Who Determines Bolt Length? 1

[swearingen]

Generally, when specifying high strength bolts for structures, we give the type and diameter but not the length. The contractor is left to decide what his length should be, allowing him to leverage cost reductions using large-quantity ordering. The contractor is better positioned than the engineer to determine this savings.

Our client is being asked by the contractor to provide bolt lengths. Is this common?


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[Boiler106]

which country?

 

[jayrod12]

I have never specified a length. I agree with your reasoning for not doing it.

 

[cliff234]

Based on my experience working in the U.S., the structural steel detailer always determines the bolt length.

 

[swearingen]

Boiler106 - I am U.S. based.

I have been through AISC's Code of Standard Practice and have not been able to find something specifically addressing this. I did send a query to AISC on this. Has anyone seen this written anywhere? I feel this contractor is change order fishing...


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[dauwerda]

Typically whoever creates the shop drawings specifies the bolt length (in my experience). The AISC SCM does provide the way to calculate required bolt length on page 7-2 (15th edition).
There isn't a whole lot that can vary for the length of a structural bolt as one that is too long will result in the nut bottoming out on the shoulder before the joint is actually tight and one that is too short won't have sufficient thread engagement with the nut - this in addition with manufacturing tolerances often leaves only one bolt length to choose from.

 

[Veer007]

If you are using Tekla software for detailing the job which gives you the bolt length, grade, and diameter via report, generally for both US and CANADA, the bolt length can be given by the detailer.

Also, there are other detailing software like SDS2 and Advance steel, you could try that too.

Thanks in advance!!

 

[SlideRuleEra]

Agree with cliff234 and dauwerda, the structural steel fabricator. As a former bridge contractor we never gave bolt length a thought. Could not have even if I had wanted to, fabrication details may differ from the design.

Nice thing about the fabricator making that decision... if the bolts don't "fit", for whatever reason, one phone call from the contractor to the fabricator gets new bolts on the way to the job site without quibbling about who pays.

http://www.SlideRuleEra.net

 

[HTURKAK]

Bolt length =the total thickness of all connected material+ thk of washers (if any)+ 1.4* bold diameter. The factor varies 1.4 is average .

The total length should be adjusted to the available next longer length.

The RCSC Specification requirement ; the end of the bolt be at least flush with the face of the nut.

 

[phamENG]

I agree that the bolt length should be selected when the shop drawings are developed. I also agree with the reasoning in the original post. It does sound like they priced it all at the cheapest bolt length, and are now finding out that they actual length they need is a long lead time special order and they want to stick it to you.

Did you design the connections, or were they delegated? If you designed and detailed them, I could see where they may have an argument. But even then it would be thin.

 

[cliff234]

"Did you design the connections, or were they delegated?"

phamENG - Even if the EOR designs the connections, it is the detailer's job to figure out the bolt length. There is nothing (to my knowledge) in the AISC Code of Standard Practice that puts this on the EOR in the U.S.

 

[phamENG]

cliff234 - I agree completely. Just saying that's the most likely place I could see a contractor managing to convince somebody that it wasn't his fault he priced the wrong bolt size. As I said - it would be a thin argument. But I've seen owners convinced of things with even thinner arguments than that. Sadly that can be all it takes to spoil an engineer/client relationship.

 

[Rabbit12]

I can't imagine how many different conditions you'd need to detail to show all bolt lengths. Yikes.

 

[miningman]

Dont know exactly where I developed the belief , but my understanding is bolt lengths have to provide a minimum of three threads beyond the nut face when torqued to spec. If flush , there is inadequate bolt length to get the required torque. That knowledge was generated in the mid 1980s...... say 35 years ago.

 

[dauwerda]

miningman, per the RCSC specification, Section 2.3.2:

Geometry: Heavy-hex structural bolt dimensions shall meet the requirements of
ANSI/ASME B18.2.6. The bolt length used shall be such that the end of the
bolt extends beyond or is at least flush with the outer face of the nut when
properly installed.

 

[ldeem]

I do some projects where I design and detail for the client who then provides full shop drawing to the contactor. I use Tekla so I don't have to figure lengths but I can see doing that manually would be a bear. As others have pointed out in structural bolts the threaded length is short and there are often several different lengths requierered.

I assume the contractor probably figured out what a pain it is to determine bolt lengths and is hoping someone else will do it.

 

[CANPRO]

The idea that the designer would have to provide bolt lengths is absurd. Should the designer determine the quantity as well? As others have mentioned, modern detailing software will generate bolt lengths, quantities, and point to point contact lists to tell you which bolts go where. Even for bridge work where the EOR provides highly detailed connections, there are still no bolt lengths provided and it is left for the detailer to determine.

 

[human909]

It could be anybody in the chain but the engineer IMO. (Except where there is some exceptional need.)

-Easiest for the detailer to specify the required bolt list. These days should be a relatively easy task with most detailing software
-Probably easiest for the erector or head contractor to supply. If the errector supplies there isn't quibbling about missing bolts.
-The fabricator rarely supplies in my world unless they are also the detailer/errector/head contractor.

 

[MIStructE_IRE]

We use the national structural steel specification (a UK document). Somewhere in there is a note about 3 threads to project beyond the face of the nut.

I’ve never been asked for it though! It would really make me question the contractor’s level of experience with questions like that.

 

[swearingen]

I queried AISC's Solutions Center and this was the reply:

I will rephrase your question and then provide a response.

Does the Engineer of Record typically specify all bolt lengths? No. Usually the detailer, usually hired by the fabricator, determines the length of the bolts required. Since the Engineer of Record usually does not provide detailing, the Engineer of Record usually does not provide bolt lengths.

Commentary to Section 4.2.1 of the Code of Standard Practice states, “The fabricator is permitted to use the services of independent steel detailers to produce approval documents and to perform other support services, such as producing advanced bills of material and bolt summaries.” This could be viewed as guidance related to services typically provided by the detailer.

If the Engineer of Record provided detailing, then it would seem that part of this service would be to provide bolt lengths as well.

Commentary to Section 4.5 states, “This delivery system of fabrication and erection documents is discouraged. <Referring to fabrication/erection documents NOT provided by the fabricator> The preparation of the fabrication and erection documents is very specific to the needs of the fabricator performing the work, and an integral part of the constructability and coordination assurance of the project. If the project team chooses to use this delivery method, the contract documents should be very clear as to the managing of this process, including, but not limited to, who and how the following will be handled… Standards, format and contents of the fabrication and erection documents… for the mill order and for fabrication, including field bolts.”

What I read from this appears to be the general consensus here. I think we'll still get some pushback, but this should hold them off.

Thanks for your replies, everyone. Have a great day!




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