Aluminum design-Allowable stress increase by 33% 1

[Ramezsayed EIT]

Hey all

I am designing Curtain wall Mullions which got tested per ASTM E330 and my calculations are not matching the test by 33%?

this is aluminum profile and I applied 1.65 as factor of safety per ADM 2010. is there any way that we will have to increase the allowable stresses by 33% ?

also the deflection did not match The test shows the deflection @ Mullion is 0.5'' @ 50psf while my calculation shows 0.66'' @ 50psf.

if you have any reference or clarification to the above I will be appreciated

 

[r13]

If your purpose is to verify the test results, then you need to set up your analysis model exactly the same as the test, and use the real load, not the factored load.

 

[hokie66]

There are lots of different alloys of aluminum, and various tempers of each alloy. Have you investigated what material you actually have? Just saying aluminum doesn't mean much. Even if you know, testing and calculation results can differ quite a lot.

 

[jimmytwotimes]

Odds are your stress is based on the "permanent set" of the mullion measured with a dial gage indicator after being subjected to an overload pressure. The overload pressure is usually 1.5 times the design pressure. It would be difficult to convert the permanent set to a stress because you've yielded and are non-linear.

There is typically a maximum allowable permanent set - as long as your mullion is within that limit you can call it good. I would keep any stress checks and permanent set checks independent. Apart from that a couple things to consider are 1. make sure you are comparing nominal results with nominal design values, 2. compare test pressure with project wind loads, 3. add internal reinforcement if necessary. There is a 4/3 stress increase factor you could use since the loading is from wind, but it is not industry standard and probably not permitted by the job spec.

For the deflection consider that you've got glass, glazing components, and sometimes exterior components (ie. face covers) that add stiffness. Additionally, anchors are often longer than a single point, aluminum mullions will have actual wall thickness different than what you used in your calcs, among other factors. If your test shows you are under the deflection limit, and is mostly in-line with theory then call it good. Trying to match real results will end up like a research project - there are so many factors that could influence deflection being different from theory by 3/16"