Response Spectrum Wizard : IBC (2000)

The IBC 2000 spectrum is defined by a set of parameters defined in the code.

Site Class

Sites are classed as one of A, B, C, D or E for the soil type as described in Table 1615.1.1. Type F soil requires specialist geotechnical advice and is not included as an option.

$S_S$ and $S_1$

These are the short period response acceleration parameter and the 1s response acceleration parameter as defined in Section 1615. Seismic Hazard maps for the USA are available from the U.S. Geological Survey web site by following the USGS hyperlink.

Importance Factor

Determine the importance factor ($I_E$) from Section 1616.2 and Table 1604.5.

Response Modification Factor

The structural system factor ($R$) is determined from Table 1617.6.

Frame Type and Building Period Coefficient

The approximate fundamental period of the building (Section 1617.4.2.1) is calculated from equation (16-39)

$$T = C_t(h_n)^\frac{3}{4}$$

The building period coefficient, $C_t$, depends on the type of building frame. The frame types are:

• Steel moment-resisting
• Reinforced concrete moment-resisting
• Eccentrically braced
• Other

And $h_n$ is the height of the building (in feet).

Factor for Vertical Excitation

It is common to reduce the spectral values for vertical excitation to ⅔ of that used for horizontal excitation.

Ignore Short Period Force Reduction

It may be unconservative to reduce spectral values for low periods. This option ignores the reduction and extends the plateau to cover the low periods.