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Thread Strength of HHS Stock

Thread Strength of HHS Stock

Thread Strength of HHS Stock

(OP)
I need to field tap 4"x4" 1/2 HHS square stock to mount an equipment cabinet.  As I am an electrical type I am unsure if the thread depth (and material) may be suitable for my end requirement - to withstand an earthquake.  Here is what I know:

The steel - as above
there are four bolts (corners) per cabinet
I am using 1/2 bolts (thread count/material TBD)
the Service load is 4748lbs
the bolt will project 1.5" above the frame
Pull-out strength per bolt is 2374lbs
Shear load is 1941lbs (2 bolts per side)

Will this work?  Can the tapped hole provide the required strength?  Any suggestions on the size/thread of the bolts?  My field installers are not machinists - can they effectively drill and tap in the field?

Any help would be greatly appreciated.

RE: Thread Strength of HHS Stock

I would put in the extra 4 bolts between the
corner bolts, ie, an extra bolts on each side
between the corner bolts.  Especially if this
is going to be a field service installation.
You might be able to drop down to 7/16 diameter
with more bolts. The extra measure of safety
is warranted if you are overcoming earthquake
loads.  I would also use course threads for
a field service application.  Fine threads are
supposedly stronger but need better attention
to drilling and tapping.

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