Tapped holes for structural member connection 4

[Kuhuh]

Alright I got a project that the vendor is trying to use tapped holes and a thread bolt for all their structural load bearing member connections. Essentially, their members are connecting to HSS tube steel and therefor a nut cannot be attached. Is there a code in California that prohibits this type of connection. The engaged depth of the bolt would only roughly 1/2"-3/4" thick or so. All common sense is telling me the head of the bolt would need to be welded to the connector plate but they are saying no. The structural frame is enclosing a mechanical system and I'm sure there will be vibration let alone we have to conform to ASCE 7-10 codes as well. I attached a detail for reference. any suggestions?

 

[Lomarandil]

You will certainly have significantly less capacity in a tapped hole than with a nut.

We used to have connections similar to this in substations all the time. The easy option (if it meets your other project constraints) is to widen the connection in your section view to be wider than the top tube. We typically did it with a cap plate on the end of the vertical tube mating with a plate welded to the top tube, and 4 bolts between the two.

 

[JAE]

Why not use expansion bolts for HSS?

http://www.structuremag.org/?p=7611

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[SwinnyGG]

Much depends on the bolt sizes, HSS wall thicknesses, and loads.

 

[NS4U]

I don't like the idea of using tapped holes in this situation but if you wanted to try and justify it, read on....

There are some papers that discuss methods for calculating stripping strength of threaded joints. I don't have them handy at the moment but Industrial fasteners institute has a nice 2 page tech bulletin that gives a straight forward procedure.

In general the thickness of the tapped element needs to be 1-2 times fastener diameter to develop the fastener but that is just based on my experience.

You want to make sure to get a decent number of threads engaged. UNC threads with thin material may mean you only get 1 or 2 threads engaged which I don't like.

 

[oldrunner]

We've had this problem of using A325 bolts in A36 steel on some sub station transformers. This required a analysis from some ASME data and limited torqueing with special inspection. Not recommended by us.

 

[Deadblow]

What HSS member has a 3/4" thick wall?

EIT

 

[jayrod12]

Deadblow, check out the Atlas tube website. They've got 3/4 wall on some of the 10x10 and bigger

 

[azcats]

I recently used the expansion bolts (Hollo-Bolts from Lindapter) on a project where welding was out of the question and I had to attach to hollow sections as well as a WF to which we only had access from one side. They worked well. Not cheap, but you're not spending any labor in tapping either. They have an ICC ES report with allowable uses and values.

Whether or not I'd use tapped holes would depend greatly on the loads and the size of hardware required. I believe you're outside of the RCSC recommendations and would be on your own for design. And if the loads allow, I'd be much more inclined to allow self drilling/tapping screws over some guy tapping into structural steel.

 

[Ron]

Depending on the load, consider using "Nutserts"....works like a pop-rivet but provides a nut-like structure for bolting. I've used them numerous times in aluminum construction with thin-walled aluminum tubes. They are also available for steel applications.

 

[thaidavid40]

We have run into this conundrum too on several occasions. On those cases where we didn't use box bolts, we elected to weld a thick plate to the face of the HSS member. The thick plate was pre-tapped for the bolted connection. The HSS member was pre-drilled with slightly larger oversized clearance holes, so the bolt wouldn't bottom out on the wall of the HSS. Maybe this will work for you?
Dave

Thaidavid

 

[racookpe1978]

You are risking tremendous construction difficulties with dirt, rust, grit and garbage in the conventional tapped-hole-in-structural-member, plus the expense of drilling and tapping (er, machining) the large holes deep enough and accurate enough to allow the steel mis-alignment that will happen.

As above, use the inserts if you absolutely have to use a tapped hole.