Combined Axial and Bending in Concrete

[Woody1515]

Hello,

CSA O86 (wood code) provides interaction formulas for members that are subjected to combined axial and bending loads. However, I do not see any similar equation in the concrete code (CSA A23). Why is this the case?
For example, I quite often see the axial force acting on a reinforced concrete basement wall neglected, as they say the compressive loaf will decrease the flexural tensile stresses. But when designing a PWF stud, the interaction equation must be satisfied.

 

[BridgeSmith]

Reinforced concrete is not a homogeneous material. Its capacity in combined axial and bending requires building an interaction diagram based on the shape and reinforcement of the concrete member. Sorry, it can't be done with a single equation.

For typical reinforced concrete, the compression capacity is much larger than the tension capacity, since only the reinforcing is assumed to have tensile capacity, and it typically makes up a very small percentage of the cross-section (usually less than 2%).

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Woody1515]

Thanks BridgeSmith. After a bit more thinking, I do understand how to account for both axial and bending stresses in concrete. But I’m still struggling with how to derive the interaction equations for wood design. Does anyone have any info on this? I get how to use the equation, I would just like to know where it comes from.

 

[Complete_Columns]

My guess is the wood code derives the interaction equations from the generalised procedure used to generate an interaction diagram for reinforced concrete. I would try to develop an interaction diagram using wood material properties and see if you can infer where the wood axial-moment interaction equations come from.

Complete Columns

https://www.completecolumns.com/

 

[engineering_patrol]

Hi, this is a complex matter, I use to use the software csad (

https://www.engissol.com/cross-section-analysis-design.html)

to handle interaction between bending moment and axial force on concrete sections. You can do that with hand calcs, but i think that's very complex!

 

[Celt83]

see my reply to your post in the wood forum.

The wood interaction equations take buckling and slenderness into account directly and calibrated against test data. For concrete slenderness effects are taken in the form of amplification of the loads then comparing against the standard P-M curve.

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

https://github.com/open-struct-engineer

 

[engineering_patrol]

Eurocode 2 EN1992 provides data in order to construct the interaction curve for concrete columns.