Seismosoft | Earthquake Engineering Solutions

Dear All,

I would like to ask your opinion about determining seismographs according to requirement in ASCE 7-10.
It is mentioned that:
"For each pair of horizontal ground motion components, a square root of the sum of the squares (SRSS) spectrum shall be constructed by taking the SRSS of the 5-percent damped response spectra for the scaled components (where an identical scale factor is applied to both components of a pair). Each pair of motions shall be scaled such that for a period between 0.2T and 1.5T, the average of the SRSS spectra from all horizontal component pairs does not fall below the corresponding ordinate of the response spectrum used for design"

To fulfill above requirement, can I just simply put a factor of 1/(2)^0.5 or 0.7071 on the target spectra, and generate 2 seismographs that matches to the "reduced target spectra" and use them as a "pair" ground motion?

Thank you.

Regards,

Tri

Hi trisuryadi.

Well, your proposed strategy will certainly produce a ground motion pair which does meet the stated criteria. Whether or not this would result in a realistic ground motion pair is not as certain.

Using the same target for both components loses the fact that, in most cases, one component is stronger than the other. You might also run the risk of generating two components which are strongly correlated to one another, while it has been shown that real ground motion pairs have a correlation factor typically no greater than 0.30.

The science of ground motion selection and modification is undergoing great advances in recent years and continues to do so. I recommend reading:

Hadjian, "On the Correlation of The Components of Strong Ground Motion", BSSA 71(4), 1981.
NIST GCR 11-917-15. "Selecting and Scaling. Earthquake Ground. Motions for Performing. Response-History".

The forum is really for Seismo-software suite questions. But if you need some further guidance, please feel free to send me an e-mail and I will try to calrify my comments. Best of luck.

Hi Huffte,

Thank you for your prompt reply, It is very clear and understandable.
I have one of the reference that you mentioned, I will try to look more deeper in it.

Regards,

Tri.