• Title/Summary/Keyword: Critical buckling stress

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Stability and dynamic analyses of SW-CNT reinforced concrete beam resting on elastic-foundation

  • Bourada, Fouad;Bousahla, Abdelmoumen Anis;Tounsi, Abdeldjebbar;Bedia, E.A. Adda;Mahmoud, S.R.;Benrahou, Kouider Halim;Tounsi, Abdelouahed
    • Computers and Concrete
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    • v.25 no.6
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    • pp.485-495
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    • 2020
  • This paper, presents the dynamic and stability analysis of the simply supported single walled Carbon Nanotubes (SWCNT) reinforced concrete beam on elastic-foundation using an integral first-order shear deformation beam theory. The condition of the zero shear-stress on the free surfaces of the beam is ensured by the introduction of the shear correction factors. The SWCNT reinforcement is considered to be uniform and variable according to the X, O and V forms through the thickness of the concrete beam. The effective properties of the reinforced concrete beam are calculated by employing the rule of mixture. The analytical solutions of the buckling and free vibrational behaviors are derived via Hamilton's principle and Navier method. The analytical results of the critical buckling loads and frequency parameters of the SWCNT-RC beam are presented in the form of explicit tables and graphs. Also the diverse parameters influencing the dynamic and stability behaviors of the reinforced concrete beam are discussed in detail.

Structural response of rectangular composite columns under vertical and lateral loads

  • Sevim, Baris
    • Steel and Composite Structures
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    • v.25 no.3
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    • pp.287-298
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    • 2017
  • The present study aims to determine the structural response of full scaled rectangular columns under both of vertical and lateral loads using numerical methods. In the study, the composite columns considering full concrete filled circular steel tube (FCFRST) and concrete filled double-skin rectangular steel tube (CFDSRST) section types are numerically modelled using ANSYS software. Vertical and lateral loads are applied to models to assess the structural response of the composite elements. Also similar investigations are done for reinforced concrete rectangular (RCR) columns to compare the results with those of composite elements. The analyses of the systems are statically performed for both linear and nonlinear materials. In linear static analyses, both of vertical and lateral loads are applied to models as only one step. However in nonlinear analyses, while vertical loads are applied to model as only one step, lateral loads are applied to systems as step by step. The displacement and stress changes in some critical nodes and sections and contour diagrams are reported by graphs and figures. At the end of the study, it is demonstrated that the nonlinear models reveal more accurate result then those of linear models. Also, it is highlighted that composite columns provide more and more safety, ductility compared to reinforced concrete column.

Innovative approach to determine the minimum wall thickness of flexible buried pipes

  • Alzabeebee, Saif;Chapman, David N.;Faramarzi, Asaad
    • Geomechanics and Engineering
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    • v.15 no.2
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    • pp.755-767
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    • 2018
  • This paper uses a finite element based approach to provide a comprehensive understanding to the behaviour and the design performance of buried uPVC pipes with different diameters. It also investigates pipes with good and poor haunch support and proposes minimum safe wall thicknesses for these pipes. The results for pipes with good haunch support showed that the maximum pipe wall stress and deformation increase as the diameter increased. The results for pipes with poor haunch support showed an increase in the dependency of the developed vertical displacement on the haunch support as the diameter or the backfill height increased. Additionally, poor haunch support was found to increase the soil pressure, with the effect increasing as the diameter increased. The design of uPVC pipes for both poor and good haunch support was found to be governed by critical buckling. A key outcome is a new design chart for the minimum wall thickness, which enables the robust and economic design of buried uPVC pipes. Importantly, the methodology adopted in this study can also be applied to the design of flexible pipes manufactured from other materials, buried under different conditions and subjected to different loading arrangements.

A Study on the Nonlinear Instability Behavior of Hybrid Structures(I) - Characteristic of Static In-Plane Torsional Buckling by Initial Shape Imperfection- (Hybrid 구조물의 비선형 불안정 거동에 관한 연구(I) -초기형상 불완전에 의한 정적 면내비틀림 좌굴 특성-)

  • Kim, Seung Deog;Son, Su Deok;Kim, Hyung Seok;Kang, Moon Myung
    • Journal of Korean Society of Steel Construction
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    • v.13 no.5
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    • pp.587-597
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    • 2001
  • The structural system that discreterized continuous shells is frequently used to make dome-type structures and these structures show the unstable phenomena by snap-through or bifurcation when a load level reaches certain critical value. The characteristic structural behaviour of a cable dome shows a strong nonlinearity and very sensitive according to the initial imperfection. In this study the shape finding problem by applying initial tension stress is investigated and using this the unstable phenomena of perfectly shaped and initially imperfected shape model by external forces are examined to grasp the unstable behavior of cable dome using the Geiger-type model.

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Flexural Strength Design Equation of Concrete Filled Steel Tube(CFT) Column Reinforced by Carbon Fiber Sheet (탄소섬유쉬트로 보강한 콘크리트 충전강관(CFT) 기둥의 휨내력식)

  • Park, Jai-Woo;Hong, Young-Kyun;Hong, Gi-Soup
    • Journal of the Earthquake Engineering Society of Korea
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    • v.12 no.3
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    • pp.29-36
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    • 2008
  • The TR-CFT(Transversely Reinforced Concrete Filled Steel Tube) column is proposed to control or at least delay the state of local buckling at the critical section by wrapping the CFT columns with a carbon fiber sheet. In this study, an equation to determine the flexural strength of TR-CFT is proposed. The ACI-318 code, in which the contribution of the confining effect in the concrete filled steel tube is not appropriately accounted for, may be conservative. Therefore, flexural strength design equations for CFT columns and TR-CFT columns are proposed based on the concrete strain-stress curve, which contributes to the confining effect. Finally, the predicted results for the CFT and TR-CFT columns are shown to be in good agreement with actual test results.

Optimization of the cross-section regarding the stability of nanostructures according to the dynamic analysis

  • Qiuyang Cheng;H. Elhosiny Ali;Ibrahim Albaijan
    • Advances in concrete construction
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    • v.15 no.4
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    • pp.215-228
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    • 2023
  • The vibrational behavior of nanoelements is critical in determining how a nanostructure behaves. However, combining vibrational analysis with stability analysis allows for a more comprehensive knowledge of a structure's behavior. As a result, the goal of this research is to characterize the behavior of nonlocal nanocyndrical beams with uniform and nonuniform cross sections. The nonuniformity of the beams is determined by three distinct section functions, namely linear, convex, and exponential functions, with the length and mass of the beams being identical. For completely clamped, fully pinned, and cantilever boundary conditions, Eringen's nonlocal theory is combined with the Timoshenko beam model. The extended differential quadrature technique was used to solve the governing equations in this research. In contrast to the other boundary conditions, the findings of this research reveal that the nonlocal impact has the opposite effect on the frequency of the uniform cantilever nanobeam. Furthermore, since the mass of the materials employed in these nanobeams is designed to remain the same, the findings may be utilized to help improve the frequency and buckling stress of a resonator without requiring additional material, which is a cost-effective benefit.

Structural Design and Analysis for Carbon/Epoxy Composite Wing of A Small Scale WIG Vehicle (소형 위그선의 탄소/에폭시 복합재 주익의 구조 설계 및 해석에 관한 연구)

  • Park, Hyun-Bum;Kang, Kuk-Jin;Kong, Chang-Duk
    • Composites Research
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    • v.19 no.5
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    • pp.12-19
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    • 2006
  • In this paper, conceptual structural design of the main wing for a small scale WIG(Wing in Ground Effect) among high speed ship projects, which will be a high speed maritime transportation system for the next generation in Rep. of Korea, was performed. The Carbon/Epoxy material was selected for the major structure, and the skin-spar with a foam sandwich structural type was adopted for improvement of lightness and structural stability. As a design procedure for the present study, firstly the design load was estimated through the critical flight load case study, and then flanges of the front and rear spars from major bending loads and the skin and the spar webs from shear loads were preliminarily sized using the netting rule and the rule of mixture. Stress analysis was performed by a commercial FEA code, NASTRAN. From the stress analysis results for the first designed wing structure, it was confirmed that the upper skin between the front spar and the rear spar was unstable fer the buckling. Therefore in order to solve this problem, a middle spar and the foam sandwich type structure at the skin and the web were added. After design modification, the structural safety and stability for the final design feature was confirmed. In addition to this, the insert bolt type structure with eight high strength bolts to fix the wing structure to the fuselage was adopted for easy assembly and removal as well as in consideration of more than 20 years fatigue life.

A Study on the Stability of the Single-Layer Latticed Dome during Erection Using the Step-Up Method (Step-Up 공법에 의한 단층래티스돔의 시공시 안정성 연구)

  • Koo, Choong-Mo;Jung, Hwan-Mok;Kim, Cheol-Hwan
    • Journal of Korean Association for Spatial Structures
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    • v.12 no.4
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    • pp.109-118
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    • 2012
  • The large-space single-layer lattice dome is relatively simpler in terms of the arrangement of the various framework members and of the design of the junction than the multi-layered lattice dome, can reduce the numbers and quantity of the framework members, and has the merit of exposing the beauty of the framework as it stands. The single-layer lattice dome, however, requires a stability investigation of the whole structure itself, along with an analysis of the stress of the framework members, because an unstable phenomenon called "buckling" occurs when its weight reaches critical levels. Many researchers have systematically conducted researches on the stability evaluation of the single-layer lattice dome. No construction case of a single-layer lattice dome with a 300-m-long span, however, has yet been reported anywhere in the world. The large-space dome structure is difficult to erect due to the gigantic span and higher ceiling compared with other common buildings, and its construction cost is generally huge. The method of erecting a structure causes major differences in the construction cost and period. Therefore, many researchers have been conducting various researches on the method of erecting such structure. The step-up method developed by these authors can reduce the construction cost and period to a great extent compared with the other general methods, but the application of this method inevitably requires the development of system supports in the center section as well as pre-existing supports in the boundary sections. In this research, the safety during the construction of a single-layer lattice dome with 300-m-long span using pre-existing materials was examined in the aspect of structural strength, and the basic data required for manufacturing the supports in the application of the step-up method developed by these authors during the erection of the roof structure were obtained.

Static analysis of nonlinear FG-CNT reinforced nano-composite beam resting on Winkler/Pasternak foundation

  • Mostefa Sekkak;Rachid Zerrouki;Mohamed Zidour;Abdelouahed Tounsi;Mohamed Bourada;Mahmoud M Selim;Hosam A. Saad
    • Advances in nano research
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    • v.16 no.5
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    • pp.509-519
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    • 2024
  • In this study, the static analysis of carbon nanotube-reinforced composites (CNTRC) beams resting on a Winkler-Pasternak elastic foundation is presented. The developed theories account for higher-order variation of transverse shear strain through the depth of the beam and satisfy the stress-free boundary conditions on the top and bottom surfaces of the beam. To study the effect of carbon nanotubes distribution in functionally graded (FG-CNT), we introduce in the equation of CNT volume fraction a new exponent equation. The SWCNTs are assumed to be aligned and distributed in the polymeric matrix with different patterns of reinforcement. The rule of mixture is used to describe the material properties of the CNTRC beams. The governing equations were derived by employing Hamilton's principle. The models presented in this work are numerically provided to verify the accuracy of the present theory. The analytical solutions are presented, and the obtained results are compared with the existing solutions to verify the validity of the developed theories. Many parameters are investigated, such as the Pasternak shear modulus parameter, the Winkler modulus parameter, the volume fraction, and the order of the exponent in the volume fraction equation. New results obtained from bending and stresses are presented and discussed in detail. From the obtained results, it became clear the influence of the exponential CNTs distribution and Winkler-Pasternak model improved the mechanical properties of the CNTRC beams.