Mode Shape
Mode Shapes depends on the following parameters
1. Flexural Stiffness of Structural Elements
2.Axial Stiffness of Vertical Elements
3.Fixity
4.Building Height
5.Distribution of lateral Stiffness along the height
6. Stiffness distribution in plan.
We generally prefer buildings with zero stiffness eccentricity 😁 which in practice is difficult.
Some common modelling mistakes that may lead to wrong judgement of mode shape is to ignore stair or ramp stiffness by replacing it with reactions. There are cases where this stairs can cause torsional mode which considerably increases forces in the system.
Ideally we need a translational mode shapes dominating in plan view, even diagonal modes are not preferred.
