Abstract

Corrosion of reinforcing steel causes cracking and spalling of concrete structures, reduces the effective cross-sectional area of the reinforcing steel and the concrete simultaneously decreases the bond strength at the steel-concrete interface. The detrimental effect of corrosion on the service life of reinforced concrete structures highlights the need for modeling of bond strength between the corroded steel and the concrete. This research presents a nonlinear finite element model for the bond stress at the steel-concrete interface for both uncorroded and corroded reinforcing steel. The nonlinear finite element program ABAQUS is used for this purpose. The expanded volume of corroded product of reinforcing steel produces radial and hoop stresses which cause longitudinal cracks in the concrete. The increased longitudinal crack width, the loss of effective cross-sectional area of the steel and the concrete is also reduced due to the lubricating effect of flaky corroded layer. This research models the loss of contact pressure and the decrease of friction coefficient with the mass loss of the reinforcing steel. The model analyzes the pullout tests of Amleh (2002) and a good agreement is noted between the analytical and the experimental results. Both in FE analysis and experimental results, the loss of bond capacity is almost linear with mass loss of rebar. FE analysis and experiemental result show that, up to 5% mass loss, the bond capacity loss is moderate, at 10 to 15% mass loss, significant amount of bond capacity is lost and at about 20% mass almost all bond capacity is lost. The model is also validated by analyzing the pullout tests performed by Cabrera and Ghoddoussis (1992) and those by Al-Sulaimani et al.(1990).

Highlights

  • 1.1 BackgroundThe durability of reinforced concrete structures depends largely on the resistance of concrete against the chemical and physical factors and its ability to protect its embedded reinforcing steel against corrosion

  • The following observations are made for the specimens with 75 mm thick concrete cover: 1) For a mass loss of 2.5%, the results for the experimental and finite element (FE) analysis show that the bond stress-slip curves are almost same as for the uncorroded specimen but the bond capacity increases by about 5%

  • 5.3.1 Cabrera and Ghoddoussis’ (1992) Pullout Test The bond model is validated by using the results of Cabrera and Ghoddoussiss’ (1992) pullout tests which were performed on 150 mm cubes with 12 mm diameter reinforcing bar centrally embedded in the cube to find the effect of corrosion on the bond strength at the steel-concrete interface

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Summary

Stress Ratios and Strain Ratio to Define Failure

= the shear stress due to adhesion of concrete and steel = shear stress, in the tangential = average bond stress = concrete cover thickness = diameter o f the reinforcing steel = cross-sectional area o f the concrete section = cross-sectional area o f the reinforcing steel = elastic modulus o f concrete = elastic modulus o f reinforcing steel = principle stresses of concrete = crack width = thickness of corrosion product = ratio between the volumes of corroded and virgin steel = number of transverse ribs at section —rib area in the plane at right angles to bar axis = depth o f corrosion at cracking = concrete strain when reaches / j = a factor to control the slope o f the descending branch of the compressive stress-strain curve o f concrete = total strain of concrete = elastic strain of concrete = plastic strain o f concrete = the clearance between master and slave surface at which contact pressure decreases to zero.

Background
Scope and Objective
Thesis Layout
Introduction
Definition of
Bond Mechanisms
Failure Modes of Bond
Factors Affecting the Bond Strength
Influence of Concrete Strength
Effect of Concrete Cover Thickness
Bar Profile
Effect of Corrosion
Summary
Constitutive Equation of Bond-Slip Relationship
The Comité Euro-International du Béton (CEB) Code Model (1990)
Idda’s Model (1999)
Lundgren and Gylltofts’ Bond Model (2000)
Russo and Paulettas’ Model (2002)
Bar-Concrete pressure
Bond Capacity of Anchored Bar
Lundgren‘s Model for Bond between Corroded Reinforcement and Concrete (2002)
Modeling the Bond at the Steel-Concrete Interface
Details of Pullout Specimens
Elastic Properties
Compressive Behaviour
20 So U 10
43.2.2 Concrete Smeared Cracking Model
Tension Stiffening
Modeling Contact Interface between Reinforcing Steel and Concrete
Defining Contact Surfaces
Modeling Contact Pressure and Friction
Modeling Contact Pressure at the Uncorroded-Steel Concrete Interface
Boundary Conditions of the Pull-out Test
Developing the Mesh
Input File
Sum m ary
Relationship of Bond Stress and Slip
Bond Stress and Slip using Very Fine Mesh
Effect of Concrete Cover Thickness on Bond Strength
Effect of Compressive Strength on Bond Strength
Comparison of Finite Element Analysis with Experimental Results
Bond Stress-Sllp Relationship for Corroded Specimens
Effect of Corrosion on Bond Strength
Effect of Concrete Cover Thickness on the Bond strength at the Corroded Steel-Concrete Interface
Effect of
Validation of the Model
Cabrera and Ghoddoussis’ (1992) Pullout Test
Summary The bond model developed in
Conclusions
Findings
Future Research Work
Full Text
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