Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 61-62). Also available via the Internet.

Floor vibration is a serviceability limit state problem as opposed to limit state of collapse. People find excessive vibrations annoying and it leads to unacceptable floor performance. Improvements in design techniques and use of higher strength materials have made floors lighter and more sensitive to vibrations. The existing code" criteria for limiting floor deflection are not satisfactory as they do not relate to human perception of vibrations. A finite element computer program is developed for a rational analysis of floor vibrations due to human footfall impact. The approach followed in the solution is to use a Fourier series expansion of displacement functions along the span and a finite element approximation in the transverse direction. A time step analysis is followed to obtain the floor's dynamic response at any point on the floor due to footfall impact elsewhere. A sensitivity analysis is done to study the effect of various floor parameters on floor performance. A reliability study of floor performance as affected by variability of joist stiffness is made by simulation. Floors simulated by randomly selecting joists from a population are analyzed and vibration response ratings are obtained by relating the response to human perception criteria. The probability of people rating the floor as of a certain performance level is predicted. Based on the reliability analysis, allowable spans and allowable deflections for a certain level of floor performance and a target reliability are proposed. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Modern lightweight floor systems are susceptible to annoying vibrations induced by the forcing action of human locomotion. This investigation considered several experimental methods to reduce unwanted floor motion as well as analytical procedures aimed at a better understanding of the phenomenon. A series of test floors were designed and constructed expressly for vibration experiments. Various viscoelastic treatments and second mass damper devices were applied to each test floor and the resulting reduction of vibration tendency was measured. These results are compared and the best-performing treatments and devices are discussed and investigated in detail. The relationship of frequency ratios of structural components was investigated analytically and reasonable design precautions necessary to avoid beating vibrations are discussed. A mathematical model of the forcing function of human locomotion is presented, as well as its implications for statistically-based design criterion. Finally, recommendations for future research are discussed based on the experimental and analytical results of the investigation. / Master of Science

The active control of structures is a diverse field of study, with new applications being developed continually. One structural system, which is often not considered a dynamic system, is the floor of a building. In many cases the dynamics of a floor system are neglected in the design phase of a building structure. Occasionally, this omission results in a floor which has dynamic characteristics found to be unacceptable for the intended use of the building. Floor motion of very small amplitudes, often caused by pedestrian movement, is sometimes found objectionable by occupants of the building space. Improving an unacceptable floor system's dynamic characteristics after construction can be disruptive, difficult and costly. In search of alternative repair measures, analytical and experimental research implementing active control techniques was conducted to improve the vibration characteristics of problem floors. Specifically, a control scheme was developed utilizing the measured movement of the floor to compute the input signal to an electromagnetic actuator which, by the movement of the actuator reaction mass, supplies a force that reduces the transient and resonant vibration levels. Included in the analytical component of this research is the development of a mathematical model for a full scale experimental test floor. This model is studied, using a matrix computation software, to evaluate the effectiveness of the control scheme. The experimental component of the research serves two purposes. The first is the verification of the system behavior assumed in the analytical component of the research. The second is the verification of control system effectiveness for various excitations, control gains, and actuator locations on the experimental test floor and six additional floors. / Ph. D.

Four aspects influencing the vibration characteristics of steel member supported floors were investigated. The four aspects are: 1) the number of tee-beams effective in resisting a heel-drop impact for steel joist and steel beam-concrete slab floors, 2) the effective moment of inertia of steel joist and joist-girder members, 3) the ability of joist seats to provide composite behavior between the supporting member and overlying slab, and 4) the effects of extending and restraining the bottom chords of joist members. A new equation was developed to predict the number of effective tee-beams. The proposed equation is recommended to replace the two current equations. The proposed equation is a regression equation based on the results of a finite element analysis of 240 floor systems and is considered to be more accurate than the current equations. Next, a study was undertaken to determine the relationship between the span-to depth ratio of a joist or joist-girder member and it's effective moment of inertia. Twenty five joists and joist-girders were modeled and analyzed using the finite element method and their effective stiffnesses calculated. The effective stiffness of each member was plotted against the respective span-to-depth ratio. A linear regression line was then fit to the data to mathematically represent the trend. Finally, a vibration test floor was constructed to investigate the joist seat behavior and extended bottom chords. Finite element models were developed and analyzed and frequency and stiffness tests were performed to evaluate the floor's behavior. Conclusions were then drawn and recommendations made concerning the joist seat behavior and the effects of extending joist bottom chords. / Master of Science

This thesis investigates the footfall excitation of higher modes of vibration in low-frequency floor structures. This is motivated by the increased number of floors reportedly failing to meet the required occupants comfort level although being designed in accordance with the current state-of-the-art design guidelines. In particular modern, lightweight, and slender floor structures. The contribution to knowledge of this thesis can be summarised as: quantifying the signal energy of measured walking forces within and above the natural frequency cut-off proposed by the current state-of-the-art design guidelines; quantifying the contribution of higher modes of vibration to the overall response of low-frequency floors to human walking; propose measures to judge the response nature of low-frequency floors, these are the relevant change of the point stiffness and the shape of frequency response functions; proposing a frequency-domain approach that enables designers to include higher modes of vibration in the design against human-induced vibration. It was found that the signal energy of walking forces is distributed well beyond the natural frequency cut-off proposed by the current state-of-the-art design guidelines. Also, the contribution of localised, higher, modes of vibration to the overall response of ultra-lightweight floors was significant. Moreover, it was found that higher modes affect the response of floors of various construction types in one way or another. Hence, it was recommended to consider their contribution in the design of floors against human-induced vibration. Also, it was found that the higher the relative change of the point stiffness the more higher modes contribute to the overall response of floors. Finally, the frequency-domain analysis was found less expensive than time-domain analysis and could result in similarly useful information.