Splice in the mid-span 5

[xyyy]

It is an aluminum beam. The span is 36 feet. The load is 210 plf (dead load + live load). It needs to be spliced at mid-span at the construction site and field welding is impossible. This is requested by the contractor.

I am uncomfortable with this. But the contractor already cut the beam. Can a beam be spliced at mid-span?
Your help is appreciated.

 

[MikeHalloran]

Field welding of aluminum is impractical, for a lot of reasons.

Yes, a beam can be spliced at mid-span, but someone has to design and engineer the splice. This would ordinarily be the engineer who originally designed in and ordered the original full-length beam. Said engineer will likely be upset because he probably could have saved some money buying two shorter beams, and now (s)he has to engineer a splice, try to get paid for the extra effort, and answer questions about why there's a splice at mid-span, for the life of the beam.

You probably do not want to be in the same room when that EOR meets that contractor.
Be on the other side of something bullet-resistant.







Mike Halloran
Pembroke Pines, FL, USA

 

[MrHershey]

Yeah, I'd be pretty pissed if a contractor called me up and said they cut a beam in half to try to save money and need me to now design a splice connection. Would definitely be getting billed for additional services and I wouldn't feel bad in the slightest about taking my time to do it right and then some.

 

[hokie66]

Not sure how I would try to splice an aluminum beam to maintain its full moment capacity. You can't do it by welding, as the welding lowers the yield of the metal, so that leaves bolting. You might provide flange and web plates bolted to each piece. Even then, the holes would take away some of the metal, leaving you with somewhat less capacity than the original beam. Depends on whether the full capacity is required.

 

[dik]

It's not a great idea... but,

As long as the weld can develop the strength it should be OK; but, it's a bad idea to splice at max moment locations...

You may have him cut the one piece in half and weld the shorter pieces to the ends of the long beam portion, so that the splices are a 1/4 points...

The welds should be tested by NDT...

Dik

 

[MikeHalloran]

No, it's a lot worse than just not a good idea.

Welding heat leaves aluminum in a near-annealed state, so you can't get back the beam's capacity.

Bolting with lots of bolts and big splice plates is all that remains, other than billing the contractor for a replacement beam.



Mike Halloran
Pembroke Pines, FL, USA

 

[fcu45]

If you have Aluminium structure other than this beam you can utilize these two halves (Each 18 feet) and order new full piece.
Simple and win win solution.

Good luck

 

[kingnero]

How did the contractor cut the beam? is there significant loss of material (due to method of cutting, or by cutting not entirely straight)?

I'd certainly not be happy with this situation...

 

[dik]

Mike... problem occurs if the beam were an alloy aluminum and/or heat treated...

Dik

 

[MikeHalloran]

Yes, and structurals commonly are alloys, 606x, and hardened by strain, heat treatment, aging, or some combination thereof.

Unalloyed annealed aluminum gets down in the range of Syp <10ksi, so a 36 ft beam wouldn't likely support itself.





Mike Halloran
Pembroke Pines, FL, USA

 

[hokie66]

Mike is correct, all structural aluminum sections are one alloy or another, and welding drastically reduces the strength.

The properties of one aluminum alloy discussed:

http://en.wikipedia.org/wiki/6061_aluminium_alloy

 

[hawkaz]

I agree with Mike and Hokie- Welding Aluminum is a bad idea unless the beam was designed with reduced material properties in the first place. Is there anywhere along the span where you could introduce an additional column (preferably at the splice location)?

 

[rb1957]

bolt, don't weld ... you should be able to design splice plates on the top and bttm flanges, double shear (inner and outer surfaces) if you really have to; and on the web

and charge for the extra design

 

[TXStructural]

Maybe consider cutting one of them again? That is to say, move the splices to 1/4 points nearer the ends, rather than at midspan. You reduce moment demand at splices, and shear demand will be relatively low. You can probably end up bolting it without fear of inadequate capacity. You will obviously still need moment-resisting connections (bolted web and flange plates, most likely.)

 

[tony1851]

But why an aluminium beam? Is this another of those 'the-architect-wants' situations?

 

[xyyy]

Thanks a lot for every's response.

The contractor proposed end-plated type splice. I mean the beam is welded with end plate and the end plates of the two pieces of beams are bolted together by 8 stainless steel bolts in four rows. Two small aluminum plates are welded to each end plate to increase its out-of-plane stiffness. Is this type of connection good for moment connection?

 

[hokie66]

Not for aluminum! That is a typical moment splice in structural steel, but in aluminum, the welding of the beam to the end plate reduces the strength dramatically. Please read the reference I posted earlier.

 

[steellion]

I wouldn't allow a mid-span splice as described, especially for aluminum. There's a reason your "spider-sense" is tingling. Make them buy a new beam.

 

[MikeHalloran]

This is a put-on, right?

Could any real contractor be _that_ arrogant AND _that_ ignorant?



Mike Halloran
Pembroke Pines, FL, USA

 

[CANPRO]

if you're fastening aluminum with stainless steel bolts you might want to consider some kind of seperator between the two to prevent galvanic corrosion.