Aluminum Beam - Minimum web stiffener depth, local buckling
Aluminum Beam - Minimum web stiffener depth, local buckling
(OP)
We don't normally do aluminum, but we're trying to help out a client that is in a bind without sticking our neck out in the process.
My question is: does the ADM or AISC SCM specify the required depth of a stiffener at intermediate locations of an element (10" leg on a L-shape) with a free edge to prevent local buckling? See ADM B.5 (custom extrusion, not welded)
I have found the required I (m.o. inertia) for a stiffener along a web supported at top and bottom at ADM B.5.5.3, Fig B.5.5, but this is not our case unfortunately. I want to use ADM B.5.5.4 Alternate Method with stiffeners, but it doesn't specify minimum stiffener depth.
Background:
I have a 2" x 10" custom extruded 'L' shape aluminum facade vertically spanning 11'6" x 2 stories spaced 6" apart all around a parking garage (shiny!). I'm taking the wind load partially in the weak axis worst case, and for a thickness of 3/16" it's failing in local buckling (using ADM F.5 procedure).
Increasing the thickness to .26" solves the problem for us, but will cost the client $x0,000 above the budget.
I have found that ADM F.8 (pointing to B.5) will allow me to add stiffeners to the 10" leg along the length of the 'L' shape (but I can NOT add at the tip of the leg) and avoid the painful b/t ratio of the leg. The problem now is that it doesn't tell me what the required depth of a stiffener on a leg with a free edge will be
My question is: does the ADM or AISC SCM specify the required depth of a stiffener at intermediate locations of an element (10" leg on a L-shape) with a free edge to prevent local buckling? See ADM B.5 (custom extrusion, not welded)
I have found the required I (m.o. inertia) for a stiffener along a web supported at top and bottom at ADM B.5.5.3, Fig B.5.5, but this is not our case unfortunately. I want to use ADM B.5.5.4 Alternate Method with stiffeners, but it doesn't specify minimum stiffener depth.
Background:
I have a 2" x 10" custom extruded 'L' shape aluminum facade vertically spanning 11'6" x 2 stories spaced 6" apart all around a parking garage (shiny!). I'm taking the wind load partially in the weak axis worst case, and for a thickness of 3/16" it's failing in local buckling (using ADM F.5 procedure).
Increasing the thickness to .26" solves the problem for us, but will cost the client $x0,000 above the budget.
I have found that ADM F.8 (pointing to B.5) will allow me to add stiffeners to the 10" leg along the length of the 'L' shape (but I can NOT add at the tip of the leg) and avoid the painful b/t ratio of the leg. The problem now is that it doesn't tell me what the required depth of a stiffener on a leg with a free edge will be






RE: Aluminum Beam - Minimum web stiffener depth, local buckling
RE: Aluminum Beam - Minimum web stiffener depth, local buckling
BA
RE: Aluminum Beam - Minimum web stiffener depth, local buckling
RE: Aluminum Beam - Minimum web stiffener depth, local buckling
RE: Aluminum Beam - Minimum web stiffener depth, local buckling
why are you using the weak axis ? surely the critical load is the wind impacting dead onto the door ? surely (despite your drwg note to minimise Ds) you've got the 10" flange normal to the door surface, so that the wind load is causing the stiffener to bend about it's strong axis, no?
increasing the thickness would be a problem (if you've made the extrusion already), what about reducing the pitch ??
RE: Aluminum Beam - Minimum web stiffener depth, local buckling
I think that the best way is to add the lip at the end
RE: Aluminum Beam - Minimum web stiffener depth, local buckling
RE: Aluminum Beam - Minimum web stiffener depth, local buckling
And the condition that controls (weak axis of L with load resolved into principal axis) is expressed by
Mn=3.14^2*E*Sc/(4*b/t)^2 <-- notice the denominator (4*b/t)^2
where Sc is the section modulus using the portion of the angle that is in compression only. You can see that the b/t ratio hurts exponentially, and only being allowed to use the compression-only section hurts as well.
To re-state the condition, the angle is attached at 3 points spanning 11'6" vertically story to story, 30' total span including cantilever above and below, bolted to a support with the 2" leg.
I want to know if there is research or other books that would specify the required depth or I of a stiffener. ADM B.5.5.3, Fig B.5.5 specifies a stiffener required based on the flexural stress in the member it is stiffening.
RE: Aluminum Beam - Minimum web stiffener depth, local buckling
I am not sure that this would apply for aluminum, but it is the only thing I could find.
It is Ia = 399t^4[(w/t)/S - 0.328]^2 is less than or equal to t^4[115(w/t)/S + 5]
t= thickness of section
w= flat dimension of element
S= 1.28SQRT(E/f)
f= stress in compression flange
RE: Aluminum Beam - Minimum web stiffener depth, local buckling