Structural frames, demonstrate both elastic and plastic behaviour depending on their load. At early stages of earthquake loading structural systems remain in the elastic phase, but when the loading increases, plastic hinges form and affect the structural response. Determining the location and time of this damage is critical. The aim of previous methods such as Fourier, short time Fourier or wavelet transform was to find the time and location of hinge formation. This was conducted by changing response space, with the use of vibration properties of a system like vibration frequency or vibration modes of the structure. However, these methods are not very effective in early warning applications since the vibration properties do not change significantly at the beginning of plastic hinge formation. In this research, the capability of wavelet transform in extracting local signal information will be used to determine the time and location of plastic hinge formation. These signals are recorded responses of the structure under seismic excitation. The obtained results indicate that the proposed method can effectively determine the time and location of damage without employing complicated methods and concepts.
Key words: Damage detection, plastic hinge, impulse response, shear frame.
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