Geology Reference
In-Depth Information
With respect to the elastic cable seismic
isolation device, the isolation mechanism, the
influences of the elastic cable stiffness on the
bridge structural dynamic characteristics, the
force transmission paths and the displacement and
force demands have been discussed for another
floating cable-stayed bridge. Numerical analysis
results show that the fundamental period of the
bridge decreases rapidly when the cable stiffness
increases. The vibration modes will change if the
cable stiffness increases to some extent, and the
displacement demands decrease rapidly when the
stiffness increases. The bending moment demands
fluctuate in small amplitude, while the seismic
shear force demands monotonically increase.
For the new-type SCC bridge, the seismic
potential is further confirmed based on response
spectrum analyses of a four span continuous
girder bridge and a long span SCC arch bridge.
Analysis results show that the SCC continuous
girder bridge with same span and deck width has
lighter superstructure, less pier stiffness and fun-
damental period. Also the shear force and bending
moment at the pier bottom and the displacement
at pier top all decrease significantly. For the long
span SCC arch bridge, it also has lower seismic
force and displacement demands than a reinforced
concrete bridge.
When the components of bridge locally become
plastic, the overall conceptual seismic design is
not applicable because of the limitation of overall
linear analyses. The local nonlinear seismic capac-
ity design is therefore beneficial for its economy,
applicability and validity.
Innovation of Cable Sliding Friction
Aseismic Bearing for Bridges
The girders of continuous bridges are generally
supported by bearings which transmit loads to
underlying piers and abutments. Bearing system
generally comprises a fixed bearing on one pier and
several frictional bearings on other piers. Under
minor or moderate horizontal earthquake actions,
almost all the superstructure's earthquake-induced
forces are transmitted to the fixed pier which may
thus be damaged because of the excessive shear
force or bending moment. If the fixed bearing is
designed to fail under severe earthquakes so as
to protect the pier system, all the other frictional
bearings will be mobilized to slide so that the bridge
system will be difficult to maintain equilibrium.
A new cable sliding friction aseismic bearing
(Figure 14) is invented and presented, which is
composed of the pot bearing, some cables and a
shear bolt. Through reasonable design, the bearing
may perform as same as a fixed bearing system,
namely keep in service under minor or moderate
earthquakes. Moreover, the shear bolt of the new
bearing will fail during severe earthquakes, and
then a bearing originally used as a fixed bearing
will be converted into a frictional one. Hence, the
seismic force can be shared by all the piers not
only by the fixed pier, while the excessive seismic
displacement can be restricted by the cables at-
tached to the base of the bearing.
As an improved type of frictional isolation
devices, the new bearing is characterized by its
insensitivity to the frequency content of earthquake
excitations. It can be used in conventional girder-
system bridges, cable-stayed bridges, suspension
bridges and other similar structures. Compared
LOCAL SEISMIC CAPACITY DESIGN
FOR COMPONENTS OF BRIDGES
Earthquakes have a habit of identifying structural
weaknesses and concentrating damage at these
locations (Priestley, Seible & Calvi, 1992). Lots
of investigations on earthquake disaster show
that bridge damage caused by earthquakes mainly
focuses on local regions and weak points of bridge
components, such as bearing failures, pier failures,
pile foundation failures, expansion joint failures,
and so on. Considering the stochastic character-
istics of earthquakes, keeping bridges in elastic
state permanently is impossible and unreasonable.
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