Replacing old traffic/utilities with utilities bridge, 36" water main

[ivanlocke]

I am looking at options/cost for replacing a bridge. The bridge carries a 36" & 8" water main, 3" gas, and new may carry fiber or other communications. The options are to build a new bridge adjacent to the old, or to use the old abutments. The water main can only be down for a short time, so if the old abutments are used the old bridge will have to be taken out and probably a prefab bridge installed.

This is my first bridge work, so I don't know what should be excluded right from the start. I would assume new abutments and bridge would be significantly more? Is prefab cheaper even if building new abutments. What types would be able to span - steel, concrete slab?

Current span is 105'. If new bridge span could be 10' less (does that make much difference?). The old pipe goes through the abutment and was hung under the deck.

Straight lowest cost may not be what we want as there are many other issues - if the pipe is above bridge deck pipe will have to come out of ground past the abutments (possible space issues), if pipe is hung again we may need someone else to install pipe instead of ourselves, time line is out of service with old bridge is removed and new put in place. I imagine the cost of alternatives is going to be quite a spread, but are somethings definately out of the picture (mainly building new abutments and bridge or does prefab cost more than a bridge built on site with new abutments). Also one thing I wanted to look at was if we used current abutments, is it practical to design a bridge with a deck that hangs bellow the seats such that where the current pipe comes throught the abutments would be on top of the deck.

Thanks for any help

 

[PM]

Snipped from ivanlocke's . . ."This is my first bridge work . . .".

In some ways your example is quite complex, so the best advice I can offer you after more than 25 years experience in transportation infrastructure design is for you to seek expertise within your own organization. If you are practicing alone or don't have such expertise in-house, you should engage a bridge engineer from a local consulting firm. The lives and or environmental damage you save may be your own. I'm sure your professional liability insurer and your engineering licensing agency would be pleased if you do engage expert advice to guide you.

Regards,