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


Designing A Rectangular Concrete Foundation 2ft deep

Designing A Rectangular Concrete Foundation 2ft deep

Designing A Rectangular Concrete Foundation 2ft deep

  Looking for some help. I am designing a foundation that is 2' x 19'-9 1/2" x 11'-9". The structure that sits on the foundation is rectangular as well, 6'x 14'. I am having trouble developing the moment diagrams for the longitudinal and transverse sections since the only support is the soil pressure. I need the max moment value to find how much rebar i will need. The structure has a wind load of 2.5 kips at 16' above the foundation. It is perpendicular to the longer side of the structure and centered. The other load is a gravity load of 2.5 kips, which I centered since the structure is uniform. Oh, and the structure has 4 columns(4" std. pipe) which sits on the foundation. How could I simplify this to get my moment values?

     I am a fresh out of college and just gaining experience, any advise will be helpful!

RE: Designing A Rectangular Concrete Foundation 2ft deep

This is a simple problem, but it's not easy to walk someone through it in a forum like this. Basically, you figure the reactions on the equipment supports, convert them to a soil pressure, and calculate shear and moments at critical sections. Soil pressures are likely to vary based on the layout and loads. It's a merger of the principles of foundation design and concrete design.
Is there a more experienced engineer there you can ask? I know it's a little embarrassing, but believe me, it's the way we all learn.

RE: Designing A Rectangular Concrete Foundation 2ft deep

Hello Jed, thanks for the reply.

   Well one of the experienced engineers told me to assume a triangular soil pressure distribution, with that I took the moment about the edge of the foundation to find my values of soil pressure.I also compared the soil pressure I calculated to the allowable (1200psf). I also asked how to simulate the soil pressure as a support in order to develop the diagrams for shear and moment and he told me to put supports at 1 foot apart from each other throughout the width of the foundation. Wouldn't it make it like a indeterminate beam?  

RE: Designing A Rectangular Concrete Foundation 2ft deep

Since you have four supports I would treat it as a combined footing in both directions.  If your supports are centered on the foundation and the loads are equal you would have a uniform load distribution.  If they are unequal than you would have a linear varying distribution.

Find the c.g of you pier loads and that is the location of you soil reaction, than turn that single load at a location into a distributed load that would produced the same load and moment.

Like Jed explained it is hard to discussion on the forum, but any good soils book should have an example.

RE: Designing A Rectangular Concrete Foundation 2ft deep

Hey guys, thanks again for the help. Found some information in a book I had.

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!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close