Conference Paper

Guidelines definition for in-situ vibration measurements of buildings

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As an attempt to find a correlation between dynamic response of timber and timber-concrete composite floors and users’ comfort feeling, an in-situ measurements campaign will be carried out within the framework of a research project started at ESB, France. A large variability of buildings typology, as multi-unit housing, open-space offices and long-span offices with partition walls will be tested. The first experimental experience has shown that choices of means of excitation, type and positioning of sensors, data acquisition device, data analyses methods, depend on the floor configuration. Using in-situ test campaign as a database to compare different measurement protocols and assess the influence of different in-situ conditions, the paper will propose some guidelines for the measurement architecture, the equipment choice and the data analysis to be performed according to each building configuration.

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... Bui et al. [27] experimentally investigated the natural frequencies, damping ratios, and mode shapes of multilayered timber beams. Lanata et al. [28] attempted to establish correlations between the dynamic response of in situ timber and TCC floors and human comfort perception by varying building typology. ...
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Based on classic vibrational bending theory on beams, this paper provides comprehensive analytical formulae for dynamic characteristics of two equal span continuous timber flooring systems, including frequency equations, modal frequencies, and modal shapes. Four practical boundary conditions are considered for end supports, including free, sliding, pinned, and fixed boundaries, and a total of sixteen combinations of flooring systems are created. The deductions of analytical formulae are also expanded to two unequal span continuous flooring systems with pinned end supports, and empirical equations for obtaining the fundamental frequency are proposed. The acquired analytical equations for vibrational characteristics can be applied for practical design of two-span continuous flooring systems. Two practical design examples are provided as well.
Conference Paper
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Durability and long-term behaviour of timber structures are strongly influenced by environmental and in-service conditions. Measuring the real in-service behaviour of a full-scale timber structure and its environment can help collecting experience to validate existing models and design assumptions. To this purpose, a long-term monitoring system has been installed on a three-floor structure composed by wooden trusses, composite timber-concrete slabs and timber-framed walls. The structure is located in Nantes, France, and it is an extension of the Wood Science and Technology Academy (ESB). The paper will show, through the available measurements, some of the phenomena that are strongly influenced by humidity variations. These analyses will lead to develop a numerical model to study the shrinkage effect on a structural element. The shrinkage deformation will be finally filtered from the global measured deformation to put into evidence the mechanical effects, such as mechanosorpive behaviour, creep effect, and damage impact, at the structural scale.
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This paper is concerned with the response of floors to loading produced by dancing and aerobics, especially where the dancing involves jumping. Its purpose is to provide an analytical method for determining the response of floors to these loads. The characteristics of the load time history are dealt with initially, and, for calculation purpose, the load is expressed in terms of Fourier series. An analytical solution of the forced vibration of simply supported floors is developed, using plate theory and considering several modes of vibration. The number of Fourier terms that should be considered in the analysis is determined. The solution is then extended for other structures with different boundary conditions. It is predicted that significant accelerations may occur on relatively stiff floors induced by higher Fourier components of the load. (Verification of the method is provided in ref 6.)
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Inspection and evaluation of existing timber structures have been limited to individual structural members. The objective of this study was to conduct a pilot investigation on the use of transverse vibration testing techniques for inspecting timber structures by evaluating component systems such as floor systems rather than individual members. The practical considerations were 1) the effectiveness of free vibration compared with forced vibration; 2) the optimal location of forcing function input and transducers for obtaining adequate response signals; 3) the effect of superimposed dead loads on floor vibration response; and 4) the effect of joist decay on floor vibration response. We evaluated three floors, two constructed with new joists and one with salvaged joists having some deterioration, checks, and splits. Natural frequencies and damping ratios were determined for each floor. We conclude that the practical considerations involved in the inspection of floor systems could be determined through frequency and damping ratio data. Thus, transverse vibration testing holds promise as an inspection technique. Future research is needed on a range of floor spans and joist sizes.
Conference Paper
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An innovative three-story timber building, using self-centering, post-tensioned timber shear walls as the main horizontal load resisting system and lightweight non-composite timber-concrete floors, has recently been completed in Nelson, New Zealand. It is expected to be the trailblazer for similar but taller structures to be more widely adopted. Performance based standards require an advanced understanding of building responses and in order to meet the need for in-situ performance data the building has been subjected to forced vibration testing and instrumented for continuous monitoring using a total of approximately 90 data channels to capture its dynamic and long-term responses. The first part of the paper presents a brief discussion of the existing research on the seismic performance of timber frame buildings and footfall induced floor vibrations. An outline of the building structural system, focusing on the novel design solutions, is then discussed. This is followed by the description of the monitoring system. The analysis of monitoring results starts with a discussion of the monitoring of long-term deformations. Next, the assessment of the floor vibration serviceability performance is outlined. Then, the forced vibration tests conducted on the whole building at different construction stages are reviewed. The system identification results from seismic shaking records are also discussed. Finally, updating of a finite element model of the building is conducted.
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This publication provides guidance for vibration design of all steel-framed floor and building types. It deals with the human perception of vibration and the criteria by which it is measured. The concepts of floor response and the different types of excitation produced by occupant induced vibrations are explained. Simple design procedures are presented which show how to calculate the floor acceleration, to weight it to reflect human perception, and to compare it with the acceptance levels in BS 6472 and ISO 10137 for building designs and in the NHS performance standard for hospitals, Health Technical Memorandum 08-01. The design procedures are valid for steel-framed floors using hot rolled steel sections and lightweight floors using thin cold formed steel members. The simplified procedure is particularly suited to framing arrangements that are generally regular in plan. Results from testing which have been used to develop the rules contained within this guide have been included in Appendix A. Additional information on managing problems in a remedial situation is given in Appendix B. Specialist guidance on dynamic testing of buildings is provided in Appendix C; this has been specially written by Professor Aleksander Pavic and Dr Paul Reynolds, both of Sheffield University. A set of worked examples, illustrating the design procedures is given in Appendix D.
Conference Paper
Pouvoir prédire le bruit transmis par un élément constructif est depuis plusieurs années une grande préoccupation. Cette problématique a été largement traitée pour les bruits aériens, mais reste plus complexe pour les bruits d'impacts. En effet les caractéristiques de l'excitation en termes d'amplitude et de contenu fréquentiel dans le cas d'un bruit d'impact dépendent autant de l'excitateur (la source de choc) que du récepteur (la paroi impactée). Or, ces bruits figurent en bonne place des sources d'insatisfaction citées par les occupants de bâtiments résidentiels, en particulier dans le cas de constructions légères. Un outil de synthèse sonore serait alors idéal pour à la fois pouvoir prédire les niveaux sonores dus à diverses sources d'impacts mais aussi évaluer le ressenti des occupants par l'écoute. Cette étude s'intéresse à simuler dans le domaine temporel la réponse vibratoire de planchers légers soumis à une excitation mécanique ponctuelle. Dans cette optique, un modèle analytique des modes de vibration d'une plaque mince orthotrope est utilisé. Pour des éléments constructifs homogènes, en béton plein par exemple, ce modèle permet de reproduire la réponse vibratoire temporelle avec un jeu limité de données d'entrées et sans nécessiter des ressources de calcul importantes. Cependant, les planchers légers sont souvent constitués de panneaux équipés de raidisseurs (solives) ou bien de lames assemblées entre elles (cas des éléments en bois lamellé croisé, dits « CLT »). Dans cette étude, ces spécificités de conception sont prises en compte en modélisant les planchers par des plaques minces orthotropes, dont les caractéristiques sont obtenues par une méthode d'homogénéisation. Après une présentation du modèle utilisé et des hypothèses sur lesquelles il s'appuie, deux applications sont présentées : la première concerne un plancher bois sur solives, et la seconde un plancher en CLT 3 couches. Les réponses vibratoires obtenues sont comparées à des résultats de mesures en laboratoire ou de simulations par éléments finis. Les résultats et perspectives sont ensuite discutés.
Conference Paper
Structural vibrations in a proposed fitness center area and the existing computer server room located on the third floor of multi story building was evaluated. Natural frequency of the concrete floor was evaluated in the proposed aerobics area. Aerobic activities were simulated by people spot jogging on the bare floor as well as the existing raised floor for 120, 150, 180 BPM metronomes. Vibration levels were monitored inside the computer server room, the proposed aerobics area and at a location close to the proposed treadmill area. Natural frequency of the concrete floor found to be not susceptible to structural resonance during aerobic activities. However, the vibration levels due to simulated aerobic activities in the computer server room were significantly above the published threshold for a computer equipment room. It was recommended that the floor system be modified to reduce floor vibrations in the server room.
Conference Paper
When several occupants of a newly constructed academic building raised a concern of disturbing vibrations in several of the third floor offices, an investigation ensued that aimed to capture and characterize this disturbing vibration. A remote monitoring system was utilized to monitor the offices of interest and the offending vibration was finally recorded. The recorded data indicated that this vibration was not a typical serviceability issue due to walking. The study that followed examined the dynamic characteristics of the floor structure through dynamic testing and consequently several unusual vibration sources were explored ranging from wind or traffic to mechanical equipment to an often overlooked human excitation best described as leg jiggling. Some of the findings related to this unusual and interesting case study are described in this paper.
Natural frequencies, damping ratios and mode shapes of a prefabricated timber floor element have been assessed experimentally in laboratory with different boundary conditions and in situ (in field) at different stages of construction. In laboratory the change in modal parameters was studied with free-free boundary conditions and simply supported on two sides. Three different simply supported tests with changes in boundary conditions were carried out; the floor placed on the support without any fastening or interlayer between support and floor, the floor screwed to the supports and the floor placed on an elastic interlayer between support and floor. The in situ tests were carried out first on the single floor element and then on the entire floor of the room into which the floor element was built in. The damping ratio of the floor increased from 1% to 3% when simply supported in laboratory to approximately 5% when placed upon a polyurethane interlayer (Sylodyn®) in situ, and to approximately 6% when fully integrated in the building. Thus the in situ conditions have considerable influence on the damping and the values assessed are very high in comparison with damping values suggested in design codes. Regarding natural frequencies it was concluded that the major change in these occur as the floor element is coupled to the adjacent elements and when partitions are built in the studied room, the largest effect is on those modes of vibration that are largely constrained in their movement.
Following a review of current code methods concerning the vibrational performance of timber floors, this paper describes research on the same, covering both domestic and nondomestic applications. Vibrational performance is viewed as a component of serviceability limit states design. The paper concludes with a simplified method for natural frequency prediction based on the method presented in Eurocode 5: Part 1.1 (DD ENV 1995-1-1: 1994) and modified in line with research findings. Future items for investigation in this field are identified.
Vibration of lightweight engineered timber floors (ETFs) is a problem occasionally reported by occupants of dwellings constructed with such floors. Vibration of timber floors has been studied extensively in the past resulting in the development of design criteria to prevent dynamic serviceability problems. Nevertheless, unsatisfactory serviceability continues to be reported. The present experimental investigation has examined several lightweight ETF configurations and found that most satisfy existing design criteria intended to preclude bodily oscillations under foot traffic. However, these same floors failed to display satisfactory performance with respect to vibrational disturbances such as drumminess and shaking. Common variations in design such as changes in fasteners or the inclusion of blocking have little effect on vibrational disturbances. Instead, experimental evidence suggests that minimum levels of structural damping may be required to control such phenomena.
Timber-concrete floors arc widely used in the Persian Gulf region because of their resistance to the hot and aggressive environment of the area. Because no shear connector is provided, the timber joists and concrete slab work independently. In this study, it is suggested that relatively inexpensive high-strength nails be used as shear connectors so that the timber joists and concrete slab resist the loads as a composite section. Experimental investigations have shown that it is possible to attain full composite action through the use of these high-strength nails. The proposed composite timber-concrete floor system was subjected to static short-term loading, repeated loading, and long-term sustained loading. It is observed that in terms of strength and serviceability the behavior of the proposed system is within the limits set by standard building code. This behavior is also verified by a finite-element analysis. The experimental and numerical results clearly reveal that it is possible to achieve a stiffer floor system, longer spans, and a significant reduction in the number of timber joists, while attaining the same receptivity to a hot and aggressive environment.
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Vibration measurements have been correlated on five long- span floors in a two-storey shopping centre. The floors are used primarily as walking areas and have been considered satisfactory with respect to floor vibrations. Three of the floors are steel beam composite concrete deck construction, and two are precast, prestressed, concrete beam construction. Dynamic characteristics of the floors as determined by the heel impact test were compared with quiet occupancy criteria. Results suggest that quiet occupancy criteria can be increased by at least a factor of three for walking areas in shopping centres. Calculations of fundamental frequency and initial peak acceleration from heel impact for the five floors are also presented and the results compared with measured values. On a procédé à des mesures de vibrations sur cinq planchers de longue portée dans un centre d'achat de deux étages. Ces planchers, situés principalement dans des aires de circulation, étaient considérés comme satisfaisants à l'égard des vibrations. Trois des planchers sont du type mixte à dalle de béton sur poutrelles d'acier, et les deux autres sont composés de dalles préfabriquées en béton avec nervures précontraintes. On a comparé les caractéristiques dynamiques des planchers déterminées par le test du coup de talon aux exigences anti-bruit relatives à ce genre de constructions. Ces résultats laissent voir que ces exigences pourraient être accrues par un facteur trois pour les aires de circulation des centres d'achat. L'article présente, pour les cinq planchers, le calcul des fréquences fondamentales et des accélérations initiales de pointe créées par l'impact du tallon, et en compare les résultats aux valeurs mesurées. RES
Dynamic properties have been determined for a composite steel-joist concrete-slab floor using heel impact and various shaker tests. The three modes located at 7.5, 12.4, and 18.7 Hz exhibited increasing numbers of nodal lines parallel to the joists.Application of vibration annoyance criteria for footsteps indicated that the floor was unsatisfactory. These criteria, presented in CSA Standard S16.1, Appendix G, had been derived specifically for the lowest mode of the floor. Detailed evaluation of the experimental results, however, shows that mode 1 has satisfactory vibration characteristics as a result of its high damping value, whereas mode 2 is identified as unsatisfactory. This is corroborated by subjective assessment. Vibration tests from walking steps were monitored and suitably filtered. Good agreement was found between the annoyance criteria derived from the heel impact test and those for "sustained vibrations" applied to the walking tests.Based on the dynamic properties of the floor, an assessment is made regarding the effectiveness of partitions and truss bracing for reducing footstep vibrations.
La tendance architecturale actuelle favorise la construction de grands espaces modulables et évolutifs. L'utilisation de produits industriels dérivés du bois permet de construire des planchers de grandes portées. Par contre, ces structures légères se trouvent confronter à une sensibilité aux vibrations. Dans le cadre de cette étude, les vibrations des planchers sont examinées, sous les effets de l'impact du talon et de la marche. Ces sollicitations sont retenues pour apporter la connaissance du comportement dynamique du plancher, pour positionner celui-ci vis-à-vis du niveau de confort, et des critères de dimensionnement. Ainsi, les questions suivantes sont étudiées : Quels sont les principaux paramètres structurels influençant le comportement dynamique ? Quels critères faut il choisir pour dimensionner la structure selon le niveau de confort envisagé ? Comment optimiser la conception des planchers en bois en intégrant les aspects liés au confort humain? A ce jour, seul les essais expérimentaux réalisés à l'échelle de la structure constituent le moyen pour déterminer des données subjectives du confort. Pour ces cas étudiés, un lien est établi entre la perception au confort vibratoire et les caractéristiques spécifiques dynamiques du plancher. Pour viser l'extension aux multiples paramètres constructifs avec l'aide de l'expérimentation numérique en complément d'essais limités par " type de plancher ", les analyses dynamiques sont obtenues au moyen de la simulation numérique. In fine, les données structurelles à considérer dans les critères de dimensionnement sont affinées, en vue de l'établissement d'un guide de la conception et d'une aide au dimensionnement.
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