• Structural Engineering and Mechanics
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• 제86권5호
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• pp.647-661
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• 2023

It is recognized that the installation of energy dissipation devices, such as the tuned mass damper (TMD), decreases the dynamic response of structures, however, the best parameters of each device persist hard to determine. Unlike many works that perform only a deterministic optimization, this work proposes a complete methodology to minimize the dynamic response of footbridges by optimizing the parameters of multiple tuned mass dampers (MTMD) taking into account uncertainties present in the parameters of the structure and also of the human excitation. For application purposes, a steel footbridge, based on a real structure, is studied. Three different scenarios for the MTMD are simulated. The proposed robust optimization problem is solved via the Circle-Inspired Optimization Algorithm (CIOA), a novel and efficient metaheuristic algorithm recently developed by the authors. The objective function is to minimize the mean maximum vertical displacement of the footbridge, whereas the design variables are the stiffness and damping constants of the MTMD. The results showed the excellent capacity of the proposed methodology, reducing the mean maximum vertical displacement by more than 36% and in a computational time about 9% less than using a classical genetic algorithm. The results obtained by the proposed methodology are also compared with results obtained through traditional TMD design methods, showing again the best performance of the proposed optimization method. Finally, an analysis of the maximum vertical acceleration showed a reduction of more than 91% for the three scenarios, leading the footbridge to acceleration values below the recommended comfort limits. Hence, the proposed methodology could be employed to optimize MTMD, improving the design of footbridges.

• 터널과지하공간
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• 제2권1호
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• pp.102-115
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• 1992

Blasting operations associated with rock excavation work may have an environmental impact in nearby structures or human beings. With the increase of construction work in urban areas, vibration problems and complaints have also increased. In order to determine the optimum design parameters for safe blast, it is essential to understand blast mechanism, design variables involved in blast-induced damage, and their effects on the blasting results. This paper deals with the characteristics of ground vibrations, air blast and fly rock caused by blast, including the general method of establishing the vibration predictors, and damage criteria suggested by various investigators. The results of field measurements from open pit mine and tunnel construction work are discussed. Basic concepts of how to design blast parameters to control the generation of ground vibrations, air blast and fly rock are presented.

• Tribology and Lubricants
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• 제33권4호
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• pp.148-152
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• 2017

The feel of writing is important to customers when they buy smart devices with stylus such as smartphones and tablet computers. With an aim to reproduce the tactile sensibility of writing instruments when people write on the glass display using a stylus, this study focuses on the frequency characteristics of writing instruments that can describe the vibrations of writing instruments sliding over counter surfaces. In addition, this study includes the effect of various factors influencing the friction of writing instruments such as lubricant, nib material, and contact type. We perform sliding experiments with six types of writing instruments and a sheet of paper to understand the relation between the friction conditions of the nib and the frequency characteristics. As this research focuses on the tactile perception of human skin when people use a writing instrument, the analysis of frequency characteristics is performed in the perceptible frequency range of mechanoreceptors in the human skin. As a result, three types of frequency characteristics are identified. Low frequency peaks are observed for a metal nib with ink; high frequency peaks are observed for a nib without ink; and, middle frequency peaks with a wide range of distribution occurs for fabric nibs with ink. Therefore, to implement the proper feel of writing, at least three types of vibrations have to be made.

• Structural Engineering and Mechanics
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• 제43권5호
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• pp.607-621
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• 2012

The Expo Culture Centre is one of the permanent buildings at the World Expo 2010 in Shanghai, China. The main structure has an oval shape and consists of 36 radial cantilever steel trusses with different lengths and inner frames made of concrete-filled rectangular steel tube members. Tuned mass dampers are used to reduce the excessive vibrations of the sixth floor that are caused by human-induced resonance. A three-dimensional analytical model of the system is developed, and its main characteristics are established. A series of field tests are performed on the structure, and the test results show that the vertical vibration frequencies of most structural cantilevers are between 2.5 Hz and 3.5 Hz, which falls in the range of human-induced vibration. Twelve pairs of tuned mass dampers weighing 115 tons total were installed in the structure to suppress the vibration response of the system. These mass dampers were tuned to the vertical vibration frequency of the structure, which had the highest possibility of excitation. Test data obtained after the installation of the tuned mass dampers are used to evaluate their effectiveness for the reduction of the vibration acceleration. An analytical model of the structure is calibrated according to the measured dynamic characteristics. An analysis of the modified model is performed and the results show that when people walk normally, the structural vibration was low and the tuned mass dampers have no effect, but when people run at the structural vibration frequency, the tuned mass dampers can reduce the floor vibration acceleration by approximately 15%.

• Smart Structures and Systems
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• 제19권1호
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• pp.1-10
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• 2017

The operation of subway trains induces secondary structure-borne vibrations in the nearby underground spaces. The vibration, along with the associated noise, can cause annoyance and adverse physical, physiological, and psychological effects on humans in dense urban environments. Traditional tethered instruments restrict the rapid measurement and assessment on such vibration effect. This paper presents a novel approach for Wireless Smart Sensor (WSS)-based autonomous evaluation system for the subway train-induced vibrations. The system was implemented on a MEMSIC's Imote2 platform, using a SHM-H high-sensitivity accelerometer board stacked on top. A new embedded application VibrationLevelCalculation, which determines the International Organization for Standardization defined weighted acceleration level, was added into the Illinois Structural Health Monitoring Project Service Toolsuite. The system was verified in a large underground space, where a nearby subway station is a good source of ground excitation caused by the running subway trains. Using an on-board processor, each sensor calculated the distribution of vibration levels within the testing zone, and sent the distribution of vibration level by radio to display it on the central server. Also, the raw time-histories and frequency spectrum were retrieved from the WSS leaf nodes. Subsequently, spectral vibration levels in the one-third octave band, characterizing the vibrating influence of different frequency components on human bodies, was also calculated from each sensor node. Experimental validation demonstrates that the proposed system is efficient for autonomously evaluating the subway train-induced ambient vibration of underground spaces, and the system holds the potential of greatly reducing the laboring of dynamic field testing.

• Wind and Structures
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• 제10권3호
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• pp.233-247
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• 2007

The insertion of steel braces has become a common technique to limit the deformability of steel framed buildings subjected to wind loads. However, when this technique is inadequate to keep floor accelerations within acceptable levels of human comfort, dampers placed in series with the steel braces can be adopted. To check the effectiveness of braces equipped with viscoelastic (VEDs) or friction dampers (FRDs), a numerical investigation is carried out focusing attention on a three-bay fifteen-storey steel framed building with K-braces. More precisely, three alternative structural solutions are examined for the purpose of controlling wind-induced vibrations: the insertion of additional diagonal braces; the insertion of additional diagonal braces equipped with dampers; the insertion of both additional diagonal braces and dampers supported by the existing K-braces. Additional braces and dampers are designed according to a simplified procedure based on a proportional stiffness criterion. A dynamic analysis is carried out in the time domain using a step-by-step initial-stress-like iterative procedure. Along-wind loads are considered at each storey assuming the time histories of the wind velocity, for a return period $T_r=5$ years, according to an equivalent wind spectrum technique. The behaviour of the structural members, except dampers, is assumed linear elastic. A VED and an FRD are idealized by a six-element generalized model and a bilinear (rigid-plastic) model, respectively. The results show that the structure with damped additional braces can be considered, among those examined, the most effective to control vibrations due to wind, particularly the floor accelerations. Moreover, once the stiffness of the additional braces is selected, the VEDs are slightly more efficient than the FRDs, because they, unlike the FRDs, dissipate energy also for small amplitude vibrations.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1992년도 가을 학술발표회 논문집
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• pp.156-161
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• 1992

Over the past twenty years, the concept of structural control has been investigated for the application to large civil engineering structures. At the early years, passive control systems, such as tuned mass damper(TMD) and tuned liquid mass bamper(TLD), have been utilized to reduce the wind induced vibrations of tall buildings, decks and pylons of long-span bridges. More recently, the active control concept has been applied to reducing the structural vibration and increasing the human comfortness in tall buildings during strong wind. In this study, the effectiveness of the active tuned mass damper(ATMD) has been investigated for reducing vibration of large structures during strong earthquake. Stochastic optimal control theory has been employed. Example analyses are carried out through analytical simulation studies.

• Earthquakes and Structures
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• 제5권2호
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• pp.225-237
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• 2013

Excessive vibrations induced by earthquake excitation and wind load are an obstacle in design and construction of tall and super tall buildings. An innovative vibration control structure system (Mega-Sub Controlled Structure System-MSCSS) was recently proposed to further improve humans comfort and their safeties during natural disasters. Preliminary investigations were performed using a two dimensional equivalent simplified model, composed by 3 mega-stories. In this paper, a more reasonable and realistic scaled model is design to investigate the dynamical characteristics and controlling performances of this structure when subjected to strong earthquake motion. The control parameters of the structure system, such as the modulated sub-structures disposition; the damping coefficient ratio (RC); the stiffness ratio (RD); the mass ratio of the mega-structure and sub-structure (RM) are investigated and their optimal values (matched values) are obtained. The MSCSS is also compared with the so-called Mega-Sub Structure (MSS) regarding their displacement and acceleration responses when subjected to the same load conditions. Through the nonlinear time history analysis, the effectiveness and the feasibility of the proposed mega-sub controlled structure system (MSCSS) is demonstrated in reducing the displacement and acceleration responses and also improving human comfort under earthquake loads.

• 화약ㆍ발파
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• 제32권3호
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• pp.18-25
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• 2014

발파에 의한 진동과 소음은 주변 지역에 대하여 인적 물적 피해를 일으킬 수 있는 대표적인 환경피해 요소이다. 본 연구에서는 지연시차를 7단계로 변화시키고 각 단계마다 3회씩 반복하여 총 21회의 발파를 수행하였으며, 총 50개의 측정값으로 환산거리에 의한 발파진동 추정식을 도출하였고, 진동속도 측정값과 주파수를 이용하여 Langefors 시차이론을 적용하였다. 지연시차가 8ms와 28ms일 경우 진동속도의 평균값은 각각 5.76cm/sec 및 5.75cm/sec로 비교적 낮은 값을 나타내었으며, 지연시차에 따라 주기적으로 높은 측정값과 낮은 측정값이 반복되어 간섭효과를 확인할 수 있었다. 진동속도와 주파수의 측정값으로 Langefors의 시차이론을 적용한 결과, 본 연구에서 발파진동을 저감할 수 있는 최적의 지연시차는 8ms와 24ms로 확인되었다.

• Steel and Composite Structures
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• 제49권5호
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• pp.487-502
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• 2023

In the realm of nanotechnology, the nonlocal strain gradient theory takes center stage as it scrutinizes the behavior of spinning cantilever nanobeams and nanotubes, pivotal components supporting various mechanical movements in sport structures. The dynamics of these structures have sparked debates within the scientific community, with some contending that nonlocal cantilever models fail to predict dynamic softening, while others propose that they can indeed exhibit stiffness softening characteristics. To address these disparities, this paper investigates the dynamic response of a nonlocal cantilever cylindrical beam under the influence of external discontinuous dynamic loads. The study employs four distinct models: the Euler-Bernoulli beam model, Timoshenko beam model, higher-order beam model, and a novel higher-order tube model. These models account for the effects of functionally graded materials (FGMs) in the radial tube direction, giving rise to nanotubes with varying properties. The Hamilton principle is employed to formulate the governing differential equations and precise boundary conditions. These equations are subsequently solved using the generalized differential quadrature element technique (GDQEM). This research not only advances our understanding of the dynamic behavior of nanotubes but also reveals the intriguing phenomena of both hardening and softening in the nonlocal parameter within cantilever nanostructures. Moreover, the findings hold promise for practical applications, including drug delivery, where the controlled vibrations of nanotubes can enhance the precision and efficiency of medication transport within the human body. By exploring the multifaceted characteristics of nanotubes, this study not only contributes to the design and manufacturing of rotating nanostructures but also offers insights into their potential role in revolutionizing drug delivery systems.