Study On The Influence Of Split Ring Casting Interface On The Static Stability Of Long-span Stiff Skeleton Concrete Arch Rib

The stiff skeleton concrete arch bridge has advantage in large stiffness,strong bearing capacity,low difficulty in arch formation for the first time and beautiful appearance.Thus,it is increasingly widely applied in highways and railways in our country.In order to ensure the safety of the structure during the construction process,the outer concrete of the arch rib is usually poured by the method of ring construction,which leads to the formation of a large number of longitudinal interface between old and new concrete in the main arch ring,which becomes the weak link of the whole structure.At the same time,with the increase of arch span,the static stability of arch ribs gradually becomes the main factor controlling the structure design.Therefore,in order to study the influence mechanism,degree and law of the interface between old and new concrete produced by the circular casting outsourcing concrete on the static stability bearing capacity of the stiffened skeleton concrete arch rib,on the background of Tian’e Longtan Bridge,which is the world’s largest span arch bridge under construction with a main span of 600 meters,based on literature research,theoretical analysis,finite element simulation and other methods,this paper studies two kinds of static stability of large-span stiffened frame concrete arch ribs with split ring casting interface in depth.The research work and main conclusions are as follows:(1)Based on the regression analysis of a large number of experimental data in the existing literature,a simplified bond-slip constitutive model of the interface between old and new concrete is proposed,and then the finite element simulation of a new and old concrete composite beam test in the existing literature is conducted by using the model.The simulation results are basically consistent with the experimental results,indicating that the finite element method and the proposed interfacial bond-slip model are reasonable and accurate.(2)Establish a three-dimensional solid finite element model of Tian’e Longtan Bridge considering the split ring casting interface and analyze the linear elastic stability.The results show that the linear elastic stability coefficient of arch ribs of Tian’e Longtan Bridge is 15.1% lower under the assumption that the interface between the two rings is completely smooth than that under the assumption that the interface is completely bonded,indicating that the bond-slip of the interface between the two rings may have a certain impact on the linear elastic stability of this kind of arch structure,which needs to be carefully considered.In addition,according to the corresponding bond-slip parameters of the proposed model of the actual structural parameters of the Tian’e Longtan Bridge,the linear elastic stability coefficient 0f the structure is only 1.6% lower than that of the fully bonded model,which indicates that the linear elastic stability analysis of the structural parameters and the actual interface treatment measures of the Tian’e Longtan bridge can be simplified as the conventional finite element model of fully bonded structure.(3)By analyzing the parameters of finite element model of linear elastic stability analysis of Tian’e Longtan Bridge with different roughness and reinforcement ratio,it is concluded that interface roughness can improve linear elastic stability,but the improvement is limited.At the same time,it is found that reinforcement ratio has little effect on the linear elastic stability.(4)Taking into account the double nonlinear of materials and geometry,a load-displacement curve of the main arch rib is obtained by analyzing the in-plane stability analysis of the main arch rib of Tian ’e Longtan Bridge,namely the ultimate stability bearing capacity analysis,considering the bond slip between the rings.The results show that the failure mode of the arch rib is that the section failure occurs at the column near the arch foot(this paper assumes that a section failure is considered as the ultimate state of the structure).The slip of the interface between the outer concrete ring is large near the arch foot and each column,so the bond strength of the interface between the outer concrete ring near the column and the arch foot should be strengthened in the design.(5)The in-plane stability ultimate bearing capacity of the main arch rib of Tian’e Longtan Bridge was analyzed by considering three interring interfaces:completely smooth,completely bonded and actual design interface treatment(roughness 2mm and reinforcement ratio 0.6%).The results show that the ultimate bearing capacity of the completely smooth interface model decreases by11.2% compared with the completely bonded interface model,indicating that the interface slip also has a significant impact on the ultimate bearing capacity of the in-plane stability,which cannot be ignored.Considering that the ultimate bearing capacity of the actual design interface treatment model is 10.9% lower than that of the commonly used interface complete bonding model,it indicates that the ultimate bearing capacity of the arch ribbed structure may be overestimated according to the assumption of complete bonding between the outer concrete rings,which is unsafe for practical projects.(6)By analyzing the influence of interface parameters,such as interface roughness and reinforcement ratio,on the ultimate bearing capacity of the structure,the results show that increasing the interface roughness of the outer concrete ring can improve the ultimate bearing capacity,but to a limited extent.When the interfacial roughness reaches 6mm,the ultimate bearing capacity of the arch rib considering interface slip is close to that of the fully bonded model.Therefore,it is suggested that when the conditions permit,the interfacial roughness should reach 6mm when the interfacial roughness is roughened between the outer concrete rings in actual engineering.The change of the planted reinforcement ratio has little effect on the ultimate bearing capacity of the arch ribbed structure.Therefore,it is inferred that the planted reinforcement ratio at the interface can be appropriately reduced in the actual engineering design compared with the Tian’e longtan bridge to avoid material waste.