Answer to Quora question, "What is 'spectral acceleration' in structural analysis?"

Quora's bots asked me to answer the above question, and below is my response. What do you think of my response? Did it answer the question? Is there anything incorrect with what I said? How would you have answered the question? Let me know in the comments.

"What is 'spectral acceleration' in structural analysis?"

I would say that this is the ordinate on a response spectrum plot which gives the acceleration of a one-degree-of-freedom system with a certain natural period subjected to the ground motion represented by that response spectrum.

If I used, say, a design response spectrum prescribed by ASCE 7–10, and I am looking at the Mode N response of a certain structure, the spectral acceleration is the ordinate on that ASCE 7–10 design response spectrum corresponding to the natural period associated with the structure’s Mode N.

If I used, say, a response spectrum that represents one direction of the classic El Centro Earthquake ground motion instead, the spectral acceleration is then the ordinate on that response spectrum corresponding to the natural period associated with the structure’s Mode N. (A design response spectrum is sort of a simplified envelope for multiple expected ground motions at a site.)

When the ASCE 7 or IBC refers to the short-period spectral acceleration, Ss, this is the ordinate on the ASCE 7–10 design response spectrum (for Site Class B, 5% damping, and corresponding to the MCE at that specific site) corresponding to a building or structural natural period equal to Ts (i.e., the design short period for that location).

When the ASCE 7 or IBC refers to the 1-second spectral acceleration, S1, this is the ordinate on the ASCE 7–10 design response spectrum (for Site Class B, 5% damping, and corresponding to the MCE at that specific site) corresponding to a building or structural natural period equal to 1 second.

The PGA (peak ground acceleration) is the spectral acceleration at a period equal to zero seconds (i.e. a rigid or very, very, very stiff structure).

Link to Quora question (and answer/s) is here.