Flange Cracking Causes of π-Shaped Concrete Girders in Under-Construction Cable-Stayed Bridge and Prevention Measures
This study presents the causes of oblique cracks in flanges of π-shaped concrete girders in under-construction cable-stayed bridge and effective cracking preventions.A cable-stayed bridge with a main span of 120 m,which bore oblique cracks in flanges of the π-shaped prestressed concrete girders during construction,is used as a case.Link-element model of the bridge and solid-element model of the concrete superstructure during construction were built up in ANSYS,to analyze the influence of multiple factors on stresses in the soffits of the flanges,including self-weight of girders,stay cable tensioning,prestressing tendons tensioning,shrinkage and hydration heat of concrete.It is shown that the self-weight of girders and the tensioning of stay cables do not induce tensile stresses in the soffits of flanges,while the tensioning of transverse and longitudinal prestressing tendons causes a degree of tensile stresses in the soffits of flanges.Minor tensile stresses are observed in the soffits of flanges due to the shrinkage of concrete,but not sufficient to trigger cracking.The hydration heat generated during the concrete curing process is considered the main cause of cracks,given that there exists temperature difference between the concrete in the soffits of flanges and the surrounding concrete,at some measurement points,the first principal normal stresses even exceed the tensile strength of concrete.To address the hydration heat,it is recommended to place cooling water pipes in the main ribs of the π-shaped concrete girders and heat the flanges from beneath using burners.A thermal-fluid coupling model was developed to analyze the anti-cracking performance of the recommended measures.It is shown that the proposed measures can help improve the hydration temperature field distribution during the main girder curing process,and the first principal stresses at measurement points do not exceed tensile strength of the concrete girder.
cable-stayed bridgeπ-shaped concrete girdercrackconstruction stagehydration heatstressfinite element methodanti-cracking measure
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