Designation of Bolted Connections...

[Rjeffery]

When drawing slip critical, direct tension or other bolted connections that would require other than a snug tight condition, how are these connections designated on prints?

 

[Lion06]

If you have a great number of these connections, maybe designate them as a dot or something simlar on plan. If it is only a few at unique, detailed locations, just show it in the detail.

 

[csd72]

I would normally put a note saying "fixed connections indicated thus..." or similar. No mis-understandings then.

csd

 

[kelowna]

Usually that information is indicated on the notes:
- All bolts to be tensioned as per ... unless noted otherwise

 

[dozer]

Notes are OK but I would also use the standard nomenclature in the bolt call out such as "A325 SC" when calling out slip critical bolts. "X" is a bearing connection with threads eXcluded, "N" is a bearing connection with threads iNcluded. I guess "DT" is direct tension. I saw that on a web site but I don't remember seeing it in the steel book. I don't have it with me here to check.

Construction workers are notorious for not reading the notes. If the only place you call out a connection type is in notes it may get missed. True, just because you call out a 3/4" A325 SC bolt doesn't mean the guy reading the drawing will know what that means but at least you didn't bury the information in note 12 on the cover sheet with 57 other notes.

 

[jike]

As far as designating them on drawings, we have a general note covering the majority of bolts and then anything different is designated on the details or plans.

I prefer to use 3/4" dia. type N A325 uno. If I require SC, use TC bolts. They are easy for you, your inspector and the iron workers to check in the field. If I need larger bolts, I go two sizes larger (1") so they are not mixed up in the field.

 

[Lion06]

jike,
are all TC bolts SC?

 

[jike]

The TC (tension control) bolts have a spline on them that pops off when they are properly tensioned to the slip critical force. As you are walking around, the shiny ends indicate that they were already tensioned.

 

[Lion06]

This has me thinking now. A steel fabricator use TC bolts for bearing type connections. If the slip-critical bolt is not needed, but provided, can you ignore the slip-critical values in AISC (as they are lower than the bearing connections shear values - even using slip at a serviceability limit state) and just assume you can count on the full value of an A325N when they will slip into bearing?

 

[Lion06]

I guess I am thinking about this a little more and you should be able to use the bearing (A325N) values if slip is not a concern at any level correct? What if these bolts were installed without consideration given to the faying surfaces, then the whole slip-critical thing is not valid anyway and you would be right back to the simple A325N bolt values, correct?

 

[JKStruct]

One problem that I see with using TC bolts for connections designed as bearing (i.e. no consideration for faying surfaces, etc.), is the "banging bolts" phenomenon. However, some people at AISC said they haven't heard of that problem in years, and our office usually specifies TC bolts with or without SC connections due to ease of construction, inspection, etc.

 

[civilperson]

DTI washers are another method of proving tension minimums in Slip Critical connections.

 

[csd72]

Using slip critical bolts in a pinned connection can induce additional moments in the connection - depending on the detail, and only up to the point of slip.


i.e. it can become a partially fixed connection.

csd

 

[civilperson]

A pinned connection usually depends on the flexibility of the shear tab or the web for rotation. Slip Critical bolts will not change the modeled connection principle.

 

[csd72]

civilperson,

Are you sure about that? Dont shear tabs rely on shear ploughing to ensure this flexibility - something that wont happen until slip has occured.

Also, the connection will attract more moment due to the additional stiffness of the slip critical bolts.

As I said above, this would only be in certain situations - namely where the bolts are far enough apart to induce a significant moment.

csd

 

[nutte]

A few things:

TC bolts does not necessarily mean a slip critical connection. For a slip critical connection, there are faying surface issues to deal with.

You can fully tension bolts in bearing connections. This is mentioned implicitly in the 13th edition specification J3.1 and explicitly in RCSC specification Table 4.1.

It is OK to use slip critical bolts in shear tabs. They require no different considerations than bearing bolts. See the procedure on page 10-101 in the 13th edition manual.

Ductility in the single plate connection is provided by several things, including bolt plowing against the plate or beam web, and bending of the single plate. That is why you size the weld at the plate to be stronger than the plate, so that the plate is guaranteed to fail in flexure (ductile) before the weld fails (brittle).