I am performing Pushover Analysis for steel structure using STAAD Pro 2007.
The structure comprises of Special Moment Frame in X direction and braced frame in Z direction as seismic force resisting system.
I have some basic queries regarding input parameters in Pushover Definition.
(1) Define Gravity Load: Usually, we define gravity load in -Y direction in STAAD. However, I have applied gravity load in +X direction (as my seismic load is in X direction) as mass in X direction. Is this correct or I have to apply load in -Y direction?
(2) Define Load Pattern: I am selecting AUTO load pattern from the tab. This asks me to enter value of base shear (V1) to be distributed (it also says that if I don't define the value, STAAD will assume 10% of gravity load). I understand that the base shear value, V1, should be the value calculated from Equivalent Lateral Force Procedure. Is this correct? In Define Solution Control, it asks to input the value of base shear (V2) up to which the structure should be pushed. Say for example, I enter V1= 3000 kN (calculated base shear); if I enter V2=V1, then the programme will be terminated stating that calculated base shear exceed specified base shear. Please advise on the values of V1 and V2 to be entered.
1) You must define Y as your gravity direction for seismic loads acting in the X-Z plane.The program can then take 10% of the actualy loads by gravity (dead, live, snow, rain, etc.) and apply them laterally. Otherwise, you may provide a base shear based on your own calculations (see following).
2) If V1 = V2, then you essentially have zero load steps in this definition; resulting in the error you are seeing. You must have at least one load step for the Pushover Analysis to increment by. V1 is the initial base shear you use and V2 is the maximum (unless, of course, you are using a max. deflection limit to stop the analysis). It is up to you to determine what value of base shear is applied to the structure, but the initial conditions may be anything (including zero).If you simply wish to define a single base shear, you may define the base shear and then a number of load steps.
Jason Coleman, PE
Bentley Systems Senior Manager Technical Content