• Fire Science and Engineering
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• v.21 no.2 s.66
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• pp.36-41
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• 2007

In this study, we determined TBP(T-branched pipe) would be available in Fire Safety Codes with strength analyses. A common FEM Program(ABAQUS) was used as analyses method, and the analyses results were confirmed by strength tests of the T-branch pipe. As a result, we concluded that the T-branch pipe can be used safely. Further more, we determined what kind of stainless steel pipe can be used in place of carbon steel pipe(KS D 3507). The stainless steel pipe name Is KS D 3576(stainless steel pipe) 10S, so they can be applied for piping in fire protection system.

• Geomechanics and Engineering
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• v.28 no.1
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• pp.89-105
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• 2022

The behavior of the soil subgrade is complex and irregular against loads. When modeling, the soil is often replaced by a more straightforward system called a subgrade model. The Winkler method of linear elastic springs is a popular method of soil modeling in which the spring constant shows the modulus of subgrade reaction. In this research, the factors affecting the distribution of the modulus of subgrade reaction of elastoplastic subgrades are examined. For this purpose, critical theories about the modulus of subgrade reaction were examined. A square raft foundation on a sandy soil subgrade with was analyzed at different internal friction angles and Young's modulus values using ABAQUS software. To accurately model the actual soil behavior, the elastic, perfectly plastic constitutive model was applied to investigate a foundation on discrete springs. In order to increase the accuracy of soil modeling, equations have been proposed for the distribution of the subgrade reaction modulus. The constitutive model of the springs is elastic, perfectly plastic. It was observed that the modulus of subgrade reaction under an elastic load decreased when moving from the corner to the center of the foundation. For the ultimate load, the modulus of subgrade reaction increased as it moved from the corner to the center of the foundation.

• Structural Engineering and Mechanics
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• v.81 no.4
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• pp.493-502
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• 2022

Shear lag phenomenon has long been considered in numerous structural codes; however, the AISC provisions have now no longer proposed any unique equation to calculate the shear lag ratio in bolted connections for angles in general. It is noticeable that, however, codes used in this case are largely conservative and need to be amended. A parametric study consisting of 27 angle sections with equal legs and different with bolted connections was performed to investigate the effects of shear lag on the ultimate tensile capacity of angle members. The main parameters were: steel grade, connection length and eccentricity from the center of the plate, as well as the number of rows of bolts parallel to the applied force. The test results were compared with the predictions of the classical 1-x/l law proposed by Mons and Chesen to investigate its application to quantify the effect of shear lag. A parametric study was performed using valid FE models that cover a wide range of parameters. Finally, based on the numerical results, design considerations were proposed to quantify the effect of shear lag on the ultimate tensile capacity of the tensile members.

• Structural Engineering and Mechanics
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• v.33 no.3
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• pp.325-337
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• 2009

Structural damage detection, damage localization and severity estimation of jacket platforms, based on calculating modal strain energy is presented in this paper. In the structure, damage often causes a loss of stiffness in some elements, so modal parameters; mode shapes and natural frequencies, in the damaged structure are different from the undamaged state. Geometrical location of damage is detected by computing modal strain energy change ratio (MSECR) for each structural element, which elements with higher MSECR are suspected to be damaged. For each suspected damaged element, by computing cross-modal strain energy (CMSE), damage severity as the stiffness reduction factor -that represented the ratios between the element stiffness changes to the undamaged element stiffness- is estimated. Numerical studies are demonstrated for a three dimensional, single bay, four stories frame of the existing jacket platform, based on the synthetic data that generated from finite element model. It is observed that this method can be used for damage detection of this kind of structures.

• Structural Engineering and Mechanics
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• v.63 no.1
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• pp.11-21
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• 2017

In this paper, the efficiency and the accuracy of classical (CE) and high order (HE) beam element are improved by introducing two novel techniques. The first proposed element (FPE) provides an alternative for (HE) by taking the mode shapes of the clamped-clamped (C-C) beam into account. The second proposed element (SPE) which could be utilized instead of (CE) and (HE) considers not only the mode shapes of the (C-C) beam but also some virtual nodes. It is numerically proven that the eigenvalue problem and the frequency response function for Euler-Bernoulli beam are obtained more accurate and efficient in contrast to the traditional ones.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.6
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• pp.602-612
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• 2013

In this paper, a design and fabrication of miniaturized 5.3 GHz reflection type $360^{\circ}$ analog phase shifter with branch line coupler and $360^{\circ}$ variable reactance load. In order to miniaturize phase shifter, novel branch line coupler is proposed. The novel branch line coupler is miniaturized using transformation of transmission line to T and ${\pi}$ type equivalent circuit. The miniaturized branch line coupler has small size of above 50 % compared with conventional branch line coupler. For wide phase shift range, $360^{\circ}$ variable reactance load structure is adopted. Especially, the structure was improved for linear phase shift by adding transmission line which acts as an impedance transformer. The improved structure was miniaturized using the equivalent lumped-element of transmission line. The fabricated phase shifter with $15{\times}15mm^2$ shows wide phase shift of above $480^{\circ}$, the insertion loss of -4~-6 dB and the reflection loss of below -20 dB at 5.3 GHz under 0~10 V control voltage range.

• Steel and Composite Structures
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• v.23 no.2
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• pp.217-228
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• 2017

Braces are one of the retrofitting systems of structure under earthquake loading. Buckling restrained braces (BRBs) are one of the very efficient braces for lateral loads. One of the key needs for a desirable and acceptable behavior of buckling-restraining brace members under intensive loading is that it prevents total buckling until the bracing member tolerates enough plastic deformation and ductility. This paper presents the results of a set of analysis by finite element method on buckling restrained braces in which the filler materials within the restraining member have been removed. These braces contain core as the conventional BRBs, but they have a different buckling restrained system. The purpose of this analysis is conducting a parametric study on various empty spaces between core and restraining member, the effect of friction between core and restraining member and applying initial deformation to brace system to investigate the global buckling behavior of these braces. The results of analysis indicate that the flexural stiffness of restraining member, regardless of the amount of empty space, can influence the global buckling behavior of brace significantly.

• Structural Engineering and Mechanics
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• v.66 no.3
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• pp.379-386
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• 2018

The present study addresses the direct and indirect methods of determining the mode-I fracture toughness of concrete using experimental tests and particle flow code. The direct method used is compaction tensile test and the indirect methods are notched Brazilian disc test, semi-circular bend specimen test, and hollow center cracked disc. The experiments were carried out to determine which indirect method yields the fracture toughness closer to the one obtained by the direct method. In the numerical analysis, the PFC model was first calibrated with respect to the data obtained from the Brazilian laboratory test. The crack paths observed in the simulated tests were in reasonable accordance with experimental results. The discrete element simulations demonstrated that the macro fractures in the models are caused by microscopic tensile breakages on large numbers of bonded particles. The mode-I fracture toughness in the direct tensile test was smaller than the indirect testing results. The fracture toughness obtained from the SCB test was closer to the direct test results. Hence, the semi-circular bend test is recommended as a proper experiment for determination of mode-I fracture toughness of concrete in the absence of direct tests.

• Structural Engineering and Mechanics
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• v.55 no.6
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• pp.1087-1097
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• 2015

In this paper, the effect of functionally graded material (FGM) coatings on the fracture behavior of semi-elliptical cracks in cylinders is assessed. The objective is to calculate the stress intensity factor (SIF) of a longitudinal semi-elliptical crack on the wall of an aluminum cylinder with FGM coating. A three-dimensional finite element method (FEM) is used for constructing the mechanical models and analyzing the SIFs of cracks. The effect of many geometrical parameters such as relative depth, crack aspect ratio, FG coating thickness to liner thickness as well as the mechanical properties of the FG coating on the SIF of the cracks is discussed. For a special case, the validity of the FE model is examined. The results indicated that there is a particular crack aspect ratio in which the maximum value of SIFs changes from the deepest point to the surface point of the crack. Moreover, it was found that the SIFs decrease by increasing the thickness ratio of the cylinder. But, the cylinder length has no effect on the crack SIFs.

• Biomaterials and Biomechanics in Bioengineering
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• v.4 no.1
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• pp.33-44
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• 2019

This paper presents a novel structural composition for artificial bone scaffolds with an appropriate biocompatibility and biodegradability capability. To achieve this aim, carbon nanotubes, due to their prominent mechanical properties, high biocompatibility with the body and its structural similarities with the natural bone structure are selected in component of the artificial bone structure. Also, according to the piezoelectric properties of natural bone tissue, the barium titanate, which is one of the biocompatible material with body and has piezoelectric property, is used to create self-healing ability. Furthermore, due to the fact that, most of the bone tissue is consists of hydroxyapatite, this material is also added to the artificial bone structure. Finally, polycaprolactone is used in synthetic bone composition as a proper substrate for bone growth and repair. To demonstrate, performance of the presented composition, the mechanical behaviour of the bone scaffold is simulated using ANSYS Workbench software and three dimensional finite element modelling. The obtained results are compared with mechanical behaviour of the natural bone and the previous bone scaffold compositions. The results indicated that, the modulus of elasticity, strength and toughness of the proposed composition of bone scaffold is very close to the natural bone behaviour with respect to the previous bone scaffold compositions and this composition can be employed as an appropriate replacement for bone implants.