×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

TC bolts vs High Strength bolts
3

TC bolts vs High Strength bolts

TC bolts vs High Strength bolts

(OP)
What's the difference between a A325 TC bolt and a A325 High strength bolt and their proper use?

RE: TC bolts vs High Strength bolts

goolge images will give you a pretty good idea!

RE: TC bolts vs High Strength bolts

TC stands for tension control, and has to do with their tightening means.  As the proper torque is reached the driving head breaks off, twists off or pulls off.  Google "A325 TC bolts" and take a look at the various ASTM bolt specs., AISC, and RCSC.

RE: TC bolts vs High Strength bolts

(OP)
dhengr,
Are you saying that they both have the same use except their tightening means are different?

RE: TC bolts vs High Strength bolts

(OP)
Also, I have a case where A325 HS was specified for a equipment dunnage on top of a roof.The equipment will have some vibration. The client is asking for the use of A325 TC to avoid some inspection requirements. Is that possible to do the switch?

RE: TC bolts vs High Strength bolts

ASTM A325 is simply a material and geometry specification for a type of high strength bolt.

A325TC bolts look nothing like normal A325 Heavy Hex Bolts but, they both meet the ASTM A325 specification for geometry and material properties.

RE: TC bolts vs High Strength bolts

I imagine the inspection requirements for A325TC's is easier b/c, as dhengr state, the TC bolts have a twist off mechanism that breaks off when the bolt is properly installed with very specific equipment.
TC inspection requirements fall under RCSC 9.2.3
RCSC is a free download and is included in the steel manual AISC 360-05
To my knowledge, the inspection requirements are easier to meet with these bolts than most others

RE: TC bolts vs High Strength bolts

(OP)
ToadJones,

Will it be ok then to just switch them in the case I mentioned?

RE: TC bolts vs High Strength bolts

pond-
I am not sure what "HS" stands for unless it is "high strength".

If this is the case, you are simply trading one ASTM A325 bolt for another and there is no reason I see why this couldn't be done.

Note that just b/c you are using a TC bolt does not necessarily guarantee you a slip critical joint.
This should be addressed as well.  

RE: TC bolts vs High Strength bolts

(OP)
ToadJones,

Yes "HS" stands for high strength.
The connections are bearing type. is that an issue?

RE: TC bolts vs High Strength bolts

"High strength" means it is A325 (or A490, or F1852, or ...).  Whether it's TC, or heavy hex head, or some crazy type with a pentagonal nut and reverse threads, if it's A325, it's "high strength."  By using TC bolts, you're not switching HS for TC.  TC are HS.

RE: TC bolts vs High Strength bolts

yes, it could be depending on the design of the bolt and whether they were designed with the threads included or excluded from the shear plane("N" or "X").
You should ensure that the bolts you are swapping are the same in this regard.

I'm not sure why you need fully pretensioned TC bolts in a bearing connection unless vibrations are an issue.

Maybe ConnectEgr will chime in.
This is in his wheelhouse.  

RE: TC bolts vs High Strength bolts

(OP)
nutte,

So they both are the same except their tightening means?

RE: TC bolts vs High Strength bolts

(OP)
ToadJones,

So if the connections were slip-critical type, then the use of a fully pretensioned TC bolts will make more sense?.

RE: TC bolts vs High Strength bolts

Pond-
read the posts!
The meet the material and geometric requires of ASTM A325.
saying "they are the 'same' except for their tightening means" might be a bit of a blanket statement.

Also make sure your contractor can install TC bolts.
The bolt "head" on a TC bolt is not hex but rather looks like a rivet head. You have to have the proper tools and clearances for installation.  

RE: TC bolts vs High Strength bolts

(OP)
ToadJones,
Ok. What about the slip-critical...it will make more sense to use TC bolts in that situation?

RE: TC bolts vs High Strength bolts

(OP)
Does A307 classify as TC shear bolt?

RE: TC bolts vs High Strength bolts

Steel Interchange

A325SC Bolts?

How are ASTM A325SC bolts designed and installed? In past projects we typically used A325N and we are now using A325SC. Do both of these types of bolts need to be checked for bearing?
Answer

When dealing with high-strength bolted connections, it is probably best to consider the difference in terminologies pertaining to the bolt type versus that of the connection type. The A325 example refers to the bolt type, while the SC or N refers to required installation details for the connection type and geometry respectively.

Bolt Types

The most common types of bolts used in structural steel applications meet either the ASTM A325 or A490 Standard. There are also twist-off types of bolts, which are equivalent to these bolt types: ASTM F1852 equivalent to ASTM A325, and ASTM F2280 equivalent to ASTM A490. The property requirements are the same for a particular bolt type regardless of the type or details of the connection in which it is to be used.
Connection Types

There are three basic connection types used in structural steel applications: Snug-Tightened, Pretensioned, and Slip-Critical. Descriptions of these connection types and installation requirements can be found in the RCSC Specification (a free download at www.boltcouncil.org). In all joint types the connection is required to be checked for bearing, which could occur at some time during the life of the structure.

Snug-Tightened Connections: In this connection type, it is required that the faying surfaces of the connection be brought into firm contact. While some pretension of the bolts is required to bring the surfaces into firm contact, there is no specific requirement for a level of pretension that must be induced into the bolts. Thus, while there is some level of clamping force in the connection as a result of the installation requirement to bring the surfaces into firm contact, this type of connection is assumed to provide the least level of safety against slip. The bolts in these connection types are always assumed to be in bearing against the base material, and thus the connection is defined as a bearing connection.

Pretensioned Connections: This type of connection generally is just like a snug-tightened joint, except it also requires that a specified pretension be applied to the bolts in the connection, once the firm contact of faying surfaces has been achieved. It is still a bearing-type joint, and the shear strength design parameters are identical to those of the snug-tightened joint.

Slip-Critical Connections: This connection type is just like a pretensioned connection with the addition of surface preparation requirements to provide the required level of slip resistance. To achieve this goal, there is a specified level of friction coefficient required for the faying surfaces in the connection. After the faying surfaces are brought into firm contact, the bolts are required to be installed to a specified level of pretension, which is the same as that required for a pretensioned connection. Thus, the bolt installation procedure for slip-critical connections is identical to that required for pretensioned connections, the difference being in the preparation requirements for the faying surfaces of the respective connection types.

Threads In or Out of the Shear Plane

One parameter that we have not discussed to this point is the N designation cited in your example. This designation is an indication of where the threads of a bolt are assumed to be located with respect to the shear plane(s) in a connection. The N assumes that the threads of the bolt will be located within the shear plane; an X assumes that the plies are detailed to exclude the threads from the shear plane. The shear strength is reduced if the plies are detailed such that the threads are located within the shear plane.

Kurt Gustafson S.E., P.E

RE: TC bolts vs High Strength bolts

Pond, it seems that you are not at all familiar with bolting terminology and requirements.  Unfortunately, there is way too much information to be effectively communicated in this manner.

RE: TC bolts vs High Strength bolts

Download RCSC from boltcouncil.org and read the whole entire thing this weekend. Its only about 60 pages (excluding tables etc). You can read the whole thing quite quickly.  

RE: TC bolts vs High Strength bolts

(OP)
Thanks for the info.
However I have another question...does TC shear bolt the same terminology as A325 TC?

RE: TC bolts vs High Strength bolts

mad

RE: TC bolts vs High Strength bolts

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.
 

RE: TC bolts vs High Strength bolts

Pond68, consider signing up for Bob Shaw's 1 day Structural Steel and Bolting Seminar. http://www.steelstructures.com/  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.
http://www.skidmore-wilhelm.com/

Most erectors prefer TC bolts and will tighten them beyond ST until the splined ends break off even if you specify ST joints.

RE: TC bolts vs High Strength bolts

(OP)
henri2

Thanks

RE: TC bolts vs High Strength bolts

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.

RE: TC bolts vs High Strength bolts

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.  

http://www.FerrellEngineering.com

RE: TC bolts vs High Strength bolts

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   

RE: TC bolts vs High Strength bolts

(OP)

Thanks all...

RE: TC bolts vs High Strength bolts

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.   

http://www.FerrellEngineering.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources