AASHTO Bridge Abutment Design - Minimum Vertical Abutment Steel 2

[PEVT]

I am designing a small bridge abutment for a single span, single lane cast-in-place slab bridge. The factored vertical load on top of the abutment and the factored moment at the stem of the abutment wall are shown on the attached sketch. In the final reinforcement design I need clarification for two items:

1) Do the provisions of 5.7.4.2-3, Limits for Reinforcement for Compression Members, apply to abutments? I realize this is a compression member and a bending member but I need to be sure about this provision, as it will have a substantial impact on the amount of steel. That is do I need to include (As*fy)/(Ag*f'c)>.135 for the vertical reinforcement. By my calculations this is 2 in^2 per foot.
2) Do the provisions of of 5.8.2.4, Regions Requiring Transverse Reinforcement, apply to abutments? That is do I need to provide stirrups?

I have reviewed several very detailed AASHTO design examples and they all seem to utilize the above mentioned provisions for the piers and then ignore them at the abutment.

 

[Qshake]

You have a cantilever retaining wall as an abutment. Your details are not typical for this type of abutment and I suggest you seek other sources of information.

You either need to provide continuity steel at the top of the wall and into the abutment which will make this a rigid frame or you need to provide a seat for the slab at the top. In this case you will have free standing cantilever abutment wall and a simple span deck.

Please consider that first.

When you are done with the above you'll need to view the requirements for walls and not for abutment arrangements that are more toward the beams. You have a wall and walls are not reinforced the same as beams or columns.



Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[bridgebuster]

If you look at the CalTrans website there are illustrations of what QShake is describing

http://www.dot.ca.gov/hq/esc/techpubs/

pre-designed abutment NON-LRFD:

http://www.dot.ca.gov/hq/esc/techpu...-standard-detail-sheets/pdf_files/xs4-010.pdf

 

[PEVT]

Hello Bridgebuster and Qshake,

Thank you for your input would you please follow up if you have a chance. The design is intended to be cantilever abutment wall on a spread footing. My sketch does not show all of the reinforcement or any of the connection details to the superstructure. For now, although it may feel like a stretch, please assume these will be addressed adequately.

The project is located in a Seismic Zone 1 with SD1 < 0.1, so seismic ties are not required. With that said do you think you could take a moment to specifically address questions 1 and 2. That is, do the provisions referenced above apply? Do I need to provide As minimum for this compression member and do I need transverse reinforcement via ties in the wall? Perhaps if you know of the reference in AASHTO LRFD where it says these provisions don't apply to walls?

I reviewed the files you referenced and have attached a copy of an abutment wall similar to mine. Note no transverse ties and only T&S reinforcement in outside face.

 

[bridgebuster]

I've always designed stems as a cantilver beam, using the earth pressure only. I read the LRFD sections you cite as requirements for a traditional column.

Often with an abutment the minimum reinforcing requirements are usually enough.

It's been a few years since I used LRFD for an abutment design; as I recall the requirements for temperature and crack control were more stringent than the standard specs.

I hope this helps.