Dear Dmitry,
1. if you mention a longer period, I assume you are working with the Creep module of ATENA Science?
2. It is not clear from your question which "level" of modelling the long-time response you are using:
A. using the Static module (or ATENA Engineering) with adjusted material properties (E modulus or/and other),
B. using the Creep module with properties constant for the whole volume (i.e., only defining the average distance from the surface),
C. using the Creep module with imported temperature or/and humidity from the Transport module
?
3. Or does "long term" rather mean "due to cyclic loading"? If so, please see ATENA Troubleshooting, 2.2.26 How can I model cyclic or fatigue loading?
4. For force loading up to failure, you have to use the Arc Length solution method (see also ATENA Troubleshooting, 2.4.6.1 Solution methods).
5. If you have further questions / seek help with your particular model, you can follow Troubleshooting, 2.1.1 to send us your model along with information about what are you modelling and what are the questions to be answered by your analysis.
Regards.