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Re: Questions on UBC-97 Seismic code[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaoc(--nospam--at)seaoc.org
- Subject: Re: Questions on UBC-97 Seismic code
- From: "Samuel K Kassegne, Ph.D." <ramusa(--nospam--at)ramanalysis.com>
- Date: Thu, 13 Nov 1997 16:27:30 -0800
November 13, 1997 Hi: Thanks Sasha, Bill, Stan and Chang for taking the time to address the question posed last week. Sasha said: "I just attended the SEAONC seminar on UBC'97. I have to say that I also share your confusion. Unfortunately, your question has not been addressed there. One thing that I've noticed is that the Ca coeff. is for short period of vibration part of the spectrum (flat area of constant acceleration). Could it be that the soft soils are not affecting stiff buildings as much? But then again it should be the same for all seismic zones, but it is not? Any other opinions? " Exactly....look at the Cv coefficient which controls the base shear for less stiff buildings (relatively high period). You will notice that this coefficient (also referred to as the "velocity-related acceleration") indeed increasers with soil type. It assumes a value of 0.96 for Soil SE and 0.64 for Soil SD, 0.32 for soil SA. What this means is that for less stiff buildings, the design base shear under SE could be 1.5 times that of Soil SD; However, for stiffer buildings, the design base shear could be as low as 80% of that of Sd soil condition. Again, this leaves one with the question: * Why does the non-linear effect reduce only Ca and not Cv, especially, since according to the sources quoted, soil loses its strength under high seismicity? Could some one attending the upcoming SEAONC seminar ask the presenters this question, please? regards, Samuel Kassegne, Ph.D.
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