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

 

[LittleInch]

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

 

[CELinOttawa]

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.

 

[JLNJ]

"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.

 

[LittleInch]

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

My motto: Learn something new every day

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

 

[a2mfk]

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.

 

[hokie66]

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?

 

[CELinOttawa]

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!

 

[hokie66]

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.

 

[BAretired]

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

BA

 

[hokie66]

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

 

[CELinOttawa]

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...

 

[hokie66]

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.

 

[paddingtongreen]

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

 

[BAretired]

https://www.google.ca/search?q=twis...source=hp&gws_rd=cr&ei=nz7kUsCLFIHboASY_4DQDQ

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

 

[mtu1972]

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

 

[paddingtongreen]

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

 

[hokie66]

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.

 

[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.

 

[hokie66]

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.

 

[paddingtongreen]

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