Geology Reference
In-Depth Information
INTRODUCTION
1. Taking a long span continuous girder bridge
as an example, an optimal design for the
layout and detail of the bridge components,
including geometry of piers, arrangement of
piers, location of expansion joint or braking
pier, is carried out so as to reduce the seismic
demands in the transverse direction as much
as possible. The seismic performance of the
bridges with different adjustments in differ-
ent site conditions is calculated respectively.
Based on the comparison of the results, the
forms of some piers and the locations of
expansion joints are required to be adjusted
to improve the bending stiffness distribution
for the bridge.
2. Taking a long span cable-stayed bridge as an
instance, the original design proposal makes
use of the inverted Y shape bridge tower,
while the seismic design dominated by the
first longitudinal vibration mode may lead
to overlarge relative displacement between
the girder and the tower. In order to solve the
critical problem, a new-type spatial bridge
tower is proposed by integrated analyses
of the structural dynamic characteristics,
design displacement and seismic responses.
Compared with the original tower, the new
spatial tower improves the seismic perfor-
mance of the bridge significantly.
3. With respect to the elastic cable seismic
isolation device installed between the girder
and the lower horizontal beam of the tower
to mitigate excessive seismic effects, the
influences of the elastic cable stiffness on
the dynamic characteristics and the seismic
demands are investigated by parametric fi-
nite element analyses of a real cable-stayed
bridge. The seismic isolation mechanism of
the elastic cables is discussed.
4. Girders of the SCC bridge are composed
of the structural steel and the concrete.
Compared with a conventional concrete
girder bridge with the same span, the su-
perstructure height and weight are gener-
To give clear and correct directions for seismic
design optimization of bridges, the “overall con-
ceptual seismic design” and the “local seismic
capacity design” methods are proposed to obtain
uniform and rational seismic demands and im-
proved seismic capacities of structural components
in seismic design of bridges.
There are many methods to realize seismic
design optimization so as to improve the seismic
performance of structures (Gong, 2003; Li, 1997;
Liu, 2003; Vagelis, 2009; Zou, 2002). However,
the structural seismic design optimization will be
in wrong direction and invalid unless the initial
structural seismic design itself is appropriate and
rational. It is hoped that the strategies and methods
proposed in the chapter are able to give clear and
correct directions for seismic design optimization
of bridges.
There are two paths to improve the seismic
design of bridges so as to make the seismic
demands more uniform and rational along struc-
tural components. One is to reduce the seismic
demands as much as possible, and the other is to
increase the seismic capacities. Correspondingly
there are two design methods, the overall linear
seismic conceptual design and the local nonlinear
seismic capacity design. From overall to local
design strategies, some new ideas and strategies
of seismic design which can effectively improve
seismic performance of bridges are proposed
separately in this chapter.
Overall conceptual seismic design is a con-
ceptual design method applicable for the whole
structure based on the linear seismic analysis.
When the components of bridges work in an elas-
tic state during the earthquakes, the conceptual
design will be an effective and efficient strategy.
From the perspective of overall conceptual seismic
design, four conceptual seismic design strategies
are proposed focusing on the whole structure.
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