By Jeff Halashewski, Dipl Arch Tech
Over the past year, this author has witnessed an increase in the design community’s awareness of the seismic requirements set out for Canadian jurisdictions. However, for both new buildings and existing construction, the destructive effects of earthquakes can be of significant concern. Damage to inadequately restrained key systems within buildings can be extensive. When a major component, such as a generator, is knocked off its supporting structure, the fall can threaten both life and property.
The cost of properly restraining such equipment is insignificant compared to the associated costs of replacing or repairing the components, along with the expense of system downtime due to damage to the building services and businesses. When thinking of it from this angle, whose responsibility is it to restrain a generator—the building owner or tenant?
This author’s previous article for Construction Canada explored why proper restraining of nonstructural components can reduce the threat to life and minimize long-term costs due to damage and associated loss of service. (In the November 2016 issue of Construction Canada, this author discussed the basic concepts that feed into larger discussions regarding ‘domestic’ earthquakes, nonstructural components, and methods of selecting seismic restraints. Click here.) It stressed the importance of minimizing risks at the design stages, which should include a well-written specification that can be taken to the delegated design engineer or person producing the shop drawings for the given component.
In this follow-up article, the author explores how this information can actually be implemented, working through the processes of setting up the performance requirements through to submittals, fabrication, inspections, and quality assurance/control (QA/QC). The goal is to be able to easily understand what is required as part of the specification for any given building.
What is a seismic restraint?
By definition, a restraint is a method to mechanically control movement, whether via dampers, bracing, containment, immobilization, or suppression. Seismic forces relate to vibrations produced by an explosion or even by the natural environment—for example, a building on the banks of a fast-moving river will experience vibrations within. With respect to ‘seismic restraints,’ then, design professionals have no control over the first word, and therefore must focus on the second—controlling the parts of the building that will move.
Seismic restraints can fit into many categories, but the most common are:
- fully restrained;
- partially restrained; and
Each type of these assemblies has its pros and cons, but it all comes down to the intent and the seismic force potential on the component requiring restraint, either being surface-mounted, suspended, or supported off another nonstructural component. The materials used can vary, ranging from those like concrete, steel section, springs, cables, rods, and premanufactured solutions.