Structural Vibrations

Walking-induced loads on office floors can generate unwanted vibrations. The current multi-person loading models are limited since they do not take into account nondeterministic factors such as pacing rates, walking paths, obstacles in walking paths, busyness of floors, stride lengths, and interactions among the occupants. This study proposes a novel video-vibration monitoring system to investigate the complex human walking patterns on floors. The system is capable of capturing occupant movements on the floor with cameras, and extracting walking trajectories using image processing techniques. To demonstrate its capabilities, the system was installed on a real office floor and resulting trajectories were statistically analyzed to identify the actual walking patterns, paths, pacing rates, and busyness of the floor with respect to time. The correlation between the vibration levels measured by the wireless sensors and the trajectories extracted from the video recordings were also investigated. The results showed that the proposed video-vibration monitoring system has strong potential to be used in training data-driven crowd models, which can be used in future studies to generate realistic multi-person loading scenarios.

Construction activities such as dynamic compaction, pile-driving, and any site activities heavy construction equipment can generate ground and structure vibration. Vibration may cause damage to nearby structures. As the current construction works are frequently located in urban areas where the distance between the nearest building structures to the construction site is not far. Therefore, this paper studied the effect of vibration produced from piling work to the nearest existing building and determination of limits in term of allowable vibration and distance limit between piling work and existing structure. An accelerometer was used to collect the vibration data from the piling activities and the data were analysed by using Microsoft Excel. The findings of the study presented several vibrations and limits based on several guidelines. The study stated not disobeying the proposed guidelines may harm and damage the existing structure. This research contributes to future development to ensure the future construction does not exceed the limit as stated in the guideline to avoid any type of damage to the existing structure. Thus, any project in the future should take into consideration the effect of vibration and the distance limit to reduce the effect of vibration from the construction site to the surrounding structures.

Purpose: This study introduces a new approximated analytical solution of the free vibration analysis to evaluate the natural frequencies of functionally graded rectangular sandwich plates with porosities. Design/methodology/approach: The kinematic relations are developed based on the classical plate theory (CPT), and the governing differential equation is derived by employing the Rayleigh-Ritz approximate method. The FGM plate is assumed made of an isotropic material that has an even distribution of porosities. The materials properties varying smoothly in the thickness direction only according to the power-law scheme. Findings: The influences of changing the gradient index, porosity distribution, boundary conditions, and geometrical properties on the free vibration characteristics of functionally graded sandwich plates are analysed. Research limitations/implications: A detailed numerical investigation is carried out using the finite element method with the help of ANSYS 2020 R2 soft...

Contemporary methods for estimating the extent of seismic induced damage to structures include the use of nonlinear finite element method (FEM) and seismic vulnerability curves. FEM is applicable when a small number of predetermined structures is to be assessed but becomes inefficient for larger stocks. Seismic vulnerability curves enable damage estimation for classes of similar structures characterised by a small number of parameters, and typically use only one parameter to describe ground motion. Hence they are unable to extend damage prognosis to wider classes of structures, e.g. buildings with a different number of storeys and/or bays, or capture the full complexity of the relationship between damage and seismic excitation parameters. Motivated by these shortcomings, this study presents a general method for predicting seismic-induced damage using Artificial Neural Networks (ANNs). The approach was to describe both the structure and ground motion using a large number of structural and ground motion properties. The class of structures analysed were 2D reinforced concrete (RC) frames that varied in topology, stiffness, strength and damping, and were subjected to a suite of ground motions. Dynamic structural responses were simulated using nonlinear FEM analysis and damage indices describing the extent of damage calculated. Using the results of the numerical simulations, a mapping between the structural and ground motion properties and the damage indices was than established using an ANN. The performance of the ANN was assessed using several examples and the ANN was found to be capable of successfully predicting damage.

ABSTRACT: The joints connecting vertical and horizontal elements are the “weak link” in structural systems assembled from wood panels. If they are too weak, local failures may occur, resulting in performance that is significantly below expectations. If they are too resistant, the joints may be unable to dissipate energy during vibrations, thus possibly initiating a fast progressive failure. This paper re-processes and re-elaborates the results of shaking table tests previously carried out by the author and other co-workers. The goal is to assess the feasibility of a joint which is able to dissipate energy during vibration, without degrading the connection performance.

KEYWORDS: dynamic excitation - energy dissipation - wood panels joint - monitoring system - shaking table tests

A new class of drill strings is investigated whereby strategically designed and placed periodic inserts are utilized to filter out the vibration transmission along the drill strings. Such mechanical filtering capabilities allow the vibrations to propagate along the periodic drill string only within specific frequency bands called the 'pass bands' and completely block it within other frequency bands called the 'stop bands'. The design and the location of the inserts are selected to confine the dominant modes of vibration of the drill string within the stop bands generated by the periodic arrangement of the inserts in order to completely block the propagation of the vibrations. A finite element model (FEM) that simulates the operation of this new class of drill strings is developed to describe the complex nature of the vibration encountered during drilling operations. Experimental prototype of the passive periodic drill string was built and tested to demonstrate the feasibility and effectiveness of the concept of periodic drill string in mitigating undesirable vibrations. The experimental results are used to validate the developed theoretical model and to develop a scalable design tool that can be used to predict the dynamical behavior of this new class of drill strings.

A numerical approach for a simulation of the effect of moving loads on the vibration of a railway track and the vibration of a structure in the surrounding of the track is presented. Comparative analyses are performed. The rails, sleepers, elastic pads as well as the structure in the surrounding are described by finite elements, and the ballast and subsoil by boundary elements. The simulation is performed in the frequency domain. The investigation indicates that the speed of a moving load has a significant influence on the track and ground vibrations. The results show that in order to obtain a more realistic characteristic of the structural response to the ground motions it is not enough just to consider the vertical component of the ground motions.

Performance-based optimization of energy dissipation devices in structures necessitates massive and repetitive dynamic ‎analyses. In the endurance time method known as a rather fast dynamic analysis procedure, structures are subjected to ‎intensifying dynamic excitations and their response at multiple intensity levels is estimated by a minimal number of analyses. ‎So, this method significantly reduces computational endeavors. In this paper, the endurance time method is employed to determine the optimal placement of viscous dampers in a weak structure to achieve the desired performance at various hazard levels, simultaneously. The viscous damper is one of the energy dissipation systems which can dissipate a large amount of seismic input energy to the ‎structure. To this end, hysteretic energy compatible endurance time ‎ ‎excitation functions are used and the validity of the results is investigated by comparing them with the results obtained from a suite of ground motions. To optimize the placement of the dampers, the genetic algorithm is used. The damping coefficients of the dampers are considered as design variables in the optimization procedure and determined ‎in such a way that the sum of them has a minimum value. The behavior of the weak structure before and after rehabilitation is also investigated using endurance ‎time and nonlinear time history analysis procedures in different hazard levels.‎

En este artículo se estudia la “no Lie” simetría de la ecuación de viga, se construyen todos los operadores de simetría diferenciales lineales, hasta tercer orden. Se constata que el problema de resolución de dicha ecuación se reduce a la búsqueda de soluciones de dos ecuaciones de Kolmogorov. Se despejan varias clases de soluciones de la ecuación, particularmente las que verifican la ley de conservación de la velocidad areolar inicial y las que verifican la ley de conservación de elasticidad inicial. Se ilustra la equivalencia entre el problema de Cauchy y la existencia de una simetría específica. Se encuentra el paralelismo sorprendente que existe entre la ecuación de viga y la ecuación de onda. Aplicando el “método Ansatz” se construye una amplia familia de nuevas soluciones exactas que incluye particularmente las que describen la propagación de ondas con amortiguamiento. Todos los resultados del artículo son nuevos, los pocos resultados conocidos en la literatura son siempre mencionados.

PACS: 43.40.+s

MSC: 83C05, 82B23

"En este trabajo se presenta el resultado del análisis de datos de vibraciones inducidas por la propagación de ondas originadas por el paso de trenes, metro y tranvía. Dichos datos han sido tomados con aelerómetros de fibra óptica,dentro del marco del proyecto de investigación TRAVIESA (Transmisión de Vibraciones del ferrocarril urbano al entorno: Estrategias, Tecnologías y materiales para su atenuación) financiado por el CDTI y el Ministerio De Ciencia e Innovación del Gobierno de España. La metodología desarrollada permite caracterizar el nivel de las vibraciones que afectan a los diferentes elementos de la infraestructura ferroviaria y los edificios cercanos. La tecnología de los acelerómetros es la fibra óptica y las mediciones fueron realizadas por el Instituto Tecnológico de Óptica, Color e Imagen (AIDO)"

The theory of microlocal analysis shows that the energy density associated with the high-frequency vibrations of a three-dimensional Timoshenko beam satisfies a Liouville-type transport equation. In the present application, the material of the beam is assumed to be isotropic. Its parameters are allowed to vary along the beam axis at length scales much larger than the wavelength of the high-frequency waves traveling in it. Moreover, the curvature and torsion of the beam are accounted for. The first part of the paper focuses on the derivation of the transport model for a single three-dimensional beam. In order to extend this model to beam trusses, the reflection/transmission phenomena of the energy fluxes at junctions of beams are described by power flow reflection/transmission operators in a subsequent part. For numerical simulations, a discontinuous Galerkin finite element method is used on account of the discontinuities of the energy density field at the junctions. Thus, a complete mechanical–numerical modeling of the linear transient dynamics of beam trusses is proposed. It is illustrated by numerical examples highlighting some remarkable features of high-frequency vibrations: The onset of a diffusive regime characterized by energy equipartition rules at late times. Energy diffusion is prompted by the multiple reflection/transmission of waves at the junctions, with possible mode (polarization) conversions. This is the regime applicable to the statistical energy analysis of structural acoustics systems. The main purpose of this research is to develop an effective strategy to simulate and predict the transient response of beam trusses impacted by acoustic or mechanical shocks.

A Magnetorheological fluid (MRF) damper gives a real solution for semi-active vibration control in vibrations for structures. The performance of the MRF damper depends significantly on the electromagnetic circuit which is integrated into it. The force which is developed by MR fluid damper is greatly influenced by the magnetic flux density induced in the fluid flow gap. In the fields of Civil and Mechanical Engineering, Magnetorheological fluid (MRF) damper based semi-active systems offer protection to structures subjected to mechanical vibrations and also lateral loads due to wind and earthquake forces. In the present work, structural and magnetic analysis of the MR damper is studied and also, the dynamic behavior of a frame when subjected to different forcing frequencies has been discussed.

Annoying vibrations in grandstand structures have been receiving more attention due to the increasing slenderness of the architectural components and the complexity of the crowd loading for engineers. The vibration serviceability checks under these conditions become a challenge in the design and operation stages. Regarding human comfort, excessive vibrations due to occupant activities may affect comfort and/or cause panic, especially for passive occupants who do not participate in generating excitations. Although durations of excessive vibrations have been considered as one of the most important factors affecting occupant comfort, incorporating the vibration duration in the occupant comfort analysis has not been addressed yet. In addition, the currently available approaches using raw acceleration, weighted RMS acceleration, vibration dose values (VDV), and so on may not always be sufficient for serviceability assessment due to the lack of guided procedure for calculating the integration time and implementing the duration of vibration into the process. Therefore this study proposes a new parameter and framework for assessing human comfort which incorporates the duration of vibration with conventional data processing. The aim is to better examine vibration levels and the corresponding occupant response focusing on grandstand structures. A new parameter, the area of RMS (ARMS), is introduced using the running RMS values of acceleration weighted by the frequency weighting functions. Furthermore, perception ranges for human comfort levels based on the proposed parameter are presented. The experimental study reveals that the proposed framework can successfully address the impact of duration time on determining the levels of vibrations and comfort using the proposed parameter.