• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.5
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• pp.39-52
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• 1993

For the lateral-torsional buckling analysis of the thin-walled space frame and circular arch with the unsymmetric cross section, the tangent stiffness matrices are derived by introducing Vlasov's assumption for the thin-walled beam and using the principle of virtual displacement. In the cases of the unrestrained torsion and the restrained torsion, the elastic and geometric stiffness matrices corresponding to semitangential rotation and semitangential moment are evaluated by using the Hermitian polynomials as the shape function. In order to illustrate the accuracy and convergence characteristics of the derived formulations, numerical examples for the lateral-torsional buckling analysis of the hinged circular arch under pure bending and uniform compression are presented and compared with the analytic solutions of references.

• Explosives and Blasting
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• v.31 no.1
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• pp.1-10
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• 2013

In blasting demolition, a method would be chosen among many depends on shape and system of a structure and its surround. To demolish using explosives a structure, which is asymmetric and with high aspect ratio, pre-weakening, explosive locations, detonating delay, and surround conditions are needed to be considered in front to design blasting demolition plan. In this study, to over turn asymmetric and high aspect ratio structure in safe, a simulation using a software named Extreme Loadings for Structures, ELS, had performed. In results, it is achieved optimized pre-weakening shapes and locations, which prevent kick back motion of the structure when it collapse, by analyzing moment distribution caused by pre-weakening. And of structural collapse and by minimizing asymmetric structure's torsional moment. Also, after the demolition, simulation results are also compared with actual collapse behavior. In results, it is confirmed the accuracy of collapse behaviour simulation results, and in blasting demolition, kick back motion can be controled by adjusting pre-weakening shape and location, and the torsional moment of an asymmetric structure also can be solved by optimizing detonation locations and its time intervals.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.03a
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• pp.321-328
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• 2003

The objective of this study is to investigate the seismic response of high-rise RC bearing-wall structures with irregularity. For this purpose, three 1:12 scale 17-story reinforced concrete model structures were constructed according to the similitude law, in which the upper 15 stories have a bearing-wall system while the lower 2-story frames have three different layouts of the plan : The first one is a moment-resisting frame system, the second has a infilled shear wall with symmetric plan and the third has a infilled shear wall with eccentricity, Then, these models were subjected to a series of earthquake excitations. The test results show the followings: 1) the existence of shear wall reduced greatly shear deformation at the piloti frame, but has almost the negligible effect on the reduction of the overturning-moment angle, 2) the frame with shear wall resists most of overturning moment in severe earthquake, 3) the torsional behavior is almost independent of the translational, 4) the absorbed energy due to the overturning deformation has the largest portion in the total absorbed energy.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.7
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• pp.3495-3501
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• 2013

The cross-sections of continuous multi-span beams are sometimes suddenly increased or stepped at the interior supports of continuous beams to resist high negative moments. This paper investigates inelastic lateral-torsional buckling of monosymmetric stepped I-beams subjected to pure bending. A three-dimensional finite-element program ABAQUS and a regression program were used to analytically develop new design equation. The flange thickness ratio, flange width ratio and stepped length ratio were considered as parameters of this study. The combined effects of residual stresses and geometric imperfection on inelastic lateral-torsional buckling of beams are considered. The proposed solution can be easily used to calculation for inelastic lateral torsional buckling strengths of monosymmetric beams with doubly stepped cross sections and to develop new design equations for inelastic lateral-torsional buckling resistances of stepped beams.

• Structural Engineering and Mechanics
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• v.55 no.3
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• pp.655-674
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• 2015

In this paper, a new and simplified method is presented in which the natural frequencies of the uniform and non-uniform beams are calculated through simple mathematical relationships. The various vibration problems such as: Rayleigh beam under variable axial force, axial vibration of a bar with and without end discrete spring, torsional vibration of a bar with an attached mass moment of inertia, flexural vibration of the beam with laterally distributed elastic springs and also flexural vibration of the beam with effects of viscose damping are investigated. The governing differential equations are first obtained and then; according to a harmonic vibration, are converted into single variable equations in terms of location. Through repetitive integrations, the governing equations are converted into weak form integral equations. The mode shape functions of the vibration are approximated using a power series. Substitution of the power series into the integral equations results in a system of linear algebraic equations. The natural frequencies are determined by calculation of a non-trivial solution for system of equations. The efficiency and convergence rate of the current approach are investigated through comparison of the numerical results obtained with those obtained from other published references and results of available finite element software.

• Structural Engineering and Mechanics
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• v.64 no.1
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• pp.11-21
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• 2017

It has been observed in the past that, the reinforced concrete (RC) bridge columns are very often subjected to torsional moment in addition to flexure and shear during seismic vibration. Ignoring torsion in the design can trigger unexpected shear failure of the columns (Farhey et al. 1993). Performance based seismic design is a popular design philosophy which calls for accurate prediction of the hysteresis behavior of structural elements to ensure safe and economical design under earthquake loading. However, very few investigations in the past focused on the development of analytical models to accurately predict the response of RC members under cyclic torsion. Previously developed hysteresis models are not readily applicable for torsional loading owing to significant pinching and stiffness degradation associated with torsion (Wang et al. 2014). The present study proposes an improved polygonal hysteresis model which can accurately predict the hysteretic behavior of RC circular and square columns under torsion. The primary curve is obtained from mechanics based softened truss model for torsion. The proposed model is validated with test data of two circular and two square columns. A good correlation is observed between the predicted and measured torque-twist behavior and dissipated energy.

• Steel and Composite Structures
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• v.4 no.4
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• pp.281-301
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• 2004

The paper begins by presenting a unified variational approach to the lateral-torsional buckling (LTB) analysis of doubly symmetric prismatic and tapered thin-walled beams with open cross-sections, which accounts for the influence of the pre-buckling deflections. This approach (i) extends the kinematical assumptions usually adopted for prismatic beams, (ii) consistently uses shell membrane theory in general coordinates and (iii) adopts Trefftz's criterion to perform the bifurcation analysis. The proposed formulation is then applied to investigate the influence of the pre-buckling deflections on the LTB behaviour of prismatic and web-tapered I-section simply supported beams and cantilevers. After establishing an interesting analytical result, valid for prismatic members with shear centre loading, several elastic critical moments/loads are presented, discussed and, when possible, also compared with values reported in the literature. These numerical results, which are obtained by means of the Rayleigh-Ritz method, (i) highlight the qualitative differences existing between the LTB behaviours of simply supported beams and cantilevers and (ii) illustrate how the influence of the pre-buckling deflections on LTB is affected by a number of factors, namely ($ii_1$) the minor-to-major inertia ratio, ($ii_2$) the beam length, ($ii_3$) the location of the load point of application and ($ii_4$) the bending moment diagram shape.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.2
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• pp.58-64
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• 2019

This paper describes the analysis of dynamic characteristics and prediction of the stiffness for the joint between structural members. In the process of deriving the governing equations, the stiffness values responsible for the moment and shear force were modelled by using linear and torsional springs in the middle of a clamped-clamped beam. The sensitivities of the natural frequency and modal assurance criterion were investigated as a function of the dimensionless linear and torsional spring stiffness. The reliability of the predictions for the linear and torsional stiffness values was verified by the inverse computations of the stiffness matrix. The predictive and exact theoretical stiffness values were compared for the stiffness element in the finite element formulation, and their results show an excellent correlation. It is strongly anticipated that although the proposed methodology is currently limited to the analytical utilization, it will provide a useful tool to estimate unknown joint stiffness values based on the experimental natural frequency and mode shape.

• Transactions of the Korean Society of Mechanical Engineers
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• v.1 no.2
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• pp.73-81
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• 1977

It is well known fact that there is a theoretical analogous relation ship in terms of differential equation between the stress distribution of a bar under pure torsional moment and the deflection of a membrane subjected to a uniform pressure. This relationship has been applied to the experimental determination of torsional stresses with troublesome and elaborative measuring procedure since Griffith's invention of the soap-film apparatus. In this paper, the soap-film was replaced by a highly polished steel plate and whole visualable deflectional contour-line-map was able to obtain by using Michelson Interferometer with Ne-He Gas Laser lignt source enabling to determine the stress distribution in the vicnity of the symmetrical inner-boundary in a section. Experimental results were satisfactory and the margin of error in the measurement was lower than 1%.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.6
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• pp.78-86
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• 2010

This paper aims to investigate the natural frequency of a cracked cantilever L-beams with a coupled bending and torsional vibrations. In addition, a theoretical method for detection of the crack position and size in a cantilever L-beams is presented based on natural frequencies. Based on the Euler-Bernoulli beam theory, the equation of motion is derived by using extended Hamilton's Principle. The dynamic transfer matrix method is used for calculation of a exact natural frequencies of L-beams. In order to detect the crack of L-beams, the effect of spring coefficients for bending moment and torsional force is included. In this study, the differences between the actual data and predicted positions and sizes of crack are less than 0.5% and 6.7% respectively.