Bridge Widening and Pinning to an Existing Foundation

[anominal]

I'm checking a number of calculations for a bridge widening in which a new wingwall foundation is pinned with dowels at mid-footing height to an existing wingwall footing. While my gut says that how it has been designed is fine, I don't know how to analyze a foundation with what is effectively a hinge in it, nor do I know how to estimate the soil pressure acting on the rear face of the new wingwall stem.

See the attached file for clarification.

 

[rowingengineer]

uStationChump,
I would look at making the dowel connection a moment carrying connection, or tying the retaining wall to the existing retaining wall, at as 1/4 heights to act as an anchor, effectively doubling the size of the retaining wall. Because even though the design load would be reduced it would not be that much of a reduction, especially if you used gravel backfill and compacted, (this could even be worse).


When in doubt, just take the next small step.

 

[anominal]

Converting the pinned connection to a moment connection was already considered - however there is no top layer of reinforcement in the toe of the existing footing. I'm not sure how you could transfer moment with this configuration, drilling and grouting a top and bottom bar would just result in tensile stress in the top of the existing toe, eliminating your moment carrying capacity.

Tying the wall back however was NOT discussed and I will see if anyone likes this idea.

Now you said that the design load will be reduced, but not by much. How do you know this? Also, we are planning on using pervious structure backfill for drainage... effectively, compacted granular fill. Why would that be even worse?

 

[rowingengineer]

ustationchump,
To get a moment connection i believe you would have to carrying your new footing over the existing and dowel into the main wall, then rely on some strut tie action down to the existing foundation.

The design load will be reduced due to the wedge area being reduced I would think, I believe there is something in the coulomb equation about the wedge area, How you figure this out is very hard to do, the reduction isn't worth the time.

Granular fill friction angle is low and these is no cohesion, hence it will nearly be fully compacted once you pour it in, then when you compact you will transfer your compaction effort into the wall.


When in doubt, just take the next small step.