Aluminum Mullion Reinforcing!
Aluminum Mullion Reinforcing!
(OP)
I have an aluminum curtain wall mullion which needs to be re-inforced using steel tube. I would be inseting the tube into the mullion hollow space. Now how do i analyse this combination for strength & deflection. Do i need to connect the steel stiffener to the aluminum member at regular intervals and check for shear just like in composite structures. What about Bending Moment, how do i analyse for strength. Can i distribute the Bending Moment among the stiffener & the mullion as per ratios of their respective rigidities (EI/L).
Thanks in advance
Thanks in advance






RE: Aluminum Mullion Reinforcing!
RE: Aluminum Mullion Reinforcing!
RE: Aluminum Mullion Reinforcing!
LowLax is correct. As long as their deflection are the same (as they must be) then the amount of the wind force they take is porportional to their EI
RE: Aluminum Mullion Reinforcing!
more importantly i have to prove this system works using some theory in textbooks...what do u all suggest?
RE: Aluminum Mullion Reinforcing!
w1/(E1*I1)=w2/(E2*I2)
w1+w2=wtotal
RE: Aluminum Mullion Reinforcing!
Potentially with a 3mm gap the middle of a simply supported member would deflect by 6mm before the two ends and the middle were all in contact with the steel.
The principle of relative stiffness does still hold true but the aluminium would be 'pre-loaded'.
RE: Aluminum Mullion Reinforcing!
RE: Aluminum Mullion Reinforcing!
If you cannot connect these two members enough to make a composite section, you'll have to add their strengths together, properly proportioned for the difference in stiffness of the two. Keep in mind that you will need to connect them somehow at least enough to insure that load is transferred into the steel whether it is composite or not. If your steel section is not connected to supports then you will have a nonprismatic beam and will have some additional work to do (different from what is being discussed so far), as well as additional thinking to understand how the two members will interact.
RE: Aluminum Mullion Reinforcing!
RE: Aluminum Mullion Reinforcing!
Forget composite action.
Assume the sections are locked together, say with a series of self tapping screws along the length; you then have 'compatiblity of deflection'.
As deflections are the same (for UDL, simply supported);
w1*L4/(76.8*E1*I1)=w2*L4/(76.8*E2*I2)
Cancel out like terms and you end up with;
w1/(E1*I1)=w2/(E2*I2) as posted by LowLax
You also know w1 = w2;
2 unknowns and 2 equations; what could be simpler?
How can a checking engineer argue against that?
RE: Aluminum Mullion Reinforcing!
It should have been w1+w2 = wtotal
Note to self; always double check if there is no edit function
RE: Aluminum Mullion Reinforcing!
what if the sections are only connected at their ends by means of a thru bolt?
and there is the other problem of thermal variation...what happens then?
RE: Aluminum Mullion Reinforcing!
defl1=defl2+1/4
which would lead to:
w1/(E1*I1)-1/4 = w2/(E2*I2)
and
w1+w2=wtotal
Just check that you don't exceed the yield point of both members and your deflections are acceptable and you should be good. And provide a vertically slotted hole if you're worried about thermal elongation.
RE: Aluminum Mullion Reinforcing!
w1/(E1*I1)-1/4*(76.8/L4) = w2/(E2*I2)
where w1 is the load on the aluminium mullion.