• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.153-160
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• 2001

In this study, the size effect on axial compressive strength for concrete members was experimentally investigated. Experiment of mode I failure, which is one of the two representative compressive failure modes, was carried out by using double cantilever beam specimens. By varying the eccentricity of applied loads with respect to the axis on each cantilever and the initial crack length, the size effect of axial compressive strength of concrete was investigated, and new parameters for the modified size effect law (MSEL) were suggested using least square method (LSM). The test results show that size effect appears for axial compressive strength of cracked specimens. For the eccentricity of loads, the influence of tensile and compressive stress at the crack tip are significant and so that the size effect is present. In other words, if the influence of tensile stress at the crack tip grows up, the size effect of concrete increases. And the effect of initial crack length on axial compressive strength is present, however, the differences with crack length are not apparent because the size of fracture process zone (FPZ) of all specimens in the high-strength concrete is similar regardless of differences of specimen slenderness.

• Smart Structures and Systems
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• v.20 no.6
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• pp.709-728
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• 2017

This disquisition proposes a nonlocal strain gradient beam theory for thermo-mechanical dynamic characteristics of embedded smart shear deformable curved piezoelectric nanobeams made of porous electro-elastic functionally graded materials by using an analytical method. Electro-elastic properties of embedded curved porous FG nanobeam are assumed to be temperature-dependent and vary through the thickness direction of beam according to the power-law which is modified to approximate material properties for even distributions of porosities. It is perceived that during manufacturing of functionally graded materials (FGMs) porosities and micro-voids can be occurred inside the material. Since variation of pores along the thickness direction influences the mechanical and physical properties, so in this study thermo-mechanical vibration analysis of curve FG piezoelectric nanobeam by considering the effect of these imperfections is performed. Nonlocal strain gradient elasticity theory is utilized to consider the size effects in which the stress for not only the nonlocal stress field but also the strain gradients stress field. The governing equations and related boundary condition of embedded smart curved porous FG nanobeam subjected to thermal and electric field are derived via the energy method based on Timoshenko beam theory. An analytical Navier solution procedure is utilized to achieve the natural frequencies of porous FG curved piezoelectric nanobeam resting on Winkler and Pasternak foundation. The results for simpler states are confirmed with known data in the literature. The effects of various parameters such as nonlocality parameter, electric voltage, coefficient of porosity, elastic foundation parameters, thermal effect, gradient index, strain gradient, elastic opening angle and slenderness ratio on the natural frequency of embedded curved FG porous piezoelectric nanobeam are successfully discussed. It is concluded that these parameters play important roles on the dynamic behavior of porous FG curved nanobeam. Presented numerical results can serve as benchmarks for future analyses of curve FG nanobeam with porosity phases.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.284-293
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• 2016

One of the most efficient procedures for the solution of partial differential equations is the method of differential quadrature. The differential quadrature method (DQM) has been applied to a large number of cases to overcome the difficulties of complex algorithms of computer programming, as well as the excessive use of storage due to the conditions of complex geometry and loading. The in-plane vibrations of curved beams with extensibility of the arch axis, including the effects of rotatory inertial and shear deformation, are analyzed by the DQM. The fundamental frequencies are calculated for members with various slenderness ratios, shearing flexibilities, boundary conditions, and opening angles. The results are compared with the numerical results obtained by other methods for cases in which they are available. The DQM gives good mathematical precision even when only a limited number of grid points is used, and new results according to diverse variations are also suggested.

• Journal of Korean Society of Steel Construction
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• v.18 no.2
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• pp.225-237
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• 2006

Based on the study conducted by Kim et al. (205a, b), an improved stability design method for evaluating the effective buckling lengths of beam-column members is proposed herein, using system elastic/inelastic buckling analysis and second-order elastic analysis. For this purpose, the stress-strain relationship of a column is inversely formulated from the reference load-carrying capacity proposed in design codes, so as to derive the tangent modulus of a column as a function of the slenderness ratio. The tangent stiffness matrix of a beam-column element is formulated using the so-called "stability functions," and elastic/inelastic buckling analysis Effective buckling lengths are then evaluated by extending the basic concept of a single simply-supported column to the individual members as one component of a whole frame structure. Through numerical examples of several structural systems and loading conditions, the possibilities of enhancement in stability design for frame structures are addressed by comparing their numerical results obtained when the present design method is used with those obtained when conventional stability design methods are used.

• Journal of Korean Society of Steel Construction
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• v.23 no.2
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• pp.169-177
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• 2011

This paper presents the results of the systematic finite element analysis of the in-plane bending moment of T-joints subjected to cyclic loadings. T-joints were fabricated using high-strength, circular, hollow sections. Three-dimensional, nonlinear finite element models of the welded T-joints were constructed to investigate the strength, rotational-stiffness characteristics, and failure modes. A wide scope of structural behaviors explain the influence of the joint geometric parameters, such as the chord and brace wall slenderness ratios and the ratio of the brace to the chord diameter, as well as the yield strength ratios and compressive-chord-stress effects on the ultimate in-plane bending moment capacity of the T-joint.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.12
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• pp.970-978
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• 2002

The differential equations governing free vibrations of the elastic arches with unsymmetric axis are derived in Cartesian coordinates rather than in polar coordinates. in which the effect of rotatory inertia is included. Frequencies and mode shapes are computed numerically for parabolic arches with both clamped ends and both hinged ends. Comparisons of natural frequencies between this study and SAP 2000 are made to validate theories and numerical methods developed herein. The convergent efficiency is highly improved under the newly derived differential equations in Cartesian coordinates. The lowest four natural frequency parameters are reported, with and without the rotatory inertia, as functions of three non-dimensional system parameters the rise to chord length ratio. the span length to chord length ratio, and the slenderness ratio. Also typical mode shapes of vibrating arches are presented.

• Structural Engineering and Mechanics
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• v.67 no.2
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• pp.207-217
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• 2018

In past years, numerous problems have vexed engineers with regard to buckling, corrosion, bending, and overloading in damaged steel structures. This article sets out to investigate the possible effects of carbon fiber reinforced polymer (CFRP) and steel plates for retrofitting deficient steel square hollow section (SHS) columns. The effects of axial loading, stiffness, axial displacement, the position and shape of deficient region on the length of steel SHS columns, and slenderness ratio are examined through a detailed parametric study. A total of 14 specimens was tested for failure under axial compression in a laboratory and simulated using finite element (FE) analysis based on a numerical approach. The results indicate that the application of CFRP sheets and steel plates also caused a reduction in stress in the damaged region and prevented or retarded local deformation around the deficiency. The findings showed that a deficiency leads to reduced load-carrying capacity of steel SHS columns and the retrofitting method is responsible for the increase in the load-bearing capacity of the steel columns. Finally, this research showed that the CFRP performed better than steel plates in compensating the axial force caused by the cross-section reduction due to the problems associated with the use of steel plates, such as in welding, increased weight, thermal stress around the welding location, and the possibility of creating another deficiency by welding.

• International Journal of High-Rise Buildings
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• v.8 no.3
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• pp.177-183
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• 2019

This paper describes the structural design of a 212 m tall building currently under construction in the Tokiwabashi District Redevelopment Project facing Tokyo Station. In this project there was a requirement to rationally solve many issues arising from the conditions of the redevelopment project. In particular, the following two points were considered to be important from the point of view of structural design. 1) To provide an overhang frame with the perimeter columns on the lower stories inclined, in order to enable a typical floor area that greatly exceeded the limitations of the underground structure shape. 2) To provide high grade seismic performance for the office buildings to be constructed on prime city center land. LSCVCS (Lower Stories Concentrated Vibration Control System) was proposed as the method of rationally designing the overhang frame, which is an extremely disadvantageous element in the structural scheme of the tall building with a large slenderness ratio. LSCVCS is a system to provide effective damping by arranging vibration control devices in a concentrated manner in a lower story with large story height, that produces large deformation in an earthquake. Also, the vibration control devices arranged in the lower story are limited to viscous devices, to take into consideration the residual deformation of the overhang frame after an earthquake. The results of investigations into the specific effects of the system for the seismic design are reported, including Performance-based seismic design.

• Structural Engineering and Mechanics
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• v.72 no.1
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• pp.43-60
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• 2019

This paper presents a finite element model which can simulate the axial compression behavior of steel reinforced recycled concrete (SRRC) filled square steel tube columns using the ABAQUS software. The analytical model was established by selecting the reasonable nonlinear analysis theory and the constitutive relationship of material in the columns. The nonlinear analysis of failure modes, deformation characteristics, stress nephogram, and load-strain curves of columns under axial loads was performed in detail. Meanwhile, the influences of recycled coarse aggregate (RCA) replacement percentage, profile steel ratio, width thickness ratio of square steel tube, RAC strength and slenderness ratio on the axial compression behavior of columns were also analyzed carefully. It shows that the results of finite element analysis are in good agreement with the experimental results, which verifies the validity of the analytical model. The axial bearing capacity of columns decreased with the increase of RCA replacement percentage. While the increase of wall thickness of square steel tube, profile steel ratio and RAC strength were all beneficial to improve the bearing capacity of columns. Additionally, the parameter analysis of finite element analysis on the columns was also carried out by using the above numerical model. In general, the SRRC filled square steel tube columns have high bearing capacity and good deformation ability. On the basis of the above analysis, a modified formula based on the American ANSI/AISC 360-10 was proposed to calculate the nominal axial bearing capacity of the columns under axial loads. The research conclusions can provide some references for the engineering application of this kind of columns.

• Advances in nano research
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• v.5 no.4
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• pp.281-301
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• 2017

In this disquisition, an exact solution method is developed for analyzing the vibration characteristics of magneto-electro-elastic functionally graded (MEE-FG) beams by considering porosity distribution and various boundary conditions via a four-variable shear deformation refined beam theory for the first time. Magneto-electroelastic properties of porous FG beam are supposed to vary through the thickness direction and are modeled via modified power-law rule which is formulated using the concept of even and uneven porosity distributions. Porosities possibly occurring inside functionally graded materials (FGMs) during fabrication because of technical problem that lead to creation micro-voids in FG materials. So, it is necessary to consider the effect of porosities on the vibration behavior of MEE-FG beam in the present study. The governing differential equations and related boundary conditions of porous MEE-FG beam subjected to physical field are derived by Hamilton's principle based on a four-variable tangential-exponential refined theory which avoids the use of shear correction factor. An analytical solution procedure is used to achieve the natural frequencies of porous-FG beam supposed to magneto-electrical field which satisfies various boundary conditions. A parametric study is led to carry out the effects of material graduation exponent, porosity parameter, external magnetic potential, external electric voltage, slenderness ratio and various boundary conditions on dimensionless frequencies of porous MEE-FG beam. It is concluded that these parameters play noticeable roles on the vibration behavior of MEE-FG beam with porosities. Presented numerical results can be applied as benchmarks for future design of MEE-FG structures with porosity phases.