A truss chord accidentally bent in plane and in place. 8

[IJR]

Friends

The fabricator, by mistake has fabricated a truss diagonal a couple of inches short. The erector, erects the chords(pipe sections) first, then bolts the diagonals to the chord. To fit in the short diagonal, he forces his way. The result is a chord with a kink. And the kink is about 4 inches(10cm) from design axis.

The concern is the force has locally yielded the pipe section.

How would you evaluate the future performance of this pipe chord?

thanks in advance
ijr

 

[TehMightyEngineer]

Is this the tension or compression chord?

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

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

 

[bootlegend]

Can you fabricate the correct diagonal and see if the chord returns to correct position when you replace the diagonal?

 

[IJR]

Thanks.

TehMightyEngineer: it is a tension chord. Why?
bootlegend : That is the plan that is resisted because of difficulty in removing the diagonal.

ijr

 

[TehMightyEngineer]

TehMightyEngineer: it is a tension chord. Why?

You got a chance then, I'd not even bother if it was the compression chord as post-buckling design is very involved if you've never done one.

I'd start by modeling it in your software of choice with accurate dimensions of the kink. See what flexural/torsional forces this results in and make sure it's not completely failing at first glance.

Where along the truss span is it kinked? Got any pictures of it you can share?

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

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

 

[JStructsteel]

Some pics, dimensions, etc would help.

I would consult the owner. If he is ok with a fix, have them cut it out and full pen welds.

If not, have them fabricate it right.

 

[kipfoot]

From a technical perspective, you'd have to verify that the truss works with its current geometry... with stresses from the analysis superimposed on the internal stresses that exist due to the forced deformation.

From a practical perspective, you shouldn't have to get to that point because a new web member should already be fabricated and on the way to the site. Sometimes owners are willing to accept the mistakes of a contractor...as long as an engineer accepts the liability.

 

[bootlegend]

If the chord was displaced 4" because of the short diagonal what did that do to the other diagonal framing into the joint? Was it short as well?
Interested in seeing a photo or at least a sketch.

 

[TehMightyEngineer]

jrisebo and kipfoot are ultimately correct; it's realistically not likely that your time and effort are going to be cheaper/easier than just replacing or repairing this. It's also highly likely that you'll spend a lot of time on this to find that it doesn't work anyway and you're back to square one.

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

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

 

[racookpe1978]

SO, some force from something forced a major truss 4 inches out of design shape?

You MUST determine where that force came from (a crane, sledge hammers, bolted stress at the connectins from some other parts still in the structure? ) If a crane, at least the forces are not locked in - other than at the other end of the truss.
If caused by bolting up the truss, then every other connection in the assembly is carrying the extra stress - waiting to fail under some future load.

 

[IJR]

My friends

Thanks for the great contribution and time. I mentioned the chord is a pipe section. It can easily bend anyway.

@TehMightyEngineer : The kink is at the node where the diagonal(brace) joins the chord. I am not allowed to share photos yet by the erector.

thanks
ijr

 

[dik]

The client should be the one that authorises photos... not the erector.

Dik

 

[IJR]

Dik

My company is hired by the erector to investigate. He is the boss and he is following the owner's orders. We want the chord replaced. But life is not that easy sometimes. We have to go on investigating all aspects of the problem and I want to see how my fellow engineers would review this problem.

ijr

 

[dik]

IJR: didn't realise that you were working for the erector.

Dik

 

[hokie66]

The beauty of structural steel is that yielding does not destroy it. I would insist on fabricating a new diagonal of the appropriate length, and bolting it in. If the erector is incapable of doing that, he is in the wrong business.