Structural Connection Design (Metal to PVC)

[banfillb]

Hey All,

I am familiar with some of the practices of bolted connections between steel plates, or steel beams etc. I am currently facing a design problem at work dealing with a composite metal panel being screwed to a hallow PVC beam. The PVC beam is screwed into a hallow aluminum beam. However, for simplicity I will just consider the PVC section supported, and perform analysis on both the composite metal panel and the aluminum, and find the limiting factors. My problem is I cant seem to find any procedures dealing with PVC to metal connections.

Im looking for some links to information that might help me.

anything on tension, and shear would be helpful. Basically what im looking for is at what force will the screw pull out of the PVC (stripping), and what downward force will cause the PVC to deform thus voiding the connection.

I've attached a RUFF sketch of what I'm talking about

Any info will be helpful. Thanks guys!

[nvn]

banfillb: You can assume your polyvinyl chloride (PVC) has tensile yield strength Sty = 44 MPa, and shear yield strength Ssy = 25 MPa. You could use a yield factor of safety of FSy = 2.0. Compute the PVC thread shear stress, tau, as follows.

tau = F/(0.625*pi*dp*t1),

where F = bolt tensile force, pi = 3.14159, dp = dn – 0.75*p*sin(60 deg), dn = bolt nominal (major, outside) diameter, p = bolt thread pitch, and t1 = PVC tube wall thickness. To prevent PVC thread shear pull-out (stripping), ensure Ry does not exceed 100 %, where Ry = FSy*tau/Ssy.

[nvn]

banfillb: Alternately, you might consider rivet nuts (also called jack nuts), such as part number JN605 (http://www.memfast.co.uk/shop/Vprod2.asp?cat=2257001824), JN610 (http://www.memfast.co.uk/shop/Vprod2.asp?cat=2257004356), 90186A313 (http://www.mcmaster.com/#90186A313), or similar. Find one having a grip range corresponding to your PVC square tube wall thickness.

[Danger]

Since the diagram doesn't offer much detail, such as dimensions, this might be way off track. It seems to me that the simplest and safest approach would be to run bolts straight through all three materials, with nuts on the back side of the aluminum beam.

[banfillb]

I have much more detailed drawings of what im working with. I "dumbed" down the design just to get an idea of where to go with it. I will post some more detailed drawings of exactly what I'm talking about tomorrow when I get back to work.

Basically, if your familiar with the terms, it is a curtain wall mullion, with a PVC thermal break leg which has been extended outwards to create a continuous thermal barrier, separating the aluminum from outside cold air. Then the composite panels are attached to the mullion (frame) by means of screws into the fiberglass.

bolts inside of the tube will not work, because it would be nearly impossible to access the tube to hold bolts, etc. I should have mentioned this earlier.

But, I will post some more drawings tomorrow when I'm back in the office.

Thanks again guys!

[banfillb]

banfillb: Alternately, you might consider rivet nuts (also called jack nuts), such as part number JN605 (http://www.memfast.co.uk/shop/Vprod2.asp?cat=2257001824), JN610 (http://www.memfast.co.uk/shop/Vprod2.asp?cat=2257004356), 90186A313 (http://www.mcmaster.com/#90186A313), or similar. Find one having a grip range corresponding to your PVC square tube wall thickness.

Very cool!

[banfillb]

OK here is an updated drawing of what is actually happening.

This is an overhead view of an aluminum curtain wall (window) frame. The blue is aluminum. The PVC adapter is being screwed into the aluminum through one wall via access holes. The composite panel bracket is being screwed into the other end of the PVC adapter, offset from the access holes.

[Danger]

Wowziewoo! That is indeed more detailed, and unfortunately far beyond my experience.
I like Nvn's suggestion. That is very reminiscent of what we Canuks call "drywall anchors", but of a much heavier duty.

[pantaz]

OK here is an updated drawing of what is actually happening. ...
Rivet-nuts are great, but many other types of threaded inserts exist, including designs specifically for use in plastic.
http://www.google.com/search?q=threaded+inserts+for+plastic