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CONTENTS
Volume 70, Number 4, May25 2019
 

Abstract
If an alternative path would not be considered for redistribution of loads, local failure in structures will be followed by a progressive collapse. When a vertical load-bearing element of a steel structure fails, the beams connected to it will lose their support. Accordingly, an increase in span\'s length adds to the internal forces in beams. The mentioned increasing load in beams leads to amplifying the moments there, and likewise in their corresponding connections. Since it is not possible to reinforce all the elements of the structure against this phenomenon, it seems rational to use other technics like specified strengthened connections. In this study, a novel connection is suggested to handle the stated phenomenon which is introduced as a passive connection. This connection enables the structure to tolerate the added loads after failing of the vertical element. To that end, two experimental models were constructed and thereafter tested in half-scale, one-story, double-bay, and bolted connections in three-dimensional spaces. This experimental study has been conducted to compare the ductility and strength of a frame that has ordinary rigid connections with a frame containing a novel passive connection. At last, parametric studies have been implemented to optimize the dimensions of the passive connection. Results show that the load-bearing capacity of the frame increased up to 75 percent. Also, a significant decrease in the displacement of the node wherein the column is removed was observed compared to the ordinary moment resisting frame with the same loads.

Key Words
progressive collapse; alternative path; passive connection; rigid connection; ductility; strength

Address
Masoud Mirtaheri: Associate professor, Department of Civil Engineering, K.N.Toosi University of Technology, Tehran, Iran
Fereshteh Emami: Assistant professor, Department of civil engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
Mohammad A. Zoghi: PhD, Department of Civil Engineering, K.N.Toosi University of Technology, Tehran, Iran
Mojtaba Salkhordeh: PhD candidate, Department of Civil Engineering, K.N.Toosi University of Technology, Tehran, Iran

Abstract
In the present work, the effects of cutting parameters on surface roughness parameters (Ra), tool wear parameters (VBmax), tool vibration (Vy) and material removal rate (MRR) during hard turning of AISI 4140 steel using coated carbide tool have been evaluated. The relationships between machining parameters and output variables were modeled using response surface methodology (RSM). Analysis of variance (ANOVA) was performed to quantify the effect of cutting parameters on the studied machining parameters and to check the adequacy of the mathematical model. Additionally, Multi-objective optimization based desirability function was performed to find optimal cutting parameters to minimize surface roughness, and maximize productivity. The experiments were planned as Box Behnken Design (BBD). The results show that feed rate influenced the surface roughness; the cutting speed influenced the tool wear; the feed rate influenced the tool vibration predominantly. According to the microscopic imagery, it was observed that adhesion and abrasion as the major wear mechanism.

Key Words
cutting parameter; surface roughness; wear; vibration; hard turning; coated carbide; multi-objective optimization

Address
Ouahid Keblouti: Département Construction Mécanique et Productique, FGM&GP. Université des Sciences et de la Technologie
Houari Boumediene. B.P. 32, El-Alia Bab-Ezzouar 16111, Alger, Algérie
Ouahid Keblouti, Lakhdar Boulanouar, Mohamed W. Azizi and Abderrahim Bouziane: Advanced Technologies in Mechanical Production Research Laboratory (LRTAPM),
Badji Mokhtar Annaba University BP12, Annaba, 23000, Algeria.
Mohamed W. Azizi : Département science technique/Centre Universitaire Abdelhafid Boussouf- Mila, 43000, Algeria

Abstract
In the present work, an attempt is made to explore the effects of shear in-plane preload on the wave propagation response of small-scale plates containing nanofibers. The small-scale system is assumed to be embedded in an elastic matrix. The nonlocal elasticity is utilized in order to develop a size-dependent model of plates. The proposed plate model is able to describe both nanofiber effects and the influences of being at small-scales on the wave propagation response. The size-dependent differential equations are derived for motions along all directions. The size-dependent coupled equations are solved analytically to obtain the phase and group velocities of the small-scale plate under a shear in-plane preload. The effects of this shear preload in conjunction with nanofiber and size effects as well as the influences of the elastic matrix on the wave propagation response are analyzed in detail.

Key Words
shear preload; nanofibers; small-scale plates; size effects

Address
M.R. Farajpour:Borjavaran Center of Applied Science and Technology, University of Applied Sciences and Technology, Tehran, Iran
A.R. Shahidi and A. Farajpour: Department of Mechanical Engineering, Isfahan University of Technology, Isfahan 8415683111, Iran

Abstract
This paper presents an analytical model for the estimation of initial lateral stiffness of steel moment resisting frames with masonry infills. However, rather than focusing on the single bay-single storey substructure, the developed model attempts to estimate the global stiffness of multi-storey and multi-bay frames, using an assembly of equivalent springs and taking into account the shape of the lateral loading pattern. The contribution from each infilled frame panel is included as an individual spring, whose properties are determined on the basis of established diagonal strut macro-modeling approaches from the literature. The proposed model is evaluated parametrically against numerical results from frame analyses, with varying number of frame stories, infill openings, masonry thickness and modulus of elasticity. The performance of the model is evaluated and found quite satisfactory.

Key Words
masonry infills; steel frames; initial stiffness; analytical model; openings

Address
Minas E. Lemonis: School of Civil Engineering, National Technical University of Athens, Greece
Panagiotis G. Asteris, Dimitrios G. Zitouniatis and Georgios D. Ntasis: Computational Mechanics Laboratory, School of Pedagogical and Technological Education, Heraklion, GR 14121, Athens, Greece

Abstract
The present paper illustrates a numerical investigation on the failure behaviour of ring-stiffened cylinder subjected to external hydrostatic pressure. The published test data of steel welded ring-stiffened cylinder are surveyed and collected. Eight test models are chosen for the verification of the modelling and FE analyses procedures. The imperfection as the consequences of the fabrication processes, such as initial geometric deformation and residual stresses due to welding and cold forming, which reduced the ultimate strength, are simulated. The results show that the collapse pressure and failure mode predicted by the nonlinear FE analyses agree acceptably with the experimental results. In addition, the failure mode parameter obtained from the characteristic pressure such as interframe buckling pressure known as local buckling pressure, overall buckling pressure, and yield pressure are also examined through the collected data and shows a good correlation. A parametric study is then conducted to confirm the failure progression as the basic parameters such as the shell radius, thickness, overall length of the compartment, and stiffener spacing are varied.

Key Words
Ring-stiffened cylinders; collapse pressure; failure mode criterion; hydrostatic pressure test; non-linear FEA

Address
Teguh Muttaqie, Do Quang Thang, Aditya Rio Prabowo, Sang-Rai Cho and Jung Min Sohn
Teguh Muttaqie,Jung Min Sohn: Department of Naval Architecture and Marine Systems Engineering, Pukyong National University, Busan, Republic of Korea
Teguh Muttaqie: Agency for the Assessment and Application of Technology,
Center of Technology for Defense and Security Industries - BPPT, Jakarta, Indonesia
Do Quang Thang: Department of Naval Architecture and Ocean Engineering, Nha Trang University, Nha Trang, Viet Nam
Aditya Rio Prabowo: Department of Mechanical Engineering, Sebelas Maret University, Surakarta, Indonesia
Sang-Rai Cho: School of Naval Architecture and Ocean Engineering, University of Ulsan, Republic of Korea.
Sang-Rai Cho: Ulsan Lab, Inc, Ulsan, Republic of Korea

Abstract
Since the days of yore, plate\'s flexural analysis and formulation were dependent on the assumed coordinate system. In uncovering the coordinates-independent flexural interpretation, in this study, the plate bending analysis has been interpreted in terms of the tensor\'s components of curvatures and bending moments, in accordance with the continuum mechanics. The paper herein presents the theoretical formulations and conceptual perspectives of the Hydrostatic Method of Analysis (HM) that combines the continuum mechanics with the elasticity theory; the graphical statics and analysis; the theory of thin isotropic and orthotropic plates.

Key Words
hydrostatic formulation; plates flexural; spatial curvature; tensors; coordinates independent formulation

Address
Department of Civil Engineering, Jordan University of Science and Technology, Irbid, Jordan

Abstract
This study develops a damage detection method based on neural networks. The performance of the method is numerically and experimentally verified using a three-story shear building model. The framework is mainly composed of two hierarchical stages to identify damage location and extent using artificial neural network (ANN). The normalized damage signature index, that is a normalized ratio of the changes in the natural frequency and mode shape caused by the damage, is used to identify the damage location. The modal parameters extracted from the numerically developed structure for multiple damage scenarios are used to train the ANN. The positive alarm from the first stage of damage detection activates the second stage of ANN to assess the damage extent. The difference in mode shape vectors between the intact and damaged structures is used to determine the extent of the related damage. The entire procedure is verified using laboratory experiments. The damage is artificially modeled by replacing the column element with a narrow section, and a stochastic subspace identification method is used to identify the modal parameters. The results verify that the proposed method can accurately detect the damage location and extent.

Key Words
artificial neural network; damage detection; normalized damage significance index; modal identification; structural health monitoring

Address
Minwoo Chang: Northern Railroad Research Center, Korea Railroad Research Institute, 176 Cheoldo bangmulgwan-ro,
Uiwang-si, Gyeonggi-do 16105, Republic of Korea
Jae Kwan Kim: Department of Civil and Environmental Engineering, Seoul National University, 1 Gwanak-ro,
Gwanak-gu, Seoul 08826, Republic of Korea
Joonhyeok Lee: Infrastructure ENG Team, Samsung C&T Corporation, 26 Sangil-ro 6-gil, Gangdong-gu, Seoul 05288, Republic of Korea

Abstract
The objective of this work is to analyze by traction tests, the mechanical behavior of an assembly of type metal / metal by various assembly processes; bonding, riveting and hybrid, on the one hand to show the advantage of a hybrid assembly with respect to the other processes, and on the other hand, to analyze by the finite element method the distribution of the stresses in the various components of the structure and to demonstrate the effectiveness of the use of a hybrid assembly with respect to other processes. The number of rivets has been considered. The results show clearly that the value of the different stresses is reduced in the case of a hybrid junction and that the number of rivets in an assembly can be reduced by using a hybrid joint.

Key Words
riveted-bonded joint; Von Mises stress; Absorption Energy; steel E24

Address
M.C.Ezzine, K.Madani: Laboratoire Mécanique Physique des Matériaux (LMPM), Department of Mechanical Engineering,
University of Sidi Bel Abbes, Sidi Bel Abbes 22000, Algeria
M.Tarfaoui: ENSTA Bretagne, MSN/LBMS/DFMS, 2 Rue François Verny, 29806, Brest, CEDEX 9, France
S. Touzain and S. Mallarino: LaSIE, UMR7356, Laboratoire des Sciences de l\'Ingenieur pour l\'Environnement, University of La Rochelle,
Av. Michel Crépeau, 17042 La Rochelle, France

Abstract
In the current code design, the use of a uniform internal pressure coefficient of cooling towers as internal suction cannot reflect the 3D characteristics of flow field inside the tower body with different ventilation rate of shutters. Moreover, extreme weather such as heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind. In this study, the world\'s tallest cooling tower under construction, which stands 210m, is taken as the research object. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed iteratively using continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind speed and rainfall intensity on the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower body is analyzed. The combination of wind velocity and rainfall intensity that is most unfavorable to the cooling tower in terms of distribution of internal pressure coefficient is identified. On this basis, the wind/rain loads, distribution of aerodynamic force and working mechanism of internal pressures of the cooling tower under the most unfavorable working condition are compared between the four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the amount of raindrops captured by the internal surface of the tower decreases as the wind velocity increases, and increases along with the rainfall intensity and ventilation rate of the shutters. The maximum value of rain-induced pressure coefficient is 0.013. The research findings lay the basis for determining the precise values of internal surface loads of cooling tower under extreme weather conditions.

Key Words
super-large cooling tower; two-way coupling between wind and rain; CFD; combination of wind velocity and rainfall intensity; pressure distribution on the internal surface

Address
Shitang Ke: Department of Civil Engineering, Nanjing University of Aeronautics and Astronautics, 29 Yudao Road, Nanjing 210016, China
Wenlin Yu: Jiangsu Power Design Institute Co., LTD, China Energy Engineering Group, 58-3 Suyuan Road, Nanjing 211102, China
Yaojun Ge: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China

Abstract
In this study, the axial compressive behavior of novel quadruple C-channel built-up cold-formed steel columns with different slenderness ratio was investigated, using the experimental and numerical analysis. The axial compressive capacity and failure modes of the columns were obtained and analyzed. The finite element models considering the geometry, material and contact nonlinearity were developed to simulate and analyze the structural behavior of the columns further. There was a great correlation between the numerical analyses and test results, which indicated that the finite element model was reasonable and accurate. Then influence of, slenderness ratio, flange width-to-thickness ratio and screw spacing on the mechanical behavior of the columns were studied, respectively. The tests and numerical results show that due to small slenderness ratio, the failure modes of the specimens are generally local buckling and distortional buckling. The axial compressive strength and stiffness of the quadruple C-channel built-up cold-formed steel columns decrease with the increase of maximum slenderness ratio. When the screw spacing is ranging from 150mm to 450mm, the axial compressive strength and stiffness of the quadruple C-channel built-up cold-formed steel columns change little. The axial compressive capacity of quadruple C-channel built-up cold-formed steel columns increases with the decrease of flange width-thickness ratio. A modified effective length factor is proposed to quantify the axial compressive capacity of the quadruple C-channel built-up cold-formed steel columns with U-shaped track in the ends.

Key Words
cold-formed steel; built-up section; compressive tests; numerical analysis; axial compressive capacity; effective ratio of width-to-thickness method; direct strength method

Address
Shaofeng Nie, Tianhua Zhou, Fangfang Liao: School of Civil Engineering, Chang\'an University, 710061, China
Donghua Yang: China West Airport Group, Xian, 710075,China


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