×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Concrete Pile Caps - Shear Design

Concrete Pile Caps - Shear Design

Concrete Pile Caps - Shear Design

(OP)
In designing the pile caps for a simple span bridge with piles that are centered under each girder, ie/ 5 piles/ abutment and 5 girder arrangement for the superstructure all which are centered over the pile locations, apart from the self weight, wingwalls and soil pressures, there appears to be relatively no load in the cap between the piles.  What then would be the basis for the shear deign?  Simply minimum reinforcemnt requirements.

Thx in advance for any advice.  

RE: Concrete Pile Caps - Shear Design

The cap beam will carry no load, only if assumption is made that the supports are indefinitely stiff. However, both piles and supporting substrata are elastic, so I would advise to re-analyse the cap beam treating it as a beam with elastic (spring) supports. This approach would definitely provide shear forces in the cap beam. Also, if the connection in between piles and cap beams are rigid or semi-rigid, there will be shears and moments in the cap beam generated by transverse loads (wind, seismic).
If the piles used to support the cap beam are friction type, uneven settlement will generate moments and shears as well.

RE: Concrete Pile Caps - Shear Design

In many cases, DOT's will strive to place piling under each girder at abutments in order to minimize the amount of reinforcing that otherwise may be required.  And so you'll wind up with the results you've noted for vertical dead and live loads.  For the DOT, who will do hundreds of bridge designs per year, this makes sense economically.  Yet, as consultants working on only a single bridge for this or that agency we might lose sight of that.

At the same time, you don't want to forget to evaluate the impact of some of the loads mentioned by wiktor above.  However, in most cases for the situation you've described these will result in negligable shears in the beam.  Though their impact might be greater for other parts of the structure.

Regards,
Qshake

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

RE: Concrete Pile Caps - Shear Design

I forgot to add one of the most important requirements for the cap beams, which should be capable of supporting the jacks during servicing/replacement of the bearings.
I agree with Qshake, that agencies are pushing for reduced loading in such elements, in order to reduce the costs. However, I have seen a bridge, where outer pile failed due to the scour, and the extra reinforcement in the cap beam (not needed by normal calculations) prevented catastrophic collapse.
I would reinforce cap beam for the 1.10 of the vertical reaction from the girder (outer bay, inner bays less) for shear, and provide enough rebars for bending to avoid collapse, but with damage, with any single pile failing.

RE: Concrete Pile Caps - Shear Design

Maybe consider the wet concrete of the diaphragm if there is one?

Most states have standardized reinforcing for simple pile caps  at abutments and the reinforcing need not be checked if piles are under the girders. Make sure you satisfy yourself with this of course.

One easy method is to just check your cap beam as simple span between piles and provide same reinforcing for positive and negative steel.

I have treated the piles as springs and artificially created the shears but it's just an excercise to create some loads.

If the piles settle they should move together (as in downdrag). If the bridge is getting wide (100+) you may consider it if the borings indicate a lot of changes going on. Consult your geotech...

Right now I have a wide bridge where the bedrock slopes 20% so it's something to consider and possibly provide for.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources