Role of engineers and manufacturers
There are numerous reasons why the engineer of record is being asked to be more involved in the design of seismic restraint of non-structural components. This has not always been the case, as the design of both vertical and horizontal restraint for non-structural components was traditionally delegated to the contractor. The engineer of record’s role was to provide necessary performance criteria for any required bracing, and this was handled via notes on the drawings or through project specifications.
However, owners are now recognizing the value of having the seismic restraint of non-structural components clearly designed and specified by the engineer of record in the contract documents thereby eliminating any uncertainty the contractor(s) may have on interpretation of the owner’s requirements.
Owners have typically learned this as a result of actual experience when healthcare facilities, for example, experienced severe operational problems in spite of the fact the structure itself remained standing during a seismic event.
At the same time, experience has clearly shown the cost and effort in adequately restraining this equipment is much less than the expense involved in replacement, repair, and system downtime that may result from seismic damage. While protecting occupant safety is one of the primary concerns, in many cases, owners are also aware disruption of services may cause additional damage and may result in considerable building damage or significant financial losses.
Experience has also shown improper installations of restraints can result in failure during an actual earthquake. For example, problems have occurred as a result of connection of bracing at improper locations on the structure. Seismic braces are typically diagonal members carrying axial forces to the support. Thus, there is both a horizontal and vertical component of the brace force that must be taken by the support. A common improper installation deficiency is related to attaching bracing to steel joists. Most steel joists are not designed for these vertical forces and, depending on the magnitude of the force, could fail.
Due to heightened awareness and firsthand-observed problems, owners are turning to the engineer of record more than ever before to design bracing. Many engineers have developed specific procedures to assess buildings and equipment components enabling them to determine the best course of action and identify potential life/safety hazards. They have also developed plans to minimize the disruptions to normal building operation.
Manufacturers are becoming more cognizant of seismic bracing requirements, as well as some of the exemptions in the building codes. To that end, HVAC engineers have been developing innovative designs for non-structural equipment that incorporate bracing and connection details sufficiently flexible to withstand building movement without failure or displacement. With such infrastructure pre-designed, the code is much more accommodating without the need for additional seismic bracing.
Conclusion
Experience with earthquakes in Canada has demonstrated some of the country’s building infrastructure (such as non-structural components) may actually be quite vulnerable—failure or loss of functionality can occur at a time when the need is critical. It is possible to mitigate the seismic risk for these components; when restraints are properly designed and installed, negative outcomes can usually be avoided.
Typically, mechanical and electrical equipment supports were designed for gravity loads and did not take into account the horizontal and upward loading caused by earthquakes. Seismic restraints of mechanical and electrical equipment can resist seismic forces when they do occur and ensure systems remain secure. Provision of these restraints can reduce the threat to life and minimize long-term costs that result from equipment damage and associated loss of service. Building owners should have a vested interest in this—aside from the risk to public safety and employees, there are almost certainly other concerns that are not fully addressed by insurance coverage.
Notes
1 Mechanical, electrical, and other non-structural components may be installed in areas where there may be limited space and, in some cases, the components will be located in close proximity to each other and other building systems. Installing restraints after systems are in place can make both access and restraint installation difficult and time-consuming. (back to top)
2 The provisions in Part 4 of NBC provide guidance with regard to the structural design of buildings. Structural engineers undertake a number of calculations using the equations provided here to determine the appropriate level of seismic protection. (back to top)
3 Shear-wave (S-wave) velocity is highest in bedrock and lowest in soft clay and artificial fill. Seismic shaking amplification depends on the velocity at which the rock or soil transmits S-wave—shaking is stronger where the velocity is lower. (back to top)
Edward Kolodziejski, M. Eng., P.Eng.,is a professional structural engineers with exp Services. He has 30 years of experience in institutional, commercial, and industrial buildings, and has worked on many projects that have involved seismic restraint of non-structural components. Kolodziejski can be contacted at ed.kolodziejski@exp.com.
Brian Burton is the author of “Fenestration Forum,” published five times a year by Glass Canada magazine. Part of exp, he was also recently appointed to the Canadian Standards Associations (CSA) Fenestration Installation Technician Certification Program Committee. Burton can be contacted at brian.burton@exp.com.
Does the equipment need to be certified by the manufacture that it will be operational after the design earthquake in Canada? In California manufacture must certify equipment for a given seismic event and provide a label on the equipment. For post disaster facilities the equipment is tested on a shake table.