Experimental Study On Stiffness Identification And Degradation Of Prestressed Concrete Box Girders

Prefabricated Prestressed concrete box girders are widely used in modern bridge due to light weight,good durability,large span ability.But in the process of normal operation of Bridges,the structure will have different degrees of damage because of the material erosion,environmental degradation,loads,natural disasters,etc.Studies on prestressed concrete beam degradation at home and abroad include the analysis of the causes of crack and deflection,the main factors influencing the structure crack and deflection,some countermeasures for preventing bridge cracking downwarping disposal,evaluating the static stiffness of the prestressed concrete beam in service.But for the damaged prestressed concrete bridges in service nicole dynamic stiffness degradation rule research and the use of dynamic method of prestressed concrete box girder attenuation diagnosis research,the current domestic research is not mature,need related research work.Through the whole damage process law to find a kind of economic,fast,practical and high predicated detection method in regular inspection,maintenance and strengthening bridge has great engineering practical value and economic benefits.In this article,three pieces of 30 m Prestressed concrete simply supported box girder do damage to the whole process of loading test,box Nicole stiffness and dynamic stiffness damage process were studied.In this article,the main research contents and results are as follows:1.Experiment with the prestressed concrete simply-supported box nicole dynamic load.Use hierarchical load test loading process in prestressed concrete simply supported box girder,make the box girder cracking and develop until the beam maximum crack width is reach about 1 mm to get a different degree of damage of the beam.Loading record each load stage box girder unloading level before and after the unloading fissure situation and carries on the static and dynamic test of box girder to get the corresponding damage condition of static and dynamic characteristics of box girder.2.Establish ANSYS finite element model of prestressed concrete simply supported box girder,select concrete elastic modulus,the concrete density,poisson's ratio,prestress as parameters,by changing the parameters of the finite element model to analyze the dynamic characteristics of simply supported box girder material parameters affect.3.Through the ANSYS finite element model of optimization design and Structure model of the variable stiffness to finite element model for model parameter correction to different dynamic characteristic value for each load stage and calculate the dynamic stiffness reduction factor under different crack condition.With simply supported beam in mechanics of materials deflection formula calculated elastic stage of a simply supported beam with cracks in the static stiffness.Cracks in beam after the static stiffness calculation using piecewise model using structural mechanics diagram multiplication cross beam deflection formula after the injury in the static stiffness reduction factor under different crack condition.4.Through the static and dynamic state of crack characteristic value and the stiffness reduction factor,return the reduction factor and the relation between the fracture parameters.Analyze the laws of the static stiffness and dynamic stiffness degradation to Provide a reference for rapid detection of structural stiffness recession.