Relative stiffness = cracked stiffness?


Hello everyone,

I hope you’re all doing well. I’m currently working on my master’s thesis, and I’m delving into the analysis of reinforced concrete columns using the general method outlined in Eurocode. Specifically, I’m using the example file aseaqb_1_column_cracked.dat.

In my attempt to comprehend the mechanism, I’m focusing on a simple beam. When analyzing a simply supported beam and displaying the relative stiffness in Sofistik, I observe a stiffness drop of up to 20% along the entire length of the beam. My question is: Does the term “relative stiffness” refer to the stiffness after the beam has cracked?

Furthermore, I’m puzzled by the fact that even when the bending moment is smaller than the cracking moment, the stiffness drop remains consistent across the entire span. Shouldn’t the stiffness reduction be more pronounced for a larger bending moment, and why does it persist uniformly?

I would greatly appreciate any insights or guidance on this matter.

Thank you in advance for your assistance!