1. Draw ET response curves

Various approaches can be followed in presenting ET response curves. The following procedure is recommended:

Step 1. Extract response history data for a particular response of interest. For example, Figure 1. shows the Displacement response history of a linear SDOF with T=1.0 s subjected to ETA20inx01 record. Note that any other response or damage measure of interest can also be considered. These may include parameters such as interstory drift ratios, plastic rotations, damage indices, damage costs, etc.

Step 2. Calculate maximum of the absolute value of the response from time 0.0 to t. This is called MaxAbs response function. Figure 2 shows such a plot for previous response data.

Step 3. Repeat steps 1 and 2 for all ET analyses. Normally, it is recommended to use three ET response history analyses in order to increase the resolution of obtained response. Figure 3. shows the result of repeating above steps for ETA20inx02 and ETA20inx03.

Step 4. Average MaxAbs response curves to obtain the Mean of MaxAbs responses. This is shown in Figure 4.

Step 5. Use a fitting function to draw a smoothed response curve through the Mean curve. This is shown in Figure 5. A spline or a moving average fitting curve is recommended. The degree of smoothing should be chosen carefully. Random jumps should be filtered out while preserving general trend in the response. Due consideration should be given to flattening of the curve (after 17th second in Figure 5) that may have been caused from response truncation at the end of record ( 20th second in this example). It is recommended to ignore or use appropriate extrapolation in the region of the last horizontal section of the curve.

This final curve is called the ET response curve. Response at each particular time will be evaluated using this curve representing the response as a a function of time.