- See Section 2.268.
- Response parameter is displacement for 2, 5, 10, 20 and 30% damping. Choose displacement because of
aimed use of equations for displacement-based design.
- Only use records within their usable range, defined as a fraction of the cut-off frequency used and depending
on instrument type (digital or analogue), magnitude and site class.
- Note that drop-off in available records from analogue instruments is much more rapid (starting around 1s)
than for records from digital instruments (starting around 3s). Due to lack of data for longer periods limit
regression to periods ≤ 4s.
- Due to jagged appearance of predicted response spectra, particularly at long periods where different
data was used for each period, apply negative exponential smoothing. Try smoothing using low-order
polynomials, to achieve very smooth spectra, but complex functional form means results are sensitive to
trade-offs between smoothed coefficients. Find that for periods > 3s spectra predicted from the raw and
smoothed coefficients show differences, especially for low damping ratios.
- Find that coefficients b7-b10 weakly dependent on damping ratio so present these coefficients for 2 and 5%
damping (combined), 10% and 20 and 30% damping (combined).