Damage Monitoring For A Concrete-steel Hybrid Tubular Tower Using PZT Patches And Simulation With Spectral Element Method

In face of the energy shortage and environmental problems, the utilization ofwind power is in rapid development in our country for its renewability and cleanness.For the past decades, a large number of wind turbines have been built up withenlarged individual installed capacity, which corresponds to higher demand instructural performance. The advanced reinforced concrete-steel hybrid wind turbinetower is upgraded to combine the merits of concrete structures and steel structures,but it also has the weakness of protential concrete cracks. Therefore, it is critical tomonitor and assess the hybrid wind turbine tower. However, the conventionaldetection method is unsuitable. In this paper, a wave propagation analysis method isproposed based on the advantages of piezo ceramic (PZT) material to monitor thereinforced concrete-steel hybrid tubular wind turbine tower. The specific study isshown as below.1、The experiment on a concrete-steel tubular hybrid wind turbine tower ofreduced scale model is conducted to monitor the damage on the concrete tubular tower.Subjected to cyclic loadings, the specimen is monitored by the PZT patches stickingto its surface from the first emerging of concrete cracks to ultimate failure. The PZTand hammer are respectively used as signal generator in different monitoring method.2、Both sinusoidal harmonic signal and sinusoidal sweep frequency signal areselected for the PZT activator. A damage index based on the frequency amplitudeanalysis for harmonic signal and another index based on wavelet packet energy (WPE)for sweep frequency signal are employed respectively to process the sampled signaldata. Both of the damage indices accord with the location of cracks and are ofsufficient feasibility and efficiency in detecting cracks emerging and accumulation atdifferent load level.3、 The Frequency response function (FRF) method with respect to defineddamage index is used in processing hammer-activated signal. However, the method isnot very significant in detecting initial cracks until the cracks accumulate enough andis unable to precisely locate the cracks as well.4、In this paper, the spectral element method (SEM) is adopted for damagemonitoring simulation of one-dimensional structure based on stress wave propagationanalysis. Based on the vibration differential equation, the axial vibration rod’s element stiffness matrix of SEM is established and the assembly of global stiffnessmatrix is deduced. The time-frequency transform utilized in the SEM numericalanalysis is introduced. Finally, an SEM example of axial vibration rod is taken toverify the wave propagation analysis method in structure damage detection. The resultshows that the proposed wave propagation analysis method is able to detect damageeffectively.