Experimental Study on the Damage Evolution of Re-bar Concrete - - PowerPoint PPT Presentation

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

• btained 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

~ < < ≥ ≥    =

ii ii ii ii i i

and

• r

when D D ε σ ε σ

• 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)

• z

y x 8 7 6 5 4 3 2 1 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 test

No-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 Bottom 3: 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 Test

Uniaxial-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 mm 15mm R Concrete 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 Pipe PVC Pipe Concrete Figure 2.4 The Stress State of Specimen

Stress 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 Plate Glue

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

100 200 300 400 500 600 700

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

St r ai n St r ess ( M Pa) Bar 1 Bar 2 Bar 3

• 2. Test of Steel Bar

y = 65948x + 18. 185 50 100 150 200 250 300 350 400 450

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

St r ai n St r ess ( M Pa)

• 5. Specimen Analysis before Test

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 m e ( m i l i second) Test Num ber

• 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

• f 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 Test

St r ess- St r ai n 5 10 15 20 25 30 35

• 2000

2000 4000 6000 8000 10000 12000 St r ai n St r ess ( M Pa) C yl i nder 1 C yl i nder 2 C yl i nder 3

Lognitudinal-stress-strain Curve

• 9. Standard Specimen Test

σ

3-ε 2, ε 3

• 0. 2
• 0. 4
• 0. 6
• 0. 8

1

• 1. 2

1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

ε

2, 3

σ3/ f c

C yl i nder 1 C yl i nder 2 C yl i nder 3

Side-stress-strain Curve

• 9. Standard Specimen Test

Poi sson Fact or

• 0. 2
• 0. 4
• 0. 6
• 0. 8

1

• 1. 2
• 0. 5

1

• 1. 5

2

• 2. 5

Poi sson Fact or

σ3/ f c

C yl i nder 1 C yl i nder 2 Cyl i nder 3

Stress- Poisson Ratio

• 3. Experimental Data Analysis

Load- D i spl acem ent of 10- 5

• 5

5 10 15 20 25

• 6
• 5
• 4
• 3
• 2
• 1

1 di spl acem ent ( m m ) Load ( KN ) TopC ent er 1 TopCent er 2 TopEdge TopST

Topical Experiment Original Data

• 3. Experimental Data Analysis

The following information can be obtained from the experimental data:

• 1. τ-∆1+∆2 Curve
• 2. Influence of Height and Radius of Specimen
• 3. Shear Stress Distribution of Steel Bar and Deformation
• f Concrete
• 4. Slip Damage Zone

Original Data

Load- Di spl acem ent of 10- 5

• 5

5 10 15 20 25

• 6
• 5
• 4
• 3
• 2
• 1

1 di spl acem ent ( m m ) Load ( KN ) TopC ent er 1 TopCent er 2 TopEdge TopST

τ-∆1+∆2 Curve

St r ess- Δ1+Δ2

• 2

2 4 6 8 10 12

• 2

2 4 6 8 10

Δ1+Δ2 ( m

m ) St r ess ( M Pa) 10- 1 10- 2 10- 3 10- 4 10- 5 10- 6

τ-∆1+∆2 Curve

St r ess- Δ1+Δ2

• 2

2 4 6 8 10

• 2

2 4 6 8 10 12

Δ1+Δ2 ( m

m ) St r ess ( M Pa) 15- 1 15- 2 15- 3 15- 4 15- 5 15- 6 15- 7

τ-∆1+∆2 Curve

St r ess- Δ1+Δ2

• 2

2 4 6 8 10 12

• 2

2 4 6 8 10

Δ1+Δ2 ( m

m ) St r ess ( M Pa) 20- 1 20- 2 20- 3 20- 5 20- 6 20- 7

τ-∆1+∆2 Curve

St r ess- Δ1+Δ2

• 2

2 4 6 8 10 12

• 2

2 4 6 8 10

Δ1+Δ2 ( m

m ) St r ess ( M Pa) 30- 1 30- 2 30- 3 30- 4 30- 5

τ-∆1+∆2 Curve Fitting

St r ess- Δ1+Δ2

• 2

2 4 6 8 10 12

• 2

2 4 6 8 10 12

Δ1+Δ2 ( m

m ) St r ess ( M Pa) 10- 1 10- 2 10- 3 10- 4 10- 5 10- 6 f i t t i ng

τ-∆1+∆2 Curve Fitting

St r ess- Δ1+Δ2

• 2

2 4 6 8 10

• 2

2 4 6 8 10 12

Δ1+Δ2 ( m

m ) St r ess ( M Pa) 15- 1 15- 2 15- 3 15- 4 15- 5 15- 6 15- 7 Fi t t i ng

Empirical Formula

87 . 2 2 . 3 max

) ( 642 . ) ( 916 . 1 ) ( 061 . ) ( 7260 . ξ ξ ξ ξ ξ ξ ξ ξ τ τ + − + =

τ, Average bond stress ξ, Value of ∆1+∆2 ξ0, Value of ∆1+∆2 at peak point

Influence of Height of Specimen

St r engt h t o H ei ght 2 4 6 8 10 12 74 76 78 80 82 84 86 88 90 H ei ght ( m m ) Shear St r engt h ( M Pa) Ave St r engt h t o Hei ght Fi t t i ng f or St r ent h- Hei ght

Influence of Radius of Specimen

St r engt h t o Radi us 2 4 6 8 10 12 5 10 15 20 25 30 35 Radi us( m m ) St r engt h( M Pa) St r engt h Aver age St r engt h

Shear Stress Distribution along Steel Bar

Obtain the Shear Stress Distribution from

the following conditions

• 1. Elongation of the steel bar
• 2. Relationship between τ and ∆
• 3. Linear assumption in RCED model

Shear Stress Distribution along the Steel Bar

St eel Bar Shear St r ess Tm i n/ Tm ax( Load Peak Poi nt )

• 0. 1
• 0. 2
• 0. 3
• 0. 4
• 0. 5
• 0. 6
• 0. 7
• 0. 8
• 0. 9

1 5 10 15 20 Tm i n/ Tm ax( Load Peak Poi nt ) St r ess R at i o Aver age

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 Results

R esul t of Test and FEA( St r ess- Δ1+Δ2) , Speci m en Ser i es 10

• 2

2 4 6 8 10 12

• 0. 2
• 0. 2
• 0. 4
• 0. 6
• 0. 8

1

• 1. 2
• 1. 4

Δ1+Δ2 ( m

m ) Shear St r ess ( M Pa) Test Poi nt Li near FEA Non- l i near FEA Fi t t i ng f or Test Poi nt

Comparison with Test Result

R esul t of Test and FEA( St r ess- Δ1+Δ2) , Speci m en Ser i es 15

• 2

2 4 6 8 10 12

• 0. 2
• 0. 4
• 0. 6
• 0. 8

1

• 1. 2
• 1. 4
• 1. 6
• 1. 8

Δ1+Δ2 ( m

m ) Shear St r ess ( M Pa) Test Poi nt Li near FEA N

• n- Li near FEA

Fi t t i ng f or Test Poi nt

Comparison with Test Result

St r ess- Def or m at i on of Concr et e 10 2 4 6 8 10 12

• 0. 05
• 0. 1
• 0. 15
• 0. 2
• 0. 25

Def or m at i on ( m m ) St r ess ( M Pa) Test Poi nt FEA Li near Resul t FEA N

• n- Li near Resul t

Fi t t i ng t o Test Poi nt

Comparison with Test Result

St r ess- D ef or m at i on of C

• ncr et e ( 15)

2 4 6 8 10 12

• 0. 05
• 0. 1
• 0. 15
• 0. 2
• 0. 25

Def or m at i on ( m m ) St r ess ( M Pa) Test Poi nt FEA Li near Resul t FEA Non- Li near R esul t Fi t t i ng t o 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 t he Speci m en 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 D i st ance t o Top Sur f ace ( cm ) Sl i p ( * 0. 1 m m ) Speci m en 10 Speci m en 15 Li near Sl i p Fi el d Assum pt i 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 Bar

St r ess Di st r i but i on ( 10) 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 Di st ence t o Top ( cm ) Shear St r ess ( M Pa) Li near Assum pt i on Resul t FEA Non- Li near R esul t

Bond Stress along Steel Bar

St r ess Di st r i but i on( 15) 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 D i st ence t o Top ( cm ) Shear St r ess ( M Pa) Li near Assum pt i on Resul t FEA Non- Li near Resul t

Change of Bond Stress

Bondi ng St r ess Di st r i but i on ( G r oup 10) 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 D i st ance t o Top ( cm ) Shear St r ess ( M Pa) l oad1 l oad2 l oad3 l oad4

Conclusions

Obtain the full curves of the relationship of

τ-∆1+∆2 . The empirical formula of τ-∆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 (τ-∆1+∆2 )

Δ1+Δ2

• 2

2 4 6 8 10 12

• 2

2 4 6 8 10

Δ1+Δ2( m

m ) M Pa 10s1 10s2 10s3 10s4 10s5 10s6 f i t pr ogr am

Result (Deformation of Concrete)

• 2

2 4 6 8 10

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

t est poi nt

• 0. 1
• 0. 2
• 0. 4
• 0. 6
• 0. 85
• 0. 9
• 0. 95

1

系列12 系列3

Mesh of Case 2

4 RCED elements

250 150

Result (Steel bar axial-force)

10 20 30 40 50 60 70 80 1 2 3 4 5 6 7 8 For ce ( KN ) F=20KN , Test F=40KN, Test F=70KN , Test F=20KN, RC ED F=40KN , R CED F=70KN , RC ED

Element Number to Obtain the Same Precision

Traditional 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