Seweryn Kokot

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)

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.

Chapter 17 – Mitigating Rockburst Effects for Civil Engineering Infrastructure and Buildings

Abstract As induced seismicity from deep mining may cause quakes with a local magnitude of 4.5–5.5 and surface ground motion with Modified Mercali intensities up to VIII, such strong ground motions may result in serious damages to civil infrastructure. In the case of natural earthquake preparedness, seismic design codes are used to ensure that newly designed buildings are well prepared to sustain such strong loads. However, any adaptation of classic seismic design codes to account for mine tremors faces a problem of differences in spectral content and duration between the surface records of the rockbursts versus natural earthquakes and in their different risk definitions. This chapter briefly presents a system to define design seismic load based on forecasted surface horizontal ground velocity from the rockbursts expected during the planned mining activities. For this purpose the European seismic code, Eurocode 8 has been adapted.

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.

Application of Rotational Measurements in Stiffness Reconstruction of Beams and Frames

A stiffness reconstruction method is tested when rotational degrees of freedom are added to the dynamic model of the structure. The inverse problem is formulated as a minimization problem in terms of harmonic vibrations of the structure and its finite element model. An example of frame structure is analyzed by numerical simulations. The results of these numerical analyses show that the damage detection appeared to be much more effective when the angular amplitudes of harmonic vibrations are acquired. This makes very good prospects for the future applications of angular sensors in damage detection of structures.

Reconstruction Problem of Reinforced Concrete Beams under Harmonic Excitations

A damage detection method based on harmonic structural vibrations has been applied to reconstruct realistic damage patterns of reinforced concrete beams. It was shown that the application of a hybrid method (genetic algorithm and Levenberg-Marquardt minimization technique) makes it possible to effectively reconstruct the flexural stiffness drops as small as 10-20% with the maximum error of 4%. The error increases to about 7 to 9% with the presence of 1% measurement noise.