A490 pre-tension vs sort-of tight, maybe 1

[boffintech]

Am inspector on a project with spliced joist-girders.

Problem #1 = A number of joist-girders were assembled and erected prior to the inspector being notified and, yep, the bolt assemblies were incorrectly marked for pre-tensioning verification by turn-of-nut method and as a result the inspector is unable to verify bolt pre-tension. Specifically, the bolts were not marked prior to tightening; only the turned element, the nut, and the structural member were marked. Since the bolt was not marked it is not possible to know if it turned while tightening the assembly.

Problem #2 = During observation the next joist-girder assembly/erection it was discovered that during tightening of the bolts that as tightening progressed, you guessed it, previously tightened assemblies loosened.

So basically i can write a great daily report which states i know jack and sh%&.

Question: If an A490 assembly is loosened during tightening of addition bolts can the lessened bolt be re-tighten or must it be replaced? My understanding of the spec is that once a tightened A490 bolt is lessened it can not be re-used.

Also, any ideas on the other issues? EOR is coming to project but a heads-up what be appreciated.

 

[connectegr]

The first question is to determine if they were ever actually pretensioned. As a bolt pattern is sequenced and all plies are brought into contact initially snug tightened, other bolts will loosen. If bolts were loosened by the installation process then re-tensioning is not considered reuse (RCSC 2.3.3).

http://www.FerrellEngineering.com

 

[boffintech]

"not considered reuse" (RCSC 2.3.3), thanks. Will re-read.

On the tightening pattern: I scoured the shops, no pattern found. Called the engineer to ask but am waiting on a call back.

But even if the members are marked correctly, if the inspector is not there to obs, and some bolts loosen during the process, these marks are looking pretty useless.

 

[connectegr]

Without adequate inspection, the other bolts may require verification per the Arbitration section of the RCSC Spec. I am not a fan of calibrated wrench or torque values, but there may not be an alternative. Establishing an acceptable torque value can be another problem.

http://www.FerrellEngineering.com

 

[Ron]

I'll start by saying that I don't particularly like any of the accepted methods for bolt tensioning inspection. They all have their problems, but as connectegr noted, you will probably have to resort to a calibrated wrench method.

Establishing a torque value is best done with a tension indicator such as a Skidmore-Wilhelm device. Not perfect, but better than calculating or guessing. I guess the positive side of this method is that it is relatively consistent, so you can expect similar results as long as you are in the same lot of bolts. Lot to lot there will be variation.

A490 bolts require high torque and if you have anything over a 3/4-inch bolt you'll need a monster of a torque wrench.

 

[connectegr]

As an arbitration method, calibrated wrench works best when done relatively near the installation time. However, I have rarely seen a case that escalated to arbitration within days or weeks of the discovery of loose bolts. We spend weeks discussing the cause, cost of repairs, and who done it. I have had a case that took 18 months to begin repairs. During this time lubrication is lost and mother nature begins changing things. So determining an acceptable torque using a new lot of bolts in the Skidmore is irrelevant to the torque required for the existing bolts in the holes.

Best solution... Do it right the first time and document the inspection/installation process. There will still be an occasional problem, but the solutions are infinitely simpler.

http://www.FerrellEngineering.com

 

[boffintech]

Well let me ask you this, since only 5 of 11 grid lines of joist-girders have been installed and thus many bolts/washers from the same lot are available, is there any reason that we can't now use the pre-installation verification calibrated wrench method manual torque wrench calibration procedure with the skidmore and then back-check the fasteners already installed?

BTW, the bolts are 1" dia 4in long A490.

 

[connectegr]

According to RCSC you can.

But, how are the bolts stored and have the installed bolts been exposed to the elements and how long? These factors can skew the calibrated wrench torque value. If these are not an issue then the arbitration method is probably a good choice.

Are these connections slip critical, in standard or OVS holes? Or is pretension require for combined shear and tension loading?

I have also seen inspectors simply lubricate, remark, and make an additional 1/4 turn on tight bolts. Lubricate, snug-tighten loose bolts, mark, and make 1/3 turn.

http://www.FerrellEngineering.com

 

[boffintech]

All bolts, washers, and whatnot are stored in the original kegs in a con-ex container. No problem there.

Installed bolts been exposed to the elements for less than a week.

Are these connections slip critical? no.

In standard or OVS holes? standard

Or is pretension require for combined shear and tension loading?

Not sure. The members are spliced joist-girders.

 

[connectegr]

If splices are in shear only and not slip critical, pretension may not be required (per RCSC). Pretension may be EOR specified or required for fatigue.

If pretension is not required, simply snug-tighten the bolts. Simply the strength of an iron worker or "tightened sufficiently to prevent the removal of the nuts without the use of a wrench".

A picture of the connection might help.

http://www.FerrellEngineering.com

 

[evelrod]

Connectegr..."Strength of an Ironworker", I love it!
Why would any engineer design a "snug tight" connection requiring a one inch dia A-490 or, for that matter, any HS fastener?

Boffintech, I've been in your shoes, so to speak...11/4" HS fasteners on a nuclear facility in SoCal. Calibrated tq wrench was my solution...Monster Ironworker? Naw. I used a reasonably sized one (they do come in all sizes, you know)...with a std. tq. wrench/tq. multiplier. Not exactly 'high tech' and, it was about 30 years ago, but it worked then---it will probably work for you today.

Sure hope these things are not TS, 'cause the "calibrated wrench" idea is pretty much DOA in that case!

Rod

 

[boffintech]

The specification for Structural Joints Using High-Strength Bolts requires that the EOR indicate the connection type. See below.

As near as I can tell the words snug-tight, pretensioned, and slip-critical do not appear on the drawings or in the specs. Why not? Maybe I should him on the discrepancy log...just kidding...


SECTION 4. JOINT TYPE
For joints with fasteners that are loaded in shear or combined shear and tension, the
Engineer of Record shall specify the joint type in the contract documents as snugtightened,
pretensioned or slip-critical. For slip-critical joints, the required class of slip
resistance in accordance with Section 5.4 shall also be specified. For joints with fasteners
that are loaded in tension only, the Engineer of Record shall specify the joint type in the
contract documents as snug-tightened or pretensioned. Table 4.1 summarizes the
applications and requirements of the three joint types.

 

[connectegr]

evelrod
For the majority of connections snug-tight is all that should be required. I can ramble on about costs and increased ductility, but the simple fact is that you should not pre-tension unless necessary. A list of conditions requiring pretension is in RCSC 4.2. Some inspectors and engineers require pre-tension so they at least get snug-tight and have a method to document proper installation. The determination of the bolt diameter and grade is relative to the shear and/or tension on the bolt, and the size of a connection.

In California additional factors may have required pretension, seismic design and/or fatigue.

http://www.FerrellEngineering.com

 

[evelrod]

connectegr...(I love that handle)
I can agree, in theory. However, the 'bean counters' would have your head requiring HS where common A307 would suffice.

Rod

 

[connectegr]

boffintech
There should be more information in the contract drawing General Notes or project Structural Steel Specification. In general most connections in standard holes without preparation of the faying surfaces are bearing connections and should be snug-tight installation. A325 bolts with combined shear and tension do not required pretension. BUT A490 bolts with combined shear and tension do require pretension. AISC seismic connections typically required pretension.


Since my little world revolves around connection design, I try to be clear on the installation requirements. From your comments I assume you are an erector or contractor. You should not be expected to know this without a clear indication on the contract drawings or erection drawings. You should also not be required to pretension every bolts, "just in case". That is a waste of your time/money and ultimately the owner's money.

This is the weakness of a forum. The responses are general and hypothetical. With your current issue, the solution would require more specifics.

Another thought... In Canada and some other countries all bolts are pretensioned.

http://www.FerrellEngineering.com

 

[connectegr]

evelrod
Just a difference in project types. I have only used A307 bolts for small miscellaneous steel, stair, and handrail. Everything we see is 3/4 A325 or larger.

http://www.FerrellEngineering.com

 

[evelrod]

Here in the Los Angeles area, at least 14 years ago when I retired, all A325 required pretension/100% inspection and, there at the last, almost all A325 were TS because of all the noise "pollution" requirements in many areas, hospitals, schools and, of course, anything in Beverly Hills ... ;o) The company I worked for used nothing but TS for all connections save, as you said, stairs, handrail and the like.

Rod

 

[TLHS]

connectegr,

Not all high strength bolts in Canada are pretensioned.

As per clause 22.2.1 in S16-09 you can use snug tightened high strength bolts for everything that isn't listed in clause 22.2.2. Those types of connections are:

- Slip critical connections
- Shear connections designed under the seismic provisions
- Crane loading
- Cyclic loading
- Bolts under tension
- Bolts in oversized or long slots unless designed for movement.

So for most types of construction, bolts in non-seismic connections where the bolts are in shear can be snug tight.