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Re[2]: MBMA Code and Wind Loads

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I would tend to agree that the source of wind load provisions in ASCE 7-95 is 
not MBMA.  About 3 years ago I compared the wind loads on a metal building 
design determined using MBMA and ASCE 7 (either 93 or 88, doesn't matter 
here). The MBMA loads were much less.  MBMB has some justification for this, 
but I am not sure what it is. Since wind loads for low rise buildings from 
ASCE 7-95 end up being not largely different from those determined from ASCE 
7-93, I suspect that MBMA wind loads are still much less than the 
corresponding ASCE 7-95 values. In the process of this work, I was developing 
a metal bldg. spec, and I specified that the building was to be designed to 
1993 BOCA Code, particularly in regards to wind loads.

Incidentally, the edition of MBMA Low Rise Bldg. Systems Manual I used was 
1986, with a 1990 Supplement. Is there a more recent version now, anybody?


______________________________ Reply Separator _________________________________
Subject: Re: MBMA Code and Wind Loads
Author:  seaoc(--nospam--at)seaoc.org at Internet
Date:    2/16/98 1:12 PM


In a message dated 98-02-16 10:05:40 EST, you write:

<<  The MBMA wind load provisions are now part of the ASCE 7-95 
      Provisions.  Regardless of their merit, they are now "code".  Be 
      careful when mixing ASCE 7-93 criteria (fastest-mile wind speed) with 
      ASCE 7-95 criteria (3-second gust speed).
       >>

I do not believe that the source of the ASCE 7-95 wind load provisions is 
MBMA.  I attended a seminar given by Dale Perry (one of the authors of ASCE 7) 
shortly after ASCE 7-95 came out.  My understanding is that ASCE 7 now uses 
three second gusts rather than fastest mile wind speeds because that is the 
more prevalent way of measuring wind speeds  these days and that 
internationally most codes are written around three second gust speeds.  The 
change to three second gusts meant changing a lot of factors so that the 
pressures derived came out about equal to ASCE 7-93.  They also increased some 
factors, resulting in higher wind loads, based on research or experience. 

Jan M Harris, PE
Liberty Engineering, PC
Virginia Beach, VA

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