Damage Detection Of Prestressed Concrete Beams Based On Nonlinear Vibration

In service period prestressed concrete structure, due to load, fatigue, corrosion,aging, environmental conditions and such many unfavorable factors of interaction, willinevitably produce damage accumulation, and lead to concrete crack, prestress loss, oreven sudden accidents. Therefore, work performance evaluation of prestressedconcrete component in service period, the key component of that, especially workingcondition assessment of prestressed steel strand, is an important part of structuralhealth detection and inspection in current. This paper discusses the relation ofnonlinear characteristics and prestress change based on the structural nonlinearvibration.This paper first introduces the reinforced concrete beam’s vibration nonlinearitybecause of crack and material nonlinear, blind source separation technique principleand Hilbert transformation. Then describes static test and two-stage equal amplitudefatigue test of prestressed concrete beams, and uses fiber grating sensors and straingauge to collect the prestress value of strand. This paper gets first order isolatedvibration signal by appling the blind source separation technology to the vibrationsignal analysis under various damage, obtains amplitude-frequency curves by Hilberttransformation. Finally, this paper will try to use the breathing crack and the influenceof the steel strand to explain the nonlinear dynamic characteristics of experimentalbeams, and the nonlinear dynamic characteristics are used to explore the prestressedconcrete beams’ damage detection.Compared amplitude-frequency curves in static load test with fatigue test undervarious damage, they have common points as follows:1) transient frequency willincrease with vibration amplitude decreasing, and it is more obvious when theamplitude value is small;2) steel strand will compress beams, reduce the residualstrain of cracked region, influence cracks closure, and cracks "breathing" effect, whichaffects the nonlinear characteristics of beams;3) it is more available for damageidentification by comparing the frequency-amplitude curve than the natural frequencyand so on。Their differences are following: in static load test, the cracks affect profoundlythe nonlinear vibration characteristics of reinforced concrete beam; Nonlinearvibration characteristic strengthens with the increase of the early beam damage, reach its peak before reinforcement yields, and decrease with the increase of beam’s damage.In low-amplitude fatigue stage, with the accumulation of damage, the nonlineardynamic characteristics of prestressed concrete beams increase first, and then decrease;in high-amplitude fatigue stage, it is monotone decreasing.In the end of the paper, the nonlinear vibration can be applied to damageidentification, and it’s better to study damage detection for prestresses concretestructure than reinforced concrete structure.