Seismosoft | Earthquake Engineering Solutions

Dear SeismoSoft Team,

I am performing Incremental Dynamic Analysis (IDA) in SeismoStruct for reinforced concrete shear wall-frame buildings with different heights (3, 7, 13 and 15 storeys).

The analyses terminate with the message:
“Unable to apply the next load step. Analysis terminated.”

However, this occurs at very small displacement levels (on the order of a few millimetres), which is far below any expected collapse or severe damage state.

This behaviour is consistently observed in all models, regardless of building height.

Could you please clarify why the analysis stops at such low displacement levels?

This is divergence of the numerical solution. There are several reasons that could cause such problems.
In the SeismoStruct manual there is a dedicated section on the possible reasons for divergence and on how to overcome such difficulties. Furthermore, there are dozens of posts on convergence problems in this forum. You can access them with a simple search.

Since the problems occur at very small deformation levels, possibly there is a connectivity error in the strengthened model. Have you checked the shapes of all the modes in eigenvalue analysis?
Also, make sure that you are applying the correct ground motion in dynamic analysis; it is a typical error in dynamic analysis to confuse the units (e.g. g against m/sec2) and adopt very large or vey small scaling factors.
Seismosoft Support

You may also read the relevant sections in the help of the program:
https://help.seismosoft.com/seismostruc ... oblems.htm
Seismosoft Support