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

 

[racookpe1978]

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.

 

[LittleInch]

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

 

[mtu1972]

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

 

[paddingtongreen]

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

 

[vvaccare]

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!

 

[azcats]

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.

 

[TDIengineer]

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".

 

[TDIengineer]

A325.. typo of course

 

[hokie66]

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?

 

[BAretired]

California is lovely at this time of year, hokie.

BA

 

[hokie66]

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

 

[TDIengineer]

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.

 

[vvaccare]

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!

 

[BAretired]

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

BA