• 무역학회지
• /
• 제42권5호
• /
• pp.93-112
• /
• 2017

본 연구는 수출 중소기업의 FTA 정보학습의 역할을 실증분석하는데 목적을 두었다. 이에 중소기업 수출성과 경로에서 FTA 정보학습의 조절효과를 포함한 통합적 모형을 구축했다. 중소기업의 현지화 전략, 제품혁신 역량, FTA 정보학습의 관계를 수출성과에 연계하여 수출 중소기업 195개를 대상으로 실증분석을 시행했다. 구조방정식모형을 사용하여 경로분석을 시행했으며, 조절효과를 포함한 6개 가설을 검정했다. 분석결과 중소기업의 현지화 전략은 제품혁신 역량에 긍정적 영향을 주었다. 반면 FTA 정보학습은 유의한 결과를 보여주지 못했다. 수출성과 선행요인으로 제품혁신 역량과 FTA 정보학습은 모두 유의한 결과를 보여주었다. 조절효과의 경우 현지화 전략과 FTA 정보학습은 제품혁신 역량에 유의한 조절효과를 나타내지 못했다. 반면 제품혁신 역량과 FTA 정보학습은 중소기업 수출성과에 유의한 영향을 미치는 것으로 나타났다.

• Steel and Composite Structures
• /
• 제50권4호
• /
• pp.383-401
• /
• 2024

The research comprehensively studies the axial compression performance of T-shaped concrete-filled thin-walled steel tubular (CTST) long columns after fire exposure. Initially, a series of tests investigate the effects of heating time, load eccentricity, and stiffeners on the column's performance. Furthermore, Finite Element (FE) analysis is employed to establish temperature and mechanical field models for the T-shaped CTST long column with stiffeners after fire exposure, using carefully determined key parameters such as thermal parameters, constitutive relations, and contact models. In addition, a parametric analysis based on the numerical models is conducted to explore the effects of heating time, section diameter, material strength, and steel ratio on the axial compressive bearing capacity, bending bearing capacity under normal temperature, as well as residual bearing capacity after fire exposure. The results reveal that the maximum lateral deformation occurs near the middle of the span, with bending increasing as heating time and eccentricity rise. Despite a decrease in axial compressive load and bending capacity after fire exposure, the columns still exhibit desirable bearing capacity and deformability. Moreover, the obtained FE results align closely with experimental findings, validating the reliability of the developed numerical models. Additionally, this study proposes a simplified design method to calculate these mechanical property parameters, satisfying the ISO-834 standard. The relative errors between the proposed simplified formulas and FE models remain within 10%, indicating their capability to provide a theoretical reference for practical engineering applications.

• Structural Engineering and Mechanics
• /
• 제53권5호
• /
• pp.939-956
• /
• 2015

In this study, in order to propose an efficient model to predict the torque capacity of steel fiber reinforced concrete (SFRC) beams, the existing experimental data related to torsional response of beams is reviewed. It is observed that existing data neglects the effects of some parameters on the variation of torque capacity. Thus, an experimental research was also conducted to obtain the effects of neglected parameters. In the experimental study, a total of seventeen SFRC beams are tested against torsion. The parameters considered in the experiments are concrete compressive strength, steel fiber aspect ratio, volumetric ratio of steel fibers and longitudinal reinforcement ratio. The effect of each parameter is discussed in terms of torque versus unit angle of twist graphs. The data obtained from this experimental research is also combined with the data got from previous studies and employed in artificial neural network (ANN) analysis to estimate the ultimate torque capacity of SFRC beams. In addition to parameters considered in the experiments, aspect ratio of beam cross-section, yield strengths of both transverse and longitudinal reinforcements, and transverse reinforcement ratio are also defined as parameters in ANN analysis due to their significant effects observed in previous studies. Assessment of the accuracy of ANN analysis in estimating the ultimate torque capacity of SFRC beams is performed by comparing the analytical and experimental results. Comparisons are conducted in terms of root mean square error (RMSE), mean absolute error (MAE) and coefficient of efficiency ($E_f$). The results of this study revealed that addition of steel fibers increases the ultimate torque capacity of reinforced concrete beams. It is also found that ANN is a powerful method and a feasible tool to estimate ultimate torque capacity of both normal and high strength concrete beams within the range of input parameters considered.

• 한국지반공학회지:지반
• /
• 제13권5호
• /
• pp.145-154
• /
• 1997

말뚝재하시험방법 중 정적재하시험은 시험에 소요되는 시간과 비용측면에서 불리하여 이를 개선하기 위한 여러 가지의 시험방법이 개발되어 소개되고 있다. 국내에 소개된 시험방법으로는 동재하시험으로 불리는 항타분석기 (PDA : Pile Driving Analyzer)를 이용한 방법을 비롯하여 STATNAMIC. Osterberg cell등이 있다. 이들 중 동재하시험의 사용은 상당히 활성화되어 있는 실정이나 지반조건과 말뚝시공방법에 따라서는 지지력산정시 추가적인 해석모델을 사용하여야 보다 정확한 지지력을 평가 할 수 있는 것으로 알려져 있다. 본 논문에서는 현장에서 수행한 정적 및 동적 재하시험결과의 비교1분석으로 부터 주로 SIP말뚝에 대한 동재하시험시 발생할수 있는 기하감쇠(geometrical damping)의 영향을 고찰하였다. 해석결과로 부터 기하감쇠가 발생한 지반의 경우 CAPWAP에 의해 산정된 지지력이 정재하시험에 의한 지지력에 비해 30~60% 정도 과소평가 되었으며 이때 말뚝주면에 대한 Smith의 감쇠계수 (SSkn)가 1.0 sec/m를 초과 하였다. CAPWAP해석시 기하감쇠를 고려한 해석모델을 사용함으로써 정재하 시험결과와 근사한 지지력을 얻을 수 있었으며 SSkn값도 0.7sec/m이하의 일반적인 범위로 해석되었다.

• Steel and Composite Structures
• /
• 제22권4호
• /
• pp.797-820
• /
• 2016

This paper simulates the hysteretic behavior of steel reinforced recycled concrete (SRRC) columns under cyclic loads using OpenSees software. The effective fiber model and displacement-based beam-column element in OpenSees is applied to each SRRC columns. The Concrete01 material model for recycled aggregate concrete (RAC) and Steel02 material model is proposed to perform the numerical simulation of columns. The constitutive models of RAC, profile steel and rebars in columns were assigned to each fiber element. Based on the modelling method, the analytical models of SRRC columns are established. It shows that the calculated hysteresis loops of most SRRC columns agree well with the test curves. In addition, the parameter studies (i.e., strength grade of RAC, stirrups strength, steel strength and steel ratio) on seismic performance of SRRC columns were also investigated in detail by OpenSees. The calculation results of parameter analysis show that SRRC columns suffered from flexural failure has good seismic performance through the reasonable design. The ductility and bearing capacity of columns increases as the increasing magnitude of steel strength, steel ratio and stirrups strength. Although the bearing capacity of columns increases as the strength grade of RAC increases, the ductility and energy dissipation capacity decreases gradually. Based on the test and numerical results, the flexural failure mechanism of SRRC columns were analysed in detail. The computing theories of the normal section of bearing capacity for the eccentrically loaded columns were adopted to calculate the nominal bending strength of SRRC columns subjected to vertical axial force under lateral cyclic loads. The calculation formulas of horizontal bearing capacity for SRRC columns were proposed based on their nominal bending strength.

• 한국지반공학회지:지반
• /
• 제13권1호
• /
• pp.75-84
• /
• 1997

본 고에서는 지하공동위에 위치한 확대기초의 지지력 산정기법을 제시하였다. 지지력 산정기법의 개발을 위해서 필자에의해 개발된 3차원 탄소성 유한요소해석 프로그램을 이용하여 지하공동위에 위치한 확대기초의 지지력에 대한 매개변수 변환연구를 수행하였다. 매개변수 변환연구의 결과를 이용하여 각 경계조건의 지지력을 평가하고 이를 지지력 산정기법 개발에 필요한 데 이터 베이스로 활용하였으며, 수집된 데이터 베이스에 대한 다중회귀분석을 통해 반 경험적 지지력 산정기법을 개발하였다. 개발된 지지력 산정기법은 기존의 모형기초실험 및 유한요소해석 결과와의 비교를 통해 그 타당성이 검증되었으며, 그 결과 본 연구의 범위내에 해당하는 실제 현장문제에 효율적으로 적용될 수 있을 것으로 사료된다.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제8권9호
• /
• pp.3016-3033
• /
• 2014

The downlink performance of distributed antenna systems (DAS) with antennas selection is investigated in Rayleigh fading multicell environment, and the corresponding system capacity and bit error rate (BER) analysis are presented. Based on the moment generating function, the probability density function (PDF) and cumulative distribution function (CDF) of the effective signal to interference plus noise ratio (SINR) of the system are first derived, respectively. Then, with the available CDF and PDF, the accurate closed-form expressions of average channel capacity and average BER are further derived for exact performance evaluation. To simplify the expression, a simple closed-form approximate expression of average channel capacity is obtained by means of Taylor series expansion, with the performance results close to the accurate expression. Besides, the system outage capacity is analyzed, and an accurate closed-form expression of outage capacity probability is derived. These theoretical expressions can provide good performance evaluation for DAS downlink. It can be shown by simulation that the theoretical analysis and simulation are consistent, and DAS with antenna selection outperforms that with conventional blanket transmission. Moreover, the system performance can be effectively improved as the number of receive antennas increases.

• Advances in concrete construction
• /
• 제13권 2호
• /
• pp.163-181
• /
• 2022

To study the mechanical properties of steel reinforced recycled concrete (SRRC) filled circular steel tube columns under eccentric compression loads, this study presents a finite element model which can simulate the eccentrically compressed columns using ABAQUS software. The analytical model was established by selecting the reasonable nonlinear analysis theory and the constitutive relationship of materials in the columns. The influences of design parameters on the eccentric compressive performance of columns were also considered in detail, such as the diameter-thickness ratio of circular steel tube, replacement percentage of recycled coarse aggregate (RCA), slenderness ratio, eccentricity, recycled aggregate concrete (RAC) strength and steel strength and so on. The deformation diagram, stress nephogram and load-displacement curves of the eccentrically compressed columns were obtained and compared with the test results of specimens. The results show that although there is a certain error between the calculation results and the test results, the error is small, which shows the rationality on the numerical model of eccentrically compressed columns. The failure of the columns is mainly due to the symmetrical bending of the columns towards the middle compression zone, which is a typical compression bending failure. The eccentric bearing capacity and deformation capacity of columns increase with the increase of the strength of steel tube and profile steel respectively. Compared with profile steel, the strength of steel tube has a greater influence on the eccentric compressive performance of columns. Improving the strength of RAC is beneficial to the eccentric bearing capacity of columns. In addition, the eccentric bearing capacity and deformation capacity of columns decrease with the increase of replacement percentage of RCA. The section form of profile steel has little influence on the eccentric compression performance of columns. On this basis, the calculation formulas on the nominal eccentric bearing capacity of columns were also put forward and the results calculated by the proposed formulas are in good agreement with the test values.

• Journal of electromagnetic engineering and science
• /
• 제2권1호
• /
• pp.1-4
• /
• 2002

Performance improvement of the DS-CDMA system by the spectrum-overlap is important for better service quality or more system capacity. In this paper, an analysis thor capacity improvement is newly considered when the Lanczos chip waveform is used for the spectrum-overlapped DS-CDMA system. RC(relative capacity) is the ratio of the capacity of overlapping system to that of non-overlapping system, which is used for the expression of the capacity improvement. The optimal overlapping ratio is numerically found to make the maximum capacity improvement When the rectangular chip waveform is used far the overlapping system, maximum capacity improvement is increased by about 10% at the required BER=$10^{-3}$TEX> and the optimal overlapping ratio is 1.23. When the 95 % power bandwidth is considered for the Lanczos chip waveform, maximum capacity improvement is increased by 34.4% at overlapping ratio of 1.55 when the required BER is $10^{-3}$TEX>. The lower required BER far the better communication quality makes gradually smaller capacity improvement.

• Structural Engineering and Mechanics
• /
• 제27권4호
• /
• pp.477-499
• /
• 2007

The main purpose of this paper is to investigate the ultimate behavior of steel cable-stayed bridges with design variables and compare the validity and applicability of computational methods for evaluating ultimate load capacity of cable-stayed bridges. The methods considered in this paper are elastic buckling analysis, inelastic buckling analysis and nonlinear elasto-plastic analysis. Elastic buckling analysis uses a numerical eigenvalue calculation without considering geometric nonlinearities of cable-stayed bridges and the inelastic material behavior of main components. Inelastic buckling analysis uses an iterative eigenvalue calculation to consider inelastic material behavior, but cannot consider geometric nonlinearities of cable-stayed bridges. The tangent modulus concept with the column strength curve prescribed in AASHTO LRFD is used to consider inelastic buckling behavior. Detailed procedures of inelastic buckling analysis are presented and corresponding computer codes were developed. In contrast, nonlinear elasto-plastic analysis uses an incremental-iterative method and can consider both geometric nonlinearities and inelastic material behavior of a cable-stayed bridge. Proprietary software ABAQUS are used and user-subroutines are newly written to update equivalent modulus of cables to consider geometric nonlinearity due to cable sags at each increment step. Ultimate load capacities with the three analyses are evaluated for numerical models of cable-stayed bridges that have center spans of 600 m, 900 m and 1200 m with different girder depths and live load cases. The results show that inelastic buckling analysis is an effective approximation method, as a simple and fast alternative, to obtain ultimate load capacity of long span cable-stayed bridges, whereas elastic buckling analysis greatly overestimates the overall stability of cable-stayed bridges.