define spectrum

02-Analytical capabilities
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hosseini_memory
Posts: 7
Joined: 04 Dec 2016, 08:03

define spectrum

Post by hosseini_memory »

hi
Please help me about define spectrum (from file) for matching and scaling.
should I multiply values of spectrum by 1.4 before matching as UBC cobe said
" (SRSS) Of The Two Horizontal Components Should Not Be Less Than 1.4 The Design Spectrum Ordinates In The Range From 0.2T To 1.5T (UBC 1997 )"
huffte
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Joined: 22 Jul 2011, 10:19
Location: Cookeville, Tennessee, USA
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Re: define spectrum

Post by huffte »

If you are strictly bound to use the UBC SRSS criteria, then there are a number of ways to go. This SRSS-method of modification is not the preferred method using the current science however. It is critical that you know the nature of the target spectrum - is it a geometric mean spectrum, or is it a maximum direction spectrum? For guidance on preferred modification methods, see NIST GCR 11-917-15, Selecting and Scaling Ground Motions for Performing Response-History Analyses. It is freely available online.

If you are bound to the SRSS scaling/matching, then you could match each component to the target (not 1.4 times the target). Then the SRSS of the components would be SQRT(2) times the target = 1.414 times the target. In doing this, however, you lose the relative intensity variation of the two components. Another way would be to assume some value - say y - for the ratio of the maximum component to the minimum component. Then, to make the SRSS of the two components equal to 1.4 times the target:

SQRT[(H1)^2 + (H2)^2] = 1.4TARGET
SQRT[(H1)^2 + (yH1)^2] = 1.4TARGET
..
..
H1 = 1.4TARGET(1/SQRT[1+y^2])
H2 = 1.4TARGET(y/SQRT[1+y^2])

Using, as an example, y=1.2 gives:
H1 = 0.8963TARGET
H2 = 1.0755TARGET

You would match one component to 0.8963 times the target and the second component to 1.0755 times the target.
Tim Huff
hosseini_memory
Posts: 7
Joined: 04 Dec 2016, 08:03

Re: define spectrum

Post by hosseini_memory »

thanks so much for nice reply
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