Time-dependent modeling of loss of flexural strength of corroding RC beams

Abstract

Corrosion of reinforcing steel in reinforced concrete structures is a concern for durability, particularly in the aggressive environments like that prevailing in the Arabian Gulf. As a result of reinforcement corrosion, several problems arise. Severe cracking in the concrete cover ultimately causes the spalling of concrete. Loss of bond between the steel and concrete, and reduction in the cross-sectional area of the reinforcement, in turn cause a reduction in the strength of the reinforced concrete member, rendering it unsafe to carry the loading because of the reduction in the strength. The reduction of the strength depends upon the degree of damage caused by the corrosion. Corrosion also increases the deflection due to reduction in the stiffness. Significant research has been carried out for predicting the time-to-corrosion initiation. However, the prediction of the residual strength, or the degree of strength damage of reinforced concrete members undergoing reinforcement corrosion, is not yet fully addressed to a level where it can be applied to practical problems with sufficient confidence. In a recently completed research work, Azad et al (2007) [39] developed a method for predicting the residual flexural strength of corroded concrete beams. This proposed method is based on test data generated in the laboratory through accelerated corrosion. This approach predicts the residual flexural strength of a corroded beam for which the degree of corrosion, rebar diameter, cross-sectional details and materials strength are known. The approach suggested by Azad et all (2007) [39] is based on the test data generated from beams of smaller and similar depths and having smaller rebars diameters (10 and 12 mm). However, Azad et all (2007) did not study the size effect of beams and bar diameter (if any) on the accuracy of the predicted model. The present thesis aims to verify of the applicability of the method of Azad et al (2007) for the prediction of residual strength of corroded beams of different cross-sections and bigger diameter steel bars. The data required was generated through an experimental program, which included: (1) Casting of reinforced concrete beam members of different sizes and steel bars of varying diameters, designed to fail in flexure, (2) Inducing different degrees of accelerated reinforcement corrosion in the prepared concrete specimens, and (3) Testing the corroded specimens in a four-point bend test. The present research corroborates the findings of Azad et al (2007) pertaining to the residual strength and safety of the corroded beams. Based on the analysis of the experimental data, two steps are suggested to determine the residual flexural strength of corroding RC beams. These two steps have been verified with data gathered from other studies.