Development And Application Of Noncontact Laser Type Sensor For Displacement Measurement

Experimental study for structures is one of the most important aspects in both of the civil engineering and earthquake engineering research. The development of experimental techniques has profound meanings for understanding of the damage mechanism, damage identification, modifying the numerical models and consequently enhancing of the seismic resistant capacity of structures at last.In earthquake engineering research area, although the earthquake simulation test for structures by using the shaking table has been emphasized in past investigations, the accurate measurement for relative displacement is pretty critical but it has not been solved satisfactory so far. There are many kinds of displacement sensors have been developed but almost none of them can be properly fit for the measurement of the space displacement in earthquake simulation test. The lower measurement accuracy is mainly due to the design and manufacture error of the sensor itself. Considering of this point, the development of new non-contact-type sensor for measurement of relative displacement is taken as one of the basic aims of the thesis study. On the basis of sensor development, the mechanic characteristics of RC structural elements under the condition of small deformations is experimentally studied, including the experimental measurement and comparison of the dynamic and static stiffness, the relationship between the dynamic stiffness and deformation, the variation of the damping ratio with the change of the vibration frequency and the coupling influence of the stiffness change with the bi-directional excitation. In addition, the new developed sensor is used and compared with other type of sensors in displacement measurement for a river-across pipe in earthquake simulation test. Principal investigation results are summarized as follows:A new non-contact type laser sensor for displacement measurement was developed on the basis of the international sensor technique developing. The new developed sensor consist of the laser origin and light-sensitive devices. It can satisfy the requirement of relative displacement measurement. For catering for different measurement cases, the focus distance of the optical lens can be adjusted according to the measurement range and the location of the target. The reasonable mechanism and the design of the new developed sensor obviously enhances the differentiate ratio, linear degree and frequency response characteristics for relative displacement measurement of structures in earthquake simulation test.__________________________Moreover, this type of sensor has the advantage of simple, cheap and easy to use.Using the unique feature of the high accuracy for small dynamic deformation measurement of the non-contact type laser sensor, the experimental study for the mechanic characteristics of the RC structural elements under the condition of tiny deformation was carried out. Study shows that the dynamic stiffness is larger than the static stiffness about 20% in experiments. And even in condition of tiny deformation, the concrete material is not perfect elastic but nonlinear. In tested frequency range, the damping ratio keeps constant under different vibration frequency, which is verified again that the concrete is not the ideal sticky elastic material whose dissipation characteristic is correlative with frequency. The fact of the dynamic stiffness of concrete member changes not too much with the frequency variation demonstrates that there are no obvious frequency-change related characteristics of the mechanics parameters. And even under tiny deformation, the dynamic stiffness of the concrete members could be changed obviously due to the spacial excitation state. After experiencing tiny distortion at the orthogonal direction, the member stiffness can reduce up to 20% measured by unidirectional deformation test. The test results above mentioned can supply meaningful references for further research on numerical models, vibration control and health diagnosis for concrete structures.In the earthquake simulation...