A490 Bolt Tension Problem!!! 2

[SmithJ]

I have a situation here.

We designed a riding arena structure and asked that the erector put up the steel using turn-of-the nut method since all the bolts were high strength A490 Bolts. The Erector does not indicate a problem with this and goes ahead to erect the building. Fast forward a few months, trying to get occupancy and the building department says they need a bolt inspection. Bolt inspector goes on site and says that he can't sign off on turn-of-the nut because he wasn't present during erection and can't see the chalk marks.

The inspector suggested that he would sign off if we state that snug tight is adequate on this project. I refused and said we can't recommend anything contrary to the code (Code clearly states that A490 bolts can't be snug tightened).

Any ideas on how best to resolve this? I went through the RCSC spec and it seems that Table 4.1 gives minimum fastener tension for varying bolt sizes. Is it okay to say that these minimum tensions meet the preloading requirements of turn-of-the nut method?

Any help is much appreciated.

Thanks,
JS.

 

[CoryPad]

But how can you verify that the minimum tension levels are present?

Did the erector in fact use the turn-of-the-nut method?

You could use the M-Alpha method developed by Shoberg:

http://www.rstechltd.com/index.htm

This technique measures torque and angle to rotate a previously tightened fastener a small amount. Then, it can extrapolate the elastic origin and estimate the preload level.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Rjeffery]

There is an arbitration inspection that uses a Skidmore/Wilhelm (sp)to determine when the proper tension is reached (at n torque value) and a torque wrench that will provide assurance that the bolts were tensioned correctly. this inspection is found in the ASIC manual...

Although, the inpsector may have a point. if the connections are NOT in direct tension or are NOT slip critical, the snug tight condition may be applicable as nothing prohibits a designer from using high(er) strength bolts to make these connections where a lower strength or common bolt would do.

 

[unkamiko]

The inspector should have known that the arbitration method described in the ASTM for A325 and A490 bolts. This basically involves determining a torque from 5 bolts brougnt to full tension in the skidmore. This is a simple procedure, and is described in detail in the ASTM. This can be found on pg. 5-265 of the ASD manual.

I am unaware of any specification that states A490 bolts must be fully tensioned. Can you refer me to a specification.

Is this job in Wa. state?

 

[henri2]

In addition to Rjeffery's well thought out comments I'd like to chime in with a few more.

As you are aware, three connections are covered in the spec for A325/A490 HSBs in the 9th edition of the AISC Manual. They are:

1. Shear/bearing with bolts included or excluded from the shearing plane---for these connections only a snug tight condition is required and both A 325 and A490 bolts can be specified for these connections, albeit I see mostly the former specified.

2. Slip critical connection---bolts are tightened to snug tight condition and then further tightened to full pretension

3. Direct tension connections--snug tight followed by full pretension

The arbitration procedure is outlined in Section 9 (b) of the A325/A490 spec in AISC Manual and applies to SC and DT connections.

Structural Bolting Handbook written by Robert Shaw of SSTC is a good resource for this sort of problem. In the 2001 edition arbitration of disputes is covered in pages 42-46.

http://www.steelstructures.com/

IBC special inspection requirements for high strength bolting is covered in IBC Section 1704.3.3 and table 1704.3. Table 1704.3 directs one to applicable referenced standards

I have a few questions.

1. What type of connection(s) was/were specified?

2. Was any special inspection of the bolting materials and installation/tightening required?