Field Welding to Tension Flange - Pedestrian Truss

[GBS29X]

Hi:

I am designing repairs for a pedestrian truss bridge. There is a splice at mid span of span 2 (span 2 is 139'-6" long). one of the spliced members is detriorated (diagonal). I want to completely remove the existing spliced diagonal and repalce in-kind. The existing diagonal that is deteriatead is welded at the ends to the top and bottom chords. I am concreted about field welding to the bottom chord as it is a tension member... can anyone offer insight related to field welding in tensions areas?? Please remember this is a pedestrian bridge. I know for PennDOT bridges (vehicle bridges) welding in tension areas is a big NO... What about for my case, should i not specify welding to bottom chord?

Thanks in advance!

 

[Triangled]

My main concern would be any transverse weld such that undercut would reduce effective cross sectional area in a tension member. There may be other issues of which I am not aware....

 

[KootK]

If this is truly replacement in kind, you'll need to shore up the truss, right? If so, can you simultaneously relive the bottom chord tension prior to welding?

This article has some info: Link. The big difference between pedestrian and vehicular is surely fatigue susceptibility.

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.

 

[GBS29X]

Yes i was giong to crib the truss, not sure about a stress reversal though..

The cribbing would have to be 40 ft, steep wooded site.

 

[bridgebuster]

Can you just reinforce the diagonal rather than replace it?

 

[hokie66]

A diagonal at midspan won't have much load in it. I would rather clean it up and reinforce it than remove it.

 

[jayrod12]

Hokie it sounded like it's at the end of the beam.

To which I say, there can't be an incredible amount of tension in the chords at the ends of a truss beam.

Depending on the extent of the deterioration I'd be trying to go bridgebusters route.

 

[hokie66]

He did say it is at midspan...

 

[jayrod12]

My bad, read right past the splice part and went straight to the "end of the top and bottom chords" part.