Earthquake and Wind Action on Buildings - Load Deformation Graphs

The action of Wind and Earthquake will result in dynamic action on buildings. But the building design for wind and earthquake forces are different in nature. 

Basic Concept in Wind Design of Structures

Mainly in the design based on a followed philosophy, force is considered as the basis for of structural design. This is more applied in the Wind design. Here, the idea is that the building surface is subjected to a force or pressure  (i.e. the wind force). This type is called as the force-type loading. The action is explained in the figure-1 below.

Fig.1. The Building Under Wind Force (Fw). It is maximum at the top story. Maximum displacement (Δ)is caused at the top of the building.

Fig.2. Nature of Wind Action - Non-zero mean- Oscillatory

Basic Concept in Earthquake Design of Structures

During an earthquake, the building is subjected to a random motion in the ground at the base of the structure. This will result in the formation of inertia forces in the building. This later gets converted into stresses. This type of loading is called the displacement -type loading.

Fig.3. Earthquake Ground Motion at the base of the structure

Load - Deformation Graph

The load- deformation graph of the building will properly help in differing both the type of loadings. 

• In the case of force type loading that is imposed by wind pressure, the demand for the building will be the force ( Along the vertical axis).

• The demand on the building will be displacement ( Along horizontal Axis) when it is displacement type loading that is imposed due to earthquake shaking.