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CONTENTS
Volume 48, Number 3, November10 2013
 

Abstract
Structural health monitoring is crucial to maintain the structural performance safely. Moreover, the Kullback-Leibler divergence (KLD) is applied usually to asset the similarity between different probability density functions in the pattern recognition. In this study, the KLD is employed to detect the damage. However the asymmetry of the KLD is a shortcoming for the damage detection, to overcoming this shortcoming, two other divergences and one statistic distribution are proposed. Then the damage identification by the KLD and its three descriptions from the symmetric point of view is investigated. In order to improve the reliability and accuracy of the four divergences, the gapped smoothing method (GSM) is adopted. On the basis of the damage index approach, the new damage index (DI) for detect damage more accurately based on the four divergences is developed. In the last, the grey relational coefficient and hypothesis test (GRCHT) is utilized to obtain the more precise damage identification results. Finally, a clear remarkable improvement can be observed. To demonstrate the feasibility and accuracy of the proposed method, examples of an isotropic beam with different damage scenarios are employed so as to check the present approaches numerically. The final results show that the developed approach successfully located the damaged region in all cases effect and accurately.

Key Words
KLD; symmetric description; GSM; DI; GRCHT

Address
Shaohua Tian, Xuefeng Chen, Zhibo Yang, Zhengjia He and Xingwu Zhang : Key Laboratory for Manufacturing Systems Engineering, Xi\'an Jiaotong University, 710049 Xi\'an, China

Abstract
An integrated superelement concept is proposed to improve the computational efficiency when analyzing structural responses during progressive collapses of large-scale structures, such as multi-storey reinforced concrete buildings. While the proposed methodology is straightforward and can be implemented into an existing finite element program with little effort, it is able to significantly reduce the computational cost without the loss of any critical information of the structural responses. Compared with the models without superelement, significant saving in computational cost and satisfactory prediction accuracy can be obtained with the proposed approach.

Key Words
superelement; computational efficiency; structural analysis; large-scale structures; progressive collapse

Address
Xu Long, Weifeng Yuan, Kang Hai Tan and Chi King Lee : School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore

Abstract
This paper deals with the development of expressions relating structural seismic response parameters to the epicentral distances of an earthquake and the natural period of several reinforced concrete buildings (6, 9 and 12 storey), with three floor plans: symmetric, monosymmetric, and unsymmetric. These structures are subjected to seismic spectrum of accelerations collected during the Boumerdes earthquake (Algeria, May 21st, 2003, Mw=6.8) at different epicentral distances. The objective of this study is to develop relations between structural responses namely: base shear, storey displacements, interstory drifts and epicentral distance and fundamental period for a given earthquake. The seismic response of the buildings is carried out in both longitudinal transverse and directions by the response spectrum method (modal spectral approach).

Key Words
structural seismic response; epicentral distance; earthquake; reinforced concrete buildings; storey displacement

Address
S. Dorbani and D. Benouar : Built Environment Lab. (LBE), Faculty of Civil Engineering, Algeria
M. Badaoui : Construction Supply & Services Integrated (CSSI), France

Abstract
In this paper, unified nonlocal shear deformation theory is proposed to study bending, buckling and free vibration of nanobeams. This theory is based on the assumption that the in-plane and transverse displacements consist of bending and shear components in which the bending components do not contribute toward shear forces and, likewise, the shear components do not contribute toward bending moments. In addition, this present model is capable of capturing both small scale effect and transverse shear deformation effects of nanobeams, and does not require shear correction factors. The equations of motion are derived from Hamilton\'s principle. Analytical solutions for the deflection, buckling load, and natural frequency are presented for a simply supported nanobeam, and the obtained results are compared with those predicted by the nonlocal Timoshenko beam theory and Reddy beam theories.

Key Words
nonlocal beam models; shear deformation; bending; buckling; vibration; nanobeam

Address
H.M. Berrabah, Abdelouahed Tounsi, E.A. Adda Bedia : Laboratoire des Materiaux et Hydrologie, Universite de Sidi Bel Abbes, Faculte de Technologie, Departement de Genie Civil, Algeria
Abdelouahed Tounsi : Laboratoire des Structures et Materiaux Avances dans le Genie Civil et Travaux Publics, Universite de Sidi Bel Abbes, Faculte de Technologie, Departement de Genie Civil, Algeria
Abdelwahed Semmah : Universite de Sidi Bel Abbes, Faculte des Sciences exactes, Departement de Physique, Algeria

Abstract
Different types of long slender pile shall buckle with weak soil and liquefied stratum surrounded. Different from considering single side earth pressure, it was suggested that the lateral earth pressure can be divided into two categories while buckling: the earth pressure that prevent and promotes the lateral movement. Active and passive earth pressure calculation model was proposed supposing earth pressure changed linearly with displacement considering overlying load, shaft resistance, earth pressure at both sides of the pile. Critical buckling load calculation method was proposed based on the principle of minimum potential energy quoting the earth pressure calculation model. The calculation result was contrasted with the field test result of small diameter TC pile (Plastic Tube Cast-in-place pile). The fix form could be fixed-hinged in the actual calculation assuring the accuracy and certain safety factor. The contributions of pile fix form depend on the pile length for the same geological conditions. There exists critical friction value in specific geological conditions that the side friction has larger impact on the critical buckling load while it is less than the value and has less impact with larger value. The buckling load was not simply changed linearly with friction. The buckling load decreases with increased limit active displacement and the load tend to be constant with larger active displacement value; the critical buckling load will be the same for different fix form for the small values.

Key Words
pile; buckling; critical buckling load; active and passive earth pressure considering displacement; fix form

Address
Yong-hui Chen, Long Chen, Lin Liu : Research Institute of Geotechnical Engineering, Hohai University, Nanjing 210098, China
Yong-hui Chen : Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Hohai University, Nanjing 210098, China
Kai Xu : Nanjing Hydraulic Research Institute, Nanjing, 210098, China
Charles W.W. Ng : The Hong Kong University of Science and Technology, Hong Kong


Abstract
Cold-formed profiles have been largely used in the building industry because they can be easily produced and because they allow for a wide range of sections and thus can be utilized to meet different project requirements. Attainment of maximum performance by structural elements with low use of material is a challenge for engineering projects. This paper presents a numerical study aimed at minimizing the weight of lipped and unlipped cold-formed channel columns, following the AISI 2007 specification. Flexural, torsional and torsional–flexural buckling of columns was considered as constraints. The simulated annealing method was used for optimization. Several numerical simulations are presented and discussed to validate the proposal, in addition to an experimental example that qualifies its implementation. The ratios between lips, web width, and flange width are analyzed. Finally, it may be concluded that the optimization process yields excellent results in terms of cross-sectional area reduction.

Key Words
cold-formed structures; steel; optimization; simulated annealing; columns; compression

Address
Moacir Kripka and Zacarias Martin Chamberlain Pravia : Engineering Graduate Program, University of Passo Fundo, Brazil

Abstract
The present study fundamentally investigated the mechanical performance of the rib-stiffened super-wide bridge deck with twin box girders in concrete, which is a very popular application to efficiently widen the bridges with normal span. The shear lag effects of the specific cross-sections were firstly studied. The spatial stress distribution and local stiffness of the bridge deck with twin box girders were then investigated under several typical wheel load conditions. Meanwhile, a comparative study for the bridge deck with and without stiffening ribs was also carried out during the investigation; thereby, a design optimization for the stiffening ribs was further suggested. Finally, aiming at the preliminary design, an approximate methodology to manually calculate the bending moments of the rib-stiffened bridge deck was analytically proposed for engineers to quickly assess its performance. This rib-stiffened bridge deck with twin box girders can be widely applied for concrete (especially concrete cable-stayed) bridges with normal span, however, requiring a super-wide bridge width due to the traffic flow.

Key Words
twin box girders; super-wide bridge deck; stiffening ribs; concrete; mechanical performance; optimization

Address
Wen Xiong, Jianshu Ye, Xuemei Gai : Department of Bridge Engineering, School of Transportation, Southeast University, Nanjing, 210096, China
C.S. Cai : Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge, LA 70803, USA

Abstract
This work is concerned with transverse vibrations of axially traveling nanobeams including strain gradient and thermal effects. The strain gradient elasticity theory and the temperature field are taken into consideration. A new higher-order differential equation of motion is derived from the variational principle and the corresponding higher-order non-classical boundary conditions including simple, clamped, cantilevered supports and their higher-order \"offspring\" are established. Effects of strain gradient nanoscale parameter, temperature change, shape parameter and axial traction on the natural frequencies are presented and discussed through some numerical examples. It is concluded that the factors mentioned above significantly influence the dynamic behaviors of an axially traveling nanobeam. In particular, the strain gradient effect tends to induce higher vibration frequencies as compared to an axially traveling macro beams based on the classical vibration theory without strain gradient effect.

Key Words
critical speed; natural frequency; size dependent; strain gradient; thermal effect

Address
Cheng Li : School of Urban Rail Transportation, Soochow University, Suzhou 215006, China


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