Research On Effective Prestress Value Identification Of Prestressed Concrete Continuous Beam Bridges Based On Natural Vibration Characteristics Of Structures

In the course of using the prestressed concrete structure,due to the damage of the prestressed tendon in the concrete,the cases of the prestressed concrete component destruction are numerous.Therefore,it is crucial to make a correct assessment of the effective prestress value in the prestressed structure.However,for the bridges after completion,effective prestress value detection and identification has always been a problem.If you want to know more accurately the effective prestress value of the prestressed concrete structure,you can install intelligent detection instruments and equipments during the construction of the structure.In addition to this method,it is difficult to use conventional detection methods and means to measure.However,in recent years,some experts have found that the natural vibration frequency of prestressed concrete bridges has a certain sensitivity to the effective prestress value of bridges.It is a very valuable research direction to use the dynamic characteristics of bridges to confirm the size of its effective prestress value.Some scholars have already pushed out the relationship between the dynamic parameters of prestressed beams and the effective prestress value of the structure.This paper is based on the background of a prestressed concrete continuous girder bridge,applying the method of scholars to prestressed concrete continuous beam bridges.Based on the measured natural frequency,the effective pre-stress loss of the beam body is reversed.The dissertation is based on the approach of the approach route of the Baisha River super large bridge,which is a 4-span 120 meter prestressed concrete continuous box girder bridge.Firstly,a modal test was performed on this bridge to obtain the measured natural vibration frequency of the bridge.Then use ANSYS software to build a model and calculate,using the method of initial strain in the software to prestress the concrete beam;The continuous girder bridge is divided into multiple segments,and the maximum tensile stress value and the maximum compressive stress value of the cross section in each segment are calculated;Then use the stiffness correction formula to correct the elastic modulus of each segment,use the modified elastic modulus to calculate the theoretical natural vibration frequency of the model,and then compare the theoretical natural vibration frequency with the measured natural vibration frequency of the bridge.If the difference between the two is large,the iterative effective prestress value is again substituted into the model calculation.In this way,the difference between the measured natural frequency and the theoretical natural frequency is within a reasonable error range.At this time,the prestressed tendon stress in the model is considered to be the existing prestress value of the bridge.This method is only applicable to crack-free structures.Cracks affect the stiffness of the structure,so this method cannot be used in cracked structures.This paper calculates the effective prestress value of the prestressed tendons when the prestressed concrete girder bridge is to be cracked by the model,which is also the limit of the use of this method.