please check error.8272.Structural Staircase-3-1.STD
Hi Sandesh,
I am moving your thread to the Structural Analysis forum since this seems to be for a STAAD product (you posted to the Building products forum instead).
You are using ST 5 parameter. To calculate the time period of these type structures (ST 5), program needs the base dimension along both plan direction at lowest support level.
In this structure, program could not find any nodes along Z direction at the lowest support level to calculate the base dimension.
Program calculates the time period along X direction taking the Base dimension 1.5 m.
Please use PZ parameter (Time period along Z direction).