| In recent years, the phenomena that trucks overload are more and more widespread in China. With the increase of service life of existing bridges, problems of fatigue damage is more and more serious because of vehicle load, especially for overload trucks, which become one of the main causes of bridge failure. Collecting the accurate vehicle loads, establishing a scientific and reasonable vehicle weight limit standard and ensuring the operational safety of bridges are of great significance. Based on the vehicle load data from weigh-in-motion system, the vehicle load spectrum of a main traffic in Hunan Province was established. The influence of illegal overload trucks crossing the bridge was studied and the differences between actual vehicle load effects and the code of highway bridge were compared. Finally, a methodology of vehicle weight limit based on fatigue strength of bridges was proposed. The main works of this thesis were summarized as follows:(1) The six-month traffic vehicle load of a main traffic in Hunan Province were collected via a weigh-in-motion system. Based on mathematical statistical methods. the vehicle load spectrum including daily traffic volume, vehicle type, vehicle composition, lane distribution, vehicle spacing distribution and vehicle weight distribution were establishded.(2) Based on vehicle load spectrums from chapter 3 in this thisis and another typical heavy traffic and a program for modeling random traffic flow and loading influence line which were developed by MATLAB and Monte Carlo method, vehicle load effect of simply supported beam bridges were calculated and they were also compared with the code of highway bridge. The influence of illegal overload trucks crossing the bridge was studied. The results showed that: As the bridge span increases, the bending moment and shear ratio decreased gradually. The vehicle load in both two areas exceeds the code of highway bridge in varying degrees.(3) A methodology of vehicle weight limit based on fatigue strength of bridges was proposed. A program for calculating structural fatigue damage with rain-flow counting method was developed by MATLAB. Take a typical simply-supported T-beam bridge with span length of 20 m, for example. The influence of fatigue life of the bridge on average daily traffic volumes and violation rates of overload trucks were studied. The results showed that: both average daily traffic volumes and violation rates would significantly affect fatigue life of the bridge. The higher aver age daily traffic volum, the shorter fatige life of the bridge. The higher violation rates, the less effective method of adjusting vehicle weight limit to enhance fatigue life of the bridge. |
