Beam Problem

I sell hollow metal (steel) doors and frames. For the largest part, designers are not allowed to figure steel door frames as structural elements. This is applicable to the portion of your question about beams.

But it sounds like you may be asking about wind load rating... clarify, please.

I'm looking at structural integrity of the door under wind loads. Trying to get an RC50 or better on a 8 ft high patio door. Having the knowledge of what shapes and materials that can be used inside the PVC for structural support and how they would preform on paper would be a plus before building one and taking it to the lab for testing.

Most the failure is due to bending. Under the test the door sash will bend to the point that it leaves the tracks it slides in. Was wondering if i looked at the cross sectional shape of the door as a beam could i get a rough estimate of how different materials and shapes would preform.

OK. My comment #1 is of no value here.

Have you reviewed the NFRC CMA Program? This may be what you are looking for.

How many copies you want.

All our products are NFRC, AAMA, Energy Star rated plus some others. There are copies of those ratings and the changes around here going back 25 years plus.

All those organization do is set performance ratings do not tell you how to get there.

We have put PVC in up to 18 stories where only aluminum has gone before. But that was a standard height door. The extra 16" or so lets the sash bow and fails when it slips out of the tracks. Trying to help over come this with beam analysis tools which may help.

The behavior of the door will be different depending on whether you are designing for pressure or suction. I assume the swing side will be supported by the frame from floor to ceiling, and supported by the hinges on the hinge side.

In the case of suction, the door will only be supported by the hinges and the lock.

If the door is in the exterior of a normal building, the suction is seven eighths of the pressure so the suction might well provide your worst case.

I would suggest that you consider the interior stiffeners and edges to be structural with plates in between supported by them (I made some assumptions as to the construction of your door).

The door in question is a patio door no hinges. A sliding door in track of the frame. Under test the pressure is done both ways to simulate actual wind stresses the door may be subject to. We do use interior stiffeners. What we have has failed on a door of this height. Looking to possibly redesign the extrusion. Trying to use software to get an idea how any change in the shape of our re-enforcement will improve performance.

Now I understand better. The basic information in transforming the sections of the various materials can be found here. Scroll down to the "Composite Beams" section.

Could you increase the number of vertical extrusions, perhaps cut down on the window/screen size? Or, perhaps, use two extrusions to double the thickness for the middle part of the span, leaving the top and bottom single to fit the standard tracks.

Thanks for the info!!

As far as the changes that you have recommended. Yes we could do all that and get it to work. Getting the customer to go for the change from the norm is then an issue.

Take the worst condition.

Make the track deeper? And perhaps that is deforming in addition to beam deflection.

That extra 18 inches increases the sail area about 20%. That would be a considerable jump in the applied energy.

That's being considered, it's a longer process to get the vinyl extruder to make the die. As of now they only have the one frame available. Which was never designed to preform to an RC50.

First you pick one material to evaluate with. Then transform the area of the other materials into an equivalent area for the first material using the ratio of moduli E2/E1 (E1 being the material that you picked). Multiply the ratio by the area of the other materials to get the equivalent area.

Then you find the moment of inertia and neutral axis so you can solve for stress (bending).

This is used a lot for reinforced concrete beams.

Hello Ozzb,

From what I understand of your dilemma is that you have different materials with differing Modulus of Elasticities, and hence different allowable shear stresses and bending stresses.

You need to calculate the new section as a "transformed section", much like a "flitch beam" for example like that consisting of a vertical steel plate sandwiched between 2 pieces of lumber and bolted together. In your case, you must calculate the new section about it's Y-Y axis as the wind forces are acting on your door or window horizontally (laterally).

If you can find a decent Statics or Strength of Materials textbook it'll show you how to hand calculate he transformed section and derive the sectional properties, such as Area, Section Modulus and Moment of Inertia.....

Some more advance structural software analysis packages will calculate all of the above for you once you've inputted the geometries and Modulus of Elasticities of the various pieces.

If you need more help I'll gladly scan the relevant sample calcs for you and send them to your private email.....may take some time to find what I need as we're in the middle of reconstructing a portion of our house and all of me handy/dandy reference textbooks are piled into a mountain of storage boxes!

Thanks Capt some of the terms you used I Googled info on like "transformed section". Some of which is getting me pointed in the right direction.

Already use a CAD program that gives me geometric parameters. The modulus of elasticities I have for all the materials.

Assuming you are at, or near, the 100 mm (4") beam height (similar to aluminium sections in this application), have you considered adding glass filler to your extrusion material?

You say an aluminum beam has been used in this situation before. How about a proven aluminum design, clad in pvc to match your door?

Aluminum is being used to reinforce a lot of the products. Aluminum extrusion are inserted into the open core of a PVC shape. Fastened in place, the PVC extrusion is the thermally welded together. The aluminum is not just there for structural strength in all application. In some it there to attach and reinforce the hardware.

I don't know if this would fit your situation, but from both architectural and engineering points of view, I would think about adding curved vertical stiffening ribs to a sliding door; "deep" at midpoint to serve also as a handle, and tapering toward top and bottom. (I think the ideal is a shallow parabolic arc.)

Thanks that's a thought would have to be decorative. For right now trying to get internal reinforcement to work.