Earthquake Engineering

[teckert]

I am wondering what the spectral acceleration graph tells you? How is this used in determination of roof displacements, etc? I have plotted one using an inelastic dynamic analysis program. The plot is of the El Centro 1940 north-south ground motion.You can see the different % of damping- what does this mean. I would greatly appreciate your help.

Thanks,
Tim

 

[ishvaaag]

Look like a single response spectrum for each of the damping quoted. Sets of these, or their simplified envelope are used to test the response for the corresponding damping. If you were to do time history would usually use one after another ground motion records, that are not this.

So the general practice when using response spectra is not use one specific, but an envelope. This way you cover the gamut of wanted cases.

 

[ishvaaag]

Not to forget that the response spectra to use is usually specified by the code. This way they control to what amount of force they want your structure be tested. This is lower than the observed values of response (say, instant measured accelerations) since it has been observed structures survive well the earthquakes when designe for the specified reduced values of response, what is generally attributed to inelastic behaviour and non-structural sor secondary estructural contribution.