Study On Dynamic Peculiarity For Unbonded Pre-stressed Concrete Beam

With the development of technology, pre-stressed concrete structures are being appliedmore and more widely. But the pre-stress forces in tendons will loss gradually in the usingprocess, and the structure safety is threatened. So the detection of pre-stress loss is theimportant problem of the health monitoring and detection of pre-stressed concrete structure.The relation between force of pre-stressed tendons and dynamic characteristic is discussedthrough theoretical analysis and experimental research for unbonded pre-stressed concretesimply supported beam.In this paper dynamic characteristic of five pre-stressed concrete simply supportedbeam is researched. According to the analysis of natural frequency in levels pre-stressedforce through the technique of dynamic test, the test results indicate that the frequencies ofthese beams with eccentricity are reducing with the increasing of the pre-stress force, but thefirst and second steps frequencies in every grade pre-stressed force are not change when thepre-stressed tendons is placed in the center of the beam. Static load was put on the beamthrough two symmetric points for the pre-stressed beam, causing these beams to differentdegrees of damage, the frequencies of these beams are reducing with the increasing of thecrack, and vibration mode appears mutationThe flexural vibrate equation of simply-supported beam which is subjected to the axialcompressive force is analyzed by the theory of structural dynamics. On this foundation, thevibrate equation is established according to D’ Alembert’s principle, considered that steelconcrete simple supported beams is subjected to the eccentric compressive force. Theformula which is used to calculate natural frequency of simple supported beams is derivedunder both pre-stressing force and the influence of position of pre-stressed tendons. Theresults of calculation indicate that the calculated frequencies of pre-stressed concrete beamsare reducing gradually with the increasing of the pre-stress force. This conclusion is identicalto the result of test.In the end, the model of unbonded pre-stressed concrete beam has been established byANSYS, and then the frequencies of test beams were calculated by it. The results ofcalculation indicate that the calculated frequencies of these beams are reducing graduallywith the increasing of the pre-stress force, but reduced of the frequencies is very poor. Andthe analysis of theoretical calculation result and experimental data is carried. It is reasonable that the relative error of the first order natural frequency and it has good reference value onproject.