Geology Reference
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Figure 7. Original and alternative spatial bridge towers
Comparison of Seismic Responses
the tower top increases from 0.20 m to 0.41 m, this
0.41 m figure is considered small and practically
acceptable for the long span cable-stayed bridge.
The force demand comparisons are shown in
Table 5 between the original inverted Y shape and
the proposed spatial tower models. The total force
demands at the spatial tower bottoms are slightly
larger than those at the inverted Y tower, while
the demands in each column No. 1, 2, 3 and 4
(Figure 7) of the spatial tower model are less than
or almost equal to those of the original one. It can
be concluded that the conceptual design strategy
for the cable-stayed bridge, which adopts the
spatial tower to replace the original inverted Y
shape tower, enables the seismic demands more
uniform along the structural components and
obtain a balance between the force and displace-
ment demands.
By using the design response spectra (Figure 5)
which are from the geological safety evaluation
in the field and fit for the site situation for the
bridge, the response spectrum analyses are con-
ducted respectively in the longitudinal direction
and in the transverse direction under correspond-
ing horizontal and vertical ground motions. The
displacement demand comparisons are shown in
Table 4 for the original design tower model and the
alternative spatial tower model. It can be seen that
the maximum longitudinal seismic displacements
at the deck end, the tower top and the midspan are
reduced significantly for the spatial tower model.
Since the spatial towers' constraint to the deck
becomes stronger, the transverse displacement
at the midspan of the alternative model is also
reduced. Although the transverse displacement of
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