Nonstructural components consist of architectural, mechanical, plumbing and electrical components that are permanently attached to structures. There is often debate as to who is responsible for the anchorage and restraint of nonstructural components. Is it the structural engineer, architect, mechanical engineer, etc.? Chapter 12 of FEMA 389 discusses how a uni- ed approach can be used by the design team to ensure that a scope of work is provided for each element thus clarifying who in the design team is responsible for that item. FEMA 389 also includes sample checklists to aide in this endeavor.
Concerning forces and displacements, Chapter 13 of ASCE 7 provides clear guidance on how to calculate the seismic design force for each component. Separate response modi cation and component amplification factors are provided in Table 13.5-1 for architectural components and in Table 13.6-1 for mechanical, plumbing and electrical components. If the component has multiple connection points, the design must also take into account displacement that can occur within the structure or displacements that could occur between separate structures.
When not exempt by Chapter 13 of ASCE 7, the construction documents must show the seismic restraint requirements for nonstructural components and their supports and attachments. They shall also note the special inspection requirements for their installation per Section 13.2.7 of ASCE 7. In addition, Section 1705.12.3 of the International Building Code (IBC) re- quires that the design professional list on the construction documents the certification requirements for designated seismic systems. Section 202 of the IBC defines designated seismic systems as “those nonstructural components... for which the component importance factor is greater than 1”. Chapter 13 of ASCE 7 then clarifies that the following conditions would result in an importance factor of greater than 1:
➤ The component is required to function for life-safety purposes after an earthquake
➤ The component conveys, sup- ports or otherwise contains hazardous, highly toxic or explosive substances and can pose a threat to the public
➤ The component is in or attached to a Risk Category IV structure, and failure could impair the continued operation of the facility
In essence, designated seismic systems are those nonstructural components that are most likely to affect life-safety after a seismic event. Section 1705.11.4 of the IBC also requires that special inspection be provided for designated seismic systems.
When it comes to supports and anchorage, nonstructural components shall be “bolted, welded or otherwise positively fastened without consideration of frictional resistance produced by the effects of gravity.” This anchor- age shall be provided for not only the component but also its support. A good example would be of a rooftop unit. While appropriate anchorage may be provided for the unit to the rooftop curb, the curb itself must also be properly anchored to the supporting structure. Per Section 13.4.2 of ASCE 7, anchors in concrete are to comply with Appendix D of ACI 318, anchors in masonry are to meet TMS 402/ACI 530/ASCE 5, post- installed anchors are to be prequalified for seismic applications and power-actuated fasteners resisting sustained tension loads or friction clips are not allowed in high-seismic regions.
A quick note on seismic design requirements: The current requirements for non- building structures are found in Chapter 15 of ASCE 7 while the requirements for nonstructural components are located in Chapter 13 of ASCE 7. For nonbuilding structures such as vehicular bridges, electrical transmission towers, hydraulic structures, buried utility lines and their appurtenances, nuclear reactors and piers or wharves, the seismic design requirements are not provided in ASCE 7 but rather in industry standards specific to the element type.
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