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					           EFECTIVE ESS OF I -CORE SHIELD METHOD FOR
       IMPROVI G THE SEISMIC PERFORMA CE OF RC COLUM S

          Student Number: 08M16170 Name: Guilian QUAN Supervisor: Kazuhiko KAWASHIMA

        In-Core Shield工法の提案及び応答載荷実験に基づくその有効性に関する研究

                                                  全      貴蓮

      世界最大の震動台E-ディフェンスを用いた実大RC橋脚に対する震動実験では,圧壊したコアコ
      ンクリートが鉄筋かごから逸脱して橋脚が終局状態を迎えることが明らかとなった.本研究で
      は,破砕したコアコンクリートの逸脱を防止するため,鉄筋かごの内側にインコアシールドと呼
      ぶ板もしくは層状の壁を設ける構造を提案し, その効果を縮尺模型実験と解析に基づいて検討し
      た.この結果,パンチングメタルやアラミド繊維シートをインコアシールドとして用いることに
      より、破砕したコアコンクリートの噴出防止が可能であることを明らかにした.また,ファイバ
      ー要素解析を行い,実験により得られた曲げモーメント~水平変位の履歴特性を再現できた.

       Key Words : In-Core Shield, Seismic Design, RC Bridge Column ,Seismic Response Loading, E-Defense



1. I TRODUCTIO                                               material inside the steel cages is proposed in this
                                                             investigation. The plate-like material set inside the
   A full-scale RC bridge column (designated                 steel cages is hereinafter called as in-core shield
hereinafter as C1-5 column) excitation experiment            (ICS). In this study, the effectiveness of ICS is
was conducted at the National Institute of Earth             clarified based on seismic excitation experiments
Science and Disaster Prevention using E-Defense              using two types of ICS; one is a punching metal plate
shake table in 20081,2). The C1-5 column was a               (designated as ICS-PM column) and the other is and
typical reinforced concrete column designed in               aramid fiber reinforced plastic sheet (designated as
accordance with the current design requirements. In          ICS-AFS column). Analytical correlation for the
the E-Defense shake table experiment, C1-5 column            experimental results is also conducted.
was subjected to five excitations using a near-field
ground motion which was recorded during the 1995
Kobe earthquake. C1-5 column survived the first and          2. CO CEPT OF THE I -CORE SHIELD
second excitations with limited damage, however, it             METHOD
suffered extensive damage during the fifth
excitation. The core concrete crushed in compression             The in-core shield column aims at preventing
due to repeated excitations, and blocks of crushed           spilling out of crushed core concrete from the steel
core concrete spilled out from the steel cages like          cages, when a column is subjected to a strong
explosion (refer to Photo 1). Such a failure was             near-field ground motion with long duration. In the
never seen in the past quasi-static cyclic or hybrid         steel jacket retrofit widely adopted for seismic
loading experiments3). The ground motions                    retrofit of standard reinforced concrete bridge
developed during the 1995 Kobe earthquake are not            columns, steel plates with sufficient strength and
necessarily the strongest ground motions, and in fact        rigidity are required because they are set around the
several ground motions which were stronger than the          existing columns. However, since ICS is set inside
ground motions developed during the Kobe                     steel cages, ICS does not need to be as strong as the
earthquake were recorded after the Kobe earthquake.          steel jacket.
The result of C1-5 column revealed that the columns              However, in-core shield method has two
would suffer extensive damage no matter how they             problems for practical implementation. One is the
are designed in accordance with the current seismic          difficulty of setting of an ICS inside steel cages.
design requirements if they are subjected to stronger        Because tie bars are developed inside the core
ground motions with longer duration.                         concrete using 135 degree bent hooks, the ICS would
   Based on the abovementioned background, a new             interfere with the hooks. Therefore it is required to
method for preventing the spilling out of crushed            develop tie bars without hooks. For this purpose, tie
core concrete from steel cages by setting a plate-like       bars may have to be connected by pressure welding.


                                                         1
                                                                     400


                                             Loanding
                                             Point                                                                  350




                                                                                   700
                                                                                                           26 17




                                                             B                 B




                                             1370
   Photo 1 Failure of the C1-5 column                                                                                          D4 ctc 56 mm
                                                                                                     D6@36 bars                D4 ctc 28 mm




                                                      1110
                                                             930
                                                                                                         (b) Standard Section (B-B)




                                                                                    In-Core Shield
                                                             A                 A                                     350




                                                                                          544
                                                    420                                                     26 17




                                                                                                                                D4 ctc 56 mm
                                                                     700
                                                                                                     D6@36 bars
                                                                                                                                 D4 ctc 28 mm
                                                          (a) Column Reinforcement                        (c) Plastic Hinge Section (A-A)
Photo 2 Setting of in-core shield inside                                                 Fig.1 Experimental model
        steel cages (punching metal plate)

The other problem is difficulty of casting concrete in                     3. EXPERIME TAL MODELS
the core concrete and the cover concrete, Because an
ICS isolates cover concrete from core concrete, the                        3.1 Experimental models
concrete has to be cast such that the pressure from                           Two 6/35 scaled models of C1-5 column were
the core concrete is balanced with that of the cover                       designed and constructed. The scaled columns were
concrete.                                                                  circular with a 350mm diameter, and they were 1630
     Note here that a similar method called “inside                        mm tall with an effective height from the bottom to
spiral reinforcement method” was already developed                         the loading point of 1370mm. Column reinforcement
4,5)
    . The inside spiral reinforcement method aims of                       and section are shown in Fig. 1. A column each was
increasing the displacement capacity of reinforced                         constructed for ICS-PM column and ICS-AFS
concrete columns by mitigating rupture of                                  column. Table 1 shows how the models were
longitudinal bars. For this purpose, ties are                              scaled-down from C1-5 column. Sixty four deformed
developed using 90 degree bent hooks so that they                          six mm diameter (SD345-D6) longitudinal bars were
can loose the lateral confinement during an extensive                      provided in two layers. Deformed four mm diameter
event, which in turn develops local buckling of                            (SD295-D4) circular ties were set at 28 mm and 56
longitudinal bars to occur freely. An interesting point                    mm interval in the outer and inner longitudinal bars,
of the inside spiral reinforcement method is to aim of                     respectively. ICS was placed up to of 1.5 times the
mitigating rupture of longitudinal bars by allowing                        column diameter D (= 525 mm) from the column
local buckling to occur freely. Spiral reinforcements                      base. In this zone, the tie bars were pressure welded
are set inside the steel cages so that the flexural                        to connected each other. In other zone, the tie bars
capacity of a column does not significantly                                were developed in the core concrete using 135
deteriorate. The existence of spiral reinforcement                         degree bent hooks. Longitudinal reinforcement ratio
inside the steel cages is somehow similar to the                           was 2.37% and the tie volumetric reinforcement ratio
in-core shield method. However, because the inside                         was 0.92%. The thickness of covering concrete was
spiral reinforcement method does not aim of                                26mm, and shear span ratio was 4.60. Because the
preventing spilling out of crushed core concrete from                      maximum aggregate size of C1-5 column was 20mm,
steel cages, the purpose of the in-core shield method                      the expected maximum aggregate size should be
is similar but the concept is different to those of the                    3.4mm in the models if the aggregate were scaled
inside spiral reinforcement method.                                        down based on geometrical scale of 6/35. However,
                                                                           because such small aggregates were not available,
                                                                           the aggregates with the maximum size of 5 mm were


                                                                     2
                             Table 1 Properties of Two 6/35-sclaed models and C1-5 column
                    Properties                          (A) : In-Core Shield Column          (B) : C1-5      (A)/((B) × 6/35)
                         Height (mm)                                1630                       7500              ---------
                     Effective Height(mm)                           1370                       8000                1.00
   Column
                        Diameter (mm)                     6/35 × 2000=342 → 350                2000                1.02
                       Shear Span Ratio                             4.60                        4.71             ---------
                          Diameter (mm)                            6-SD345                   35-SD345                 1.00
                             Number                                  2@36                       2@36                   1.00
 Longitudinal         Elastic Modulus (GPa)                           180                        189                 ---------
    Bars
                      Yield Strength (MPa)                            379                        364                 ---------
                     Tension Strength (MPa)                           550                        562                 ---------
                Longitudinal Reinforcement Ratio                     2.37%                     2.19%                  1.08
                          Diameter (mm)                        6/35 × 22=3.77 → 4                 22                  1.06
                             Spacing                          6/35 × 150=25.7 → 28               150                   1.09
   Tie Bars          Elastic Modulus (GPa)                             203                       186                 ---------
                      Yield Strength (MPa)                             430                       382                 ---------
                     Tension Strength (MPa)                            603                       555                 ---------
                Volumetric tie reinforcement Ratio               0.92%                         0.92%                  1.00
                 Design Concrete Strength (MPa)                   27.0                          27.0                  1.00
                                                         ICS-PM: 27.4, ICS-AFS:
                      Elastic Modulus (GPa)                                                      27.6                ---------
                                                                  27.3
  Concrete                                               ICS-PM: 30.1, ICS-AFS:
                  Compression Strength (MPa)                                                     32.2                ---------
                                                                  29.3
                 Maximum Aggregate Size (mm)                   6/35 × 20=3.4 → 5                  20                  1.47
                Tie Bars Spacing/Aggregate Size                       5.6                        7.5                  1.34


                                                                     Table 2 Material properties of in-core shield

                                                                                                Aramid Fiber Reinforced
                                                                Punching Metal Plate
                                                                                                        Plastic Sheet
                                                                  Material       SS400      Tension Strength          2,060 MPa
                                                                                                                        1.2×105
                                                                 Thickness      0.8 mm      Elastic Modulus
                                                                                                                          MPa
                                                                 Mesh Size       5 mm        Rupture Strain                2%

                                                               used, so that blocks of crushed core concrete did not
                                                               spill-out from the holes. Photo 2 shows setting of a
                Photo 3 setup of column                        punching metal plate inside the reinforcements. A
                                                               aramid fiber reinforced plastic sheet was also set in
used in this experiment.                                       similar way with the punching metal plate.
   It is important to select an economical and stable
ICS material that can be constructed easily. Various           3.2 Experimental setup
materials may be used for this purpose, but in this               The columns were loaded by three dynamic
research, a punching metal plate and a two direction           actuators at the Earthquake Engineering Facility in
aramid fiber reinforced plastic sheet were used for            Tokyo Institute of Technology. The setup of
ICS. Table 2 shows the material properties. Because            specimens is shown in Photo 3. Table 3 shows the
the maximum aggregate size was 5mm, a punching                 loading sequence of C1-5 column excitation and ICS
metal plate with 5 mm × 5 mm square holes were                 column excitation. C1-5 column with a mass of 307 t


                                                          3
                                              Table 3 Loading sequence

                               In-Core Shield Column                                 C1-5 Column
        Excitation    Intensity of lateral   Intensity of vertical                      Mass of         Intensity of
                                                                       Excitation
                        displacements               force                               the deck         excitation

        C1-5S(1)-1     6/35 × C1-5(1)-1      (6 / 35) 2 × C1-5(1)-1     C1-5(1)-1
                                                    2                                     307t
        C1-5S(1)-2     6/35 × C1-5(1)-2      (6 / 35) × C1-5(1)-2       C1-5(1)-2                          100%
                                                        2
         C1-5S(2)       6/35 × C1-5(2)        (6 / 35) × C1-5(2)         C1-5(2)
                                                    2
        C1-5S(3)-1     6/35 × C1-5(3)-1      (6 / 35) × C1-5(3)-1       C1-5(3)-1         372t
                                                    2                                                      125%
        C1-5S(3)-2     6/35 × C1-5(3)-2      (6 / 35) × C1-5(3)-2       C1-5(3)-2
        C1-5S(3)-3       C1-5S(3)-2              C1-5S(3)-2
        C1-5S(4)-1 125% × C1-5S(3)-2             C1-5S(3)-2                   ---------------------------------
        C1-5S(4)-2 125% × C1-5S(3)-2             C1-5S(3)-2

was subjected to the 100% E-Takatori ground motion
twice (C1-5(1)-1 and C1-5(2)-2 excitations). After              4.1 C1-5S(1)-1 and C1-5S(1)-2 excitations
the mass was increased by 21% from 307 t to 372 t,                  During the C1-5S(1)-1 excitation, only
C1-5 was subjected to the 100% E-Takatori ground                longitudinal bars yielded in both ICS-PM column
motion once (C1-5(2) excitation), then C1-5 was                 and ICS-AFS column. No other visible damage
subjected to the 125% E-Takatori ground motion                  occurred on the surface ICS columns. During the
twice (C1-5(3)-1 and C1-5(3)-2 excitations). Note               C1-5S(1)-2 excitation, only a few flexural cracks
that the 100% E-Takatori ground motion implies the              occurred in the W-E face at 200 mm from the base
ground motion with an intensity of 80% the original             and W-SW face at 120 mm from the base in ICS-PM
of JR Takatori station recorded during the 1995                 column and ICS-AFS column, respectively.
Kobe earthquake. The bilateral response                             Fig. 2 shows strains of a longitudinal bars at 104
displacements of C1-5 column were scaled to 6/35,               mm from the base and tie bars at 93mm from the
and there were imposed to the models by two                     column base on the SW face wherein the response
horizontal dynamic actuators under the displacement             displacement was largest. The results of C1-5S(2)
control. On the other hand, the vertical inertia force          and C1-5S(3)-1 excitations which will be described
of C1-5 column was scaled to (6/35)2, and this was              later are also shown here for comparison. Under the
imposed to the models by the vertical actuator under            C1-5S(1)-1 and C1-5S(1)-2 excitations, strains of the
the force control.                                              longitudinal bar and the tie bar have no significant
   This loading procedure is called hereinafter as the          differences between ICS-PM column and ICS-AFS
seismic response loading. Because of limitation of              column. In ICS-PM column, the peak compression
the experimental facility, the bilateral displacements          and tension strains of the longitudinal bar are 1680 µ ,
and the vertical force were loaded at 1/10 velocity of          936 µ , respectively, under the C1-5S(1)-1 excitation,
C1-5 shake table experiment.                                    and they progressed to 7760 µ , 1350 µ , respectively,
   In the seismic response loading, the models were             under the C1-5S(1)-1 excitation. Similarly the peak
subjected to 5 times loading in the same sequences of           strain in tension side of the tie bar is 300 µ under the
the C1-5 column shake table experiment                          C1-5S(1)-1 excitation, and it progressed to 500 µ
(C1-5S(1)-1, C1-5S(1)-2, C1-5S(2), C1-5S(3)-1,                  under the C1-5S(1)-2 excitation. Note that the
C1-5S(3)-2) excitations. Then C1-5S(3)-2 excitation             longitudinal and tie bar strains increased
was repeated once (C1-5S(3)-3) and C1-5S(3)-2                   significantly by repeating the loading with the same
excitation was repeated by increasing the intensity of          intensity of ground motion.
grown motion by 125% twice (C1-5S(4)-1 and
C1-5S(4)-2 excitations).                                        4.2 C1-5S(2) excitations
                                                                   During C1-5S(2) excitation, cracks at 300 mm
                                                                from the column base occurred around ICS-PM
4.    FAILURE MODES OF I -CORE                                  column and ICS-AFS column. In particular, ICS-PM
      SHIELD COLUM S                                            column suffered significant damage at the 50 mm


                                                            4
  Strian (10 )    20                               ICS-PM                        1                                    ICS-PM




                                                                      Strian (10 )
 -3




                                                                   -3
                  10                               ICS-AFS                     0.5                                    ICS-AFS
                   0                                                             0
                 -10                                                          -0.5
                 -20                            C1-5S(1)-1                                                          C1-5S(1)-1
                                                                                -1
                                                                                 1
    Strian (10 )




                                                                      Strian (10 )
 -3




                  20




                                                                   -3
                  10                                                           0.5
                   0                                                             0
                 -10                            C1-5S(1)-2                    -0.5                                 C1-5S(1)-2
                 -20
                                                                                -1
                                                                                 2




                                                                         Strian (10 )
  Strian (10-3)




                  20




                                                                      -3
                                                                                 1
                  10                                                             0
                   0
                 -10                                                            -1                                 C1-5S(2)
                                                C1-5S(2)
                 -20                                                            -2
                                                                                10
 Strian (10-3)




             20



                                                                        Strian (10 )
                                                                      -3
             10                                                                  5
              0                                                                  0
            -10                                                                 -5                                 C1-5S(3)-1
            -20                                 C1-5S(3)-1
                                                                               -10
               0       5   10      15      20    25      30                        0    5   10      15       20      25       30
                                Time (s)                                                          Time (s)
(a) Strains of a longitudinal bar at 104mm from the column base                  (b) Strains of a tie bar at 93mm from the column base
                                      Fig. 2 Strains of a longitudinal bar and a tie bar at SW face

from the base on W-S face. On the other hand,                              C1-5S(3)-2 excitation, a tie bar at 37 mm from the
ICS-AFS column did not so suffered such extensive                          column base was exposed, and two longitudinal bars
damage.                                                                    buckled on the SW face in ICS-PM column. On the
   The peak compression strain of longitudinal bar                         other hand, four tie bars were exposed (including a
in ICS-AFS column became ( 8070 µ ) Larger than                            tie bar exposed during C1-5S(3)-1 excitation) and
that of ICS-PM column ( 5290 µ (refer to Fig. 2)).                         eight outer longitudinal bars buckled totally. Photo 4
The peak tension strains of tie bar was the same                           shows the damage of columns after C1-5S(3)-2
range between ICS-AFS column and ICS-PM                                    excitation. For comparison, the damage of C1-5
column.                                                                    column after C1-5S(3)-2 excitation is also shown
                                                                           here. From this photo, ICS-AFS column suffered
4.3 C1-5S(3)-1, C1-5S(3)-2 and C1-5S(3)-3                                  more significant damage than ICS-PM column, and
excitations                                                                the concrete between the outer and inner longitudinal
   Figs. 3 and 4 show damage of ICS-PM column                              bars spalled between 50 mm to 100 mm from the
and ICS-AFS column after the C1-5S(3)-1,                                   base in the ICS-AFS column.
C1-5S(3)-2 and C1-5S(3)-3 excitations, respectively.                           During the C1-5S(3)-3 excitation, the failure
The damage progressed during C1-5S(3)-1                                    extensively progressed in both ICS-PM column and
excitation such that the covering concrete spalled off                     ICS-AFS column. In the ICS-PM column, two outer
between W and S face up to 150mm from the base                             tie bars were exposed and five longitudinal bars
and 50mm in the ICS-PM column and ICS-AFS                                  buckled and crushed concrete between the punching
column, respectively. In particular, the damage of                         metal and the outer longitudinal bars were spalled.
ICS-PM column was more significant than that of                            On the other hand, in ICS-AFS column, the crushing
ICS-AFS column during this excitation. Three tie                           of concrete between aramid fiber reinforced plastic
bars at 65 mm, 93 mm, 121 mm from the column base                          sheet and the outer longitudinal bars extensively
was exposed in ICS-PM column, while only one tie                           progressed, and aramid fiber reinforce plastic sheet
bar at 65 mm from the column base was exposed in                           was exposed at W face. Furthermore, in ICS-AFS
ICS-AFS column.                                                            column, six outer longitudinal bars and five inner
   Until C1-5S(3)-1 excitation, the spalled cover                          longitudinal bars buckled, and an outer tie bar at 93
concrete and exposed number of tie bars is more                            mm from the column base ruptured at W face. From
significant in ICS-PM column than ICS-AFS                                  Photo 4(c), damage of C1-5 column after C1-5(3)-2
column. However, from C1-5S(3)-2 excitation, the                           excitation is very significant. The core concrete of
damage in ICS-AFS becomes more significant than                            C1-5 column was crushed completely as deep as
ICS-PM column. For example, during the                                     265mm from the extreme fiber of the core concrete.


                                                                  5
                                 W          S        E                       W         S           E                  W        S       E
                           930

                           800
Height From Footing (mm)




                           600


                           400


                           200


                            0

                                     (a) C1-5S(3)-1 Excitation                   (b) C1-5S(3)-2 Excitation                 (c) C1-5S(3)-3 Excitation
                                                                 Fig. 3 Damage of ICS-PM column after excitations

                                 W          S        E                       W         S          E                   W        S       E
                           930

                           800
Height From Footing (mm)




                           600


                           400


                           200


                            0

                                     (a) C1-5S(3)-1 Excitation                 (b) C1-5S(3)-2 Excitation                   (c) C1-5S(3)-3 Excitation
                                                              Fig. 4 Damage of ICS-AFS column after excitations




                                 (1) ICS-PM                             (2) ICS-AFS                                  (3) C1-5
                                          Photo 4 Damage of ICS-PM, ICS-AFS and C1-5 columns after C1-5S(3)-2 excitation

This is equivalent to the depth of 45 mm in the                                                crushing of concrete in the ICS-AFS column is more
6/35-scaled column.                                                                            significant than ICS-PM column.
   Because of damage of strain gauges, strains of                                                  Fig. 5 shows the interaction of a longitudinal bar
longitudinal bars and tie bars could not be measured                                           at 104 mm from the base and a tie bar at 93 mm from
from C1-5S(3)-2 excitation, the result until                                                   the base at the SW face during four excitations. An
C1-5S(3)-1 excitation is shown in Fig. 2. In ICS-PM                                            increase of strain in the tie which resulted from the
column, the peak tension strain increased to 21500 µ ,                                         local bucking of the longitudinal bar subjected to
which is 1.94 times the strain measured during the                                             high compression strain is clearly seen during the
C1-5S(2) excitation ( 11100 µ ). However, the peak                                             C1-5S(3)-1 excitations both ICS-PM and ICS-AFS
compression strain ( 4590 µ ) during C1-5S(3)-1                                                columns.
excitation becomes smaller than strain during the
C1-5S(2) excitation ( 5290 µ ). On the other hand, in                                          4.4 C1-5S(4)-1 and C1-5S(4)-2 excitations
ICS-AFS column the compression strain increased to                                                During C1-5S(4)-1 and C1-5S(4)-2 excitations,
 20800 µ . It is 4.53 times the compression strain of                                          damage of ICS-AFS column was more significant
longitudinal bar in ICS-PM column during the                                                   than that of ICS-PM column. After the C1-5S(4)-2
C1-5S(3)-1 excitation ( 4590 µ ). This means that                                              excitation, three outer and seven inner longitudinal


                                                                                           6
                                            10


                      Strian of ties εh (10-3)
                                                 8
                                                 6                       C1-5S(1)-1
                                                 4                       C1-5S(1)-2
                                                                         C1-5S(2)
                                                 2                       C1-5S(3)-1
                                                 0
                                                 -2
                                                  -20 -15 -10 -5 0 5 10 15 20
                                                      Strian of longitudinal εl (10-3)                         (a) Punching metal plate

                                                        (a) ICS-PM column
                               6
                                                          C1-5S(1)-1
         Strian of ties εh (10-3)




                               4                          C1-5S(1)-2
                                                          C1-5S(2)
                                                          C1-5S(3)-1
                               2

                               0

                         -2
                           -25 -20 -15 -10 -5 0 5 10 15                                                (b) Aramid fiber reinforced plastic sheet
                                 Strian of longitudinal εl (10-3)                                 Photo 5 Damage of in-core shield after experiment
                      (b) ICS-AFS column
Fig. 5 Hysteresis of strain of longitudinal bar at 104 mm and tie
        bar at 93 mm from base at SW face

bars and one tie bar at W face ruptured in ICS-PM
column. On the other hand, in ICS-AFS column,
eight outer and eight inner longitudinal bars at W-S
face and two tie bars at W and E faces ruptured. After
the C1-5S(3)-2 excitation, damage at the base
became extensive in ICS-AFS column, because the
lateral confinement by aramid fiber reinforced                                                                   (a) ICS-PM column
plastic sheet was smaller than that of punching metal
plate. This is due to that the difference of the
stiffness between the punching metal plate and the
aramid fiber reinforced plastic sheet and this result in
larger number of ruptured longitudinal and tie bars in
ICS-AFS column.

4.5 Damage of In-Core Shield
   Photo 5 shows the damage of ICS after
C1-5S(4)-2 excitation. In ICS-PM column, punching
metal plate buckled at 104 mm from the base with a                                                            (b) ICS-AFS column
buckling length of 20mm. On the other hand, Aramid                                           Photo 6 Damage of core concrete after C1-5S(4)-2 Excitation
fiber sheet has no significant visible damage.
   Photo 6 shows damage of the core concrete after                                           of the columns.
the C1-5S(4)-2 excitation. The core concrete at
SWW face in ICS-PM column and S face in
ICS-AFS column as deep as 10mm from the extreme                                              5.     MOME T CAPACITY OF                            THE
fiber of the core concrete. However, in the ICS-PM                                                I -CORE SHIED COLUM S
and ICS-AFS the blocks of crushed core concrete did
not spill out from the steel cages like C1-5. The                                               Fig. 6 shows bending moment vs. lateral
In-Core Shield columns developed in this research is                                         displacement hysteresis of the column in the
effective to prevent deterioration of flexural capacity                                      principal response displacement direction. For
of core concrete, and to ensure the ductility capacity

                                                                                         7
                                                                      Drift (%)                                                                                                               Drift (%)                                                                 Drift (%)
                                                             -8 -6 -4 -2 0 2 4 6 8                                                                                                   -8 -6 -4 -2 0 2 4 6 8                                                     -8 -6 -4 -2 0 2 4 6 8
                                                      150                                                                                                              150                                                                              150
                                                                           ICS-PM                                                                                                                 ICS-PM                                                          ICS-PM




                                                                                                                                           Bending Moment (kNm)




                                                                                                                                                                                                                                 Bending Moment (kNm)
                               Bending Moment (kNm)

                                                      100                                                                                                              100                                                                              100
                                                                           ICS-AFS                                                                                                                ICS-AFS                                                         ICS-AFS
                                                                           C1-5                                                                                                50                 C1-5                                                   50
                                                       50

                                                        0                                                                                                                      0                                                                          0

                                                       -50                                                                                                               -50                                                                             -50

                                                      -100                                                                                                          -100                                                                                -100

                                                      -150                                                                                                          -150                                                                                -150
                                                         -120 -60        0     60    120                                                                               -120 -60        0    60     120                                                     -120 -60        0     60    120
                                                            Lateral Displacement (mm)                                                                                    Lateral Displacement (mm)                                                            Lateral Displacement (mm)
              (1) C1-5S(3)-1 Excitation                    (2) C1-5S(3)-2 Excitation                   (3) C1-5S(3)-3 Excitation
Fig. 6 Bending moment at the base vs. lateral displacement at the column top hysteresis of ICS-PM, ICS-AFS and C1-5 Columns in the
       Principal response displacement direction

                                                                                                                                                                   ICS-PM
in Principle direction (kNm)




                                     150                                                                                                                           ICS-AFS                                            Loading
   Max Bending Moment




                                                                                                                                                                    C1-5                                              Point
                                     125
                                     100                                                                                                                                                                                     E                                         W
                                                75                                                                                                                                                                                                                    Beam
                                                50                                                                                                                                                                                                                    Element
                                                              C1-5S(1)-1

                                                                           C1-5S(1)-2



                                                                                                    C1-5S(3)-1

                                                                                                                 C1-5S(3)-2

                                                                                                                              C1-5S(3)-3

                                                                                                                                                                  C1-5S(4)-1

                                                                                                                                                                                    C1-5S(4)-2
                                                                                        C1-5S(2)




                                                                                                                                                                                                              1370

                                                                                                                                                                                                                     930
                                                                                                                                                                                                                           286



                                                                                                   Exication                                                                                                                                                          Fiber
                                                                                                                                                                                                                                                                      Elements
 Fig. 7 Averaged maximum bending moment at each excitation
                                                                                                                                                                                                                           239




           in principal response displacement direction
                                                                                                                                                                                                                                                                        Rotational Spring to
                                                                                                                                                                                                                     420




comparison, the response of C1-5 column is also                                                                                                                                                                                                                         represent bar pullout
shown here. The response displacement and bending                                                                                                                                                                                                                       effect
moment of C1-5 column shown in here is
scaled-down to 6/35 and (6/35)3 based on similarity                                                                                                                                                                        Fig. 8 Analytical model of column
rule. Here, the response in the principal response
displacement direction is defined as                                                                                                                                                                       maximum bending moment of C1-5 column is
                                                                                                                                                                                                           smaller than that of 6/35-scaled models. Fig. 7
                                                        u p = u LG cosθ p + uTR sin θ p                                                                                                          (1)       compares the averaged maximum bending moment
                                                      M p = M LG cos θ p + M TR sin θ p                                                                                                          (2)       in the positive and negative direction for ICS-PM
                                                                                                                                                                                                           column, ICS-AFS column and C1-5 column. The
i n w h i c h , u LG a n d uTR a r e t h e r e s p o n s e                                                                                                                                                 averaged maximum bending moments of ICS-PM
displacement in the longitudinal and transverse                                                                                                                                                            column and ICS-AFS column are nearly the same
direction, respectively, M LG and M TR are the                                                                                                                                                             similar until C1-5S(3)-2 excitation. However, after the
bending moment in the longitudinal and transverse                                                                                                                                                          C1-5S(3)-3 excitation, averaged maximum moment of
direction, respectively, and θ p is the angle between                                                                                                                                                      ICS-AFS column decreased significantly compared to
the longitudinal direction and the principal response                                                                                                                                                      ICS-PM column. It is interesting to note that the
displacement direction. The angles θ p which was                                                                                                                                                           maximum averaged bending moment of C1-5 column
determined in the C1-5 excitation were 196.0, 192.3,                                                                                                                                                       is smaller than that of 6/35-scaled models during the
203.1, 206.6 and 211.3 degree for C1-5 (1)-1,                                                                                                                                                              five times excitations. Note that difference may be
C 1 -5 ( 1 ) -2 , C 1 -5 ( 2 ) , C 1-5( 3) -1, C1-5( 3) -2                                                                                                                                                 attributed to the effect of ICS and the size effect. It is
excitations, respectively. If is seen from Fig. 6 that                                                                                                                                                     hard to distinguish the effect of ICS from this
the response of ICS-PM column and ICS-AFS                                                                                                                                                                  difference, however based on the fact that ICS
column are similar during the C1-5S(3)-1,                                                                                                                                                                  prevented the blocks of crushed core concrete to spill
C1-5S(3)-2 and C1-5S(3)-3 excitations, however, the                                                                                                                                                        out from the steel cages, it is reasonable to consider
                                                                                                                                                                                                           that in-core shield method is effective.

                                                                                                                                                                                                       8
                                                  Drift (%)                                                                      Drift (%)
                                        -8 -6 -4 -2 0 2         4   6   8                                             -8 -6 -4 -2 0 2            4   6   8
                                 150                                                                              150
          Bending Moment (kNm)




                                                                                           Bending Moment (kNm)
                                              Experiment                                                                   Experiment
                                 100                                                                              100
                                               Analysis                                                                     Analysis
                                  50                                                                               50
                                   0                                                                                0
                                  -50                                                                              -50
                                 -100                                                                             -100
                                 -150                                                                             -150
                                     -120      -60       0      60    120                                             -120      -60       0       60     120
                                            Lateral Displacement (mm)                                                        Lateral Displacement (mm)
                                            (a) ICS-PM column                                                                (a) ICS-PM column
                                                  Drift (%)                                                                        Drift (%)
                                        -8 -6 -4 -2 0 2         4   6   8                                                -8 -6 -4 -2 0 2         4   6   8
                                 150
         Bending Moment (kNm)




                                                                                                                  150




                                                                                           Bending Moment (kNm)
                                              Experiment                                                                       Experiment
                                 100                                                                              100
                                              Analysis                                                                         Analysis
                                   50                                                                              50
                                    0                                                                               0
                                  -50                                                                              -50
                                 -100                                                                             -100
                                 -150                                                                             -150
                                     -120      -60       0       60     120                                           -120      -60       0       60     120
                                            Lateral Displacement (mm)                                                        Lateral Displacement (mm)
                    (b) ICS-AFS column                                                                 (b) ICS-AFS column
Fig. 9 Bending Moment vs. lateral displacement of column                          Fig. 10 Bending Moment vs. lateral displacement of column
       models in the principal response displacement direction                            models in the principal response displacement direction
       (C1-5S(2) Excitation)                                                              (C1-5S(3)-1 Excitation)

                                                                                  under the excitations. In ICS-PM column, the
6. FIBER ELEME T A ALYSIS                                                         positive peak bending moments during the C1-5S(2)
                                                                                  excitation is 134.87 kNm and 132.21 kNm in the
6.1 Analytical idealization                                                       experiment and in the analysis, respectively. The
    The columns were idealized as shown in Fig. 8.                                positive peak bending moments during the
The columns at the plastic hinge was idealized by                                 C1-5S(3)-1 excitation is 132.97 kNm and 133.95
fiber elements, and the rest of the plastic hinge                                 kNm in the experiment and in the analysis,
including the lateral beams were idealized by elastic                             respectively. Consequently, the computed positive
beam elememts. The hysteric behavior of the core                                  peak moment capacities is in the rage of 98 % and
concrete was evaluated with Hoshikuma et al.                                      101 % of the experimental responses during the
model6) and reloading and unloading hysteresis was                                C1-5S(2) and C1-5S(3)-1 excitations, respectively.
evaluated with Sakai and Kawashima model7). The                                   Similarly, in ICS-AFS column, the positive peak
stress-strain hysteresis of the longitudinal bars was                             moment capacities of analytical result correlated
idealized with Menegotto and Pinto model modified                                 which the experimental response in the rage of
by Sakai and Kawashima8). The effect of                                           110 % and 99 % the experimental responses during
deformation of longitudinal bars inside the footing                               the C1-5S(2) and C1-5S(3)-1 excitations,
was taken into account by providing a set of                                      respectively. Thus, the analytical models provides
rotational elastic springs in the longitudinal and                                good correlation for the experiment.
transverse directions. In this analysis, the
confinement effect of ICS was considered by
incorporating it in terms of an increase of the                                   7. CO CLUSIO S
volumetric tie reinforcement ratio.
                                                                                     The in-core shield method was proposed and its
6.2 Analytical results                                                            effectiveness was clarified based on the seismic
   Figs. 9 and 10 compare bending moment vs.                                      response loading for model columns using punching
lateral displacement in the principal response                                    metal plate and aramid fiber reinforced plastic sheet.
displacement direction between the analytical and                                 An analytical correlation was conducted to the model
the experiment results under the C1-5S(2) and                                     columns. Based on the experimental and analytical
C1-5S(3)-1 excitations. The analytical hystereses are                             studies presented herein, the following conclusions
in a good agreement with the experiment results                                   may be deduced:

                                                                              9
1) Punching metal plate and aramid fiber reinforced           REFERENCES
   plastic sheet are effective as a in-core shield for
   preventing blocks of crushed core concrete to              1) Kawashima, K. and Kajiwara, K.: E-Defense Bridge Project
   spill out from steel cages in the columns when                on the Seismic Performance of Reinforced Concrete Columns,
   they are subjected to extreme ground motions.                 Concrete Journal, Vol. 47, No. 11, pp. 9-15, 2009.
2) Numbers of ruptured longitudinal bars and tie              2) Kawashima, K., Sasaki, T., Ukon, H. and Kajiwara, K.: Shake
                                                                 Table Experiment on RC Bridge Columns Using E-Defense,
   bars are larger in ICS-AFS column than ICS-PM
                                                                 Proc. 1st International Conference on Computational
   column. Larger stiffness of punching metal plate
                                                                 Technologies in Concrete Structures, [1], pp. 1343-1361, Jeju,
   than aramid fiber reinforced plastic sheet                    Korea, 2009.
   resulted in larger lateral confinement of core             3) For example, Matsumoto, T., Kawashima, K., Mahin, S. A.
   concrete, and it also mitigated damage of the                 and Ukon, H.: Seismic Performance of Interlocking Spiral and
   longitudinal bars and tie bars. Consequently,                 Rectangular Columns based on Shake Table Experiment,
   ICS-PM column is more effective than ICS-AFS                  Journal of Structural Mechanics and Earthquake Engineering,
   column.                                                       JSCE, A, Vol. 65, No. 1, pp. 196-215, 2009.
3) Both ICS-PM and ICS-AFS columns have larger                4) Ishibashi, T., Kanno, T., Kino, J., Kobayashi, K., and Obara,
   flexural capacities than C1-5 column if the                   K.: Reversal Cyclic Loading Test of Renforced Concrete
   flexural capacities of C1-5 column are                        Column Reinforced by Inside round Hoop Bar, JSCE, No.
   scaled-down based on the similarity law. The                  795/V-68, pp. 95-110, 2005.
   difference may be attributed to the effect of ICS          5) Kanno, T., Ishibashi, T., Kino, J., and Kobayashi, K.:
                                                                 Deformation Capacity under Earthquake on Reinforced
   and the size effect between the full-scale model
                                                                 Concrete Column Reinforced by Inside Spiral Reinforcement,
   and 6/35 scaled models. It is hard to distinguish
                                                                 Concrete Research and Technology, Vol. 20, No.2 ,2009.
   the effect of ICS from this difference, however            6) Hoshikuma, J., Kawashima, K., Nagaya, K. and Taylor, A.W.:
   based on the above conclusion 1) the in-core                  Stress-Strain Model for Confined Concrete in Bridge Piers,
   shield method is effective.                                   Journal of Structural Engineering, ASCE, 123(5), pp.
4) The fiber element analysis provides a good                    624-633, 1997.
   correlation for the moment capacity of the                 7) Sakai, J. and Kawashima, K.: Unloading and Reloading
   in-core shield columns until the effect of                    Stress-Strain Model for Confined Concrete, Journal of
   longitudinal bar buckling become significant.                 Structural Engineering, ASCE, 132(1), pp. 112-122, 2006.
   However, idealization of the in-core shield needs          8) Sakai, J. and Kawashima, K.: Modification of the Giuffre,
   to be further improved so that the real                       Menegotto and Pinto Model for Unloading and Reloading
   mechanism of in-core shield can be modeled in                 Paths with Small Strain Variations, Journal of Structural
                                                                 Mechanics and Earthquake Engineering, JSCE, No. 738/I-64,
   analysis.
                                                                 pp. 159-169, 2003.




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