| With the continuous development of our country’s infrastructure construction,roads and railways cross over each other from time to time.When the proposed bridge wants to cross an existing busy route,compared with the conventional bridge construction method,the rotation superstructure construction technology not only ensures the normal operation of the existing route but also greatly reduces the hidden dangers of construction safety.Therefore,it widely uses in engineering practice.Because the rotation superstructure construction method has broad development prospects and application space,the friction behavior research of the contact surface of the rotating mechanism has great academic research value.In the large-tonnage rotation superstructure construction,the calculation of the friction force is of great importance,but the approximate calculation method given in the existing engineering practice has a big gap with the measured value of engineering.Therefore,the accurate calculation theory of the friction force and the friction moment is an urgent problem to be solved in the rotation superstructure construction.In view of this,this thesis takes the Maozhan Railway Overpass Bridge(75m+75m)as the engineering background,and according to the characteristics of the rotation superstructure construction,the friction behavior of the contact surface of the rotating mechanism is systematically studied,and a macro-micro mechanical model is established.The main work of this thesis is as follows:(1)Optimization of the calculation method for the friction coefficient.A mathematical calculation model for the rotating spherical hinge is proposed,combined with the principle of weighing test and the theory of contact mechanics,the improved calculation formula for the friction coefficient of the spherical hinge is deduced,and the calculation constant table of the friction moment of vertical rotation is formed.(2)Optimization of the calculation method for the traction force of horizontal rotation.Based on the proposed mathematical calculation model and the improved value of the friction coefficient,combined with the theory of contact mechanics and the principle of moment balance,the improved calculation formula for the traction force of horizontal rotation is deduced and the calculation constant table of the friction moment of horizontal rotation is formed.(3)Verification of the accuracy for the improved calculation method.Taking the Maozhan Railway Overpass Bridge as the engineering background,the accuracy of the improved calculation method for the friction coefficient and the traction force of horizontal rotation is verified by comparing the improved value in this paper,the existing approximate value,the finite element simulation value,and the actual measured value of the engineering.(4)Research on dry friction and lubricating friction characteristics.Aiming at the fluidsolid coupling characteristics of the interface contact in the actual rotation superstructure construction,the mechanical model of the rigid flat indenter and the elastic plane foundation is used,combined with molecular dynamics theory,to verified that the contact stress distribution at the nano-micro scale and the macro-scale are consistent.The influence of various factors such as sliding speed,system temperature,number of lubricating film layers,and length of lubricating molecular chain on friction is analyzed.In recent years,the author’s research group has conducted in-depth research on bridge superstructure rotation construction.Cai Xiaopeng used the finite element method to analyze the contact stress of the spherical hinge of the rotating system.At the same time,combined with the knowledge of the composite rigid surfaces,a simplified mechanical model of the rotating system is proposed.Based on the simplified mechanical model of the rotating system,the height distribution and spatial distribution of the polytetrafluoroethylene(PTFE)slide plates were optimized by Tang Yong,which improved the problem of stress concentration at the edge of the spherical hinge.Different from the above research,the innovation of this thesis are:(1)The friction calculation method is improved and a calculation constant table is formed.By viewing the calculation constant table,the friction coefficient and the traction force of horizontal rotation for the rotating bridge can be rapidly obtained,avoiding tedious numerical modeling calculations,and having excellent engineering application value.(2)Compared with the existing research that only analyzes the rotating mechanism from the macro-scale,the analysis at the nano-micro scale can explain the mechanism of contact,friction,lubrication,and wear from the root cause,so as to provide a reference for the technical control and safety assessment in the rotation superstructure construction. |
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