• Structural Engineering and Mechanics
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• v.25 no.3
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• pp.311-330
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• 2007

Model-based predictions of structural behavior are negatively affected by uncertainties of various type and in various stages of the structural analysis. The present paper focusses on dynamic analysis and addresses the effects of uncertainties concerning material and geometric parameters, mainly in the context of modal analysis of large-scale structures. Given the large number of uncertain parameters arising in this case, highly scalable simulation-based methods are adopted, which can deal with possibly thousands of uncertain parameters. In order to solve the reliability problem, i.e., the estimation of very small exceedance probabilities, an advanced simulation method called Line Sampling is used. In combination with an efficient algorithm for the estimation of the most important uncertain parameters, the method provides good estimates of the failure probability and enables one to quantify the error in the estimate. Another aspect here considered is the uncertainty quantification for closely-spaced eigenfrequencies. The solution here adopted represents each eigenfrequency as a weighted superposition of the full set of eigenfrequencies. In a case study performed with the FE model of a satellite it is shown that the effects of uncertain parameters can be very different in magnitude, depending on the considered response quantity. In particular, the uncertainty in the quantities of interest (eigenfrequencies) turns out to be mainly caused by very few of the uncertain parameters, which results in sharp estimates of the failure probabilities at low computational cost.

• Earthquakes and Structures
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• v.7 no.6
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• pp.1187-1221
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• 2014

The uplifting and rocking of slender, free-standing structures when subjected to ground shaking may limit appreciably the seismic moments and shears that develop at their base. This high-performance seismic behavior is inherent in the design of ancient temples with emblematic peristyles that consist of slender, free-standing columns which support freely heavy epistyles together with the even heavier frieze atop. While the ample seismic performance of rocking isolation has been documented with the through-the-centuries survival of several free-standing ancient temples; and careful post-earthquake observations in Japan during the 1940's suggested that the increasing size of slender free-standing tombstones enhances their seismic stability; it was George Housner who 50 years ago elucidated a size-frequency scale effect that explained the "counter intuitive" seismic stability of tall, slender rocking structures. Housner's 1963 seminal paper marks the beginning of a series of systematic studies on the dynamic response and stability of rocking structures which gradually led to the development of rocking isolation-an attractive practical alternative for the seismic protection of tall, slender structures. This paper builds upon selected contributions published during this last half-century in an effort to bring forward the major advances together with the unique advantages of rocking isolation. The paper concludes that the concept of rocking isolation by intentionally designing a hinging mechanism that its seismic resistance originates primarily from the mobilization of the rotational inertia of its members is a unique seismic protection strategy for large, slender structures not just at the limit-state but also at the operational state.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.8
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• pp.87-94
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• 2006

In this study, nonlinear crash analyses have been conducted for the skid landing gear of a helicopter. The realistic landing gear model of the commercial helicopter (SB427) is considered. Three-dimensional dynamic finite element model with variable thickness and material plastic behavior is constructed and LS-DYNA(Ver.970) is used to conduct nonlinear transient crash analyses for different impact conditions. Characteristics of nonlinear transient responses due to the ground crash are investigated for typical structural design criteria of a skid landing gear system. In addition, comparison results for maximum crash deformations of the skid landing gear are presented and the important effect of ground friction for numerical accuracy is described.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.3 s.49
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• pp.77-84
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• 2006

Unlike homogeneous material structure, the behavior of masonry structure is not perfectly elastic even in the range of small deformations because it is a non-homogeneous and anisotropic composite structural material, consisting of masonry units, mortar, and grout. This paper proposes a simplified way of investigating the evolution of the deformation and damage of the structure subjected to a series of successive ground motions with varying shaking. Especially, the most simple but useful algorithm of Fast Fourier Transformation (FFT) has been adopted to investigate the evolution of the deformation and damage of the structure tested on the shaking table. Moreover, the development of a hi-linear curve for an equivalent SDOF system which is obtained by exploiting the frequency and stiffness relationship was discussed. Finally, some important findings related to inelastic properties of the URM are summarized.

• Geomechanics and Engineering
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• v.11 no.6
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• pp.821-845
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• 2016

Extensive researches on distribution of earthquake induced damages in different regions have shown that geological and geotechnical conditions of the local soils significantly influence behavior of alluvial areas under seismic loading. In this article, the site of Babol city which is formed up of saturated fine alluvial soils is considered as a case study. In order to reduce the uncertainties associated with earthquake resistant design of structures in this area (Babol city), the required design parameters have been evaluated with consideration of site's dynamic effects. The utilized methodology combines experimental ground ambient noise analysis, expressed in terms of horizontal to vertical (H/V) spectral ratio, with numerical one-dimensional response analysis of soil columns using DEEPSOIL software. The H/V spectral analysis was performed at 60 points, experimentally, for the region in order to estimate both the fundamental period and its corresponding amplification for the ground vibration. The investigation resulted in amplification ratios that were greater than one in all areas. A good agreement between the proposed ranges of natural periods and alluvial amplification ratios obtained through the analytical model and the experimental microtremor studies verifies the analytical model to provide a good engineering reflection of the subterraneous alluviums.

• Journal of Korean Society of Steel Construction
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• v.21 no.2
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• pp.105-113
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• 2009

To improve braced frame performance, the connection strength, stiffness, and ductility must be directly considered in the frame design. The resistance of the connection must be designed to resist seismic loads and to help provide the required system ductility. In addition, the connection stiffness affects the dynamic response and the deformation demands on the structural members and connections. In this paper, current design models for gusset plate connections are reviewed and evaluated usingthe results of past experiments. Current models are still not sufficient to provide adequate connection design guidelines and the actual stress and strain states in the gusset plate are very nonlinear and highly complex. Design engineers want simple models with beam and column elements to make an approximate estimation of system and connection performance. The simplified design models are developed and evaluated to predict connection stiffness and system behavior. These models produce reasonably accurate and reliable estimation of connection stiffness.

• The Journal of Engineering Geology
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• v.16 no.1 s.47
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• pp.1-14
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• 2006

Various measurements were carried out to estimate the modulus of deformation in two dominant rock types in Korea: granite and gneiss. Four most commonly used methods were utilized: Goodman jack tests, PS well logging, laboratory ultrasonic tests and laboratory uniaxial loading tests. Laboratory static and dynamic Young's moduli depend on the magnitude of the applied axial stress, range of Sequency used for measurement and the loading/unloading condition. As the laboratory measurement condition approaches to that in situ, the resultant moduli also appear to be comparable to that in situ. This suggests that the simulation of in situ stress condition is important when the modulus of rock is determined in the laboratory Dynamic Young's modulus is generally higher than static Young's modulus because of (micro)crack behavior in response to the stress, different range of frequency used for measurements, and the effect of the amplitude of deformation. Understanding of the relations in moduli from different measurement methods will help estimate appropriate in situ values.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.2
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• pp.1-8
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• 2020

In the case of power plant facilities, seismic stability of non-structural elements is important. In particular, Cabinet structures to which electrical equipment is attached, should have functional safety against earthquakes. Therefore, in this study the dynamic characteristics of non-structural elements inside existing power plant buildings were identified and the response level generated during dynamic behavior was analyzed. In addition, The steel plate dampers were adopted and adjusted to suit the size of the target equipment. In order to derive the optimal seismic reinforcement, the variables according to the attachment location were set and the responses were analyzed by the seismic movement input before and after reinforcement.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.1
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• pp.39-48
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• 2023

Because a railway bridge is designed over a long period of time and covers a large site, it involves various environmental factors and uncertainties. For this reason, design changes often occur, even if the design was thoroughly reviewed in the initial design stage. In particular, design changes of large-scale facilities, such as railway bridges, consume significant time and cost, and it is extremely inefficient to repeat all the procedures each time. In this study, a technique that can improve the efficiency of learning after design change was developed by utilizing the learning result before design change through transfer learning among deep-learning algorithms. For analysis, scenarios were created, and a database was built using a previously developed railway bridge deep-learning-based prediction system. The proposed method results in similar accuracy when learning only 1000 data points in the new domain compared with the 8000 data points used for learning in the old domain before the design change. Moreover, it was confirmed that it has a faster convergence speed.

• Structural Engineering and Mechanics
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• v.83 no.5
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• pp.627-644
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• 2022

In past major earthquakes (1994 Northridge, 1995 Kobe, Chi-Chi 1999, Kocaeli 1999), significant damages occurred in the liquid storage tanks. The basic failure patterns were observed to be the buckling of the tank wall and uplift of the anchorage system. The damages in the industrial facilities and nuclear power plants have caused the spread of toxic substances to the environment and significant fires. Seismic isolation can be used in liquid storage tanks to decouple the structure and decrease the structural demand in the superstructure in case of ground shaking. Previous studies on the use of seismic isolation systems on liquid storage tanks show that an isolation system reduces the impulsive response but might slightly increase the convective one. There is still a lack of understanding of the seismic response of seismically isolated liquid storage tanks considering the fluid-structure interaction. In this study, one broad tank, one medium tank, and one slender tank are selected and designed. Two- and three-dimensional elastomeric bearings are used as seismic isolation systems. The seismic performance of the tanks is then investigated through nonlinear dynamic time-history analyses. The effectiveness of each seismic isolation system on tanks' performance was investigated. Isolator tension forces, modal analysis results, hydrodynamic stresses, strains, sloshing heights and base shear forces of the tanks are compared. The results show that the total base shear is lower in 3D-isolators compared to 2D-isolators. Even though the tank wall stresses, and strains are slightly higher in 3D-isolators, they are more efficient to prevent the tension problem.