What is Closely-Spaced Modes: The natural modes of oscillation of a structure, whose natural frequencies differ from each other by 10 percent or less of the lower frequency.
What is damping? The effect of internal friction, inelasticity of materials, slipping, sliding, etc. in reducing the amplitude of oscillation, expressed as a fraction of critical damping.
Design Acceleration Spectrum: An average smoothed graph of maximum acceleration as a function of natural frequency or natural period of oscillation for a specified damping ratio for the expected earthquake excitations at the base of a single-degree-of-freedom system.
What is ductility? The capacity of a structure (or its members) to undergo large inelastic deformations without significant loss of strength or stiffness.
Earthquake Zone Factor (Z): The value of peak ground acceleration considered by this standard for the design of structures located in each Earthquake Zone.
Elastic Force Reduction Factor (R): The factor by which the base shear induced in a structure, if it were to remain elastic, is reduced to obtain the design base shear.
It depends on the following factors:
- the perceived earthquake damage performance of the structure,
- characterized by ductile or brittle deformations,
- redundancy in the structure, or
- overstrength inherent in the design process.
Floor Response Spectrum: The response of a floor (expressed as responses of a spectrum of single degree of freedom systems, for a chosen structural damping value) is presented as a spectrum when the structure on which it is rested is subjected to earthquake ground shaking at its base.
Importance Factor (I): Factor used to estimate design earthquake force depending on the functional use of the structure, characterized by
- consequences of its failure,
- post-earthquake functional needs,
- historical value, or
- economic importance.
What is Limit State: A state at which one condition about a structure has reached a limiting or critical value. A limit state is said to have been attained when the loads or actions imposed on a structure are such that their effects (in terms of stresses or stress-resultant(s) in the members of the structure, or of strains, deflection, or rotations of the structure or a member) just reach a specified limiting value.
What is the Limit State of Strength: It is said to have been attained by a structure when, under the action of the designated loads or load actions imposed on it, the stresses or strains in its members just reach a specified limiting value
What is Limit State of Serviceability? It is said to have been attained by a structure when, under the action of the designated loads or load actions imposed on it, the deflection or rotations in its members just reach a specified limiting value.
What is Liquefaction: A state primarily in saturated cohesionless soils wherein the effective shear strength is reduced to a negligible value for all engineering purposes when the pore pressure approaches the total confining pressure during earthquake shaking. In this condition, the soil tends to behave like a fluid mass.