Fatigue Load Spectrum And Fatigue Behaviors Of Short Span PC Girder Bridges In Heavy Highwa

Bridge safety has been paid much attention in the engineering field. Generally, the design reference period of the service life of the bridge is 100 years. With the development of social economy in China, highway traffic volume and vehicle load show a growth trend, especially in the central and western regions in our country. The traffic load has the characteristics of large traffic volume and high axial load. The development speed of bridge damage becomes very quickly under the long-term high axial loads. It will seriously affect the service life of the bridge. The influence of vehicle load on the bridge fatigue damage cannot be ignored. General Code for Design of Highway Bridges and Culverts provides the bridge vehicle loads can be divided into two levels:highway level Ⅰ and level Ⅱ load. But the research on the fatigue design load for highway bridges is still insuficient. This paper conducts the research on heavy vehicle load on the highway, and predicts the fatigue life of typical bridges. The main contents are as follows:(1) Traffic characteristics such as types of vehicles, vehicle distance, vehicle weight and transverse distribution of vehicles are investigated in the typical sections on overloaded highway areas, and the probability density function is regressed. Based on Miner ruler, the formulas for the equivalent axle load and the equivalent wheelbase are deduced. The different vehicles that have same axis number are simplified as a typical vehicle model. Finally, the fatigue load spectrum is gained for calculating fatigue damage of overload highway bridges. The vehicle type that makes the largest contribution to fatigue damage of bridges is chosen as the basic form of standard fatigue vehicle, and the correction coefficient of axle load is calculated based on simply supported beams with different span. And the standard fatigue vehicle model is established based on simply supported beam with 20m span.(2) According to the actual traffic data, the random process of vehicle load is simulated by Matlab program. The bending moment-time curves of simply supported plate beam with 13m span and T beam with 20m span are gained by using the random process of vehicle load cross the midspan bending moment influence line. Furthermore, the probability density functions of bending moment amplitude of those two beams are developed by calculating the distribution of moment amplitude.(3) In order to determine the cracking load, the yield load and the ultimate load of those two beams, the full-range static analysis is carried out using the software ANSYS. Fatigue life prediction method based on stress that is verified to be accurate is used in those two beams’ fatigue life prediction for the reason that determine the selected simply supported beams’ service life, and the fatigue life of them are acquired. The materials’ fatigue constitutive relations are proposed to calculate the simply supported beams’ fatigue postcycle static bearing capacity by using the software ANSYS. The results show that the simply supported beams’fatigue postcycle static bearing capacity declines with the increase of fatigue load action times.