Experimental Study on the Damage Evolution of Re-bar Concrete Interface

Lu Xinzheng

SCE, THU CSE, NTU

1999/2000

Abstract

A new type of bond-slip test is developed in this study

Constitutive relationship of bond is obtained for the test

FEA using this constitutive relationship Result analysis and comparing

General Overview

Introduction and Literature Review Experiment Procedure Experimental Data Analysis Numerical Computation Study Conclusion and Discussion

1.1 Introduction

00

00

0~

iiii

iiiiii and

orwhen

DD

• Liu Yu’s Concrete Model

3

2

1

~

~

~

~

D

D

D

D

(a). (b). (c). (d).

RCED Model (RC Element Damage Model)

Damage in the reinforced concrete

1. Effective damage in concrete

2. Slip between concrete and re-bar

3. Local damage in concrete due to slip

RCED Model (RC Element Damage Model)

F

Local damage

x

l

Affected zone

Local damage zone in RCED Model

RCED Model (RC Element Damage Model)

o

z

y

x

87

6

5

4

3

21

10,12

9,11

Element in RCED Model

1.2 Literature Review

Bond Test Method

1. Pull-out Test

2. Beam-type Test

3. Uniaxial-tension Test

Pull-out Test

Figure 1.5 no-transverse bar withdrawing test Figure 1.6 with transverse bar withdrawing testNo-transverse bar pull-out test With transverse bar pull-out test

Pull-out Test

hoop rebar

Plastic Pipe Eccentric Rebar Central Rebar

Figure 1.7 Specimen With Hoop Rebar Specimen with Hoop Rebar

Pull-out Test

Plastic Pipe

Web Rebar

Bonding Area

Figure 1.8 Specimen With Web Rebar Specimen with Web Rebar

Pull-out Test

Plasitc Pipe

Figure 1.9 Rebar In Different Place Rebar in Different places

Feature of Pull-out Test

Strongpoint

1. Can determine the anchoring strength of bond

2. Easy to procedure

Shortage

Complex stress state around the surface

Beam-type Test

Plasitc Pipe

Figure 1.10 Half Beam Test to Simulate the Inclined Crack

Figure 1.11 Half Beam Test to Simulate the Vertical Crack Half-beam Test to

Simulate the Inclined Crack

Half-beam Test to Simulate the Vertical

Crack

Beam-type Test

Figure 1.12 Full Beam Test to Simulate the Vertical Crack

Figure 1.13 Full Beam Test to Simulate the Inclined Crack

Half-beam Test to Simulate the Inclined Crack

Half-beam Test to Simulate the Vertical Crack

Beam-type Test

3 2 1

Figure 1.14 Simple Supported Beam Test

1: Lever-type Strain Gauge 2: Stain Gauge On the Bottom 3: Strain Gauge on the Side

Simply Supported Beam Test

1: Lever-type Strain Gauge 2: Strain Gauge On the Bottom3: Strain Gauge on the Side

Feature of Beam-type Test

Strongpoint

1. Very close to the real state

2. Can determine bond strength of both

anchoring zone and between cracks Shortage

Complex and Expensive

Uniaxial-tension Test

Figure 1.15 Uniaxial-draw TestUniaxial-tension Test

Feature of Uniaxial-tension Test

Strongpoint

1. Can determine the bond stress between cracks

2. Easy to Procedure

Shortage

Complex distribution of bond stress

2. Procedure of Test

1. Assumption in RCED Model

a. Pure shear deformation in the bond zone

b. Linear slip field

2. Test purpose

a. Determine the evolution of Ds

b. Determine the rational size of RCED element

c. Determine the parameter of a1, a2

Test Device and Method

210

mm

75 m

m

15m

m

RConcrete

Steel Bar

Figure 2.2 Specimen

RC Specimen

Test Device and Method

Clamping Device

LVDT 5

LVDT 4

LVDT 9

LVDT 2,3

LVDT 6,7

LVDT 8

Steel Plate

Figure 2.3 Load Apply Device

Loading Device

Test Device and Method

Steel Bar

PVC PipePVC Pipe

Concrete

Figure 2.4 The Stress State of SpecimenStress State of the Specimen

Test Device and Method Assumption in RCED

Model

1. Shear deformation in bond zone

2. Linear slip field

Feature of the Test

1. Constraint force is applied through PVC pipe and glue. Concrete is under pure shear stress condition

2. Specimen is as thin as possible

Conclusion: This test can satisfy RCED model

Test Device and Method

(a) Concrete Specimen

before Test

(b) PVC Pipe before Test

Test Device and Method

(c, d) During the Test

Test Device and Method

Test Device Setup

Test Procedure

Design the Mold Test of Steel Bar Casting of Concrete Design of Loading Device Specimen Analysis before Test Trial Loading and Analysis of Failure Improving Method Formal Loading Standard Specimen Test

1. Design the Mold

Round Poly-

wood Plate

Steel Bar

PVC Pipe

Poly-wood PlateGlue

Specimen Mold

2. Test of Steel Bar

Displacement Determined By LVDT 5

Slip Between Steel Bar and Concrete

Elongation of the Free Part of Steel Bar

Slip Between Steel Bar and Clamping Device

2. Test of Steel Bar

Clamping Device

LDVT

Steel Bar

2. Test of Steel Bar

0

100

200

300

400

500

600

700

0 0. 02 0. 04 0. 06 0. 08 0. 1 0. 12 0. 14

Strai n

Str

ess

(M

Pa)

Bar1Bar2Bar3

2. Test of Steel Bar

y = 65948x + 18. 185

0

50

100

150

200

250

300

350

400

450

0 0. 001 0. 002 0. 003 0. 004 0. 005 0. 006

Strai n

Str

ess

(M

Pa)

5. Specimen Analysis before Test

0

2

4

6

8

10

12

14

21 21. 5 22 22. 5 23 23. 5 24 24. 5 25 25. 5 26 26. 5

Ti me (mi l i second)

Test

Nu

mb

er

6. Trial Loading and Analysis of Failure

Concrete Fail Surface

Steel Plate

Fail Surface of 10-7

6. Trial Loading and Analysis of Failure

Test Result of 10-7

6. Trial Loading and Analysis of Failure

Clamping Device

LVDT 5

LVDT 4

LVDT 9

LVDT 2,3

LVDT 6,7

LVDT 8

Steel Plate

Load Applied directly without PVC Pipe

6. Trial Loading and Analysis of Failure

Load Applied directly without PVC Pipe

6. Trial Loading and Analysis of Failure

Conclusion obtained from trial loading

1. The adhesive isn’t process properly

2. The confinement is still large

7. Improving the Method

Roughen the adhesive interface deeper Split the PVC pipe finely

8. Formal Loading

Test Result of 10-1

8. Formal Loading

Test Result of 15-5

8. Formal Loading

Test Result of 10-5

8. Formal Loading

Test Result of 10-4

8. Formal Loading

Test Result of 15-1

8. Formal Loading

Test Result of 15-6

8. Formal Loading

Test Result of 20-1

8. Formal Loading

Test Result of 20-5

9. Standard Specimen Test

Standard Tube Specimen• Size: 15×15×15cm

• Result:

Specimen Number 1 2 3

Max Load (KN) 953 1061 959

Max Strength (MPa) 42.36 47.16 42.62

9. Standard Specimen Test

Strain Gauge

Six Strain Gauges on Standard Cylinder Specimen

9. Standard Specimen TestStress-Strai n

0

5

10

15

20

25

30

35

-2000 0 2000 4000 6000 8000 10000 12000

Strai n

Str

ess

(M

Pa)

Cyl i nder1 Cyl i nder2 Cyl i nder3

Lognitudinal-stress-strain Curve

9. Standard Specimen Testσ 3-ε 2, ε 3

0

0. 2

0. 4

0. 6

0. 8

1

1. 2

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

ε 2, 3

σ3/f

c

Cyl i nder1 Cyl i nder2 Cyl i nder3

Side-stress-strain Curve

9. Standard Specimen TestPoi sson Factor

0

0. 2

0. 4

0. 6

0. 8

1

1. 2

0 0. 5 1 1. 5 2 2. 5

Poi sson Factor

σ3

/fc

Cyl i nder1 Cyl i nder2 Cyl i nder3

Stress- Poisson Ratio

3. Experimental Data AnalysisLoad-Di spl acement of 10-5

-5

0

5

10

15

20

25

-6 -5 -4 -3 -2 -1 0 1

di spl acement (mm)

Load

(K

N)

TopCenter1 TopCenter2 TopEdge TopST

Topical Experiment Original Data

3. Experimental Data Analysis

The following information can be obtained from the experimental data:

1. -1+2 Curve 2. Influence of Height and Radius of Specimen3. Shear Stress Distribution of Steel Bar and Deformation of Concrete4. Slip Damage Zone

Original Data

Load-Di spl acement of 10-5

-5

0

5

10

15

20

25

-6 -5 -4 -3 -2 -1 0 1

di spl acement (mm)

Load

(K

N)

TopCenter1 TopCenter2 TopEdge TopST

-1+2 CurveStress-Δ 1+Δ 2

-2

0

2

4

6

8

10

12

-2 0 2 4 6 8 10

Δ 1+Δ 2 (mm)

Str

ess

(M

Pa)

10-1 10-2 10-3 10-4 10-5 10-6

-1+2 CurveStress-Δ 1+Δ 2

-2

0

2

4

6

8

10

-2 0 2 4 6 8 10 12

Δ 1+Δ 2 (mm)

Str

ess

(M

Pa)

15-1 15-2 15-3 15-4 15-5 15-6 15-7

-1+2 CurveStress-Δ 1+Δ 2

-2

0

2

4

6

8

10

12

-2 0 2 4 6 8 10

Δ 1+Δ 2 (mm)

Str

ess

(M

Pa)

20-1 20-2 20-3 20-5 20-6 20-7

-1+2 CurveStress-Δ 1+Δ 2

-2

0

2

4

6

8

10

12

-2 0 2 4 6 8 10

Δ 1+Δ 2 (mm)

Str

ess

(M

Pa)

30-1 30-2 30-3 30-4 30-5

-1+2 Curve FittingStress-Δ 1+Δ 2

-2

0

2

4

6

8

10

12

-2 0 2 4 6 8 10 12

Δ 1+Δ 2 (mm)

Str

ess

(M

Pa)

10-1 10-2 10-3 10-4 10-5 10-6 fi tti ng

-1+2 Curve FittingStress-Δ 1+Δ 2

-2

0

2

4

6

8

10

-2 0 2 4 6 8 10 12

Δ 1+Δ 2 (mm)

Str

ess

(M

Pa)

15-1 15-2 15-3 15-4 15-5 15-6 15-7 Fi tt i ng

Empirical Formula

87.2

00

2.3

00max

)(642.0)(916.01

)(061.0)(7260.0

, Average bond stress

, Value of 1+2

0, Value of 1+2 at peak point

Influence of Height of SpecimenStrength to Hei ght

0

2

4

6

8

10

12

74 76 78 80 82 84 86 88 90

Hei ght (mm)

Sh

ear

Str

en

gth

(M

Pa)

Ave Strength to Hei ght Fi tt i ng for Strenth-Hei ght

Influence of Radius of Specimen

Strength to Radi us

0

2

4

6

8

10

12

0 5 10 15 20 25 30 35

Radi us(mm)

Str

en

gth

(MPa

)

Strength Average Strength

Shear Stress Distribution along Steel Bar Obtain the Shear Stress Distribution from

the following conditions

1. Elongation of the steel bar

2. Relationship between and 3. Linear assumption in RCED model

Shear Stress Distribution along the Steel Bar

Steel Bar Shear Stress Tmi n/ Tmax(Load Peak Poi nt)

0

0. 1

0. 2

0. 3

0. 4

0. 5

0. 6

0. 7

0. 8

0. 9

1

0 5 10 15 20

Tm

in/T

max(L

oad

Peak P

oin

t)

Stress Rati oAverage

Slip Damage Zone

In this test, there is no obvious slip damage zone founded with UPV. So we consider that the slip damage zone is very small, which appears just around the interface of concrete and re-bar.

Numerical Study

Objectives

1. Whether the empirical relationship of bond-slip obtained from the test can be used directly in finite element analysis

2. To verify the assumption in RCED model

Numerical Study

Finite Element Analysis Software

1. Linear analysis: MARC k 7.3.2

2. Non-linear analysis: Sap 91 Element Type and Mesh

Concrete, Steel bar, Glue and PVC pipe: 20 nodes 3D element.

Bond: Spring element

Mesh of Specimen Series 10

Mesh of Specimen Series 15

Numerical Result

Comparison with Test ResultsResul t of Test and FEA(Stress-Δ 1+Δ 2), Speci men Seri es 10

-2

0

2

4

6

8

10

12

-0. 2 0 0. 2 0. 4 0. 6 0. 8 1 1. 2 1. 4

Δ 1+Δ 2 (mm)

Sh

ear

Str

ess

(M

Pa)

Test Poi nt Li near FEA Non- l i near FEA Fi tt i ng for Test Poi nt

Comparison with Test ResultResul t of Test and FEA(Stress-Δ 1+Δ 2), Speci men Seri es 15

-2

0

2

4

6

8

10

12

0 0. 2 0. 4 0. 6 0. 8 1 1. 2 1. 4 1. 6 1. 8

Δ 1+Δ 2 (mm)

Sh

ear

Str

ess

(M

Pa)

Test Poi nt Li near FEA Non-Li near FEA Fi tt i ng for Test Poi nt

Comparison with Test ResultStress-Deformati on of Concrete 10

0

2

4

6

8

10

12

0 0. 05 0. 1 0. 15 0. 2 0. 25

Deformati on (mm)

Str

ess

(M

Pa)

Test Poi nt FEA Li near Resul t FEA Non-Li near Resul t Fi tt i ng to Test Poi nt

Comparison with Test ResultStress-Deformati on of Concrete (15)

0

2

4

6

8

10

12

0 0. 05 0. 1 0. 15 0. 2 0. 25Deformati on (mm)

Str

ess

(M

Pa)

Test Poi nt FEA Li near Resul t FEA Non-Li near Resul t Fi tt i ng to Test Poi nt

Comparison with Test Result

The errors between the test results and numerical results are smaller than 10%.

Hence, the bond-slip relationship obtained from the test can be directly used in finite element analysis.

Slip Field in the Specimen

Sl i p Fi el d i n the Speci men

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6 7 8

Di stance to Top Surface (cm)

Slip

(*0

.1 m

m)

Speci men 10 Speci men 15 Li near Sl i p Fi el d Assumpti on

Slip Field in the Specimen

The linear degree of slip field is 0.925. The assumption of linear slip field in RCED model is rational.

The size of the specimen influences the slip field lightly.

Bond Stress along Steel BarStress Di stri buti on (10)

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6 7 8

Di stence to Top (cm)

Sh

ear

Str

ess

(M

Pa)

Li near Assumpti on Resul t FEA Non-Li near Resul t

Bond Stress along Steel Bar

Stress Di stri buti on(15)

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6 7 8

Di stence to Top (cm)

Sh

ear

Str

ess

(M

Pa)

Li near Assumpti on Resul t FEA Non-Li near Resul t

Change of Bond Stress

Bondi ng Stress Di stri buti on (Group 10)

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6 7 8

Di stance to Top (cm)

Sh

ear

Str

ess

(M

Pa)

l oad1l oad2l oad3l oad4

Conclusions

Obtain the full curves of the relationship of -1+2 . The empirical formula of -1+2 is obtained for the curves. Numerical study proves that this formula can be used in FEA directly.

The influence of specimen size to the local damage zone is not obvious.

The linear slip field in RCED model is rational

Appendix

To apply the RCED model in real structure analysis.

Case 1: Using RCED model to analyze our test.

Case 2: Using RCED model to analyze the Doerr’s uniaxial-tension test (ASCE Vol.113, No.10, October, 1987)

Mesh of Case 1

Common Concrete Element

RCED Element

Result (-1+2 )

Δ 1+Δ 2

-2

0

2

4

6

8

10

12

-2 0 2 4 6 8 10

Δ 1+Δ 2(mm)

MPa

10s110s210s310s410s510s6fi tprogram

Result (Deformation of Concrete)

-2

0

2

4

6

8

10

-0. 05 0 0. 05 0. 1 0. 15 0. 2 0. 25 0. 3 0. 35 0. 4

test poi nt 0. 1 0. 2 0. 4 0. 6 0. 85 0. 9 0. 95 1 12系列 3系列

Mesh of Case 2

4 RCED elements250

150

Result (Steel bar axial-force)

0

10

20

30

40

50

60

70

80

0 1 2 3 4 5 6 7 8

Forc

e (

KN

)

F=20KN, Test F=40KN, Test F=70KN, Test F=20KN, RCED F=40KN, RCED F=70KN, RCED

Element Number to Obtain the Same PrecisionTraditional element

Case 1

Element used: 656

Case 2

Element used: 192

RCED model

Case 1

Element used: 5

Case 2

Element used: 4

Conclusion: the element number RCED model

needed is much less than the traditional ones.

RCED model is useful in real structure analysis