Field Issue During Steel Erection

[SteelPE]

I received a call this morning from a site this morning in regards to a building that is currently in the erection phase. The building is a warehouse utilizing open-web steel joists and joist girders with wide flange columns and bolts cast into concrete (4-3/4" dia ASTM F1554 Gr 36 (edited from 46) bolts in a 5" ga pattern). The detail we are using requires the use of a leveling plate an grout in the final configuration.

Due to cold temperatures, the GC is saying that they were not able to place the grout under the columns prior to steel erection, so they elected to use leveling nuts (which I just found out are only 1/2 the thickness of regular nuts... at least that is what I have been told). When the GC left the project last week everything was fine, then storms came in and not they have a group of columns that are no longer plumb (saying that they are not leaning considerably at the top (I don't recall if they said 3 feet or 3 inches).

The GC is saying that something stripped under the base plate (bolts or nuts). It sounds to me like the erector didn't brace the building properly (We went around about this a few times before I got off that ride as the GC insisted that everything was braced correctly). In the end, there is damage somewhere and I am not exactly sure where.

Two questions:

Has anyone run into this issue before (leveling nuts stripping)?
How do you fix the issue?

I am thinking they will need to plumb the building again and then the will need to install new post-installed bolts (not going to be easy). However, I am not sure if we should be having them do additional work.

 

[CANPRO]

I have not run into this issue before. The erector may be able to pull the column back with come-alongs. 3 feet or 3 inches is a big difference.

How far along was the erection? Was any of the permanent bracing in place? Stripping the threads on a half-nut engagement would take (ball-park) half the ultimate load of an anchor rod tensile capacity - which would be significant for construction loads, in my experience. Seems a bit fishy to me. It'd be interesting to run a rough analysis of the structure during the failure and see if the numbers match the story.

If the anchor rods are in acceptable condition, once the building has been plumbed I think you just need to shim and grout under the base plate. The thread is stripped but this is no different than having no nut and a grouted base plate. Although I do wonder if having the threads stripped from the anchor rod would impact the capacity of the net area.

 

[JStructsteel]

I agree with CANPRO. First you need to confirm 3" or 3 feet. 3" could be a nut stripped, where 3 feet could be a anchor bolt bent.

 

[SteelPE]

Erection started last week and is scheduled to take a few months..... but the column is currently surrounded by framing. However, no permanent bracing or decking has been installed. There is on WF beam attaching to a column on this line and the GC suspects that this beam is what caused the issues (catching the wind where the other joist girders allowed the wind to pass through the girder). The columns are 40'-0" tall (won't take much load to push these things over).

One other option that popped up would be to do a tensile test on the bolts to determine if there are any other issues with the bolts other than the stripped threads.

 

[dvd]

Leveling nuts do not allow for anchor rod stretch on post-grouted baseplates. Attached excerpt from "The Grouting Handbook" has discussion for machine leveling and grouting.

 

[JLNJ]

I agree that it's more likely the base plate or the anchor rods bent. It doesn't take much base plate deformation to let a column go out of plumb, especially if the temporary bracing is not well-executed. This is why I'm not too fond of using leveling nuts. They also seem like a place for pier/grout stress risers in the final condition.

I have seen erectors do the absolute minimum for temporary bracing. Sometimes it works out OK, sometimes it doesn't. The code of standard practice isn't overly specific on the HOW. It gives a lot of latitude to the erector.

 

[Aesur]

Leveling nuts are just that, for leveling prior to grout placement, if you rely on the leveling nuts to support a larger area of framing before grouting then you better design said baseplate for bending, this could quickly increase baseplate thickness. You mention there is framing around the column already, was there even a plan to grout the baseplate later? The contractors argument for cold temperatures being the reason doesn't set well with me, what he is saying imo is it's cold and we don't want to pay to use the proper grout or heat up the area. I have personally seen grout, epoxy and concrete be poured in -11 degree F weather and -20 when wind chill was counted, it's possible with the proper procedures.

 

[BridgeSmith]

Leveling nuts are just that, for leveling prior to grout placement,

For our sign structures and high mast light towers, the leveling nuts are the permanent support, and no grout is used. Of course, we're using Grade 105 anchor bolts and heavy hex nuts.

If they wanted the leveling nuts to be the permanent support, they needed to use at least regular hex nuts, rather than jam nuts.

I would think they'll probably need to pressure grout now, unless they can raise the base plate off the leveling nuts a little, so they can tighten the top nuts and pull the base plate tight against the grout after grouting.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[JedClampett]

I don't know if this helps, but our procedures are to level the columns using the leveling nuts, installing shims, then backing off the leveling nuts before pressure grouting. We want the columns supported by non-shrink grout. The bolts are for shear and uplift only. And the leveling nuts do nothing. If you don't have moment, shear or uplift, maybe you can calculate this away.
Saying that, I hate to let the contractor off the hook. If there's a way to make them suffer, I encourage it.

 

[dik]

It used to be that the City of Toronto used to require levelling plates so they could be lifted off to ensure that there was grout under the entire base plate. I've always preferred steel shims and grout and not levelling nuts.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

Grade 55, here, even if Grade 36 works... I also like my anchor rods to be weldable... too many problems in past.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[bones206]

I'd have to go take a look in person to make a judgment on something like this, or at least have some good photos. Unless there is some pretty significant damage to the bolts or surrounding concrete, I would lean towards them being ok to remain as-is. I wouldn't consider stripping of the leveling nuts as a deal breaker for the anchor rods, since it shouldn't affect the effective tensile area.

 

[SteelPE]

I ended up making a trip to the field yesterday to assess the existing conditions. When I arrived the columns were back to being plumb again. When I dug a bit deeper, the site superintendent said columns were not braced at all in the orthogonal direction they were leaning.

This was the column line before plumbing again.

This was the best picture that I could get of the condition under the bolt.

We are planning on doing a pull test on the bolts..... maybe to 100% of the design load to make sure there are not any issues (not sure if this is a good idea, but I am 95% sure that everything is OK, but I'm not willing to die on the 5%). One column doesn't technically need any bolts as there is only downward loading on the column in that location. We are planning to test one bolt there... and then test one additional bolt in each column if things go OK.

 

[azcats]

Man they're really lucky that whole thing didn't topple over...

Looks like there was plenty of thread. Did they explain why the use of half height leveling nuts?

 

[human909]

Agreed. Poor practice that somebody really needs to be informed in no uncertain way that it is unsuitable.

Though I would question whether the engineered design is partly the cause. If this is a design that relies on the roof diaphragm then you really need some temporary bracing in the mean time. Maybe that is the norm in this locality, but temporary bracing is often as troublesome to install and remove as some permanent cross bracing.

Likewise engineers love to pass off temporary bracing requirements to the GC, but often the GC is not suitably informed to provide appropriate temporary bracing. Again this is my experience in my locality, but may or may not be applicable elsewhere.

 

[SteelPE]

Generally, the stability of the building is up to the contractor/steel erector to figure out during construction. This isn't an overly complex building so no real fancy erection engineering is necessary. Yes, the building utilized a roof deck diaphragm to distribute the lateral loads to a concentric bracing system. The steel erector will typically use steel cables to brace the building. In this instance, this wasn't done on this line..... but was done on others were there was no issue.

 

[XR250]

I mean, don't most buildings use a roof diaphragm?
To me, this is means and methods. The fee for temp. bracing design would be too for much most customers to stomach. And, given the liability and lack of it being standard practice, I am usually a NO.

 

[human909]

Fair enough. I suppose my comments aren't really applicable in this locality (presumable USA/Canada).

The steel erector will typically use steel cables to brace the building.

Ahhhh. Certainly not a common practice here.

I mean, don't most buildings use a roof diaphragm?

Normally not for a single story steel structure here down under.

To me, this is means and methods. The fee for temp. bracing design would be too for much most customers to stomach. And, given the liability and lack of it being standard practice, I am usually a NO.

Interesting.... So it is preferable to have a non engineered temporary bracing than an engineered one. That certainly makes sense for a fee and liability perspective. Not really from a safety perspective, but if it mostly works then all good.

My comments are just my own observations of differences in engineering/construction methodologies. I'm sure engineers from the USA would be aghast at how easy it is to become a PE down here. And similarly shocked at the lack of requirements for 'signed and sealed' drawings let alone recorded calculations or even reviewed calcs.

 

[SteelPE]

Man they're really lucky that whole thing didn't topple over...

Looks like there was plenty of thread. Did they explain why the use of half height leveling nuts?

Yes, I told them had it toppled over they would be replacing all the steel... which they have been waiting arrive for months.

Why did they use 1/2 nuts.... they actually use jam nuts for this application. We typically specify 3/4" of grout under leveling plates. If they had used full sized nuts then they might not have had enough adjustment in some instances (the footing in question looks slightly low so it looks like they could have used full sized nuts here).

I told the GC to use a different method for shoring up the column after proper elevation has been achieved. Now he keeps asking for approval for different methods he is proposing. Unfortunately I am not offering any solutions for him at this point for the reason XR250 outlined above.

We are going to have the bolts tested to 110% of the demand to see if they are compromised. I don't know if this is appropriate or not, but it is the only way I can think of that we can prove no other damage has occurred to the bolts during the stripping process.

FYI, this picture was taken 800 feet from the entrance to the jobsite.

 

[gte447f]

SteelPE, I vaguely recall that I think I also used to spec 3/4" or 1" of grout below baseplates. Then, somewhere along the way I came across the advice (I can't recall when or from whom) to specify a minimum of 2" of grout below baseplates. I think this is part of the reason why.