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RE: Load Combinations for ASD 9th

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Mike,

Maybe this is over simplistic on my part, but if your looking as the roof
separate from the walls or columns (ie: no moment frame to transfer the
lateral wind pressure through the roof rafters)Combo 4 should be a mute
point.

Say you've got a flat or shallow pitch roofed building.  Uplift and Lr will
act against each other making Combo's 2 & 3 the more severe cases.

Now then if you do have a steep roof (> 30 degrees) or a moment frame
system, the lateral wind force in combination with Lr or Snow may affect the
design.

So is the combination unrealistic?  For Lr, yes.

For Snow?  Is it possible in a nor'easter to receive for max snow load have
maximun loads?  Seems logical.

Hope this helps,

David B. Tehranchi

A pessimist says the glass is half empty,
An optimist says the glass is half full,
Ands the engineer says...
    "It's a good thing I put half my
     water in a redundant glass"
                            ---Dilbert


-----Original Message-----
From: Michael Zaitz [mailto:mzaitz(--nospam--at)hgbd.com]
Sent: Friday, August 18, 2000 10:12 AM
To: seaint(--nospam--at)seaint.org
Subject: Load Combinations for ASD 9th


Hello,

The load combinations are referenced as ANSI 58.1 "Minimum Design Loads for
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
newer ASCE manual?

Thanks,

Mike


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