Seismic Site Response Analysis with 2007 CBC and ASCE-7
Seismic Site Response Analysis with 2007 CBC and ASCE-7
(OP)
Hello all,
The new 2007 CBC which is based on the 2006 IBC provides requirements for performing seismic site response analysis. The 2007 CBC actually references ASCE 7 for the details of the requirements.
A big problem I see with the ASCE 7 recommendations is that they require you to develop the response spectrum and time-histories using the MCE (2475 year return period EQ), then to scale the response down by 2/3 to come up with the design response spectrum and time-histories.
The problem is the site response you obtain by using the MCE input ground motion will be very different from what I would obtain by using 2/3 of the MCE ground motion. In using the MCE input ground motion, most all saturated sandy sites will liquefy and will have a base-isoltaed type of response after the liquefaction occurs. This is because the MCE PGA is at least 0.6g at least in my area of Southern California. I am using a non-linear effective stress code for the analysis.
Scaling this response down by 2/3 will retain the characteristics of the base-isolated type of response.
I believe the input ground motions should be based on 2/3 of the MCE, this way the estimated site response would be more represetitive of the site. But the ASCE 7 appears very clear that the input motion should be based on the MCE.
Anyone have thoughts on this topic?
Thanks
The new 2007 CBC which is based on the 2006 IBC provides requirements for performing seismic site response analysis. The 2007 CBC actually references ASCE 7 for the details of the requirements.
A big problem I see with the ASCE 7 recommendations is that they require you to develop the response spectrum and time-histories using the MCE (2475 year return period EQ), then to scale the response down by 2/3 to come up with the design response spectrum and time-histories.
The problem is the site response you obtain by using the MCE input ground motion will be very different from what I would obtain by using 2/3 of the MCE ground motion. In using the MCE input ground motion, most all saturated sandy sites will liquefy and will have a base-isoltaed type of response after the liquefaction occurs. This is because the MCE PGA is at least 0.6g at least in my area of Southern California. I am using a non-linear effective stress code for the analysis.
Scaling this response down by 2/3 will retain the characteristics of the base-isolated type of response.
I believe the input ground motions should be based on 2/3 of the MCE, this way the estimated site response would be more represetitive of the site. But the ASCE 7 appears very clear that the input motion should be based on the MCE.
Anyone have thoughts on this topic?
Thanks
Talk To Other Members
RE: Seismic Site Response Analysis with 2007 CBC and ASCE-7
http
in particular, look at 451 and 451B under "new buildings". maybe this will help.
RE: Seismic Site Response Analysis with 2007 CBC and ASCE-7
Thanks but those publications are for design of structural aspects and are also not specific to the requirements of the California Building Code (CBC) and the ASCE-7 publication that is referenced in the CBC. I know how to perform the analysis and have done it before, it is the new requirement that the base motion conform to the MCE motion that I do not agree with.
RE: Seismic Site Response Analysis with 2007 CBC and ASCE-7
Mike McCann
McCann Engineering
RE: Seismic Site Response Analysis with 2007 CBC and ASCE-7