Human-induced Excitation Research Articles

Vibration Problems of an Example of Temporary Steel Grandstand under Human-Induced Excitation / Problemy Drgań Przykładowej Tymczasowej Trybuny Stalowej Poddanej Oddziaływaniom Dynamicznym Wywołanym Przez Ludzi

Lighter and slender structural members of a typical grandstand leads to a significant reduction in the frequencies, that is why such structures are more easily induced to vibrations. The aim of the present paper is to show the results of the experimental tests and the numerical analyses focused on the behaviour of a part of a typical temporary steel grandstand under dynamic loads. The peak values of accelerations of a steel scaffolding grandstand under human-induced excitation have been determined and compared with the limit values concerning the perception of vibrations by people. The results of the study indicate that the human-induced excitation may induce structural vibrations which substantially exceed the allowable limits.

Investigations on serviceability control of long-span structures under human-induced excitation

The increasing strength of new structural materials and the span of new structures, accompanied by aesthetic requirements for greater slenderness, are resulting in more applications of long-span structures. In this paper, serviceability control technology and its design theory are studied. First, a novel tuned mass damper (TMD) with controllable stiffness is developed. Second, methods for modeling human-induced loads are proposed, including standing up, walking, jumping and running, and an analysis method for long-span floor response is proposed based on a finite element model. Third, a design method for long-span floors installed with a multiple TMD (MTMD) system considering human comfort is introduced, largely based on a study of existing literature. Finally, a design, analysis and field test is conducted using several large scale buildings in China including the Beijing Olympic Park National Conference Center, Changsha New Railway Station and the Xi’an Northern Railway Station. The analytical and field test results show that the MTMD system designed using the proposed method is capable of effectively mitigating the vertical vibration of long-span floor structures. The study presented in this paper provides an important reference for the analysis of vibration serviceability of similar long-span floors and design of control system for these structures.

Field measurements and assessment of vibration serviceability of as-built long-span concrete floor

Vertical vibration serviceability of an as-built concrete floor, whose 41.55 m span is currently the longest in China, are investigated in this paper by field measurements and numerical analysis. A vibration monitoring system were designed and installed on the floor. Different types of human-induced excitation are simulated such as single person walking, multi-person walking at the same pace rate, multi-person jumping and multi-person randomly walking. The dynamic properties and responses of the floor are also computed using finite element method. It is found in this paper that the acceleration vibration amplitudes of the floor under different excitations are lower than the limitation. The amplitudes of floor response are quite different for different types of excitation. The response of wooden floor is much higher than the structure floor at the same location therefore, cannot be directly adopted for serviceability assessment. The fundamental frequency of the floor can be accurately predicted if the mass properties and boundary conditions are properly modelled. Finally, it is suggested that the vibration amplitude control is much more important than frequency control for vibration serviceability design of long-span concrete floor.

Dynamic property analysis and development of composite concrete floor (CCF) and vibration serviceability: A review

This review article concerns floor vibration, describes the nature of floor vibration and provides options for avoiding it through design, or in the case of existing buildings, reducing or eliminating it through alterations. Excessive floor vibration has become a greater problem as new rhythmic activities, such as aerobics, generators, air conditioners and long-span floor structures have become more common. The current push towards stronger concrete materials and the use of prestressing is resulting in increasing fineness and dynamism of long-span concrete floors in buildings. Although concrete floors have a good vibration serviceability track record, this trend may lead to an increasing number of floors failing their vibration serviceability. There is a current trend towards ever more slender concrete floor structures, which is resulting in more frequent problems with their vibration serviceability. Predictive methods for vibration serviceability must consider not only the structures themselves, but also the non-structural elements which are attached to them, as these may have a significant effect on the dynamic characteristics of the floor structural system. As there has been very little past research in this area, this article describes an investigation into the effects of raised access floors on the vibration serviceability of long-span concrete floors. The development of a new modal testing facility based on electrodynamics shaker excitation, which was capable of producing high quality estimates of the modal properties of full-scale floor structures, is described. This was subsequently utilized to determine the modal properties of three full-scale floor structures, first concrete floor, secondly concrete floor with profiles steel sheet (PSS) and finally concrete floor with PSS and vibration damping compound (VDC) before and after the installation of various configurations of raised access floors. The vibration damping compound (VDC) is used on composite concrete floor (CCF) for getting special performance from floor because vibration damping compound is a water based co-polymer emulsion, with mineral fillers dispersed in a low permeable, polymeric binder. It is solvent free, easy to apply and can be used in most interior and semi-exposed areas. It is designed to reduce noise by damping resonant vibration caused by continuous or impulsive excitation of the substrate to which it is applied. The response of these structures to controlled pedestrian excitation was also measured. Realistic finite element models of all structures were developed and updated using the results from the experimental work. These were subsequently utilized for investigation of the experimentally measured effects of the raised access floors. Reductions in natural frequencies due to the increased mass were, to some extent, offset by the slight increases in stiffness following the installation of the access floors. Modal damping ratios increased for some modes of vibration, but these changes were rather unpredictable: hence they were too unreliable to be used in design. The response of the structures under controlled pedestrian and other excitation was reduced following the installation of various configurations of raised access floors. The reduction appeared to be greater for relatively long access floors (2000 mm) than for relatively width access floors (1200 mm) and height (54 mm). Therefore, it is recommended that the effects of access floors may be included in vibration serviceability analyses by applying a reduction factor to predicted responses calculated by assuming a bare floor. Key words: Rhythmic activities, long-span concrete floor vibration serviceability, profiled steel sheet (PSS), vibration damping compound (VDC), human-induced excitation, natural frequency, whole-body vibration.

Crowd dynamics on a moving platform: Mathematical modelling and application to lively footbridges

This paper proposes a mathematical model and a computational approach to study the complex multiphysical non-linear coupled system that results from the interaction between a moving platform and the pedestrians who walk on it. The described method is based on the mathematical and numerical decomposition of the coupled system into two subsystems and on the two-way interaction between them. In particular, the dynamics of the crowd is modelled referring to a macroscopic description in analogy to that of a compressible flow. The proposed approach is applied to the lateral vibrations of footbridge decks under human-induced excitation. First, the computational parameters of the model are optimized. Then, the effects of the crowd initial density and of the runnability conditions are evaluated on a motionless platform. Finally, the results obtained from the simulations of the crowd–structure interaction are commented on.

Some relevant aspects of footbridge vibrations

Considering the contemporary structural inaterials that are becoming more resistant, having higher strength to weight ratio, and the fact that live load of footbridges is low, the design based on static analysis only, respecting ultimate limit states requirements, leads to slender bridge structures for pedestrian and cycle track use. As a consequence, stiffness and masses decrease, facing lively, easy to excite structures, with smaller natural frequencies. The excitation of a footbridge by a pedestrian passing over it can be unpleasant for a person walking or standing on the bridge, but usually not destructive for the structure itself. Recent experiences regarding dynamic behavior of slender footbridges have especially shown that vibration serviceability limit states are very important requirements in any structural design. We are presenting a general algorithm for analytical testing of dynamic parameters of structures, calculation of deflection, thus speed and acceleration of superstructure under human-induced excitation, as predicted by Eurocode, British and Canadian standards in use, since no Yugoslav code deals with the problem. The evaluated system is a footbridge in a system of a simply supported concrete girder. The presented model is used to show correspondence of results, obtained by the algorithm, with the results obtained using the simplified methods suggested by the Codes of Practice, since the latter exists only for certain structural systems.

Evaluation of design requirements for footbridges excited by vertical forces from walking

The continuing trend towards the design of more slender, lighter, and livelier footbridges has created new challenges that are not properly addressed in a number of widely used codes of practice in Europe and Canada. Recent research into vibration serviceability of slender structures under human-induced dynamic loading suggests that improvements to the existing footbridge design guidelines are possible in the area of modelling human-induced excitation in the vertical direction. This paper evaluates the performance of currently used codes of practice regarding vibration serviceability of footbridges under human-induced loads due to walking. The evaluation is supported by experimental evidence from tests carried out by the authors on potentially lively footbridges. A description of recent research advances is included, together with a comparative analysis of the approaches of some pertinent guidelines used internationally to tackle this design problem. In addition, suggestions are made for re-addressing the problem of vibration serviceability of footbridges by focusing attention on a more realistic definition of vertical pedestrian loading and the corresponding frequency ranges of interest. It was found that the codes are either conservative or lack appropriate safety margins, depending on the frequency range excited by moving pedestrians. This is principally due to the lack of proper consideration for the frequency content of the pedestrian load, which would take into account developments since the 1970s when the scientific data used in the majority of the current codes of practice were produced.Key words: vibration, serviceability, walking, footbridges, design, codes, dynamic loading factor, evaluation.