Reply To: Static, quasi static, dynamic, transient

[Sandeep Medikonda]

Hello Adisa,

Just to add to what Peter already said:

In a static problem, we assume acceleration is zero.

Quasi-static means that at a given instant in time we can assume the problem is static. The fundamental assumption is that the loading is applied so slowly (very low frequency when compared to that of the structure) that basically the structure deforms in a static manner and inertia effects can be neglected. This assumption works well when inertial effects are very low. Also, this helps simplify the non-linear problems to a linear system.  

So, In static and quasi-static loading we are solving,  F = KU   and finding the displacements U (Neglect damping, inertia, K is the stiffness matrix)

Note that a load quasi-static for a given structure (made of some material) may not be quasi-static for another structure (made of a different material)

This is not the case in a dynamic analysis where inertia forces are not small enough to be neglected. Inertial forces result from Newton's second law (F = MA). So in a dynamic analysis, we need to account for the accelerations. Where MA is the inertial component and KU is the elastic component (assuming no damping).

In dynamic loading we are solving, F = MA + KU + damping (again we are solving for the displacements in this equation)

Hope this helps!