• Title/Summary/Keyword: axial stiffness

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Residual static strength of cracked concrete-filled circular steel tubular (CFCST) T-joint

  • Cui, M.J.;Shao, Y.B.
    • Steel and Composite Structures
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    • v.18 no.4
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    • pp.1045-1062
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    • 2015
  • Concrete-filled circular t steel tubular joints (CFSTJs) in practice are frequently subjected to fluctuated loadings caused by wind, earthquake and so on. As fatigue crack is sensitive to such cyclic loadings, assessment on performance of CFSTJs with crack-like defect attracts more concerns because both high stress concentration at the brace/chord intersection and welding residual stresses along weld toe cause the materials in the region around the intersection to be more brittle. Once crack initiates and propagates along the weld toe, tri-axial stresses in high gradient around the crack front exist, which may bring brittle fracture failure. Additionally, the stiffness and the load carrying capacity of the CFSTJs with crack may decrease due to the weakened connection at the intersection. To study the behaviour of CFSTJs with initial crack, experimental tests have been carried out on three full-scale CFCST T-joints with same configuration. The three specimens include one uncracked joint and two corresponding cracked joints. Load-displacement and load-deformation curves, failure mode and crack propagation are obtained from the experiment measurement. According to the experimental results, it can be found that he load carrying capacity of the cracked joints is decreased by more than 10% compared with the uncracked joint. The effect of crack depth on the load carrying capacity of CFCST T-joints seems to be slight. The failure mode of the cracked CFCST T-joints represents as plastic yielding rather than brittle fracture through experimental observation.

A nonlinear model for ultimate analysis and design of reinforced concrete structures

  • Morfidis, Konstantinos;Kiousis, Panos D.;Xenidis, Hariton
    • Computers and Concrete
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    • v.14 no.6
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    • pp.695-710
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    • 2014
  • This paper presents a theoretical and computational approach to solve inelastic structures subjected to overloads. Current practice in structural design is based on elastic analysis followed by limit strength design. Whereas this approach typically results in safe strength design, it does not always guarantee satisfactory performance at the service level because the internal stiffness distribution of the structure changes from the service to the ultimate strength state. A significant variation of relative stiffnesses between the two states may result in unwanted cracking at the service level with expensive repairs, while, under certain circumstances, early failure may occur due to unexpected internal moment reversals. To address these concerns, a new inelastic model is presented here that is based on the nonlinear material response and the interaction relation between axial forces and bending moments of a beam-column element. The model is simple, reasonably accurate, and computationally efficient. It is easy to implement in standard structural analysis codes, and avoids the complexities of expensive alternative analyses based on 2D and 3D finite-element computations using solid elements.

Prestressed concrete bridges with corrugated steel webs: Nonlinear analysis and experimental investigation

  • Chen, Xia-chun;Bai, Zhi-zhou;Zeng, Yu;Jiang, Rui-juan;Au, Francis T.K.
    • Steel and Composite Structures
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    • v.21 no.5
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    • pp.1045-1067
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    • 2016
  • Concrete bridges with corrugated steel webs and prestressed by both internal and external tendons have emerged as one of the promising bridge forms. In view of the different behaviour of components and the large shear deformation of webs with negligible flexural stiffness, the assumption that plane sections remain plane may no longer be valid, and therefore the classical Euler-Bernoulli and Timoshenko beam models may not be applicable. In the design of this type of bridges, both the ultimate load and ductility should be examined, which requires the estimation of full-range behaviour. An analytical sandwich beam model and its corresponding beam finite element model for geometric and material nonlinear analysis are developed for this type of bridges considering the diaphragm effects. Different rotations are assigned to the flanges and corrugated steel webs to describe the displacements. The model accounts for the interaction between the axial and flexural deformations of the beam, and uses the actual stress-strain curves of materials considering their stress path-dependence. With a nonlinear kinematical theory, complete description of the nonlinear interaction between the external tendons and the beam is obtained. The numerical model proposed is verified by experiments.

Mechanical Behavior of Slender Concrete-Filled Fiber Reinforced Polymer Columns

  • Choi Sokhwan;Lee Myung;Lee Sung-Woo
    • Journal of the Korea Concrete Institute
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    • v.16 no.4 s.82
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    • pp.565-572
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    • 2004
  • The mechanical behavior of concrete-filled glass fiber reinforced polymer columns is affected by various factors including concrete strength, stiffness of tube, end confinement effect, and slenderness ratio of members. In this research the behavior of slender columns was examined both experimentally and analytically. Experimental works include 1) compression test with 30cm long glass fiber composite columns under different end confinement conditions, 2) uni-axial compression test for 7 slender columns, which have various slenderness ratios. Short-length stocky columns gave high strength and ductility revealing high confinement action of FRP tubes. The strength increment and strain change were examined under different end confinement conditions. With slender columns, failure strengths, confinement effects, and stress-strains relations were examined. Through analytical work, effective length was computed and it was compared with the amount of reduction in column strength, which is required to predict design strength with slender specimens. This study shows the feasibility of slender concrete-filled glass fiber reinforced polymer composite columns.

Development of a Bellows Finite Element for the Analysis of Piping System (배관시스템 해석을 위한 벨로우즈 유한요소의 개발)

  • 고병갑;박경진;이완익
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.6
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    • pp.1439-1450
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    • 1995
  • Bellows is a familiar component in piping systems as it provides a relatively simple means of absorbing thermal expansion and providing system flexibility. In routine piping flexibility analysis by finite element methods, bellows is usually considered to be straight pipe runs modified by an appropriate flexibility factor; maximum stresses are evaluated using a corresponding stress concentration factor. The aim of this study is to develop a bellows finite element, which similarly includes more complex shell type deformation patterns. This element also does not require flexibility or stress factors, but evaluates more detailed deformation and stress patterns. The proposed bellows element is a 3-D, 2-noded line element, with three degrees of freedom per node and no bending. It is formulated by including additional 'internal' degrees of freedom to account for the deformation of the bellows corrugation; specifically a quarter toroidal section of the bellows, loaded by axial force, is considered and the shell type deformation of this is include by way of an approximating trigonometric series. The stiffness of each half bellows section may be found by minimising the potential energy of the section for a chosen deformation shape function. An experiment on the flexibility is performed to verify the reliability for bellows finite element.

Evaluation of the Cochlear Electrode Behavior in the 3D Human Cochlea Model by FEM Analysis (3차원 달팽이관 모델에서의 인공와우 전극의 거동에 대한 유한요소해석)

  • 임윤섭;박세익;김용협;오승하;김성준
    • Journal of Biomedical Engineering Research
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    • v.25 no.3
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    • pp.207-215
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    • 2004
  • A finite element analysis is used in this study to model 6 kinds of electrode by a genetic program in order to evaluate the mechanical effect on the 3D human cochlea model and the behavior of electrode. Human cochlea is modeled by the spiral-approximation method and the shape of scala tympani is extracted from the mid section of the human cochlea. Contact pressure at the tip and the insertion force are found to be highest when the wires stack horizontally. Axial rotation of electrode is minimal comparing with the stimulating current spread. The results indicate that the electrode stiffness is important to minimize the trauma.

A Study on the Reinforced Method of Doubler Plate in Ship Hull Structure (선박 이중판의 보강법 연구)

  • HAM JUH-HYEOK
    • Journal of Ocean Engineering and Technology
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    • v.17 no.5 s.54
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    • pp.39-47
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    • 2003
  • A study of the structural strength evaluation on the doubler plate, considering various load cases that were subjected to in-plane and out of plane combined load, has been performed through the systematic evaluation process. In order to estimate the proper static strength of doubler plate for various load cases, elasto-plastic large deflection analysis is introduced, including the contact effect between main plate and doubler. The characteristics of stiffness and strength variation are discussed, based on the results. In order to compare the doubler structure with the original strength of main plate, without doubler, simple formulas for the evaluation of the equivalent flat plate thickness are derived for each load case, respectively, based on the additional series of analysis of flat plate structure. Using these derived equations, the thickness change of an equivalent flat plate is analyzed according to the variation of various design parameters of doubler platesome design guides are suggested in order to maintain the original strength of main plate without doubler reinforcement. Finally, correlation between derived equivalent flat plate formula and the developed buckling strength formulas are discovered, and these relations are formulated for the future development of simple strength evaluation formula of general doubler plate structure.

Analytical Study on Behaviour of Plane Steel Frame with Semi-Rigid Beam-to-Column Connection (반강접 접합부를 갖는 평면 강골조의 거동에 관한 해석적 연구)

  • Kim, Jong Sung
    • Journal of Korean Society of Steel Construction
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    • v.21 no.5
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    • pp.483-492
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    • 2009
  • In this study, nonlinear analysis of steel plane frame was performed using the refined plastic hinge method of advanced analysis techniques. In deterioration of stiffness in plastic zone, influences by flexural bending, residual stress, geometrical non-linearity, and semi-rigid connection are considered. And also, further reduced tangent modulus was used for geometrical non-linearity, top and seat angle were chosen for semi-rigid connection. Furthermore, 3 parameter power model was used for moment-rotation behaviour of beam to column connection. The loading conditions are combined with axial and lateral force and the inverse triangle distribution of lateral and eight type of analytical models were used in analysis. The results of analyses were compared with semi-rigid and rigid connection on behaviour of numerical analysis models. And also, the behaviors of frame with changes of semi-rigidity were analyzed by using the results obtained from MIIDAS-GENw.

Behavior of High Strength Reinforced Concrete Wide Beam-Column Joint with Slab (슬래브가 있는 고강도 철근 콘크리트 넓은 보-기둥 접합부의 거동)

  • 최종인;안종문;신성우;박성식;이범식;양지수
    • Proceedings of the Korea Concrete Institute Conference
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    • 2002.05a
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    • pp.493-498
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    • 2002
  • An experimental investigation was conducted to study the behavior of high-strength RC wide beam-column joints with slab subjected to reversed cyclic loads under constant axial load. Six half scale interior wide beam-column assemblies representing a portion of a frame subjected to simulated seismic loading were tested, including three specimens without slab and three specimens with slab. The primary variables were compressive strength of concrete( $f_{ck}$ =240, 500kgf/c $m^2$), the ratio of the column-to-beam flexural capacity( $M_{r}$=2$\Sigma$ $M_{c}$$\Sigma$ $M_{b}$ ; 0.77-2.26), extended length of the column concrete($\ell$$_{d}$ ; 0, 9.6, 30cm), ratio of the column-to-beam width(b/H ; 1.54, 1.67). Test results are shown that (1) the behavior of specimen using high-strength concrete satisfied the required minimum ductile capacity according to increase the compressive strength, (2). In the design of the wide beam-column joints, one should be consider the effects of slab stiffness which is ignored in the current design code and practice.ice.e.e.

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Analysis of Structural Characteristics of HDPE Pipe for Manganese Lifting Test (근해역 양광시험을 위한 HDPE Pipe의 구조특성 연구)

  • Lee, Jae-Hwan;Yoon, Chi-Ho
    • Journal of Ocean Engineering and Technology
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    • v.25 no.6
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    • pp.86-90
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    • 2011
  • The mining of imitated manganese noodles in 1000 m of seawater is planned for 2012. Thus, it is necessary to prepare the lifting pipes to be used for the test. Because of storage and expense constraints, flexible and economic HDPE pipe is being considered, making it necessary to test the structural safety. Material, pressure-chamber tests and finite element analysis of HDPE pipe for the 1000-m depth were performed. The tangential stiffness of HDPE was obtained through tension and three-point bending material tests and used for a structural analysis. FEA results show that the current sample pipe segment is safe for 1000 m of water pressure, and the stress result is also within the safe value. From the current results, the HDPE pipe seems to be acceptable only for the currently suggested constraints. However, more numerical and pressure tests need to be considered by applying additional physical conditions such as gravitational and hydrodynamic loads, external and internal fluid pressure, axial force induced ship motion, and heavy pump pressure to determine future usage.