# RE: Load Combinations for ASD 9th

• To: "SEAOC List Server (E-mail)" <seaint(--nospam--at)seaint.org>
• Subject: RE: Load Combinations for ASD 9th
• From: "Ritter, Mike" <mritter(--nospam--at)lgt.lg.com>
• Date: Fri, 18 Aug 2000 11:06:02 -0400
```My gripe is with the alternate ASD load combinations shown in the new
IBC 2000...

1,  D + L + (Lr or S or R)

2.  D + L + (omega W)

3.  D + L + (omega W) + S/2

4.  D + L + S + (omega W)/2

5.  D + L + S + E/1.4

6.  0.9D + E/1.4

Am I the only one who sees something missing?  Where is the good old .9D
+ W?  Or, as in the basic load combinations, 0.6D + W?  I think this
combination is very basic, and should be checked whether the code lists
it or not.

Mike

> -----Original Message-----
> From:	Bill Allen [SMTP:Bill(--nospam--at)AllenDesigns.com]
> Sent:	Friday, August 18, 2000 10:46 AM
> To:	seaint(--nospam--at)seaint.org
> Subject:	RE: Load Combinations for ASD 9th
>
> 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
> live load) is pretty ridiculous.
>
> 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
> ||one story building will be fully loaded with its live load
> ||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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