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Mixing Welds and Bolts...

Mixing Welds and Bolts...

Mixing Welds and Bolts...

(OP)
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

RE: Mixing Welds and Bolts...

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?

RE: Mixing Welds and Bolts...

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.

RE: Mixing Welds and Bolts...

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

RE: Mixing Welds and Bolts...

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 .... "

RE: Mixing Welds and Bolts...

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.

RE: Mixing Welds and Bolts...

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

RE: Mixing Welds and Bolts...

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.

RE: Mixing Welds and Bolts...

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.

RE: Mixing Welds and Bolts...

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.

RE: Mixing Welds and Bolts...

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

RE: Mixing Welds and Bolts...

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.

RE: Mixing Welds and Bolts...

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

RE: Mixing Welds and Bolts...

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

RE: Mixing Welds and Bolts...

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.

RE: Mixing Welds and Bolts...

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

RE: Mixing Welds and Bolts...

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

Best regards - Al

RE: Mixing Welds and Bolts...

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.

RE: Mixing Welds and Bolts...

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

RE: Mixing Welds and Bolts...

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.

RE: Mixing Welds and Bolts...

Forgive me for continuing this on washers, but surely if the hole in the steel is too big, it's too big and a washer won't do anything for you. If the bolt is in shear it then needs the steel to move before it comes into contact or it means the steel is being held by two or three bolts instead of four??

The temptation is then to use a washer which is bigger in OD than the OD of the nut to hide the fact that there is no steel under the bolt and a lot of your tension goes through the washer. That's how you get pull through, not by using a washer which is the same OD as the bolt. I've never heard of these special tension washers before though...

As hokie66 says, take one bolt out at a time and have a look.

My motto: Learn something new every day

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

RE: Mixing Welds and Bolts...

Well the controls on what size of holes gets nade are pretty multiparty, so it would need to be an out and out conspiracy to have the hope that oversized. Besides the washer size to each bolt size is standard as well. They can't just put in an extra large washer without someone crying foul.

As to the possibility of anything being wrong, I have been known to insist on a bolt or two being removed to satisfy me... I see this as being little different than any other situation where something I need to see has been concealed.

RE: Mixing Welds and Bolts...

"these beams are cantilevered and moment connected"

The flanges look to be beveled as if they will be welded. Why the web stiffeners otherwise?

@LittleInch - The special washers squirt a little colored goo out when they are squished the correct amount (intending to directly indicate the pretension applied to the bolt). But you wouldn't likely use the twist-off type bolts with the washers.

RE: Mixing Welds and Bolts...

Umm, interesting - piping systems use torque wrenches normally to do the same thing - a tadj more reliable and repeatable.

I guess I'm just so used to not seeing washers on bolted items that it makes me wonder what purpose they serve, but I admit I'm in the wrong forum here.

We don't seem to have heard from the OP on this thread - any response from you?

I'll shut up now smile

My motto: Learn something new every day

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

RE: Mixing Welds and Bolts...

It looks like they may have welded the top edge of the plate too. But if the connection was designed as a bolted connection, the eccentricity of the connection is the center of the group of bolts. The welding has now moved that further out to the right, which is going to put more moment into that connection. If you are using a pre-qualified AISC table shear plate connection, then rotation of the bolted connection is part of the assumption in reducing the moment transferred into the shear plate.

But it sounds like this is a moment connection so maybe that becomes moot, not sure. I think if I am signing off on this I have them grind it off and be done with it, takes a couple of minutes.

RE: Mixing Welds and Bolts...

LittleInch,
Using hardened washers under the turned element in a high strength bolted connection has always been the norm for structural work. It is not to conceal oversized holes, but in this case a problem with the hole locations is the only reason I can see for the temporary welding.

vvaccare,
Where are you?

RE: Mixing Welds and Bolts...

And the ink spitting washers are a particular product... Most pretensioned bolts are installed using torque wrenches, just like in your pipe works.

Also the ink spitters are a new variation on the old theme... They are still much less common than washers that simply squish, and much much less common than regular washers.

The tolerance of an extra 2mm in the bolt holes beyond the bolt diameter is necessary in structural steel erection to allow for long do mentions sometimes in the hundreds of feet to actually work. Nothing would ever have fit before laser surveying without this tolerance, and I'd hazard a guess that few things would today either!

RE: Mixing Welds and Bolts...

There may be larger issues in this project than just some sloppy temporary welding, as bad as that is. As others have pointed out, the gap for flange welding seems very wide. This, and the likelihood of enlarged holes in the erection process, may indicate some fundamental setout and/or fabrication errors.

One more thing, those twist-off bolts are only reliable as tension controls when the spline is broken off soon after the bolts are removed from proper storage. As the spline is still on the ones in the picture, I doubt that you can depend on the tightness.

RE: Mixing Welds and Bolts...

I have never seen twist-off bolts used on structural steel. What is the advantage over regular hex head bolts?

BA

RE: Mixing Welds and Bolts...

That makes two of us, BA. A strange sight.

RE: Mixing Welds and Bolts...

Twist off bolts are meant to be a single-sided and faster application. I don't like them and they only even became available to Canadian engineers in the last edition of the S16 code. I don't think they'll be making much headway anytime soon, but who know as these things target the erectors. The real judge will be seeing the requests for substitution come into the office...

RE: Mixing Welds and Bolts...

For those like me who are not very familiar with twist off bolts, this attachment from Nucor has a lot of information, including cautions about storage and leaving the bolts in place too long before tightening. To me, this precludes their use in most structural applications.

RE: Mixing Welds and Bolts...

I worked on a job where we did extensive tests with TC bolts because we didn't know them well, this was back in the late seventies.
BA, they have an installation tool where an inner sleeve grabs the end of the bolt while an outer wrench, grabs the nut. They torque against each other, no need to grab the bolt head, that's why it is round. The end held by the inner tube, breaks of in the torsion range to provide the correct tension. The tool is electrical,like a big drill, so they don't need a compressor operator.

We didn't have any bolts fail to make the range as long as they were fresh and the lubricant film was still on them.

There is a QC component in that you can see if the end has been torqued off.

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

RE: Mixing Welds and Bolts...

https://www.google.ca/search?q=twist-off+bolts+adv...

This method usually defaults to "twist-off" bolts, sometimes called "tension-control" bolts. These assemblies function by calibrating the torque needed to twist off a splined extension manufactured into the bolt shank. Made correctly, the "twist-off" will occur at a bolt tension above the minimum required.

The main advantage of "twist-off" bolts is that they can be tightened from one side by one person, although bolt installers now realize that regular hex bolts and DTI's can also be installed one-side, one-man, too.

There are a number of disadvantages to the "twist-off" system:

Special wrenches are needed.
Special connection clearances must be detailed for wrench access.
Frequently more expensive than hex bolts and DTI's.
Galvanized twist-off assemblies are in VERY limited supply.
Field relubrication is prohibited by code.
Compacting plies must be accomplished prior to twist-off.
Deterioration of the thread condition for any reason will change the torque-tension relationship, and Kulak has shown in an ASCE paper that in as little as three days out of protected storage, one-third of all the twist-off bolts he tested did not develop the required tension at break-off.

BA

RE: Mixing Welds and Bolts...

It's apparent that many things are regional in nature, but I've worked on several big industrial building projects where these types of bolts were requested by the Contractor when their inputs for "Value Engineering" were being presented. These bolts do require a special tool for final installation but must have resulted in cost savings, as outlined in the attachment above, for them to be specifically required.

gjc

RE: Mixing Welds and Bolts...

When the steel is erected, they place a minimum number of bolts to hold the connection. When there are enough connections waiting, a "bolt stuffing" crew places the additional bolts in the holes complete with nuts and washers. They are followed by a "torquing crew" who snug the bolts as required, and then torque them fully. Sometimes, the snugging is a separate step.

Snugging entails going around the bolts several times when there are many bolts or if there are wide gaps between the plies, similar to re-installing the wheel of your car with a hand wrench.

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

RE: Mixing Welds and Bolts...

Michael,
That is a common sequence, but according to the literature, the delays between steps would have an adverse impact on reliability of tightening of these twist off bolts.

RE: Mixing Welds and Bolts...

The "crappy weld" is slag: the weld has not been chipped. Zoom in on the photo. It's pretty typical for vertical fillet with 7018 rod. I can't tell much about weld quality from the photo.

RE: Mixing Welds and Bolts...

mtu1972,
The main way I can see a contractor benefitting financially from use of these bolts is relaxation of inspection requirements. If breakoff of the splines is accepted in lieu of inspection by other means, and the contractor was required to pay for inspection, then he would benefit. But being the cynic that I am, I wouldn't buy it. Another thought...those splines can easily be removed with a pipe wrench, so if no one is watching, he doesn't even have to have the installation tool.

RE: Mixing Welds and Bolts...

hokie, there were only short delays. The coating lasted easily for a weeks, and we did pull a few that look as if they had been there too long but the touching surfaces still held the factory lubricant coat. They broke on the Skidmore at the right tension. We found some in a basket that had been left out in the weather over a New England winter, they looked bad and performed worse, but with a wire brush cleanup and an oil film they tested fins.

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

RE: Mixing Welds and Bolts...

Quote (DVD)

The "crappy weld" is slag: the weld has not been chipped. Zoom in on the photo. It's pretty typical for vertical fillet with 7018 rod. I can't tell much about weld quality from the photo.

Oh, I concur with your opinion that the weld "could be" covered with slag. It most certainly is STILL covered with welding "fumes" and the surrounding metal has never been cleaned or wire-brushed.

Thus, my opinion of the "bad quality" of the weld: If the welder (and his supervisor/foreman/accepting engineering or boss) did not care enough to even clean off the weld, how does anybody know how good a weld is on the joint between two pieces of steel up in mid-air? If the welder does not even "brush off" (chip off) the slag, how does anybody know how long, high, wide, or evenly the weld itself is?

Obviously NOBODY inspected the weld - "No body" could inspect a weld still covered by slag and with fume residue on the base metal! The weld should either be inspected by a qualified NDE or removed.

RE: Mixing Welds and Bolts...

I know the subject matter has drifted a bit, but it's fascinating to see how two branches of engineering have drifted so far apart when it comes to bolts. Piping connections may depend more on tension than structural bolts, but if you're torqueing up a bolt to the extent tat you snap off a bit of steel, that bolt is under a fair bit of tension. If you suggested this to an oil and gas client you wouldn't get it past first base.

You only see stud bolts (without washers) on piping connections as there were failures of the bolt head due to the high stress concentration at the head / shaft interface, which just doesn't exist with a stud bolt and nut and is very difficult to spot being on the inside. Similarly washers don't make sense as they don't do anything - Only if you're nut is considerably harder than the structural steel (I hope not!) does it make sense and the risks e.g. non hardened washers, slightly oversize washers, allowing use of undersize bolts - are not worth the miniscule advantage of having washers. IMHO that is.

We still await feedback from the OP....

My motto: Learn something new every day

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

RE: Mixing Welds and Bolts...

Hokie66 -
These projects were in central Wisconsin 15+ years ago. "Inspections" were not required as things were much simpler then. I was with the Owner's engineering department and was the structural project engineer when this came up. We designed the building and then observed the installation procedures, but the State permitting did not require the independent inspections that are now "required". We did observe some of the connections being installed, but certainly not all. When the splines were off, we assumed that the connections were OK.

At the end of the project, as the EOR, I verified to the State that the building was constructed in conformance with the drawings and specification. We were then granted the occupancy permit.

We then adopted these bolts for our smaller projects which were done by our in-house trades. We bought the wrenches and ordered the bolts with the feeling that there would be a net cost savings. Maybe that was wrong.

gjc

RE: Mixing Welds and Bolts...

Given the drift of the subject, I was working at a refinery around 1960, when they had a problem with the piping connections, the fitters were breaking the bolts when they installed them. It turned out that the fitters had been using regular steel bolts and they could "feel" when they reached the yield point. They were now installing alloy bolts that don't have a sudden yield so they kept going. The makers of torque wrenches suddenly did a lot of business.

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

RE: Mixing Welds and Bolts...

(OP)
Sorry to get back so late everyone. We decided to grind off the welds which were added to the shear tabs. Just as a2mfk mentioned, we wanted to limit the eccentricity in the connections. To clarify some of the questions that came out throughout the thread, the beam in question is supposed to be moment connected. The root opening for several of the beams were in fact quite large (as pictured), and this was because of a fabrication error. It took almost six hours for one of our moment welds to be completed. The erectors idea when adding the extra weld to the shear tab, was to keep the steel level while his welders got in there to perform some of these moment welds. Our office designed the structure, and when we went out to visually inspect the welds, we noticed the extra welds. Those are TC bolts as mentioned by everyone, and they are pretty common on projects in my area.

Thanks again everyone!

RE: Mixing Welds and Bolts...

Quote (LittleInch)

Similarly washers don't make sense as they don't do anything - Only if you're nut is considerably harder than the structural steel (I hope not!)

One of the few locations that (F436) washers are actually required in structural connections is when using pretensioned A490 bolts and the material being connected has a MSYS of less than 40 ksi.

RE: Mixing Welds and Bolts...

BA and hokie. Come to california. You'll see twist offs used more than not. Not uncommon at all. A352SC is often used in drag connections. Either 7/8" OR 1".

RE: Mixing Welds and Bolts...

A325.. typo of course

RE: Mixing Welds and Bolts...

TDI,
Thanks for the gracious invitation, but no thanks. I'll avoid California.

vvaccare,
Did you check to see if they had enlarged the holes, also due to fabrication error?

RE: Mixing Welds and Bolts...

California is lovely at this time of year, hokie.

BA

RE: Mixing Welds and Bolts...

Too shaky for me. I'll take my chances with the fires, storms, and floods where I am.

RE: Mixing Welds and Bolts...

We have fires here too... 250,000 acres burned directly above my town.. Largest fire in california history.

Although we are seismically active here, I think many modern structures are very safe because so much attention is put into the detailing of the structures.. especially steel moment frame buildings. After Northridge earthquake the industry went nuts on weld procedures and detailing of SMRF's.

When you have seismic design category "D" and all your drags are designed for overstrength, double row of 1" dia A325SC (with twist offs) are often used at every beam to col connection along the drag line.



RE: Mixing Welds and Bolts...

(OP)
hokie66, we spot checked a few of the bolts and they checked out fine.

You guys should come on down to Florida! Nice weather and no worries about seismic design here! Just wind and the occasional sinkhole!

RE: Mixing Welds and Bolts...

We're on our way. Make sure you have lots of beer.

BA

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