مهندسی عمران شریف (Aug 2020)
NUMERICAL MODELING FOR SIMULATION OF OPENING MODE IN FRACTURE MECHANIC OF CONCRETE COLD-JOINT
Abstract
A cold joint is a plane of weakness in concrete caused by an interruption or delay in the concreting operations. It occurs when the first batch of concrete has begun to set before the next batch is added so that the two batches do not intermix. Sometimes, cold joints occur because of emergency interruptions and delays and sometimes because of the work stoppage at the end of the day; however, they can occur due to poor consolidation. Usually, the latter condition can be seen at the top and bottom of columns in concrete frames because of the traditional construction method. Basically, the interface of the cold-joint is relatively weaker than both sides of materials. For this reason, the performance of concrete elements with the cold-joint is under the influence of that behavior. In a system with a cold-joint, the chances of failure by cracking along the interface of cold-joint are higher. This paper presents a model to simulate the cold-joint in concrete elements in the ABAQUS finite element package. Simply supported beams under three-point bending with the same compressive strengths of concrete on both sides of the cold-joint are considered, and three different sizes of geometrically similar cold jointed interface specimens are evaluated to consider the size effect using the Bazant's size effect model of concrete. The Mode-I of fracture mechanics is working in the three-point bending tests by notched beams in plain concrete. In order to achieve the best results of numerical modeling on the concrete beam, a number of stress-strain relations of concrete for compression and tension in different combinations were evaluated on the beam with monolithic concrete and, among them, the pair had the best results, compared to the experimental result, which was used for the modeling of concrete beam with a cold- joint. In addition, negligibly small thickness of the cohesive element with a linear softening relationship in the traction-separation law was used for modeling the cold-joint. The comparisons are made for load-deflection and load-crack mouth opening displacement (CMOD) plots. The finite element analysis results are in good agreement with the observations and data in experimental testing.
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