Specifying seismic restraints for nonstructural components

2. Normal Importance
All buildings not classified as ‘Low,’ ‘High,’ or ‘Post-disaster’ are ‘Normal.’ It is important to remember, though, there is a broad range of buildings, so questions may arise for some facilities not specifically listed, such as wind turbines, private versus public bus terminals or airports, or private clinics and non-emergency treatment facilities unlikely to be considered essential to provision of services to the public in a disaster. Discussions with the owner, structural engineer, and AHJ may be required to appropriately assign the Importance Category.

3. High Importance
This category applies to schools, community centres, and industrial or storage facilities having hazardous or toxic materials. It is not limited to the specific facilities noted, and might apply to a college, sports facility, arena, or large place of worship. The code uses the term “likely to be used as post-disaster shelters,” but it should be noted this is not the code-defined term “Post-disaster Importance” (shown below), but a lower category of importance that requires professional judgment to assign.

4. Post-disaster Importance

Post-disaster buildings are essential to the provision of services in the event of a disaster. Examples include:

• hospitals, emergency treatment facilities, and blood banks;
• telephone exchanges;
• power-generating stations and electrical substations;
• control centres for land transportation;
• emergency response facilities, including fire, rescue, and police stations (and storage facilities for vehicles or boats used for those purposes);
• public water treatment and storage facilities;
• water and sewage pumping stations; and
• communications facilities, including radio and television stations.

Site classification
The site class (A to F) relative to substrate type (e.g. rock, hard, or soft soil) is one of three factors required for the calculation of the seismic hazard index. It is assigned by a geotechnical engineer following soil tests.

A shear wave velocity test may be required by the geotechnical engineers to assign a site class better (i.e. higher) than can be ascertained without the test (e.g. C rather than D, or B rather than C). The shear wave test would be an additional cost over simple borehole analysis, but may ultimately save the project considerable cost.

Seismic hazard index
While the building’s structural design involves complex seismic restraint calculations, a reasonably simple formula is used to determine the seismic hazard index. The seismic hazard index formula is:

IE F_a S_a(0.2)

Where:

IE = Earthquake Importance Factor for the structure (taken from National Building Code of Canada [NBC] Table 4.1.8.5.);

F_a = Acceleration-based site co-efficient (NBC Table 4.1.8.4.B); and

S_a(0.2) = five per cent damped spectral response acceleration (NBC SB-1 Table 1.2, Column 17).

If the value of the seismic hazard index is equal to or greater than 0.35, it triggers the need to restrain architectural elements like suspended ceilings, parapets, ornamentations, and masonry veneer connectors, as well as mechanical and electrical systems and equipment in all buildings.

When specifying for any nonstructural component necessitating seismic requirements, it is imperative the performance requirements are identified for the engineer preparing the shop drawings so the most appropriate design for the component can be provided.

Another important aspect to the requirements is the design intent. For example, if the restraint assembly is exposed to public view, the architect might want the restraint hardware to have an architecturally exposed finish to highlight the exposed condition. Within the specification section, there should be content requiring the intent of architectural finish, identified by a detail located on the drawings showing the intended configuration of the restraint system.