Composite member - welding on only one side of web 4

[canwesteng]

Suppose you have a composite member (built up T, but it could a W section or any similar built up section), what is the consequence of welding on only one side of the web to resist shear flow between the flange and the web? I'm thinking either a) nothing happens b) there is flexure in the weld and it breaks c) there is some weak axis bending in the section.

 

[MotorCity]

From a design stand point, it can certainly be done. You may have an issue with the weld being pre-qualified depending on the thickness and arrangement of the plates and the type of weld. You may also end up with distortion in the plates (depending on their thickness) since you are only welding from one side.

 

[KootK]

This has come up in several recent thread here if only someone would tell you the right terms to search for. I don't have time to dig up everything this morning but here's what I remember:

1) In general, it's fine and there are no consequences.

2) The PEMB guys do this all the time apparently so there's plenty of precedent.

3) Thomas Murray of vibration design guide fame once wrote a letter defending this practice. I have it... somewhere.

4) You can't do this at the ends of special moment frame beams in high seismic areas of the US which, no doubt, is of no relevance at all to whatever you're tinkering with.

5) When there are problems, they seem to be related to cyclic load at high levels of flexural strain.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[TehMightyEngineer]

Nice summary, KootK. Can't think of anything you missed.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[KootK]

I believe the Newman book on PEMB also touches on this favorably.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[WARose]

Assuming we are talking it just seeing flexural loads (i.e. no significant axial loads, etc).....I don't think it's much of an issue.

 

[kingnero]

It's no standard practise in Europe that I'm aware of, but if calcs proved it to work, I'd still weld the first few inches at the extremities at both the sides to ensure a nice, evenly distributed flow of (compression) forces. But that's just my $.02.

Here's at least one thread that touches this topic:

http://www.eng-tips.com/viewthread.cfm?qid=424184

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http://be.linkedin.com/in/fusionpoint

 

[canwesteng]

That's the thread I was thinking of, I couldn't find it when searching. Thanks all

 

[WARose]

[blue](kingnero)[/blue]

..... I'd still weld the first few inches at the extremities at both the sides to ensure a nice, evenly distributed flow of (compression) forces.

If we are talking a compression load (via a external axial force).....weld will be needed along the full length, not just at the ends. The pieces will try to separate as the axial load gets higher.

For analytical treatment on this (and some useful formulas) see:

'Analytical Criteria for Stich Strength of Built-Up Compression Members', by: Aslani & Goel, 3rd Quarter (1992), AISC Journal


That's why I said what I said before: it's one thing if this is just for flexural/shear.....but a whole other ballgame if the member is subjected to other forces.

 

[jike]

I am not a PEMB engineer but have encountered this situation a number of times when adding on to existing buildings. An existing beam located along a masonry wall that needs to be reinforced with a Tee on the bottom has a restriction on welding from one side. Rather than use a fillet weld on one side, I have had the fabricator grind the edge at 45 degree intermittently with backup bar so that we can provide a single bevel weld intermittently. We also provide end welds by the same method.

I hope this helps.....

 

[canwesteng]

I did make a contractor do a full pen groove from one side when reinforcing a W with a T once, but it was supporting a crane rail so I wasn't willing to chance it.