Method And Experiment Research On Highway Reinforced Concrete Simply-supported Girder Bridge’s Fatigue Residual Service Life Forecast

Reinforced concrete bridges were very rife in highway engineering. Along with the servicing time increasing, bridges’bearing capacity will be attenuated gradually under the action of vehicle load and environment attack, and this induced much bridges’be destroyed before design reference period. To insure bridges safety and to provide technology gist for bridges’ reinforce, load limited or rebuilt, it is very important to evaluate existing bridges’residual service life. Based on the several years traffic investigation and laboratory fatigue experiment, this paper researched the reinforced concrete bridges’residual service life by experiment and theory manner, which were listed as following:(1) Based on the traffic and vehicle weight investigation information, predigest vehicle type’s equivalent axis weight and wheelbase, vehicle’s gross weight and percentage of every kind vehicle were calculated out. Gross weight’s probability density function of every kind vehicle was imitated. Then fatigue load vehicle model was established. The bending moment breadth in middle span of Maocaochong Bridge was achieved by Monte Carlo method. Then the the stress and distributing frequency of different moment bending breadth were acquired. Double-exponent distributing frequency formula of bending moment were imitated, the bending moment breadth which can be used in fatigue test and fatigue analysis was achieved out. A grey-Markov stochastic process traffic forecasting model which considering the disciplinarian and randomicity of traffic development was set up using GM(1,1) model and Markov chains model, and it can forecast the traffic development of future years. The probability density function of gross weight of traffic was acquired, the vehicle load stochastic process model which can calculate the vehicle numbers in a certain gross weight range overpassing the bridge in No. N years were established. The traffic and vehicle load of Guixin highway was forecasted using the model.(2) The unvaried amplitude fatigue experiment of deferent stress breadth were carried using 5 hollow slab beams and 5 T beams, and the unvaried amplitude fatigue test properties of crack development, deflection development, reinforcing steel bar and concrete’s strain development, as well as fatigue life, destroy form and destroy property when the beam fatigue destroyed. The S-N curves were fitted out. The low-high amplitude and high-low amplitude (two grade varied amplitude) fatigue experiment were carried using 2 hollow slab beams and 2 T beams. According to the highway bridge’s fatigue load spectrum, a random fatigue load bending moment breadth which can be used at laboratory fatigue experiment were weaved, then the random load fatigue experiment using a hollow slab beams and a T beams were done, the beam’s random load fatigue life and the fatigue destroy properties were obtained. Based on Miner ruler and Corten-Dolan ruler, a equivalent unvaried amplitude fatigue stress breadth calculation formula of multilevel or random load was deduced, Fatigue life of Maocaochong Bridge was triumphantly doped out by the formula.(3) Bridge’s relationship model of bearing capacity degeneration-stiffness degeneration was established. The stiffness of the bridge was calculated by deflection curve equation under load action, and it showed three phases linearity disciplinarian of bridge stiffness degeneration in fatigue experiment, a stiffness degeneration formula was established at last. A beam bridge’s bearing capacity was forecasted by using the model.(4) It was approved that the strain energy can showing the energy dissipating in fatigue processand the irreversible plastic power dissipated in every circular were defined as dissipated energy density. Five T beams’ dissipated energy density were tested, and researches detected that the dissipated energy density in fatigue test had quite obviously three phase law. The non-linear equation between dissipated energy density and the ratio of load breadth to stiffness as well as the non-linear equation between fatigue life and dissipated energy density in fatigue stabilization phase were established. The fatigue life forecasting method based on dissipated energy density were validated to be feasible through random fatigue experiment, and Maocaochong Bridge’s service life were triumphantly doped out with this method.(5) Using the bearing capacity degradation time-dependent model under environment infection and the fatigue bearing capacity degradation time-dependent model under vehicle load repeated action, existing reinforcing steel concrete bridge’s bearing capacity degradation time-dependent model under the action of environment and repeated vehicle load was established. Using existing bridge’s permanent load and load effect probability model, reinforcing steel concrete bridge’s time-dependent reliability forecasting model was erected, and the reliability index of bridge in every period of time were calculated out by using JC method. Maocaochong Bridge’s residual life forecast, reliability index in design reference period was acquired, and the Maocaochong Bridge’s service life at target reliability index and critical reliability index were doped out.