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much higher than the bending strength. Seismic
capacity comparisons between the piers wholly
and locally strengthened with SFRC show that
applying SFRC locally in a reasonable area of
the single-column pier almost has the similar
effect in improving the ductility and the bending
strength as applying the SFRC in the whole pier.
Then the plastic hinge length and the reasonable
range locally strengthened with SFRC are clearly
determined, considering that the present seismic
guidelines of several countries have different
definitions of the plastic hinge length for the
single-column bridge pier reinforced with SFRC.
For pile group foundations reinforce with SPPs,
the seismic capacities, the hysteretic performance
and energy dissipation capabilities are studied
by numerical simulations and low cycle loading
experiments. The pushover analysis results show
that the seismic capacity, including the ductility
and the lateral resistance of the pile group foun-
dation reinforced with SPPs, is better than the
original one without SPPs. The lateral resistance
of the edge piles increases, while the maximum
curvature decreases significantly along with the
increasing of the SPPR. The experiments and the
finite element analysis comparisons show that
the strength and the ultimate displacement of the
foundation models strengthened with SPPs are
better those of the RC ones. The hysteretic energy
dissipation capabilities of the models strengthened
with SPPs are much better than those of the RC
models, while the equivalent viscous damping
ratio is reduced by 41.7%. The pinching effects of
RC models are more obvious, while the hysteretic
loops are plumper for models strengthened with
SPPs. Comparisons between the experimental
and numerical responses show that the numerical
results agree with the experimental trends well.
tion. Undoubtedly, there are still many aspects
need to be studied to obtain more optimal seismic
performance for bridges, while this chapter mainly
focuses on two methods: (i) the overall conceptual
seismic design for whole bridges in a linear and
elastic state; (ii) local seismic capacity design for
components of bridges in a nonlinear and plastic
state. The seismic design strategies proposed in the
chapter consider the displacement requirements
of bridges greatly, but they are still not enough to
attain the complete displacement-based design. So
the displacement-based design methods should be
further promoted in the future, since the limitations
of the force-based design methods are more and
more obvious for bridges.
The overall conceptual seismic design mainly
focuses on typical bridges in this chapter. With
the increase of irregular bridges constructed in
earthquake regions, more attention should be paid
to their seismic performance, and how to conduct
the overall conceptual seismic design and local
seismic capacity design of them in the future.
Moreover, the stochastic seismic performance of
bridges with the cable sliding friction aseismic
bearing should be emphasized in future research,
since the determinate seismic performance has
been carefully studied in the chapter. For the pile
group foundation strengthened with SPPs, the
erosion problem of steel pipes and its influences
on the seismic design of foundations should be
further promoted.
CONCLUSION
To give clear and correct directions for seismic
design optimization of bridges, some new seismic
design strategies are presented to obtain uniform
and rational seismic demands and improved
seismic capacities of structural components in
seismic design of bridges, according to two design
methods: the “overall conceptual seismic design”
and the “local seismic capacity design”.
FUTURE RESEARCH DIRECTIONS
As an important lifeline project, seismic design
of bridges should be paid more and more atten-
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