Bridge Widening 1

My experience in this application is to place a new beam or girder line under the sidewalk. Many sidewalks are supported with beams while only a few are actually cantilevered off the main slab. Those bridges with sidewalk girders usually have a full-depth slab that can be used for vehicle travel in the future should it become necessary.

Occasionally, the sidewalk is cantilevered off the main slab but its reinforcing is embedded in the main slab. In most cases, the sidewalk is less than 6' or 1.8 meters. The sidewalk is placed after the main slab has reached the 28-day strength. Typically the load is distributed to all the girders as a super-imposed dead load. Not really what it appears but that is how it is handled by some.

At any rate, for you to use the cantilevered sidewalk you will have to evaluate the existing girders. And dig into the existing slab. Using a new girder line won't effect the old girders so long as a joint is present and won't impact the main slab either. Of course if you want to tie the new into the old you can do that too.

Regards,
Qshake

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Hi Asdwinnipeg,

How does 0.9m increase in sidewalk result in a 1.37m overhang increasing to 2.8m?

At any rate, does your client have a history with regards to bridge widening? If so they should be prepared for options like another girder line and a wider road, if not they want something for nothing. Getting a sidewalk in should be no problem then, but it will cost significant money per square meter compared to typical new construction. Phased removal of portions of the deck should be considered, as well as extensions to the existing abutments where wingwalls exist.

If you can't do this you will most probably require a thicker deck over the exterior girder tapering down in thickness to the next interior girder while maintaining the existing top of deck elevation. That is, the haunched area may envelop the top flange of the existing exterior girder.

2.8m cantilever is probably not going to work, because thickening the cantilever that much will affect the exterior girder's effective inertia within the bridge as a whole, which will attract more load to it than it was designed for. Either way you may need to replace the existing exterior girder with a new exterior girder due to this. You will also be restricted to the existing beam height.

If my comments seem general, it's because that is a large overhang and one needs to do a full analysis of the entire bridge and check the exterior girder in order to say whether it will work.

HTH

VOD