×
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

Caisson Foundation Design, Steel Requirements

Caisson Foundation Design, Steel Requirements

Caisson Foundation Design, Steel Requirements

(OP)
I am designing a high-ecentricity caisson foundation two support a transmission line pole and am looking for some recommendations on the vertical steel requirements.  Can anyone point me in the right direction.  I can't find anything in the ACI that specifies a steel area for this type of foundation.  I will treat it like a beam.  I found one formula in a company standard that says the required steel area is As = (3.33 x Mult x 12)/ (fy x Ds)

Thanks!
Scott

RE: Caisson Foundation Design, Steel Requirements

It is basically a circular column with a high moment and a low axial load.  The point of maximum moment will be below the ground line by several feet depending on the type of soil.  The amount of steel required will be a function of the maximum moment, the concrete strength, and the diameter of the foundation.  Usually the vertical steel is run inside of horizontal hoops and the hoops should have a 3 inches of clear cover.  A good concrete design text might help with the rest.
Mike  

RE: Caisson Foundation Design, Steel Requirements

The geotechnical engineer should be able to provide an L-Pile (or other) analysis with a shear and moment diagram.

RE: Caisson Foundation Design, Steel Requirements

I often find that the minimum reinforcing is more than adequate to carry the maximum bending moment.  I use 1/2% of the gross area as the minimum.  

RE: Caisson Foundation Design, Steel Requirements

jmiec is correct to explain a bit further: "Section 10.9.1 of the ACI code states that the area of longitudonal reinforcement for concrete columns must be not less than 1 percent of the gross concrete area, Ag. If, however, the cross-section is larger than required by considerations of structural resistance, then Section 10.8.4 allows a reduced effective area, Ag', not less than one half the total area, to be used to determine the minimum reinforcement and design strength. This means that if the column has sufficient axial strength using only half the gross concrete area, Ag/2, then the longitudonal reinforcement ratio can be reduced to 0.5 percent of the gross concrete area, Ag."

The reference for the above quote is Drilled Shafts: Construction Procedures and Design Methods, Publication No. FHWA-IF-99-025, pg. 363. It goes on to say that the above criterio can be used often because drilled shafts are typically designed with large diameters in order to develop sufficient side friction and end bearing in both soil and soft rock.

RE: Caisson Foundation Design, Steel Requirements

(OP)
Typically high-ecentricity caisson foundations for transmission structures are designed as beams as opposed to columns because of the requirement for a high-moment resistance.  Thanks for all of your input!

Scott

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