Piotr Bobra

Application of rotation rate sensors in an experiment of stiffness ‘reconstruction’

Preliminary results of an application of rotation rate sensors in dynamic identification of a vibrating beam are reported. Three rotational sensors, measuring the response of a cantilever beam to kinematic harmonic excitations are applied in the reconstruction of its stiffness. A successful reconstruction of 15% stiffness drops is demonstrated. With the development of angular sensors and the decrease in their cost one can expect further progress of this new area of vibration-based damage detection. (Some figures may appear in colour only in the online journal)

Rotational Ground‐Motion Records from Induced Seismic Events

Surface rotational ground‐motion records that were collected by a network of deep mining exploration monitoring in the Polish region of the Upper Silesian Coal basin are reported. A set of 51 rotation records acquired during the first two months of the recording program is analyzed. The three strongest records are discussed in detail in this article. Thus far, the maximum measured rotation velocity has reached 0.03°/s, whereas the respective maximum rotational acceleration was equal to 2.53°/s2. Based on the maximum horizontal ground velocity of 2  cm/s, this corresponds to the modified Mercalli intensity (MMI = IV). The recorded “time history” records of ground rotations have similar durations to those of their respective translational records. However, their Fourier spectra are shifted to higher frequencies in a characteristic way, as predicted by earlier, theoretical considerations. The long‐term objective of the research program is to acquire robust surface rotation records that correspond to MMIs VI or even VII, since mine tremors with a magnitude of 4 or higher are expected to occur in this area in the near future.

Review of the Usefulness of Various Rotational Seismometers with Laboratory Results of Fibre-Optic Ones Tested for Engineering Applications

Starting with descriptions of rotational seismology, areas of interest and historical field measurements, the fundamental requirements for rotational seismometers for seismological and engineering application are formulated. On the above basis, a review of all existing rotational seismometers is presented with a description of the principles of their operation as well as possibilities to fulfill formulated requirements. This review includes mechanical, acoustical, electrochemical and optical devices and shows that the last of these types are the most promising. It is shown that optical rotational seismometer based on the ring-laser gyroscope concept is the best for seismological applications, whereas systems based on fiber-optic gyroscopes demonstrate parameters which are also required for engineering applications. Laboratory results of the Fibre-Optic System for Rotational Events & Phenomena Monitoring using a small 1-D shaking table modified to generate rotational excitations are presented. The harmonic and time-history tests demonstrate its usefulness for recording rotational motions with rates up to 0.25 rad/s.

Application of Rotation Rate Sensors in Measuring Beam Flexure and Structural Health Monitoring

This paper presents a new approach to measure and monitor structural vibrations in civil and seismic engineering which uses new rotational sensors which can measure flexural vibrations of a beam axis. First a rotation rate sensor (measuring rotational velocity) is tested with respect to its ability to follow changes of strains in a beam during its vibrations. Next a system of rotation rate sensors is applied to effectively reconstruct stiffness variations of a simple, cantilever beam. It is demonstrated that the rotation rate sensors can be used to effectively reconstruct three unknown stiffness drops of a cantilever beam under harmonic vibrations. Both experiments are carried out using small plexi beams in laboratory scale. At this moment the rotational sensors are still rather expensive and with limited range and accuracy. However with the time passing by, their quality will improve and prices decrease making them very effective instruments in seismic engineering and health monitoring of structural systems.

An Analysis of the Effectiveness of Application of Rotation Rate Sensors in Non Destructive Damage Evaluation

This paper reports the analysis of the effectiveness of the application of rotation rate sensors in structural damage identification problem using harmonic vibrations for plexiglass models of cantilever beams. The two types of sensors are applied: angular rate sensors and conventional translational, piezoelectric accelerometers. The amplitudes of dynamic response under harmonic kinematic excitations were subsequently used in the stiffness reconstruction procedure. Particularly promising results are obtained by using only rotation rate sensors in the reconstruction procedure.