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# equivalent rectangular section for a round concrete beam

## equivalent rectangular section for a round concrete beam

(OP)
Hi everyone,

What is the best fitting equivalent rectangular section for a circular concrete beam?

I am designing a concrete pile which is loaded laterally. The pile has circular cross-section but I design it as a rectangular beam. I do have some hand-outs giving some equivalent rectangular beam dimensions for each diameter but I was wondering if there is any academic/practical article which would give a scentific based solution for this question.
Replies continue below

### RE: equivalent rectangular section for a round concrete beam

Solve for the bending strength of the circular section with associated reinforcement.  Compare to a square section with the bending about the diagonal.  This is the weakest axis for the square section with equal steel in all four faces.

### RE: equivalent rectangular section for a round concrete beam

I have seen a book that mentions this, I will get back to you tommorow with the name of the method.

### RE: equivalent rectangular section for a round concrete beam

I don't believe there is any recognized conversion.  Hate to say this, but you probably whould be analyzing these piles as circular sections.  If one were to fail, you'd have a hard time defending a conversion analysis thats not officially recognized.  CRSI publishes a calculation method for circular sections in the CRSI Handbook.

### RE: equivalent rectangular section for a round concrete beam

It is called the charles whitney method from 1942.

2 layers of half the reinforcement 0.67Ds apart, and a concrete section 0.8D deep by (As/0.8D) wide?

This is an approximation, and as such you should always ensure that you have at least 10% or so up your sleeve for any inaccuracies. I would also not that I imagine it would be very inacurate if there were any significant axial loads.

You really need some design charts in this country, this problem would be done in 5 minutes with circular column design charts (like the ones I used in Australia) I havent seen any here.

Check out this web site to see if you can find a spreadsheet (check it before you use it):

http://civilengineer.webinfolist.com/structure.htm

### RE: equivalent rectangular section for a round concrete beam

Aren't interaction charts available for circular sections?  Do you not have a program such as enercalc?  It will design the reinforcement for a circular section rather quickly.  I did this recently.  The only conversion I had to make to a "rectangular section" was during the shear checks.  There is no clear 'd' for a circular section.  At that point, for the shear check, ACI gives guidance in 11.3.3.
If you don't have a program like enercalc to design the flexural reinforcing, I would look for those interaction charts for circular sections.

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