Environmental Engineering Reference
In-Depth Information
Period = 6.0 sec
100
75
60
25
0
−
25
−
50
−
75
−
100
0
5
10
15
Seconds
20
25
30
Period = 0.4 sec
12
9
6
3
0
−
3
−
6
−
9
−
12
0
5
10
15
20
Seconds
0.01
0.1
1.0
Period (sec)
10.0
100.0
Input acceleration history
1.0
0.5
0.0
FIGURE 11.43
Construction of tripartite elastic
design response spectrum. (From
USACE, U.S. Army Corps of
Engineers, ER 1110-2-6050, June
30, 1999. With permission.)
−
0.5
−
1.0
−
1.5
0
5
10
15
sec
20
25
30
Response spectra are typically used to illustrate the characteristics of earthquake shak-
ing at a site. There are two forms of response spectra, standard or normalized and site-spe-
cific.
Site-specific response spectra
are usually plots of accelerations
g
vs. a range in period
for a specific percent damping. An example is given in
Figure 11.18,
a family of curves for
the Mexico City event of 1985 (see discussion
Section 11.2.6)
.
Standard or normalized response spectra
plots are provided for particular areas based on
strong motion data. For example, the USGS has prepared a series of maps for California
and Nevada, and the Continental United States, showing pseudo-acceleration spectral
response for 5% damping, for various periods, and 10% probability of exceedance of 50
and 250 years (USACE, 1995). An example is given in the
Figure 11.44.
Such maps are
included in the 2000 International Building Code.
Applications
Response spectra are used as input in dynamic analysis of linear elastic systems, i.e., they are
a convenient means of evaluating the maximum lateral forces developed in structures sub-
jected to a given base motion. If the structure behaves as a single-degree-of-freedom system,
