New hole near composite steel beam
New hole near composite steel beam
(OP)
We are putting a new hole through a composite RC slab on metal decking adjacent to an existing composite steel beam. The hole is within the effective concrete flange width but not right next to the beam. I can frame the hole with new non-composite steel members but I can't find any guidance on the effect on longitudinal shear in the slab. Presumably if the flange is now not symmetrical with a wider flange one side of the beam, this means that the longitudinal shear will now be correspondingly less on the side with the narrower concrete flange. I am asking because the longitudinal shear is critical here and obviously I can't do anything to the concrete or the shear studs on the beam. All the guidance I can find relates to either an internal beam with symmetrical flanges or an edge beam where the flange is all on one side.






RE: New hole near composite steel beam
RE: New hole near composite steel beam
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: New hole near composite steel beam
RE: New hole near composite steel beam
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: New hole near composite steel beam
Mike McCann, PE, SE (WA)
RE: New hole near composite steel beam
RE: New hole near composite steel beam
First off, if the beam works as non-composite, I believe that most engineers would be satisfied to leave it at that. I know I would. If it were necessary, I'd just count on one sided composite action like an edge beam.
Other thoughts:
- when the opening is cut, the flange compression forces will redistribute. You may well get some concrete cracking as that happens.
- failure of the studs is pretty ductile actually. Usually it takes the form of localized concrete crushing low on the studs. Were it not somewhat ductile, we wouldn't be able to space the required studs uniformly.
- for a variety if reasons, many beams in a composite floor are often designed to work as non-composite but are provided with a nominal amount of studs anyhow. Nothing ever seems to go awry so, at least, there's precedent for this not being a problem.
- have you calculated the longitudinal shear capacity of the concrete either side of the deck? It should be greatly in excess of the demand. I wouldn't assume that it was anywhere near maxed out originally.
- even with the new opening, you haven't actually changed the longitudinal shear capacity of the deck right beside the beam flange. It would still be your allowable shear stress multiplied by the distance from the peak moment to the end of the beam. Or something similar. You'd just reduce longitudinal shear demand on the opening side of the beam as there would be less compression in the flange on that side after installing the opening.
You've raised some interesting points here that we rarely consider in these situations.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: New hole near composite steel beam
RE: New hole near composite steel beam
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.