seismic performance of circular concrete bridge piers
TRANSCRIPT
1. Introduction
Bridges are one of the most critical and important structures in the transportation systems that are constantly subjected to different
kinds of loadings. At times of natural disasters, transportation systems must withstand the calamities in order to sustain transport
connections and communication for better crisis management. One of the most commonly encountered and destructive natural calamities
is earthquake, thus, the seismic performance of the bridges should be strictly observed, especially the seismic performance of existing
bridges.
* 상명대학교 건설시스템공학과 석사과정 (Sangmyung University ․ [email protected])
** 종신회원 ․ 교신저자 ․ 상명대학교 건설시스템공학과 교수 (Corresponding Author ․ Sangmyung University ․ [email protected])
Received December 8, 2019/ revised January 29, 2020/ accepted February 6, 2020
Copyright ⓒ 2020 by the Korean Society of Civil Engineers
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0)
which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Journal of the Korean Society of Civil Engineers ISSN 1015-6348 (Print)
Vol. 40, No. 2: 197-208/ April, 2020 ISSN 2287-934X (Online)
DOI: https://doi.org/10.12652/Ksce.2020.40.2.0197 www.kscejournal.or.kr
Seismic Performance of Circular Concrete Bridge Piers Externally
Strengthened by Carbon Fiber Reinforced Polymer
Catuira, Mabel*, Park, Jong Sup**
마벨*ㆍ박종섭**
탄소섬유강화 플라스틱(CFRP)로 보강된 원형콘크리트 교각의 지진성능 평가
ABSTRACT
This paper evaluated the optimum Carbon Fiber Reinforced Polymer (CFRP) using a circular concrete bridge pier subjected to dynamic
loading. A three-dimensional finite element model was simulated using finite element program, ABAQUS. Concrete Damage
Plasticity (CDP) option and plastic properties of the materials were incorporated to model the non-linearity of the structure. The
analyses parameters were changed in length-to-height ratio and width-to-span ratio where columns were subjected to dynamic loading.
Numerical analysis was conducted, and the seismic performance of the structures were evaluated by analyzing the ductility behavior
of the structure. Results showed that the use of CFRP enhances the structural performance of column and revealed that the increase
in length-to-height ratio plays vital role of improving the performance of the structure than the change in width-to-span ratio.
Key words : Concrete bridge pier, CFRP, Finite element analysis, Dynamic loading
초 록
본 연구에서는 콘크리트 원형 교각의 동적거동 특성을 향상시키기 위하여 최적의 탄소섬유강화 플라스틱 설치 방법에 대해서 해석적 기법을 적
용하여 평가하였다. 범용구조해석 프로그램인 ABAQUS가 해석연구에 사용되었으며, 소성 및 손상 콘크리트 재료특성을 적용하여 구조물의
비선형해석을 실시하였다. CFRP 적용에 따른 내진성능 향상도를 분석하고자 교각높이와 보강된 높이 비율, 교각 지름 대비 CFRP 보강 두께
를 해석변수로 고려하여 거동특성과 연성도를 비교 분석하였다. 해석결과를 토대로 보강에 따른 정량적인 성능향상을 확인할 수 있었으며, 보강
재료 두께 증가보다는 교각높이 대비 보강높이 비율이 보다 성능에 큰 영향을 미치는 것을 알 수 있었다.
검색어 : 콘크리트 교각, 탄소섬유 강화플라스틱, 유한요소해석, 동적하중
구조공학Structural Engineering
Seismic Performance of Circular Concrete Bridge Piers Externally Strengthened by Carbon Fiber Reinforced Polymer
Journal of the Korean Society of Civil Engineers198
The majority of existing bridges were built based on old
building codes and structural manuals. Old bridges constructed
from old structural standards assumed less service loads, which
made them vulnerable to structural damages resulting to possible
poor performance during an earthquake. In addition to that, most
of the existing bridges were made from reinforced concrete that
are constantly exposed to hostile physical and chemical conditions.
This aggressive environment contributes to the progressive damage
of reinforced concrete which made the structure susceptible to the
fatigue behavior of concrete, exposing the reinforcing steel to rust
and corrosion.
The minor damages in the concrete element such as cracks and
spalling in column of the bridges affects the confinement of
concrete to the structure, thus, leading to brittle failure of the
column that could result into serious failure or worse, total
collapse of the structure. The column of bridges is one of the main
structural members of the bridge that resist lateral seismic forces
and vertical forces, thus, the performance and reliability of the
column is vital regarding the performance of the entire structural
system. Therefore, in order to prevent the brittle failure, it is
essential to enhance the ductility of the columns, thus, increasing
the performance and reliability of existing bridges.
Ductility criteria of a concrete column member is a one of the
most important parameters in evaluating the seismic performance
of the structure. In order to increase this type of criteria, con-
finement or external strengthening of concrete column structures
could be provided in order to increase the ductility criteria.
Therefore, in this paper the seismic performance of the structure
was evaluated using the calculated ductility. The progressive
development of computer simulations was utilized using a finite
element software, ABAQUS (2013), to numerically evaluate and
observe the relationship of ductility of the structure with respect
to length-to-height ratio and width-to-span ratio of CFRP.
2. Background of Related Literatures
2.1 Research and Development of Bridge Rehabilitation
Techniques
Researchers and engineers have been interested in the continuous
development of bridge rehabilitation techniques since the mid
1980’s. According to the study of Saadatmanesh et al. (1996),
Özcan et al. (2008) Ye et al. (2003) and Rashid and Mansur (2005),
the problem with the columns constructed based on old codes
faces poor detailing of starter bars and inadequate lateral reinfor-
cement that leads to seismic performance deficiency. Forces
induced by seismic loads that result into shear forces are mainly
resisted by lateral reinforcement, if properly designed, buckling
of the longitudinal bars and sudden loss of bond could be
prevented. Therefore, existing columns with inadequate lateral
reinforcement must be provided by external confinement to
enhance the ductile behavior of the structure.
Many techniques have been implemented into the retrofit design
process mainly based on experimental testing of scaled-down
models of bridge structures. Previous researches, such as study
of Priestley et al. (1984), Chai et al. (1991), and Sun et al. (1992)
in University of California in San Diego have indicated that
strengthening of columns by using steel jackets significantly
improves the performance and ductility of a column. However,
rehabilitation techniques that utilize steel and concrete, such as
section enlargement of columns, confinement by concrete covers,
and attachment of steel jackets are time consuming and difficult
in execution of construction methodologies, therefore, considering
the disadvantages of existing materials, a study for new material
is necessary to develop new techniques.
Since then, researchers have conducted experimental tests to
find an effective and economical alternative material for bridge
rehabilitation. Priestley et al. (1992) presented the study of
column seismic retrofit using Fiberglass/Epoxy, Yamasaki et al.
(1993) investigated the use of Fiber Reinforced Polymers (FRP)
bars to retrofit concrete bridges, and Ehsani et al. (1993) analyzed
the use of glass fiber reinforced polymer (GFRP) bars by circum-
ferentially wrapping the columns around the plastic region. After
years of study using FRP bars and straps as retrofit materials,
Toutanji (1999) extended the study to FRP sheets and presented
a structural model for the behavior of GFRP and CFRP confined
concrete columns using large-scale samples in experiments. The
researches presented that the use of FRP as a material for retrofit
provided desirable results in increasing the performance of the
structure.
The desirable properties of FRP make it to be an appropriate
substitute material for rehabilitation techniques of existing
bridges. FRP is superior to resist corrosion, good adhesion to
concrete, has high strength-to-weight ratio, capability of vibration
absorption, and moisture resistance. In addition to that, Guide for
Catuira, MabelㆍPark, Jong Sup
Vol.40 No.2 April 2020 199
the Design and Construction of Externally Bonded FRP Systems
for Strengthening Concrete Structures (ACI, 2002), reported that
FRP has thermal expansion coefficient of close to concrete and
steel which made it to be a suitable material for externally
strengthening reinforced concrete. Although FRP laminates, bars
and straps are generally more expensive than concrete and steel,
research of Katsumata et al. (1988) and Teng et al. (2002) revealed
that the use of CFRP and GFRP is approximately 20 % less cost
than steel considering construction methodology.
In the recent years, development of computers and various
finite element software has progressed and provided accurate
results. Numerous researchers had corresponded to experimental
tests in the previous decades and conducted numerical experiments
through finite element simulations. In 1999, Tedesco et al. (1999)
assessed a FRP laminate-repaired bridge by finite element
method, Wang and Restrepo (2001) reported that good agreement
of results was observed between the numerical and analytical
results using a short-term assessment of axial load-deformation
of reinforced columns confined with GFRP and steel, Monti et
al. (2001) and Pantelides and Gergely (2002) presented formulae
for calculation of required FRP wrapping thicknesses and
provided design and analysis techniques for seismic retrofit of
concrete members by FRP.
Due to popularity and the increasing demand of research
matter, more and more researches with parametric studies have
been conducted to optimize the application of retrofit materials
to bridge columns. Experimental and analytical parametric
studies were made to establish relationship of column and retrofit
materials. In 2013, Taghia and Bakar (2013) studied parametric
studies and assessed the relationship of varying cross-section of
reinforced short column and varying CFRP layers based on finite
element analysis. Studies of varying reinforcing materials were
also made. Pateriya et al. (2015) presented a numerical analysis
of compressive strength of columns reinforced with varying
materials using steel, GFRP and CFRP and Han et al. (2016)
conducted experimental tests on reinforced concrete evaluating
the performance between CFRP, steel plate and fiber steel
composite plates (FSC). Varying shape of FRP reinforcement
were also studied such as the study of Zeng et al. (2018) which
investigated the behavior and three-dimensional finite element
modeling of circular concrete columns partially wrapped with
FRP strips.
2.2 Ductility Defined using Load-Displacement Curve
Ductility of a concrete bridge column is an important design
factor to consider in seismic performance of the structure. The
ductility of the structure is critical in aspect of dissipation of
seismic energy during earthquake, therefore, the reliability of
existing bridges is enhanced by improving ductility.
In 1994, Jeong (1994) developed energy based method using
load- displacement curve. This method defines the ductility of a
structure using concept of energy by the relating any two of
inelastic, elastic, and total energy as shown in the ductility indices
on Fig. 1. In order to determine the slope that distinguishes elastic
energy from inelastic energy, the slope, S, is calculated as:
(1)
where, slopes S1, S2, S3, were obtained through analytical
calculation and the loads, P1 and P2, were the intersection points
of extended slopes and P3 as the ultimate load. The inelastic,
elastic and total energies were calculated through numerical
integration and in this paper, the ratio of inelastic energy to total
energy is considered.
(2)
It is suggested by Grace et al. (1998) that the structure having
an energy ratio of greater than 75 % is classified to be ductile, and
semi-ductile behavior of energy ratio ranging from 70~74 %.
Fig. 1. Energy Index
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Journal of the Korean Society of Civil Engineers200
3. Finite Element Modeling
Finite element program ABAQUS was chosen to simulate the
model. The software has wide variety of modelling capability and
has concrete damage plasticity (CDP) option that captures the real
behavior of concrete. Rodríguez et al. (2013) recommended that
the use of CDP model exhibits good behavior for concrete under
monotonic, cyclic and dynamic loading.
(a) Length-to-Height Ratio (b) Width-to-Span Ratio
Fig. 2. Nomenclature of Parametric Models
Table 1. Nomenclature of Length-to-Height Ratio Cases
Case Profile Analysis Designation Length (m) Height (m) Ratio Percentage (%)
Initial CFRP_0 0 1.65 0 0
Length-to-Height
CFRP_25 0.4 1.65 0.25 25
CFRP_50 0.825 1.65 0.50 50
CFRP_75 1.24 1.65 0.75 75
CFRP_100 1.65 1.65 1.0 100
Table 2. Nomenclature of Width-to-Span Ratio Cases
Case Profile Analysis Designation Width (m) Span (m) Ratio Percentage (%)
Initial CFRP_0 0 0.4 0 0
Width-to-Span
CFRP_1 mm 0.001 0.4 0.0025 0.25
CFRP_2 mm 0.002 0.4 0.0050 0.50
CFRP_3 mm 0.003 0.4 0.0075 0.75
(a) Mechanics of Hydraulic Actuator Test (b) Schematic Diagram of Numerical Model
Fig. 3. Model Configuration Setup
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Vol.40 No.2 April 2020 201
The simulated structure was analyzed under three (3) model
cases, the initial case, the change in height of CFRP (length-
to-height ratio or wrapping height), and the change in thickness
of CFRP (width-to-span ratio or relative wrapping thickness). In
order to account for the effect of change in height of CFRP, the
cross-section of the circular concrete bridge pier was constant and
the thickness of the CFRP and set 2mm. In order to evaluate the
effect of change in thickness of CFRP, the cross-section of the
circular concrete bridge pier were to set to a fixed dimension and
the height of the CFRP were set to height of ¼ of the column. Fig.
2 demonstrates the finite element model cases and Tables 1 and
2 show the corresponding nomenclature of ratio with respect to
each case analysis.
The dimensions of the structure were taken from experimental
specimens subjected to real life hydraulic actuator as shown in
Fig. 3(a). In order to avoid creating unnecessary elements, the
foundation of the structure was not modelled and changed into
encased boundary condition to account for the footing. Fig. 3(b)
shows the schematic design of the numerical model. A three-
dimensional finite element was modelled as shown in the Fig. 4,
having C3D8R hexahedral elements for concrete structure as S4R
shell elements for CFRP.
In this study, numerical models were subjected to gravity
loading and dynamic loading were applied until failure of the
structure. Fig. 4 illustrates the direction and location of dynamic
loading which is positioned in the middle of the loading cap in
order to equally distribute the loads. Tie constraint option was
used in defining the interaction between CFRP and concrete
structure. CFRP was tied to concrete in order to force the nodes
to behave in the same translations. The assumed values of the
Table 4. Material Properties of Concrete
Density
(kg/m3)
Young’s
Modulus (GPa)Poisson’s Ratio
Dilation Angle
(°)Eccentricity fbo/fco Kc
Viscosity
Parameter
2400 28 0.2 36 0.1 1.16 0.667 0
Compressive Behavior Compressive Damage Tensile Behavior Tensile Damage
Yield Stress
(MPa)Inelastic Strain Damage Parameter Inelastic Strain Yield Stress (MPa) Cracking Strain Damage Parameter Cracking Strain
15 0 0 0 3 0 0 0
23 0.003 0.2 0.000333 2 0.0002 0.2 0.0002
29 0.00055 0.3 0.0007 1.5 0.0003 0.3 0.0003
33 0.00147 0.4 0.0013 1.2 0.0004 0.4 0.0004
25 0.0066 0.45 0.002 1 0.0005 0.5 0.0005
22 0.008 0.5 0.003 0.8 0.0008 0.6 0.0008
20 0.009 0.6 0.0043 0.5 0.001 0.8 0.001
10 0.01 0.8 0.007 0.4 0.002 0.7 0.002
0.9 0.01 0.2 0.003 0.9 0.003
0.1 0.005 0.99 0.005
Fig. 4. Boundary and Loading Conditions of Meshed Numerical Model
Table 3. Material Properties of CFRP
Density
(kg/m3)
Young’s Modulus
(MPa)
Poisson’s
Ratio
Yield Stress
(MPa)
Plastic
Strain
1500 2.35 0.3 344 0
Seismic Performance of Circular Concrete Bridge Piers Externally Strengthened by Carbon Fiber Reinforced Polymer
Journal of the Korean Society of Civil Engineers202
mechanical properties of the materials were listed in Tables 3 and
4 while the dynamic loading is shown in Fig. 5.
The values of CFRP were taken from the experimental study
of Han et al. (2016) and the values of concrete properties were
taken from the study of Senturk and Pul (2017). Senturk and Pul
(2017) published a calibrated concrete damage plasticity parameter
by performing a standard cylinder test on ABAQUS using a f’c=30
MPa concrete. Table 4 listed the parameters of concrete material
where fb0/fc0 is the ratio of strength in biaxial state (fb0) to strength
in uniaxial state (fc0) and Kc, is the ratio of the distances between
the hydrostatic axis and respectively the compression meridian
and the tension meridian in the deviatoric cross section. Fig. 6
shows the graph of tensile and compressive stress-strain for the
numerical model of concrete.
4. Discussion of Results
The stress-strain and load-displacement hysteresis curve were
investigated through finite element results and the ductility of the
structure were obtained by numerical integration.
4.1 Finite Element Results
After performing finite element analysis, an element within the
plastic hinge section of the column was evaluated as shown in Fig.
7. The structure without CFRP reinforcement was compared to
CFRP with increasing thickness and wrapping ratio. Fig. 8 and
Table 5 show the effect of increasing the length-to-height ratio
of CFRP to stress-strain of the structure. It shows that the use of
Fig. 5. Applied Dynamic Loading
Fig. 6. Stress-Strain Curve of Simulated Concrete
Fig. 7. Evident Deformation at Plastic Hinge Region
(a) Stress-Strain Curve according to Length-to-Height Ratio
(b) Stress-Strain Curve according to Width-to-Span Ratio
Fig. 8. Comparison of Stress-Strain Curve without CFRP to Structurewith CFRP
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Vol.40 No.2 April 2020 203
CFRP improves the performance of the structure in terms of
stress-stain. In addition to that, it was observed that the increase
of height in CFRP significantly enhanced the behavior of the
column than the increase of thickness of CFRP.
Load-displacement hysteresis curve was also analyzed and
compared with respect to length-to-height ratio. The follow
figures, Figs. 9, 10, and 11 shows the individual load-displacement
hysteresis curve and skeleton curve of the original structure, and
the cases of varying length-to-height ratio and width-to-span
ratio. Figs. 12 shows the comparison of hysteresis curve of
structure without CFRP to Fig. 12(a), structure with varying
wrapping ratio, and Fig. 12(b), structure with varying wrapping
relative thickness. Fig. 13 displays the combined skeleton curve.
Based from the finite element results, Fig. 13(a) illustrates that
the base shear of the structure and the displacement increases as
length-to-height ratio increases. In addition to that, it could be
observed from Fig. 13(b) that the combined skeleton curve with
respect to change in width-to-span ratio indicates that there is
insignificant change in the load-displacement of the structure as
the thickness of the CFRP is being increased. Tables 6 and 7
present the base shear and deformation as the length-to-height
Table 5. Comparison of Stress according to CFRP Ratio
Case RatioStress (kPa)
Yield Ultimate
Initial 0 1143.66 1980.51
Length-to-Height Ratio
0.25 2171.50 2303.76
0.50 2246.91 2507.11
0.75 2926.41 3049.41
1.00 2979.74 3211.01
Width-to-Span Ratio
0.0025 1651.31 2227.48
0.0050 2246.91 2507.11
0.0075 2280.45 2301.23
Fig. 9. Load-Deflection Curve of Concrete Column without CFRP
(a) Load-Deflection Hysteresis Curve and Skeleton Curve with L/H of 0.25
(b) Load-Deflection Hysteresis Curve and Skeleton Curve with L/H of 0.50
(c) Load-Deflection Hysteresis Curve and Skeleton Curve with L/H of 0.75
(d) Load-Deflection Hysteresis Curve and Skeleton Curve with L/H of 1.00
Fig. 10. Individual Load-Deflection Hysteresis Curve and Skeleton Curve with Varying Length-to-Height Ratio
Seismic Performance of Circular Concrete Bridge Piers Externally Strengthened by Carbon Fiber Reinforced Polymer
Journal of the Korean Society of Civil Engineers204
ratio and width-to-span ratio varies. Based from the results, it was
observed that the increase of thickness in CFRP is capable of
slightly improving the performance of the structure but not as
significant as change in length-to-height ratio.
4.2 Seismic Performance Evaluation
The ductility of the structure was evaluated using numerical
analysis. The elastic, inelastic and total energy were obtained
through numerical integration. Table 8 lists the ductility of the
structure according to change in wrapping ratio and relative
thickness of the reinforcement. Based from the results, each of
the specimen confined by CFRP reduced the risk in brittle failure,
thus, improving the seismic performance of the structure. In
particular, the increase of length-to-height ratio of the reinforcement
significantly contributed to the enhancement of ductility of the
structure than the increase of width-to-span.
(a) Load-Deflection Curve of 1mm thick CFRP (b) Load-Deflection Curve of 2mm thick CFRP (c) Load-Deflection Curve of 3mm thick CFRP
Fig. 11. Individual Load-Deflection Hysteresis Curve and Skeleton Curve with Varying Width-to-Span Ratio
(a) Combined Load-Deflection Hysteresis Curve with Varying Length-to-Height Ratio
(b) Combined Load-Deflection Hysteresis Curve with Varying Width-to-Span Ratio
Fig. 12. Comparison of Load-Deflection Hysteresis Curve with and without CFRP
(a) Combined Load-Deflection Skeleton Curve according to Varying Length-to-Height Ratio
(b) Combined Load-Deflection Skeleton Curve according to Varying Width-to-Span Ratio
Fig. 13. Comparison of Load-Deflection Skeleton Curve with and without CFRP
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Vol.40 No.2 April 2020 205
4.3 Summary of Results
The discussion in this section summarizes the relationship of
length-to-height ratio of the CFRP to the overall performance of
the structure. Fig. 14(a) to Fig. 14(d) show that the same increasing
trend was observed in general, the response of the circular
concrete column strengthened with CFRP improved as the height
of the reinforcement increased. The increasing trend indicates
that as the ratio of length-to-height increases, the capacity in
stress, load, deflection and ductility of the structure also increases.
Table 9 summarizes the performance of the structure under the
change in length-to-height ratio and it was found out that the full
Table 6. Comparison of Base Shear according to CFRP Ratio Table 8. Comparison of Ductility according to CFRP Ratio
Case RatioLoad (kN) Case Ratio Ductility (%)
Yield Ultimate Initial 0 77.921
Initial 0 30090.35 31785.50
Length-to-Height
Ratio
0.25 88.549
Length-to-Height
Ratio
0.25 38880.75 39965.20 0.50 90.149
0.50 53500.31 55626.30 0.75 91.812
0.75 86912.82 109029.60 1.00 91.917
1.00 113832.49 138392.00
Width-to-Span Ratio
0.0025 84.781
Width-to-Span
Ratio
0.0025 39369.27 39814.20 0.0050 88.549
0.0050 38880.75 39965.200.0075 89.186
0.0075 39466.61 40466.60
(a) Relationship of Stress and Length-to-Height Ratio (b) Relationship of Base Shear and Length-to-HeightRatio
(c) Relationship of Deformation and Length-to-HeightRatio (d) Relationship of Ductility and Length-to-Height Ratio
Fig. 14. Effect of Increasing Length-to-Height Ratio to the Performance of the Structure
Table 7. Comparison of Displacement according to CFRP Ratio
Case RatioDisplacement (mm)
Yield Ultimate
Initial 0 9.854 29.969
Length-to-Height Ratio
0.25 12.482 31.730
0.50 18.876 58.294
0.75 30.641 75.597
1.00 61.460 120.486
Width-to-Span Ratio
0.0025 9.785 31.312
0.0050 12.482 31.730
0.0075 9.609 32.821
Seismic Performance of Circular Concrete Bridge Piers Externally Strengthened by Carbon Fiber Reinforced Polymer
Journal of the Korean Society of Civil Engineers206
confinement, length-to-height ratio of 1:1, exhibits significant
improvement in the seismic performance of the structure.
The relationship of increasing thickness of the reinforcement
and general behavior of the structure is discussed in this section.
Fig. 15(a) to 15(d) show that there is only slight improvement in
the performance of the circular concrete column as the thickness
of the CFRP increases. Based from the graphs of Fig. 15, there
is a seemingly flat slope trend observed as the width-to-span ratio
moves from 0.0025 to 0.0075. This gradual incline indicates that
there is only slight improvement in the performance of the
structure as the thickness of the CFRP is being increased. Table
10 summarizes the behavior of the structure with respect to change
in width-to-span ratio.
Table 9. Performance of the Structure according to Change in Length-to-Height Ratio
CASEStress (kPa) Load (kN) Displacement (mm) Energy Ratio
(%)Remarks
Yield Ultimate Yield Ultimate Yield Ultimate
0 1143.66 1980.51 30090.35 31785.20 9.854 29.969 77.921 Ductile
0.25 2171.50 2303.76 38880.75 39965.20 12.482 31.730 88.549 Ductile
0.50 2216.91 2477.11 53500.31 55626.30 18.876 58.294 90.149 Ductile
0.75 2926.41 3049.41 86912.82 109029.60 30.641 85.597 91.812 Ductile
1.00 2979.74 3211.01 113832.49 138392.00 61.460 120.486 91.917 Ductile
(a) Relationship of Stress Capacity to change in Width-to-Span Ratio (b) Relationship of Base Shear to change in Width-to-Span Ratio
(c) Relationship of Deformation and Width-to-SpanRatio (d) Relationship of Ductility and Width-to-SpanRatio
Fig. 15. Effect of Increasing Width-to-Span Ratio to the Performance of the Structure
Table 10. Performance of the Structure according to Change in Width-to-Span Ratio
CASEStress (kPa) Load (kN) Displacement (mm) Energy Ratio
(%)Remarks
Yield Ultimate Yield Ultimate Yield Ultimate
0 1143.66 1980.51 30090.35 31785.50 9.854 29.969 77.921 Ductile
0.0025 1651.31 2227.48 39369.27 39814.20 9.785 31.312 84.781 Ductile
0.0050 2171.50 2303.76 38880.75 39965.20 12.482 31.730 88.549 Ductile
0.0075 2280.45 2301.23 39466.61 40466.60 9.609 32.821 89.186 Ductile
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5. Conclusion
The following conclusions are drawn based by means of the
results of the conducted finite element analysis. The main aim of
this paper was to optimize the application of CFRP. The
performance of a circular concrete column was analyzed according
to the of change in length-to-height ratio and width-to-span ratio
of CFRP.
(1) For the change of length-to-height ratio, it was found out that
using CFRP as reinforcement with ratio of 0.25 to 1.0 could
increase the ductility of the circular concrete column from 78 %
ranging up to 89~92 %. In this regard, the continuous use of
CFRP throughout the length of circular concrete structure
showed significant improvement in the base shear, stress
capacity, lateral deformation and ductility. Furthermore, this
proves that the full confinement of the structure using CFRP
or the length-to-height ratio of 1.0 is the optimum wrapping
ratio of CFRP.
(2) The change of width-to-span ratio indicated that the increase
in the thickness of CFRP also increases the ductility of the
structure. It was found out that from the ductility of the
original structure, 78 %, it could be improved ranging from
85 % up to 89 % with a wrapping thickness ratio of 0.0025
to 0.0075. However, the effect of increasing the thickness of
CFRP to the overall performance structure tends to be
insignificant. It was observed that the increase of thickness
of the confining material could enhance the structure,
however, there is only slight improvement in the behavior of
the structure.
(3) For circular concrete columns, increasing the wrapping height
of external confinement developed significant improvement
than increasing the wrapping thickness of CFRP. The increase
in wrapping height provided more confinement to reduce the
brittle failure and to increase the ductility and earthquake
resistance of circular bridge pier columns.
Acknowledgement
This research is supported by the Ministry of Land, Trans-
portation and Maritime Affairs (19SCIP-B146946-02) and National
Research Foundation (NRF-No.2019R1F1A1060708), Republic
of Korean.
본 논문은 2019 CONVENTION 논문을 수정·보완하여 작성되
었습니다.
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