In IBC 2000, the following basic
information is required to determine the seismic loads:
1. Seismic Use Group According to the
nature of Building Occupancy, each structure is assigned a Seismic
Use Group (I, II, or III) and a corresponding Occupancy Importance
(I) factor (I = 1.0, 1.25, or 1.5).
Seismic Use Group I structures are
those not assigned to either Seismic Use Group II or III. Seismic Use
Group II are structures whose failure would result in a substantial
public hazard due to occupancy or use.
Seismic Use Group III is assigned to
structures for which failure would result in loss of essential
facilities required for post-earthquake recovery and those containing
substantial quantities of hazardous substances.
2. Site Class Based on the soil
properties, the site of building is classified as A, B, C, D, E, or F
to reflect the soil-structure interaction. Refer to IBC 2000 for Site
Class definition.
3. Spectral Response Accelerations SS
and S1 The spectral response seismic design maps reflect seismic
hazards on the basis of contours. They provide the maximum considered
earthquake spectral response acceleration at short period SS and at
1-second period S1. They are for Site Class B, with 5% of critical
damping. Refer to the maps in IBC 2000.
4. Basic Seismic-Force-Resisting System
Different types of structural system have different energy-absorbing
characteristic. A response modification coefficient R is used to
account for these characteristics.
Systems with higher ductility have
higher R values. With the above basic parameters available, the
following design and analysis criteria can be determined.
