Design Spectrum for Site-Specific Ground Motion

For ZF, a site-specific ground motion design spectrum is created as user-defined.

ICONS

T = Natural vibration period [s]
T _A = Horizontal elastic design acceleration spectrum corner period [s]
T _B = Horizontal elastic design acceleration spectrum corner period [s]
S _ae (T ) = Horizontal elastic design spectral acceleration [g]
S _aR (T ) = Reduced design spectral acceleration [g]
D = Excess Strength Factor
I = Building Importance Factor
R = Structural System Behavior Factor
R _a (T) = Earthquake Load Reduction Factor depending on the anticipated ductility capacity and period
λ = Empirical coefficient used in limiting relative story drifts

First, the R _a values are calculated using the TBDY 2018 Equations 4.1a and 4.1b , using the field T (period) and S _ae (acceleration for elastic design spectrum) values obtained for the spectrum given as a result of the soil-specific study. Then, as stated in Equation 4.8 , the S _ae values are divided by the R _a values you calculated . In this way, you obtain the Elastic Design spectrum to be defined in the program.
Import the design spectrum T (time) and S _aR (acceleration) values you obtained into a txt file. Make sure that the decimal numbers in the txt file are written with dots.
Open the Analysis Settings dialog.
Go to the Response Spectrum - TBDY 2018 tab.
Check the box that says Custom (SF).
Take into consideration the warning that says "Please define the S_aR (T) spectrum function". The design spectrum that you will define should be the spectrum processed according to R , I and D values using TBDY 2018 - Equation 4.8 .
Click on the Define box and pay attention to the second warning, Please make sure that you defined suitable R, D and I parameters in the ‘Analysis Settings → TDY Options’ tab according to your project. These values are important because they are used in earthquake regulation checks such as relative displacement, second order, etc.
After passing the warning, use the import option in the window that opens. Import the .txt file you created earlier.
When you complete the above steps, you should have a curve as seen in the image below. There should be no plateau region in the graph. If there is a plateau region, it means that the elastic design spectrum has not been reduced by Ra . In this case _, please return to the top of the page and make sure that you have completed the steps outlined in the first 3 items.
In the TBDY 2018 Design Spectra tab, you need to enter the lambda (λ) coefficient under SF correctly. The program uses the lambda (λ) coefficient in the calculation for the relative displacement value. Since only one value can be entered in the interface for the current situation, you can enter the lambda (λ) coefficient that gives an unfavorable result for use in the x and y directions.
If different Building Structural Systems are selected for the X and Y earthquake directions, the R and D coefficients will be different, so the S _aR (T) spectrum can be defined differently for both directions.
In the structure tree, right-click in the Analysis → Response Spectrum Analysis → Response Spectrum Functions and click the Add New Response Spectrum Function command.
The Response Spectrum Function window will open. Define the S _aR (T) spectrum for the relevant earthquake direction by applying the same operations as above . It would be appropriate to change the function name in a distinctive way here. For this example, the function name was selected as “SaRX” to be defined in the X earthquake direction.
In the structure tree, double-click the relevant earthquake case Ex or Ey in the Analysis → Response Spectrum Analysis → Response Spectrum Cases section. The Design Spectrum Case window will open.
Select the function you defined in the relevant earthquake direction from the Design Spectrum Status window. Since an S _aR (T) spectrum is defined for the X direction in this example, select the “SaRX” function that we defined as a function in the FX section.
Similar operations can be performed for the Y earthquake direction and two different S _aR (T) spectrum functions can be defined for two different earthquake loadings.

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Earthquake Ground Motion Records in Time History

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