RESEARCH SIGNIFICANCE

The paper describes the behavior of reinforcing bars suffering irregular loss of cross section as a consequence of corrosion and identifies the factors that will affect the residual mechanical behavior of the bars。 Although the mathematical modeling techniques deployed are unlikely to find direct use in practice, the understanding developed through their use will guide engineers to be responsible for safe operation of corrosion-affected concrete structures in the application of empirical knowledge。

NUMERICAL MODELING

A simple nonlinear numerical model was constructed to assess the influence of various parameters on residual strength and ductility of corroded reinforcement, including the effects of pitting attack。 The model was implemented through a spreadsheet。

A stress-strain relationship for an undamaged bar was first obtained through testing (or, in the case of the parametric study, assumed)。 Steel properties were assumed uniform throughout the volume of the bar and to be unaffected by corrosion。 There is evidence from other studies, including Palsson and Mirza,4 to support the latter assumption。 In analyses reported herein, a simple trilateral approximation to the measured stress-strain relationship has been considered adequate (Fig。 1, Plot A)。

The bar was pided into short incremental lengths for analysis。 The variation of the cross-sectional area along a bar was then measured, or an assumed variation was derived。 The elongation of each increment of bar length was then

ACI Materials Journal, V。 102, No。 4, July-August 2005。

MS No。 04-217 received July 9, 2004, and reviewed under Institute publication policies。 Copyright © 2005, American Concrete Institute。 All rights reserved, including the making of copies unless permission is obtained from the copyright proprietors。 Pertinent discussion including authors’ closure, if any, will be published in the May-June 2006 ACI Materials Journal if the discussion is received by February 1, 2006。

ACI member John Cairns is a senior lecturer in the School of the Built Environment, Heriot-Watt University, Edinburgh, UK。

ACI member Giovanni A。 Plizzari is a professor of structural engineering in the Department of Engineering Design and Technology, the University of Bergamo, Italy。 His research interests include material properties and structural applications of high-performance concrete, fiber-reinforced concrete, concrete pavements, fatigue and fracture of concrete, and steel-to-concrete interaction in reinforced concrete structures。

Yingang Du is a lecturer of civil and structural engineering at Telford College, Edinburgh。 He received his BEng and MEng from Xian University of Architecture and Technology, China, and his PhD from The University of Birmingham, UK。 His research interests include the safety and durability of concrete structures under corrosion, earthquakes, fire, and high temperature。

David W。 Law is employed by the Advanced Materials Group for Maunsell Australia, Melbourne, Australia。 His research interests include corrosion monitoring using nondestructive electrochemical techniques, durability assessment, predictive modeling, and life-cycle management of reinforced concrete structures。

Chiara Franzoni is a professional engineer。 She received her degree in civil engineering from the University of Brescia。 Her research interests include the durability of concrete, corrosion of reinforcing bars, and zinc-coated reinforcing bars。

calculated under successive increments of load using the average stress-strain relationship for the undamaged bar and the residual cross-sectional area for that increment of length。 The model ignores stress concentration and eccentric load effects, which test results show to have no appreciable effect for an embedded bar under static loading。 Average strain was calculated by taking a summation of incremental elongations and piding by the gauge length。 Fracture is taken to occur when the most highly strained increment reaches εu, the strain at maximum load measured in the undamaged bar。 Average strain at fracture and ultimate load were calculated at this point。 Yield stress was also determined as 0。002 proof stress, based on average elongation and stress。