Seismosoft | Earthquake Engineering Solutions

Hello,
I am working on an 80-story reinforced concrete building. I am applying dynamic wind load by introducing a dynamic time history wind record 3600 second length, and nodal dynamic time history loads on given points on each story. the results show large variance in the displacement values at the first two minutes of the record (displacement curve keeps going up and down in a small time interval), which results in very large values of nodal velocities and accelerations at this period relative to the rest of the results, then everything goes to normal till the end of the record. I have tried different records (even using a constant record with the same load value at all steps) and still get the same behavior.

Please advise

With such a long time history of 3600 seconds, the first thing that comes to mind is to ask what time step are you using for the solution. To obtain an accurate solution to a dynamics problem, the maximum time step is typically on the order of 1/10 to 1/20 times the smallest significant period (which could be rather small to start with, for an 80 story building). Certainly, the fundamental period would be rather large, but to include enough modes to capture at least 90% of the mass might require including very small periods.

Did you do an eigenvalue analysis to determine periods and mass participation for each mode?

What is the time step in your analysis stages input?