Experimental Study On The Axial Mechanical Properties And Functional Properties Of Flexible Joints In Pipelines

Underground water supply network is an important part of the lifeline project.To ensure the normal operation of the underground water supply pipeline is an indispensable key factor to speed up the modernization construction,ensure the order of daily life and urban safety.It is of great significance to study the mechanical properties and water supply capacity of the flexible interface of the pipeline for the seismic design of the underground pipe network,the guarantee of water supply capacity and the planning of urban disaster prevention and mitigation.According to the seismic damage data over the years,the main failure mode of water supply network is interface failure,and the axial failure of pipeline interface accounts for the largest proportion.At present,most of the researches focus on the large deformation of the buried pipeline site,the liquefaction of the site and the seismic performance of the pipeline interface itself.The interaction between the pipe body and the rubber ring at the pipeline interface needs to be supplemented.It is difficult for the skeleton curve based on the test results or the viscous damping spring model based on the finite element to effectively reflect the interface stiffness reduction of the pipeline under the reciprocating load However,there is a lack of mathematical model which can accurately estimate the reciprocating deformation process of flexible joints.In view of this,this paper takes the rubber ring interface of ball milled cast iron pipe as the research object,and conducts the axial mechanical properties test and theoretical research of the flexible interface of the pipe.The main contents are as follows:(1)Through the non-water test and water pressure test under the axial monotonic load and reciprocating load of the flexible joints of pipe diameters DN150,DN200,and DN300,the curves between force and displacement in the drawing process of the pipe orifice under different working conditions are obtained.It is found that in the monotonic loading test with and without water,the pull-out resistance of the pipe is greatly affected by the loading rate and the pipe diameter,and all of them show a positive correlation;in the step-by-step reciprocating loading test It is found that the peak force decreases with the increase of the pipe diameter,which indicates that the equivalent stiffness of the flexible interface of the pipeline is degraded;(2)Based on the results of monotonic drawing test and the interaction relationship between the rubber ring and the pipe body in the drawing process of the pipe orifice,it is revealed that the axial tension displacement curve of the flexible interface of the pipe has gone through three stages,namely,the elastic stage,the elastic-plastic stage and the sliding friction stage,and the corresponding axial stiffness equation of the interface is put forward;the influence of different loading methods and different loading rates on the pulling resistance of the flexible interface of the pipe is analyzed,At the same time,the axial tension displacement curve of the interface with initial water pressure of 0.2MPa and no water is compared,and the law of the influence of water pressure on the mechanical properties of the flexible interface is obtained;(3)Based on the results of the step-by-step reciprocating test and the simplified deformation stress history of the rubber ring,the axial hysteretic model of the spigot socket flexible interface of the pipeline is proposed.The results of the model are in good agreement with the test results.The relevant research results can provide a reference for the seismic design of the pipeline engineering.