2　Terms and Symbols

2.1　Terms

2.1.1　Seismic precautionary intensity

The seismic intensity approved by the national specified authorities as the basis for seismic protection of an area.It is generally taken as the seismic intensity with a probability of exceedance of 10% in 50 years.

2.1.2　Site

An area where a project cluster is located and response spectrum characteristics are similar.Its scope is equivalent to that of a plant area，residential area，natural village，or plane area no smaller than 1.0km2.

2.1.3　Earthquake action

Dynamic action of structure induced by seismic ground motion，including horizontal earthquake action and vertical earthquake action.

2.1.4　Design basic acceleration of ground motion

The acceleration of ground motion with a probability of exceedance of 10% in the 50-year design reference period，taken as the design acceleration of ground motion in general construction projects.

2.1.5　Design characteristic period of ground motion

The period corresponding to the starting point of the declining curve reflecting such factors as the earthquake magnitude，epicentral distance，and site class in the curve of seismic influence coefficient used for seismic design，abbreviated as characteristic period.

2.1.6　Seismic measures

Seismic design contents other than earthquake action computing and resistance computing，including details of seismic design.

2.1.7　Details of seismic design

Various details required for various structural and non-structural parts which are determined according to seismic concept design principles without the need of computing.

2.1.8　Natural frequency

The free vibration frequency that depends on only the physical features（mass，stiffness and damping）of the structure.

2.1.9　Time history curve

The curve of a physical quantity such as acceleration，velocity，and displacement versus the time，respectively referred to as the acceleration time history curve，velocity time history curve，and displacement time history curve.

2.1.10　Sine beat

Continuous sinusoidal wave of one frequency which is modulated by a sinusoidal wave of a lower frequency.The duration of one sine beat is half the period of the modulating frequency.