NCEES Problem 601(a)

[Kamba]

in NCEES problem 601(a) to design a CMU for axial and flexure, the solution used an interaction equation for combined stresses (Pu/phi.Pn + Mu/phi.Mn). I haven't seen such interaction equation in before in concrete or masonry codes or textbooks. My understanding that this problem should be solved by finding the natural axis for the transformed section or using the interaction diagrams.
any thoughts?

 

[E720]

Yes there are interaction equations for masonry and concrete. I can provide references when I get home from work. The interaction diagrams are based on the interaction equations.

 

[Kamba]

linear interaction equations similar to the one used in that problem are valid if the section is un-cracked. when the section is cracked you end up with the interaction diagrams and not just a single line because it accounts for the change in NA location based on the applied moment (tension) and the cracked section.

 

[YAZRABADI]

Dont over think it buddy. Just make sure you have the correct load combination a long with the correct checks per MSJC 13. Make sure you have jot down out-of-plan procedure and in-plan procedure for CMU. 

Remember you have to show like you know what you are doing, dont get into the weeds too much. make sure you get the overall concept of things.