Canadian Earthquakes: Specifying seismic support for non-structural building components

by Katie Daniel | November 15, 2016 10:15 am

By Jeff Halashewski, Dipl Arch Tech
Flood, fire, blizzards, and ice storms are among the major natural disasters having an impact on the built environment in Canada. Among the least-discussed, and most misunderstood, are seismic events. Yes, there are regular earthquakes in this country, and, yes, they can be significant enough to have negative effects on buildings and occupants.

As a person who has been in the field of architecture for almost two decades, this author admits that until recently ‘earthquakes’ and ‘seismic’ were terms most associated with news reports of far-off places. However, once I started writing for B.C. base projects, I learned seismic activity was indeed an important consideration. Reading the Vancouver Building Code, the National Building Code of Canada (NBC), and then resources from the Association of Professional Engineers and Geoscientists of British Columbia (APEGBC) and Architectural Institute of British Columbia (AIBC), I gained a better sense of why West Coast projects demand taking these events into account.

What is an earthquake?
An earthquake occurs when rocks break and slip along a fault in the earth. Energy is released during an earthquake in several forms, including as movement along the fault, as heat, and as seismic waves radiating out from the source in all directions, causing the ground to shake, sometimes hundreds of kilometres away.

Earthquakes are caused by the slow deformation of the outer, brittle portions of tectonic plates—the Earth’s outermost layer of crust and upper mantle. Convection resulting from the heating and cooling of the rock below these plates causes the adjacently overlying plates to move, and, under great stress, deform. The rates of this movement range from approximately 20 to 120 mm (0.8 to 4.8 in.) annually. Sometimes, tremendous energy can build up within a single plate, or between neighbouring ones. If the accumulated stress exceeds the strength of the rocks making up these brittle zones, the rocks can break suddenly, releasing the stored energy as an earthquake.

An earthquake’s magnitude or size (i.e. energy release), focal depth, faulting type, and distance are important factors in determining the amount of ground shaking that might be produced at a particular site. Where there is an extensive history of earthquake activity, these parameters can often be estimated. In general, bigger earthquakes produce ground motions with larger amplitudes, longer durations, and stronger shaking over much larger areas.

Additionally, the amplitude of ground motion decreases with increasing distance from the focus of an earthquake. The frequency of the shaking also changes with distance. Close to the epicentre, both high (rapid) and low (slow)-frequency motions are present. Farther away, low-frequency motions are dominant, a natural consequence of wave attenuation in rock. The frequency of ground motion is an important factor in determining the severity of damage to structures and which structures are affected.

Despite what Hollywood blockbusters would have you believe, earthquakes do not result in holes in the ground that open to swallow up unfortunate victims. After a strong earthquake, some cracks may be seen on the ground or in basements, but these are not faults or crevasses that will close back up—rather, they are probably simply due to soil settlement caused by the ground shaking.

Earthquakes in Canada
While earthquakes occur all over the world, almost 90 per cent happen on only 10 per cent of the planet’s surface—the active faults defining major tectonic plates. The Ring of Fire circling the Pacific Ocean, including Canada’s West Coast, is one of the most active areas in the world.

However, it is also important to keep in mind minor earthquakes have been triggered by human activities such as mining (e.g. rock bursts and cavity collapses), the filling of reservoirs behind large dams, and the injection of fluids into wells for oil recovery or waste disposal. Large dams hold back enormous quantities of water. Some of this water may penetrate into cracks in the underlying rock, triggering small earthquakes under or very near the reservoir. (These human-caused earthquakes always occur close to the site of the activity. There is no link between activities like these and earthquakes occurring hundreds or thousands of kilometres away.)

On average, the Geological Survey of Canada (GSC) records and locates more than 4000 earthquakes in Canada each year—about 11 a day! However, of these, only about 50 are generally felt. Most occur along the active plate boundaries off the B.C. coast, and along the northern Cordillera (southwestern corner of the Yukon Territory and in the Richardson Mountains and Mackenzie Valley) and arctic margins (including Nunavut and parts of northern Québec). Earthquakes also occur frequently in the Ottawa and St. Lawrence Valleys, in New Brunswick, and the offshore region to the south of Newfoundland.

The largest earthquake recorded (during historic times) in Canada was a magnitude 8.1 event that struck just off the Haida Gwaii on Canada’s Pacific coast on August 22, 1949. This earthquake (which was larger than the 1906 San Francisco earthquake) ruptured a 500-km (310-mi) long segment of the Queen Charlotte fault and was felt over almost all of British Columbia—as far north as the Yukon Territory and as far south as Oregon.

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 The owner’s first responsibility is the appointment of the design team. The owner must also identify the amount of risk for which they are willing to be responsible. Life safety and property damage are the two areas of most concern. 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 The consultant’s responsibility is to preparer drawings and specifications, which are to include the following: design operational and functional component (OFC) restraints and their connections in accordance with requirements outlined in CAN/CSA S832, Seismic Risk Reduction of Operational and Functional Components (OFCs) of Buildings; review shop drawings; and review site conditions—looking at installed restraints and their connections to ensure conformity with shop drawings and specifications. Constructor’s responsibility The constructor’s responsibility is to interpret the drawings and specifications for construction. This includes preparation of seismic restraint shop drawings for OFCs, which includes: material specifications being used locations and dimensions of restraints; and details of connections. 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).

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Methods of selecting seismic restraints
The adequacy of seismic restraints for OFCs in any particular application may be evaluated by using analytical or prescriptive methods (or a combination of the two), or employing seismic qualification testing methods. These methods may be applied to both new and existing restraints.

This is important because it gives the designer options in designing or selecting restraint systems that are appropriate for a given area or seismic zone.

Prescriptive method
Prescriptive methods are applicable only to certain types of OFCs. These procedures are based on sound engineering standards and practices, as established by the appropriate industry associations. This means there is no need for analysis or engineering calculations beyond basic information for choosing the appropriate mitigation action in accordance with published standards. Examples include the Ceilings and Interior Systems Construction Association (CISCA) standards covering suspended ceilings and the Sheet Metal and Air-conditioning Contractors National Association (SMACNA) standards for support of ductwork and piping.

With the use of prescriptive-type standards, the restraint details can be selected directly from manufacturer details and information referencing the appropriate standards by sector.

Analytical method
The analytical method is the direct opposite of the prescriptive path. It involves engineering specifically for the OFC. Forces and displacements are introduced in the OFCs by the movement of the buildings when subjected to earthquakes. These forces and displacements can be calculated by one or more of the following analytical methods:

• simplified: approximate methods based on an equivalent static force analysis approach; and
• refined: methods dealing with dynamic behaviour of the building and with varying degrees of complexity (used where there is a direct impant from the OFC onto the structure of the building).

Where do we go from here?
The big question becomes, ‘How can I apply seismic restraints for non-structural components to specifications?’ In research for this article, this author has found a section from the U.S Government of Veteran Affairs labeled Section 13 05 41–Seismic Restraint Requirements for Non-structural Components. Looking at the 2016 edition of MasterFormat, perhaps the most appropriate number for non-structural components would be a mix of both. In other words:

• 13 48 53−Manufactured Seismic Control Components; and
• 13 48 63−Fabricated Seismic Control Assemblies.

If one is looking for a specific section for non-structural components, then maybe creating new sections is the way to go:

• 13 48 05−Common Work Results for Sound Vibration and Seismic Controls; and
• 13 48 50−Seismic Control Requirements for Non-Structural Components.

While research continues, this author would love to hear from readers about their own experiences. How do you specify seismic restraints for non-structural components? In your province, are there special requirements from your AHJ, or the provincial or local associations?

Conclusion
The risk associated with the failure or damage of any operational or functional component during an earthquake depends on far more than simply a building’s vulnerability to strong shaking and differential movement of the supporting structure. As a specification writer, this author believes it is important to have good knowledge of what information is needed prior to the start of the project. It would be appropriate to begin with a good plan:

1. Set up a seismic risk plan for the project, including all the performance requirements and seismic information required to perform calculations. (This can be done by having a good master specification setup. Create new Section 13 48 05−Common Work Results for Sound, Vibration, and Seismic Controls.)

2. Know which components are within the realm of the contract between the owner and consultant. Is this a shell building, tenant improvement, or both?

3. Confirm whether the owner intends to extend any of the seismic restraint design of OFCs to one of the prime consultants outside of the main contract.

4. Verify all seismic restraint carried under MasterFormat Divisions 20 to 28.

5. Ensure structural drawings have notes pertaining to seismic design of non-structural components—all work for designing seismic restraints is outside the structural scope.

Jeff Halashewski, Dipl Arch Tech, is a specifications writer for the Edmonton office of DIALOG. He is a member of the executive for the CSC Edmonton Chapter, and also a member of the Canadian Association of Earthquake Engineering (CAEE). Halashewski has 17 years of experience in institutional, commercial, and industrial buildings, and has worked on projects that involved seismic restraint of non-structural components. He can be reached at jhalashewski@dialogdesign.ca[2].

Source URL: https://www.constructioncanada.net/canadian-earthquakes-specifying-seismic-support-for-non-structural-building-components/

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