Floor Vibration Serviceability Research Articles

Experimental and Theoretical Studies on the Vibration Serviceability of Composite HCS Floors with RC Topping

Composite hollow–core slab floor with reinforced concrete topping (i.e. CHFT) is relatively new, which can be applied to various long-span structures. However, these systems are typically lightweight and exhibit low damping, posing potential serviceability concerns related to human vibrations. This paper presents a comprehensive vibration test on a 9[Formula: see text]m-long CHFT system. Natural frequencies, damping ratios, and mode shapes of the floor system were obtained through modal tests. The peak acceleration, root–mean–square acceleration, maximum transient vibration value, and perception factor of the floor under heel-drop excitation were obtained through the perceived vibration test and were checked against the available design codes and standards. Sensitivity studies using the finite element method were made to investigate the vibration performance of the CHFT system. Analytical formulas for the fundamental frequency and peak acceleration were derived, which are therefore suggested for practical use. Additionally, an approach for evaluating the vibration serviceability of CHFTs is described.

Vibration Serviceability and Environmental Impact of Steel-Concrete Composite Floors Featuring Openings and Partitions

Vibration Serviceability and Environmental Impact of Steel-Concrete Composite Floors Featuring Openings and Partitions

Effect of partition walls on the vibration serviceability of cross-laminated timber floors

The current standards need more specific serviceability criteria for Cross-Laminated Timber (CLT) floors. This paper presents a comprehensive analysis of a relevant case study in Norway, which presented unexpectedly high accelerations in the CLT floors after construction. The lack of a sufficiently detailed design process resulted in the poor vibration performance of the floors, which partially compromised their functionality. The paper thoroughly investigates and discusses the experimental dynamic characterization of seven CLT floors within the considered building. The authors estimated the modal parameters and serviceability metrics based on both Eurocode 5 (EC5) and the new draft version of it. Specifically, the authors compared the analytical predictions of the fundamental frequency and the root mean square acceleration against the corresponding experimental estimations. Using a sensor-roving approach, a dense sensor configuration was adopted to describe seven floors’ mode shapes and serviceability metrics. These metrics include mean square acceleration and Vibration Dose Value. The scenarios examined in this study shed light on the significance of partition walls, a factor not considered in the practical design for serviceability verifications. The presence of partition walls can enhance the vibration comfort of timber floors by providing a stiffening effect, leading to a significant increase in the first fundamental frequency. A parametric finite element model was developed using OpenSeesPy to investigate this phenomenon further. The model, firstly validated against selected experimental results, is employed to assess the influence of partition walls on floor dynamics. The model predicts the increase in the first frequency caused by randomly generated partition walls. The paper proposes an empirical expression calibrated on the simulated data to estimate the relative increment of the floor’s fundamental frequency based on the partition walls’ layout. This formulation can be included in the analytical expression enclosed in the EC5 draft to predict the fundamental frequency of timber floors.

Vibration serviceability of hybrid CLT-steel composite floors based on experimental and numerical investigations using random walk models

Cross-laminated timber (CLT) floors often encounter vibration issues when employed in large spans bearing heavy loads, and the enhancement of their vibration performance frequently centres around achieving composite action. This study delves into the effectiveness of hybrid CLT-steel composite floors as potential substitutes for traditional, long-span CLT floors. A parametric model was developed using OpenSeesPy and validated with prior vibration experimental tests on hybrid and pure CLT floors. It was then employed in examining the sensitivities of the floors to various excitation scenarios via an integrated random walk model used to generate random dynamic responses. Two extreme boundary conditions: pinned–pinned and clamped–clamped, were also simulated to investigate the limits of the vibration response of the hybrid composite floor. The chosen metrics for assessment comprised fundamental frequency, vibration dose value, peak acceleration and velocity, response factor, as well as root-mean-square acceleration and velocity. These metrics were also juxtaposed against the predictions put forth by the new Eurocode 5 draft. Though the fundamental frequency of the much-stiffer hybrid composite floor was about thrice that of the bare CLT, the considerably lower damping of the former — about 60 % less, resulted in a comparable acceleration response with the CLT floor. Also, despite a 55% increase in fundamental frequency when the hybrid floor was simulated with clamped supports, the resulting serviceability metrics did not indicate a clear-cut performance improvement over the pinned boundary condition. The results highlight the leading influence of damping rather than bending stiffness and fundamental frequency on the serviceability metrics of hybrid CLT-steel composite floors.

Quantifying the effect of end support restraints on vibration serviceability of mass timber floor systems: Testing

Design of mass timber floor systems is commonly governed by vibration serviceability due to high stiffness-to-weight ratio and low inherent damping of timber. Research and design practice have shown that static deflection under a concentrated load and fundamental natural frequency can be effective and robust indicators for vibration performance of mass timber floors. These design parameters are normally calculated by assuming simply supported conditions in existing design methods. However, such an assumption deviates from actual floor supports, especially in platform-framed buildings, and in-situ end support restraints have been widely recognized as a significant factor affecting the vibration performance. The purpose of the study is to quantify the influence of end support restraints on vibration serviceability of mass timber floors in platform construction through a comprehensive experimental program and analytical treatment. This paper is the first part and focus specifically on the experimental work on cross-laminated timber (CLT) panels. In particular, extensive laboratory tests have been conducted on different CLT floor panels with various end support restraints induced by top loads, self-tapping screws and steel angle brackets. The fundamental natural frequency and mid-span deflection under a concentrated load were measured for each end support configuration. The rotational restraint stiffness was determined by comparing results of restrained supports to those of simple supports and represented as end fixity factors. The analysis of test results shows that the CLT floor-to-wall connection exhibited inherent non-linear behaviour and such characteristic was more significant for higher top loads. Compared with screws and brackets, the top loads dominated the partially restrained effect but such dominance gradually diminished for lower-level top loads. In addition, support wall thickness notably impacts the support restraint. It was then suggested that the clear span could be used to determine deflection and frequency in the design, but further investigation is needed.

Human-induced vibrations of floors: A probabilistic approach

The current design guidelines for assessing floor vibration performance rely on a simplified approach that considers a single pedestrian as a fixed load with multiple harmonic components applied to the anti-nodes of the floor mode shapes. However, these guidelines do not account for the influence of variability in the walking path on the dynamic response of floors. Moreover, the deterministic approaches used in these guidelines may yield unreliable estimates of vibration response due to the stochastic nature of pedestrian walking force. The aim of this paper is to investigate the dynamic response of floors under a single pedestrian walking load while considering the randomness of the walking path and the walking load itself. A probabilistic perspective is adopted to analyze the dynamic response under different random loading scenarios. Furthermore, the effectiveness of the current guidelines in predicting the dynamic response of floors is critically assessed. The importance of incorporating probabilistic approaches is emphasized to achieve a more comprehensive understanding of the vibration serviceability of floors and to enhance design practices in this context.

A design-oriented method for response prediction of light-weight timber floors under bouncing excitation

Owing to the light weight and high fundamental frequency, timber floors exhibit impulse-like responses under human-induced excitation, which is different with the resonance-like responses for heavy concrete structures. The vibration serviceability of timber floors thus needs to be considered in a different manner. Many design codes for timber structures have required that the static displacement or dynamic response under human excitation should be limited within a threshold for the purpose of serviceability, while failing to provide appropriate method for predicting structural responses considering various affecting factors. Inspired by the idea of response spectrum, this paper proposed a design-oriented method for the peak acceleration prediction of high-frequency floors under human bouncing excitation. The prediction can be obtained for any desired confidence level. Statistical analysis shows that the acceleration responses are mostly dependent on structural fundamental frequency, structural damping ratio, and excitation frequency, which are considered in the proposed mathematical model. The application procedure and the experimental assessment of the proposed model are provided, showing the decent applicability of the proposed method.

Vibration behavior of timber-concrete composite floors under human-induced excitation

The design of timber-concrete composite (TCC) floors is usually subject to the requirement of serviceability rather than strength. Most studies reported so far focus on the dynamic characteristics of the TCC floor. However, there are few studies conducted on the vibration comfort of TCC floors under human-induced excitation. In this paper, dynamic experiments were performed to obtain the fundamental frequency and the damping ratio of a glulam-concrete composite floor under simply supported and fixed support boundary conditions, respectively. Besides, an in-depth investigation was carried out considering the influences of walking path, step frequency, number of pedestrians, arrangement of walking loads and walking mode on the vibration response of the composite floor. Test results showed that the peak acceleration of the floor increased with an increase in step frequency and the number of pedestrians. Regular walking caused a higher peak acceleration compared to irregular walking. At the same step frequency, marking time caused a larger peak acceleration than normal walking. Three existing analytical models were applied to predict the fundamental frequency of the floor, which conformed to the experimental results. In addition, a calculation model and finite element (FE) models were proposed to predict the peak floor acceleration under a single person walking, and the numerical model results agree well with the test results. A double-index was proposed to evaluate the vibration serviceability of TCC floors; the fundamental frequency of the floor is required to exceed 15 Hz and the peak acceleration ought to be less than 0.15 m/s2.

Determination of equivalent rigidities of cold-formed steel floor systems for vibration analysis, Part I: Theory

Cold-formed steel (CFS) floor systems have been increasingly used in residential and commercial buildings. The evaluation of vibration performance of these floors is a great challenge to be dealt with in the design stage. One of the reasons is that there is a lack of an applicable procedure to accurately determine the structural properties of the floors for vibration serviceability evaluation. Current design approaches for floor vibration serviceability are based on simplified equivalent models which lack the capability to account for effects of rotationally restrained floor edges and transverse elements. In this study, comprehensive analytical and experimental investigations have been carried out on the elastic rigidities of CFS floors for vibration analysis based on equivalent orthotropic plate model and results are reported in the present paper and its companion paper. In the present paper, the equivalent rigidities were determined by using Rayleigh's method with considerations of the rotational restraints on the joist ends and different transverse elements. Rotational fixity factors were introduced to represent the rotational restraints and restraint coefficients were designated for frequency calculation. A joist contribution factor was defined to suitably consider the stiffness contribution of joists for a vibration mode. Upon validating the proposed flexural rigidities for vibration analysis, a design equation was developed in the companion paper for predicting the fundamental frequency of the floor system for vibration serviceability evaluation. The results obtained from the equation were compared to those of tests. In addition, in the companion paper, rotational fixity factors for different type of CFS framings were discussed for evaluating the fundamental frequency based on the existing experimental data.

Vibration responses of glulam beam-and-deck floors

Floor vibration serviceability problems can exist for floors constructed from low mass-to-stiffness engineered-wood products. This paper addresses responses of beam-and-deck floors constructed using glued-laminated-timber (glulam) products. Such floors have widely spaced parallel beams supporting flat wise oriented deck elements and are a relatively new construction option for floors having spans up to about 10 m. The primary focus of discussion here is the experimental investigation of how design variables like span, support arrangement, beam spacing and the addition of non-structural topping materials alter vibration responses of floors. Focus group opinions of acceptability of motions of floors resulting from walking footfall impacts were collected as an indication of the practicality of using engineering design decisions to control vibration of beam-and-deck floors. Collected opinions support the premise that dynamic motions of floors can be controlled in desired ways using practical engineering design methods. However, it was also apparent from the data that suitable methods need to be ones specifically calibrated to suit beam-and-deck floors rather than those applied to other types of low mass-to-stiffness engineered-wood products. No attempt is made to propose new vibration serviceability performances criteria or design methods. This is because it would conflict with ongoing international efforts to create criteria and methods that apply across a wider range of floor construction technologies.

Predicting effects of design variables on modal responses of CLT floors

New ultralight materials like cross-laminated-timber (CLT) enable attainment of longer floor spans than are possible with traditional shallow-profile timber construction. Their low modal mass to stiffness ratios make ensuring satisfactory dynamic responses under normal building occupancy conditions a primary design consideration. This paper presents numerical techniques for accurate prediction of modal frequencies, which are essential input to contemporary floor vibration serviceability design criteria. Recommendations are made for minimum requirements for design level prediction of modal responses of CLT floors, based on numerical and experimental studies of effects engineering design variables have on such characteristics.

Dynamic Forces Induced by a Single Pedestrian: A Literature Review

With the use of lighter construction materials, more slender architectural designs, and open floor plans resulting in low damping, vibration serviceability has become a dominant design criterion for structural engineers worldwide. In principle, assessment of floor vibration serviceability requires a proper consideration of three key issues: excitation source, system, and receiver. Walking is usually the dominant human excitation for building floors. This paper provides a comprehensive review of a considerable number of references dealing with experimental measurement and mathematical modeling of dynamic forces induced by a single pedestrian. The historical development of walking force modeling—from single harmonic loads to extremely complex stochastic processes—is discussed. As a conclusion to this effort, it is suggested that less reliance should be made by the industry on the deterministic force models, since they have been shown to be overly conservative. Alternatively, due to the random nature of human walking, probabilistic force models seem to be more realistic, while more research is needed to achieve enough confidence to implement in design practice.

Duality between time and frequency domains for vibration serviceability analysis of floor structures

For vibration serviceability of floors, current design guidelines adopt different criteria to assess vibration levels due to human walking dynamic excitation. Whatever the adopted criterion is, it requires a quantified vibration response of the structure. This quantification could be achieved following either a time- or a frequency-domain approach to response analysis. Each approach has its advantages and disadvantages. For instance, when using the time-domain analysis, exact time-domain amplitudes of the response time histories could be quantified but the process could take time. On the other hand, a frequency-domain analysis approach could reduce the calculation time, but it is impossible to recover exact time-domain amplitudes of the response, which is essentially averaged by the process of calculation. In this paper, the theoretical duality between time and frequency domains is examined practically in the context of vibration serviceability of a floor structure. Weight-normalised vertical ground reaction force (GRF) measured on an instrumented treadmill due to walking is used for that purpose because it has realistic distribution of energy in the frequency domain. This GRF is applied on a finite element model of a reinforced concrete high-frequency floor and the responses are calculated via both time and frequency domain analyses. Comparison of these two methods reveals that time-domain analysis could introduce significant errors in the calculated vibration responses. This is due to the errors in the numerical solution of equation of motion.

Vibration serviceability performance of timber floors

Vibration serviceability of timber floors is becoming increasingly relevant due to their increased long-span applications in pure timber and hybrid structures. As a serviceability limit state, the check of acceptable floor vibrations is part of some current timber design standards. However, a universal agreement on acceptance levels and design procedures has not been achieved. This paper gives an overview of traditional and recent design approaches for floor vibrations, with those approaches intended to allow engineers to implement design strategies that produce floors that perform acceptably under service conditions. The subsequent discussion does not catalogue all relevant technical literature, information in design manuals and aids, nor list all relevant design code rules related to vibration serviceability of timber floors. Instead what is written is intended to convey and critique the state of background knowledge, design recommendation and code rules using illustrative examples from the literature. The objective is to contribute to resolution of debate about control of floor response characteristics by engineering design methods.

Floor Vibration Serviceability in a Multistory Factory Building

AbstractExperimental and analytical modal analysis and in-operation vibration measurements were performed on the massive concrete structural floors of several structurally connected ‘units’ of a six-level, multitenant industrial complex with total floor usable area exceeding 0.1 km2. The aim of the systematic study was to characterize vibration sources and factors that affect vibration serviceability, which is a major concern when changing usage patterns lead to conflicting requirements for vibration generation and tolerance for different types of industrial/commercial user. This was a rare investigation aiming to provide information on specific performance and relevant technologies for occupancy decisions by tenants and building management of similar structures. Floors evaluated were within different types of industrial single-occupant unit stacked up to six levels and having multibay floors with spans up to 12 m with first vibration mode frequencies greater than 8 Hz. These “high-frequency floors” disp...

가속도 크기 변수에 따른 수직진동에 대한 인지수준 고찰

Occupants induced floor vertical vibrations may cause other occupants annoyance and lead to social loss. To help control such floor vibrations, several criteria have been developed mostly based on human perception tests and floor vibration tests. Floor vibration is evaluated by comparison with criteria and vibration parameters of subject floor, such as frequency, damping ratio, acceleration value, vibration duration time and occurrence frequency. Three acceleration value parameters are used in criteria; peak acceleration, rms acceleration and VDV, when a floor vibration serviceability is evaluated. Meanwhile rms acceleration and peak acceleration are adopted as vibration limit value in criteria and researches of human perception for vibration. Occupants induced floor vibration is transient rather than steady state. However, rms acceleration is not reliable parameter for evaluating transient vibration. The objective of this study is to investigate the characters of human perception level according to acceleration value parameters for vibration induced by heel impacts and walking activities.

Modal Parameter Variations due to Joist Bottom Chord Extension Installations on Laboratory Footbridges

AbstractFor steel-framed structural systems, strength and deflections have been the two fundamental limit states for the design. However, the use of high-strength steel, lighter sections, and low inherent damping resulted in more lively structures, and floor vibration serviceability has become a governing factor for structural design. While annoying floor vibrations can be significant in open web steel joist-supported footbridges; a common application in the North American construction industry is the installation of bottom chord extensions in an attempt to strengthen the floor and increase the natural frequency of the floor systems. Even though extending joist bottom chords is very common, there has not been any publication on the topic studying the dynamic effects of this application. The study presented in this paper aims to fill this gap and identify the effect of bottom chord extensions on the modal parameters of joist-supported structures, by studying two laboratory footbridges. The goal is not to s...

Uncertainties Concerning the Free Vibration of Inhomogeneous Orthotropic Reinforced Concrete Plates

Abstract Analyzing nearly collapsed and broken structures gives good insights into possible architectural and engineering design mistakes and faults in the detailing and mismanagement of a construction by building contractors. Harmful vibration effects of construction operations occur frequently. The background reviews have demonstrated that the problem of the vibration serviceability of long-span concrete floors in buildings is complex and interdisciplinary in nature. In public buildings, floor vibration control is required in order to meet Serviceability Limit States that ensure the comfort of the users of a building. In industrial buildings, machines are often placed on floors. Machines generate vibrations of various frequencies, which are transferred to supporting constructions. Precision machines require a stable floor with defined and known dynamic characteristics. In recent years there has been increasing interest in the motion of elastic bodies whose material properties (density, elastic moduli, etc.) are not constant, but vary with their position, perhaps in a random manner. Concrete is a non-homogeneous and anisotropic material. Modeling the mechanical behavior of reinforced concrete (RC) is still one of the most difficult challenges in the field of structural engineering. One of several methods for determining the dynamic modulus of the elasticity of engineering materials is the vibration frequency procedure. In this method, the required variables except for the modulus of elasticity are accurately and certainly determined. In this research, the uncertainly analysis of the free vibration of inhomogeneous orthotropic reinforced concrete plates has been investigated. Due to the numerous outputs obtained, the software package has been written in Matlab, and an analysis of the data and drawing related charts has been done.

Floor Vibration Serviceability Problems in Wood Light-Frame Buildings

AbstractExcessive floor vibrations can occur in wood light-frame buildings and cause inconvenience to occupants in terms of unsatisfactory serviceability. There has been much unresolved debate about how to perform vibration serviceability design calculations for such floors. The research reported in this paper is built around field observations of the vibration behaviors of floors in building superstructure constructed using alternative contemporary wood materials using advanced vibration test and data analysis techniques, and synthesis of findings with existing knowledge. Field investigations were performed on residential units of two multioccupancy multistory buildings having distinctly different architectural and construction features. Those buildings are similar to many in North America. Detailed modal testing was performed with the objective of understanding effects associated with construction method choices made by engineers. Analysis of the data showed that architectural and construction detailing...

On methods for extending a single footfall trace into a continuous force curve for floor vibration serviceability analysis

An experimentally measured single footfall trace (SFT) from a walking subject needs to be extended into a continuous force curve, which can then be used as load for floor vibration serviceability assessment, or on which further analysis like discrete Fourier transform can be conducted. This paper investigates the accuracy, applicability and parametrical sensitivity of four extension methods, Methods I to IV, which extends the SFT into a continuous time history by the walking step rate, stride time, double support proportion and the double support time, respectively. Performance of the four methods was assessed by comparing their results with the experimentally obtained reference footfall traces in the time and frequency domain, and by comparing the vibrational response of a concrete slab subjected to the extended traces to that of reference traces. The effect of the extension parameter on each method was also explored through parametrical analysis. This study finds that, in general, Method I and II perform better than Method III and IV, and all of the four methods are sensitive to their extension parameter. When reliable information of walking rate or gait period is available in the test, Methods I or II is a better choice. Otherwise, Method III, with the suggested extension parameter of double support time proportion, is recommended.