I have two issues when designing a combined footing.
- Issue 1 has been reported by someone here previously and was never resolved or updated. It is about reinforcing of the combined footing not "developing" or being found at the edges of the footing, if the reinforcement is specified from one end of the footing to the other as can be seen below: (Pier 3 footer)
Footing Reinforcing 1
Design Results 1
This can be solved (not sure if it actually solves the issue) by extending the reinforcing outside of the boundary of the footing, as seen below:
Footing Reinforcing 2
Design Results 2
- Issue 2 has to do with the analysis of these combined footings. The program help menu doesn't really address how these footings are analyzed. I have two very similar pier configurations that only differ in the distance between the columns. Pier 2 receives larger loads as the spans are longer than for Pier 3, however, the analysis of the footers shows larger AND more negative moments controlling for the combined footer of Pier 3. See below:
Pier 3 Combined Footer
Pier 2 Combined Footer
The moments for flexure design of footer for Pier 2 are positive and the ones for footer of Pier 3 are negative indicating tension at the top of the footer. See flexure results above for Pier 3 and below for Pier 2:
Design Results Footer Pier 2
My question is, how does the program analyze footers when they are combined and how could there be such large negative moments on the footer?
I would suggest you to check the RCPier Tutorial - Example 2 combined footing example .