Arash Behnia

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 space, time and heel impact descriptions. The FRP deck or beam was satisfactory in terms of serviceability and comfort level. There were no significant differences between the results when fiber reinforced polymer materials or common concrete-steel composite floors were used.

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 of load and passive live load intensities. This study shows that an increase in crowd size and the intensity of the active load are not directly proportional to the dynamic responses especially for displacement. It is also found that the synchronisation of active load plays a part in reducing structural dynamic responses, an observation that has not been highlighted before in previous studies.