The Influence Study To The Safety Of Existing Large Span Reinforced Concrete Truss Arch Bridges By Overload Operation

The hyperbolic arch bridge structure is a kind of horizontal thrust of arch truss bridge. It not only has the characteristics of light weight, saving material similar to the truss bridge,but its tress is reasonable like the arch.The bridge is suitable for soft foundation, therefore in 50-70 s of the 20 th century it was widely used in various cities and provinces and becomes one important style of the highway and agriculture bridges, playing a major role for the development of social economy at that time.However,with the rapid development of transportation industry, the density of vehicles and vehicle load are increasing,a considerable part of old truss arch bridges get damaged,their bearing capacity decrease obviously,and cannot meet the requirements of use or even threat to operational safety.So doing the safety performance impact study for existing reinforced concrete truss arch bridge and evaluating its reliability have become an urgent problem.But at present the study to the reliability of existing reinforced concrete truss arch bridges by overload operation is not much, this is the starting point of this dissertation.In this dissertation,regarding the 2 # bridge on dingxi city to longxi county line in Gansu Province as the engineering background,the safety performance of the existing reinforced concrete truss arch bridges on the influence of overload operation is studied on the basis of the related theory and the random reliability method.The main contents and the fruitful results of the dissertation are as follows:The vehicle loads and the impact coefficient values between the old and the new specifications are calculated and compared.Deduce the calculation formula of the impact coefficient under the influence of the bridge deck flatness and discusses the overload of vehicle and bridge weight limit standard.Adopt the combination of the four normal probability density function to reflect the vehicle load multi-peak distribution and adopt the segmental distribution of probability density function to reflect the characteristics of the general vehicle load and the overweight vehicle, in the end establish the measured vehicle load model.Select several common forms of bridge(cable-stayed bridge?rigid frame arch bridge?continuous rigid frame bridge?continuous girder bridge?simply supported girder bridge) and analyze the load effect under the action of the auto- 20 th level load and the measured vehicle load.For different forms of bridge the measured vehicle load effect is always about 1.4 times of the auto- 20 th level load effect.Describe the diseases of the truss arch bridge from four aspects:the structure, components, connections, and ancillary facilities.The harm of overload operation on bridge deck system, bridge panel and other main stress components are analyzed.The resistance attenuation probability model of a structure in serviceis established based on the study of the change of the deterioration of concrete, steel bar corrosion and bond between concrete and reinforcing steel bar over time.On the basis of the above research results, an overloading reinforced concrete truss arch bridge is evaluated under normal operation and overload operation with the checking point method based on reliability theory. Introduce the corresponding reinforcement methods in view of the main diseases of the 2 # bridge on dingxi city to longxi county line and analyze the resistance and reliability index of the bridge panel before and after the reinforcement.After reinforcement the structure is safe and reliable, and its resistance increases significantly.