• Computers and Concrete
• /
• v.4 no.3
• /
• pp.187-206
• /
• 2007

A rational three-dimensional nonlinear finite element model is described and implemented for evaluating the behavior of high strength concrete slabs under transverse load. The concrete was idealized by using twenty-nodded isoparametric brick elements with embedded reinforcements. The concrete material modeling allows for normal (NSC) and high strength concrete (HSC), which was calibrated based on experimental data. The behavior of concrete in compression is simulated by an elastoplastic work-hardening model, and in tension a suitable post-cracking model based on tension stiffening and shear retention models are employed. The nonlinear equations have been solved using the incremental iterative technique based on the modified Newton-Raphson method. The FE formulation and material modeling is implemented into a finite element code in order to carry out the numerical study and to predict the behavior up to ultimate conditions of various slabs under transverse loads. The validity of the theoretical formulations and the program used was verified through comparison with available experimental data, and the agreement has proven to be very good. A parametric study has been also carried out to investigate the influence of different material and geometric properties on the behavior of HSC slabs. Influencing factors, such as concrete strength, steel ratio, aspect ratio, and support conditions on the load-deflection characteristics, concrete and steel stresses and strains were investigated.

• Computers and Concrete
• /
• v.9 no.6
• /
• pp.469-486
• /
• 2012

This paper presents Neuro-Fuzzy (NF) based empirical modelling of torsional strength of RC beams for the first time in literature. The proposed model is based on fuzzy rules. The experimental database used for NF modelling is collected from the literature consisting of 76 RC beam tests. The input variables in the developed rule based on NF model are cross-sectional area of beams, dimensions of closed stirrups, spacing of stirrups, cross-sectional area of one-leg of closed stirrup, yield strength of stirrup and longitudinal reinforcement, steel ratio of stirrups, steel ratio of longitudinal reinforcement and concrete compressive strength. According to the selected variables, the formulated NFs were trained by using 60 of the 76 sample beams. Then, the method was tested with the other 16 sample beams. The accuracy rates were found to be about 96% for total set. The performance of accuracy of proposed NF model is furthermore compared with existing design codes by using the same database and found to be by far more accurate. The use of NF provided an alternative way for estimating the torsional strength of RC beams. The outcomes of this study are quite satisfactory which may serve NF approach to be widely used in further applications in the field of reinforced concrete structures.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.19 no.8
• /
• pp.35-42
• /
• 2020

In discharge machining, material is removed by electrical discharge between the electrode and the workpiece. An important consideration in EDM is that the wear of the electrodes decreases the final precision of the workpiece. The edge wear of the electrodes proceeds very quickly because sparks occur more frequently at the edges with high local electrical strength. In this study, mold steel was discharged with a wedge-shaped graphite electrode to measure the edge wear of the electrode according to the depth. The electrode edge wear increased with depth during EDM and a wear model was developed. The model predicted that the edge wear can be reduced by approximately 70% using two electrodes instead of a single electrode. The model was supported by the experimental comparison of the dual electrode method and the single electrode method.

• Journal of the Society of Naval Architects of Korea
• /
• v.45 no.5
• /
• pp.538-546
• /
• 2008

In this paper, the constitutive equation is developed to analyze the characteristics of strain-induced plasticity in the range of low temperature of 316 stainless steel. The practical usefulness of the developed equations is evaluated by the comparison between experimental and numerical results. For 316 stainless steel, constitutive equations, which represent the characteristics of nonlinear material behavior under the cryogenic temperature environment, are developed using the Bodner's plasticity model. In order to predict the material behaviour such as damage accumulation, Bodner-Chan's damage model is implemented to the developed constitutive equations. Based on the developed constitutive equations, 3-D finite element analysis program is developed, and verified using experimental results.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2002.09a
• /
• pp.239-246
• /
• 2002

Viscoelastic dampers are known effective devices for response reduction under earthquakes and winds. This study addresses how to design the optimum viscoelastic dampers installed at the full scale five-story steel building and novel approach to carry out the experimental work to verify the damper performance. First, an exciter of hybrid mass-type actuator is designed, which can move the building and its mathematical model is derived. The integrated system of building-actuator is experimentally analyzed for mathematical model. Second, convex model is applied for the prediction of required additional damping ratios to reduce responses below a specified target level. Chevron-type viscoelastic dampers are manufactured and installed at the first and second inter-stories, which are optimum places for response reduction. Sine-sweep and white noise excitations, which are generated by the hybrid mass-type actuator, are applied to the full scale building without and with dampers for performance verification. The transfer function of the building with four dampers, two of them installed at each first and second inter-story, are found to be lower than that of the building with two dampers installed at the first inter-story

• Journal of the Earthquake Engineering Society of Korea
• /
• v.21 no.6
• /
• pp.311-322
• /
• 2017

In this study, the seismic performance of concrete-steel composite moment frame structures equipped with seismic retrofitting systems such as seismic reinforcement, base isolators, and bracing members, which are typical earthquake damage mitigation systems, is evaluated through nonlinear dynamic analyses. A total of five frame models were designed and each frame model was developed for numerical analyses. A total of 80 ground acceleration data were used to perform the nonlinear dynamic analysis to measure ground shear force and roof displacement, and to evaluate the behavioral performance of each frame model by measuring inter-story drift ratios. The analysis results indicate that the retrofitting device of the base isolator make a significant contribution to generating relatively larger absolute displacement than other devices due to flexibility provided to interface between ground and column base. However, the occurrence of the inter-story drift ratio, which is a relative displacement that can detect the damage of the structure, is relatively small compared with other models. On the other hand, the seismic reinforced frame model enhanced with the steel plate at the lower part of the column was found to be the least efficient.

• Journal of the Korean Society for Precision Engineering
• /
• v.22 no.11 s.176
• /
• pp.118-124
• /
• 2005

An automotive bushing is a device used in automotive suspension systems to reduce the load transmitted from the wheel to the frame of the vehicle. A bushing is a hollow cylinder, which is bonded to a solid steel shaft at its inner surface and a steel sleeve at its outer surface. The relation between the force applied to the shaft and the relative deformation of a bushing is nonlinear and exhibits features of viscoelasticity. In this paper, an automotive bushing is regarded as nonlinear viscoelastic incompressible material. Instron 8801 equipment was used for experimental res earch and ramp-to-constant displacement control test was used for data acquisition. Displacement dependent force relaxation function was obtained from the force extrapolation method and expressed as the explicit combination of time and displacement. Pipkin-Rogers model, which is the direct relation of force and displacement, was obtained and comparison studies between the experimental results and the Pipkin-Rogers results were carried out.

• Transactions of Materials Processing
• /
• v.15 no.8 s.89
• /
• pp.556-561
• /
• 2006

Most of auto-body members are composed of stamping parts. These parts have the non-uniform thickness and plastic work hardening distribution during the forming process. This paper is concerned with the side impact analysis of the ULSAB-AVC model according to the US-SINCAP in order to compare the crashworthiness between the model with and without considering the forming effect. The forming effect is ca]ciliated by one-step forming analysis for several members. The crashworthiness is investigated by comparing the deformed shape of the cabin room the energy absorption characteristics and the intrusion velocity of a car. The result of the crash analysis demonstrates that the crash mode, the load-carrying capacity and energy absorption can be affected by the forming effect. It is noted that the design of an autobody should be carried out considering the forming effect for accurate assessment of crashworthiness.

• Journal of Korean Society of Steel Construction
• /
• v.14 no.1
• /
• pp.31-40
• /
• 2002

Free vibration of a thin-walled laminated composite beam is studied. A general analytical model applicable to the dynamic behavior of a thin-walled channel section composite is developed. This model is based on the classical lamination theory, and accounts for the coupling of flexural and torsional modes for arbitrary laminate stacking sequence configuration. i.e. unsymmetric as well as symmetric, and various boundary conditions. A displacement-based one-dimensional finite element model is developed to predict natural frequencies and corresponding vibration modes for a thin-walled composite beam. Equations of motion are derived from the Hamilton's principle. Numerical results are obtained for thin-walled composite addressing the effects of fiber angle. modulus ratio. and boundary conditions on the vibration frequencies and mode shapes of the composites.

• Earthquakes and Structures
• /
• v.14 no.3
• /
• pp.203-214
• /
• 2018

Predictive demand and collapse fragility functions are two essential components of the probabilistic seismic demand analysis that are commonly developed based on statistics with enormous, costly and time consuming data gathering. Although this approach might be justified for research purposes, it is not appealing for practical applications because of its computational cost. Thus, in this paper, Bayesian regression-based demand and collapse models are proposed to eliminate the need of time-consuming analyses. The demand model developed in the form of linear equation predicts overall maximum inter-story drift of the lowto mid-rise regular steel moment resisting frames (SMRFs), while the collapse model mathematically expressed by lognormal cumulative distribution function provides collapse occurrence probability for a given spectral acceleration at the fundamental period of the structure. Next, as an application, the proposed demand and collapse functions are implemented in a seismic fragility analysis to develop fragility and consequently seismic demand curves of three example buildings. The accuracy provided by utilization of the proposed models, with considering computation reduction, are compared with those directly obtained from Incremental Dynamic analysis, which is a computer-intensive procedure.