Study On Operation Performance Of Small-and Medium-span Concrete Girder Bridge Under Overloading And Chloride Environment

With the rapid development of national economy in recent decades,highway traffic volume enlarges,which leads to large amount of short-medium-span bridges in overloading status.Heavy vehicle load results in the damage of these bridges.Meanwhile,in the operation period,the bridge structure is often being attracted by chloride environment,which results in the corrosion of the reinforcement and the spalling of the concrete cover,and further the degradation of the whole structural performance.In the thesis,the vehicle load information on highway bridges is statistically analyzed in accordance with the data gathered from the Weigh-in-Motion system on Shaoxin segment of National Route 104.The load effect of the actual vehicle load on the girder bridge is compared with the effect values of the loads in current bridge design specification.Based on the fatigue damage theory,the equivalent relationship between heavy vehicle load and concrete fatigue damage is carried out,verified with the prediction of the bridge service life.After that,experimental study on the concrete members under chloride environment and loading is carried out.The fatigue damage evolution of prestressed concrete box-girder bridge under overloading and chloride environment is analyzed by numerical simulation method.Finally,the ratio of the measured response gathered from WIM and the calculated value based on the random-traffic-across-bridge theory is proposed as a dynamic calibration coefficient.Taking it as a threshold value,a health monitoring system for short-medium-span prestressed concrete girder bridges is developed.The main contents are as follows:(1)Based on the 10 months vehicle data gathered from the Weigh-in-Motion system on Zhongjiawan Bridge of National Route 104,the type,gross weight,axle weight and axle distance of the vehicle are statistically analyzed.It is illustrated that two-axle-vehicle is the main traffic type on highway bridges,and the vehicle load is in multi-normality distribution.All axle types of the vehicle present the overloading.The comparison results of the vehicle load effect on the approach bridge(simply-supported prestressed concrete hollow slab structure)show that the smaller the span of the simply supported beam bridge,the larger the vehicle number of actual load effect values beyond the effect value in current specification.(2)Taking the main bridge of Zhongjiawan Bridge,a three-span prestressed concrete box-girder bridge,as the study subject,the vehicle load effect is analyzed by numerical method.It is proposed a simplified method for the calculation of the multi-axle vehicle load effect.Based on the concrete fatigue damage theory.The results of the fatigue damage values under different levels of vehicle loads show that the concrete fatigue damage increases with an exponential function as the vehicle load increases.Then,an equivalent relationship between the two values is established,and is applied to the prediction of the bridge service life.(3)According to the environment in Zhejiang coastal areas,an experimental study on the concrete members under chloride environment and loading is carried out.The result shows that the stress impact factor increases as the compression stress increases.(4)To stimulate the whole process of prestressed concrete bridge in the operation period,the material degradation and sectional degradation model are established to investigate the evolution of the structural performance under overloading and chloride environment.By calculating the fatigue damage values of the prestressed concrete structure under different levels of vehicle loads,it is illustrated that in the expansion stage,the sectional area and mechanical properties of the prestressing strand is gradually deteriorated;in the crack propagation stage,the crack of the concrete appeared,and the fatigue damage is increasing rapidly.It also presents an exponential relationship between the fatigue damage value and the vehicle load.The parameter bf in the function reflects the three stages of the prestressing strand corrosion.(5)In accordance with random traffic information gathered by WIM,the chloride environment,the temperature indexes and the actual structure response under random traffic,a health monitoring system is developed for short-medium-span prestressed concrete girder bridges.?A dynamic calibration coefficient? is proposed as a threshold value for the grading prewarning of the bridge safety operation.The effective monitoring of short-medium-span prestressed concrete girder bridges under overloading and chloride environment can compensate insufficient technical capacity of local highway maintenance and management department,and enhance the bridge management level.