Welding to Existing Steel Under Load

[jropert]

I had a question regarding the effects and possible requirements of welding to existing wide flange beams while these beams are under load.

This particular job requires cutting holes into an existing concrete floor slab, which is currently supported by wide flange beams (no metal deck; this is an older building). My company and I are not the EOR, but are the contractors in charge of constructing this project. The given structural drawings call for added steel beams and channels to frame around the new openings in the floor slab (there will be relatively light mechanical units and floor drains supported by this framing). These are indicated to be welded to the existing wide flange beams of the floor structure.

My question is this: The structural drawings don't call for any special shoring to be put in place prior to welding to the existing wide flange beams. This isn't unusual for this type of application from what I've seen in past projects (at least at my previous employment with a structural consulting company). However, I am not sure if it should be automatically implied that we as the contractor are responsible to figure out shoring requirements during the welding process (btw, this floor is 30 feet above the ground floor). The concern is that by welding the shear connection tabs to the existing beams, this will "weaken" the localized area while the beam is still under floor load.

Does anyone have some commentary, code requirements, guidelines, etc. for this situation? I can't imagine that this is a unique situation, but don't really know the best place to look.

Thanks,
Josh R

 

[BAretired]

It is not advisable to weld to steel while it is under stress. This rule can be breached if the stress is deemed minor, but without knowing the exact circumstances, I would suggest shoring the beams which will be weakened by welding.

Alternatively, check with the EOR and see if he has considered the matter. My guess is he hasn't.



BA

 

[paddingtongreen]

Time was when I would regard that issue as part of my work, but then the lawyers came into the business and we stopped interfering with the Contractor's "means and methods" and the risk of taking on avoidable liability.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[TXStructural]

Remove any remaining live and transient loads during the work. Shear tabs are usually welded only to the web, and it is unlikely that dead load will be placing significant shear on the web where you need to be welding. If you are concerned, check how much stress is on the web at the weld locations. Look at actual loading, not factored design loads.

 

[ToadJones]

Ask the EOR to consider clip angles, possibly a one-sided clip angle connection. Bolted-Bolted or Welded to new beam, bolted to existing. As the contractor you can use a mag-drill on the existing web.

 

[ToadJones]

If they are simple shear connections making the change from a welded shear tab to a clip shouldn't be a design challenge at all.

 

[jropert]

Good idea ToadJones, we were actually thinking of requesting a change to a bolted clip angle instead of welding, more for the purposes of not having to deal with containing sparks falling from 30 feet up (this building must remain fully operational to the user while we construct, so there's more safety involved of course). We are hoping however that this request will not take a life time to get approved which is why we are still considering the welded option (no offense, but this is a government contract so time is not on our side). Does anyone think that the EOR should be responsible for pointing this out if it were a big deal? I know what you mean Paddington about involving oneself in the contractor's "means and methods" as I once worked on the design side, but now I'm on the other side of the "fence" so-to-speak.

Just in general and for future reference, are there design guides or code requirements (such as in AISC, etc.) that would provide insight to such issues?

 

[slickdeals]

Just in general and for future reference, are there design guides or code requirements (such as in AISC, etc.) that would provide insight to such issues?

I think only experience will.

 

[ToadJones]

Like I said, if they are simple shear connections, they can basically pull the connection out of the steel manual.
There might be reasons that they want welded connections, but changing them to bolted is not a serious design challenge.

 

[ToadJones]

...in fact, a bolted-bolted clip might make erection easier if you are fishing the new beams in between existing.

 

[paddingtongreen]

If there is a fishing job, and there usually is, it pays to use bolted/bolted but with diagonally opposite clip angles welded or extra bolted to the beam, the "bolt to ship" angles can be removed before installation and added back when the beam is held in place by the fixed angles.


Michael.
Timing has a lot to do with the outcome of a rain dance.