Research On Bending Bearing Capacity Evaluation Method Of Highway Prestressed Concrete Simply Supported Beam

Medium and small span highway prestressed concrete bridges occupy a large proportion in highway lines of our country,there have been many reports of the bridge accident with the service period go on.So,quickly and accurately assess the bearing-capacity of existing bridges is increasing urgency.Currently,there are mainly assessment methods:appearance detection method,load test method,dynamic detection method,reliability theory method and check-calculation method.Check-calculation method based on test results,increase or decrease the design resistance by introducing different reduction factors.Differenting from other detection methods,check-calculatio method have a broad application prospects because of fast speed,accurate and low cost.This thesis propose multi-parameter ealuation method and classified the parameters of the check-calculation method,based on existing literature research results.What’s more,verified with a simple supported box girder bridges of 40m.The main works and conclusions are as follows:(1)researched and studied the existing bridge detection methods,introduced the advantages and disadvantages of various evaluation methods,emphatically introduced the problem in our country rules.(2)sort out the diseases of bridge according to the characteristics and causes and the effects,classificated the diseases according to the mechanical performance and the durability performance and facilitated the selection of cactors in evalution of the bearing-capacity in future.(3)aiming at the problems,existing in our country’s rules,which used same check-caculation coefficient to evalute different indexes,this thesis adjusted and put forward a multi-parameter evaluation model.That is,according to the different state of the bridge(the bearing-capacity of the limit state and the normal-use of the limit state),using different coefficients to evalute different indicators.According to the characteristics of the bridge materials,introducted working conditions coefficient Φ to respect the overall performance of the bridge.The bearing-capacity limit state consideres meterial property,using concrete strength grade and steel meterial property to evaluate bearing-capacity;the nomal use limit state consideres overall stiffness of structure,using apparent defect and stiffness to evaluate bridge traffic capacity;structural work conditions consider bridge deck pavement,meterial work performance and structural geometrical properties,determining the reduction factor under different scales according to lrfr of Unite States and bridge failure test results of China.(4)the concrent creck have little influce on the ultimate load bearing-capacity and great on the evaluation index(stress,deflection and crack).The appearance defect only has a great influence on the evaluation index under the normal use limit condition.(5)the results show that the insufficient effective prestressing will affect the overall stiffness of the structure,which will have a great influence on the normal performance,but small on the bearing capacity,indicating that the addition of prestress will not improve the ultimate bearing capacity of the bridge.