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Response Spectrum Wizard : UBC (1997)

The UBC 1997 spectrum is defined by a set of parameters defined in the code.

Zone Number

This is the Zone in which the structure is to be located and is one of 1, 2A, 2B, 3, 4 as defined in Table 23-I).

Seismic Source Type

For Zone 4 the seismic source type is categorised by types A, B or C determined form Table 16-U.

Closest Distance to Known Seismic Source

For Zone 4 the spectrum will depend on the distance to a known seismic source in the range 2km to 15km. See Table 16.

Soil Type

Enter SA, SB, SC, SD or SE for the soil type as described in Section 1636. Type SF soil requires specialist geotechnical advice.

Importance Factor

Determine the importance factor (II) from Table 16-K.

Structural System Factor

The structural system factor (RR) is determined from Table 16-N (building structures) or 16-P (non-building structures).

Empirical Building Period

Enter the value of the empirical building period derived from the code (Section 1630.2.2) or set to zero for automatic calculation based on frame type.

Frame Type and Building Period Coefficient

The empirical period of the building (Section 1630.2.2 – Method A) is calculated from equation (30-8)

T=Ct(hn)34T=C_t(h_n)^\frac{3}{4}

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

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

And hnh_n is the height of the building (in feet).

This is ignored if the building period is specified directly.

Target Base Shear

Select from 90% or 100% as determined from Section 1631.5.4.

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.