Can I use A325 bolts in tapped (threaded) holes?

[JezzaJames]

Hey fellow Structural Engineers,

I am designing a bolted rectangular HSS splice connection that will carry the full bending capacity of the connecting parts, and am wondering if I can use A325 bolts (3/4" dia. in this case)in tapped/threaded holes?

I have read many manuals, and publications, but have not seen an explicit yes or no. I am assuming I can, as the AISC 13th Edition allows flow-drilling (pg 7-13), which incorporates tapped holes:

http://www.wagnercompanies.com/Flowdrill.aspx.

JJ

 

[racookpe1978]

Why would you want the expense of a very short drilled and tapped hole rather than a properly long through bolt and fully torqued nut?

 

[MikeHalloran]

Probably because you can't easily get inside an HSS to buck a bolt through one wall, and a bolt through two walls will crush the tube unless you weld in a sleeve.

The flowdrill (note that tapping is still also required) provides only~ half again as much engagement as just tapping the tube wall. It's kind of a pita to do; it may be easier to just use more, smaller bolts.

Easier still is to weld the tube to rectangular plate flanges, and join them with axial bolts and nuts, sort of like a flanged joint in a round pipe.

Easier still, if you can take the time to custom fit it, is a solid bar inside the tube, with a couple of cross-bolts.

Easier still; use a longer tube, and put the joint at one or both ends.




Mike Halloran
Pembroke Pines, FL, USA

 

[msquared48]

Still seems like a lot more work than using backer bars and welding the sections together full pen.

Mike McCann
MMC Engineering

 

[MikeHalloran]

Or, you could do that.

I guessed the bolted splice was a response to an unstated constraint, like a flammable atmosphere. Else it makes little sense.



Mike Halloran
Pembroke Pines, FL, USA

 

[connectegr]

RCSC and AISC do not allow the use of drilled and tapped material in place of an A563 Heavy Hex Nut. I have designed a bolted 4-plate splice for an HSS section and used Lindapter Hollo-Bolts.

http://www.FerrellEngineering.com

 

[JezzaJames]

Thanks for the feedback everyone.

Connectegr, if you know specifically where the language is in AISC and RCSC stating that drilled and tapped holes are not allowed as a substitute for A563 HHN, it would be appreciated if you passed it along.

For those of you who are curious, a requirement of this connection is to not have any critical welded joints, as in a typical flange-flange splice connection for HSS. One solution, as stated above is to insert a welded plate (non-critical welds) or a solid bar inside the tube to brace the wall of the HSS, as our HSS12x4x3/8 members which would be crushed by a through bolt.

This connection has been prototyped with a rivet similar to the Hollo-bolts that connectegr described, but we are unsatisfied with the clamping force of the fasteners, which slip exceeding our tolerance requirements.

It is our hope to use A325 bolts in some fashion to give us a greater clamping force. Several of the ideas discussed are still being pursued for cost (we will many of these connections on our project).

Thanks again for the help,

JJ

 

[connectegr]

Unlike a riveted connection, Hollo-bolts allow the connector to be "pre-tensioned", thus providing the clamping force you may need.

I don't have my RCSC spec, since I am typing on my phone. But, I think in 1.2 or 1.3 specific ASTM information is given for the components of the structural bolt assemblies. Also in 2.3(?) the specific requirements for nuts are given. The properties of hardened bolts cannot be match in a tapped HSS wall.

http://www.FerrellEngineering.com

 

[racookpe1978]

Kike - Thank for noting my oversight of the HSS connection.

Now, what if you get a realllly skinny guy, then lowering him down inside the HSS with a big wrench .... 8<)

Sounds like you could conventionally bolt 4x flat bars inside the lower HSS section, since both inside and outside joints are accessible for all bolts. then you need to fasten the Lindapter Hollo-Bolts (or equal nuts) to the upper half of each of the 4x flat bars . What's essential is being able to prevent these nuts from rotating as they are torqued, without destroying the inherent strength of the nuts by tack welding them to the flat bar. (The outside surface of the upper flat bars needs to be flush after assembly of the nuts so the upper HSS can slide down over the joint.) Maybe use square HS nuts with a captive plate around the nuts? The captive plate could be welded (not as a critical assembly) to the flat bars at a bench inside a jig.

Then you lower the upper HSS in place, then fasten the bolts through holes in the upper HSS member, through the matching holes in the upper half of the flat bars, then into the nuts inside. Torque up the bolts from the outside to spec.

 

[Duwe6]

Use the "Hollo-bolts", or use "Huck bolts". Tapped holes in A36/A500 material won't calc out until about Hole depth = 2 bolt diameters.

The exclusion of welds is an uneducated, prejuidiced position to take. But "the customer is always right [as long as his checkbook is open]"