Study On Vehicle Load Effect Model And Reliability Analysis Of Widening For Small-span And Medium-span Beam Bridge

With the development of economy,many highways built in the early stage can not meet the increasing traffic demand,so they need to be widened and rebuilt urgently,and bridge engineering is a key point.However,there are few studies on the reliability of widened Bridges at home and abroad,and no theoretical system or relevant specifications have been established for the design of widening existing Bridges.Moreover,after the highway is widened,trucks tend to drive to the right side,with obvious diverging phenomenon.So it is necessary to study the reliability of widened Bridges.The vehicle data of a highway for 9 months(39 weeks)was collected through the WIM system,then the vehicle load effect was calculated by using the influence line loading method and the weekly maximum value of load effect was taken as the short-term load effect maximum sample which was used to establish a short-term vehicle load effect distribution model.Then the maximum value distribution of vehicle load effect in design reference period is deduced by the extreme value theory.The cases of simply supported girder bridge widening with standard spans of 6m,8m,10 m,13m,16 m,20m,25 m and 30 m are respectively adopted The reliability indexes of the longitudinal beams before and after the extension of the old bridge are analyzed,and its variation rules before and after widening are analyzed.The research results show that:1.The establishment of vehicle load effect model(1)The Generalized Extreme Value Distribution curve-selecting method is proposed to calculate the extreme value sample distribution of vehicle load effect.Comparing the fitting degree of Generalized Extreme Value Distribution curve adjusted by curve-selecting method,Generalized Extreme Value Distribution curve calculated by the maximum likelihood method and Gumbel distribution curve with one third of the data at the end of the larger value side respectively,it is found that the Generalized Extreme Value Distribution curve obtained by curve-selecting method is in good agreement with the original data and is very suitable for the establishment of short-term load effect model.(2)The actual vehicle load of the highway is much greater than highway grade Ⅰ vehicle load of General Code for Design of Highway Bridges and Culverts(JTG D60-2004)and General Code for Design of Highway Bridges and Culverts(JTG D60-2015).2.Highway bridge widening reliability research(1)After the bridge is widened,the reliability index of the longitudinal beam of the old bridge near the widening side has decreased to some extent,and the closer to the wideningside,the greater the decrease,but the reliability index meets the relevant requirements in the code.(2)Since the heavy vehicles in the two-lane 8-lane highway mainly travel on the third and fourth lanes in practice,the reliability of the longitudinal beams away from the widening side has been greatly improved after the bridge is widened.