Overall Conceptual Seismic Design and Local Seismic Capacity Design for Components of Bridges - Structural Seismic Design Optimization and Earthquake Engineering - page 278

Figure 5. Design response spectra for the Sutong
Yangtze River Bridge (Yan & Yuan, 2004)

tions to the towers. The design acceleration and
displacement response spectra are shown in Fig-
ure 5 and the peak value of the design horizontal
ground acceleration is 0.197g, which is about
twice of the vertical acceleration input.

Conceptual Seismic Design

Flexible structures always have relatively long
fundamental periods. From dynamic analysis,
the fundamental period of the above cable-stayed
bridge is estimated as 13.40 s, a typical long period.
Since the fundamental period is much affected by
the flexural stiffness of the tower, a new-type spa-
tial tower scheme is proposed as shown in Figure
7b after a series of response spectrum analyses
and comparisons. The bending stiffness of the
proposed alternative tower (65.5×10 3 kN/m) is
9.66 times of the original tower (6.78×10 3 kN/m),
while the weight (1.17×10 6 kN) is just 1.83 times
of the original (0.638×10 6 kN). In conclusion the
proposed spatial tower can significantly increase
the flexural stiffness yet with relatively small
additional material cost. The fundamental period
of the bridge with the proposed spatial towers is
reduced from 13.40 s to 5.87 s.

to adopt an optimal tower type for the bridge's
fundamental period within a proper range so that
acceptable force and displacement demands can be
achieved in the seismic conceptual design phase.
The Sutong Yangtze River Bridge (Yan &
Yuan, 2004), whose finite element model is shown
in Figure 6, is a long span floating cable-stayed
bridge originally with inverted Y shape bridge
towers. The spans are 100 m, 100 m, 300 m, 1088
m, 300 m, 100 m, 100 m and the superstructure
is designed as a floating system without connec-

Figure 6. Finite element model of the Sutong Yangtze River Bridge