Aluminum Beam - Design Manual Verbage

[pelotoner]

I need help translating from the Aluminum Design Manual.

Under Section 7. Welded Construction, one of the affected members are "columns or beams supported at both ends with transverse welds affecting their entire cross-section and no farther than 0.05L from the ends".

Of course, I am using a tube section as a beam. Which means, if I put base-plates on the end of my tube-beam and bolt it between two concrete walls (10' apart), I have to use welded aluminum properties??

This doesn't make sense; I am obviously assuming my moment to be Zero at the supports (nearly zero, due to bolting). My high moment regions are Very far from any welded sections.

Am I interpreting "transverse welds" properly? I don't want to overdesign by a factor of 2.

 

[civilperson]

The allowable stresses from Table 3.3-2 apply only adjacent to the welds. Thus the shear values listed will apply at the welded ends but the bending strengths,(tension and compression), in the middle come from Table 3.3-1.

 

[pelotoner]

That's what I would expect. But where does "columns or beams supported at both ends with transverse welds affecting their entire cross-section and no farther than 0.05L from the ends" ever come into play?

 

[apsix]

It does seem strange that the extent of weld affected section depends on the member length, but 0.05L would still be well away from maximum moment, where's the problem?

 

[civilperson]

The greatest shear is at the ends and the lesser shear value from welded aluminum strength table will apply.

 

[pelotoner]

Let me expand:
Because my "beam (is) supported at both ends with transverse welds affecting their entire cross-section and no farther than 0.05L from the ends" (i.e. only at the supports),
then "Allowable stresses for tubes in axial or flexural compression or shear...shall be calculated using the welded mechanical properties..." See section 7.2.1

So, since I have welded supports at the ends, I have to use welded mechanical properties for my flexural compression at the middle of the beam?
FYI, welded mechanical properties reduce the allowable stresses by about half.

 

[pelotoner]

I have come to the conclusion that the "Aluminum Design Manual" is one of the worst written codes I have ever come across.
That being said, I am interpreting the code to read that the weld-affected zone only extends 1" from the centerline of the weld, regardless of the transverse weld locations...

Please, give me steel or concrete any day...

 

[csd72]

Thats exactly what it said in the old code.

Personally i would design the mid span as unwelded and the ends as welded regardless of the confusion.

Aluminum structures are being designed all over the country to this old tried and true logic and I dont hear any issues on the safety of these!

It could be very easily argued in court.

 

[dozer]

Your right, it's really not written very well. I believe what is at issue here is how a transverse weld affects the the lateral-torsional buckling. Someone has figured out if a weld is more than 0.05L away from the end it will adversely affect the buckling strength. In this case, you should use the weld affected equation for lateral-torsional buckling. This should be conservative.

In your case, since the base plates are at the end of the beam, your weld is less than 0.05L away from the end, so you can use the unwelded equation for the moment at the center.