Geology Reference
In-Depth Information
Table 9. Two different design schemes with dif-
ferent arrangements of bearings
demands are significantly reduced by 59%, when
the new bearing takes the place of the original
one. And other shear forces are also reduced at
the pier bottoms of other piers except for the almost
equal shear forces at the pier bottoms of the pier
PN2. Furthermore, the possible maximum dis-
placements of the deck relative to the piers during
a severe earthquake that causes the conventional
fixed bearings at pier PS1 to lose fixity may range
from 268 mm to 280 mm. Yet the deck displace-
ments at all four piers are controlled to be less
than 160 mm by using the new bearing.
Moreover, the seismic capacity checks are
shown in Table 11 for the most unbeneficial pile
of the bridge. It can be seen that the checks can-
not pass when the original bearing is used on the
fixed pier PS1. However, the checks can pass
when the new bearing replaces the original one.
So it can be concluded that the new bearing can
decrease the seismic demands and be effective to
protect the bridge piers and foundations.
Design
scheme
Pier
PN2
Pier
PN1
Pier PS1
Pier
PS2
Original
design
Slid-
ing
bear-
ings
Sliding
bearings
Conventional fixed
bearings
Slid-
ing
bear-
ings
Alterna-
tive
design
Slid-
ing
bear-
ings
Sliding
bearings
Proposed cable slid-
ing friction
aseismic bearings
Slid-
ing
bear-
ings
For the nonlinear time history analysis of the
bridge, two design schemes are considered, (i)
the original design with the conventional fixed
bearings on the fixed pier PS1; (ii) the alternative
design with the cable sliding friction aseismic
bearings on the same pier. Besides, all other bear-
ings are the same sliding ones for the two design
schemes and the arrangement of the bearings is
listed in Table 9.
Considering the seismic demand variations of
the bridge along with the stiffness of the cables
and many cables used in the new bearing resulting
in the larger supplied stiffness, so the cable stiff-
ness in the horizontal direction is taken as about
3.0×10
5
kN/m in the application study. After the
analyses, shear force demands at pier bottoms and
deck-pier relative displacements are shown in
Table 10. Note that the shear force is normalized
with the deck weight. For the shear force com-
parisons, the bearings at PS1 are of conventional
fixed type in the theoretical models of the bridge,
because the bearings in fixed conditions have
relative more disadvantageous seismic force
demands. For the deck-pier relative displacement
comparisons, the fixed bearings are assumed to
have lost fixity and be free to move during a severe
earthquake, focusing the performance of the
original and the new bearings. It can be seen that
the shear force demand at PS1 is much larger than
those at the other three piers by using the original
bearing on the fixed pier PS1. Yet the excessive
Seismic Performance of Bridge Piers
Reinforced with SFRC
There have been numerous studies on steel fiber
reinforced concrete (SFRC), most of which aimed
at the constitutive behavior (Zollo, 1997). These
studies generally ignored an important fact that
the SFRC is more likely conducted in confined
conditions. Ramesh, Seshu and Prabhakar have
made experimental analyses of 90 specimens and
pointed out that the SFRC confined by lateral ties
has improved material properties (Ramesh, Seshu
& Prabhakar, 2003). Then a constitutive model
of SFRC, which has been widely accepted, is
offered as Figure 21. The constitutive equations
are also shown as Eq. (2), (3) and (4), in which
C
)
(
)
(
'
and
RI
is the rein-
f
f
b s
=
P
−
P
v
c
i
b
bb
forced index.
(
)
(
(
)
)
'
P
=
f
1
+
0 55
.
C
1 0228
.
+
0 1024
.
RI A
+
f A
c
i
g
y
g
(2)
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