 Using the coefficients obtained from the map, the spectrum curve given in Figure 11.4-1 with Equation 11.4-5 - 11.4-7 is automatically determined by the programme. Due to the need for site-specific analysis for site class F, the design spectrum isn’t determined automatically. The reduced design spectrum needs to be imported as a .txt file.

SYMBOLS

Fa = Short-Period Site Coefficient
Fv = Long-Period Site Coefficient for a period of 1.0 seconds
SMS = Short-period design spectral response acceleration parameter [dimensionless]
SM1 = Design spectral response acceleration parameter for a period of 1.0 seconds [dimensionless]
SS = the mapped MCER spectral response acceleration parameter at short periods as determined in accordance with Section 11.4.2,
S1 = the mapped MCER spectral response acceleration parameter at a period of 1 s as determined in accordance with Section 11.4.2
SD1 = Design spectral response acceleration parameter for a period of 1.0 seconds
SDS = Design earthquake spectral response acceleration parameters at short periods
T = Natural vibration period [s]
T0 =Horizontal elastic design acceleration spectrum corner period [s]
TS   = Horizontal elastic design acceleration spectrum corner period [s]
TL = Transition period to constant displacement region in horizontal elastic design spectrum [s]
Sa = Horizontal elastic design spectral acceleration [ g]

Horizontal elastic design spectral accelerations Sa, are defined in terms of gravity [g] depending on the natural vibration period.

With the spectral response acceleration parameters obtained from USGS depending on the coordinates, horizontal elastic design spectrum Sa is determined according to the formula below. It is represented by a total of 4 functions, different in each region. It’s shown in the graph below.

• It’s determined with the equation 11.4-5 from T=0 to T0 .

• It’s equal SDS from T0 to Ts .

• It’s determined with the equation 11.4-6 from Ts to TL .

• It’s determined with the equation 11.4-7 for periods greater than TL.

In the Analysis Settings - Response Spectrum Function tab, the horizontal design spectrum is determined and showed by using the design spectral response acceleration parameters.  