The applications of composite materials have been widely practiced in modern construction. Structural engineers are often urged to consider aesthetic values as well as the financial aspects in their work, which results in structures that have long span, lightweight and low natural frequencies. These structures exhibit excessive vibrations that cause major discomforts to the occupants. The purpose of this study is to establish a methodology using finite element analysis for assessing the dynamic responses of composite floors and determining the corresponding level of comfort. Linear elastic finite element analysis was conducted using more realistic load models with respect to the application of different geometries of concrete slab and fiber reinforced polymer materials. The composite floor investigated included FRP deck, FRP beams, and concrete slabs of various thicknesses. The resulting maximum peak accelerations indicated the need for more realistic load models to generate a time function including spac...

Finite Element Analysis of the Dynamic Response of Composite Floors Subjected to Walking Induced Vibrations

This paper explores the vibration behaviour of composite floors in an existing building using a comprehensive study of the modal dynamic responses. Different panels are subjected to loads induced by human motion. The computed fundamental natural frequency and vibration modes are first verified against experimental and numerical results from previous studies. Departing from close correlation established by comparisons, this study investigates the effects of coordinated passive live loads as additional stationary mass due to crowds jumping. In another case, the effects of different intensities and the loads created by different jumping crowd sizes are investigated. Thirty modes of vibrations are selected to obtain all the possible excitations and to make a third harmonic load frequency available to excite the critical modes. In addition, the presence of different coordinated passive live loads on the composite floor results in different behaviours for each particular panel that is associated with location o...

Effects of coordinated crowd motion on dynamic responses of composite floors in buildings

Modal Mass of Floors Supported by Beams

One of the contemporary architecture trends is the design of structural elements that cover longer clearances to provide flexibility in the architecture of buildings. The technological and constructive evolutions in civil engineering assure the feasibility of such trends due to the use of structural elements with increased slenderness and reduced weight, such as steel structures that utilize dry slabs. However, structures of this type present greater susceptibility to the vibrations related to human activities. Hence, this study aims to evaluate, from the human comfort point of view, the dynamic behavior of an existing steel floor system with composite structural panels, subjected to vibrations due to human walking. To obtain the dynamic responses, the present study employs: (1) simplified procedures of the AISC and SCI design guidelines and (2) modal and transient analyses performed to a numerical model developed using the ANSYS software. The dynamic responses were compared with human comfort criteria prescribed by design guides, ISO 10137:2007 and the Brazilian standards. The influence of the value taken for structural damping and effect of more than one walking individual simultaneously on the structure may be evaluated through numerical results. It was concluded that the simplified procedures underestimate the dynamic responses of the floor system under study.

Dynamic Analysis of a Steel Floor System with Dry Slabs Subjected to Vibrations Due to Human Walking

Accidental actions caused by vibrations of supporting structures in mechanical systems represent the dynamic tasks of specific scientific and professional research in the field of human and equipment safety. This paper determines the mathematical model of physical excitation force created by   human power, based on the discrete-time Fourier transformation. For experimental verification of the model, we made a special platform for measuring bouncing force of people who create natural impulse oscillation. The paper shows the results of individual and group experimental testing of living force as the cause of accidents and dangerous effects on the structure. In the end, the excitation of the human operation of a malicious nature (heavy transport machine – crane) has been used to show the application of Fourier model to simulate one incident. For this purpose, the transient FEM analysis and the eigenvalues predetermined modal analysis are used. The paper is illustrated with photographs of experimental tests of dangerous human impulse in several working machines (objects).

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A human crowd effect modelled by the discrete-time fourier series

Light weight and long span composite floors are common place in modern construction. A critical consequence of this application is undesired vibration which may cause excessive discomfort to occupants. This work investigates the composite floor vibration behavior of an existing building based on a comprehensive study of high modal dynamic responses, the range of which has been absent in previous studies and major analytical templates, of different panels under the influence of loads induced by human motion. The resulting fundamental natural frequency and vibration modes are first validated with respect to experimental and numerical evidences from literature. Departing from close correlation established in comparison, this study explores in detail the effects of intensity of passive live load as additional stationary mass due to crowd jumping as well as considering human structure interaction. From observation, a new approach in the simulation of passive live load through the consideration of human structure interaction and human body characteristics is proposed. It is concluded that higher vibration modes are essential to determine the minimum required modes and mass participation ratio in the case of vertical vibration. The results indicate the need to consider 30 modes of vibration to obtain all possible important excitations and thereby making third harmonic of load frequency available to excite the critical modes. In addition, presence of different intensities of passive live load on the composite floor showed completely different behavior in each particular panel associated with load location of panel and passive live load intensity. Furthermore, implementing human body characteristics in simulation causes an obvious increase in modal damping and hence better practicality and economical presentation can be achieved in structural dynamic behavior.

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Mohammad Mehdi Shabazi

Papers

Finite element analysis of high modal dynamic responses of a composite floor subjected to human motion under passive live load