Integral Abutments

[RFreund]

This might vary by DOT but -
In general can partial depth abutments be integral abutments or are stub abutments only allowed to be used for integral abutments?

Thanks!

EIT

http://www.HowToEngineer.com

 

[bridgebuster]

How do you define partial depth abutment and stub abutment. I'm not trying to be a wise guy; it's just that to me they're both the same. With that said, you can have a short stemmed abutment on spread footings as part of an integral abutment bridge.

 

[OSUCivlEng]

I agree. What is the definition of "partial depth abutment" and "stub abutment"?

 

[RFreund]

Sorry, I was going based on the AASHTO definition:

Stub Abutment: Stub abutments are located at or near the top of approach fills, with a backwall depth sufficient to accommodate the strucgture depth which sit on the bearing seat.

Partial-Depth Abutment - located approximately at middepth of the front slope of the approach embankment. The higher backwall and wingwalls may retain fill material or the embankment slope may continue behind the backwall....

What about a pile supported abutment that is not a stub abutment? Do you just need to account for the thermal effects?

This particular question is in regards to Illinois DOT but it applies as a general question. The IDOT manual give a maximum and minimum depth below the bottom of the beam (see below):

EIT

http://www.HowToEngineer.com

 

[RFreund]

The other question I have -
When using an integral abutment would/can you use the bridge deck to brace the top of the abutment (against overturning).

Thanks again!

EIT

http://www.HowToEngineer.com

 

[OSUCivlEng]

I would say if the dimension you have circled in red gets bigger than a couple of feet your bridge is too long.

I'm not sure how a pile foundation would overturn. Are you putting this on a spread footing?

The integral abutments I have designed looked similar to the drawing you posted. The lower portion of the abutment is usually 3'-5' in height with H Piles cast into it. The abutment diaphragm that encases the ends of the beams sits on top of that.

You have to design the abutment to account for the passive force that develops behind it due to the thermal movement (expansion). I have never worried about Some also design the piles to account for the thermal movement, others don't check it.

This is a pretty document about integral abutments.

http://vtrans.vermont.gov/sites/aot/files/highway/documents/structures/SEI-08-004-1.pdf

This is an older NSBA document from 1996.

https://www.google.com/url?sa=t&rct...jw0o-ei53QAhXJlVQKHXuxDD8QFggdMAA&url=http://

http://www.smdisteel.org/~/media/Fi...L3r3u3X--9Kx69C7w&sig2=bpWI3yZUm7Wml_ZDFyYkPw

 

[RFreund]

@OSU thanks for the responses.
Some further information regarding my case:
The bridge is 3 span steel bridge (total length about 175') supported by piles.

A few responses:

I would say if the dimension you have circled in red gets bigger than a couple of feet your bridge is too long.

I assume when you say too long, you mean too long to use an integral abutment, right? In this specific case, even if the abutment was moved back to meet the requirement it would still be shorter than the recommended maximum length.

I'm not sure how a pile foundation would overturn. Are you putting this on a spread footing?

I suppose I stated that question poorly. I should have said is the top of the abutment considered 'pinned' because it is attached to the bridge deck. If yes then I suppose they would need to construct the deck prior to constructing and backfilling the approach slab (does that seem reasonable?).

The integral abutments I have designed looked similar to the drawing you posted. The lower portion of the abutment is usually 3'-5' in height with H Piles cast into it. The abutment diaphragm that encases the ends of the beams sits on top of that.

That sounds about right and what I'm finding. I have about 8'-9' of the lower abutment portion and I'm wondering if that is too much and I can't use an integral abutment.

Thanks again!




EIT

http://www.HowToEngineer.com

 

[OSUCivlEng]

When I say too long, I do not mean too long for an integral abutment. Bridges up to 600' and longer can be constructed with integral abutments. If there is more than a couple of feet between the bottom of the beam and the bridge header, you could move the abutment towards the center of the bridge and shorten the bridge. I hope that makes sense. However I could also see where hydraulics or geometric constraints might require something different.

Normal practice is to not backfill until the deck and abutment diaphragm concrete have reached a certain strength.

I have always treated the abutment as a cantilever. However when it is backfilled the abutment diaphragm and deck should already be in place and of sufficient strength. I suppose you could treat it as pinned with respect to the active or at rest soil pressure acting against it. I wouldn't treat it like that for the passive forces acting against it when the bridge expands or contracts because of where the temperature forces are acting.