• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.6
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• pp.359-366
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• 2019

Experimental and analytical studies on the behavioral characteristics of a pre-stressed (PS) steel girder are conducted to investigate the effects of deviators on the non-linear inelastic properties of the PS system. In this regard, 4 test specimens consisting of a steel H-beam, a straight cable with eccentricity, anchorages, and deviators are built and failure tests are performed under two-point loading. In addition, in-plane elastic deformation theories for the PS system without a deviator, and with three deviators at regular intervals are analytically formulated and solved using a symbolic calculation technique. To verify the validity of the experimental and the proposed analytical theories, the results obtained using FEM models composed of beam elements, rigid beam elements, and truss cable elements, are compared to the experimental results and the analytical solutions. As a result, it is determined that externally installed un-bonded deviators inhibit flexural deformation of the deformed beam to such an extent that their elastic stiffness, and failure strength are significantly improved compared to those of the PS system without deviators.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.3
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• pp.193-201
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• 2023

In this study, a nonlinear truss finite element is developed to analyze structures with negative Poisson effect-induced tensile buckling. In general, the well-known buckling phenomenon is a stability problem under a compressive load, whereas tensile buckling occurs because of local compression caused by tension. It is not as well-known as classical buckling because it is a recent study. The mechanism of tensile buckling can be briefly explained from an energy standpoint. The nonlinear truss finite element with a torsional spring is formulated because the finite element has not been reported in the literature yet. The post-buckling analysis is then performed using the generalized displacement control method, which reveals that the torsional spring plays an important role in tensile buckling. Structures that mimic a negative Poisson effect can be constructed using such post-buckling behaviors, and one of the possible applications is a mechanical switch. The results obtained are compared to those of analytical solutions and commercial finite element analysis to assess the validity of the proposed finite element model. The numerical results show that the developed finite element model could be a viable option for the basic design of nonlinear structures with a negative Poisson effect.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.9
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• pp.1099-1103
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• 2011

Since the mechanical strength and stiffness of wire-woven bulk Kagome (BK) have been theoretically estimated by assuming that WBK is composed of straight struts, the analytical solutions occasionally give substantial errors as compared with the experimental results. The struts of WBK are helically formed, which results in errors in the estimations In this study, for accurately predicting the mechanical properties of WBK, the effects of waviness and brazed part are taken into account for estimating the strength and stiffness of WBK. The results are compared with the measured experimental results and the results estimated by a finite element analysis performed on a unit cell under periodic boundary conditions (PBC).

• Journal of the Korean Society for Advanced Composite Structures
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• v.2 no.3
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• pp.1-11
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• 2011

The typical truss-lattice material successively packed by repeated cubic symmetric unit cells consists of sub-elements (SE) proposed in this study. The representative continuum model for this truss-lattice material such as the effective strain and stress relationship can be formulated by the homogenization procedure based on the notation of averaged mechanical properties. The volume fractions of micro-scale struts have a significant influence on the effective strength as well as the relative density in the lattice plate with replicable unit cell structures. Most of the strength contribution in the lattice material is induced by axial stiffness under uniform stretching or compression responses. Therefore, continuum based constitutive models composed of homogenized member stiffness include these mechanical characteristics with respect to strength, internal stress state, material density based on the volume fraction and even failure modes. It can be also recognized that the stress state of micro-scale struts is directly associated with the continuum constitutive model. The plastic flow at the micro-scale stress can extend the envelope of the analytical stress function on the surface of macro-scale stress derived from homogenized constitutive equations. The main focus of this study is to investigate the basic topology of unit cell structures with the cubic symmetric system and to formulate the plastic models to predict pressure dependent macro-scale stress surface functions.

• Journal of Korean Society of Steel Construction
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• v.20 no.1
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• pp.131-149
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• 2008

A transmission tower was designed according to general and special load cases based on KEPCO Design Specifications. The special load case such as unbalanced load a cording to some broken wires has not been considered significantly. Therefore, this paper presents investigations on the stability and safety of main post members subjected to unbalanced load and design wind load. In this study, all cases totally considered. From the finite element analyses using LUSAS program, the stresses on the tower subjected to unbalanced load and design wind load were very high in comparison to the allowable stresses of the steel post member that was used. Some of the post member had higher stresses than the yield stress of the steel member. This paper also shows an example to improve the capacity of the post members using increased cross-section members. Based on the analyses results, when investigating the safety of the transmission tower, one must consider thenew design philosophy including ultimate strength of the member and reliability of the special loading cases.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.533-539
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• 2009

In this study, the femur, the tibia, the articular cartilage and the menisci are three dimensionally reconstructed using MR images of healthy knee joint in full extension of 26-year-old male. Three dimensional finite element model of the knee joint is fabricated on the reconstructed model. Also, the FE models of ligaments and tendons are attached on the biologically suitable position of the FE model. Bones, articular cartilages and menisci are considered as homogeneous, isotropic and linear elastic materials, and ligaments and tendons are modeled as truss element and nonlinear elastic springs. The numerical results show the contact pressure and the von Mises stress distribution in the soft tissues such as articular cartilages and menisci which can be regarded as important parameters to estimate the failure of the tissues and the pain of the patients.

• Journal of Korean Society of Steel Construction
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• v.23 no.2
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• pp.199-210
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• 2011

The cables in cable-stayed bridges are under high stress and are very sensitive to vibration due to their small section areas compared with other members. Therefore, it is reasonable to evaluate the cable impact factor by taking into account the dynamic effect due to moving-vehicle motion. In this study, the cable impact factors were evaluated via moving-vehicle-load analysis, considering the design parameters, i.e., vehicle weight, cable model, road surface roughness, vehicle speed, longitudinal distance between vehicles. For this purpose, two steel composite cable-stayed bridges with 230- and 540-m main spans were selected. The results of the analysis were then compared with those of the influence line method that is currently being used in design practice. The road surface roughness was randomly generated based on ISO 8608, and the convergence of impact factors according to the number of generated road surfaces was evaluated to improve the reliability of the results. A9-d.o.f. tractor-trailer vehicle was used, and the vehicle motion was derived from Lagrange's equation. 3D finite element models for the selected cable-stayed bridges were constructed with truss elements having equivalent moduli for the cables, and with beam elements for the girders and the pylons. The direct integration method was used for the analysis of the bridge-vehicle interaction, and the analysis was conducted iteratively until the displacement error rate of the bridge was within the specified tolerance. It was acknowledged that the influence line method, which cannot consider the dynamic effect due to moving-vehicle motion, could underestimate the impact factors of the end-cables at the side spans, unlike moving-vehicle-load analysis.

• Explosives and Blasting
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• v.36 no.1
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• pp.20-33
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• 2018

A locally damaged structure is a structure that cannot be reused due to having parts that have lost their structural function as a result of abnormal load across the interior or exterior of the structure. The causes of the abnormal load occurrences can be classified into natural disaster and artificial disaster. Locally damaged structures caused by this abnormal load have risk factors that may lead to the possibility of additional secondary collapses, so such structures require immediate and complete dismantling. The case presented in this study involves the application of explosive demolition to a steel truss structured bridge in the Philippines that was damaged due to construction failures and the hurricane. Although shaped charges were needed in explosive demolitions, difficulties in locally obtaining such material. So, we made a charge container to charging of emulsion explosive during the explosive demolition. The explosive demolition resulted in the vertical free fall of the mid-section of the bridge and the free fall rotating of the both end section of the bridge. The neighboring posts and bridge piers did not show signs of damages, while post-demolition fragmentation of removed parts was found to be satisfactory.

• Journal of Bio-Environment Control
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• v.3 no.2
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• pp.128-135
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• 1994

Recently, regionally characterized greenhouses have been built every place around the country. These greenhouses insist of their higher performance by considering regional merits than the greenhouses without considering regional ones, but it is not clear. The purpose of this study was to make clear the characteristics of the regionally characterized greenhouses through the analyses of actual state and structural safety. The greenhouses were investigated and classified into wide span house, large pipe house, arched lattice house, wooden house, viniculture house, and domed pipe house. The frames of wide span house, arched truss house, viniculture house and domed pipe house were analyzed to be structurally stable under the design wind speeds and snow depths in recurrence intervals of 15 or 30 years, but large pipe house was a little unstable and required some reinforcements, and wooden house turned out to be unstable. In addition, foundations of all characterized greenhouses were stable against pull - out capacity under the design wind speeds in recurrence interval of 30 years.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.3
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• pp.7-17
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• 1990

The objective of this paper is to provide a method of optimizing are as of the members as well as shape of both truss and arch structures. The design process includes satisfaction of stress and Euler buckling stress constraints for truss and combined stress constraints for arch structures. In order to reduce the number of detailed finite element analysis, the Force Approximation Method is used. A finite element analysis of the initial structure is performed and the gradients of the member end forces are calculated with respect to the areas and nodal coordinates. The gradients are used to form an approximate structural analysis based on first order Taylor series expansions of the member end forces. Using move limits, a numerical optimizer minimizes the volume of the structure with information from the approximate structural analysis. Numerical examples are performed and compared with other methods to demonstrate the efficiency and reliability of the Force Approximation Method for shape optimization. It is shown that the number of finite element analysis is greatly reduced and that it leads to a highly efficient method of shape optimization of structures.