טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentHanum Eran
SubjectDynamic Characterization of Structures to Man Induced
Vibrations
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Emeritus Izhak Sheinman


Abstract

Low-frequency structures are characterized by sensitivity to human activity, since the characteristic frequencies of the structure and the activity are close.

The difficulty in characterizing the dynamic behaviour of the structure is due to the nonlinear nature of the problem - the time pattern of the contact between the structure and the human body, which in turn dictates the representative dynamic load.

The present study reviews current models for the dynamic behaviour in the linear domain, and proposes an approximate solution for its nonlinear counterpart, with an ultimate view to an Israeli code for human activity (HA)-induced frequencies.

Examination of the current dynamic load models indicates that an additional, hitherto absent, activity-oriented parameter is needed for covering the whole range of HA-induced loads.

An improved load model, combined with an envelope for the loads associated with a given activity, yields the relevant parameters for the latter.


Modeling the structure as an SDF system with a response spectrum for each activity provides two meaningful parameters of the structural response: (1) the dynamic load factor - D.L.F, (2) the serviceability load factor - S.L.F. These two parameters permit clear differentiation between the impact factor (increase of the static load) and the dynamic load factor (increase of the static response), and moreover provide a notion of the predicted peak responses for different structures.

Results regarding the differentiation between in-place activities and migratory activities show significant differences in the response even for activities with identical parameter characterization, because of the relatively short impacts of the migratory load.

The final part of the study deals with the nonlinear domain of the dynamic problem and presents an approximate model in which human activity is modeled as a dynamic system rather than as a dynamic load. Under this approach human body has to be treated in terms of degrees of freedom. Since its properties differ for each type of vibration and since their evaluation increases in complexity with the number of DOF’s, the HA-oriented SDF model is resorted to, verified on the response of a rigid beam which obviates the D.L.F influence.

The model also permits determination of the interrelationship of the activity frequency, its characteristic contact factor, and the structure frequency.

Results are in agreement with experimental findings which indicate that the stronger the human/structure interaction, the greater the difficulty in achieving resonance, namely reduction of the influence of the dynamic load.