| Concrete-concrete interface widely exists in the strengthening and maintenance of old structures,the post-cast strip of construction projects and the prefabricated structures.Due to the difference in material properties and hydration degree of different concrete substrates near the interface layer,the interface layer has the problem of deformation coordination.Under the action of load and shrinkage,it will form a weak part.As a crucial part affecting the structural safety,the direct shear performance of the interface has become an urgent research topic.In this paper,the direct shear performance of concrete to concrete interface was regarded as the study object.The ultimate shear stress,crack width-vertical slip curve and stress-slip curve of the interface were obtained by considering interface roughness,longitudinal reinforcement,axial pressure and the coupling effects of longitudinal reinforcement and axial pressure.The direct shear evolution law was studied,and the interface shear constitutive model was established.The coupling effect of the axial stress and longitudinal reinforcement on the influence rule of interface direct shear performance was studied.Finally,according to the connection interface of sleeve grouting in prefabricated buildings,factors such as grouting layer thickness,longitudinal reinforcement ratio,corrosion rate of longitudinal reinforcement and axial pressure were considered.The ultimate shear stress,crack width-vertical slip curve and stress-slip curve of the sleeve grouting connection interface were obtained.The evolution law of direct shear performance of sleeve grouting connection was summarized.the following researches were carried out.1.By considering the influence factors such as the interface roughness,axial pressure,longitudinal reinforcement and the coupling effect of multiple factors,a total of 15 direct shear specimens in 5 groups were designed.The crack development,failure pattern,crack width-slip curve and stress-slip curve in the concrete interface were analyzed.The variation of the direct shear performance of the interface was studied.The results show that the interface cracking stress,ultimate shear strength and residual shear strength increased significantly under axial pressure.The interface cracking stress,ultimate shear strength and residual shear strength under 4MPa axial compression were respectively increased to 5.70 times,4.53 times and 2.64 times of the specimens without axial compression.When the axial compression was increased to 8MPa,the shear strength was only slightly increased compared with that under 4MPa axial compression.The interface cracking stress,ultimate shear strength and residual shear strength of specimens with 0.5%reinforcement ratio were increased to 1.71 times,1.37 times and 2.48 times of the specimens without reinforcement respectively.When axial compression and reinforcement were applied at the same time,the direct shear performance of specimens was improved compared with that of specimens with only reinforcement or axial compression,but the shear strength was less than the sum of the shear strength of specimens with reinforcement and axial compression.2.Based on the theory of "shearing friction" and the stress-slip curve of the direct shear test of the concrete-concrete interface,the constitutive model of the stress-slip of the concrete-concrete interface was established.The relationship between characteristic parameters and reinforcement ratio,axial pressure was analyzed.The two-independent variable stress-slip curve model of the reinforcement ratio and interface slip was established.The two-independent variable stress-slip curve model of the axial pressure and interface slip was also established.At the same time,the whole process function model of cohesion,friction and dowel action changing with shear slip was established.The stress-slip curve of the coupling effect of longitudinal reinforcement and axial pressure was compared and analyzed.3.For the type of concrete interface of the sleeve grouting connection,by considering the influence factors such as grouting layer thickness,axial pressure,longitudinal reinforcement,the reinforcement ratio and the corrosion ratio of the longitudinal reinforcement,a total of 27 direct shear specimens in 9 groups were designed.The crack development,failure pattern,crack width-slip curve and stress-slip curve in the concrete interface of the sleeve grouting connection were analyzed.The variation of the direct shear performance of the interface was studied.The results show that the thickness of grouting layer decreases from 20mm to 10mm,which has little influence on the shear strength of the interface,and when the thickness decreases to 1mm,the ultimate shear strength of the interface is 1.69 times that of the specimens in the 20mm grouting layer.Longitudinal reinforcement can significantly improve the ductility of and inhibit the development of cracks.The ultimate shear strength of specimens with 0.9%reinforcement ratio is increased to 1.58 times that of specimens without longitudinal steel bar.When the reinforcement ratio of longitudinal reinforcement is increased to 1.8%,the ultimate shear strength of specimens is increased to 1.89 times that of specimens without longitudinal steel bar.Axial pressure can significantly improve the shear strength of the interface.The initial crack stress and ultimate shear stress of specimens under 11.6mpa axial pressure were increased to 4.42 times and 6.06 times that of specimens without axial pressure respectively.When the pressure is increased to 23.2mpa,the initial crack stress and ultimate shear stress were increased to 5.83 times and 7.81 times that of specimens without axial pressure respectively and the failure mode changes into substrate failure.After the electrified corrosion of longitudinal steel bar produces rust-filled cracks,the shear strength of the interface of the sleeve grouting connection decreases obviously.The shear bearing capacity of the interface of the longitudinal reinforcement with a corrosion rate of 3.5%and a corrosion rate of 7.5%is 0.59 times and 0.51 times of that of the uncorroded specimens,respectively. |
