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RE: Question on ASCE 7-02 Load Combinations
[Subject Prev][Subject Next][Thread Prev][Thread Next]- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: Question on ASCE 7-02 Load Combinations
- From: "Carter, Charlie" <carter(--nospam--at)aisc.org>
- Date: Mon, 29 Dec 2003 15:39:54 -0600
Wow! I'm not sure the text in those sections in Chapter 9 could be any more confusing of what I think is a fairly simple concept. Self-criticism, of course, since I probably voted for the language I just criticized when ASCE 7 was balloted. In both Sections 9.5.2.7 and 9.5.2.7.1, there are two equations for the amplified seismic load. In each of the first, you have a function of QE plus 0.2SDSD. In each of the second, you have a function of QE minus 0.2SDSD. The text tells you (in many, many words) to substitute the first for E in load combinations in Sections 2.3 and 2.4 when the earthquake effect is additive to the other loads and use the second when the earthquake effect is to be counteracted by the other loads. So, I think ASCE 7 has an editorial error in the referencing to the ASD load combinations as pointed out. Bill Scott already knew this and asked the question with the answer in it. (-: I'll pass this along to ASCE so it can be corrected. Thanks. Charlie -----Original Message----- From: Scott, William N. [mailto:William.Scott(--nospam--at)veco.com] Sent: Monday, December 29, 2003 2:54 PM To: seaint(--nospam--at)seaint.org Subject: Question on ASCE 7-02 Load Combinations The following are exerted from ASCE 7-02. 2.4.1 Basic Combinations. Loads listed herein shall be considered to act in the following combinations; whichever produces the most unfavorable effect in the building, foundation, or structural member being considered. Effects of one or more loads not acting shall be considered. 4. D + H + F + 0.75(L + T ) + 0.75(Lr or S or R) 5. D + H + F + (W or 0.7E) 6. D + H + F + 0.75(W or 0.7E) + 0.75L + 0.75(Lr or S or R) 7. 0.6D + W + H 8. 0.6D + 0.7E + H" "9.5.2.7 Combination of Load Effects. ..... for load combination 5 in Section 2.3.2 or load combination 4 in Section 2.4.1: E = ?QE + 0.2SDSD (Eq. 9.5.2.7-1) for load combination 6 in Section 2.3.2 or load combination 3 in 2.4.1: E = ?QE - 0.2SDSD (Eq. 9.5.2.7-2) where E = the effect of horizontal and vertical earthquake-induced forces Should the load case and LC 5 for ASD instead of LC4? "9.5.2.7.1 Special Seismic Load. ...the special seismic load of Eq. 9.5.2.7.1-2 shall be used to compute E in load combination 7 in Section 2.3.2 or load combination 5 in Section 2.4.1: E = =oQE + 0.2SDSD (Eq. 9.5.2.7.1-1) E = =oQE - 0.2SDSD (Eq. 9.5.2.7.1-2)" Should the load case be LC 8 for ASD instead of LC 5? Bill Scott, P.E., S.E. Principal Engineer VECO Alaska, Inc. 949 E. 36th Street, Suite 500 Anchorage, AK 99508 Phone 907-762-1655, FAX 907-762-1734 ******* ****** ******* ******** ******* ******* ******* *** * Read list FAQ at: http://www.seaint.org/list_FAQ.asp * * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to: * * http://www.seaint.org/sealist1.asp * * Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ******** ******* ****** ******* ******** ******* ******* ******* *** * Read list FAQ at: http://www.seaint.org/list_FAQ.asp * * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to: * * http://www.seaint.org/sealist1.asp * * Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********
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