• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1993년도 가을 학술발표회 논문집
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• pp.290-295
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• 1993

The purpose of the present study is to propose a realistic method to analyze the prestressed concrete members subjected to pure torsion. The present study device a method to realistically take into account the tensile stiffness of concrete after cracking. The effect of biaxial compressive and tensile loading on the compressive and tensile strength of concrete is also taken into account in the present model. The present model can predict not only the service load behavior, but also up to the behavior of ultimate load stages. The comparison of the present theory with experimental data indicates that the proposed model dipicts reasonably well the actual behavior of prestressed concrete members.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.585-590
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• 2001

Turbine blade is subject to torsional load by torsion-mount, centrifugal load by rotation of rotor and repeated bending load by steam pressure. Turbine with partially cracked blade has normal working condition at initial repair time but vibratory working condition at middle repair time due to crack growth. Finite element analysis on turbine blade indicates that repeated bending load out of all loads is the most important factor on fatigue strength of turbine blade. Therefore, this study shows root mean square roughness has linear relation with stress intensity factor range in 12% Cr steel and can predict loading condition of fractured turbine blade.

• Computers and Concrete
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• 제10권5호
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• pp.489-505
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• 2012

This paper presents a simplified grid beam model for simulating the nonlinear response of reinforced concrete flat-plate structures. The beam elements are defined with nonlinear behavior for bending moment and torsion. The flexural stiffness and torsional strength of the beam elements are defined based on experimental data to implicitly account for slab two-way bending effects. A failure criterion that considers the interaction between the punching strength and slab flexural behavior is incorporated in the model. The effects of bond-slip of slab reinforcement on connection stiffness are examined. The proposed grid beam model is validated by simulating large-scale tests of slab-column connections subjected to concentric gravity loading and unbalanced moment. This study also determines the critical parameters for a hysteretic model used to simulate flat-plates subjected to cyclic lateral loading.

• Structural Engineering and Mechanics
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• 제23권4호
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• pp.339-352
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• 2006

Observing the unique stress-strain curves of the superelastic shape memory alloy (SMA) in tension and compression, the primary intention of this study is to investigate the behavior of the shafts made of the same material, under torsional loading-unloading cycles for large angle of twist. Experiments have been performed for the superelastic SMA shafts with different unsupported lengths and angles of twist and the results are compared with those of stainless steel (SUS304) shafts under similar test conditions. As expected for the superelastic SMA, the residual strains are small enough after each cycle and consequently, the hysteresis under loading-reverse loading is much narrower than that for the SUS304. For large angle of twists, the torsional strength of the superelastic SMA increases nonlinearly and exceeds that of SUS304. Most interestingly, the slender solid superelastic SMA shafts are found to buckle when acted upon torsion for large angle of twist.

• Structural Engineering and Mechanics
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• 제58권4호
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• pp.661-676
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• 2016

This paper presents an elastic/plastic model that neglects strain hardening during loading, but accounts for the Bauschinger effect. These mathematical features of the model represent reasonably well the actual behavior of several materials such as high strength steels. Previous attempts to describe the behavior of this kind of materials have been restricted to a class of boundary value problems in which the state of stress in the plastic region is completely controlled by the yield stress in tension or torsion. In particular, the yield stress is supposed to be constant during loading and the forward plastic strain reduces the yield stress to be used to describe reversed yielding. The new model generalizes this approach on plane stress problems assuming that the material obeys the von Mises yield criterion during loading. Then, the model is adopted to describe reversed yielding in thin hollow discs subject to external pressure.

• 한국공간구조학회논문집
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• 제22권2호
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• pp.29-37
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• 2022

The collapse of reinforced concrete (RC) frame buildings is mainly caused by the failure of columns. To prevent brittle failure of RC column, numerous studies have been conducted on the seismic performance of strengthened RC columns. Concrete jacketing method, which is one of the retrofitting method of RC members, can enhance strength and stiffness of original RC column with enlarged section and provide uniformly distributed lateral load capacity throughout the structure. The experimental studies have been conducted by many researchers to analyze seismic performance of seismic strengthened RC column. However, structures which have plan and vertical irregularities shows torsional behavior, and therefore it causes large deformation on RC column when subjected to seismic load. Thus, test results from concentric cyclic loading can be overestimated comparing to eccentric cyclic test results, In this paper, two kinds of eccentric loading pattern was suggested to analyze structural performance of RC columns, which are strengthened by concrete jacketing method with new details in jacketed section. Based on the results, it is concluded that specimens strengthened with new concrete jacketing method increased 830% of maximum load, 150% of maximum displacement and changed the failure modes of non-strengthened RC columns.

• 한국강구조학회 논문집
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• 제16권5호통권72호
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• pp.529-541
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• 2004

콘크리트 충전 강관에 대한 기존의 연구는 단일 압축상태, 휨모멘트 상태, 편심 압축력 상태의 연구만이 행해 졌을 뿐 압축력과 비틀림이 조합된 응력 상태에 대한 연구는 거의 이루어지지 않고 있다. 따라서 본 연구에서는 압축력과 비틀림을 받는 원형 CFT 부재의 거동에 대한 특성을 살펴보고 합리적인 해석법을 연구하였다. 원형 CFT부재가 압축력과 비틀림을 받을 경우의 압축 강도와 비틀림 강도를 결정하는데 중요 요소인 구속효과와 부착 응력에 의한 스파이럴 효과를 본 모델에 고려하였다. 이를 위하여 단일 압축응력을 받을 경우 원형 강관에 의해 구속된 콘크리트 코어에 대한 연구가 선행되었다. 또한 비틀림을 받을 경우는 비틀림에 의한 크랙이 콘크리트의 표면을 따라 발생하게 된다. 크랙 발생이후 비틀림을 계속 받게 되면 크랙은 나선형태로 진전되어 콘크리트가 솟아 나오려 하나 강관과 콘크리트 사이의 부착 응력에 의해 억제 되게 된다. 이러한 이유 때문에 코어 콘크리트는 압축응력을 받게 되고 강관만 인장응력을 받게 되는데 이러한 영향 효과를 실제적으로 고려하였다. 연구 결과는 기존의 실험결과와 비교하였으며 제안된 이론은 압축력과 비틀림을 받는 원형 CFT부재의 실제 거동을 합리적으로 설명하고 있다.

• Steel and Composite Structures
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• 제37권2호
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• pp.117-136
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• 2020

Curved steel-concrete composite box girder has been widely adopted in urban overpasses and ramp bridges. In order to investigate its mechanical behavior under complicated and combined bending, shear and torsion load, two large-curvature composite box girders with interior angles of 25° and 45° were tested under static hogging moment. Based on the strain and deflection measurement on critical cross-sections during the static loading test, the failure mode, cracking behavior, load-displacement relationship, and strain distribution in the steel plate and rebar were investigated in detail. The test result showed the large-curvature composite box girders exhibited notable shear lag in the concrete slab and steel girder. Also, the constraint torsion and distortion effect caused the stress measured at the inner side of the composite beam to be notably higher than that of the outer side. The strain distribution in the steel web was approximately linear; therefore, the assumption that the plane section remains plane was approximately validated based on strain measurement at steel web. Furthermore, the full-process non-linear elaborate finite element (FE) models of the two specimens were developed based on commercial FE software MSC.MARC. The modeling scheme and constitutive model were illustrated in detail. Based on the comparison between the FE model and test results, the FE model effectively simulated the failure mode, the load-displacement curve, and the strain development of longitudinal rebar and steel girder with sufficient accuracy. The comparison between the FE model and the test result validated the accuracy of the developed FE model.

• Computers and Concrete
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• 제13권2호
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• pp.291-308
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• 2014

A nonlinear, three-dimensional finite element analysis was conducted on six intermediate L-shaped spandrel beams using the "ANSYS Civil FEM" program. The beams were constructed and tested in the laboratory under eccentric concentrated load at mid-span to obtain a combined loading case: torsion, bending, and shear. The reinforcement case parameters were as follows: without reinforcement, with longitudinal reinforcement only, and reinforced with steel bars and stirrups. All beams were tested under two different combined loading conditions: T/V = 545 mm (high eccentricity) and T/V = 145 mm (low eccentricity). The failure of the plain beams was brittle, and the addition of longitudinal steel bars increased beam strength, particularly under low eccentricity. Transverse reinforcement significantly affected the strength at high eccentricities, that is, at high torque. A program can predict accurately the behavior of these beams under different reinforcement cases, as well as under different ratios of combined loadings. The ANSYS model accurately predicted the loads and deflections for various types of reinforcements in spandrel beams, and captured the critical crack regions of these beams.

• 대한기계학회논문집A
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• 제24권6호
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• pp.1446-1455
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• 2000

Fatigue crack initiation and propagation behavior under cyclic biaxial loading has been investigated using thin-walled tubular specimen with a hole. Two types of biaxial loading system, i.e. cyclic tensile loading with super-imposed static torsional load and cyclic torsional loading with superimposed static tensile load, with various values of the biaxial loading ratio, $\tau$ s/ $\sigma$ max (or $\tau$ max/ $\sigma$s) were employed. Fatigue tests show that fatigue crack near the hole initiates and propagates at 900 and 450 direction to the longitudinal direction of the specimen under cyclic tensile and torsion loading with static biaxial stress, respectively, and the static biaxial stress doesn't have any great influence on fatigue crack initiation and growth direction. Stress analysis near the hole of the specimen shows that the crack around the hole initiates along the plane of maximum tangential stress range. Fatigue crack growth rates were evaluated as functions of equivalent stress intensity factor range, strain energy density factor range and crack tip opening displacement vector, respectively. It is shown that the biaxial mode fatigue crack growth rates can be relatively consistently predicted with these cyclic parameters.