The Caculation Of Short-term Crack Width Of Flexural Members

Cracks occur in flexural reinforced concrete members inevitably in service, and it is the foundation to control the crack width and guarantee durability to predict the crack width accurately. The commonly adopted theories to calculate crack width are based on the plane cross-section assumption applied for any section between cracks. In fact, concrete around the steel bar in tensile zone retracts after crack occurs, while the retraction will be impeded by the bond stress between the reinforcement and concrete. Thus, compatibility of deformation is not applied for the reinforcement and concrete in tensile zone. Furthermore, the tensile stress of concrete around the steel bar is related to the bond stress, as a result, the stresses of concrete in compressive zone and tensile zone in same section no longer hold certain relationship.In this thesis, a flexural crack model, in which plane cross-section assumption is not applied for any section between cracks and the loads conditions are reflected, is estabished to meet the real crack characteristics. In this bending crack model, by introducing a quadratic funtion of tensile concrete stress and a bond-slip assumption, with a classification for concrete stress in tensile zone according to the applied loads, an analytical solution of concrete stress and steel bar stress in tensile zone in any section between cracks is deduced, then the formula of the bond stress and the uneven coefficient of tensile reforcement strain are derivated, and at last the caculation of short-term crack width is obtained in the new model. Additionally a discussion of the caculation of crack width and tensile concrete stress and steel bar stress and the uneven coefficient of tensile reforcement strain is raised, and a comparision between the solution of this thesis with some codes and experimental results is made, which shows the rationality of the solution of this thesis. This thesis provides a new thought for the caculation of short-term crack width.