Keywords: vibration, steel structures, composite floors, parametric study, serviceability, human comfort, dynamic structural design,walking loads.

Structural designers have long been trying to develop more economic design, as well as to use lightweight materials and increase the structure erection speed. This procedure has produced slender structural solutions, modifying the ultimate and serviceability limit states that govern their structural behaviour. On the other hand, the risk of vibrations in composite floors becoming a serious concern has increased in recent years [1,2,3,4,5].

There are a number of distinct possible causes of the dynamic excitation of floors. The important characteristics of these excitations vary to the extent that quite different check procedures may be appropriate depending on which potential cause is more important. The obvious excitation is the effect of walking on the floor. The geometry of the human body walking is, to a first approximation, a straight-leg motion that necessarily causes the main body mass to rise and fall with every pace. This rise and fall is typically about 50mm, peak to peak, but is sensitive to the angle of the leg at full stretch, and thus to the extent to which the walker is forcing the pace [6].

To a better understanding of the dynamical behaviour of composite floors subjected to human walking and a proper consideration of all the aspects mentioned before this paper describes a parametric analysis focusing on the use of different composite floor panel geometries and their influence in the dynamical response of the structural system. A review of the available acceptability criteria for the walking vibrations of composite floors is presented. The present investigation is carried out based on a more realistic loading model developed in order to incorporate the dynamical effects induced by people walking when the dynamical response of composite floors is investigated.

The movement of legs that cause an ascent and descending of the effective mass of the human body in each passing was considered and the position of the dynamical loading is changed according with the individual position. The generated time function, corresponding to the excitation induced by people walking, has a space and time description in this loading model.

The investigated structural system consists of a typical interior bay of an office building. The proposed computational model, developed for the composite floor dynamic analysis, adopted the usual mesh refinement techniques present in the finite element method [7]. The parametric analysis considered correlations between analytical and numerical results found in the technical literature [6,8,9].

Based on an extensive parametric study the composite floor dynamic response in terms of displacements and accelerations was obtained and compared to the limiting values proposed by several authors and design standards [6,8,9]. From a comparison of the available criterion for walking vibrations of composite floors, it may be concluded that the modelling of the dynamical excitations is very important in order to obtain reliable results. The results obtained along the investigation indicated that the walking loads could induce the composite floors to reach high vibration levels and in these situations the floors are therefore judged not satisfactory in terms of human comfort.

1

Zaman, A.; Boswell, L.F., "Review of acceptability criteria for the walking induced vibration of composite floors", Joint ISructE/City University International Seminar, City University, London, 1-3 July, pp 48.1-48.8, 1996.

2

Osborne, K.P.; Ellis, B.R., "Vibration design and testing of a long-span lightweight floor", The Structural Engineer, Vol. 68(10), 181-186, 1990.

3

Bachmann, H.; Ammann, W., "Vibrations in structures induced by man and machines", Structural Engineering Document 3e, International Association for Bridges and Structural Engineering, 1987.

4

Murray, T.M., Howard, J.N., "Serviceability: Lively Floors - North American and British Design Methods", Journal of Constructional Steel Research, 46 (1-3), Paper N0 251, 1998. doi:10.1016/S0143-974X(98)00155-2

5

Moreira, B.C., "Avaliação comparativa de pisos de edificações em estrutura metálica quanto ao critério de conforto humano", MSc Dissertation (In Portuguese), Federal University of Ouro Preto, Civil Engineering Department, Ouro Preto, Brazil, 182 pgs, 2004.

6

British Standard, "Evaluation of Human Exposure to Vibration in Buildings (1 to 80Hz)", Vol. 6472, pp 2359-2378, BSI, 1992.

7

ANSYS, "Swanson analysis systems", Inc., P.O. Box 65, Johnson Road, Houston, PA, 15342-0065, Version 8.0, Basic analysis procedures

8

Murray, T.M.; Allen, D.E.; Ungar, E.E.; "Floor Vibrations Due to Human Activity", Steel Design Guide Series, American Institute of Steel Construction, AISC, 1997.

9

International Standard Organization, "Evaluation of Human Exposure to Whole-Body Vibration, Part 2: Human Exposure to Continuous and Shock-Induced Vibrations in Buildings (1 to 80Hz)", International Standard, ISO 2631-2, 1989.

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