• Title/Summary/Keyword: 등가선형강성

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P-△ Analysis for Design of Reinforced Concrete Slender Columns (철근 콘크리트 장주 설계를 위한 P-△ 해석)

  • Lee, Jae Hoon
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.12 no.4_1
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    • pp.87-96
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    • 1992
  • Moment Magnifier Method has been generally used in estimation of total column moment induced by geometric nonlinearity for reinforced concrete slender column design, however second order analysis such as P-${\Delta}$ method has been recommended by Code for better result. Member stiffness estimation is the most significant factor for accuracy of second order analysis. Equivalent Column stiffness based on theoretically obtained moment-curvature-thrust relationship has been proposed and the analytical results of the proposed method, MacGregor-Hage Method, Furlong's Method, and Moment Magnifier Method are compared with experimentally obtained data.

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Equivalent Linear Stiffness Matrix of Pile Foundation for the Seismic Response Analysis of Bridges (교량의 지진응답해석을 위한 말뚝기초의 등가 선형 강도행렬)

  • 박형기;조양희
    • Journal of the Earthquake Engineering Society of Korea
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    • v.5 no.3
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    • pp.1-8
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    • 2001
  • Seismic design forces for bridge components may be determined by modifying elastic member forces of design earthquakes using appropriate response modification factors according to the national design code of bridges Modeling technique of pile foundation system is one of the important parameters which greatly affects the results in the process of the elastic seismic analysis of a bridge system with pile foundation. In this paper, a approximate and simplified modeling technique of a pile foundation system for the practical purposes is presented. The modeling technique is based on the stiffnesses of pile foundation during earthquake. The horizontal stiffnesses are determined from the resistance-deflection curves derived from the results of dynamic field tests using cyclic loads and the vertical stiffness includes the effects of the end bearing capacities and side friction of piles as well as the pile compliances under the expected vertical load level. The applicability of the proposed technique has been validated through the some example bridge analyses.

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Seismic Performance and Flexural Over-strength of Circular RC Column (원형 RC 기둥의 내진성능과 휨 초과강도)

  • Ko, Seong-Hyun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.17 no.5
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    • pp.49-58
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    • 2013
  • Eight small scale circular reinforced concrete columns were tested under cyclic lateral load with constant axial load. Test specimens were designed with 4.5 aspect ratio. The selected test variables are longitudinal steel ratio, transverse steel ratio, yielding strength of longitudinal steel and axial load ratio. The test results of columns with different longitudinal steel ratio, transverse steel ratio and axial load ratio showed different seismic performance such as equivalent damping ratio, residual displacement and effective stiffness. It was found that the column with low strength of longitudinal steel showed significantly reduced seismic performance, especially for equivalent damping ratio and residual displacement. The regulation of flexural over-strength is adopted by Korea Bridge Design Specifications (Limited state design, 2012). The test results are compared with nominal strength, result of nonlinear moment-curvature analysis and the design specifications such as AASHTO LRFD and Korea Bridge Design Specifications (Limited state design).

Experimental Vibration Analysis of a Super-Structure Model Using Curve Fitting Method (곡선맞춤법을 이용한 선체상부구조 모델의 진동해석)

  • Oh, Chang-Geun;Je, Hae-Kwang;Park, Sok-Chu
    • Journal of Navigation and Port Research
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    • v.26 no.3
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    • pp.281-288
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    • 2002
  • It might be true that both experimental and analytic techniques have been developed in the vibration analysis end engineering. It could not be said, however, that the experimental method has been also developed as much as analytic method, such as Finite Element Method One of the reason is that computation time becomes longer and that the solution often diverges depending on the choice of initial value in solving nonlinear equation. The equation in experimental modal analysis is usually composed of the nonlinear term of natural frequency and modal damping ratio, and the linear one of equivalent stiffness. In this study, the nonlinear terms were solved first, and then the linear term was obtained. The experimental modal parameters were estimated, applying the developed experimental modal analysis curve-fitting method to the super-structure model. In addition, the number of modes and modal damping ratio could be easily determined by the developed program with the application of graphical techniques and with easy handling button.

Nonlinear Subgrade Reaction Analysis of the Soil-Pile System for Mooring Dolphin Structures (계류식 돌핀구조물에 대한 지반-말뚝계의 비선형 지반반력 해석)

  • 오세붕;이진학;이상순;김동수;정태영
    • Journal of the Korean Geotechnical Society
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    • v.15 no.2
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    • pp.3-16
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    • 1999
  • The objective of BMP( Barge Mounted Plant) project is to construct plants on mooring floating structures at sea. To analyze the pile behavior under mooring dolphins, generally, axial or lateral behavior of soil-pile system is evaluated by using a nonlinear subgrade reaction method which models the pile as a structural element and the soil as series of nonlinear springs along the depth. As a result, load-displacement curves at pile head can be solved by finite difference method and the equivalent stiffness of bottom boundaries of dolphin structure is evaluated. In this study off-shore site investigation was performed on the marine area of Koje Island and axial and lateral load transfer curves of the ground were modeled with depth. The subgrade reaction analysis was performed for piles under axial or lateral loadings, and the required penetration depth and section of the pile were determined. Subsequently, the spring boundaries under the dolphin structure could be modeled from the calculated load-displacement curve and then the dynamic response of the dolphin structure was analyzed reasonably by considering ground conditions. The analysis considering the stiffness of the soil-pile system has resulted in larger displacement amplitudes than those for rigid foundations. Furthermore, moment distributions of the casing were dependent on the soil-pile system so that deformable foundation induces the larger moment of top section of casing and the smaller moment of pile head.

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Stability Analysis of Steel Cable-stayed Bridges under Construction Stage (폐합 전 강사장교의 안정성 해석)

  • Kim, Seung-Jun;Shim, Kyung-Suk;Won, Deok-Hee;Cho, Sun-Kyu;Kang, Young-Jong
    • Journal of Korean Society of Steel Construction
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    • v.23 no.1
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    • pp.99-111
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    • 2011
  • This paper presents an investigation of the structural stability of cable-stayed bridges in the construction stage, using geometric nonlinear finite-element analysis and considering various geometric nonlinearities, such as the sag effect of the cables, the P-${\Delta}$ effects of the girder and mast, and the large displacement effect. Initial shape analysis and construction-stage analysis were performed to determine the equilibrium of the structure in the construction stage. After that, geometric nonlinear analysis was performed to study structural stability. In this study, the weight of the derrick crane and the key segment were considered the main external loads, which were applied to the tip of the center span. The cable arrangement type and the stiffness ratios of the girder and mast were considered the main parameters of the analytic research. Based on the results of the analysis, the change in the buckling mode and critical load factors with respect to the cable arrangement type and the stiffness ratios of the girder and mast was investigated. The buckling modes of the steel cable-stayed bridges in the construction stage were classified, and the ranges of the stiffness ratios of the girder and mast, which show these classified buckling modes, were suggested.

The Role of the Plastic Flow Rules in the Elasto-Plastic Formulation of Joint behaviour (절리거동의 탄소성해석에서 소성유동법칙의 역할)

  • 이연규
    • Tunnel and Underground Space
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    • v.10 no.2
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    • pp.173-179
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    • 2000
  • The influence of the plastic flow rules on the elasto-plastic behaviour of a discrete joint element was investigated by performing the numerical direct shear tests under both constant normal displacement and normal displacement conditions. The finite interface elements obeying Plesha’s joint constitutive law was used to allow the relative motion of the rock blocks on the joint surface. Realistic results were obtained in the tests adopting the non-associated flow rule, while the associated flow rule overestimated the joint dilation. To overcome the computational drawbacks coming from the non-symmetric element stiffness matrix in the conventional non-associated plasticity, the symmetric formulation of the tangential stiffness matrix for a non-associated joint element was proposed. The symmetric elasto-plastic matrix it derived by assuming an imaginary equivalent joint with associated flow rule which shows the same plastic response as that of original Joint with non-associated flow rule. The validity of the formulation was confirmed through the numerical direct shear tests under constant normal stress condition.

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Reliability of Nonlinear Direct Spectrum Method with Mixed Building Structures (복합구조물에 대한 비선형 직접스펙트럼법의 신뢰성)

  • 강병두;김재웅
    • Journal of the Earthquake Engineering Society of Korea
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    • v.7 no.2
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    • pp.75-84
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    • 2003
  • Most structures are expected to deform beyond the limit of linearly elastic behavior when subjected to strong ground motion. Seismic evaluation of structure requires an estimation of the structural performance in terms of displacement demand imposed by earthquakes on the structure. The nonlinear response history analysis(NRHA) among various nonlinear analysis methods is the most accurate to compute seismic performance of structures, but it is time-consuming and necessitate more efforts. The nonlinear approximate methods, which is more practical and reliable tools for predicting seismic behavior of structures, are extensively studied. Among them, the capacity spectrum method(CSM) is conceptually simple, but the iterative procedure is time-consuming and may sometimes lead to no solution or multiple solutions. This paper considers a nonlinear direct spectrum method(NDSM) to evaluate seismic performance of mixed building structures without iterative computations, given dynamic property T from stiffness skeleton curve and nonlinear pseudo acceleration $A_{y}$/g and/or ductility ratio $\mu$ from response spectrum. The nonlinear response history analysis has been performed and analyzed with various earthquakes for estimation of reliability and practicality of NDSM with mixed building structures.

A Study on the Optimum Design of Stiffened Plates under Combined Loads (조합하중이 작용하는 보강평판의 최적설계 연구)

  • 원종진
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.5
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    • pp.1059-1068
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    • 1990
  • The minimum weight design for the simply-supported eccentrically stiffened plates subjected to combined loads is studied according to the stiffening configuration. The optimal programming is accomplished by formulating the design requirements in terms of a mathematical programming problem, and by using the gradient projection algorithm. The Huber type equilibrium equation is used as the governing equation for the overall buckling. The overall buckling of stiffened plates and the local buckling of the unstiffened plate between stiffeners and the stiffeners themselves are used as behavior constraints. Results of design examples for the orthogonally stiffening case compared with those of the other study support that the present study is feasible. Design examples for the symmetrically oblique stiffening case are presented and the results indicate that a significant improvement in design efficiency may be achieved through symmetrically oblique stiffening compared to the orthogonal stiffening under the combined loading condition.

Shell Finite Element of Reinforced Concrete for Internal Pressure Analysis of Nuclear Containment Building (격납건물 내압해석을 위한 철근콘크리트 쉘 유한요소)

  • Lee, Hong-Pyo;Choun, Young-Sun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.29 no.6A
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    • pp.577-585
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    • 2009
  • A 9-node degenerated shell finite element(FE), which has been developed for assessment of ultimate pressure capacity and nonlinear analysis for nuclear containment building is described in this paper. Reissner-Midnlin(RM) assumptions are adopted to develop the shell FE so that transverse shear deformation effects is considered. Material model for concrete prior to cracking is constructed based on the equivalent stress-equivalent strain relationship. Tension stiffening model, shear transfer mechanism and compressive strength reduction model are used to model the material behavior of concrete after cracking. Niwa and Aoyagi-Yamada failure criteria have been adapted to find initial cracking point in compression-tension and tension-tension region, respectively. Finally, the performance of the developed program is tested and demonstrated with several examples. From the numerical tests, the present results show a good agreement with experimental data or other numerical results.