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TC bolts vs High Strength bolts 3
- Thread starter pond68
- Start date
- Thread starter
- #21
![[mad]](/data/assets/smilies/mad.gif "[mad] [mad]")
Pond68:
Are you a Structural Engineer? You really should know some of this stuff, and must kinda study it on your own as Nutte and Toad suggested, to really learn and understand it. Everyone gets confused by the use of too many acronyms, when they are thrown around too loosely; TC is fairly specific in this discussion and topic; but HS is almost meaningless here (except as a very generic term) since ASTM A325 or A490 already says it all, and is the way the bolt should be called out, not HS.
You should talk with your client and get a better understanding of what he is really trying to accomplish by his request. Some Bldg. Depts. like the positive indication that the bolt has been tightened to the break-off point, without any guessing at if it was torqued adequately, and by what method. And thus, the lesser concern about final inspection. But, then you say the bolts are just in a bearing connection on some roof structure, to carry some vibrating mech. equip., in which case the important criteria might be that you provide some means of locking the nuts so they can’t vib. loose. You may still want to use A325 bolts and nuts, and tighten them adequately, but some of the other connection considerations mentioned above are still different matters and considerations. And, you must know all of this to serve your client properly and fairly. Some of this stuff is covered in various posts above, and you should reread them more closely, and read btwn. the lines a bit too. You are basically getting good, free, advice here, but you gotta dig a little too, the RCSC Spec. is particularly good, and likely covers many of your questions and options. We don’t offer college degrees in engineering here.
Are you a Structural Engineer? You really should know some of this stuff, and must kinda study it on your own as Nutte and Toad suggested, to really learn and understand it. Everyone gets confused by the use of too many acronyms, when they are thrown around too loosely; TC is fairly specific in this discussion and topic; but HS is almost meaningless here (except as a very generic term) since ASTM A325 or A490 already says it all, and is the way the bolt should be called out, not HS.
You should talk with your client and get a better understanding of what he is really trying to accomplish by his request. Some Bldg. Depts. like the positive indication that the bolt has been tightened to the break-off point, without any guessing at if it was torqued adequately, and by what method. And thus, the lesser concern about final inspection. But, then you say the bolts are just in a bearing connection on some roof structure, to carry some vibrating mech. equip., in which case the important criteria might be that you provide some means of locking the nuts so they can’t vib. loose. You may still want to use A325 bolts and nuts, and tighten them adequately, but some of the other connection considerations mentioned above are still different matters and considerations. And, you must know all of this to serve your client properly and fairly. Some of this stuff is covered in various posts above, and you should reread them more closely, and read btwn. the lines a bit too. You are basically getting good, free, advice here, but you gotta dig a little too, the RCSC Spec. is particularly good, and likely covers many of your questions and options. We don’t offer college degrees in engineering here.
Pond68, consider signing up for Bob Shaw's 1 day Structural Steel and Bolting Seminar. Most of the seminar participants are special inspectors and practising design engineers which leads to great discussions during Q and A sessions between design professional and inspectors who are like the designers "eyes and ears" out in the field.
The folks over at Skidmore-Wilhelm also offer a free 1 hour presentation on the use of tension calibrators for pre-installation verification testing, which is required by code when you specify SC or PT joints but not for ST joints. Unfortunatley pre-installation verification is not widely done on many projects in certain parts of the country.
Most erectors prefer TC bolts and will tighten them beyond ST until the splined ends break off even if you specify ST joints.
The folks over at Skidmore-Wilhelm also offer a free 1 hour presentation on the use of tension calibrators for pre-installation verification testing, which is required by code when you specify SC or PT joints but not for ST joints. Unfortunatley pre-installation verification is not widely done on many projects in certain parts of the country.
Most erectors prefer TC bolts and will tighten them beyond ST until the splined ends break off even if you specify ST joints.
- Thread starter
- #25
Hi pond68
Have a look on page 17 of this reference:-
Have a look on page 17 of this reference:-
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- #27
paddingtongreen
Structural
Pond68:, The TC only refers to the method of installation. On my jobs, I only specified A325 or A490 and left it up to the erector which method to use.
A307 is simply a mild steel bolt, it is not a heat treated bolt. It cannot be used for a slip critical connection.
If there are many bolts in the connection, they must all be snugged before torquing. If this is not done properly, some of the bolts may have less tension than expected so such connections need to be tested with a torque wrench anyway.
Michael.
Timing has a lot to do with the outcome of a rain dance.
A307 is simply a mild steel bolt, it is not a heat treated bolt. It cannot be used for a slip critical connection.
If there are many bolts in the connection, they must all be snugged before torquing. If this is not done properly, some of the bolts may have less tension than expected so such connections need to be tested with a torque wrench anyway.
Michael.
Timing has a lot to do with the outcome of a rain dance.
connectegr
Structural
Pond68
If you are responsible for the installation and specification of bolts, you question is a scary reflection. The site and the posts can be helpful. And the recommendations to read the RCSC Spec and attending a few of Bob Shaw's lectures would be a big step in the right direction. Proper installation and understanding of this information is critical. Regretfully the iron workers rarely know the specifics. The insight you have gained thus far is just enough to make you dangerous.
If you are responsible for the installation and specification of bolts, you question is a scary reflection. The site and the posts can be helpful. And the recommendations to read the RCSC Spec and attending a few of Bob Shaw's lectures would be a big step in the right direction. Proper installation and understanding of this information is critical. Regretfully the iron workers rarely know the specifics. The insight you have gained thus far is just enough to make you dangerous.
paddingtonongreen---Michael, a star for you, sir. On any job I was ever on where A325 (or whatever)were required I never had a specific notation for TC bolts unless it was an environmental consideration (noise).
However, in the early years before TC fasteners were common in structural steel erection, many inspectors would require a physical check with a tq wrench. That caused problems galore until we finally got specifications for the 'actual' tq readings on TC bolts. Somewhat less than on the conventional A325HS done up with an impact. Time and usage/familiarity has probably taken care of that problem. Following your directions is still a must, however.
Keep in mind that I've been retired for 14 years and specs can change. OP needs to go back to class or consult qualified help from what I read above.
Rod
However, in the early years before TC fasteners were common in structural steel erection, many inspectors would require a physical check with a tq wrench. That caused problems galore until we finally got specifications for the 'actual' tq readings on TC bolts. Somewhat less than on the conventional A325HS done up with an impact. Time and usage/familiarity has probably taken care of that problem. Following your directions is still a must, however.
Keep in mind that I've been retired for 14 years and specs can change. OP needs to go back to class or consult qualified help from what I read above.
Rod
- Thread starter
- #30
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1
- #31
connectegr
Structural
Just a clarification on the paddington's wording...
Within RCSC "torque" has no place in the installation of high strength bolts. The RCSC provides the pre-installation and installation inspection requirements, for all the approved installation methods. The use of TC bolts does not eliminate these installation procedures. Torque and bolt tension are not directly proportional and therefore torque is not an RCSC installation method.
Pond68
All of these posts provide pieces of the puzzle. But, the most important aspect is the design performance intent. Required pretension, may or may not indication slip critical requirements. Slip critical may require additional fabrication and erection consideration for the faying surfaces. Simple providing adequate pretension of the bolts is not the only consideration. Also, requiring TC bolts does not clearly define the requirement for pretension or slip critical connections. Some engineers or contractors use TC bolts as an assurance that at least a snug tight installation will be achieved. But this is not a guarantee. Sequencing of bolt tightening and bringing all plies into firm contact are all part of the equation. If the design intent is not clearly specified in the contract documents, that is the most important question. This intent cannot be simply shown in the bolt designation.
Within RCSC "torque" has no place in the installation of high strength bolts. The RCSC provides the pre-installation and installation inspection requirements, for all the approved installation methods. The use of TC bolts does not eliminate these installation procedures. Torque and bolt tension are not directly proportional and therefore torque is not an RCSC installation method.
Pond68
All of these posts provide pieces of the puzzle. But, the most important aspect is the design performance intent. Required pretension, may or may not indication slip critical requirements. Slip critical may require additional fabrication and erection consideration for the faying surfaces. Simple providing adequate pretension of the bolts is not the only consideration. Also, requiring TC bolts does not clearly define the requirement for pretension or slip critical connections. Some engineers or contractors use TC bolts as an assurance that at least a snug tight installation will be achieved. But this is not a guarantee. Sequencing of bolt tightening and bringing all plies into firm contact are all part of the equation. If the design intent is not clearly specified in the contract documents, that is the most important question. This intent cannot be simply shown in the bolt designation.
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