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RE: Bar Joist

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That is how we design our roof and floor decks and joists.  Another reason for staying with the same size joist with a closer spacing is to eliminate the chance the larger joist is put in the wrong place.  Depending on shipping of joists and the erector, there is no guarantee that they will be placed in the right place.

 

 

 

Gary W. Loomis, P.E., Senior Structural Engineering

Master Engineers and Designers, Inc.

-----Original Message-----
From: Jordan Truesdell, PE [mailto:seaint1(--nospam--at)truesdellengineering.com]
Sent
:
Friday, April 06, 2007 2:00 PM
To:
seaint(--nospam--at)seaint.org
Subject: Re: Bar Joist

 

I haven't seen any replies, so I'll put in my $0.02:

I don't (bother to) account for load sharing.  Usually I'll just decrease the spacing to account for the added load at the perimeter, since I think it's cheaper to buy an extra 4-6 joists of a series that you're already building 100 of instead of adding 2 or 3 joists of a unique type.  You could do a deflection/stiffness analysis to get a more accurate picture, but you have to be cognizant of the price of engineering analysis vs the return in the field (and whether or not you're getting paid to do the added scope).

For non-composite concrete floors, I count the concrete like it's sand - no stiffness, just dead weight. If it won't actually span the distance , it's the only prudent thing to do. The advantage to this "method" is that there actually is some residual load sharing that will occur when some numbnut does something stupid to the structure. Instead of collapsing, the floor system just sags locally or you get cracks in hard surfaces.

Jordan



Wesley Werner wrote:

    When you distribute roof loads to your bar joists, do you consider the continuity of the metal decking, or do you figure the decking is pinned between joists? Continuity makes a big difference particularly for the second joist from an edge where there is snow drift. In addition, what about floor loads when you have deck with concrete?

 

Wesley C. Werner

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