# Re: Response Spectrum Analysis

• To: <seaint(--nospam--at)seaint.org>
• Subject: Re: Response Spectrum Analysis
• From: "Jason Emoto" <jasone(--nospam--at)kpff.com>
• Date: Fri, 4 Feb 2000 10:12:40 -0800
```The equations for spectral accelerations for the '97 UBC design response
spectra (Figure 16-3) are as follows:

IF T<To             SA = Ca+1.5*Ca/To*T*g
IF To<T<Ts      SA = 2.5*Ca*g
IF T>Ts             SA = Cv/T*g

Plugging your values into these equations yields:

T(s)       SA(g)
0.000   0.360
0.120   0.900
0.600   0.900
1.600   0.875
2.600   0.850
3.600   0.825
4.600   0.800
5.600   0.775
6.600   0.750
7.600   0.725
8.600   0.700
9.600   0.675

The number of period time steps you use will affect the accuracy of your
analysis.  Because these numbers are fairly easy to generate using a
spreadsheet and computing time is pretty fast these days, I would recommend
using a fairly small time step after Ts.

Jason Emoto

----- Original Message -----
From: "Gobo, Gina" <ggobo(--nospam--at)DLRGROUP.com>
To: "'seaint'" <seaint(--nospam--at)seaint.org>
Sent: Friday, February 04, 2000 9:47 AM
Subject: Response Spectrum Analysis

I am doing a response spectrum analysis of a steel covered playground. I am
using an older version of SAP2000 that has the 94 UBC response spectrum
functions for soil types S1, S2, S3. I would like to manually input a
response spectrum from the 97UBC. I understand that when T = 0, Ca = 1.00
and from To through Ts Ca = 2.5. What I am not clear about are the points in
between. I know that when T>Ts, Ca =Cv/T, but I was not sure what increments
of T should be used. I just used increments of 1.00. after Ts. I have
generated the response spectrum curve from the 97UBC as follows:

Cv = 0.54
Ca = 0.36

T Ca
0 1
.12 2.5
.60 2.5
1.6 0.34
2.6 0.21
3.6 0.15
4.6 0.12
5.6 0.10
6.6 0.08
7.6 0.07
8.6 0.06
9.6 0.06

Is this correct? or, should I figure out an equal number of increments from
Ts = 1.6 to T = 10? Does someone have an example function that I could look
at? What parameters are typically used for the response spectrum analysis
using SAP2000?

Gina T. Gobo, E.I.T.
Structural Engineering
DLR Group
Seattle
Ph. 206.461.6000
Fax 206.461.6049
ggobo(--nospam--at)dlrgroup.com

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