steel joists
steel joists
(OP)
What is the benefit in extending the bottom chord of a joist and welding it to either the column or a steel beam if the beams run over the top of the columns? This is for a shear wall building, so the joists are not participating in any moment frames. The design of the columns is based on the height from the top of foundation to the joist seat. If you are extending the bottom chord and welding it to the steel, shouldn't you be telling the joist manufacturer to design the bottom chord for fixed end moments?






RE: steel joists
1. Older engineers used to do this to "add" lateral stiffness to the framing in a nebulus sort of way - just a judgement thing. - Usually specifying that the connection must be made after all roof dead loads are in place.
2. The extension to the bottom of the beam flange would add lateral stability to the beam and prevent lateral buckling at the beam/top plate connection where the beam would rotate off the column.
3. The extension of the bottom chord provides full connections for hung ceiling grids.
All of the above do have the same effect that you mentioned - the addition of fixity to the joist end and should be noted for the joist manufacturer.
RE: steel joists
RE: steel joists
From the Cdn Steel code commentary....
The function of tie-joists is mainly to assist in erection & plumbing of the steel frame. Either the top or bottom chord is connected by bolting and after plumbing the columns, the other chord is usually welded. If the designer wants to use the joist to brace the columns, or resist lateral forces on the finished structure, the appropriate moments and forces are to be shown on the building design drawings to enable the joist manufacturer to design the joists and joist-to-column connections properly. In cantilever suspended span roof framing, joists may also be used to provide stability for girders passing over columns.
RE: steel joists
RE: steel joists
RE: steel joists
RE: steel joists
I agree that extending the bottom chord to a beam running over the top of a column will brace it. In my experience, I have not seen many engineers give consideration to the fact that attaching the bottom chord creates an end moment in the joist and the supporting structure, even for vertical loads.
RE: steel joists
Joist bottom chord extensions should not be welded at the column
unless they are part of a moment frame system. SJI joist are designed as
simple span members, the fixity that would be produced is not
investigated unless the design requires it, then the moments would have
to be given to the joist manufacturer for his analysis.
OSHA requires that joist at columns must have their bottom chords
extended to a column stablizer plate for safety concerns during
erection. They are not to be welded.
Carl Pugh, P.E.
VP Engineering
RE: steel joists
RE: steel joists
Thanks a lot
RE: steel joists
While there request or download the joist manual. Also you may contact SJI (steel Joist Institute) for their publications and design guides.
I use a simple but handy program that I bought few years back from Spencer Engineering. What I like about it is the vibrations analysis. Here is the web site
http://www.spencer-engineering.com/software.html
Good luck
RE: steel joists
RE: steel joists