Seismic response spectrum parameters 2

[LOKSTR]

Why in the ASCE7 or other codes, the Seismic acceleration parameters(Ss and S1) for 0.2sec and 1.0 sec period only?

What is the significance of 0.2 sec and 1.0 sec time period in Response spectrum curve?

Does it have something to do with natural frequency range of ground?

I am looking for relevant references/papers for reasoning.

Thx.

 

[Qshake]

You can find an answer in Chopra's Dynamics of Structures: Applications to Earthquake Engineering.

The essence of this is that you have the envelope of two considerations affecting structures based on their natural period.

The 0.2s is obviously the short period RS and represents a moderate earthquake close to the structure site. Here you will have maximum values of acceleration at small periods but your longer period portion of the curve dissapates rapidly.

On the other hand, a long period RS, 1.0s, representing a large earthquake far from the structure site, has a smaller acceleration in the lower periods but the curve doesn't drop off the way the 0.2s curve does and remains relatively flatter for a longer period.

At some point the two curves will overlap and so you have a controlling situation for which to take the envelope of for the both.

The text will reference more papers.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[LOKSTR]

Thanks Qshake.