# 11.4.6 Horizontal Elastic Design Spectrum

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**

* F_{a} = *Short-Period Site Coefficient

*Long-Period Site Coefficient for a period of 1.0 seconds*

**F**_{v}=*Short-period design spectral response acceleration parameter [dimensionless]*

**S**_{MS}=*Design spectral response acceleration parameter for a period of 1.0 seconds [dimensionless]*

**S**_{M1}=*the mapped MCER spectral response acceleration parameter at short periods as determined in accordance with Section 11.4.2*

**S**_{S}=

**,***the mapped MCER spectral response acceleration parameter at a period of 1 s as determined in accordance with Section 11.4.2*

**S**_{1}=*Design spectral response acceleration parameter for a period of 1.0 seconds*

**S**_{D1}=*Design earthquake spectral response acceleration parameters at short periods*

**S**_{DS}=*Natural vibration period [s]*

**T =***Horizontal elastic design acceleration spectrum corner period [s]*

**T**_{0}=*Horizontal elastic design acceleration spectrum corner period [s]*

**T**_{S}=*Transition period to constant displacement region in horizontal elastic design spectrum [s]*

**T**_{L}=*Horizontal elastic design spectral acceleration [ g]*

**S**_{a }=**Horizontal elastic design spectral accelerations S _{a}**, 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 **S**** _{a} **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 T

_{0 }._{ }

It’s equal S

_{DS }from T_{0 }to T_{s }._{ }It’s determined with the equation 11.4-6 from T

_{s}to T_{L }._{ }

It’s determined with the equation 11.4-7 for periods greater than T

_{L}._{ }

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