Terminology for Analysis of Earthquake Resistance Structure

Damping in structure is a dissipation of energy due to effect of internal friction, inelasticity of material, slipping, sliding, movements, etc.

Soil Liquefaction is a phenomena in which soil effective shear strength is reduced to negligible value by earthquake shaking. In this state, soils tend to behave like a fluid.

Natural Period of structure is defined as a time taken by a structure to complete one cycle of oscillation.

Center of mass in structure is defined as a point in floor of building through which resultant of inertia force of that floor is considered to act during earthquake shaking.

Center of resistance or center of rigidity is a centroid of stiffness of structure located at in floor. It is a point at which inertia force act during earthquake, than floor experience only the translation displacement.

Diaphragm in structure is defined as a horizontal structural system such as reinforced concrete floor, horizontal bracing system, etc. which transfer the lateral force to the vertical structural member connected to it.

It is a part of the total seismic mass of the structure that is effective in natural mode of oscillation during vertical and horizontal ground motion.

Mode shape is deflection pattern of the structure at a particular natural frequency.

Mode of oscillation is defined as a oscillation in which all points of structure oscillate harmonically at the same frequency and reach their individual maximum responses simultaneously.

Ordinary moment resisting frame is a moment resisting frame which is designed and detailed as per Indian standard IS:456 and IS:800, but not meeting any special detailing requirement for ductile behavior as per IS:13920.

Special moment resisting frame is a moment resisting frame which is designed and detailed as per Indian standard IS:456 and IS:800, and meeting special detailing requirement for ductile behavior as per IS:13920.

Soft storey is defined as a storey which lateral stiffness is less than the above storey.

Storey drift is defined as a relative displacement of the floor between above and below of the considered storey.

Importance factor is a constant value recommended by the Indian standard that is used to increase the seismic load based on importance of structure. For example, Importance factor is 1.5 for Hospital, School, Metro station, telephone station, etc. and it is 1.2 for Residential and other moderate important building.