Square HSS connection using Huck BOM's

[TpaRAF]

The application I have is to connect a large, square steel tubular section (HSS) to a connection "socket" made of plate steel. The item is being used for a cantilever arm 38 feet in length, supporting a 3700 pound sign panel at it's end. The HSS member is TS 16 x 16 x 1/2", and the socket "flanges" will be at least 3/4" thick. The difficult part of this connection is the tubular member will require a blind connection -- the nut side of a bolt will not be accessible! The connection forces should be primarily shear, without applied tension.

The Huck BOM fastener seems to provide an adequate shear strength, and also seems much larger than what a similar A307 bolt would provide. A 3/4" - A307 bolt will provide about 7 kips working shear (LRFD), while a BOM fastener is supposed to provide 45 kips ultimate shear! This would provide a factor-of-safety of more than 6.

Does anyone have any experience with the Huck BOM's performance? Is it suitable for this connection, or should I use through-bolts instead?

Thanks in advance for your consideration of this problem!

 

[evelrod]

I am not a great fan of Huck bolts but, be that as it may, using through bolts(with suitable sleeve) or welded nuts I would not use A-307 (or any ungraded fastener) in an application such as this.
At least A-325 or better, automotive grade 5, etc.

Rod

 

[TpaRAF]

Thanks for the advice, Rod! I concur a A307 bolt should not be used; ideally A325 should be used here.

Sleeves cannot be installed, since the interior of the HSS is not accessible. Our concern with welding the washer & nut to the interior is a) large numbers to attach and b) if something breaks loose inside.

What are the shortcomings of the Huck BOM's? In the structures forum, you said you've used them a lot. Personally, I can't believe the claim of 45k shear capacity, since an A325 bolt the same size can only provide about 41k !

Thanks for sharing your insights! Robert

 

[evelrod]

Hi Robert. Sorry I can do no better than general advice aside the link to Duncan. I've been retired for several years and out of the picture. I worked for Temcor Co. for a year or so and they were a primary user of Huck bolts, mostly in geodesic dome construction. I can only guess that perhaps the metalurgy may contribute to the shear capacity claims. This type of claim should be easily verified. I am a little bit confused, perhaps this system is something new that I am not familiar with (it has been a LOT of years...)---How did you plan to install the compression cones?
As to the sleeves, weld them in allignment prior to assembly or, as you suggest, add sufficient stiffeners. I was always nervous with cantilever construction.
Good luck with the job. It sounds like you have it under control.

Rod

 

[TpaRAF]

Greetings, Rod !

The compression cones are used with the Lindapter Hollobolts (not with Huck bolts). The report cited/linked by "structuresguy" discusses testing with that product, which is essentially an expansion bolt. They reversed the cone so the end that flared was in contact with the plies first, rather than being pulled up last. I think the paper shows it best (see thread 507-68730 over in structures).

Where the Huck bolts problematic in your use of them? What sort of issues came up?

Again, thanks for the advice. I wish I had it under control -- this cantilever is too much too far, in my opinion! Making it 10' shorter would be much better ...

Regards, RAF

 

[evelrod]

As far as I know, Temcor still uses the same system world wide. The only real problems was in the reliability of the installation tools needing frequent repair, etc.
3700lb sign 38 feet out would be a tough call in SoCal where quakes and very high winds prevail. Hope ya got them ducks all lined up!!! ;-)

Rod