The Method Research Of Determing Limited Load Value For Overweight Vehicles Cross Bridges Based On Reliability Theory

In recent decades, the metallurgy, electricity and petrochemical industrial equipment which imported and domestic manufactured expand increasingly toward to large and heavy, highway transportation system faces more and more pressure, the bridge is the throat of the highway system, the security of overweight vehicles that carry a large component lies on its bridge safety, so the issue of security which is about the overweight vehicles cross the bridge is a burning question.The safety and reliability evaluation of overweight vehicles that cross the existing bridge is a complex task, and many factors need to be considered, such as:overweight vehicles rate, bridge span, bridge service life,environment and so on, so the calculate and assessment is complicated.The thesis relys on the project of scientific and technological project of Guangdong province department of transportation (2010-02-16)-The method research of determining limited load value for overweight vehicles cross bridges based on reliability theory, we can get the following conclusion based on reliability theory and simulation analysis of the scientific computing software MATLAB.(1) By analyzing the advantages and disadvantages of the structural reliability calculation method,for analysis of varying reliability values under the especially heavy vehicle loads in this article when the existing bridge resistance is decaying, comparing and analyzing from its calculation accuracy,grate of the simple calculation, practical and operational, first order reliability JC method meet structural reliability analysis of the existing bridge under the heavyweight car loads;(2) Considering the various factors that affect the resistance attenuation of the existing bridge,this paper proposed an improved resistance decay model, in particular calculating time-varying strength and area of prestressed steel impact on the decay resistance of the bridge structure.When the bridge have not prestressed tendons, its ratio is1;(3) Based on reliability theory JC method and simulation of MATLAB, considering the existing bridge resistance reduceed in accordance with0%,5%,10%,15%,20%, 25%,30%and calculating time-varying reliability value under four kinds of overweight vehicles load,which are224t,287t,412t, and559t, curve of the overweight vehicles load and time-varying for the different types and various spans bridge can be obtained.The time-varying curve shows the first decrease and then increase trend, because559t overweight vehicle’s uniaxial wheel number is six, the front three vehicles are four, the vehicle wheel load increase first and then a slight decreases, which can show that the wheel weight affects the bridge safety and it is a important parameter,so the single-axis and multi-wheel vehicles should be voted and the safety of the bridge will be improved;(4) When the overweight vehicles cross over the hollow ban bridge,T-beam bridge and continuous beam bridge, the reliability calculated of bending moment is greater than the maximum shear reliability value, safety of the bridges depends on the the relative distance of the cross-section shear reliability and the target reliability index.so that it affects safety of the bridges;(5) For the rigid frame arch bridge,the reliability value of the arch legs roots bending moment is the smallest of the roots section’s on the arch legs, so it is the control section when assess the bridge safety;(6) Through site data testing when overweight vehicles cross the bridge, the method of determing limited load value for overweight vehicles cross bridges should be verified, so that it can give a reference quickly by determining how weight overweight vehicle cross the bridge is safe.This study gives a more effective way to determine the limited load for the overweight vehicles cross the existing bridges, and the research results can provide a technical reference to judge security of the bridges quickly when the overweight vehicles cross the bridge and put guidances to the relevant departments.