy loads, and other environmental loads (e.g. wind, snow, rain, ice, and earthquakes). A building is made up of components that can be divided into two groups: structural and OFCs. This latter category is commonly referred to as ‘non-structural components,’ but this terminology is deliberately avoided in the CSA standard to acknowledge the interaction between the seismic behaviour of a building’s structural system and the seismic performance of all other building components.
Structural components are those basic components designed and constructed to carry and transfer all loads to the ground without total or partial collapse of the building. Some OFCs can contribute to the structural integrity of a building, depending on their location, type of construction, and method of fastening, but these are not generally considered structural components.
OFCs are divided into two categories—‘operational’ (i.e. mechanical, electrical, and other parts that keep the building services going) and ‘functioning.’ This second category has various sub-components:
- architectural:
– exterior components (e.g. curtain walls, canopies, wind-load-bearing steel studs, masonry veneer); and
– interior components (e.g. suspended ceiling systems, framed interior walls, non-load-bearing block walls, and elevators);
- building content:
– common building contents (e.g. movable partitions, filing cabinets, and office equipment); and
– specialized common contents (e.g. antiques, artifacts, hazardous materials, and various medical supplies).
Most efforts to improve the seismic behaviour of buildings have been directly related to the safety and integrity of the structural system. Continuing advances in analysis and design have led to improvements to the structural system’s capacity to resist earthquake effects. As a result of damage caused by earthquakes over the last century, focus has now shifted to the behaviour of OFCs in overall building performance.
Risk to safety, damage to property, and loss of function and operation in a building can be significantly affected by the failure or malfunction of OFCs, even if the building structural system has performed well during an earthquake. The damage resulting from these components can be considerably worse than that arising from structural component failure, particularly in areas of low and moderate seismic intensity.
Buildings in Canada that are designed in accordance with early codes can be vulnerable to the failure or malfunctioning of OFCs after an earthquake. In many cases, improvements to the overall seismic performance of the building can be made by improving the performance of OFCs.
Design procedures
Under CAN/CSA S832, the seismic design team shall:
- identify the importance category of the particular building (i.e. low, normal, high, and post-disaster) and determine the performance objectives (e.g. life safety, limited/full functionality, property protection) of individual OFCs and their subsystems accordingly;
- review the final design to ensure provisions have been made to minimize the seismic risk to OFCs;
- prepare engineering drawings and project specifications;
- review equipment specifications in order to ensure the adequacy of design;
- review shop drawings to ensure conformity with project equipment specifications,; and
- provide site inspection during the construction phase for quality control and acceptance by the authority having jurisdiction (AHJ).
Thanks Jeff, great article.
Thanks to all for making this readable article available for reference by other designers.