TC bolts

Date 01-16-2009 22:30

By TC bolts, I assume you are talking tension controlled bolts such as those twist-offs? If so, the twist off capacity is related to torque and the resulting tension has to be calibrated to this torque with the tension calibrator. If you are talking, direct tension indicator bolts, with those compressible nubs, these read directly in tension and the tension calibrator should not be necessary.

Bob Garner

By clutch

Date 01-16-2009 23:50

yes, Bob I am refering to the tension control bolts. I understand what your saying about the calibration, but wouldnt the spleen sheer off when the required tension is achieved? What would be the reason the spleen would sheer and the bolt not be properly tensioned? Arent these bolts designed to be at the proper tension once the spleen is severed? I understand torque vs. tension, what I fail to understand is the design of these bolts. help me out please! I know there is extra torque involved to tension a rusty or dry TC bolt but they should not be used anyway. If their new fresh out of the bucket, then they should be equal by design, unless one is defective? If thats the case I guess during the verification test out of the 3 you pick hopefully its not the defective one.

By aevald

Date 01-17-2009 00:21

Hello clutch, I might add a few comments that can affect the torque. If an oil of any sort is present on the fasteners or the nuts this could drastically affect the end result of the process. If the surface that the nuts are being tensioned against has any variances, such as one had a thicker layer of primer, one is dry, one is wet, one has oil from a punching process or drilling process, one has rust, I believe you get the idea. The method of tightening could also have an effect, if the shear is achieved through a steady pull as opposed to using some sort of impact type tool the point of shear could be different. These are just a few examples of how the torques could end up being different. Best regards, Allan

By CHGuilford (****)

Date 01-17-2009 04:14

The pre-installation verification test is intended to prove those lot numbers, with those nuts,bolts, and washers, stored under those conditions, installed & tightened in that way will achieve minimum bolt tension.

It is true that TC bolts are designed shear off the spline when the proper tension is achieved but how do you know there has not been a manufacturing error, or the lube dried out or got dirty, or whatever..unless you test them? And consider this, there has been a very real problem with counterfeit bolts showing up in this country (imagine that!). Testing is not foolproof but it's still a good idea.

By DaveBoyer (*****)

Date 01-17-2009 05:31

As a side note, many auto engines have "Torque to Yield" head bolts that are not supposed to be re used. I changed the head gasket on My van using new bolts from the gasket manufacturer. Some of these bolts yielded prematurely while tensioning, I removed them and got replacements and some of those had the same problem. The third try was golden, they all came up properly. I replaced that gasket and the bolts 2 more times while I owned that van, and never had any problems with the bolts.

The point being that sometimes products don't make the specifications they are supposed to.

By jwright650 (*****)

Date 01-19-2009 15:44

Hi Chet,
You and I have been doing the pre-verification (3 bolt minimum) tests now for quite a while on TC bolts. So far in my 10+ years our purchasing agent must do a pretty good job buying our "shop applied" bolts, because I feel that I have wasted 3 TC bolts for every lot that my purchasing agent has bought. I haven't found a lot that hasn't at least twisted off at the minimum on the Skidmore. I still perform these tests but only because RCSC says that I have to.

Have you, or any of the others here, ever find any that did not meet the minimum tension required during your pre-verification testing(speaking of TC bolts here)?
- if you have, you don't have to name the mfg, I was just wondering, as it "seems" to be a waste of time and bolts, IMHO.

By CHGuilford (****)

Date 01-19-2009 17:38

Yes, I've seen some bolt failures during testing. A few bolts from one lot had broken before reaching the full tightening rotation after snug. And some TC bolts from the same lot that snapped in 2 before the spline sheared off. But that's been it. Those lots were sent back and I never heard any more about them.

As long as the bolt didn't break, none have failed to reach 105% of minimum bolt tension, unless we screwed up the test (no pun intended).

The biggest problems I see with TC bolts has nothing to do with testing.
1st - Very often, ironworkers will snap off the bolts as they go, without snugging the bolts and compacting the joints first. Then when they're done, the first bolts are loose.
2nd- We are constantly being directed (by the owner) to install TC bolts in the shop snug tight so the fiels can "snap" them later. Maybe it's OK if the bolts only need snug tightening at final installation. But if that's the case why use TC's? But cest la vie.

By Bob Garner (***)

Date 01-20-2009 15:48

Has anyone tensioned connecting rod bolts in a car engine using the micrometer stretch gage setup? Maybe it was just me, but I never could get that thing properly positioned on the bolts to get a good reading.

On the buildings that I have been involved with, we only had one experience where the Skidmore regularily broke the bolts. Later we found out the bolts were from a "foreign" source. Otherwise, I would estimate that there would be a problem with about one job in four. It seems to vary with the fabricator in my experience. Those that bought from commonly known suppliers were no problema.

Bob Garner

By jwright650 (*****)

Date 01-20-2009 16:11

Bob,
Yes, we do use a bolt stretch mic before and after torquing the rod bolts. You have to rotate the crank a little bit to check the inside and outside bolt at each rod. The torque required is very close but varied somewhat to achieve the recommended stretch dimns by ARP using their lube on their bolts.

Here is ARP's stretch chart....
http://www.arp-bolts.com/Tech/TechTorque.html

By DaveBoyer (*****)

Date 01-21-2009 01:55

The critical bolts in aircraft engines are drilled on the ends so that they have a uniform surface to measure with a conical anvil micrometer. Trying to measure stock bolts is like pissing into the wind.

By leterburn (**)

Date 01-21-2009 02:12

The drilled ends of aircraft bolts are typically for safety tying (on the heads such as engine parts you don't want falling off) or utilizing with castle type nuts in order to secure the nuts - typically on movable control bolts such as throttle linkages, control surface attachments, etc... although perhaps this would help in your measurements. regards, Lucky

By DaveBoyer (*****)

Date 01-22-2009 03:35

I was not refering to cross drilled for safety wire, center drilled in the ends for measuring purposes.

By Joseph P. Kane (****)

Date 01-21-2009 13:50

John, Chet

With the exception of one black A-490 (the head of the bolt came off), and some galvanized bolts during RC testing, all the bolt failures I have seen in the past 16 years have been with TC bolts. What I mean by failure, is that it fails to achieve the required tension during preinstallation verification testing before twist-off. Most of these failures were attributable to storage conditions such as drying, dust, grinding grit. In the field, when TC bolts were "snug tighted" in the shop, the beams stored on the shipping trailer and shipped to be fully tensioned during and after erection, rust and drying was deemed to be the cause. Sometimes the local supplier was the problem (loss of material control, Lack of material control procedure practice, open storage, mixing lots, and outright fraud).

From my experience, the preinstallation verification test is almost more needed with the TC bolts than with regular bolts. On the other hand, I consider the companies that I wind up inspecting as the third party inspector, to be the proximate cause of all the problems. (I am not commenting on your company or Chet's company. I found them to be very code compliant and well run.)

By ziggy

Date 02-03-2009 18:37

John

Recently I witnessed a pre-installation verification test where the A490 fastener assembly (non TC) failed to achieve the minimum tension. This was due, however, to the tech not following their written bolt procedure. They forgot to snug the bolt before putting the gun on it. They tested another bolt, followed their procedure, and everything was fine.

Just a side note (and I know you already know this) but the markings on the Skidmore dials are BELOW the testing tension minimums. When testing bolts (and only when testing) we have to achieve 1.05 times the value of Table 8.1 in the RCSC book. For some reason Skidmore's markings (red for A325 and green for A490) are at the ASTM minimum tension values, not the RCSC minimum testing values.

Hope all is well in Lynchburg!

ziggy

By jwright650 (*****)

Date 02-03-2009 19:10

Hi ziggy!
Yes, I commented on those markings on the Skidmore dial several years back, you do need to make up for that and use the Table in RSCS and then do the multiplication or just use Table PIV-1 directly out of the Structural Bolting Handbook by SSTC, Inc....I find that little book is very handy to keep in my Skidmore box.

All is well in Lynchburg, thanks for asking.

By mpitt

Date 02-19-2009 17:31

Once I had 2 out of the 3 bolts twist off dead on the line, not including the 5 percents that RSCS requires them to be over and had a hard time getting the bolt supplier to repalce them but he finally did.

Another time I had all three bolts twist off below the required tension during a pre-verification test. I called our bolt supplier and he wanted to watch me do the pre-verification test. I got three more and 2 of them twisted off below the required tension and the third failed in the middle without twisting the spline off at the end. He said he had never witnessed a bolt fail before. He had more bolts from the same lot at his store and sent all of them back to the manufacturer. After this the bolt supplier has never questioned me on any other complaint I have.

By ziggy

Date 02-24-2009 01:07

Keep in mind that if the contract documents specify the RCSC A325/A490 bolt spec for shop and/or field connections, then the fabricator (if tensioning bolts at the shop) or the erector (if tensioning bolts in the field) are required to perform this test "at the site of installation." (RCSC 7.2)

Of course, if the engineer of record stipulates snug tight only connections this test is not mandatory per RCSC. (RCSC 8.1)

ziggy

By hogan

Date 02-24-2009 14:36

I have noticed that this is the least followed requirement in RCSC. At least from my experience.

By jwright650 (*****)

Date 02-24-2009 15:00

Yeah, when I have been asked in the past to help in the field regarding welding/bolting procedures and such with a few of our subs, I also find that bolting isn't a very well known subject. How can businesses be in that type of business for years/decades and know so little about the bolting requirements?

By ziggy

Date 02-24-2009 15:39

Sadly I have to agree with you hogan. I might add storage requirements to the list too. Especially in the field.

If folks could think of bolts as stitches in a garment. What happens when you pull that one thread that is hanging out? Pretty soon the garment starts to come apart. Same can happen with bolts, if bolts in a connection begin to fail, what can happen to the connection?

Remember the story "For the want of a nail, the shoe was lost. For the want of a shoe, the horse was lost. For the want of a horse the soldier was lost. For the want of a soldier the battle was lost. For the want of a battle, the war was lost. All for the want of a nail!"

When required, test those high strength bolts, please.

ziggy

By hogan

Date 02-24-2009 16:34

We store our bolts in kegs on a rack(20 rows across and 6 rows tall) . The kegs are sitting at a 45 degree angle to allow easy access. The best way I have found to keep them protected from the elements is a shower cap. Very cheap and works well.

By jwright650 (*****)

Date 02-24-2009 17:11

We use something similar, but they were purchased from a bolt supplier...ours are stored in a locked storeroom with nothing but bolts and studs, with one person responsible for bolt/stud distribution into the shop, all lots tested and kegs marked with the date and initials of the person who did the pre-verification tests on that lot.

By HgTX

Date 01-21-2009 00:14

"wouldnt the spleen sheer off when the required tension is achieved?"

Not necessarily. The spline will shear off when the torque that is typically associated with the required tension is achieved. "Tension control" is a misnomer; they ought to be called "torque control". Anything that might interfere with the torque-tension relationship can make them shear at the wrong time. Most common culprit would be bolt not stored properly so that the lubrication is not as it should be; in that case it will could snap off too soon.

Hg

By Duke

Date 01-26-2009 03:59

If the bolts are too long they will "shank out" splines snap and you can still spin em around in the hole

By 803056

Date 05-30-2009 22:18

As you can tell, I don't usually take the time to read this section. Today I should have been doing something else, but this caught my eye.

I have not had major problems with "TCs" as a rule during verification testing. I did run into a problem on a project many years ago. A large number of joints I checked were "loose". Checking into the problem a little further I was able to correlate the problem connections to those being tightened early in the morning when the temperature was below 30 degrees F.

I ctested a number of bolts in my Skidmore early in the morning when the winter temperatures were below 30 degrees and sure enough, they all failed well below the required tension. Then we had a dog and pony show with the erector, bolt supplier, and EOR in attendence. The results were the same, the splines broke off at a low tension value when the temperature was below 30 degrees. They were fine if the temperature was above 35 or 40 degrees.

The fix was simple enough. We didn't fully tighten the connections until the temperature was above 40 degrees and the problem was no more.

Best regards - Al

By trapdoor (**)

Date 06-10-2009 14:51

As a third party inspector doing QA. I find that well over 90% of the companies here in CA that are erecting steel buildings do not, on their own accord, use a skidmore to verify pre tension of TC bolts. The companies that I work (inspection labs) for generally provide me with a skidmore for this purpose, but I am in the opinion that the fabricator/erector should have and use this equipment themselves. My rationale being that if this same company were to erect a building without QA inspection, how would they perform a verification test? It is scary that there is such a lack of interest, in the erectors part, in performing these tests witch i can only attribute to overconfidence in TC bolts and ignorance of the importance of verification testing. It only takes a few minutes to check a "lot" and the potential money and lives possibly saved far outweigh the time lost.

By 803056

Date 06-10-2009 18:56

I would attribute the problem as being "ignorance" of the requirements on the part of the erectors and "ignorance" on the part of the owners because they don't insist on it being done by either the third party inspector or the erector.

I agree that the erector can not fulfill their obligations to the owner if they don't have the equipment to perform the required verification testing if they don't own the necessary equipment. The third party inspector should witness the verification testing to ensure it is being done and it is being done properly.

Your assessment is spot on.

Best regards - Al

By eekpod

Date 06-10-2009 19:01

On the east coast there is wording in the specs that says something to the effect "the contractor shall provide a skidmore wilhelm type tensioning device to confirm pre-installation verification". We are always the contractor, thats why we have like 5 skidmores in our company. I am surprised to hear that from California, I thought they were always on the leading edge becasue of the seismic issues out there. I guess erectors are erectors all over.

By thcqci

Date 06-11-2009 16:10

Been following these 2 TC bolts thread and was not sure I had anything significant to contribute, but...

1) It is also my opinion that the fabricatior/erector shall have their own "Skidmore". It should not be the inspector supplying the Skidmore, he should be observing it being done. 2 of my pet peeves when going on a jobsite is care and installion of bolts and all that goes along with that and care of low hydrogen rods (open containers, no rod oven, buckets, boxes, back pockets of sweaty welders, sitting around jobsite loose and uncontrolled, etc.). These 2 things will almost always tell me just about everything I need to know about that erector's quality knowledge, care, or approach to a project.

2) On one of our projects we supplied domestic, top name brand, TCs that did not pass pre-installation verification and were rejected. In a pinch the erector was able to obtain more bolts, but they were foreign, not domestic. When I was able to see a samples of both bolts, one was shiny, oiled well and domestic and was failing while the foreign ones looked dry (not rusty, just dry) and were easily passing the pre-installation inspection. There goes that theory! This may not usually be the case, but it was this time.

3) We rarely install shop tensioned bolts (twice in my 8 years here). We NEVER supply TCs (or for that matter any bolts that will not be simply snug tightened) installed in steel when we ship it. We send 307s in clips, etc. Erectors are responsible for testing and installation of "real" bolts which we supply in kegs with paperwork. Questions (one was touched on above):

A) How do you keep proper manufactured supplied lubrication on TC bolts that will be blasted, painted, stored, rained upon, sun, shipped 2 weeks later, dumped off truck in dirt and muck, stored, rained on, erected in field in various points in structure, etc. You get the idea.

Further...

B) Don't you perform pre-installation verification on LOTS of bolts? What is the "lot" on a shipment of 2, 3, 4 trucks of steel??? How does that erector have a clue which lot these bolts came from? Steel shipped this week and more 2 weeks later with bolts from different kegs and lots. Same with any tensioned bolt assembly components of A325 or A490 bolts that you ship to a jobsite pre-installed in steel and not in kegs. This is why we don't shop install bolts that will be tensioned during erection.

And...

C) Why would you not verify DTIs? See first sentence of RCSC 9.2.4. Sorry Bob, I respectfully disagree.

Just a few things that make me say HMMMM.