Seismosoft | Earthquake Engineering Solutions

Hello,
During the checks of the linear dynamic analysis, I had some doubts regarding the approach used to calculate the value of x, the depth of the compression zone. I'm curious to know what kind of methodology the software follows, since I wasn't able to reproduce the values obtained by the software using the calculation method by Fardis (2009), x = ξ·d.
When using the stiffness reduction option — either applying the effective stiffness or reducing the structural stiffness to 50% — I noticed that the vertical load acting on the beams is reduced to approximately half of the actual load. I compared a model using 100% stiffness with another using 50% stiffness for the quasi-permanent combination, and found that the 'Global Force at Supports' is the same in both models. However, when I check the internal forces in a beam, I observe that both shear force and bending moment are reduced by around 50% in the model with reduced stiffness. Is there an explanation for this behavior, and how can it be addressed?

Best regards,
Nuno Ribeiro.

Hello NunoRibeiro,

1) The section internal quantities, like the depth of the compression zone, are directly calculated from the element fibers, since the program knows which fibers are under tensions and under compression
2) This discrepancy is due to stress recovery, which employs the uncracked stiffness. We are working in a way to change this to take into account the cracked stiffness.

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