Aluminum Design Manual ? 1

[cmbyrd77]

I am working on my first Aluminum structure....thankfully it's only a small carport. My question is in regards to the Allowable Stress Tables in Part VI of the Aluminum Design Manual (Tables 2-1 thru 2-24). There are tables for "welded" and "unwelded," but I'm having trouble understanding what that means. Is that a fabrication item to where if I were to be using a built-up section then I would use the "welded" tables, or if does that mean if you are welding at all to the member then you must use the "welded" tables. Thanks for the help.

 

[ToadJones]

I believe that in areas near welds on Aluminum structures, the allowables can be lowered as much as 66%. I think the heat from welding seriously compromises the material strength.

 

[cmbyrd77]

Yeah, after I submitted my post I found where it talks about the reduced design parameters due to welding. Thank you.

 

[MiketheEngineer]

Toad is right. Welding can seriously affect AL unless re-tempered and you don't want that expense. Many people go for "bolted" or "screwed" connections to get away from that.

 

[spats]

Agree with ToadJones.

 

[Ron]

Agree with above. ADM provides separate tables and equations for allowable stresses within 1 inch of a weld, without regard to the size of the weld.

Metallurgically, the result of welding on aluminum is not predictable by heat alone. One reason for this is that for most structural alloys of aluminum, part of the strength is gained by ambient temperature ageing, after controlled thermal input for tempering. If the thermal input is not controlled (e.g., welding) then the tempering is not controlled and the aged strength gain is unpredictable. For these reasons, the allowable stresses are reduced within 1 inch of the weld to accommodate the unpredictable strengths.