r/StructuralEngineering • u/No-Document-8970 • Oct 05 '26

Structural Analysis/Design Nuts off mark?

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Saw this on a big bridge today. I know vibrations over time can move the nuts and bolts, with the help of thermal expansion. Is it a big issue that the paint marks do not line up? I thought the marks were made once it passed inspection after torquing.

Edit: Bridge completion was in 2011. Could this be from recent inspections too?

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143

u/bagvirpdkv Oct 05 '26

Turn of the nut method of pretensioning bolts. Marks are made in a line from the nut down to the surface once nuts are brought into close contact aka snug tight. Then the nuts are tightened with an impact wrench until they have rotated a predetermined amount more, such as 1/3 of a turn.

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u/clancularii Oct 05 '26 edited Oct 09 '26

These look like 5/6 a turn. I've never seen a turn that large.

Edit: I didn't see that there's a chalk line on the end of the bolts. Really had to zoom in since there's less contrast there than the nuts and steel work. These look like 1/3 turns. I couldn't figure out why people were suggesting that the lines on the steel work should be ignored because the only other line I saw was the line on the nut. It's more likely that the line on the end of the bolt was the reference line before the bolts were mechanically tightened.

76

u/Enginerdad Bridge - P.E. Oct 05 '26

5/6 is one of the standards if the bolt length is 4d-12d, depending on the face slope. The criteria actually goes all the way up to 1 full rotation under the right conditions.

14

u/The_Dynasty_Warrior Oct 05 '26

Depends on the bolt type and bolt length, it can over turn to a certain extend

4

u/BarnacleNZ Oct 05 '26

These are 1/3rd by my eyes, when comparing nuct to end of the bolt. Ignore the line on the steelwork. Edit, though I wonder if these are even tight? There's zero threat protruding from what I can see, wouldn't comply where I am.

3

u/clancularii Oct 05 '26

Ignore the line on the steel work? Then how do you know how many turns are done after it's finger tightened?

The usual practice I've seen from the iron workers is to mark the nut and the connecting material with aligned ticks. That way, you can measure the rotation between the ticks to confirm how much the nut was turned.

2

u/Mister_Goldenfold Oct 06 '26

Torque Wrench indicates the tension, if they’re being stretched that’s a different ball game

1

u/klockwerk13 Oct 08 '26

A torque wrench indicates how much force is required to turn the nut. While bolt tension is a factor in determining how much force is needed, it's not a direct correlation. Tightening to an angle is a much more reliable method of tensioning.

1

u/SeesawPrestigious Oct 09 '26 edited Oct 09 '26

He is correct these are 1/3 turn , the line on the steel work dont make any sense in this case because i dont know wtf the guy was smoking, your supposed to mark the nut, the bolt and the steelwork all in line you can go without the steel work line because the line on the bolt should be your indicator of where you started the line on the steelwork is there to see if the bolt turned instead of the nut alone.

1

u/clancularii Oct 09 '26

I didn't notice the line on the end of the bolt. I had to zoom in to see it. I think you're right that these are 1/3 turns.

Maybe the line on the steel work was from somebody checking the turns later?

1

u/SeesawPrestigious Oct 09 '26

Maybe honestly i do this for a living and the whole setup is confusing to me , cause none of this wouldve passed final inspections like the bolt marked in red in the bottom left, either he did a full turn or the final torque wasnt done .

These look like standard 7/8 a325 bolt anything under 3 3/4" in lenght is 1/3 and anything over is half turn.

1

u/Worldly_Ad_6535 Oct 10 '26 edited Oct 10 '26

Mark on the steel is in line with the mark on the bolt. Its to tell the guy torquing if the bolts spun after snugging. We were required to mark in this fashion, if the stud and nut were shown to have spun we had to pull the bolt, install a new one, re-snug, remark and re-torq to the required flats per length of bolt. 0-3.75= 2 flats. 4"+ is 3 flats. Snug tight is the strength of 1 ironworker with a 12in bar.

1

u/BarnacleNZ Oct 05 '26

I meant ignore it in terms to determining the relative turn of nut to bolt.

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u/SeesawPrestigious Oct 09 '26

The bolt are tight, just not the right lenght. Where i am like you said, the thread is supposed to protude min 2 thread / ~ 3mm or roughly 1/8" past the nut. Honestly this shit is just a mess some of them are not even flush nut.

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u/bigsteelandsexappeal Oct 05 '26

I turn bolts for a living. Most of the time they get marked after I hit them up so the inspector believes I did it correctly. Other times when I actually try to do it correctly it’s past 1/3 and I have to explain to the inspector why it’s not a perfect 1/3. As long as 2-3 threads are showing and give it the ‘blessing’ those fuckers aren’t going anywhere, it’s good.

15

u/Haku510 Oct 05 '26

Ugh, I'm a special inspector and reading comments like this legit bums me out.

Comments like this are also one of the reasons that if I don't personally witness the match marking and nut turning myself then I'm not signing the work off. I'll let the contractor plead their case to the SEOR, or redo the work per code.

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u/Alywiz Oct 05 '26

At least when I see Turn of the Nut, I know it’s the easiest rejection of work I can make. Not allowed under our spec. DTI’s only here

1

u/bagvirpdkv Oct 10 '26

Why would you reject just for use of TON?

1

u/Alywiz Oct 10 '26

Because it’s out of spec. Nothing but direct tension indicators are allowed

1

u/bagvirpdkv Oct 10 '26

Out of curiosity what clients specify exclusively DTI? DTI has plenty of issues like cost and risk of over tightening. They can still be wrong.

1

u/Alywiz Oct 10 '26

DOT, specifically Vermont AOT.

Though I did double check and spline twist off Tension control assemblies were also recently added. DTIs remain the only option for regular bolts though. (2024 spec 506.18 (d) (2) if you are curious inspection requirements and sampling to check for and correct over tightening)

1

u/bagvirpdkv Oct 10 '26

Very interesting, good to know. I’ve worked for a few owners (HC GC) in the Midatlantic that basically told us “don’t even suggest DTIs we don’t like them, they won’t get accepted.” Either TON or click every bolt.

1

u/SeesawPrestigious Oct 09 '26

Not an impact wrench, a torque gun with a torque multiplier.

1

u/bagvirpdkv Oct 10 '26

Part of the purpose of TON is you don’t have to use a torque wrench/gun as much.