Study On Mechanical Properties Of Restrainer Based On Ductile Fracture

The girder bridge is the first choice for the Small and Medium-span Bridges because of its simple design and construction,and it is often used in approach bridges of many long span bridges.In all kinds of earthquake damage to bridges,the falling girder is the most serious and the most common earthquake damage,and it can directly lead to traffic disruption and seriously affect the rescue action after the disaster.Damage to the falling girder of the girder bridge occurred during all previous disastrous earthquake.So it is necessary to carry out seismic retrofit for girder bridges of the already built and under construction.Unseating prevention systems consists of three parts:the seat length,restrainers and unseating prevention devices.However,the existing restrainers have more or less different defects,therefore,it is necessary to develop a restrainer having good performance and quantitative design.In this paper,a new restrainer is proposed.The restrainer is developed combining the characteristics of the daily load of bridges and characteristics of earthquake.The restrainer is mainly made up of three parts:the steel ring with restricted displacement and dissipation,the upper guiding steel wheel and the downward guiding steel wheel.The steel ring,with restricted displacement and dissipation,is composed of two parts:the line segment and the arc segment.And horizontal free movement ability of the restrainer is provided through the part of the line segment,to adapt to the expansion deformation of the bridge under the action of temperature and daily vehicle load,so the secondary internal forces of the bridge construction,induced by the restrainer,cannot occur.The arc segment is designed to provide good buffering performance and dissipate the seismic energy.The finite element software ABAQUS was used to model and analyze to study mechanical properties of the new restrainer under monotonic loading.The guiding steel wheel was simplified into a rigid body,and the steel ring,with restricted displacement and dissipation,used three-dimensional solid element.In order to better simulate the whole process that the steel ring can show mechanical behavior,a ductile fracture model based on micromechanical mechanism was adopted.In order to study the influence of four main parameters(d,a,R,D),the parameter d is the diameter of the steel ring,the parameter a is the straight line of the steel ring,the parameter R is the arc radius of the steel ring,and the parameter D is the diameter of the guiding steel wheel,four groups of 54 models were conducted.For the research object,on the one hand,the simulation object has less change parameters,and on the other hand,in order to avoid the modeling error caused by repeated manual operation and improve the efficiency of modeling,so Python is used for parametric modeling in this study.The specific research results are as follows:(1)When the parameters a,R and D are constant,the displacement at the maximum bearing capacity first decreases and then increases with the increase of the parameter d,while the maximum bearing capacity increases with the increase of the parameter d;(2)When the parameters d,R and D are constant,the displacement at the maximum bearing capacity increases with the increase of the parameter a,and they are in approximate linear relationship,and the maximum bearing capacity also increases gradually with the increase of the parameter a;(3)When the parameters d,a and D are constant,the displacement at the maximum bearing capacity increases with the increase of the parameter R,and they are in approximate linear relationship,while the maximum bearing capacity decreases gradually with the increase of the parameter R;(4)When the parameters d,R and a are constant,the displacement at the maximum bearing capacity decreases with the increase of the parameter D,and they are in approximate linear relationship,while the maximum bearing capacity increases gradually with the increase of the parameter D;(5)The restrainer has good buffering performance under monotonic loading through the force-displacement curve of the finite element results.The force-displacement curve of the restrainer are dimensionless.And 5 feature points are selected from the force-displacement curve of the model,combined with the characteristics of daily load of bridges and characteristics of earthquake.According to the finite element results of each feature point,the relevant feature points are fitted and the formulas of displacement and force of each feature point are given,combined with mathematical statistics knowledge,and the constitutive relation of the restrainer is provided for engineers to design.In order to verify the accuracy of the fitting formulas,eight FE verification models were added at last and the errors at the maximum bearing capacity were controlled in ±5%.Additionally,the finite element force-displacement curve is in good agreement with the curve of the formulas.It can be seen that the fitting formulas have high accuracy and can be used as a simplified design method for the restrainer.