Reinforced Concrete Column Design

[Mark1921]

A noob question right here:

To analyze the reinforced concrete capacity via computation method: First, I have to know if all steel (compression and tension) yields or just some. The acquired load capacity is then compared to the required load. It's tedious work.

If I utilize the interaction diagram, I can easily compute the steel area given the required axial and moment load. But, is there a way to know from the interaction diagram whether all the steel will yield or not?

Thank you!

 

[IDS]

I suppose you could work out the moment capacity assuming that all the steel was yielded, then if the interaction diagram moment was less than that you would know that some of the steel was not yielded.

Or just calculate the depth of the neutral axis on a apreadsheet, which seems easier to me.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[JoshPlumSE]

Uniaxial isn't too bad. Although it does require some iteration.

Biaxial column bending is the real pain. Hand calculations would generally be done using some sort of interpolation method based on the two uniaxial cases (PCA Load Contour). It is certainly possible to perform an exact solution. But, the amount of work required to do so is significant.

 

[IDS]

Josh - OK, a true biaxial solution needs a bit of work (although there is a spreadsheet for that), but if you are using interaction diagrams you are going to do the two perpendicular axes separately then combine them, so why not use the same approach using calculations?

I'm not saying people shouldn't use interaction diagrams, just that if you want to know if the reinforcement is yielded it seems easier to me to calculate the depth of the neutral axis directly, rather than trying to back-calculate it from an interaction diagram.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[JoshPlumSE]

A generalized rectangular bar layout in bi-axial bending just gets really complicated. The area of compression isn't a rectangle anymore. All the bars are at a variable distance. You've got to enforce statics about multiple axes.... Not really worth the time to do it yourself if you're a practicing engineer. So much easier to use an already written program.