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Volume 24, Number 3, June30 2017

Single-storey industrial buildings are one of the most often type of structures built among various skeletal framed steel constructions. These metallic buildings offer an exceptional opportunity to minimise the material employed, contributing to a more sustainable construction. In particular, the mansard portal frame is a typology made up of broken beams that involves different lengths and discontinuous slopes. This study aims the weight reduction of the standard mansard portal frame with design purposes by means of varying four parameters: the kink position, the eaves-apex slope, the span and the columns height. In this work, we suggest some guidelines that can improve the economical competitive capabilities of their structural design. In all the cases analysed, the joints of the portal frame are placed over the theoretical non-funicular shape to uniform loads. This allows reducing the bending moment and the shear force, but increasing the axial force. In addition, the performance of mansard and typical pitched portal frames submitted to the same boundary conditions is compared in terms of efficiency in the use of steel. In the large majority of the cases, mansard typologies are lighter than the common pitched frames and, hence, more economical.

Key Words
steel structures; structural design; structural steel; limit state design; hot-rolled steel members; mansard portal frame; kink joint

(1) P.A. Morales-Rodríguez, J.A. López-Perales:
Departamento de Producción Vegetal y Tecnología Agraria, Escuela Técnica Superior de Ingenieros Agrónomos, University of Castilla-La Mancha (UCLM), Ronda de Calatrava 7, 13071 Ciudad Real, Spain;
(2) P.A. Morales-Rodríguez, M.C. Serna Moreno:
Instituto de Investigaciones Energéticas y Aplicaciones Industriales, Escuela Técnica Superior de Ingenieros Industriales (UCLM), Avda. Camilo José Cela s/n, 13071 Ciudad Real, Spain.

The buckling capacity of a radially retractable hybrid grid shell in the closed position was investigated in this paper. The geometrically non-linear elastic buckling and elasto-plastic buckling analyses of the hybrid structure were carried out. A parametric study was done to investigate the effects rise-to-span ratio, beam section, area and pre-stress of cables, on the failure load. Also, the influence of the shape and scale of imperfections on the elasto-plastic buckling loads was discussed. The results show that the critical buckling load is reduced by taking account of material non-linearity. Furthermore, increasing the rise-tospan ratio or the cross-section area of steel beams notably improves the stability of the structure. However, the cross section area and pre-stress of cables pose negligible effect on the structural stability. It can also be found that the hybrid structure is highly sensitive to geometric imperfection which will considerably reduce the failure load. The proper shape and scale of the imperfection are also important.

Key Words
retractable roof; grid shell; stability; elasto-plastic; failure load

(1) Jianguo Cai, Qian Zhang, Youbao Jiang, Jian Feng:
Key Laboratory of C & PC Structures of Ministry of Education, National Prestress Engineering Research Center, Southeast University, Nanjing 210096, China;
(2) Youbao Jiang:
School of Civil Engineering and Architecture, Changsha University of Science and Technology, Changsha, China;
(3) Yixiang Xu:
Department of Civil Engineering, Strathclyde University, Glasgow G12 8QQ, United Kingdom;
(4) Xiaowei Deng:
Department of Civil Engineering, University of Hong Kong, Hong Kong, China.

A unified mathematical model of phase-lag Green-Naghdi magneto-thermoelasticty theories based on fractional derivative heat transfer for perfectly conducting media in the presence of a constant magnetic field is given. The GN theories as well as the theories of coupled and of generalized magneto-thermoelasticity with thermal relaxation follow as limit cases. The resulting nondimensional coupled equations together with the Laplace transforms techniques are applied to a half space, which is assumed to be traction free and subjected to a thermal shock that is a function of time. The inverse transforms are obtained by using a numerical method based on Fourier expansion techniques. The predictions of the theory are discussed and compared with those for the generalized theory of magneto-thermoelasticity with one relaxation time. The effects of Alfven velocity and the fractional order parameter on copper-like material are discussed in different types of GN theories.

Key Words
generalized magneto-thermoelasticity; caputo fractional derivatives; phase-lag Green-Naghdi theories; laplace transforms; numerical results

(1) M.A. Ezzat:
Department of Mathematics, Faculty of Education, Alexandria University, Alexandria, Egypt;
(2) A.A. El-Bary:
Arab Academy for Science and Technology, P.O. Box 1029, Alexandria, Egypt.

This paper conducted both numerical and theoretical studies to investigate the composite action of notched circular concrete-filled steel tubular (CFT) stub columns under axial compression and established a theoretical method to predict their ultimate bearing capacity. 3D finite element (FE) analysis was conducted to simulate the composite action and the results were in good agreement with experimental results on circular CFT stub columns with differently oriented notches in steel tubes. Parametric study was conducted to understand the effects of different parameters on the mechanical behavior of circular CFT stub columns and also the composite action between the steel tube and the core concrete. Based on the results, a theoretical formula was proposed to calculate the ultimate bearing capacity of notched CFT stub columns under compression with consideration of the composite action between the steel tube and the core concrete.

Key Words
circular concrete-filled steel tubular columns; notch; finite element analysis; ultimate bearing capacity; composite action

(1) Fa-xing Ding, Bing Wen, Hai-bo Wang:
School of Civil Engineering, Central South University, Changsha, Hunan Province, 410075, P.R. China;
(2) Xue-mei Liu:
School of Civil Engineering and Built Environment, Queensland University of Technology, Brisbane, QLD 4001, Australia.

This paper presents the results of a comprehensive experimental investigation on the compressive behaviour of steel tube-confined concrete (STCC) stub columns with active and passive confinement. To create active confinement in STCC columns, an innovative technique is used in which steel tube is laterally pre-tensioned while the concrete core is simultaneously pre-compressed by applying pressure on fresh concrete. A total of 135 STCC specimens with active and passive confinement are tested under axial compression load and their compressive strength, ultimate strain capacity, axial and lateral stress.strain curves and failure mode are evaluated. The test variables include concrete compressive strength, outer diameter to wall thickness ratio of steel tube and prestressing level. It is shown that applying active confinement on STCC specimens can considerably improve their mechanical properties. However, applying higher prestressing levels and keeping the applied pressure for a long time do not considerably affect the mechanical properties of actively confined specimens. Based on the results of this study, new empirical equations are proposed to estimate the axial strength and ultimate strain capacity of STCC stub columns with active and passive confinement.

Key Words
compressive behaviour; pre-compressed concrete; active confinement; steel tube-confined concrete; stub column

(1) Mahdi Nematzadeh, Akbar Haghinejad:
Department of Civil Engineering, University of Mazandaran, Babolsar, Iran;
(2) Iman Hajirasouliha:
Department of Civil and Structural Engineering, University of Sheffield, Sheffield, UK;
(3) Morteza Naghipour:
Faculty of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran.

In this paper, a conventional refined plastic hinge analysis is improved to account for the effects of local buckling and lateral-torsional buckling. The degradation of flexural strength caused by these effects is implicitly considered using practical LRFD equation. The second-order effect is captured using stability functions to minimize modeling and solution time. An incremental-iterative scheme based on the generalized displacement control method is employed to solve the nonlinear equilibrium equations. A computer program is developed to predict the second-order inelastic behavior of space steel frames. To verify the accuracy and efficiency of the proposed program, the obtained results are compared with the existing results and those generated using the commercial finite element package ABAQUS. It can be concluded that the proposed program proves to be a reliable and effective tool for daily use in engineering design.

Key Words
stability function; plastic hinge; local buckling; lateral-torsional buckling; generalized displacement control method

(1) Huu-Tai Thai:
School of Engineering and Mathematical Sciences, La Trobe University, Bundoora, VIC 3086, Australia;
(2) Huu-Tai Thai, Seung-Eock Kim and Jongmin Kim:
Department of Civil and Environmental Engineering, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul 05006, Republic of Korea.

Due to the increasing competition, automotive manufacturers have to manufacture highly safe and light vehicles. The parts which make up the body of the vehicle and absorb the energy in case of a crash, are usually manufactured with sheet metal forming methods such as deep drawing, bending, trimming and spinning. The part may get thinner, thicker, folded, teared, wrinkled and spring back based on the manufacturing conditions during manufacturing and the type of application methods. Transferring these effects which originate from the forming process to the crash simulations that are performed for vehicle safety simulations, makes accurate and reliable results possible. As a part of this study, firstly, the one-step and incremental sheet metal forming analysis (deep drawing + trimming + spring back) of vehicle front bumper beam and crash boxes were conducted. Then, crash performances for cases with and without the effects of sheet metal forming were assessed in the crash analysis of vehicle front bumper beam and crash box. It was detected that the parts absorbed 12.89% more energy in total in cases where the effect of the forming process was included. It was revealed that forming history has a significant effect on the crash performance of the vehicle parts.

Key Words
steel processing; vehicle safety; crash analysis; forming history

(1) TOFAS-FIAT, R&D Department, 16369, Bursa, Turkey;
(2) Sakarya University, Department of Manufacturing Engineering, 54187, Sakarya, Turkey.

In this work, transient heat transfer analysis of functionally graded (FG) carbon nanotube reinforced nanocomposite (CNTRC) cylinders with various essential and natural boundary conditions is investigated by a mesh-free method. The cylinders are subjected to thermal flux, convection environments and constant temperature faces. The material properties of the nanocomposite are estimated by an extended micro mechanical model in volume fraction form. The distribution of carbon nanotube (CNT) has a linear variation along the radial direction of axisymmetric cylinder. In the mesh-free analysis, moving least squares shape functions are used for approximation of temperature field in the weak form of heat transform equation and the transformation method is used for the imposition of essential boundary conditions. Newmark method is applied for solution time depended problem. The effects of CNT distribution pattern and volume fraction, cylinder thickness and boundary conditions are investigated on the transient temperature field of the nanocomposite cylinders.

Key Words
transient heat transfer analysis; carbon nanotubes; nanocomposite cylinders; mesh-free method; various boundary conditions

(1) Rasool Moradi-Dastjerdi:
Young Researchers and Elite Club, Khomeinishahr Branch, Islamic Azad University, Khomeinishahr, Iran;
(2) Gholamhassan Payganeh:
Department of Mechanical Engineering, Shahid Rajaee Teacher Training University (SRTTU), Tehran, Iran.

This study investigates the reliability of the performance levels of moment resisting steel frames subjected to lateral loads such as wind and earthquake. The reliability assessment has been performed with respect to three performance levels: serviceability, damageability, and ultimate limit states. A four-story moment resisting frame is used as a typical example. In the reliability assessment the uncertainties in the loadings and in the capacity of the frame have been considered. The wind and earthquake loads are assumed to have lognormal distribution, and the frame resistance is assumed to have a normal distribution. In order to obtain an appropriate limit state function a linear relation between the loading and the deflection is formed. For the reliability analysis an algorithm has been developed for determination of limit state functions and iterations of the first order reliability method (FORM) procedure. By the method presented herein the multivariable analysis of a complicated reliability problem is reduced to an S-R problem. The procedure for iterations has been tested by a known problem for the purpose of avoiding convergence problems. The reliability indices for many cases have been obtained and also the effects of the coefficient of variation of load and resistance have been investigated.

Key Words
steel frames; FORM; performance; reliability; safety

Department of Civil Engineering, Maltepe University, Marmara Egitim Koyu, 34857, Maltepe, Istanbul, Turkey.

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