Overall Conceptual Seismic Design and Local Seismic Capacity Design for Components of Bridges - Structural Seismic Design Optimization and Earthquake Engineering - page 277

Figure 4. Conceptual design strategy for bridge
pier in soil type III condition

From the comparison between the results in
Table 3 and those in Table 1, it can be seen that
the displacements, the shear and normal stresses
are all reduced, indicating that the proposed con-
ceptual design strategies can improve the seismic
performance of the bridge.

Design of Towers for Long
Span Cable-Stayed Bridge

From the perspective of overall conceptual seismic
design, both force and displacement demands
should be taken into consideration. However the
force and displacement responses are usually mu-
tually contradictive. As can be seen from the design
response spectra (Figure 5) for a special bridge,
the Sutong Yangtze River Bridge in China (Yan
& Yuan, 2004), in the long period range the ac-
celeration amplification is relatively small and yet
the displacement amplification may be too large
to be tolerated. So for the flexible cable-stayed
bridge, a structural period lengthening would be
effective to reduce the force demands and yet
ineffective to decrease the excessive displacement
demands at the tower top and the deck ends. It is
obvious that the flexural stiffness of the tower has
a major influence on the fundamental period of
the cable-stayed bridge. Therefore it is preferable

Therefore for soil Type III, the conceptual design
strategies are proposed as follows: (i) relocate the
expansion joint at pier No. 10 to No. 8 in order
to adjust the stiffness distribution of the super-
structure and to avoid the uneven seismic force
demands caused by the transverse rotation of
girders, (ii) separate the SSPs No. 8, 9 and 10 into
STPs (Figure 4) to modify the transverse stiffness
thus to restrict the seismic displacements for these
piers. The seismic demands are listed in Table 3
for the upgraded bridge.

Table 3. Seismic demands of the upgraded bridge for soil type III condition

Pier No. Pier type Bending stiffness

(×10 3 kN/m)

Disp. (m) Shear stress (MPa) Normal stress (MPa)

1 STP 521.0 0.030 5.840 5.480

2 STP 52.60 0.060 1.200 1.460

3 SSP 4.170 0.089 0.920 9.360

4 HSP 3.170 0.098 0.180 6.790

5 HSP 2.800 0.110 0.210 7.320

6 HSP 2.490 0.120 0.270 8.310

7 HSP 2.800 0.130 0.250 8.680

8 STP 24.60 0.140 2.780 1.770

9 STP 30.50 0.120 2.840 2.310

10 STP 43.20 0.094 3.150 1.900