# RE: Load Combinations for ASD 9th

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Load Combinations for ASD 9th
• From: "Bill Allen" <Bill(--nospam--at)AllenDesigns.com>
• Date: Fri, 18 Aug 2000 07:45:44 -0700
Even if you can visualize an earthquake occurring during a re-roofing job, I

What is the probability of THAT happening?

Isn't the design level earthquake something like 2% exceedance in 50 years?

A re-roof occurs every 10-20 years?

Are we talking about a 500-1,000 year event for a structure that won't last
50 years anyway?

Yes, it CAN happen. But, so can an engine falling off an airplane hitting a
roof. Are we going to design for THAT?

O.K., so my statistical analysis isn't accurate, but you get the idea.

IMO, combining wind OR earthquake load with roof live load (even 50% roof

Regards,

Bill Allen, S.E. (CA #2607)
ALLEN DESIGNS
Consulting Structural Engineers
Laguna Niguel, CA
http://www.AllenDesigns.com
V (949) 365-5696
F (949) 249-2297

||-----Original Message-----
||From: Michael Zaitz [mailto:mzaitz(--nospam--at)hgbd.com]
||Sent: Friday, August 18, 2000 7:12 AM
||To: seaint(--nospam--at)seaint.org
||Subject: Load Combinations for ASD 9th
||
||
||Hello,
||
||The load combinations are referenced as ANSI 58.1 "Minimum
||Buildings and Other Structures".  The oldest copy I have is
||the ASCE 7-95 that
||gives the following combinations:
||
||1. D
||2. D+L+F+H+T+(Lr or S or R)
||3. D+ (W or E)
||4. D+L+(Lr or S or R) + (W or E)
||
||What I am wondering about is how people handle the 4th
||combination with respect to
||one story buildings?  It seems to me that it is highly
||unlikely that the roof of a
||capacity at the same
||time a hurricane comes through (I can see it being reroofed
||when a earthquake
||hits).  How do others handle this?  Is there anything I am
||missing due to having a
||
||Thanks,
||
||Mike
||
||
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