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Eugene City Hall R32.19.04 Rev. B. September 9, 2003 <br /> <br /> Figure 2-16. Alternate Style Vibration Isolation Mounts <br /> <br /> Figure 2-17 shows the typical suspended ceiling system used in the office buildings. It is <br /> assumed that the t-bar ceiling system is lightly strong form the concrete roof system <br /> above, with little to no suitable seismic lateral supports. <br /> <br /> This type of ceiling system will tend to "disassemble" itself under moderate to strong <br /> ground shaking. At shaking levels of PGA = 0.25g and higher, many of the ceiling tiles <br /> will fall, creating a mess (but not a significant life safety hazard), and the t-bars may <br /> become warped. It will usually take a day to clean this up. <br /> <br /> Possible seismic mitigation would include the addition of diagonal wires, to connect the <br /> t-bars to the roof above (this would be a code-style retrofit, intended to provide minimum <br /> protection to occupants). Note: code-only diagonal wires have not shown to be effective <br /> in limiting damage to the roof: their primary function is to limit the chance of <br /> components falling. In areas of the City Hall complex where continued operations are <br /> essential (not even allowing a few hours to clean up racked t-bar ceiling components), <br /> then a more expensive style of retrofit is suggested, including structural load-rated t-bars; <br /> connections or t-bars to walls; and lateral bracing using compression struts and diagonal <br /> angles, etc. This more elaborate type of suspended ceiling retrofit might cost about $20 <br /> per square foot. For cost estimating purposes, it is assumed that about 1,000 square feet <br /> of office space will be so-designated; and the remainder being upgraded just for life- <br /> safety purposes. <br /> <br /> G&E Engineering Systems Inc. Page 14 <br /> <br /> <br />