Steel Joist Bend Loads & Local Joist Reinforcement

[jochav52802]

Good Day!

Regarding steel joist bend loads, when we go to hang MEP components from our joists, it's common practice to support these items by spanning angles or channels between either the joist top or bottom chord.

As a result, our steel typically only attaches to one of the two chord angles, and a lot of the time there are no connectors between the angles outside the joist panel points, so concentrated loads applied outside panel points can't be load-shared between both angles.

My questions are as follows:

1) When a bend load is specified, does that assume that the load will be equally supported by both joist chord angles?
2) When I attach my MEP support steel to one of the joist chord angles, does that imply that the available bend load must be cut in half?

The standard detail I've seen for local joist reinforcement doesn't clarify this, so it seems that a lot of Engineers could be misled into thinking that they have double the bend-load capacity, and thereby missing areas where local reinforcement is required.

Any thoughts are appreciated, thank you!

 

[phamENG]

I prefer a detail that calls for angles on both sides of the joist to prevent this very thing. For bottom chord hanging loads, I also like to have a plate welded between the chord angles that can have holes in it for attaching hangers. Again, shares the load across both chord angles.

 

[ProgrammingPE]

SJI permit concentrated loads of up to 100 pounds outside of the panel points, but they specifically say that the load must be applied to "both chord angles in a manner which does not induce torsion on the chords" (45th Edition Standard Specifications Load Tables for Steel Joists and Joist Girders, pg 15).

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