• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.6
• /
• pp.1365-1381
• /
• 1990

A $C^{0}$ continuous displacement finite element method based on a higher-order shear deformation theory is employed in the prediction of the transient response of laminated composite plates subjected to low-velocity impact. A modified contact law was applied to calculate the contact force during impact. The discrete element chosen is a nine-noded quadrilateral with 5 degree-of-freedom per node. The Wilson-.theta. time integration algorithm is used for solving the time dependent equations of the impactor and the central difference method was adopted to perform time integration of the plate. Numerical results, including the contact force history, deflection, and velocity history, are presented. Comparisons of numerical results using a higher order theory and a first-order theory show that using a higher order theory provides more accurate results. Effects of boundary condition, impact velocity, and mass of the impactors are also discussed.d.

• Publications of The Korean Astronomical Society
• /
• v.22 no.4
• /
• pp.151-168
• /
• 2007

We have analyzed the comet records in the Korean history books: Samguksagi, Goryeosa, and Joseonwangjosillok. For a comparison, the Chinese and Japanese comet records collected by Kronk (1999) have also been analyzed. Power spectrum of the time series of the comet records is used to find periodic comets. Statistically significant periodicities in the power spectrum are detected at the periods of 38-40 years, about 76 years, and 300-400 years for all Korean, Chinese, and Japanese comet records. We have also calculated the past orbits of some comets that have been recently observed, to check whether or not they were recorded in the history books. We use a multistep method to numerically integrate the comet's orbital motion backward in time to 51 B.C. The gravitational force due to the Sun and the nine planets, non-gravitational force, and the relativistic effects have been considered. Comparison of comet's perihelion passage time and the position on the sky with the historical records shows that the comet Halley were recorded at every passage in both Goryeo and Joseon periods. The orbital motion of the comet Pons-Brooks has also been compared with the Korean records. For the comet Tempel-Tuttle, Swift-Tuttle, and Ikeya-Zhang, we have compared our calculation of the orbital motions with those of the previous studies.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2002.10a
• /
• pp.513-520
• /
• 2002

This study is for seismic analysis of building structures with ambiguous modal direction This case is revealed symmetrical building structure or the structure that isn't coincided building axis with physical axis. Seismic analysis-time history analysis, response spectrum analysis and lateral force procedure-is carried out. It is concluded that analysis method for the structure with ambiguous modal direction don't suitable for lateral force procedure. It is recommended to use the CQC method for combining modal responses to the individual components and the SRSS rule for combining responses to the two horizontal components are of nearly equal intensities.

• Wind and Structures
• /
• v.31 no.1
• /
• pp.59-73
• /
• 2020

Wind fragility analysis (WFA) of concrete chimney is often executed disregarding temperature effects. But combined wind and temperature effect is the most critical limit state to define the safety of a chimney. Hence, in this study, WFA of a 70 m tall RC chimney for combined wind and temperature effects is explored. The wind force time-history is generated by spectral representation method. The safety of chimney is assessed considering limit states of stress failure in concrete and steel. A moving-least-squares method based dual response surface method (DRSM) procedure is proposed in WFA to alleviate huge computational time requirement by the conventional direct Monte Carlo simulation (MCS) approach. The DRSM captures the record-to-record variation of wind force time-histories and uncertainty in system parameters. The proposed DRSM approach yields fragility curves which are in close conformity with the most accurate direct MCS approach within substantially less computational time. In this regard, the error by the single-level RSM and least-squares method based DRSM can be easily noted. The WFA results indicate that over temperature difference of 150℃, the temperature stress is so pronounced that the probability of failure is very high even at 30 m/s wind speed. However, below 100℃, wind governs the design.

• Steel and Composite Structures
• /
• v.25 no.1
• /
• pp.19-34
• /
• 2017

The widespread damage to steel Moment Resisting Frames (MRFs) in past major earthquakes have underscored the need to understand the nonlinear inelastic behaviour of such systems. To assess the seismic performance of steel MRF, it is essential to model the nonlinear force-deformation behaviour of beam to column joints. To determine the extent of inelasticity in a beam to column joint, nonlinear finite element analysis is generally carried out, which is computationally involved and demanding. In order to obviate the need of such elaborate analyses, a simplistic method to predict the force-deformation behaviour is required. In this study, a simple, mechanics driven, hand calculation method is proposed to obtain the forcedeformation behaviour of strong axis beam to column moment joints. The force-deformation behaviour for twenty-five interior and exterior beam to column joints, having column to beam strength ratios ranging from 1.2 to 10.99 and 2.4 to 22, respectively, have been obtained. The force-deformation behaviour predicted using the proposed method is compared with the results of finite element analyses. The results show that the proposed method predicts the force-deformation behaviour fairly accurately, with much lesser computational effort. Further the proposed method has been used to conduct Nonlinear Dynamic Time History Analyses of two benchmark frames; close correspondence of results obtained with published results establishes the usefulness and computational accuracy of the method.

• Nuclear Engineering and Technology
• /
• v.43 no.4
• /
• pp.361-374
• /
• 2011

Two types of numerical modeling techniques were considered for the dynamic response of a structure subjected to a ground acceleration. One technique is based on the equation of motion relative to ground motion, and the other is based on the equation of absolute motion of the structure and the ground. The analytic background of the former is well established while the latter has not yet been extensively verified. The latter is called a large mass method, which allocates an appropriate large mass to the ground so that it causes the ground to move according to a given acceleration time history. In this paper, through the use of a single degree-of-freedom spring-mass system, the equations of motion of the two techniques were analyzed and useful theorems are provided on the large mass method. Using simple examples, the numerical results of the two modeling techniques were compared with analytic solutions. It is shown that the theorems provide a clear insight on the large mass method.

• Earthquakes and Structures
• /
• v.7 no.6
• /
• pp.1171-1186
• /
• 2014

Damping is one of the parameters that control the performance of structures when they are subjected to seismic, wind, blast or other transient shock and vibration disturbances. By adding supplemental viscous dampers, the energy input from a transient deformation is absorbed, not only by the structure itself, but also by the supplemental dampers. The aim of this study is to evaluate the values of both damping and ductility reduction factors for steel moment resisting frames with supplemental linear viscous dampers. Two-dimensional finite element models have been established for a range of low to mid rise buildings with different parameters: number of floors; number of bays; and number of dampers with different supplemental damping ratios (from 5% to 30%). A parametric study has been performed using time history analyses and a well-documented research method (N2-method). In addition, an equation has been proposed for each reduction factor based on regression analysis for the obtained results. The results of the Time history analyses are compared with those of a modified N2-method. Moreover, a comparison with values specified in the European code EC8 and the Egyptian code ECP-201 has been performed.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.27 no.5
• /
• pp.437-450
• /
• 2014

In this study, we developed a methodology to determine the reference parameter for an aircraft impact induced risk assessment of nuclear power plant (NPP) using finite element impact analysis of containment building. The target structure used to develop the method of reference parameter selection is one of the typical Korean PWR type containment buildings. We composed a three-dimensional finite element model of the containment building. The concrete damaged plasticity model was used for the concrete material model. The steels in the tendon, rebar, and liner were modeled using the piecewise-linear stress-strain curves. To evaluate the correlations between structural response and each candidate parameter, we developed Riera's aircraft impact force-time history function with respect to the variation of the loading parameters, i.e., impact velocity and mass of the remaining fuel. For each force-time history, the type of aircraft is assumed to be a Boeing 767 model. The variation ranges of the impact velocity and remaining fuel percentage are 50 to 200m/s, and 30 to 90%, respectively. Four parameters, i.e., kinetic energy, total impulse, maximum impulse, and maximum force are proposed for candidates of the reference parameter. The wellness of the correlation between the reference parameter and structural responses was formulated using the coefficient of determination ($R^2$). From the results, we found that the maximum force showed the highest $R^2$ value in most responses in the materials. The simplicity and intuitiveness of the maximum force parameter are also remarkable compared to the other candidate parameters. Therefore, it can be concluded that the maximum force is the most proper candidate for the reference parameter to assess the aircraft impact induced risk of NPPs.

• Earthquakes and Structures
• /
• v.14 no.3
• /
• pp.229-239
• /
• 2018

Under strong ground motion, pounding can be caused because of the different dynamic properties between two adjacent buildings. Using different structural systems in two adjacent structures makes a difference in the lateral stiffness and thus changes the pounding force between them. In this paper, the effect of the structural system of adjacent buildings on the amount of force applied by pounding effects has been investigated. Moment resisting frame systems (MRFs), lateral X-bracing system (LBS), shear wall system (SWS) and dual system (DS) have been investigated. Four different cases has been modelled using finite element (FE) method. The number of stories of the two adjacent buildings is different in each case: case 1 with 6 and 4 stories, case 2 with 9 and 6 stories, case 3 with 15 and 6 stories and case 4 with 10 and 10 stories. The structures have been modelled three-dimensionally. Non-linear time history analysis has been done on the structures using the finite element software SAP2000. In order to model pounding effects, the non-linear gap elements have been used.

• Coupled systems mechanics
• /
• v.9 no.4
• /
• pp.311-323
• /
• 2020

This paper deals with the effect of the mode shapes on the dynamic response of a multi-storey frame subjected to moving train loads which are modelled as loads of constant intervals with constant velocity using the finite element method. The multi-storey frame is modelled as a number of Bernoulli-Euler beam elements. First, the first few modes of the multi-storey frame are determined. Then, the effects of force span length to beam length ratio and velocity on dynamic magnification factor (DMF) are evaluated via 3D velocity-force span length to beam length ratio-DMF graphics and its 2D projections. By using 3D and 2D graphics, the directions of critical speeds that force the structure under resonance conditions are determined. Last, the mode shapes related to these directions are determined by the time history and frequency response graphs. This study has been limited by the vibration of the frame in the vertical direction.