Galvanizing Crack

[SrVaro]

We have designed a roof truss and it was galvanized. During the galvanizing,the top of the post member cracked. The truss is made up of a bottom chord beam of W12x26, the sloped top chords are W10x22, and a center post of W6x15. The crack has occured at the top of the post where the two top chords attach. Our thinking is when heated the truss members had some warping. Then when cooled after dipping the truss was restrained such that the only free point was at the top of the post and thus it cracked under the residual loads. The post is appoximately 31% stressed with a maximum load of 4.5kip. The overall span of the truss is 36'-0" nominal.

We are thinking of having them drill a hole at the end of the crack to stop future propigating and then weld the crack. This will damage the galvanzing, but we are not to concerned about that.

Any thoughs on our proposed corrective action or any better suggestions would be greatly appreciated.

I have attempted to upload a picture of the crack and a sketch of the truss.

 

[SrVaro]

The sketch was uploaded in the original post. Here is the picture of the crack.

 

[ToadJones]

repair the crack as you say by drilling a hole at the end of the crack. Do the necessary galvanizing abatement and weld the crack, CJP.
Then, I'd install a cap plate on the assembly over top the W6 to help with any uplift loads on the truss and to help with the stresses in the repaired area. you can repair the galvanizing with a cold galv paint.
Easy to say now, but having a cap on the W6 originally may have kept it from cracking...
just thoughts....

 

[csd72]

agreed, the crack looks like it happenned at the weakest point, the section where there was only a thin web.

 

[ToadJones]

after a second look.
You must fix that crack, the web of that W6 will be in compression.
I'd also install the cap or other stiffeners.

 

[Ron]

Agree with the comments. You might want to sample your wide flange material and have a chemistry run on it. That's a good size crack for just the heat from galvanizing.

I would remove the galvanizing around the tail of the crack with acid rather than grinding. That will help you find the actual end of the crack.

 

[ToadJones]

...YES....maybe some mag particle or other crack chaser

 

[hokie66]

Agree with the others, especially Toad's suggestion to add a cap plate to connect the flanges over the top. That will also stiffen up the connection of that thick gusset to the thin web.

As an aside, the fabrication is quite clumsy. Rough end cuts, holes in the welds...