Civil Engineering Reference
In-Depth Information
a
b
c
5
160
80
Field testing
Dynamic model
Field testing
Dynamic model
Field Testing
Dynamic model
4
40
64.4
km/h
(40
mph
)
64.4
km/h
(40
mph
)
120
64.4
km/h
(40
mph
)
3
0
80
2
40
1
40
0
0
0
-1
-40
02468 0 2 4 6
02468 0 2 4 6
0 2 4 6 8 10121416
Time (s)
Time (s)
Time (s)
Fig. 13.5
Model validation (
a
) Deflection data, (
b
) Velocity data, (
c
) Strain data
13.4 Comparison with Arema Specifications
The dynamic effects of moving vehicles on bridges are important in the design and evaluation of their overall performance.
In AREMA [
5
], for steel railway bridge, (
13.4
) was proposed to account for the vertical effect of the dynamic effect
excluding the rocking effect (20% of live load).
8
<
3
L
2
3
L
2
Þ
1600
¼
ð
ft
ð
m
Þ
40
40
6
)
L
80
ft
¼
24
m
148
:
IF
¼
(13.4)
:
600
182
:
9
16
þ
30
¼
16
þ
1
)
L
>
80
ft
¼
24
m
L
ð
ft
Þ
L
ð
m
Þ
9
:
where
L
is the span length.
For train speeds below 96.6 km/h (60 mph), for all spans carrying equipment without hammer below, and for all spans
other than truss spans carrying equipment with hammer below, the values of the vertical effects of the impact equations shall
be multiplied by the following factor:
2
8
2500
0
:
62
100
Skm
8
2500
0
:
2
1
60
ð
=
h
Þ
¼
1
ð
60
S
ð
mph
Þ
Þ
0
:
2
(13.5)
where
S
is the running speed.
Figure
13.6a
show the impact factor of the selected bridge under the effect of a passing 1,272 kN (286 kips) freight car.
For the static design, the maximum impact factor is 5% while the maximum impact factor for fatigue is 10%. Figure
13.6b
shows that the maximum values for dynamic impact factor and fatigue impact factor are 11% and 22%, respectively. This
suggests that the value for the fatigue impact factor is twice as high as the dynamic impact factor. This can be attributed to
the free vibration component. When the freight car runs over the bridge, both the impact factor for fatigue and dynamic
impact factor are below the value from AREMA Specifications. However, for the passenger car, when the running speed is
above 170 km/h, the impact factor for fatigue is slightly larger than the AREMA Mean Impact Factor. This suggests that
AREMA would slightly underestimates the dynamic amplification in the fatigue design at higher speeds. Therefore, for
passenger car, the speed restriction should be applied to reduce the stress range associated with dynamic amplification.
