Evaluation Of Crack Kinematics In Concrete Beams Based On Digital Image Correlation

With the continuous development of science,technology and economic level,people pay more and more attention to the safety of building structure,and the level of design and detection of building structure is in urgent need of improvement.Shear failure is one of the most critical failure modes of reinforced concrete members,especially beam members without shear reinforcement.Although extensive research has been conducted over the past decades,there is still no consensus on the theories and methods used to evaluate the shear strength of reinforced concrete members.In recent years,based on predefined fracture patterns and fracture kinematics,researchers have focused on building shear design mechanical models that assume shear can be transferred by critical shear cracks through various shear transfer mechanisms,but the mechanical models and related theories still need to be verified by detailed fracture motion measurements in experiments.Nowadays,with the rapid development of new measurement techniques,digital image correlation technology(DIC)provides a new opportunity to monitor the displacement field of the entire target sample surface and analyze the fracture development mode and kinematics.In view of this,the main research contents and achievements of this paper are as follows:(1)The research methods and progress of shear failure mechanism and crack kinematics at home and abroad are summarized,and the shear failure model and shear transfer mechanism of beam members are introduced.(2)A shear failure test study was conducted on 36 concrete beams without belly reinforcement with different shear span ratio,reinforcement ratio,section form and flange width.Meanwhile,the deformation information of 36 beam specimens during the failure process was analyzed from multiple angles through digital image correlation technology,and the motion law and influencing factors of beam cracks under shear load were explored.The results showed that,The above parameters have a certain impact on the fracture movement mechanism,in which the reasonable increase of reinforcement ratio has a particularly obvious inhibition effect on the fracture.(3)Based on the change of the crack width at the longitudinal reinforcement,an analytical method is proposed to evaluate the structural limit state,and the calculated results are compared with the measured results.The results show that the predicted critical shear crack width obtained by the analytical method is basically in agreement with the measured values for a thin and thin beam with M/Vd greater than 3.It has certain reference value.(4)Based on the crack characteristic information of beam members(inclination Angle,skeleton curve,tangential displacement and normal displacement),an integral calculation method was proposed to evaluate the limit state of the structure,and the calculated results were compared with the measured results.The results show that,The integral form calculation method proposed in this study can accurately predict the ultimate shear capacity of the no-belly beam at the critical shear moment,and has higher reliability and applicability than the analytical method.In addition,the rectangular section beam is more suitable for this evaluation method than the T-section beam.