Reliability Assessment And Economic Analysis Of Strengthening Schemes For Existing Bridge

Due to load,material degradation and environmental impact,the performance decreases with time after the bridges operation.In order to ensure the reliability during the operation of the bridge,carrying out the evaluation of reliability is an urgent task.On the other hand,bridges designed in 60~70years of the last century cannot meet the necessary requirements because of the low design standard.thus,it is necessary to reinforce the bridges.There are lots of ways of strengthening,the scheme,time and degree of improvement directly affects the economy of bridge reinforcement.Supported by the project "Research and development of technical system and equipment of reliability evaluation of existing concrete beam bridge",the evaluation method of reliability and economy analysis of bridge strengthening based on strength shortage were studied.The followings are the main contents and conclusions:(1)Three expressions of the reliability index of the bridges were summarized,and the derivation method was given.The relationship between reliability assessment and design was studied by analyzing the characteristics of existing bridges.By taking the bridges in Chinese General Drawing Collection for Highway Bridges as the research object,compared the bridge code JTJ 023-85 with JTG D62-2004 in strength of materials and the calculation formula,the statistical parameters of calculation model in different bridge codes were analyzed.What's more,the methods of determining partial coefficients and the design strength in bearing capacity evaluation of bridges was given based on measured data.(2)The test section and test point arrangement of the existing stress were analyzed,and the method of determining the effect value and partial coefficients based on the measured permanence was put forward.When the permanent loading effect was calculated in the formula which was proposed by the standard "Specification for Inspection and Evaluation of Load-bearing Capacity of Highway Bridges",the load-bearing capacity assessment method based on the existing stress was established through the corrected constant load.(3)T-beam of 30 prestressed concrete bridges in Chinese General Drawing Collection for Highway Bridges were studied.For increasing the bearing capacity of bridges,the bridge normal section was strengthened by enlarging cross-section and external prestressing respectively,and the inclined section was strengthened by plate and FRP.The statistical parameters of force resistance after reinforcement were obtained.The bending and shear bearing capacities of the strengthened T-beams were calculated,and then the corresponding increased reliabilities and direct costs were also calculated.The results showed that for reinforcement of the normal section of prestressed concrete bridge,the bearing capacity and reliability of external prestressed bridge are increased significantly larger than the those of bridge strengthened by enlarging cross-section at the same cost;The shear bearing capacity and reliability of bridges strengthened with FRP are both increased,while the corresponding increasing rate decreases with the increasing of the costs.