Post-tensioning around bearing pedestal

[skewl]

Does anyone have an idea why the below post-tensioning detail was added during construction?

We found the post-tensioning strands broken. However, it has been like this since 2017 and as far as I know not much has changed to the bridge. We are going out to take a look tomorrow.

Potential reasonings:
1. Someone found insufficient resistance in the column to resist lateral movement and detailed a quick fix during construction. Note: Bearing A has no lateral restraint capacity while Bearing B does.

2. Insufficient shear capacity at the edges of the column and therefore the need to install two new bearings.

3. Crack development during construction.
4. Transverse forces in the concrete deck.

 

[BridgeSmith]

I think you're on the right track as far as the potential cracking. It looks like possibly a seismic upgrade, especially if those extra bearings in the middle are attached to the slab and pier.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[spsalso]

So the presumption would appear to be that A and B are too close to the edge of the pier. Looking at the drawings, it feels that way to me.

I think if it was a seismic upgrade, the Powers that Be would have demanded a surrounding "box" of concrete and re-bar up there. The fix, while clever looking (AND it failed), doesn't look like it would be acceptable to PtB.


spsalso

 

[skewl]

Seismic isn't a big deal in my region so I haven't really thought about it. But still worth a look from my end.

 

[spsalso]

I live in SF Bay Area, so I see seismic retrofit a lot. This doesn't look like what I see.

But.

If someone somewhere else thought they'd give it a try, I suppose they might go with this.

I wonder if there's enough re-bar INSIDE the pier top to tie those cages together. Do you think there is? And then there's the lap length. My uninformed self would have liked to see full-span lengths of rebar connecting the cages, maybe with some bent ends.



spsalso