Research On The Recognition Method Of Loss Of Prestress For Railway Prestressed Concrete T Beam

The48th bridge of Jingtong line is located in Huairoubei and Xiaoshuiyu, centerdistance is K60+481, it is a single line bridge, built in1974, the bridge is a straightline and flat slope, it is a prestressed concrete T beam with16spans and the spen is23.8meters, the center distance of main beam is1.8meters, the hight of the beam is2.1meters, The thickness of the web located in the midspan is0.14meters, it isrockshaft bearing,and rounded shape concrete pier, the bridge is about10meters high,the prestressed reinforcements named N1、N2、N3、N4、N5of the beam are consistedof a Carbon steel wire with a diameter of5mm, a total of9bundle arranged curvealong the beam. This paper took one of the spans as the research object, through threeways of theoretical calculation、The finite element software ANSYS simulating andentity experiment to calculate and identify the existing effective prestress of the beamand use the software model to discuss the influence of prestress on the beam naturalfrequency and the relationship between them. The mainly completed work is asfollow:(1) The finite element model of Test beam established by using software ANSYS,and calculated the first five order frequency of the beam, on this basis, Theprestressed tendon were as a whole or divided into groups to constitute a variety ofcomputing situation,then calculated the natural frequency of vibration under thesituation of different prestress value combination the combination of prestressedtendon and the whole group composed of a variety of circumstances, calculation ofbeam body under the combination of different prestress value of natural frequencyvalues, the simulation results showed that the natural frequency decreases with thedecrease of the prestress value, the change of natural frequency value was obvious inthe boundaries of three kinds of states of full prestress, part prestress and nonprestress, and the location of prestressed reinforcement and the value of the prestresshad different effects on natural frequency of vibration.(2) Dynamic test were taken on original bridge to measure the natural frequencies of the bridge under effective prestress leve，Eliminate pressure load testand Grooving method test were taken on actual bridge, natural frequency under theeffective prestress has been measured, take the natural frequency get form thedynamic test into the curve of the effective prestress and frequency to get theeffective prestress, to verify the relationship between the effective prestress of thebeam and the natural frequency of vibration further and the feasibility of using thefrequency to identify the effective prestress.(3) Understood the basic situation of the experimental beam, referenced to thecalculation methods and formulas of loss of prestress of China、the United States andEurope, calculated the effective prestress value and the frequency of the experimentalbeam according to the specification of our country.(4)The research method of the paper was summarized reference to effectiveprestress of the beam got from theoretical calculation,simulation and entityexperiment and a series of dynamic property values.