Threaded circular Hollow Structural Steel connection

[453001]

I am in a unique situation in which it sould be beneficial to the project to have a threaded H.S.S. conncection to allow for some vertical erection tolerances. The column and the connection will receive vertical,shear and moment loading and needs to be independantly verfified. Do you know if the AISC covers this situation.

Regards Richard

 

[hokie66]

Trying to understand what you are asking, but I can't. Where are the threads?

 

[dhengr]

Hokie:
Where are the threads??? They’re all over the place, there’s this one, there are others on this same forum, about web stiffener spacing, unbraced column length, and there are some on conc. and welding, etc., take your pick. Boy, you’re losin it. .

All I know is that AISC frowns on threading square or rectangular HSS tubing, and threading dies and taps are hard to come by for round pipe over 3 or 4" dia. Also, pipe threads are a tapered thread, not the same as the thread on a nut and bolt. And, since running axial loads, shears and moments through a loose threaded joint might offer some problems with meaningful analysis, why not make this a continuous column with a base plate arrangement and leveling nuts which would give you some vertical adjustment.

 

[hokie66]

Ah so! He means taps and dies to fit the I.D. and O.D. of a circular column? Bad idea! But you could insert thick end plates on each, tap one, provide a big stud on the other, and turn one. Not too good for bending moment.

 

[ishvaaag]

The kind of connection seen at pipe micropiles. Bads effects of the entails are there mainly masked if wise enough to not make the joints all at the same levels, since the great number of micropiles smears the local entail of one of them within the set of many others.

 

[ishvaaag]

I meant, of course, for micropiles used in "sheet pile-like" setup. For ordinary structures doesn't semm a good idea, nor I think that the intent of the AISC code is to cover structures made with such kind of connection; otherwise at least some note about the connection should be extant.

 

[453001]

Thanks for all the information. It sounds like AISC does not have a design avenue to support this.

A little more back ground information.

A seismically qualified platform will be built on a steam generator. The connections on the steam generator are two lifting lugs in which the platform will be attached to. The other two are a steel pads on the generator.

This work has been completed before in a different unit on the same site. There was a problem with the erection of the platform. The vertical tolerances were controlled by essentially a set screw and then field welding.

This is where I had my idea of a "turnbuckle" in the column. The "turnbuckle" idea would have to be defended by code. From an erection perspective it would be very convenient and considering the work location (elevated, radiation control measures, crane dependent for erection, safety issue working under a crane load)
This is why I would like to do this. But if i cannot defend it with AISC there would be no point.

Thanks for all the idea's. If anyone has any other idea's i would really appreceiate it.

 

[paddingtongreen]

AISC does not prohibit this. You could probably use threaded pipe and couplers to make up small adjustments. Could you not use this as set-up and then use friction grip bolts on a real structural support, say channels back to back with slotted holes, or slotted connections.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[453001]

You say AISC does not prohibit this. Does it provide guidelines, if so where???

 

[paddingtongreen]

AISC does not address it, at least to my knowledge it doesn't. It does recognize but not address turnbuckles by including them in the manuals, although I am two manuals out of date so that could have changed. I would much prefer a slip critical slotted connection though, with your threaded pipe only as a means of temporary support.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[453001]

Thanks for the input. dhengr's suggestion of levelling nuts may work. Basically surrounding the H.S.S. with threaded rods to allow for vertical movement.

 

[racookpe1978]

Nuke installation subject to radiation over an SG, eh? Nasty environment.

Try very, very hard to NOT "write" or "edit" Code that will fit the Code's unintended purposes. Just over-design it against failure so there is no credible chance of failure.

What about using two tubes of the appropriate designed wall thickness that can be tightly "nested" inside one another, rather than anything with "traditional" pipe wall diameters and thicknesses? Outer tube is the longer for best rigidity, inner tube has the thicker wall and is welded circumferentially at the joint, and also with a series of "plug welds" between outer and inner pipe going up the overlapping portion of the inner pipe for as long as necessary for column stiffness. Pre-drill 2x (or more) holes at right angles to each other for shear pins through the outer pipe.

Adjust the platform height to "perfect" design height, then set the legs to the as-found base conditions with external (temporary) jacking threads.

When welding of the circumferential weld and slot welds completes, drill through the inner pipe and insert the shear pins as backup. Lockweld the shear pins in place.