• Structural Engineering and Mechanics
• /
• 제10권1호
• /
• pp.81-92
• /
• 2000

This study is an investigation of the effect of cracks on the dynamical characteristics of a cantilever beam, having multiple open-edge transverse cracks. The flexibilities due to crack have been identified for several crack depths and locations. In the study the finite element method and component mode synthesis methods are used. Coupling the components is performed by a flexibility matrix taking into account the interaction forces. Each component is modelled by cantilever beam finite elements with two nodes and three degrees of freedom at each node. The results obtained lead to conclusion that, by using the drop in the natural frequencies and the change in the mode shapes, the presence and nature of cracks in a structure can be detected. There is some counter-evidence, however, that the effects due to multiple cracks may interact to make detection more difficult than for isolated cracks.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2001년도 춘계학술대회논문집
• /
• pp.431-435
• /
• 2001

The active structural control has emerged as structural safety of structures against natural loadings such as earthquake and wind loadings. Of many control algorithms, Sliding-Mode Control (SMC) can design both linear controller and nonlinear controller. The robustness against parameter variations as well as excitation uncertainties that is imparted to the SMC due to its nonlinear control action, could make SMC an attractive control algorithm when dealing with structures where the external excitation constitutes the main uncertainty in the system. This paper demonstrates experimentally the efficacy of the SMC algorithm based on the active mass driver system in reducing the response of seismically excited buildings. The SMC control strategy is verified with the experimental study on the one-story building model equipped with the active mass driver.

• Smart Structures and Systems
• /
• 제15권5호
• /
• pp.1253-1270
• /
• 2015

In this paper Magnetic Charged System Search (MCSS) and Particle Swarm Optimization (PSO) are applied to the problem of damage detection using frequencies and mode shapes of the structures. The objective is to identify the location and extent of multi-damage in structures. Both natural frequencies and mode shapes are used to form the required objective function. To moderate the effect of noise on measured data, a penalty approach is applied. A variety of numerical examples including two beams and two trusses are considered. A comparison between the PSO and MCSS is conducted to show the efficiency of the MCSS in finding the global optimum. The results show that the present methodology can reliably identify damage scenarios using noisy measurements and incomplete data.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 1997년도 가을 학술발표회 논문집
• /
• pp.262-269
• /
• 1997

The purpose of this study is to survey the shape finding of the plane truss structures under the prescribed displacement mode by the shape analysis. The shape analysis is peformed by the existence condition of a solution and Moore-Penrose generalized inverse matrix, and the prescribed displacement mode is the homologous deformation of structures. The shape analysis of structures is a kind of inverse problem and become the problem of a nonlinear equation. Newton-Raphson method is used to improve the accuracy of approximated solution. To prove the accuracy and the effectiveness of this method, four different shape examples are analyzed.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2003년도 가을 학술발표회 논문집
• /
• pp.487-494
• /
• 2003

Recently it is used seismic analysis like single mode spectrum analysis, multi mode spectrum analysis and time history analysis in Korea. Because bridges are not special form of them but regular and simple form of them in our country, we must develope seismic analysis program of bridge based on single nude spectrum analysis. The program developed by this study reduces a Quantity and a time of calculation compared to SAP90 and gives accurate answers without errors. In the case of commercial program if we look for seismic load(P/sub e/(x)), we must increase the number of node and the larger the number of node the more a quantity and a time of calculation. But this program is exactly solved with basic node compared to commercial program.

• Structural Engineering and Mechanics
• /
• 제40권1호
• /
• pp.1-11
• /
• 2011

Ambient vibration tests were carried out to evaluate the dynamic properties of an asymmetric steel building with semi-rigid connections. The test case has many non-structural elements, constructed in the city of Tehran (Iran). The tests were conducted to obtain natural frequencies, mode shapes and damping ratio of the structure and then Fourier transform were used to analyze the velocity records obtained from the tests. The first and second natural periods of the building were obtained as 1.37 s and 1.28 s through the test and damping ratio for the first mode was calculated as 0.047. However, Natural periods obtained from finite element model have higher values from those gained from ambient vibration. Then the model was calibrated by modeling of the in-fill masonry panels at their exact locations and considering the boundary conditions by modeling two blocks near the block No. 3, but the differences were existed. These differences may be due to some hidden stiffness of nonstructural elements in the low range of elastic behavior, showing the structure stiffer than it is in reality.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2002년도 봄 학술발표회 논문집
• /
• pp.415-429
• /
• 2002

Various modeling techniques for ultrasonic wave propagation and scattering problems in finite solid media are presented. Elastodynamic boundary value problems in inhomogeneous multi-layered plate-like structures are set up for modal analysis of guided wave propagation and numerically solved to obtain dispersion curves which show propagation characteristics of guided waves. As a powerful modeling tool to overcome such numerical difficulties in wave scattering problems as the geometrical complexity and mode conversion, the Boundary Element Method(BEM) is introduced and is combined with the normal mode expansion technique to develop the hybrid BEM, an efficient technique for modeling multi-mode conversion of guided wave scattering problems.

• Steel and Composite Structures
• /
• 제19권2호
• /
• pp.385-403
• /
• 2015

This paper presents the status improvement of an old damaged deck type rural road steel truss bridge through the modal parametric study after partial retrofitting. The dynamic and static tests on bridge were carried out as in damaged state and after partial retrofitting. The dynamic testing on the steel bridge was carried out using accelerometers under similar environmental conditions with same speed of the moving vehicle. The comparison of the modal parameters i.e., frequency, mode shape mode shape curvature, modal strain energy, along with the deflection parameter are studied with respect to structural analytical model parameters. The status up gradation for the upper and downstream truss obtained was different due to differential level of damage in the bridge. Also after retrofitting the structural elemental behavior obtained was not same as desired. The damage level obtained through static tests carried out using total station indicated further retrofitting requirement.

• Structural Engineering and Mechanics
• /
• 제69권3호
• /
• pp.283-291
• /
• 2019

Accurately determining the natural frequencies and mode shapes of a structural floor is an essential step to assess the floor's human-induced vibration serviceability. In the theoretical analysis, the prestressed concrete floor can be idealized as a multi-span continuous anisotropic plate. This paper presents a new analytical approach to determine the natural frequencies and mode shapes of a multi-span continuous orthotropic plate. The suggested approach is based on the combined modal and perturbation method, which differs from other approaches as it decomposes the admissible functions defining the mode shapes by considering the intermodal coupling. The implementation of this technique is simple, requiring no tedious mathematical calculations. The perturbation solution is validated with the numerical results.

• 항공우주시스템공학회지
• /
• 제14권6호
• /
• pp.68-73
• /
• 2020

Skin-stringer structures are widely used in aircrafts due to their advantage of minimizing structural weight while maintaining load carrying capacity. However, buckling load can cause serious damage to these structures. Therefore, the buckling characteristics of skin-stringer structures should be carefully considered during the design phase to ensure structural soundness. In this study, finite element method was applied to predict the buckling characteristics of stiffened panels. In terms of the failure mode, finite element analysis showed a symmetrical buckling mode, whereas an asymmetrical mode was determined by experimentation. The numerical results were obtained and compared to the experimental data, showing a difference of 9.3% with regard to the buckling loads.