by Rania Bedair, Ph.D. Eng
Potential economic losses from damages to structures due to earthquakes can reach billions of dollars in densely populated areas. For instance, the total direct economic losses of $25 billion due to damaged buildings was paid by government and private insurance sources for recovery and reconstruction in California following the 1994 Northridge earthquake. A study by Air Worldwide (2013) Risk Company, commissioned by the Insurance Bureau of Canada, shows that there are chances of major earthquakes in British Columbia and Quebec with estimated damage costs of $70B and $60B respectively.
Economic losses due to nonstructural damage may also be significant following a seismic event. During the 1994 Northridge earthquake, nonstructural damage accounted for about 50% of the total loss of approximately $18.5 billion due to building damage (Kircher, 2003). After the 1971 San Fernando earthquake, it was found that damage to contents and the interior and exterior finishes resulted in 97% of the total economic loss while structural damage was limited to only 3% (FEMA E-74). As a result of past earthquake losses and the level of investment in nonstructural components and contents, considerable attention has been paid recently to develop a better understanding of the seismic behavior of nonstructural components. It is also recognized that damage to these elements may pose threat to life safety and impair functionality of a structure.
Photo: National Institute of Standards
and Technology (NIST GCR 17-917-44)
Typical investments in building construction (after E. Miranda)
Structural components are the basic elements which are designed to carry and transfer all loads to the ground without total or partial collapse of the building. Seismic damage of structural components causes casualties, building disruption, and repair costs. On the other hand, non-structural components (the Operational and Functional Components, OFCs) are those elements housed or attached to the floors and walls of a building or industrial facility which are not part of the main load-bearing structural system, but also be subjected to large seismic forces. While non-structural components may not play a momentous role in the overall design of the building, they have a substantial impact on how the building will perform during a seismic event.
Building Components types (CSA-S832)
OFCs are divided into three categories of sub-components: architectural (external and internal), building services (mechanical, plumbing, electrical, and telecommunications), and building contents (common and specialized).
Non-structural elements have some specific physical and response characteristics which are significantly different from those of the structural components. The OFCs are attached to or placed at different floors of a structure. Those elements are not directly subjected to the ground motion generated by an earthquake. However, they are subjected to the acceleration response of that particular floor, which depends on the dynamic characteristics of that structure. OFCs are, in general, lightweight and their mass is much smaller compared to the floor mass. Furthermore, these elements are made up of materials which are not designed to resist seismic forces like that of the structure. Also, damping properties of OFCs are considerably smaller than those of the structure. In addition, some non-structural elements, e.g. piping systems, may have multiple points of attachments to the structure, which make these elements subjected to inter-story drift during an earthquake.
Non-structural Components (CSA-S832)
OFCs can be classified into three categories in accordance with the nature of their seismic response sensitivity:
Floor-acceleration-sensitive components, and
Both Inter-story-drift and floor-acceleration-sensitive components.
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