Strengthening an Existing Girder 1

[lsmfse]

I have a situation where I would like to strengthen an existing girder, simple span. I want to add a cover plate to the bottom flange and fasten it to the flange by intermittent fillet welds. Any concerns with this?

 

[hokie66]

Fatigue.

 

[bridgebuster]

I agree with hokie. Intermittent welds - no good.

Were you planning to add the plate to the bottom of the bottom flange or the top of the bottom flange? Why not bolt a cover plate to the bottom of the bottom flange? It's faster and much cheaper than doing an overhead weld.

If you're going to weld two plates on top of the flange it could get a little tight on the side adjacent to the web.

 

[hokie66]

Careful, bridgebuster, you might promote more pack rust with bolted plates.

 

[bridgebuster]

LOL hokie. We'll make sure we paint it properly first.

 

[TomDOT]

From a corrosion POV, I really despise intermittent welds.

Also from a corrosion POV, for a bolted cover plate I would be sure to finish all drilling/cutting operations, round sharp edges, degrease, prime everything but the bolts with a good epoxy zinc primer, then assemble with galvanized bolts.

Touch up the primer and finish applying your paint system after the bolting.

 

[lsmfse]

Okay, let me give a bigger picture. The existing bridge will need to support heavier axle loads than typical H20/HL-93 (these loads produce greater moments/shears). The trucks will be multi axle trucks with typical 6' wide wheel spacing and include some 10' wheel spacing. Total LL could be 170 kips with total vehicle length of +/- 65' with 5 to 6 axles. Now for the kicker, the existing bridge comprises of two side by side rail cars. My concern is localized(stringer, outrigger) issues rather than the girder. I can deal with the localized issues. However; my concept to add strength to the bridge is to add transverse beams below the existing girders which would span to new girders located outboard of the existing bridge. I would support the added girders on driven piles. Any thoughts?

 

[MikeHalloran]

Well, that's a _whole_ lot different from adding a flange doubler to a simple beam.

Lucky for you, there has been discussion of repurposed flatcar bridges; use the 'search' button and read a bit.


Mike Halloran
Pembroke Pines, FL, USA

 

[blaxabbath]

An option to add tensile strength without the corrosion issue would be to apply carbon fiber laminate along the length of the span.

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