Mike Dolt Enterprises
Mike Dolt Enterprises
User: malachi constant, Location: Minneapolis
Asked on: Thursday, March 24, 2011 at 8:22 am EDT
Answered on: Tuesday, May 14, 2024 at 3:12 am EDT
Question: Designing an apartment, half existing/remodel, half new. Architect says it is in a seismic zone (northern Illinois/greater Chicago area) and structural engineer calculates it as "Seismic Occupancy II and Design Category B".I've looked through the NEC ('08), the IBC ('06) and this forum, but still can't figure out what to do with that information. IBC 1613 references ASCE 7, which I have not yet located a copy of in our office but assume our structural engineer has one. Does that hold the key to all my questions? Any rules of thumb? Normally I design in areas where the buildings don't shake, so not sure how to proceed.Thanks!
Seismic Occupancy II and Design Category BDefinition
Seismic Occupancy II: Buildings used for essential services or housing more than 50 people. Design Category B: Buildings with a higher risk of collapse during an earthquake.
Requirements
ASCE 7 (Minimum Design Loads for Buildings and Other Structures) provides the requirements for seismic design in seismic zones. It contains the following sections relevant to your project:
Chapter 11: Seismic Design Requirements for Buildings Chapter 12: Structural Design Requirements for Seismic Resistance Chapter 13: Nonstructural Components and SystemsImplications for Electrical Design
Building Structure
The structural engineer will provide details on the seismic bracing and reinforcement requirements for the building structure. Electrical equipment and raceways must be installed in a manner that does not weaken the structural integrity of the building.
Electrical Equipment
Panelboards and Switchboards
Must be securely anchored to the building structure and rated for seismic loads.
Conduit and Cabling
Must be properly supported and protected from damage during an earthquake.
Equipment
Heavy or vibration-sensitive equipment must be securely fastened and isolated from potential sources of vibration.
Nonstructural Components
Lighting fixtures, suspended ceilings, and other nonstructural components must be securely attached and meet seismic performance criteria.
NEC and IBC Requirements
NEC 310.15(B)(1)
Conduit and cables must be supported not more than 12 feet apart.
NEC 408.43
Panelboards and switchboards must be accessible and secured in place.
IBC Section 1613
Seismic bracing and anchorage requirements for electrical equipment.
Rules of Thumb
Use flexible conduit or cable tray to accommodate movement during an earthquake. Install conduits parallel to building braces or reinforcement for support. Secure equipment to vibration-isolating mounts or vibration-resistant brackets. Brace light fixtures and suspended ceilings securely to prevent falling.
Next Steps: Refer to ASCE 7 for specific seismic design requirements. Work with the structural engineer to determine appropriate bracing and support details.* Consult with an experienced electrical engineer in seismic design for any further guidance. Flag for review