Response spectrum wizard : GB50011 (2001, 2010)

The GB 50011-2001 spectrum is defined by a set of parameters defined in the code.

Seismic design intensity

Seismic analysis is required when the seismic intensity in 6 or greater. If the value is greater than 9 more detailed analysis than response spectrum analysis is required. For design intensities 7 and 8 there are lower and higher values of design ground accelerations. Reference should be made to the code for the appropriate intensity for a particular site.

Site class

Sites are classed depending on the soil type and shear wave velocity. from Type I (for firm soil) to Type IV (for weak, soft soil).

Building category

Buildings are categorized as one of 4 types.

Type	Structure
A	Important structures; severe hazardous consequences
B	Structures whose functionality needs to be maintained
C	Structures other than types A, B or D
D	Less important structures

The importance factor is 1 but this can increase to 1.5. Determine the importance factor (I) from Table 6.

Seismic group

Three different seismic design groups (1, 2 and 3) are defined in the code. The characteristic period is a function of this design group

Seismic recurrence

Two different scenarios are considered: frequent earthquakes with a smaller ground acceleration and rare earthquakes with a larger ground acceleration. The frequent earthquake is one with a probability of exceedance of 63% within a design period of 50 years. The rare earthquake is one with a probability of exceedance of 2-3% within a design period of 50 years.

Structure damping ratio ()

The spectrum values to use depend on the level of damping in the structure as expressed in the damping ratio. This value will adjusted the spectral accelerations.