Economical Substructure Design

[71corvette]

Does anyone have any guidance or input on ways to reduce substructure costs on local road and minor bridges designed with LRFD? What tricks have you used in the past? What exceptions in the code have you used to your advantage? Do any state DOT's out there provide guidance in their bridge design guides on this matter?

It seems to me the LRFD code sometimes yields very robust designs that are much stronger than the substructures they are designed to replace. Given this, it appears there's a lot of reserve capacity in these new substructures that could be reduced on local roads/minor bridges in order to save construction costs. As with anything, this comes with the trade off of increased risk or future maintenance, but I'm very intrested to hear others thoughts and ideas on this topic.

 

[Qshake]

I have not seen any substantial differences between the two.

one of the matters that is most pointed out is the use of shallow foundations where possible. I can't say that I've ever known a DOT or engineer to actual feel comfortable with putting a bridge on spread footings on soil when it is within their means to use rock or drive piles. The issue, of course, is settlement (scour where streams are involved) and no one really wants to have a bridge experience settlement.

However, if you can see past this matter and get your client to buy off on it (after doing the analysis and showing that settlement is neglible), then you'll see some savings.

Regards,
Qshake

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[civilperson]

Drilled shafts or drilled piers that are field tested to ultimate capacity give cost effective designs even when FOS of 3 is used. Most untested designs use much higher FOS with subsequent increase in cost.