Behavior of Columns in Composite CES Structural System

Behavior of Columns in Composite CES Structural System
Hiroshi Kuramoto
Department of Architectural Engineering, Graduate School of Engineering
Osaka University
Suita, Japan
kuramoto@arch.eng.osaka-u.ac.jp
ABSTRACT
New composite structural systems consisting of only steel and concrete, the concrete encased
steel (CES) structures, have been proposed by the author in order to realize simplification and
cost reduction in construction works for SRC structures. Experimental studies on CES columns
using fiber reinforced concrete (FRC) have been carried out to investigate the seismic
performance, in which the main test parameters were the section shape of encased steels, the
type and content of fibers used for FRC and the applied axial load levels. The experimental
results showed that CES columns had excellent seismic performance with a stable spindleshape
hysteresis characteristic and less damage. This paper introduces the summary of the
experimental studies carried out in past about eight years with the advantage of CES structure.
INTRODUCTION
Reinforced concrete encased steel structures referred to as SRC structures are typical
composite structural systems consisting of steel and reinforced concrete (RC) and possess an
excellent earthquake resistance with high capacities and deformability. However, SRC
structures have a weak point in the construction due to complex works of both steel and RC. In
order to realize simplification and cost reduction in construction works for SRC structures,
concrete encased steel structures consisting of only steel and concrete (see Figure 1),
hereafter referred to as CES structures, have been proposed by the author (Kuramoto et al.
2000). In the feasibility study to examine the structural performance of CES columns, it was
conformed that damages of the columns with an increase of lateral deformation such as
cracking and crushing in concrete can be reduced by using high performance fiber reinforced
cementitious composites (HPFRCC) instead of normal concrete. Moreover, the hysteretic
characteristics of the CES columns were almost the same as those of SRC columns. However,
significant reduction of the initial stiffness in the shear versus story drift responses and the
development of drying shrinkage in the cover concrete were observed in the CES columns due
to use of HPERCC without aggregates. In addition, the production and casting of HPFRCC were
very difficult due to less workability.
In order to solve these problems in the columns using HPFRCC, use of fiber reinforced concrete
(FRC) for CES members have been proposed, and the structural performance of the columns
(Kuramoto et al. 2002, Adachi et al. 2003, Taguchi et al. 2006) and the beam-column joints

(Matsui and Kuramoto 2007, Kuramoto et al. 2008) have been investigated.
The experimental studies on CES columns using FRC are introduced with the advantage of
CES structures in this paper.
ADVANTAGE OF CES STRUCTURES
CES structure using FRC is a simple composite structural system consisting of only steel and
FRC, as shown in Figure 1. This "simple structure" has excellent seismic performance and can
make construction cost and time reduced. In addition, CES structure is widely used for several
purposes, from low to high-rise or from small-scale to large-scale buildings, and the pre-cast
design and construction of CES structure will be easier than those of SRC structure.
The structural advantage of CES structure can be illustrated using a simple example shown in
Figure 2. The figure shows the cross-section of a column in 1st story of 13-story SRC building
and the cross-sections of RC and CES columns which have the same flexural strengths as the
SRC column. SRC column has a cross section of 900 mm square (Fc36), 2-H-600×300×16×28
(SN490), 12-D29 (SD390). If it is compared with RC column using the same concrete strength,
24+8-D38 (SD490) reinforcing bars are needed and the column section should be 900 mm
square. For CES column, on the other hand, if built-in steel 2-H-700×450×16×28 (SN490) is
used, the cross section will be 800 mm square (Fc36) which is smaller than that of SRC column.
Thus, CES column can be designed with smaller section in comparison with the SRC column
having the main reinforcement in the four corners. If the reinforcing bars in SRC column are
eliminated, the concrete cover will be smaller while the size of the steel will be larger in order to
keep the same flexural strength of the column. Also, it is possible to use the wider steel flange
for this purpose. Therefore, the effective utilization of steel is one main advantage of CES
structural system.
Another advantage of CES structure is that the structure can be applied for various construction
types, as shown in Figure 3. Basically, CES structural system consists of CES columns and
CES beams (see Figure 3(a)). In addition, the CES structural members can be designed easily
with other types of structural members such as CES columns with steel-concrete composite
(SC) beams or steel beams, as shown in Figure 3(b). Also, it is possible to use RC and SRC
beams if it is considered the method to fix the main reinforcement of beams with CES columns.
Furthermore, it is also possible to use CES beams in steel structures, SRC structures and CFT
structures (see Figure 3(c)).
In real structure, CES structure can be applied not only for the whole building but also for a part
of building (see Figure 3(d)). In addition, not only the pure CES frame can be constructed, but
many types of earthquake-proof elements can be also installed easily to CES structure such as
steel brace, shear wall, damper, etc, as shown in Figure 3(e).
SRC CES (a) SRC (b) RC (c) CES
Figure 1 – Image of Concrete Encased Steel Figure 2 – Comparison of column section

(a) CES Column+CES Beam (b) CES Column+SC or S Beam (c) SRC or CFT Column+CES Beam
(d) Lower CES Structure+Upper S Structure (e) CES Structure+Braces, etc.
Figure 3 – Examples of construction with CES structural members
STRUCURAL CHARACTERISTICS OF CES COLUMNS
Experimental Program
(1) Specimens and material used
A total of nine composite columns including seven CES columns using FRC, one CES column
using normal concrete and one SRC column were tested to investigate the structural
performance of the columns (Kuramoto et al. 2000, Kuramoto et al. 2002, Adachi et al. 2003,
Taguchi et al. 2006). The dimension and detail of specimens are shown in Figure 4 and Table 1.
The tests are divided into three phases. The first phase test was for Specimens SRC, SC, VF1,
VF2 and SF2 in which the behavior of CES columns using normal concrete and FRC with
different fiber was compared with that of SRC column. The second phase test was conducted
to investigate the effect of applied axial force using Specimens VF2N3, VF2N5 and VF2NV. The
third phase was to investigate the behavior of CES column using single H-section steel for
Specimen CESU.
In the first phase test, Specimens SC, VF1, VF2 and SF2 which are CES columns had the same
dimension and steel details. The different was only the concrete used. For Specimen SC, a
normal concrete was used while FRC with Poly-vinyl Alcohol fiber (PVA fiber: RF4000) of 1.0%
and 2.0% in the volume content ratios were used for Specimens VF1 and VF2, respectively. For
Specimens SF2, on the other hand, FRC with stainless steel fiber (SS fiber: F430D) of 2.0%
was used. All specimens had columns with a 400mm square section and 1,600mm height, and

the height-depth ratio was 4.0. Steels encased in each column had a cross shape section
combining two H-section steels (i.e., double-H section steel) of 300x150x6.5x9 mm. In
Specimen SRC, the cross section was similar with the other 4 above specimens, however, the
smaller size of H-section steel, 250×125×6×9 mm, was used due to the present of reinforcing
bars.
Specimens VF2N3, VF2N5 and VF2NV which were used in the second phase test had the
same cross section, while axial forces with different loading pattern were applied. Due to less
Column Height: 1,600
Cross Section
400 x 400
Column Height: 1,600
Cross Section
400 x 400
Column Height: 1,320
Cross Section
330 x 330
SRC SC, VF1, VF2, SF2 VF2N3, VF2N5, VF2NV CESU
Reinforcement fiber
Column
Section
Concrete
Figure 4 – Test specimens
Table 1 – Test program
Column Height: 1,600
Cross Section
400 x 400
Specimen SRC SC VF1 VF2 SF2 VF2N3 VF2N5 VF2NV CESU
Type -
Volume
content
PVA fiber
(RF4000)
SS fiber
(F430D)
PVA fiber
(RF4000)
- 1.00% 2.00% 2.00% 2.00% 1.50%
Width b(mm) 400 330 400
Depth D(mm) 400 330 400
Comp.
Strength σB(MPa) 35.5 37.3 52.3 55.5 65.3 46 38 33.5
Young
Modulus
Ec(GPa) 24.1 26.1 26.2 26.3 26.5 29.8 27.4 -
Column height h(mm) 1600 1320 1600
Shear-span ratio a/D 2
Shape Double H section (+ shaped) H section
250×125
×6×9
300×220
×10×15
Section size
300×150×6.5×9 250×125×6×9
Flange Yield
Strength σfy(MPa)
Built-in
Steel
300 323 337 335 289
Web Yield
Strength σwy(MPa) 347 412 364 393 299
Applied Axial Force
Loading
N(kN) 1100
Constant
1500 2380
Varying
2380 -910
Constant
1600
Axial yield
bDσB(kN)
No(kN)*
5680
7186
5968
8125
8368
9994
8880
10414
10448
11699
5009
6670
4138
5959
5360
6906
Axial force ratio
N/bDσB
N/No
0.19
0.15
0.18
0.14
0.13
0.11
0.12
0.11
0.11
0.09
0.30
0.22
0.58
0.40
0.58
0.40
-0.22
-0.15
0.30
0.17
*:N o= cN cu+ sN cu= cr u･σ B･ cA+ sσ y･ sA

axial loading capacity of the loading apparatus used, the cross section of these three specimens
had become smaller, 330mm square, compared with previous specimens with a 400 mm square
section. The column height of 1,320 mm was planned to be the height-depth ratio of 4.0. FRC
with PVA fiber of 2.0% in the volume content ratios and double-H section steel of 250×125×6×9
mm were used for all specimens.
On the other hand, Specimen CESU in the third phase test had the same cross section and
column height as specimens in the first phase test, while FRC with PVA fiber of 1.5% and single
H-section steel of 300×220×10×15 mm were used.
(2) Test set-up and loading procedures
In the first phase test, the specimens were loaded lateral cyclic shear forces by using two
horizontal hydraulic jacks, which were installed in parallel each other for one direction, and a
constant axial compression of 1,100kN by using four vertical actuators, as shown in Photo 1.
The axial compression ratios, N ( b ⋅ D ⋅σ
B ) , were 0.19 for Specimen SRC, 0.18 for Specimen
SC, 0.13 for Specimen VF1, 0.12 for Specimen VF2 and 0.11 for Specimen SF2, respectively.
The loads were applied through a steel frame attached at the top of a column that was fixed to
the base. The four vertical actuators to apply the constant axial compression were also used to
keep the column top beam parallel to the bottom beam, so that the column would be subjected
to anti-symmetric moments.
In the second phase test, the loading apparatus used was the same as in the first phase test.
Specimens VF2N3 and VF2N5 were subjected to constant axial load of 1,500 kN and 2,380 kN
( N ( b ⋅ D ⋅σ
B ) =0.3 and 0.58), respectively. On the other hand, Specimen VF2NV was subjected
to varying axial load of ranging from -910 kN to 2,380 kN ( N ( b ⋅ D ⋅σ
B ) =-0.22 to 0.58). This
specimen represented an external column in the lower story of 20-story frame building. The
applied varying axial force was given by N = 0.
1 ⋅ Ni
± Q , where N i = Initial axial force and Q =
applied shear force.
Specimens CESU in the third phase test was tested by using new loading apparatus shown in
Photo 2, which was almost the same function and performance as the apparatus used in the
first and second phases. Constant axial load of 1,600 kN ( N ( b ⋅ D ⋅σ
B ) =0.3) was applied to the
specimen.
Photo 1 – Test set-up for Phases 1 and 2 Photo 2 – Test set-up for Phase 3

The same loading pattern was employed in all tests. The incremental loading cycles were
controlled by drift angles, R, defined as the ratio of lateral displacements to column height, δ/h.
The lateral loading sequence consisted of two cycle to R =0.005, 0.01, 0.015, 0.02, 0.03, 0.04
rad. and half cycle to R=0.05 rad., then the test was terminated.
STRUCTURAL PERFORMANCE OF CES COLUMNS USING FRC
Failure Mode and Shear-Drift Response
The yield and maximum strengths and the corresponding drift angles in the positive loadings for
each specimen are listed in Table 2. The yielding of each specimen was assumed when the first
yielding of steel flange was observed. The shear versus drift angle responses and crack
patterns after loadings for each specimen were compared in Figure 5 and Photo 3, respectively.
In the Figure 5, dotted lines express the flexural strengths, Qfcal, calculated by the strength
superposition method (AIJ 2001) in which the flexural strengths contributed by FRC and steel
are cumulatively increased. The dotted lines are drawn by considering the P-δ effect due to the
loading system employed.
In the first phase test, Specimen SRC showed relatively stable behavior with spindle shaped
hysteresis loops which is a marked characteristic of composite column although a little
deterioration in load carrying capacity after attaining to the maximum strength was observed.
Bucking of reinforcing bars at the both column ends was also observed in the loading cycle of R
of 0.04 rad. due to spalling of cover concrete caused by compressive failure in critical hinge
regions, as shown in Photo 3.
Table 2 – Yield and maximum strengths and the corresponding drift angles in positive loading
Specimen SRC SC VF1 VF2 SF2 VF2N3 VF2N5 VF2NV CESU
at Ry (rad./100) 1.3 1.0 1.1 1.0 1.1 1.0 1.0 1.4 0.6
Yielding
Qy (kN) 620 527 612 608 643 425 415 448 592
at Max.
Rmax (rad./100) 1.5 1.0 1.5 1.5 2.0 1.5 1.2 1.5 1.3
Capacity
Qmax (kN) 638 527 689 703 738 481 439 454 734
SRC SC VF1 VF2 SF2 VF2N3 VF2N5 VF2NV CESU
Photo 3 – Crack modes of specimens after loading

Shear (kN)
Shear (kN)
Shear (kN)
800
600
400
200
0
-200
-400
-600
-800
800
600
400
200
0
-200
-400
-600
-800
600
400
200
0
-200
-400
-600
-4
-4
-4
SRC
VF1
-3
-3
VF2N3
-3
-2 -1 0 1 2 3
Drift Angle (x10 -2 rad.)
-2 -1 0 1 2 3
Drift Angle (x10 -2 rad.)
-2 -1 0 1 2 3
Drift Angle (x10 -2 rad.)
: Q fcal
4
: Q fcal
4
: Q fcal
4
5
5
5
Shear (kN)
Shear (kN)
Shear (kN)
800
600
400
200
0
-200
-400
-600
-800
800
600
400
200
0
-200
-400
-600
-800
600
400
200
0
-200
-400
-600
-4
-4
-4
SC
VF2
-3
-3
VF2N5
-3
-2 -1 0 1 2 3
Drift Angle (x10 -2 rad.)
-2 -1 0 1 2 3
Drift Angle (x10 -2 rad.)
-2 -1 0 1 2 3
Drift Angle (x10 -2 rad.)
In Specimen SC which is a CES column with normal concrete, shear cracks occurred in the
central part of the column at an early stage, R of 0.005 rad., due to no transverse reinforcement.
Then, after attaining to the maximum strength with yielding of steel flange in the both end of the
column at R of 0.01 rad., significant propagation of the shear cracks, the spalling of cover
concrete and a little deterioration in load carrying capacity were observed with an increase of
drift angles. As shown in Figure 5, however, the column showed relatively stable behavior with
spindle shaped hysteresis loops as well as Specimen SRC although the maximum strengths in
both positive and negative loadings were somewhat less than the calculated flexural strength.
In CES column specimens with FRC, on the other hand, crack modes of concrete were quite
different from those in Specimens SRC and SC.
In Specimen VF1 with PVA fiber of 1.0% in the volume content ratio, flexural cracks occurred
first at R of about 0.003 rad. at both top and bottom of the column. With an increase of drift
angles, the flexural cracks propagated and thin shear cracks dispersed all over the column. The
specimen showed stable and spindle shaped hysteresis loops with a little deterioration in load
carrying capacity after attaining to the maximum capacity at R of 0.015 rad. Specimen VF2 with
PVA fiber of 2.0% showed slightly better hysteresis loops without distinct deterioration in load
carrying capacity than those of Specimen VF1. Specimen VF2 also showed better propagation
of cracks in cover concrete that means better performance in the damage limitation than
Specimen VF1. Specimen SF2 with SS fiber of 2.0% showed high structural performance with
the highest maximum capacity among the tested specimens. As shown in Photo 3, the spalling
of cover concrete due to the propagation of cracks, crushing in concrete and so on was not
observed until R of 0.05 rad. in these three specimens.
: Q fcal
4
: Q fcal
4
: Q fcal
Figure 5 – Shear versus drift angle responses
4
5
5
5
Shear (kN)
Shear (kN)
Shear (kN)
800
600
400
200
0
-200
-400
-600
-800
800
600
400
200
0
-200
-400
-600
-800
600
400
200
0
-200
-400
-600
-4
-4
-4
CESU
SF2
-3
-3
VF2NV
-3
-2 -1 0 1 2 3
Drift Angle (x10 -2 rad.)
-2 -1 0 1 2 3
Drift Angle (x10 -2 rad.)
-2 -1 0 1 2 3
Drift Angle (x10 -2 rad.)
: Q fcal
4
: Q fcal
4
: Q fcal
4
5
5
5

In the second phase test, the compressive failure and fall down of concrete cover did not
occurred for all specimens, Specimens VF2N3, VF2N5 and VF2NV, as seen in Photo 3. In all
specimens, moreover, there was concrete unfilled part near the bottom of the column after
concrete casting which was repaired by concrete mortar, and it is observed that most of flexural
deformation concentrated with the development of significant flexural cracks on the repaired
part. In Specimen VF2N5 subjected to high constant axial force, the significant vertical cracks,
which are compressive cracks, occurred. On the other hand, for Specimen VF2NV which is
subjected to varying axial force, many small shear cracks dispersedly occurred.
Specimen VF2N3 had the highest maximum strength compared with other two specimens. It is
considered as one of the reasons that the concrete strength of this specimen was higher than
that of other two specimens, even though the lowest axial force ratio ( N ( b D ⋅σ
)
⋅ =0.32) was
applied among these 3 specimens. In this specimen, the maximum strength of 481kN was
reached at R of 0.015 rad. After attaining to the maximum strength, the load carrying capacity
decreased slightly. However, if the P-δ effect due to the behavior of the loading apparatus is
considered, it is seen that there is almost no decrease of the strength. After R of 0.03 rad. at the
second cycle, the shape of hysteresis curve was changed to be the pinching shape gradually.
Specimen VF2N5 showed larger spindle shaped hysteresis loops than those of Specimen
VF2N3. In this specimen, the maximum strength of 439 kN was reached at R of 0.012 rad. Also,
if the P-δ effect due to the loading system, there was little strength degradation after attaining to
the maximum strength, which is almost similar with Specimen VF2N3 showing a stable behavior.
However, the axial deformation reached to 10mm at R of 0.04 rad. The elastic behavior of axial
deformation was observed until R of 0.01 rad., then, the compression deformation increased
rapidly. It was observed that the development of axial deformation in this specimen was the
highest among these three specimens tested.
In Specimen VF2NV which is subjected to varying axial force, the column had the maximum
strength of 453.5kN at R of 0.0151rad. When tensile axial force was applied, moreover, the
maximum strength of 349 kN was reached at R of -0.04rad. On tensile axial force side, the
spindle shaped hysteresis loops was observed, while the curves showed a pinching shape on
compressive axial force side. For axial deformation, tensile deformation increased with the
increase of drift angles on tensile axial force side, but, on compressive axial force side, the peak
axial deformation of 1.3 mm was reached at R of 0.015rad. and then, the deformations tended
to be constant. The axial deformation versus drift angle response of Specimen VF2NV is shown
in Figure 9(b) with the analytical results.
As mentioned earlier, there was a repaired part near the bottom of the column for each
specimen where the flexural-shear and axial deformations were intensive in this portion.
However, the shear versus drift angle responses showed a stable behavior.
In Specimen CES-U, cracks occurred in the connections between the column and loading stubs
at R of 0.005 rad. in the tension side of the top and bottom of the column, and simultaneously
flexural cracks occurred in the tensile region of the top and bottom of the column due to bending
moments. These flexural cracks propagated and then, shear cracks appeared on the top and
bottom of the column at R of 0.01rad. Cracks due to compression were also observed in this
stage. Moreover, flexural and shear cracks increased with an increase of drift angles, and the
increase of compression cracks was observed significantly. The specimen showed almost
elastic behavior until the yielding of steel at R of 0.013 rad. in positive loading and -0.014 rad. in
negative loading. After attaining to the maximum strength, little deterioration in load carrying
capacity was observed until R of ±0.04 rad. At R of 0.05 rad., however, the strength degradation
was somewhat observed.
B

Simulating Behavior of CES Column
The analytical method used for simulating the behavior of CES columns is a common fiber
idealization that explicitly models the column by dividing its cross section into a number of small
areas or filaments, as shown in Figure 6. Each fiber is assumed to be uniaxially stressed and to
behave according to assumed hysteresis stress-strain characteristics of its constituting
materials, as explained below. For this analysis, the cross section of column was divided into 40
elements to obtain a higher accuracy. This method assumes that the plane sections to remain
plane, thus implying full compatibility between the steel and FRC components of a composite
cross section.
The analysis is controlled through a series of small steps by curvature or displacement history in
terms of X-axis. With the axial strain at the center of the cross section, Δε0 and the curvatures
along in terms of X-axis, Δφx, the axial strain at the fiber element of i, Δεi is found according to
Δεi =Δε0 + yi Δφx, where yi is the distance from the X-axis to the i-th fiber element on the section.
Considering the equilibrium of the section, axial force ΔN and bending moment ΔM are written
as {ΔN, ΔM} T = [K] {Δε0, Δφx} T , where [K] is stiffness matrix. In this analysis, ΔN, ΔM and Δε0
were calculated by considering the mechanical properties of steel and FRC, as Δφx was the
input data.
In this section, analytical results for Specimen VF2NV subjected to varying axial forces are
shown as an example.
The hysteretic model used for the steel was the tri-linear model proposed by Shibata (1982), as
shown in Figure 7. Yield strengths in both compression and tension are assumed to be equal.
Post yield stiffness ES3 and reduced stiffness due to the Bauschinger effect ES2 are taken as
1/200 and 1/5 of the elastic stiffness ES1, respectively. The incline of stiffness changing line C is
taken as -1/200 of ES1.
The hysteretic models of concrete adopted were the divided linear models shown in Figure 8 for
both cover and core concrete. For cover concrete, an initial linear stiffness up to 40 percent of
concrete strength EC1, a reduced linear stiffness until peak stress has reached EC2, and the
slope of failing linear branch EC3, were given as 1.6σB/εc0, EC1/3 and EC1/5, respectively,
according to the results of concrete cylinder tests, where σB is the concrete cylinder strength
and εc0 is the compressive strain at the stress peak, which was taken as -0.003. For core
concrete, on the other hand, the same values of EC1 and EC2 were adopted as the cover
concrete although EC3 was taken as EC1/80 for Specimens VF2NV. Furthermore, a magnification
factor of concrete strength K for confined core concrete was considered as 1.25 for the
specimen. Liner stiffness at unloading EC4 for both cover and core concrete was taken as σE/(εE
–εR), where σE and εE were the stress and strain at an unloading point on the envelope curve,
and εR was the residual strain (εR =5εE 1.5 and |εR| ≤ 4|εE|/ 5).
Figure 6 – Fiber model Figure 7 – Steel model Figure 8 – Concrete model

Shear (kN)
600
400
200
0
-200
-400
-600
-4
VF2NV
-3
-2
-1
0
1
2
Drift Angle (x10 -2 rad.)
: Analyzed
: Tested
3
4
5
The shear versus drift response for the columns were obtained assuming an antisymmetric
distribution of bending moments along the column height, with the inflection point at mid-height.
Considering the experimental results for curvature distribution along the column height, the
relation between curvature and drift angles, φ and R, was assumed as φ = 3.3 R/L for
Specimens VF2NV, although in elastic assumption the relation is defined as φ = 6 R/L, where L
is the column height. Moreover, the axial deformation, δv, was calculated by assuming as δv
=ε0*L/2.
Figure 9 shows the analytical results of the shear versus drift angles response and the axial
deformation versus drift angle response. As can be seen in both responses, the analytical
results showed a satisfactory agreement with the experimental results. Thus, the hysteresis
behavior of CES columns can be simulated precisely by a common fiber analysis because the
columns are simple composite structural members consisting of only steel and FRC.
CONCLUSIONS
Experimental studies on CES columns using FRC conducted by the authors in past about eight
years were introduced with the advantage of CES structures. The principle conclusions
obtained from the studies can be drawn as follows.
1) CES structure is a simple composite structural system consisting of only steel and FRC,
which can make construction cost and time reduced. CES structure can be widely used for
various scaled buildings from low to high-rise or from small to large-scale. And also the precast
design and construction of CES structure will be easier than those of SRC structure.
2) CES structural system can be applied for not only CES frame buildings but also various
mixed building types such as consisting of CES columns with other structural type of beams,
CFT columns with CES beams, CES frame with braces or shear walls, etc.
3) CES columns using FRC have almost the same structural performance as SRC columns
which possess an excellent earthquake resistance with high capacities and deformability.
4) Use of FRC makes the easy restoration of CES columns possible because the damages in
cover concrete of the columns due to flexural and shear cracks are relatively light even at the
large story drifts.
5) The hysteresis behavior of CES columns can be simulated precisely by a common fiber
analysis because the columns are simple composite structural members consisting of only
steel and FRC.
Axial Deformation (mm)
10
9
8
7
6
5
4
3
2
1
0
-1
-2
-4
-3
-2 -1 0 1 2
Drift Angle (x10 -2 rad.)
3
VF2NV
: Analyzed
: Tested
Figure 9 – Comparison between analytical and experimental results for Specimen VF2NV
4
5

REFERENCES
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Performance of Composite CES Columns Using FRC Subjected to High Axial Compression”,
Proceedings of Japan Concrete Institute, Vol. 25, No. 2, pp. 289-294. (in Japanese)
AIJ (2001). “Standard for Structural Calculation of Steel Reinforced Concrete Structures”,
Architectural Institute of Japan.
Kuramoto H., Kabeyasawa T. and Shen F-H. (1995).” Influence of axial deformation on ductility
of high-strength reinforced concrete columns under varying triaxial forces.” ACI Structural
Journal, Vol. 92, No. 5, pp. 610-618.
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