Civil Engineering Reference
In-Depth Information
C
n
T
s
Natural period,
T
n
(seconds)
FIGURE 4.27
Typical AREMA design response spectrum used with simple dynamic
analyses.
method (Equation 4.51) or the method often referred to as the 100%-30% rule
(Equations 4.50a and b) to combine the seismic loads.
F
T
+
F
L
.
F
=
(4.51)
Example 4.21
The normalized response spectrum is required for a 100 ft long steel girder
span with the following properties:
Weight: 3000 lb/ft
I
x
=
100,000 in.
4
5000 in.
4
I
y
=
ξ =
3%
The bridge is located where
A
=
10% and founded on material with
S
=
1.0 (rock)
3
/
2
T
s
=[
0.48
(
1.0
)
]
=
0.33 s
0.142
T
2
/
3
n
C
n
=
≤
0.30.
The normalized response spectrum is shown in Figure E4.11.
Normalized response spectra (ex. 4.21)
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0
0.1 0.2 0.3 0.4 0.5
Period,
T
(seconds)
0.6 0.7 0.8 0.9
1
FIGURE E4.11
