In order to perform dynamic wind load generation in STAAD.Pro you must previously define a static load case. The static load case could be any primary static load case which is defined before the Russian dynamic load case, including a static wind loading per the same code. This static load case will provide static load vector to the dynamic wind load module.

As the Russian dynamic wind load component requires modal masses and eigen vectors to calculate the dynamic wind load component at nodes, modal analysis must be performed before the dynamic wind load definition. Therefore, you must also include a separate load case for modal analysis with reference mass defined before the load case. See G.17.3.2 Mass Modeling for details. Alternatively, if the mass loads are not needed for use with other load cases (that is, a reference load case is not needed for other loads), then you may define the mass loads within the dynamic load case prior to the WIND LOAD command.