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# How to introduce a user defined response spectrum/ seismic spectrum

Contents

A user defined reponse spectrum is always a relative spectrum with values between 0 and 1. It is scaled to the correct size with the reference acceleration and reference peroid (see example).

## Example

When using this feature, make sure to use design values Sd, not elastic values Se. Diamonds has no possibility to take a behaviour factor q and /or an importance factor γI into account for user defined response spectra.

1. Assume we have this design spectrum in Excel. Column A contains the period T in [s] and column B contains the design accelaration Sd in [g].
2. Find the maximum value for the period Tmax in column A and the acceleration Sd,max in column B.
3. Select the cells containing the spectrum values, don’t select the labels! Press CTRL + C
4. Go to the the spectrum dialog  in Diamonds.
Select the relevant direction U, V or W (the vertical direction W is only selectable when you check the option Include vertical component). Click on. Diamonds will transfer the spectrum to a relative spectrum and paste the values into the table. A relative spectrum means that

• Column A will be divided by Tmax
• Column B will be divided by Sd,max

5. Set the reference period in Diamonds equal to Tmax from the Excel.
Set the reference acceleration equal to Sd,max from the Excel. Mind the units! 1g = 9.81m/s² so 0.7454g equals 7.31 m/s²!
Define the displacement factor.

6. We’ve now defined the spectrum in one horizontal direction.
Repeat the steps for the other horizontal (V) direction and the vertical (W) direction if necessary.