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CONTENTS
Volume 23, Number 3, February28 2017
 

Abstract
In this paper, thermal effect on the vibration and stability of initially stressed sandwich plates with functionally graded material (FGM) face sheets is analyzed. Material properties of FGM face sheet are graded continuously in the thickness direction. The variation of FGM properties assumes a simple power law distribution in terms of the volume fractions of the constituents. The governing equations of arbitrarily initially-stressed sandwich plates including the effects of transverse shear deformation and rotary inertia are derived. The initial stress is taken to be a combination of a uniaxial extensional stress and a pure bending stress in the examples. The eigenvalue problems are formed to study the vibration and buckling characteristics of simple supported initially stressed FGM/metal/FGM plates. The effects of volume fraction index, temperature rise, initial stress and layer thickness of metal on the natural frequencies and buckling loads are investigated. The results reveal that the volume fraction index, initial stresses and layer thickness of metal have significant influence on the vibration and stability of sandwich plates with FGM face sheets.

Key Words
thermal effect; sandwich plate; FGM face sheet; volume fraction index; initial stress

Address
(1) Chun-Sheng Chen, Fwu-Hsing Liu, Wei-Ren Chen:
Department of Mechanical Engineering, Lunghwa University of Science and Technology, Guishan Shiang, Taoyuan, 33306, Taiwan;
(2) Wei-Ren Chen:
Department of Mechanical Engineering, Chinese Culture University, Taipei 11114, Taiwan.

Abstract
A theoretical study was carried-out of mode II delamination fracture behavior of the End Loaded Split (ELS) functionally graded beam configuration with considering the material non-linearity. The mechanical response of ELS was modeled analytically by using a power-law stress-strain relation. It was assumed that the material is functionally graded transversally to the beam. The non-linear fracture was investigated by using the J-integral approach. Equations were derived for the crack arm curvature and zero axes coordinate that are needed for the J-integral solution. The analysis developed is valid for a delamination crack located arbitrary along the beam height. The J-integral solution was verified by analyzing the strain energy release rate with considering material non-linearity. The effects of material gradient, non-linear material behavior and crack location on the fracture were evaluated. The solution derived is suitable for parametric analyses of non-linear fracture. The results obtained can be used for optimization of functionally graded beams with respect to their mode II fracture performance. Also, such simplified analytical models contribute for the understanding of delamination fracture in functionally graded beams exhibiting material non-linearity.

Key Words
functionally graded structures; fracture; material non-linearity; beam theory

Address
Department of Technical Mechanics, University of Architecture, Civil Engineering and Geodesy, 1 Chr. Smirnensky blvd., 1046 – Sofia, Bulgaria.

Abstract
In this paper, it is aimed to present a detail investigation related to structural behavior of laterally unrestrained steel cantilever roof of tribune with slender cross section. The structure is located in Tutak town in A&$287;rı and collapsed on October 25, 2015 at eastern part of Turkey is considered as a case study. This mild sloped roof structure was built from a variable I beam, and supported on steel columns of 5.5 m height covering totally 240 m2 closed area in plan. The roof of tribune collapsed completely without any indication during first snowfall after construction at midnight a winter day, fortunately before the opening hours. The meteorological records and observations of local persons are combined together to estimate the intensity of snow load in the region and it is compared with the code specified values. Also, the wide/thickness and height/thickness ratios for flange and web are evaluated according to the design codes. Three dimensional finite element model of the existing steel tribune roof is generated considering project drawings and site investigations using commercially available software ANSYS. The displacements, principal stresses and strains along to the cantilever length and column height are given as contour diagrams and graph format. In addition to site investigation, the numerical and analytical works conducted in this study indicate that the unequivocal reasons of the collapse are overloading action of snow load intensity, some mistakes made in the design of steel cantilever beams, insufficient strength and rigidity of the main structural elements, and construction workmanship errors.

Key Words
collapse; finite element model; roof; snow; steel

Address
Department of Civil Engineering, Karadeniz Technical University, Trabzon, Turkey.

Abstract
Buckling-restrained braced frames (BRBFs) are commonly used as the lateral force-resisting systems in building structures in the seismic regions. The nearly-symmetric hysteretic response and the delayed brace core fracture of buckling-restrained braces (BRBs) under the axial cyclic loading provide the adequate lateral force and deformation capacity to BRBFs under the earthquake excitation. However, the smaller axial stiffness of BRBs result in the undesirable higher residual drift response of BRBFs in the post-earthquake scenario. Two alternative approaches are investigated in this study to improve the elastic axial stiffness of BRBs, namely, (i) by shortening the yielding cores of BRBs; and (ii) by reducing the BRB assemblies and adding the elastic brace segments in series. In order to obtain the limiting yielding core lengths of BRBs, a modified approach based on Coffin-Manson relationship and the higher mode compression buckling criteria has been proposed in this study. Both non-linear static and dynamic analyses are carried out to analytically evaluate the seismic response of BRBFs fitted with short-core BRBs of two medium-rise building frames. Analysis results showed that the proposed brace systems are effective in reducing the inter-story and residual drift response of braced frames without any significant change in the story shear and the displacement ductility demands.

Key Words
braced frames; buckling-restrained braces; displacement ductility; lateral load; low-cycle fatigue; seismic analysis; seismic design

Address
Department of Civil Engineering, Indian Institute of Technology Delhi, New Delhi-110016, India.

Abstract
This paper describes the finite element model for predicting the fundamental performance of embedded steel column base connections under monotonic and cyclic loading. Geometric and material nonlinearities were included in the proposed finite element model. Bauschinger and pinching effects were considered in the simulation of embedded column base connections under cyclic loading. The degradation of steel yield strength and accumulation of plastic damage can be well simulated. The accuracy of the finite element model is examined by comparing the predicted results with independent experimental dataset. It is demonstrated that the finite element model accurately predicts the behaviour and failure models of the embedded steel column base connections. The finite element model is extended to carry out evaluations and parametric studies. The investigated parameters include column embedded length, concrete strength, axial load and base plate thickness. Moreover, analytical models for predicting the initial stiffness and bending moment strength of the embedded column base connection were developed. The comparison between results from analytical models and those from experiments and finite element analysis proved the developed analytical model was accurate and conservative for design purposes.

Key Words
embedded column base connections; monotonic and cyclic loading; demountability; finite element analysis; analytical model

Address
(1) Dongxu Li, Brian Uy:
Centre for Infrastructure Engineering and Safety, School of Civil and Environmental Engineering, The University of New South Wales, Sydney, NSW 2052, Australia;
(2) Vipul Patel:
School of Engineering and Mathematical Sciences, College of Science, Health and Engineering, La Trobe University, PO Box 199, Bendigo, VIC 3552, Australia;
(3) Farhad Aslani:
School of Civil, Environmental and Mining Engineering, The University of Western Australia, Crawley, WA 6009, Australia.

Abstract
This paper presents a free vibration analysis of plates made of functionally graded materials and resting on twolayer elastic foundations by proposing a non-polynomial four variable refined plate theory. Undetermined integral terms are introduced in the proposed displacement field and unlike the conventional higher shear deformation theory (HSDT), the present one contains only four unknowns. Equations of motion are derived via the Hamilton\'s principles and solved using Navier\'s procedure. Accuracy of the present theory is demonstrated by comparing the results of numerical examples with the ones available in literature.

Key Words
vibration; functionally graded plate; elastic foundation; plate theory

Address
(1) Ali Meftah, Ahmed Bakora, Abdelouahed Tounsi, El Abbes Adda Bedia:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
(2) Fatima Zohra Zaoui:
Laboratoire de Modelisation Numerique et Experimentale des Phenomenes Mecaniques, Faculty of Sciences and Technology, Departement de Génie Mécanique, University Abdelhamid Ibn Badis of Mostaganem, 27000, Algeria;
(3) Abdelouahed Tounsi:
Laboratoire des Structures et Matériaux Avancés dans le Génie Civil et Travaux Publics, Université de Sidi Bel Abbes, Faculté de Technologie, Département de génie civil, Algeria;
(4) Abdelouahed Tounsi:
Laboratoire de Modélisation et Simulation Multi-échelle, Départment de Physique, Faculté des Sciences Exactes, Départment de Physique, Université de Sidi Bel Abbés, Algeria.

Abstract
Cold-formed lipped channel columns (CFLCCs) have been widely used in light gauge steel constructions. The distortional buckling is one of the important buckling modes for CFLCCs and the distortional buckling critical load depends significantly on the rotational restrain stiffness generated by the web to the lipped flange. First, a simplified explicit expression for the rotational restraint stiffness of the lipped flange has been derived. Using the expression, the characteristics of the rotational restraint stiffness of the lipped flange have been investigated. The results show that there is a linear coupling relationship between the applied forces and the rotational restraint stiffness of the lipped flange. Based on the explicit expression of the rotational restraint stiffness of the lipped flange, a simplified analytical formula has been derived which can determine the elastic distortional buckling critical stress of the CFLCCs subjected to axial compression. The simplified analytical formula developed in this study has been shown to be accurate through the comparisons with results from the distortional buckling analyses using the ANSYS finite element software. The developed analytical formula is easy to apply, and can be used directly in practical design and incorporated into future design codes and guidelines.

Key Words
cold-formed steel; lipped channel sections; rotational restraint stiffness; distortional buckling; axial compression

Address
(1) School of Civil Engineering, Central South University, Changsha 410075, China;
(2) National Engineering Laboratory for High Speed Railway Construction, Changsha 410075, China.

Abstract
In this paper, various nonlocal higher-order shear deformation beam theories that consider the size dependent effects in Functionally Graded Material (FGM) beam are examined. The presented theories fulfill the zero traction boundary conditions on the top and bottom surface of the beam and a shear correction factor is not required. Hamilton's principle is used to derive equation of motion as well as related boundary condition. The Navier solution is applied to solve the simply supported boundary conditions and exact formulas are proposed for the bending and static buckling. A parametric study is also included to investigate the effect of gradient index, length scale parameter and length-to-thickness ratio (aspect ratio) on the bending and the static buckling characteristics of FG nanobeams.

Key Words
analytical solution; bending; buckling; functionally graded materials; higher order beam theory; nonlocal elasticity

Address
Smart Structures and New Advanced Materials Laboratory, Department of Mechanical Engineering, University of Zanjan, Zanjan, Iran.

Abstract
This paper presents an experimental study on the behavior of composite floor slab comprised by a new steel sheet and concrete slab. The strength of composite slabs depends mainly on the strength of the connection between the steel sheet and concrete, which is denoted by longitudinal shear strength. The composite slabs have three main failures modes, failure by bending, vertical shear failure and longitudinal shear failure. These modes are based on the load versus deflection curves that are obtained in bending tests. The longitudinal shear failure is brittle due to the mechanical connection was not capable of transferring the shear force until the failure by bending occurs. The vertical shear failure is observed in slabs with short span, large heights and high concentrated loads subjected near the supports. In order to analyze the behavior of the composite slab with a new steel sheet, six bending tests were undertaken aiming to provide information on their longitudinal shear strength, and to assess the failure mechanisms of the proposed connections. Two groups of slabs were tested, one with 3000 mm in length and other with 1500 mm in length. The tested composite slabs showed satisfactory composite behavior and longitudinal shear resistance, as good as well, the analysis confirmed that the developed sheet is suitable for use in composite structures without damage to the global behavior.

Key Words
composite structures; slim-floor; composite slab; longitudinal shear; bending test

Address
University of São Paulo, Engineering School of São Carlos, Structural Department, Av. Trabalhador Saocarlense, n° 400, CEP: 13566-580, São Carlos, SP, Brazil.

Abstract
In cold-formed stainless steel lipped channel-sections, use of web openings for service purposes are becoming increasingly popular. Web openings, however, result in the sections becoming more susceptible to web crippling. This paper presents a finite element investigation into the web crippling strength of cold-formed stainless steel lipped channel-sections with circular web openings under the interior-two-flange (ITF) loading condition. The cases of web openings located centred and offset to the bearing plates are considered in this study. In order to take into account the influence of the circular web openings, a parametric study involving 2,220 finite element analyses was performed, covering duplex EN1.4462, austenitic EN1.4404 and ferritic EN1.4003 stainless steel grades. From the results of the parametric study, strength reduction factor equations are proposed. The strengths obtained from reduction factor equations are first compared to the strengths calculated from the equations recently proposed for cold-formed carbon steel lipped channel-sections. It is demonstrated that the strength reduction factor equations proposed for cold-formed carbon steel are unconservative for the stainless steel grades by up to 17%. New coefficients for web crippling strength reduction factor equations are then proposed that can be applied to all three stainless steel grades.

Key Words
cold-formed stainless steel; lipped channel-section; web crippling; finite element analysis; strength reduction factor

Address
(1) Amir M. Yousefi, James B.P. Lim, G. Charles Clifton:
Department of Civil and Environmental Engineering, The University of Auckland, New Zealand;
(2) Asraf Uzzaman:
Department of Mechanical and Aerospace Engineering, The University of Strathclyde, 75 Montrose Street, Glasgow G1 1XJ, UK;
(3) Ben Young:
Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong.


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