Assessing Immediate and Time-Dependent Instantaneous Stiffness of Cracked Reinforced Concrete Beams Using Residual Cracks

Abstract

Under normal in-service conditions, beams and slabs in reinforced concrete structures are usually cracked. Concrete cracking and steel-concrete bond damage lead to an irreversible reduction in the overall stiffness, thereby affecting the serviceability of reinforced concrete structures. The method proposed in this paper aims to assess both the steel-concrete bond damage and the bending stiffness of existing structures based on the cracking pattern observed in situ including the location of bending cracks, their spacing, and their width. The time-dependent effects of creep and shrinkage are also considered. Short-term and long-term experimental results obtained from tests on five reinforced concrete beams are used to evaluate the effectiveness of the method. For each beam, the cracking pattern and the width of cracks measured immediately after first loading and after a 6-month period of sustained loading are used to assess the immediate and time-dependent instantaneous stiffness of the beams. The stiffness and the load-deflection response determined using the proposed method are shown to agree well with experimental observations.