×
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

one way shear check for a pile cap

one way shear check for a pile cap

one way shear check for a pile cap

(OP)
Hello,

I have a circular bin supported by 8 columns. Bin dia is 12m. we are using a octagonal pilecap with 56 piles. I am using 1.5m deep pilecap. otagone has 17m dia. To check the one way shear at d from the face of column, I am having 30 piles contribute to that section. shear capacity of 1.5m mat with 30Mpa concrete is far less with 17m width. Even I am reducing shear by column loads in that section. I cannot increase the depth otherwise my piles will be overstrsed.
I can not put more piles due 3d spacing requirement.

1. Should i check one way shear based on pile capacity or actual reactions from various load combinations.
2. Is it normal to provide shear ties in a pile cap with scattered column on the top.
any reference material related to large pilecap is greatly appreciated.
All useful thougths are welcome.
Thanks in advance.

RE: one way shear check for a pile cap

Use pile capacity for shear calculation, one pile may max out prior to sharing load by settling or deflecting.  3 x dia spacing is recommended, not required. Try lesser spacing, i.e. 2.5 x dia, or higher strength concrete or thicker pile cap.  I was told never to use steel for additional shear strength in pile caps but was never told why this ban was needed.

RE: one way shear check for a pile cap

(OP)
thanks for reply.
We can not use more than 30Mpa. if I use 2.5d, my piles capacity will be reduced by 25%, which i can not afford.
However to increase the depth, i need more piles which means greater footprint. How do i justify this against shear capacity. However I can increase shear capacity by using shear ties and lesser depth.
 

RE: one way shear check for a pile cap

Your pile cap does not sound like a flexural element.  It is more like a deep beam, and I sugggest it is best designed by strut and tie methods.

RE: one way shear check for a pile cap

(OP)
thanks.
Even I designed it as strut and tie method, i still need to check oneway shear as per code.According to this all piles outside the d face of column will contribute to shear. My question is why we do not recomend to use shear ties in footing. is it due to cost of labour or material.
I mean if we have option to use shear ties to overcome this problem. I discuss with many colleagues, but all of them in opinion of increase depth to overcome shear. but my problem is that my piles would be overstressed.

RE: one way shear check for a pile cap

Perhaps if you could explain the setout of the piles it would be easier to understand your problem.  And the column loading and the pile capacity.

But there is nothing inherently wrong with using shear reinforcement in a big footing like this.  Shear reinforcement is used all the time in mat foundation slabs supported on piles for high rise buildings.

RE: one way shear check for a pile cap

(OP)
thanks for every one.

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