271828, you've got two options, depending on whether or not your company owns the SAP bridge module.
Option 1 (valid only if you have access to the bridge module): Define a bridge load moving load case, and after you've done that, go to Define>Load cases and define a new load case type "Bridge live", which is a multi-step static load case in which you can use vehicles defined in your bridge load case. Run the analysis and unlock it. Now go to Define>Analysis case and add a new load Time history type. When you do that, you'll see an option under the Loads applied for your multi-step static case (although the default is DEAD) which you will need to choose. SAP will then use that multi-step static case as the basis for the time history case. Go ahead and do that using the default time history function for the time being. Now go to Define menu>Functions>Time History, and you'll see that SAP has some automated tools for you to define sinusoidal functions. After you've defined it/them, go back to your Time History analysis case and change the default TH function to a sinusoidal function which you just defined. You should be good to go with that procedure. The benefit of the moving load case is that without it, you have to define your vehicle loads manually using joint loads or distributed loads
Option 2 (without bridge module) - Define static joint or distributed loads to your model for your vehicle loads... which will later be the basis for your sinusoidal time history analysis. Then define your Time History analysis case using the load case(s) which you just assigned. You define TH sine functions as described above. SAP lets you apply a sine and/or cosine TH functions to any joint, distributed load, or thermal loads
gergana, you can assign joint displacements at restraint or spring locations, and then Define time history cases using TH functions based on your accelerogram data to be applied using those displacement loads. For example, you could assign a 1" imposed displacement to your restraints, then define TH functions which uses displacement versus time applied to your displacement load case
