• Steel and Composite Structures
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• 제46권6호
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• pp.759-772
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• 2023

This manuscript presents a comprehensive mathematical model to investigate buckling stability and postbuckling response of bio-inspired composite beams with helicoidal orientations. The higher order shear deformation theory as well as the Timoshenko beam theories are exploited to include the shear influence. The equilibrium nonlinear integro-differential equations of helicoidal composite beams are derived in detail using the energy conservation principle. Differential integral quadrature method (DIQM) is employed to discretize the nonlinear system of differential equations and solve them via the Newton iterative method then obtain the response of helicoidal composite beam. Numerical calculations are carried out to check the validity of the present solution methodology and to quantify the effects of helicoidal rotation angle, elastic foundation constants, beam theories, geometric and material properties on buckling, postbuckling of bio-inspired helicoidal composite beams. The developed model can be employed in design and analysis of curved helicoidal composite beam used in aerospace and naval structures.

• Steel and Composite Structures
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• 제33권2호
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• pp.307-318
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• 2019

This is the first attempt to consider the nonlinear bending analysis of porous functionally graded (FG) thick annular and circular nanoplates resting on Kerr foundation. The size effects are captured based on modified couple stress theory (MCST). The material properties of the porous FG nanostructure are assumed to vary smoothly through the thickness according to a power law distribution of the volume fraction of the constituent materials. The elastic medium is modeled by Kerr elastic foundation which consists of two spring layers and one shear layer. The governing equations are extracted based on Hamilton's principle and two variables refined plate theory. Utilizing generalized differential quadrature method (GDQM), the nonlinear static behavior of the nanostructure is obtained under different boundary conditions. The effects of various parameters such as material length scale parameter, boundary conditions, and geometrical parameters of the nanoplate, elastic medium constants, porosity and FG index are shown on the nonlinear deflection of the annular and circular nanoplates. The results indicate that with increasing the material length scale parameter, the nonlinear deflection is decreased. In addition, the dimensionless nonlinear deflection of the porous annular nanoplate is diminished with the increase of porosity parameter. It is hoped that the present work may provide a benchmark in the study of nonlinear static behavior of porous nanoplates.

• Computers and Concrete
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• 제31권3호
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• pp.223-239
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• 2023

Geometric nonlinear performance simulation and analysis of complex modern buildings and industrial products require high-performance shell elements. Balancing multiple aspects of performance in the one geometric nonlinear analysis element remains challenging. We present a new shell element, flat shell DKMGQ-CR (Co-rotational Discrete Kirchhoff-Mindlin Generalized Conforming Quadrilateral), for linear and geometric nonlinear analysis of both thick and thin shells. The DKMGQ-CR shell element was developed by combining the advantages of high-performance membrane and plate elements in a unified coordinate system and introducing the co-rotational formulation to adapt to large deformation analysis. The effectiveness of linear and geometric nonlinear analysis by DKMGQ-CR is verified through the tests of several classical numerical benchmarks. The computational results show that the proposed new element adapts to mesh distortion and effectively alleviates shear and membrane locking problems in linear and geometric nonlinear analysis. Furthermore, the DKMGQ-CR demonstrates high performance in analyzing thick and thin shells. The proposed element DKMGQ-CR is expected to provide an accurate, efficient, and convenient tool for the geometric nonlinear analysis of shells.

• 한국전산구조공학회논문집
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• 제33권2호
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• pp.103-111
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• 2020

최근 건축구조물에서 전이슬래브 시스템의 사용이 증가하고 있다. 하지만 과도한 전이슬래브의 두께로 인한 경제적, 시공적인 문제가 많이 발생하고 있다. 따라서, 본 연구에서는 피트층의 설비 공간을 활용하여 전이슬래브의 두께를 절감하기 위하여 역드랍 패널을 적용한 전이슬래브 시스템을 고려하였다. 역드랍 패널을 사용하여 전이슬래브의 2면 전단강도를 증진시킴으로써 전이슬래브의 두께를 줄이고자 하였다. 따라서, 역드랍 패널을 이용한 전이슬래브 시스템의 유효성을 검증하고 전단거동을 조사하기 위하여 다양한 설계변수에 대한 역드랍 패널을 적용한 전이슬래브-기둥 접합부의 전단거동을 기존연구에서 검증된 비선형 FEM 해석방법을 사용하여 분석하였다. 최종적으로 비선형 FEM 해석결과와 기존의 2면 전단강도 평가식으로 예측한 전단강도를 비교·분석하여 기존 평가식의 역드랍 패널을 적용한 전이슬래브-기둥 접합부의 2면 전단강도 평가에 대한 유효성을 검증하였다.

• 한국전산구조공학회논문집
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• 제31권6호
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• pp.283-291
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• 2018

본 연구는 지진에 저항하는 부재인 비보강 조적벽체로 구성된 건물의 내진성능평가에 활용되는 비선형 정적해석을 위한 비보강 조적벽체의 해석모델을 수립하고자 하였다. 본 연구의 해석모델은 비보강 조적벽체의 휨거동을 모사하기 위한 파이버 요소와 비보강 조적벽체의 전단에 대한 응답을 예측하기 위한 전단스프링 요소로 구성된다. 본 논문은 먼저 제안하고 있는 모델의 형상에 대해서 설명하고, 기존에 행해진 조적조 프리즘의 실험결과로부터 얻은 응력-변형률 곡선을 근거로 파이버와 전단스프링 요소의 물성치에 대한 결정 방법을 설명한다. 제시하고 있는 모델은 비선형 정적 해석결과와 다른 연구자들에 의해 수행된 실험결과를 비교하여 타당성을 검증한다. 해당 모델은 최대강도, 초기강성, 그리고 이들로부터 얻어지는 비보강 조적벽체의 하중-변위 곡선을 적절하게 모사하고 있다. 또한, 해석모델이 비보강 조적벽체의 파괴모드를 예측할 수 있는 것으로 나타난다.

• 한국지진공학회논문집
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• 제16권2호
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• pp.15-24
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• 2012

본 논문은 전단벽과 슬래브, 인방보의 연결부재로 구성되는 독특한 구조형식으로 이루어진 국내 철근콘크리트(RC)조 공동주택의 지진거동을 정확하게 평가하기 위한 방법을 제시하기 위한 기초연구이다. 이를 위하여 인방보의 유무에 따른 RC조 전단벽식 부분구조 실험체 2개에 대하여 선형 스프링모델에 의한 비선형 정적해석을 실시하고 기존의 실험결과와 비교 분석하여 그 신뢰성을 검증 하였다. 인방보가 없는 실험체의 경우, 해석결과가 실험결과에 의한 비선형 거동을 정확히 모사하고 있는 것으로 나타났다. 반면, 인방보가 있는 실험체의 경우, 해석결과의 경우, 정방향 가력시 실험결과 보다 작은 실험체의 변형으로 인방보에 의한 커플링 효과를 기대할 수 없게 되면서, 해석결과가 실험결과보다 재하시의 동일 변형에서의 내력과 잔류변형 등을 작게 평가하는 것으로 나타났다.

• 한국전산구조공학회논문집
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• 제29권6호
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• pp.547-554
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• 2016

본 논문에서는 개구부가 있는 철근콘크리트 전단벽의 전단강도를 산정하기 위해 수정압축장 이론에 기반을 둔 비선형 유한요소해석을 수행하였다. 철근콘크리트 전단벽의 전단강도에서 개구부의 영향을 분석하기 위해 개구부 주변 정착길이 내 철근들에 대한 철근비를 해석 모델에서 감소시켰으며, 비선형 유한요소해석은 기존 문헌에 제시된 시험 결과와의 비교를 통해 검증되었다. 실험 결과와의 비교를 통해 개구부 주변 철근들의 정착길이를 고려한 비선형 유한요소해석의 경우 철근콘크리트 전단벽의 전단강도 예측에 있어 개구부의 영향을 잘 반영한 것으로 나타났다. 이에 반해, 현행 설계기준들은 전단강도를 합리적으로 예측하지 못하는 것으로 나타났다. 본 논문은 향후 기존 철근콘크리트 전단벽에 개구부를 설치하는 경우, 전단벽의 합리적인 전단강도 예측에 유용할 것으로 기대된다.

• Computers and Concrete
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• 제16권6호
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• pp.825-846
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• 2015

In this study, shear tests on steel fiber reinforced-prestressed concrete (SFR-PSC) members were conducted with test parameters of the concrete compressive strength, the volume fraction of steel fibers, and the level of effective prestress. The SFR-PSC members showed higher shear strengths and stiffness after diagonal cracking compared to the conventional prestressed concrete (PSC) members without steel fibers. In addition, their shear deformational behavior was measured using the image-based non-contact displacement measurement system, which was then compared to the results of nonlinear finite element analyses (NLFEA). In the NLFEA proposed in this study, a bi-axial tensile behavior model, which can reflect the tensile behavior of the steel fiber-reinforced concrete (SFRC) in a simple manner, was introduced into the smeared crack truss model. The NLFEA model proposed in this study provided a good estimation of shear behavior of the SFRPSC members, such as the stiffness, strengths, and failure modes, reflecting the effect of the key influential factors.

• Computers and Concrete
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• 제8권6호
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• pp.735-755
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• 2011

The capability of a multi-directional fixed smeared crack constitutive model to simulate the flexural/punching failure modes of fiber reinforced concrete (FRC) laminar structures is discussed. The constitutive model is implemented in a computer program based on the finite element method, where the FRC laminar structures were simulated according to the Reissner-Mindlin shell theory. The shell is discretized into layers for the simulation of the membrane, bending and out-of-plane shear nonlinear behavior. A stress-strain softening diagram is proposed to reproduce, after crack initiation, the evolution of the normal crack component. The in-plane shear crack component is obtained using the concept of shear retention factor, defined by a crack-strain dependent law. To capture the punching failure mode, a softening diagram is proposed to simulate the decrease of the out-of-plane shear stress components with the increase of the corresponding shear strain components, after crack initiation. With this relatively simple approach, accurate predictions of the behavior of FRC structures failing in bending and in shear can be obtained. To assess the predictive performance of the model, a punching experimental test of a module of a façade panel fabricated with steel fiber reinforced self-compacting concrete is numerically simulated. The influence of some parameters defining the softening diagrams is discussed.

• Structural Engineering and Mechanics
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• 제38권1호
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• pp.1-25
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• 2011

A new nonlinear model was developed to evaluate the shear resistance of steel fiber-reinforced concrete beams (SFRCB) using linear genetic programming (LGP). The proposed model relates the shear strength to the geometrical and mechanical properties of SFRCB. The best model was selected after developing and controlling several models with different combinations of the influencing parameters. The models were developed using a comprehensive database containing 213 test results of SFRC beams without stirrups obtained through an extensive literature review. The database includes experimental results for normal and high-strength concrete beams. To verify the applicability of the proposed model, it was employed to estimate the shear strength of a part of test results that were not included in the modeling process. The external validation of the model was further verified using several statistical criteria recommended by researchers. The contributions of the parameters affecting the shear strength were evaluated through a sensitivity analysis. The results indicate that the LGP model gives precise estimates of the shear strength of SFRCB. The prediction performance of the model is significantly better than several solutions found in the literature. The LGP-based design equation is remarkably straightforward and useful for pre-design applications.