shear stud location on a composite beam 1

[struct6]

On a composite slab the contractor welded the studs to the edge of the flange rather than the center of the beam. Moreover he poured the slab before we looked at it. My question is, now since the studs are welded off center will this reduce the capacity of my composite beam and is it written somewhere that the studs must be welded to the center of the beam?

 

[JAE]

AISC 13th Edition specification - section I3.2.d has values for Rg and Rp that adjust the stud shear capacity based on position of studs, number of studs in a deck rib, etc.

I don't see anything on the position with respect to the beam centerline.

 

[BAretired]

* How far off center are the studs?

* Do they alternate from one side to the other or are they always on the same side of beam center?

* Why did he offset the studs?

* Why did he pour without an inspection?

BA

 

[Den32]

See section 7.4.5 of AWSD1.1 for distances and tolerances.

Did your drawings show or indicate the studs to be centered?

I didn't see anything in AISC Code of Standard Practice. What else did you reference on your Drawings or Specs?

 

[ishvaaag]

Quite likely if the asymmetry induced in the behaviour can be forestalled by otherwise non computed for strength steel and concrete the behaviour will remain similar. For a simply supported composite beam the shear transfer forcing the steel beam and concrete head to work together will be like two fingers compressing the compressed flange in the side of the connectors, hence the exploding side will be the opposite to the one it has the connectors. You can dimension the required stiffness to that side and anchoring forces for such explosion by considering the factored forces applied at root of the tumbled studs, or their capacity. This will give you a glimpse of what you are required to add to counteract the asymmetry.

 

[ishvaaag]

Hmmm a moment. It is tensile action on the side of the connectors. Hence it will bent with the convex side in the side the connectors are. This is the side where the explosive stresses need to be counteracted.

 

[ishvaaag]

And "explosive" streses sounds quite excessive. Squeezing would likely be a better word. But not something that can't be analyzed.

 

[BAretired]

The more serious issue is that the contractor poured the slab without allowing the engineer an opportunity to inspect the work. Had he done so, it would have been quite easy to add a few studs on the opposite side of the beam to make up for the eccentricity. As it is, there is nothing to do but accept or reject the work.

BA

 

[msquared48]

In that some beams have three rows of studs, it cannot be a nono under the AISC to weld away from the beam centerline. However, the flange is being used to transfer shearing stresses to the web now too, not just for bending. So there is now a combination of stresses to be dealt with.

As for the contractor, I do not know what your directions were to him regarding inspections, but if you haven't already, I would have a serious discussion with him, making him an offer regarding future inspections that he cannot refuse.

Or, if you are not sure if enough studs were placed, and you have the contractural authority, make him pay for an X-Ray, or some other means of testing to prove to you what is there. However, this will not tell you if the quality of the weld to the flange is good.

In the end it is your call in how to best provide the owner with a safe product.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[struct6]

Thanks for all your info.
We have had a serious discussion with the contractor to call us prior to every pour. We are the EOR for this project and we are also doing the special inspections.
I am pretty sure he welded the studs to the side because in the consequent inspection of the same area he had made the same mistake and we had him take those studs out and re weld it on the center.
The beams were W24x55 and the studs were 2" off center.
The reason he welded the studs off center was the high flute of the deck was directly above the center of the beam so instead of cutting the deck welding the studs on center he welded it off center.
Our drawings clearly indicate that the studs should be welded on the center.

 

[BAretired]

Usually, the flutes are at right angles to the beam, so that situation does not arise. In your case, it would have been better to offset alternate studs each side of center or to use double studs at twice the spacing.

BA

 

[hokie66]

His method would have made that beam more composite than with the studs through the high part of the deck, assuming the deck wasn't removed along the beam. Did you have a detail for beams parallel to the deck?

 

[WillisV]

There is a minimum flange thickness provision in the AISC Specification Chapter I for welding studs (I believe it is stud diameter / 2.5) that if the beam does not meet the stud must be welded in the center, otherwise it does not matter at all if it is welded off center.