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Re: UBC 97 seismic section and NEHRP[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaoc(--nospam--at)seaoc.org
- Subject: Re: UBC 97 seismic section and NEHRP
- From: "Bill Sherman" <SHERMANWC(--nospam--at)cdm.com>
- Date: 10 Feb 98 12:18:16 -0500
dhorning(--nospam--at)CH2M.com wrote: >You're quite right, the 1997 seismic section is quite different, and is >based on NEHRP. Wait 'til you see IBC 2000. One difference which may >not be readily apparent is that 1997 gives loads at strength rather than >service levels (that's why it's "R" and not "Rw"). Your right - its not readily apparent. I missed it when recently comparing the '94 and '97 seismic requirements for a project. I wondered why seismic seemed to increase so much (although '97 still governs over '94 for my application). Per the '97 UBC, 1629.1 states that "Where Allowable Stress Design is used, the load combinations of Section 1612.3 shall apply." Section 1612.3 has two alternate procedures for allowable stress design, but in both "E" is divided by a factor of 1.4. Thus the seismic loads given in Chapter 16 are 40% higher than required for allowable stress design.
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