Geology Reference
In-Depth Information
Table 15. Plastic hinge lengths according to dif-
ferent guidelines
nently existence and be taken as a part of the piles
and a strengthening measure for the pile. But the
seismic performance is still not fully determined
for the pile group foundations with SPPs.
Pier model
New
Zealand
Euro Code 8
AASHTO
M3
3.750
1.840
1.890
Seismic Capacity
M4
4.000
2.240
2.290
In order to investigate the effect of the SPPs on
the seismic performance of the foundation, a real
pile group foundation comprising of 9 reinforced
concrete piles and a cap (Figure 25) is taken as
an example. Four different scale-models are es-
tablished to study the seismic capacity of the pile
group foundation: (i) Model 1, all piles without
SPPs, (ii) Model 2, only edge piles strengthened
with SPPs in local regions from the pile top to the
second plastic hinge under the ground surface, (iii)
Model 3, only the edge piles strengthened with
SPPs along the total pile height, and (iv) Model
4, all the piles strengthened with SPPs along the
total pile height. For latter three models, the area
of SPP accounts for 1.4% of the whole section
area. Other parameters of the models are listed
in Table 16.
Depending on the results of pushover analyses,
the seismic capacity comparisons are shown in
Figure 26 for Model 1 to 4. The seismic capacity
variations for the edge pile in Model 3 are pre-
sented in Figure 27 along with the steel protective
pipe ratio (SPPR) ranging from 0 to 2.5%. More-
over the section curvature variations in yielding
state and in ultimate state are presented in Figure
28 for edge piles in Model 3. It can be seen that
the seismic capacities, including the ductility and
the lateral resistance of the pile group foundation
strengthened with SPPs, is better than those of
the foundation without SPP. The lateral resistance
of the edge piles increases, while the maximum
curvature decreases significantly along with the
increasing of the SPPR. Therefore the potential
is significant for the pile group foundation
strengthened with SPPs.
of several countries, it is shown in Table 15 that
the plastic hinge lengths differ from each other
greatly for the pier M3 and M4 reinforced with
SFRC (Zhu, Fu, Wang & Yuan, 2010).
Then for a single-column bridge pier, the
reasonable length
l
c
of local region reinforced
with SFRC is given as Eq. (5), in which
f
cy
and
f
fy
are respectively the compressive yield stress-
es of the original reinforced concrete and the
SFRC.
(5)
l
= −
(
1
f
f
)
l
c
cy
fy
Considering the extra-strength of the original
reinforced concrete, the equation can be modified
as the following Eq. (6), where
φ
is the extra-
strength coefficient. And the coefficient
φ
is
suggested to be 1.2 to 1.4.
(6)
l
= −
(
1
f
φ
f
)
l
c
cy
fy
Seismic Performance of
Pile Group Foundations
Strengthened with SPPs
The pile group foundations consisting of a group
of piles and a cap supported by the pile group are
widely used in large bridge projects. The pile group
foundations are usually vulnerable components
under earthquakes. Steel protective pipes (SPPs)
are always used in construction as formworks for
the underwater in situ concrete piles. After the
bridge is completed, the SPPs can be of perma-
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