published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

This thesis studies the applicability of the Dynamic model reduction method that is used for direct plant order reduction in the active vibration control of large and flexible structures. A comparison of the performances between the reduced models produced by the Dynamic model reduction method and those obtained by other common model reduction methods such as the Guyan method, and the Mode-displacement method have been carried out. By using a full analytical model of a twenty storey building as the reference, each three degrees of freedom model was compared by computer simulation. The open-loop frequency response simulation, open-loop earthquake simulation, and the closed-loop earthquake simulation were all used to initially evaluate the reduced models. The accuracy of the frequency responses was assessed with sinusoidal applied forces, and for the closed-loop dynamic analysis, an active mass damper at the top storey and a recorded earthquake excitation was used. When compared with the simulation results of the Guyan method, the Dynamic method has many advantages, especially in terms of its accuracy at the high frequency range. The Mode-displacement method produces reduced models that are good for dynamic analysis of open-loop systems, but it was found to be inconvenient for use in active control. Finally, the Dynamic model reduction method and Guyan method were compared using experimental test results. A 2.5m tall building model with 20 floors was used as the plant, with a linear motor installed at the top storey for the purposes of active-damping. Although the results of simulations would suggest that both models perform sufficiently, experimental testing proved that only the Dynamic model performs adequately for this specific application of active control. The problem associated with most model reduction methods, such as the Guyan, is that they are based on full-order models that were derived from the linear elastic theory. The versatility of the Dynamic model reduction method is such that it provides the option of obtaining system parameters directly from experiment, not just from theory. The experimental procedure ensures that the Dynamic model reduction method forms an accurate description of the real system dynamics. The applicability of this method for obtaining low-order plant models was demonstrated through real-time active control testing of the model structure, while it was subject to a sinusoidal excitation. The tests have shown that the Dynamic model reduction method can be used as an alternative approach for the model reduction of structural systems for the purpose of active vibration control.

This thesis studies the applicability of the Dynamic model reduction method that is used for direct plant order reduction in the active vibration control of large and flexible structures. A comparison of the performances between the reduced models produced by the Dynamic model reduction method and those obtained by other common model reduction methods such as the Guyan method, and the Mode-displacement method have been carried out. By using a full analytical model of a twenty storey building as the reference, each three degrees of freedom model was compared by computer simulation. The open-loop frequency response simulation, open-loop earthquake simulation, and the closed-loop earthquake simulation were all used to initially evaluate the reduced models. The accuracy of the frequency responses was assessed with sinusoidal applied forces, and for the closed-loop dynamic analysis, an active mass damper at the top storey and a recorded earthquake excitation was used. When compared with the simulation results of the Guyan method, the Dynamic method has many advantages, especially in terms of its accuracy at the high frequency range. The Mode-displacement method produces reduced models that are good for dynamic analysis of open-loop systems, but it was found to be inconvenient for use in active control. Finally, the Dynamic model reduction method and Guyan method were compared using experimental test results. A 2.5m tall building model with 20 floors was used as the plant, with a linear motor installed at the top storey for the purposes of active-damping. Although the results of simulations would suggest that both models perform sufficiently, experimental testing proved that only the Dynamic model performs adequately for this specific application of active control. The problem associated with most model reduction methods, such as the Guyan, is that they are based on full-order models that were derived from the linear elastic theory. The versatility of the Dynamic model reduction method is such that it provides the option of obtaining system parameters directly from experiment, not just from theory. The experimental procedure ensures that the Dynamic model reduction method forms an accurate description of the real system dynamics. The applicability of this method for obtaining low-order plant models was demonstrated through real-time active control testing of the model structure, while it was subject to a sinusoidal excitation. The tests have shown that the Dynamic model reduction method can be used as an alternative approach for the model reduction of structural systems for the purpose of active vibration control.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Master / Master of Science in Engineering

Preservationists and historic sites managers need to be aware of the affects of excess man-made vibrations on historic structures. The purpose of this creative project is to examine those affects and identify some methods to mitigate them. To write this project, it was necessary to search through available literature identifying past research and studies on this subject. Research was culled from various sources examining the affects of vibrations on new and historic structures and are presented here in one volume.The affects of vibrations on historic structures is not a subject that is well represented in preservation or structural engineering literature. The information currently available is scattered through various sources. Thus, there is the lack of a single reference examining the affects of vibrations on historic structures. This project is meant to be used as a reference for historic preservationists, house museum curators, and historic sites managers who seek information about vibration effects and possible solutions to their vibration problem. / Department of Architecture

The development of high strength, light weight materials has generated more efficient designs of steel joist-concrete slab floor systems. Though the structural integrity is rarely compromised, these floor systems are more susceptible to human-induced vibrations which may be annoying to the occupants of the structure. The purpose of this investigation was to develop methods of improving the vibration characteristics of joist-supported floor systems. The frequency and first maximum amplitude of vibration can be altered by redesigning the cross-section of the floor system in order to improve its acceptability. However, damping has the greatest effect on the perceptibility of occupant-induced floor vibrations. Therefore, this study focussed on devising methods of increasing damping in joist supported floor systems. Steel joist-metal deck-concrete slab test floors were constructed for the purpose of this investigation. In addition, a two-bay building was constructed so that the developments of this research could be field tested. The experimental results were presented and recommendations were made for future work in this field. / Master of Science

The usefulness of Coulomb (friction) damping in earthquake-resistant design of structures is examined by studying the seismic response characteristics of structures with various arrangements of sliding interfaces. First, three basic arrangements are studied for their effectiveness in reducing lateral displacements of the supporting frame, accelerations of the floor slab and the resulting secondary floor spectra. These are: (1) slab sliding system which has the sliding interface between the floor slab and the supporting frame, (2) double sliding system which consists of sliding interfaces at both top and bottom interfaces (a combination of slab sliding and base sliding), and (3) spring-assisted slab sliding system which is a slab sliding system aided by lateral springs attached to the columns to resist excessive sliding displacement of the slab. The responses are obtained for structures with different frequencies and are presented in response spectrum form. The isolation characteristics of one slab sliding system are compared with those of the base sliding and hysteretic systems. Non-dimensional design parameters defined in terms of the corresponding elastic design spectra are introduced for design purposes and for a consistent presentation of the results. Methods for predicting the important response quantities using the non-dimensional parameters are discussed and their applicability is evaluated. Next, the response of a simple slab sliding arrangement to simultaneous horizontal and vertical ground motion input is studied to see the effects of the vertical excitation on the isolation efficiency of that arrangement. Finally the suitability of adopting such sliding arrangements in multi-story structures is also examined. The seismic responses of multi-story structures with floor slabs sliding at different story levels are obtained and compared with the response of non-sliding structure and base sliding to examine the effectiveness of such sliding arrangement. / Ph. D.