• Smart Structures and Systems
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• v.21 no.3
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• pp.287-303
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• 2018

Applications of energy harvesting from mechanical vibrations is becoming popular but the full potential of such applications is yet to be explored. This paper addresses this issue by considering an application of energy harvesting for the dual objective of serving as an indicator of structural health monitoring (SHM) and extent of control. Variation of harvested energy from an undamaged baseline is employed for this purpose and the concept is illustrated by implementing it for active vibrations of a pipe structure. Theoretical and experimental analyses are carried out to determine the energy harvesting potential from undamaged and damaged conditions. The use of energy harvesting as indicator for control is subsequently investigated, considering the effect of the introduction of a tuned mass damper (TMD). It is found that energy harvesting can be used for the detection and monitoring of the location and magnitude of damage occurring within a pipe structure. Additionally, the harvested energy acts as an indicator of the extent of reduction of vibration of pipes when a TMD is attached. This paper extends the range of applications of energy harvesting devices for the monitoring of built infrastructure and illustrates the vast potential of energy harvesters as smart sensors.

• Structural Engineering and Mechanics
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• v.91 no.6
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• pp.551-565
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• 2024

This study presents a methodical investigation into improving structural designs through the analytical examination of the dynamic behavior of functionally graded plates (FGPs) resting on viscoelastic foundations. By employing a four variable first-order shear deformation theory, the study computes non-dimensional frequencies for a variety of porous FGPs with diverse graded patterns and porosity distributions. Different gradient patterns of the plates are considered, and three distinct functions-sigmoid (S-FGM), exponential (E-FGM), and power-law (P-FGM)-are utilized to assess material performance in specific directions. The equations of motion are derived and solved using both Navier's method and Hamilton's principle. Analytical solutions for vibration frequency are provided to validate the proposed methodology against existing literature. Furthermore, a comprehensive parametric analysis is conducted, taking into account various factors such as ceramic material, porosity distribution, gradient index, length-to-thickness ratio, gradient pattern, and damping coefficient. The findings suggest that enhancing the damping coefficient of the viscoelastic foundation can significantly improve the free-vibrational response of functionally graded material plates.

• Steel and Composite Structures
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• v.7 no.6
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• pp.487-502
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• 2007

In recent decades there has been a trend towards improved mechanical characteristics of materials used in footbridge construction. It has enabled engineers to design lighter, slender and more aesthetic structures. As a result of these construction trends, many footbridges have become more susceptible to vibrations when subjected to dynamic loads. In addition to this, some inherit modelling uncertainties related to a lack of information on the as-built structure, such as boundary conditions, material properties, and the effects of non-structural elements make difficult to evaluate modal properties of footbridges, analytically. For these purposes, modal testing of footbridges is used to rectify these problems after construction. This paper describes an arch type steel footbridge, its analytical modelling, modal testing and finite element model calibration. A modern steel footbridge which has arch type structural system and located on the Karadeniz coast road in Trabzon, Turkey is selected as an application. An analytical modal analysis is performed on the developed 3D finite element model of footbridge to provide the analytical frequencies and mode shapes. The field ambient vibration tests on the footbridge deck under natural excitation such as human walking and traffic loads are conducted. The output-only modal parameter identification is carried out by using the peak picking of the average normalized power spectral densities in the frequency domain and stochastic subspace identification in the time domain, and dynamic characteristics such as natural frequencies mode shapes and damping ratios are determined. The finite element model of footbridge is calibrated to minimize the differences between analytically and experimentally estimated modal properties by changing some uncertain modelling parameters such as material properties. At the end of the study, maximum differences in the natural frequencies are reduced from 22% to only %5 and good agreement is found between analytical and experimental dynamic characteristics such as natural frequencies, mode shapes by model calibration.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.2
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• pp.145-151
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• 2017

As an alternative to conventional explosive methods for demolition of concrete structures and rocks, the use of non-explosive demolition agents can be considered to reduce noise, vibration, and dust emissions during the demolition process. In this study, we conduct finite element analysis for crack initiation and propagation caused by the expansion of non-explosive demolition agents in square concrete structures. The predicted crack patterns are compared with the experimental results in the literature. The minimum values of the required expansion pressure of non-explosive demolition agents are also estimated, which depend upon the arrangement of non-explosive demolition agents and empty holes. Furthermore, we investigate the effect of empty holes on the fragmentation of concrete structures, and discuss the effective arrangement of non-explosive demolition agents and empty holes for fragmentation improvement.

• Earthquakes and Structures
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• v.13 no.4
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• pp.377-386
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• 2017

Earthquake-induced pounding damages to building structures were repeatedly observed in many previous major earthquakes. Extensive researches have been carried out in this field. Previous studies mainly focused on the regular shaped buildings and each building was normally simplified as a single-degree-of-freedom (SDOF) system or a multi-degree-of-freedom (MDOF) system by assuming the masses of the building lumped at the floor levels. The researches on the pounding responses between irregular asymmetric buildings are rare. For the asymmetric buildings subjected to earthquake loading, torsional vibration modes of the structures are excited, which in turn may significantly change the structural responses. Moreover, contact element was normally used to consider the pounding phenomenon in previous studies, which may result in inaccurate estimations of the structural responses since this method is based on the point-to-point pounding assumption with the predetermined pounding locations. In reality, poundings may take place between any locations. In other words, the pounding locations cannot be predefined. To more realistically consider the arbitrary poundings between asymmetric structures, detailed three-dimensional (3D) finite element models (FEM) and arbitrary pounding algorithm are necessary. This paper carries out numerical simulations on the pounding responses between a symmetric rectangular-shaped building and an asymmetric L-shaped building by using the explicit finite element code LS-DYNA. The detailed 3D FEMs are developed and arbitrary 3D pounding locations between these two buildings under bi-directional earthquake ground motions are investigated. Special attention is paid to the relative locations of two adjacent buildings. The influences of the left-and-right, fore-and-aft relative locations and separation gap between the two buildings on the pounding responses are systematically investigated.

• Structural Engineering and Mechanics
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• v.76 no.1
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• pp.141-151
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• 2020

This manuscript tends to investigate influences of nanoscale and surface energy on a static bending and free vibration of piezoelectric perforated nanobeam structural element, for the first time. Nonlocal differential elasticity theory of Eringen is manipulated to depict the long-range atoms interactions, by imposing length scale parameter. Surface energy dominated in nanoscale structure, is included in the proposed model by using Gurtin-Murdoch model. The coupling effect between nonlocal elasticity and surface energy is included in the proposed model. Constitutive and governing equations of nonlocal-surface perforated Euler-Bernoulli nanobeam are derived by Hamilton's principle. The distribution of electric potential for the piezoelectric nanobeam model is assumed to vary as a combination of a cosine and linear variation, which satisfies the Maxwell's equation. The proposed model is solved numerically by using the finite-element method (FEM). The present model is validated by comparing the obtained results with previously published works. The detailed parametric study is presented to examine effects of the number of holes, perforation size, nonlocal parameter, surface energy, boundary conditions, and external electric voltage on the electro-mechanical behaviors of piezoelectric perforated nanobeams. It is found that the effect of surface stresses becomes more significant as the thickness decreases in the range of nanometers. The effect of number of holes becomes significant in the region 0.2 ≤ α ≤ 0.8. The current model can be used in design of perforated nano-electro-mechanical systems (PNEMS).

• Wind and Structures
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• v.34 no.2
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• pp.199-213
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• 2022

The current study investigates the dynamic effects in the tornado-structure response of an aeroelastic self-supported lattice transmission tower model tested under laboratory simulated tornado-like vortices. The aeroelastic model is designed for a geometric scale of 1:65 and tested under scaled down tornadoes in the Wind Engineering, Energy and Environment (WindEEE) Research Institute. The simulated tornadoes have a similar length scale of 1:65 compared to the full-scale. An extensive experimental parametric study is conducted by offsetting the stationary tornado center with respect to the aeroelastic model. Such aeroelastic testing of a transmission tower under laboratory tornadoes is not reported in the literature. A multiaxial load cell is mounted underneath the base plate to measure the base shear forces and overturning moments applied to the model in three perpendicular directions. A three-axis accelerometer is mounted at the level of the second cross-arm to measure response accelerations to evaluate the natural frequencies through a free-vibration test. Radial, tangential, and axial velocity components of the tornado wind field are measured using cobra probes. Sensitivity analyses are conducted to assess the variation of the structural dynamic response associated with the location of the tornado relative to the lattice transmission tower. Three different layouts representing the change in the orientation of the tower model relative to the components of the tornado-induced loads are considered. The structural responses of the aeroelastic model in terms of base shear forces, overturning moments, and lateral accelerations are measured. The results are utilized to understand the dynamic response of self-supported transmission towers to the tornado-induced loads.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.11-18
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• 1991

Stiffened plate structure, which is generally used in the various structural design to develope the load carrying capacity, is classified in two groups; one is the plate stiffened with stiffeners, the other is corrugated plate. In the studies on those structures, the studies on the stiffened plates with stiffeners have been much studied with both quantities and qualities according to requirements of the minimum-weight structural design and the development in many industrial fields, especially automobile, ship and aerospace fields, but the studies on the corrugated plates are undeveloped in comparison with the stiffened plates, and also the analytical stiffness on the corrugated plates remains as the imperfect. In the present studies, the analytical method on the stiffness of corrugated plates made by folding is proposed, and the stiffness equation of corrugated plates with some angle is derived and generalized. The purpose of the present study is to contribute to the design of corrugated plates and to determine the optimum aspect ratio for parameters that decide the aspect of corrugated plates.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.3
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• pp.523-534
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• 2002

Free vibration and buckling analysis of multi-delaminated composite beam-columns subjected to axial compressive load is performed in the present study In order to investigate the effects of multi-delaminations on the natural frequency and the elastic buckling load of multi-delaminated beam-columns, the general kinematic continuity conditions are derived from the assumption of constant slope and curvature at the multi-dclamination tip. The characteristic equation of multi-delaminated beam-column is obtained by dividing the global multi-delauunated beam-columns into segments and by imposing recurrence relation from the continuity conditions on each sub-beam-column. The natural frequency and the elastic buck)ing load of multi-delaminated beam-columns according to the incremental load of axial compression, which is limited to the maximum elastic buckling load of sound laminated beam-column, are obtained. It is found that the sizes, locations and numbers of multi-delaminations have significant effect on natural frequency and elastic buckling load, especially the latter ones.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.2 s.54
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• pp.181-188
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• 2009

Measuring the tensile strength of steel cables used to support bridges is a critical inspection item in terms of the safety of a bridge. Today, cable tension is measured with the vibration method and loadcell. Recently, some advanced countries have conducted studies on measuring tension with magnetic method and are suggesting prospective results. Since there were no such studies ongoing in Korea, we began a study on measuring tension with magnetic method as we are undergoing researches to improve the precision of measurements. It is necessary to consider the influence for the magnetic field and the temperature of steel cables in tension measurement of magnetic method. In this paper, we tested an output characteristic of tension sensor according to temperature and deduced temperature compensation coefficient in the given magnetic field and applied the compensation coefficient to the tension measurement system in the lab. We analyzed and evaluated testing results for the output voltages of the tension sensor according to cable tensions.