Mixing Welds and Bolts... 1

[vvaccare]

I am involved in a project that is currently in the construction phase. While out in the field and inspecting some of the moment connection welds, we noticed several instances where several of the shear tabs were welded off to the beams. These beams are cantilevered and moment connected. When asked why several of these pieces were welded off in addition to the bolts, the contractor said the welds were done to level/plumb the steel. The connection in question is to the right of the uploaded picture. AISC 13th edition, Section 16 Chapter J1.8 states that "in such connections the available strength of the bolts shall not be taken as greater than 50 percent of the available strength of bearing-type bolts in the connection". If this is the case, would this mean that the weld would essentially need to be designed to take the full shear capacity of the connection? We have asked for the contractor to remove the welds, but worry that if they burn/grind too much that the beam web may be damaged. Any opinions for a course of action?

Thank you

 

[CELinOttawa]

I would leave it.... I cannot see how the welds would cause a failure. Even if the welds were weak and faile, the bolts would then kick in.

I have a hard time seeing this as a dangerous condition. Have you checked tbe connection against the combined bolt and welds provisions?

 

[structSU10]

That would be correct. The load-deformation of a weld is much different than a bolt - look at AISC 13th page 7-7 figure 7-3 and page 8-13 figure 8-5 - you will see that the weld is much stiffer than the bolt. The thing is in this situation, if the weld fails the connection will still be fine as long as the bolts are designed correctly. I would be inclined to leave it, as you are also not really worried about rotational ductility of this connection since it is part of a moment connection.

 

[gtaw]

This is a situation that should be reported to the Engineer.

The Engineer is the individual responsible to determine if deviations from the design have a negative influence on the performance of a connection.

The structural welding code has a clause that addresses unauthorized welds. Unauthorized welds are a nonconforming condition that must be reported by the inspector. The inspector is not in a position to determine whether the unauthorized weld has a negative impact on the design. The inspector's function is to verify the contractor has implemented the design provided by the Engineer. Any deviation should be noted in the report so the Engineer can review the situation and make a determination whether corrective action is required. The inspector should not provide direction to the contractor on how to accomplish the corrective work required by the Engineer. The "how to" is the responsibility of the contractor.

Best regards - Al

 

[racookpe1978]

That field weld weld is very, very poor. It has no credible strength.

Thus, agree with the constructing manager, and tell him that "doubling connections" by welding and bolting is fine, and can be used. As long as there is no extra charges for the extra work nor any schedule delays for the welder and his setup on top of beams and girders and scaffolding.

Then smile and tell him to NDE that weld and grind out all indications (porosity and embedded grit and coatings) and leave a smooth, clean acceptable weld on your building, and give you the NDE results for each field weld left at joints.

His "logic" (excuse?) for "leveling/plumbing" the steel using a weld is back-asswards. BOLTS and their inherent slop allow such movement, a fixed weld cantilevered out from the theoretical center point (work point) of a joint prevents movement or adjustment. Unless that was the intent of his excuse: "We needed to lock the joint in place so we could wedge something else into the right place, but we didn't want to tell you that the other piece of steel didn't fit .... "

 

[CELinOttawa]

Good point GTAW... The course of action varies depending on who the OP is.... My comment was based on the presumption that vvaccare is the designer.

 

[Bagman2524]

The way I read J1.8 you can either take credit for the bolts only, the weld only or 50% capcaity of bearing type bolts + weld. I don't see any reason why the weld just can't be ignored.

“Faith is taking the first step even when you don’t see the whole staircase.” MLK

 

[NS4U]

These look like twist off bolts. In which case, this is a slip-critical connection. (because twist off bolts are meant to be pretensioned). You can consider bolts and welds in a SC connection working together. Therefore I don't see any negative issue with the weld. It only helps. Nothing negative.

 

[NS4U]

Well- the only negative thing I can think of is that this changes the connection from a pin to a PMC. Still probably not a big deal because you have SC bolts which also resist rotation.

The only other thing you need to look at is that the weld is a good (i.e. no notches). So it needs to be inspected. gtaw is right on about that. I would be hesitant to make the contractor rip them out unless you can definitely say what is wrong with the as-fabricated connection.

 

[wadavis]

If you are just performing field inspection, what gtaw said, record and report all deviations from the IFC drawings, stay within the scope of work.

If you are the designer, keep in mind that ~50% of the beam's shear resistance is now in a Heat Affected Zone, this may or may not change your governing design case. See the attached picture for a bolted/welded connection done wrong.

 

[paddingtongreen]

The faying surfaces must be properly prepared for TC bolts to make the connection slip-critical, otherwise, you just have tight bolts.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[ornerynorsk]

Someone else said it, I believe. That is a very crappy weld, B&B would be the usual shop parlance for it (birdshi* & bubblegum). And now you've got a big HAZ in the web just out beyond the connection.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Bagman2524]

faying surface control for slip critical joints is described in AISC commentary section 3.2.2 (page 16.2-16)

“Faith is taking the first step even when you don’t see the whole staircase.” MLK

 

[JLNJ]

Either my eyes deceive me or those are some gigantic root openings for the flange welds.

 

[hokie66]

I don't think this particular connection is intended to be a moment connection. The OP knew what he meant in saying that he was there to inspect moment connections, but noticed this in a shear connection. I agree with the answers given that an inspector should report this to the design engineer, but if I were the design engineer, I would give it the thumbs up. Agree with racookpe, though, as the logic of using welds for alignment escapes me.

 

[paddingtongreen]

I guess they never saw a drift pin.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[gtaw]

A drift pin isn't going to correct flanges that are cut twice, but they're still to short.

Best regards - Al

 

[hokie66]

The mention of drift pins brought another thought to my suspicious mind. Maybe the erector indeed did weld to aid plumbing and levelling of the steel. If the bolts were misaligned, they could have used the welds to hold the members in position while the holes were enlarged. I would want to remove enough bolts to assure myself that the holes haven't been reamed out.

 

[LittleInch]

I realise I'm out of my knowledge envelope here, but as a general engineering point, this operation raises suspicions like hokie66 says, that there is more to it than it might seem.

The "weld" is truly terrible and clearly won't take any serious load, plus appears to be done on two sides only. Is it an optical illusion or is the top bolt bigger than the bottom one?

Are washers still acceptable on this type of joint? In piping connections they were banned years ago as it was not possible to guarantee their strength and could hide some large defects in the bolt / hole size and essentially all your bolt shear was going through a rather thin steel ring of unknown strength.

Feel free to ignore - just some general observations

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[CELinOttawa]

Morning LittleInch,

I'd heard of piping connections not using washers, and I always wondered why... Now I know. Thanks for that.

For your information, washers are still standard practice as they "eat" or make up for the oversizing of our holes, and do not interfere with strength. In your case the bolt holds the pipe together more or less principally against tension. In nearly all structural steel connections, the bolts are working principally in shear. The washer is there to keep the bolt from pulling out as bearing loads get high; Even a low-grade bubblegum quality steel would likely do the job we need.

Interestingly there are even tension-indicating washers used in Structural Engineering which can tell you when a bolt has been correctly tensioned for slip-critical connections. You're not meant to rely on them alone, but a lot of engineers and erectors do.