Measurement of Structural Vibration Displacement and Frequency by Using Digital Speckle Correlation Method

The Digital Speckle Correlation Method(DSCM) was applied to the measurement of structural vibration displacement and frequency.The procedures for this measurement technique include:(1) to mark one or more artificial speckles or to select some existing obvious natural speckles on the vibrating structure as the movement target;(2) to get a series of continuous digital images from the video for capturing the structural vibration;(3) to obtain the displacement of movement target by locating the selected speckle in each image using DSCM;(4) to obtain the vibration frequency using Fast Fourier Transformation(FFT) from the displacement time-history.This method is proved to be feasible by comparing the results with those obtained by a displacement meter for sinusoidal horizontal vibrations of scaled structures excited by a vibration platform.The measurement accuracy is acceptable for engineering applications.The influence of speckle selection on the measurement accuracy was experimentally investigated in detail.The presented technique can be conveniently applied to the non-contact and panoramically simultaneous multi-target measurement of vibration displacement and frequency of civil engineering structures such as bridges,buildings and space structures.