| Since the 1990 s,countries such as Europe and the United States have gradually completed the transition from allowable stress design method to limit state design method in railway bridge design.The allowable stress design method is still used for the design of railway bridges in China.It is far behind the international mainstream mainstream limit state design method based on reliability theory.This paper discusses the study of the influence of different load combinations on the reliability of railway bridge gravity piers under the limit state method.The main research contents and conclusions are as follows:(1)It is based on the limit state design method to study of the influence law of the reliability of gravity bridge piers under different load combinations.In this paper,3 sets of standard drawings of gravity bridge piers of railway bridges are selected for the calculation of the combined eccentricity and compressive bearing capacity of the two design methods.The conclusion shows that the principle of material consumption such as gravity piers designed under the limit state design method and piers designed according to the allowable stress design method basically achieves.This is to lay the foundation for calculating the reliability of gravity bridge piers under different load combinations and discussing its changing rules.(2)The load acting on the gravity bridge piers of railway bridges are studied.In view of the fact that the design and calculation of traditional railway bridge piers do not consider the problem of long rail force and seismic force,and under the current situation that railways mostly adopt seamless line design and seismic requirements of railway bridge piers,this paper innovatively incorporates the long rail force and seismic force brought by the seamless line into the common load of gravity bridge piers of railway bridges.At the same time,for the design and calculation of traditional railway bridge piers,only the load combination of main force and additional force is considered,and the combination of main force,main force and special load,and seismic combination are innovatively included in the calculation and reliability analysis of the pier.The conclusions show that under most principal forces + special load combinations and seismic combinations,the results and reliability indexes of the bridge piers combined force eccentricity and section compressive bearing capacity are significantly smaller than those of the principal force combination and principal force + additional force combination.It proves that it is unscientific to consider the combination of main force and additional force.(3)Through the analysis of inspection results,reliability index results and their laws,the resultant force eccentricity controls the design of bridge piers.In most cases,the combined eccentricity check of the design of the control pier size under the load combination of constant load + single-span heavy load + centrifugal force + longitudinal seismic force during single-lane driving has the smallest margin and the lowest reliability index.In a few cases,it is controlled by the load combination of constant load + rail breaking force + telescopic force in the vehicle-free operation state.At the same time,the influence of the main combination of constant load + double-track long rail expansion and contraction force on the reliability of gravity bridge piers under the vehicle-free operation state can be completely ignored.From the results and reliability indexes of the resultant eccentricity of the control section design,under all load combinations,when the other conditions are the same,the variation law decreases with the increase of the pier height,reflecting that its reliability level increases with the pier height Large and reduced.(4)In order to facilitate the study of the influence of different load combinations on the reliability of railway bridge gravity piers,and at the same time for the problem of low domestic railway bridge pier design and inspection efficiency,this paper studies and analyzes related theories and design specifications,and uses Visual Basic language Check program for gravity bridge piers of railway bridges.This program can realize the inspection of various railway piers such as passenger and freight railways and high-speed railways.The program is composed of three modules,including load calculation module,resultant force eccentricity check module and section compression bearing capacity check module.In order to find the most unfavorable cross-section that is the control crosssection,the golden section optimization algorithm is used.Through the verification and analysis of the program results,the conclusion shows that the program can fully meet the requirements of inspection.This program fills the gap in the calculation procedure of gravity bridge piers of domestic railway bridges,which greatly improves the efficiency of its calculation.(5)In this paper,the Monte Carlo method is used to calibrate the reliability index of the gravity bridge pier of the railway bridge under the limit state design method,and the rule of the influence of different load combinations on its reliability is analyzed.The conclusion shows that the reliability index of the normal service limit state under different load combinations is within the normal range,while the reliability index of the load capacity limit state is higher.It shows that the size design and material consumption are conservative.This study provides suggestions for the calibration of reliable indicators in future limit state design codes.In this paper,by studying the effect of load combination on the reliability of gravity bridge piers of railway bridges,this paper provides ideas and opinions for the transition of Chinese railway allowable stress normal to limit state method.At the same time,through the calibration study of its reliability under different load combinations,it provides suggestions for the future design of the limit state design specifications of railway bridges and culverts in terms of design methods,material consumption,and size design. |
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