Advanced Theory of Concrete Structures - Chapter 3: Bond and Anchorage

1. Advanced Theory of Concrete Structures Chapter 3 Bond and Anchorage Yong Zhou College of Civil Engineering, Tongji University yongzhou@tongji.edu.cn

2. 3.1 Introduction • Why should we research bond and anchorage? ? External loads Concrete Reinforcement • Prerequisite of composite structure P • Detailing requirement C V T

3. 3.1 Introduction True bond stress In-and-out stress Bond stress will not exist unless the steel stresses change between any two sections

4. P P M  T2=T1+T T1 M2=M1+M M1 x 3.1 Introduction Average bond stress

5. before cracking after cracking Anchoring bond: ensure the concerted action of concrete and reinforcement Local bond: improve energy dissipation capacity of concrete 3.1 Introduction

6. 3.1 Introduction • Components of Bond • Chemical adhesion • Friction • Mechanical interlock • Embedded end anchorage

7. Splice length Lap splice test Development length sleeve 3.1 Introduction Pullout test (local bond) Half-beam test (anchorage) Development length test

8. plain bar mildly rusted sleeve no rusted cold-stretched wire Slip (mm) 3.2 Bond mechanism • Plain Bar ─ Friction

9. 3.2 Bond mechanism • Deformed Bar ─ Mechanical interlock Radial tensile stress Bearing stress Radial crack Uncracked concrete Internal diagonal crack Deformedbar Longitudinalcomponent Radial component Internal crack zone

10. 3.2 Bond mechanism • Deformed Bar ─ Mechanical interlock Radial crack reaching specimen surface Splitting of specimen Crushed concrete Forming new slip surface τ cr= 0.8~0.85 τu Internal diagonal crack occurrence sl = 0.35~0.4 mm Local deformation of concrete in the vicinity of ribs

11. 3.2 Bond mechanism Typical Splitting Failure modes

12. 3.2 Bond mechanism • Factors influencing bond strength: • Properties of concrete • Strength: bong strength tensile strength • adhesion and mechanical interlock • splitting strength • Superplastizer • concrete of high slump → low bond strength • Fibers: strength

13. 3.2 Bond mechanism • Factors influencing bond strength: • Properties of reinforcement • Diameter and surface (rib, rust) deformed bar better than plain bar thin bar better than thick bar • Embedded length

14. 3.2 Bond mechanism • Factors influencing bond strength: • Others • Stirrups delay the splitting failure • Transverse compression increase the friction • Reinforcement in compression or tension Possion effect → friction

15. 3.2 Bond mechanism • Factors influencing bond strength: • Others • Cover thickness or space between longitudinal bars

16. 3.2 Bond mechanism • Factors influencing bond strength: • Others • Casting position

17. 3.2 Bond mechanism • Bond under repeated loading • continuous increase of slip • speed and degree of degradation are closely related to bond stress level • splitting symbols the divergence of degradation

18. 3.2 Bond mechanism • Bond under cyclic loading

19. 3.2 Bond mechanism • Bond-slip constitutive law Alsiwat (1992) Haraji (1992) Tassios (1979) Eligehausen (1983)

20. la d p t t d c′ c ′ 3.3 Bond strength Development Length Principle: the reinforcement yields simultaneously with the bonding failure. Assumption: concrete splits before reinforcement being pulled out. Linear distribution

21. la 2c p t t d 3.3 Bond strength If the inclined angle of rib is 45º, then p τ GB50010-2010: ACI :

22. 3.4 Anchorage of steel bars

23. 3.4 Anchorage of steel bars

24. 3.4 Anchorage of steel bars

25. 3.4 Anchorage of steel bars

26. 3.5 Lap splices

27. 3.5 Lap splices Force transfer mechanism

28. 3.5 Lap splices

29. 3.5 Lap splices

30. Thank you!