Study On Reliability Index And Partial Coefficient Of The Steel Box Bridge Structures For The Slow Traffic System

Slow traffic system is an urban transportation system with pedestrians and non-motor vehicles as the main mode of travel.It can not only alleviate traffic congestion,but also provide leisure,fitness,sightseeing and other functions.Among them,steel box girder bridge is a kind of bridge structure commonly used in slow traffic system.At present,The design of bridge structure of slow traffic system in China mainly adopts《Technical Code for Urban Pedestrian Bridge and Pedestrian Tunnel》(CJJ 69-95),but there is no special design code for slow traffic system.This paper takes the simple supported steel box girder structure of slow traffic system as the research object.Based on probability and statistics theory,using numerical simulation,this paper studies the reliability index and partial coefficient of the simple supported steel box girder structure with slow traffic system,which can provide reference for design.The main research methods and conclusions of this paper are as follows:(1)Taking simply supported steel box girder structure as calculation model,using numerical simulation,the probability control region of bending moment failure and shear failure is determined.In daaition,based on the above results,the control position of the most dangerous section is found.Studies have shown that the influence degree of section thickness,width and height on component failure increases successively.According to the influence of shape parameters on the failure degree of component,the weight of bending moment and shear force was calculated by using analytic hierarchy process.On this basis,the broken value expressions of moment failure and shear failure based on weight ratio are established.Based on the quantization calculation result for the expression of broken value,using system hierarchical clustering algorithm,the probability control region of bending moment failure and shear failure is determined.In daaition,based on the above results,the control position of the most dangerous section is found.(2)Monte Carlo simulation method was used to sample and analyze the control positions of the most dangerous sections.Based on the calculative statistical eigenvalue of steel bulk density,crowd load,non-motor load and calculated span with steel box girder,the limit expression of action effect of simply supported steel box girder in chronic system is established.Finally,Monte Carlo simulation is used to calculate and analyze the sampling of internal forces at the control position of the most dangerous section,and the statistical characteristic values of the limit effect parameters,which are dominated by bending moment and shear force,are established for steel box girder structure with slow traffic system.(3)The design values of ultimate resistance of bending moment and shear force are studied by using grey prediction model.The study shows that compared with the limit effect value calculated in chapter 2,the numerical increase rate of the limit value of the structure bending moment section is 0.38%,and the numerical increase rate of the limit value of the structure shear section is 0.16%.On this basis,the mean value,standard deviation and coefficient of variation of section material tensile strength,shear strength,section height and section width were calculated by probability statistics method.Using the response surface method,the response surface expressions of the bending moment and shear force of the section,as well as the expressions of the corresponding mean and variance as the two statistical characteristics are established.Based on the calculation,the statistical characteristic values of structural resistance parameters in the simple supported steel box girder with slow traffic system are obtained,which are mainly flexural and shear capacity.(4)Considering the safety and economy of structure,the reliability index of simple supported steel box girder in slow motion system is studied by using support vector machine,and compared with traditional central point method,design checking point method and JC method.The results show that the recommended value of the reliable index of dangerous section bending moment is 4.7893,and that of dangerous section shear force is 7.4365.The analysis show that support vector machine method has higher safety reserve than central point method,design checking point method and JC method.(5)Based on the《General Code for Highway Bridge and Culver Design》(JTG D60-2015),the practical design expression of slow traffic system simply-supported steel box girder with partial coefficient is established.The partial coefficients of resistance and effect are studied by first order second moment method.The results show that in the proposed design expressions of bending moment and shear force,the recommended values of resistance coefficient of structural members can be 1.1001 and 1.1200 respectively.The recommended values of dead load effect sub-coefficients can be 1.0500 and 1.0700 respectively.The recommended values of the subcoefficients of live load effect can be set as 1.3910 and 1.4170 respectively.