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[SEAOC] Re: [SEAOC] Steel frame design[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaoc(--nospam--at)power.net
- Subject: [SEAOC] Re: [SEAOC] Steel frame design
- From: TFHSE(--nospam--at)aol.com
- Date: Wed, 19 Jun 1996 13:23:53 -0400
Re: industrial structures with knee brace to mid height of column. I try to avoid this configuration, but sometimes must provide a design. An Rw of 4 is the general default for non-building structures. With an Rw of 4 and a non-building structure, many prescriptive requirements, such as strong-col weak-beam, tension-compresion bracing, are not required. With an Rw = 4, only the connection requirements of concentric braced frames apply. Note that when the connection requirement is "strength" based (i.e. develop 3*Rw/8 times the seismic force in the brace) the allowable stress may be increased by a 1.7 factor as per UBC 2211.4.2. Thus, with an Rw=4, the connection requirement is not much higher than if the brace force were from wind loading. For an added measure of reliability, An Rw=3 may be used. An Rw = 3 should theoretically keep your forces at about or below yield (considering safety factors and overstrength provided). While the prescriptive requirements of higher Rw buildings are not required for this catagory of structure, they should be at the very least qualitatively considered during design as desireable qualities. Adding redundant locations of the bracing is also desireable. I presented a paper titled "Use of Building Code Seismic Provisions for Non-Building and Industrial Structures" at the Dec 1994 EERI regional seninar in St. Louis MO. It is in the proceedings, or I could forward you a copy on request. Thomas F. Heausler, S. E. Kansas City, MO (816) 822-1180 TFHSE(--nospam--at)aol.com ...
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