Compression Failure of RC Beams Deteriorated by Corrosion
Ryo MURAI
Master Program, University of Tsukuba, Japan
s1420936@u.tsukuba.ac.jp

Michiaki OYADO, Dr.Eng.
Senior Researcher, Railway Technical Research Institute, Japanoyado@rtri.or.jp

Akira YASOJIMA, Ph.D.
Assistant Professor, University of Tsukuba, Japanyasojima@kz.tsukuba.ac.jp

Toshiyuki KANAKUBO, Ph.D.
Associate Professor, University of Tsukuba, Japankanakubo@kz.tsukuba.ac.jp

ABSTRACT: It is important to clarify the degradation of structural performance of existing reinforced
concrete (RC) structures to manage the sustainable infrastructures. Typical factor of deterioration iscorrosion of reinforcing bar. Many studies have been conducted about the effects of reinforcing bar
corrosion on the structural performance of RC members. Because corrosion of reinforcing bars has large
influence on the safety, it is necessary to accurately assess the effects of degradation. The bending
capacity of RC beam is influenced only by the characteristics of tension bars, deformation capacity isaffected by compressive performance of concrete. The objective of this study is to investigate theinfluence of compression failure of concrete to the performance of RC member. RC beam specimens, inwhich the corrosion of compression bars and cracks in compression region are simulated, are subjected
to bending test. As the test results, it is recognized that the damages in compression region cause theremarkable decrement of deformation capacity of RC beams. Load–deflection curves of the specimens
are simulated by the section analysis. In the analysis, buckling of compression bars and deterioration ofcompression performance of concrete are considered. The analysis results show a good agreement withthe experimental ones.

1. Introduction
It’s important to clarify the degradation of structural performance of existing reinforced concrete (RC)structures to manage the sustainable infrastructures. Typical factor of deterioration is corrosion ofreinforcing bar. Many studies have been conducted about the effects of reinforcing bar corrosion on thestructural performance of RC members. Because corrosion of reinforcing bars has large influence on thesafety, it is necessary to accurately assess the effects of degradation. Corrosion of reinforcing bars
causes the degradation of bending and shear capacity of RC members. The reduction of cross-sectional
area of corroded bars exhibits the degradation of yield and tensile strength of the bars and causes
remarkable decrement of deformation capacity. In addition, cracks along the reinforcing bars due tocorrosion lead to the transition of failure mode of RC member such as bond splitting failure. Thesephenomena have been studied in many previous researches. Cracks along the reinforcing bars have apossibility to lead the degradation of concrete performance. While the bending capacity of RC beam is
influenced only by the characteristics of tension bars, deformation capacity is affected by compressivePage 1 of 7

performance of concrete (Oyado et al., 2006). The objective of this study is to investigate the influence ofcompression failure of concrete to the performance of RC member.
The objective of this study is to investigate the influence of compression failure of concrete to theperformance of RC member. RC beam specimens, in which the corrosion of compression bars and cracks
in compression region are simulated, are subjected to bending test. The experimental load-deflection
curves are simulated by section analysis using stress-strain model of cracked concrete and the reinforcing
bars in buckling. To obtain the stress-strain curves of buckling bars, the buckling test is also conducted.

2. Experiment Program
The beam specimen is shown in Fig. 1. Mechanical properties of used materials are shown in Table 1 andTable 2. Specimens with cross section of 150mm × 235mm are subjected to four point bending test. The
pure bending span is 400mm. The specimens are reinforced with high tensile strength reinforcing bars,and low strength concrete is used in order to ensure that the failure of concrete in compression sideoccurs first. Specimens list is shown in Table 3. Variation factors are the simulation method of concrete
crack and sectional area reduction in compression bars. The concrete crack is simulated by inserting slits
around the compression bars in pure bending span. Fig. 2 shows the variation of slits. The acrylic sheets
are set in the beam side in full region of pure bending span in specimens B-Sc and B-Sc(R). The 50 mm
long sheets are set in same region with the intervals of 100 mm in specimen B-Si. In specimen B-US, the50 mm long sheets are set both in the beam side and upper.
The sectional-area reduction due to corrosion is simulated by scraping the reinforcing bar. The bars arescraped using a disc sander as shown in Fig. 3. Scraping is carried out by controlling a scraped depth in
the minimum diameter direction between lugs of reinforcing bar. An ellipse having a nominal crosssectional area is assumed to determine cross-sectional area ratio, which is set to be 30%. The scraped
positions are set in the pure bending span as shown in Fig. 1. The last letter (R) in specimen ID showsthat the specimens have scraped compression bars.
Monotonic loading is carried out using a universal testing machine of 2,000kN capacity, Measurement
items are applied force, deflections at loading points, and strains of reinforcing bars as indicated in Fig. 1.

Compressive
strength(MPa)12.8

TypeD10
D16

Table 1 – Mechanical property of concrete
StrainElastic modulus
at compressive(GPa)strength (%)
0.21
20.6

Splittingstrength(MPa)1.46

Table 2 – Mechanical property of reinforcing bars
Yield strength Yield strain Elastic modulus
Remarks(MPa)
(%)
(GPa)
385
0.21185
Compression bars
597
0.29
201
Tension bars
Table 3 – Specimens list

ID
B-N
B-N(R)
B-Sc
B-Sc(R)
B-Si
B-US

Section and rebars
Cross-section
235 mm × 150 mm
Tension bars
3-D16
Compression bars
2-D10

Damage simulation of concrete
No damage
No damageSide cracks (full)Side cracks (full)Side cracks (half)
Upper and side cracks (both half)

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Damage simulation of bars
No damage
Scraped 30%
No damage
Scraped 30%
No damage
No damageFig. 1 – Dimensions of specimen (unit in mm)

Fig. 2 – Crack of cover concrete by slits (left : B-Sc center : B-Si right : B-US)

Fig. 3 – Scraping of reinforcing bar (unit in mm)

3. Test Results
Final crack patterns of specimens are shown in Fig. 4. Compression failure occurred in the shear span inspecimens B-N and B-Si, while it is observed in pure bending span in other specimens. Compression
reinforcing bars showed buckling with the deformation toward the outside of cross-section of beams.
Load-deflection curves of specimens are shown in Fig. 5. The remarkable drop of applied load and brittlebehavior can be observed in the specimens with compression failure in pure bending span. The influenceof types of damage of concrete on the load-deflection curve is recognized.

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B-N

B-N(R)

B-Sc

B-Sc(R)

B-Si

B-US

Fig. 4 – Final crack pattern

Load (kN)

150

B-N
B-N(R)
B-Sc
B-Sc(R)
B-Si
B-US

100
500010 20 30 40 50 60
Deflection (mm)Fig. 5 – Load-deflection curve

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4. Modeling of Stress-Strain Curves and Section Analysis
4.1. Buckling Test and Modeling of Reinforcing Bar
Monotonic compression loading is carried out using a universal testing machine of 500kN capacity toobtain stress-strain curve of reinforcing bars in buckling. The jigs for fixing specimen are attached to theheads of the testing machine, so the boundary condition is to be fixed-end by inserting the ends of 8d of
the reinforcing bar in the jigs. The inserted ends of reinforcing bar are polished to produce no gap
between the holes of the jigs and the reinforcing bar. The test length is set to 400 mm which is samelength with pure bending span of the beam specimen. Measurement items are compressive force and anaxial deformation using LVDTs in three positions between the jigs.
Stress-strain curves measured in loading test are shown in Fig. 6. Stress is determined by dividing
compressive force by the nominal cross-sectional area. Strain is calculated by dividing axial deformationin test region by test length. The deformation in test region is obtained by subtracting the deformations of
the bar in the hole (assumed as elastic) from the measured deformation by LVDT. Slenderness ratio of thespecimen is approximately 200, so the elastic bucking occurred. The measured post-peak curves show
similar with previous study (Suminokura et al., 2015) in which the post-peak curves are modeled byEquation (1). In this study, the experimental coefficient β is modified as 0.568.
 (1)100
 s   s max  ( s max )
s

0.5

(1)

Where,
σsmax：maximum stress of reinforcing bar
εsmax：strain at the maximum stress
β：experimental coefficientγ：cross-section reduction rate

Stress (MPa)

200

L40-1
L40-2
L40-3

150
10050
000.01
Strain0.02

Fig. 6 – Stress-strain curve in buckling test

4.2. Modeling of Concrete
The stress-strain model of concrete is described in Equation (2) based on Popovics model, considering
the influence of slits simulating cracks due to corrosion. Coefficient α is newly introduced to express thedifference of shape of curves after maximum stress. Coefficient α is given as the ratio of summation lengthof slits to target length (pure bending span). Fig 7 shows the stress-strain curves comparing the influenceof the coefficient. As the value of α increases, post-peak curves become more brittle. For specimens B-Scand B-US, α is 1.0 and for specimen Si, α is 0.5.

 c   c max c c max

nn 1 (c c max(2))

nPage 5 of 7Stress (MPa)

15

α=0
α=0.5
α=1.0
α=2.0

10
50
0

0.01
Strain0.02

Fig. 7 – Stress-strain model of concrete

4050

Moment (kN・m)

Moment (kN・m)

50

Experimental curve
Analytical curve

40

30

30

20

20

1000101 2 3 4 5 6Normalization deflection

00 1 2 3
Normalization
B-N(R)

5050

Moment (kN・m)

Moment (kN・m)

B-N

40302010004030
2010001 2 3 4 5 6Normalization deflection
B-Sc

50

Moment (kN・m)

Moment (kN・m)

1 2 3 4 5 6Normalization deflection
B-Sc(R)50

404030302020101000

4 5 6deflection

00

1 2 3 4 5 6Normalization deflection
B-Si

1 2 3 4 5 6Normalization deflection
B-US

Fig. 8 – Analysis results

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0.0582  c max  1e L  crLnWhere,
σcmax：maximum stress of concrete
εcmax：strain at the maximum stressα：coefficient for influence of cracks
L：target length (pure bending span)
Lcr：Sum of crack length in the target

4.3. Comparison of Test Result with Analysis
Section analysis using proposed stress-strain models is carried out based on the assumption that theplain section remains plain. To compare between the curvature of analysis results and the deflection ofexperimental results, each value is normalized by ones when the strain of tension bar reaches 2000μ. The
moment-normalized deflection curves are shown in Fig. 8. Analytical curves excluded specimens B-N(R)and B-Si can follow the experimental ones in the post-peak curves. Analytical curves of specimens B-N(R) and B-Si do not show good agreements with the experimental curves because of the failure at shear
span.

5. Conclusion(1) The remarkable drop of applied load and brittle behavior can be observed in the specimens with(2)

compression failure in pure bending span. The influence of types of damage of concrete on the loaddeflection curve is recognized.
The stress-strain curves both for cracked concrete and buckling reinforcing bars are modeled. The
analytical curves calculated by section analysis can follow the experimental ones in the post-peakcurves.

6. Acknowledgements
This study was supported by the JSPS KAKENHI Grant Number 24560593.

7. References
SUMINOKURA, Shun, KANAKUBO, Toshiyuki, OYADO, Michiaki, YASOJIMA, Akira, “Study on Simulated
Corrosion Reinforcing Bars Subjected to Buckling Behavior”, Proceedings of the Japan Concrete InstituteVol.37, 2015.(in Japanese)OYADO, Michiaki, KANAKUBO, Toshiyuki, YAMAMOTO, Nobuyuki, SATO, Tsutomu, ”Influence ofCorrosion of Reinforcing Bars on Bending Performance of Reinforced Concrete Members”, JSCE Journalof Materials, Concrete Structures and Pavements, Division E, Vol.62, No.3, August 2006, pp. 542-554. (inJapanese)

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