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Volume 21, Number 1, May20 2016

In the present study, the nonlinear magneto-electro-mechanical free vibration behavior of rectangular double-bonded sandwich microbeams based on the modified strain gradient theory (MSGT) is investigated. It is noted that the top and bottom sandwich microbeams are considered with boron nitride nanotube reinforced composite face sheets (BNNTRC-SB) with electrical properties and carbon nanotube reinforced composite face sheets (CNTRC-SB) with magnetic fields, respectively, and also the homogenous core is used for both sandwich beams. The connections of every sandwich beam with its surrounding medium and also between them have been carried out by considering Pasternak foundations. To take size effect into account, the MSGT is introduced into the classical Timoshenko beam theory (CT) to develop a size-dependent beam model containing three additional material length scale parameters. For the CNTRC and BNNTRC face sheets of sandwich microbeams, uniform distribution (UD) and functionally graded (FG) distribution patterns of CNTs or BNNTs in four cases FG-X, FG-O, FG-A, and FG-V are employed. It is assumed that the material properties of face sheets for both sandwich beams are varied in the thickness direction and estimated through the extended rule of mixture. On the basis of the Hamilton's principle, the size-dependent nonlinear governing differential equations of motion and associated boundary conditions are derived and then discretized by using generalized differential quadrature method (GDQM). A detailed parametric study is presented to indicate the influences of electric and magnetic fields, slenderness ratio, thickness ratio of both sandwich microbeams, thickness ratio of every sandwich microbeam, dimensionless three material length scale parameters, Winkler spring modulus and various distribution types of face sheets on the first two natural frequencies of double-bonded sandwich microbeams. Furthermore, a comparison between the various beam models on the basis of the CT, modified couple stress theory (MCST), and MSGT is performed. It is illustrated that the thickness ratio of sandwich microbeams plays an important role in the vibrational behavior of the double-bonded sandwich microstructures. Meanwhile, it is concluded that by increasing H/lm, the values of first two natural frequencies tend to decrease for all amounts of the Winkler spring modulus.

Key Words
smart materials; nonlinear vibration analysis; double-bonded sandwich Timoshenko microbeams; size effect; MSGT; GDQM

Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, Kashan, Iran.

In this study, the influence of centrally placed circular and square cutouts on vibration and buckling characteristics of different ply-oriented laminated panels under the action of compressive and/or tensile types of nonuniform in-plane edge loads are investigated. The panels are inspected under the action of uniaxial compression, uniaxial tension and biaxial, compression-tension, loading configurations. Furthermore, the effects of different degrees of edge restraints and panel aspect ratios are also addressed in this work. Towards this, a nine-node heterosis plate element has been adopted which includes the effect of shear deformation and rotary inertia. According to the results, the tensile buckling loads are higher than that of compressive buckling loads. However, the tensile buckling load continuously reduces with the increased cutout sizes irrespective of ply-orientations. This is also true for compressive buckling loads except for some particular ply-orientations with higher sized cutouts.

Key Words
laminates; cutout parameters; finite element method; heterosis element; vibration; buckling

(1) T. Rajanna, Sauvik Banerjee, Yogesh M. Desai:
Department of Civil Engineering, Indian Institute of Technology Bombay, Mumbai 400 076, India;
(2) T. Rajanna:
Department of Civil Engineering, B.M.S College of Engineering (Autonomous College under VTU), Bengaluru-560019, India;
(3) D.L. Prabhakara:
Sahyadri College of Engineering & Management, Mangalore 575 007, India.

The Poisson ratio reduction of symmetric hygrothermal aged [θm/90n]s composite laminates containing a transverse cracking in mid-layer is predicted by using a modified shear-lag model. Good agreement is obtained by comparing the prediction models and experimental data published by Joffe et al. (2001). The material properties of the composite are affected by the variation of temperature and transient moisture concentration distribution in desorption case, and are based on a micro-mechanical model of laminates. The transient and non-uniform moisture concentration distribution give rise to the transient Poisson ratio reduction. The obtained results represent well the dependence of the Poisson ratio degradation on the cracks density, fibre orientation angle of the outer layers and transient environmental conditions. Through the presented study, we hope to contribute to the understanding of the hygrothermal behaviour of cracked composite laminate.

Key Words
transverse cracking; poisson ratio; hygrothermal effect; Tsai model; desorption

(1) M. Khodjet-Kesba, A. Benkhedda, B. Boukert:
Laboratoire des sciences aéronautiques, Institut d'aeéronautique et des études spatiales, Université de Blida1, Blida, Algérie;
(2) E.A. Adda bedia:
Laboratoire des Matériaux et Hydrologie, Université de Sidi Bel Abbes, Sidi Bel Abbes, Algérie.

The use of box columns has been increased due to the rigidity in rigid orthogonal moment resisting frames. On the other hand, the installation and welding of necessary horizontal continuity plates inside the columns are both labor-consuming and costly tasks. Accordingly, in this paper, a new beam-to-box column connection by trapezoidal external stiffeners and horizontal bar mats is presented to provide seismic parameters. The proposed connection consists of eight external stiffeners in the level of beam flanges and five horizontal bar mats in Concrete Filled Tube (CFT) columns. The new connection effectively alleviates the stress concentration and moves the plastic hinge away from the column face by horizontal external stiffeners. In addition, the result shows that proposed connection has provided the required strength and rigidity of connection, so that the increased strength, 8.08% and rigidity, 3.01% are compared to connection with internal continuity plates, also the results indicate that this connection can offer appropriate ductility and energy dissipation capacity for its potential application in moment resisting frames in seismic region. As a result, the proposed connection can be a good alternative for connection with continuity plates.

Key Words
(NFT/CFT) column; rigid connection; continuity plate; trapezoidal stiffener; bar mats

(1) Omid Rezaifar:
Department of Civil Engineering and Research Institute of Novin Technologies, Semnan University, Iran;
(2) Adel Younesi:
Structure Engineering, Faculty of Civil Engineering, Semnan University, Iran.

Seismic fragility analysis is a probabilistic decision-making framework which is widely implemented for evaluating vulnerability of a building under earthquake loading. It requires ingredient named probabilistic model and commonly developed using statistics requiring collecting data in large quantities. Preparation of such a data-base is often costly and time-consuming. Therefore, in this paper, by developing generic seismic drift demand model for regular-multi-story steel moment resisting frames is tried to present a novel application of the probabilistic decisionmaking analysis to practical purposes. To this end, a demand model which is a linear function of intensity measure in logarithmic space is developed to predict overall maximum inter-story drift. Next, the model is coupled with a set of regression-based equations which are capable of directly estimating unknown statistical characteristics of the model parameters.To explicitly address uncertainties arise from randomness and lack of knowledge, the Bayesian regression inference is employed, when these relations are developed. The developed demand model is then employed in a Seismic Fragility Analysis (SFA) for two designed building. The accuracy of the results is also assessed by comparison with the results directly obtained from Incremental Dynamic analysis.

Key Words
probabilistic demand model; seismic fragility analysis; incremental dynamic analysis; generic steel moment resisting frame; Bayesian regression

Department of Civil and Environmental Engineering, Amirkabir University of Technology, Tehran, P.O. Box 15875-4413, Iran.

Concrete creep, while significantly changing the static behaviors of concrete filled steel tube (CFST) structures, do alter the structures' dynamic behaviors as well, which is studied quite limitedly. The attempt to investigate the influence of concrete creep on the dynamic property and response of CFST arch bridges was made in this paper. The mechanism through which creep exerts its influence was analyzed first; then a predicative formula was proposed for the concrete elastic modulus after creep based on available test data; finally a numerical analysis for the effect of creep on the dynamic behaviors of a long-span half-through CFST arch bridge was conducted. It is demonstrated that the presence of concrete creep increases the elastic modulus of concrete, and further magnifies the seismic responses of the displacement and internal force in some sections of the bridge. This influence is related closely to the excitation and the structure, and should be analyzed case-by-case.

Key Words
creep; seismic analysis; time-dependent analysis; concrete; steel; arch bridges

(1) Yishuo Ma, Yuanfeng Wang, Li Su, Shengqi Mei:
School of Civil Engineering, Beijing Jiaotong University, No. 3 Shangyuancun Road, Haidian District, Beijing, 100044, P.R. China;
(2) Yishuo Ma:
Center of Science and Technology of Construction, Ministry of Housing and Urban-Rural Development (MOHURD), No. 9 Sanlihe Road, Haidian District, Beijing, 100835, P.R. China.

This work focuses on the behavior of the static analysis of functionally graded plates materials (FGMs) with porosities that may possibly occur inside the functionally graded materials (FGMs) during their fabrication. For this purpose a new refined plate theory is used in this work, it contains only four unknowns, unlike five unknowns for other theories. This new model meets the nullity of the transverse shear stress at the upper and lower surfaces of the plate. The parabolic distribution of transverse shear stresses along the thickness of the plate is taken into account in this analysis; the material properties of the FGM plate vary a power law distribution in terms of volume fraction of the constituents. The rule of mixture is modified to describe and approximate material properties of the FG plates with porosity phases. The validity of this theory is studied by comparing some of the present results with other higher-order theories reported in the literature, the influence of material parameter, the volume fraction of porosity and the thickness ratio on the behavior mechanical P-FGM plate are represented by numerical examples.

Key Words
functionally graded material; higher-order theory; refined theory; volume fraction of porosity

(1) R. Benferhat, M. Said Mansour:
Laboratoire de Géomateriaux, Departement de Génie Civil, Université Hassiba Benbouali de Chlef, Algérie;
(2) T. Hassaine Daouadji, L. Hadji:
Département de Génie Civil, Université Ibn Khaldoun de Tiaret, Algérie;
(3) T. Hassaine Daouadji, L. Hadji:
Laboratoire des Matériaux & Hydrologie, Université Djillali Liabès de Sidi Bel Abbes, Algérie.

Due to excellent advantages such as better illuminative effects, considerable material savings and ease and rapidness of construction, the bolted ball-cylinder joint which is a new type joint system has been proposed in space truss structures. In order to reveal more information and understanding on the behaviour of bolted ball-cylinder joints, full-scale experiments on eight bolted ball-cylinder joint specimens were conducted. Five joint specimens were subjected to axial compressive force, while another three joint specimens were subjected to axial tensile force. The parameters investigated herein were the outside diameter of hollow cylinders, the height of hollow cylinders, the thickness of hollow cylinders, ribbed stiffener and axial force. These joint specimens were collapsed by excessive deformation of hollow cylinders, punching damage of hollow cylinders, evulsion of bolts, and weld cracking. The strain distributions on the hollow cylinder opening were mainly controlled by bending moments. To improve the ultimate bearing capacity and axial stiffness of bolted ball-cylinder joints, two effective measures were developed: (1) the thickness of the hollow cylinder needed to be thicker; (2) the ribbed stiffener should be adopted. In addition, the axial stiffness of bolted ball-cylinder joints exhibited significant non-linear characteristics.

Key Words
bolted ball-cylinder joints; full-scale experiments; failure modes; ultimate bearing capacity; axial stiffness

(1) Xiaonong Guo, Zewei Huang, Zhe Xiong, Shangfei Yang:
Department of Building Engineering, Tongji University, Shanghai 200092, China;
(2) Li Peng:
Shanghai T&D Architechral Technology Co., Ltd., Shanghai 200092, China.

It was found that the lateral stiffness changes obvious at the transfer position of the section configuration from SRC to RC. This particular behavior leads to that the transfer columns become as the important elements in SRC-RC hybrid structures. A comprehensive study was conducted to investigate the seismic behavior of SRC-RC transfer columns based on a low cyclic loading test of 16 transfer columns compared with 1 RC column. Test results shows three failure modes for transfer columns, which are shear failure, bond failure and bend failure. Its seismic behavior was completely analyzed about the failure mode, hysteretic and skeleton curves, bearing capacity deformation ability, stiffness degradation and energy dissipation. It is further determined that displacement ductility coefficient of transfer columns changes from 1.97 to 5.99. The stiffness of transfer columns are at the interval of SRC and RC, and hence transfer columns can play the role of transition from SRC to RC. All specimens show similar discipline of stiffness degradation and the process can be divided into three parts. Some specimens of transfer column lose bearing capacity swiftly after shear cracking and showed weak energy dissipation ability, but the others show better ability of energy dissipation than RC column.

Key Words
steel reinforced concrete; hybrid structure; transfer column; displacement ductility; cyclic test; seismic behavior

(1) Kai Wu, Yang Nan:
College of Civil and Transportation Engineering, Hohai University, Nanjing 210098, China;
(2) Jianyang Xue,Hongtie Zhao:
School of Civil Engineering, Xi'an University of Architecture & Technology, Xi'an 710055, China.

The cable-supported ribbed beam composite slab structure (CBS) is a new type of pre-stressed hybrid structure. The standard construction method of CBS including five steps and two key phases are proposed in this paper. The theoretical analysis and experimental research on a 1:5 scaled model were carried out. First, the tensioning construction method based on deformation control was applied to pre-stress the cables. The research results indicate that the actual tensile force applied to the cable is slightly larger than the theoretical value, and the error is about 6.8%. Subsequently, three support dismantling schemes are discussed. Scheme one indicates that each span of CBS has certain level of mechanical independence such that the construction of a span is not significantly affected by the adjacent spans. It is shown that dismantling from the middle to the ends is an optimal support dismantling method. The experimental research also indicates that by using this method, the CBS behaves identically with the numerical analysis results during the construction and service.

Key Words
cable-supported ribbed beam composite slab; pre-stress; hybrid structure; fabrication; construction; tensioning; dismantling

(1) W.T. Qiao:
School of Civil Engineering, Shi Jiazhuang Tiedao University, 17 North 2nd Ring Road, Shi Jiazhuang, Hebei, China;
(2) Q. An:
School of Civil Engineering, Tianjin University, 92 Weijin Road, Tianjin, China;
(3) D. Wang:
Department of Civil and Environmental Engineering, University of Alabama in Huntsville, 301 Sparkman Drive, Huntsville, AL, USA;
(4) M.S. Zhao:
School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore.

The dynamic characteristics of continuous steel-concrete composite beams considering the effect of interlayer slip were investigated based on Euler Bernoulli\'s beam theory. A simplified calculation model was presented, in which the Mode Stiffness Matrix (MSM) was developed. The natural frequencies and modes of partialinteraction composite continuous beams can be calculated accurately and easily by the use of MSM. Proceeding from the present method, the natural frequencies of two-span steel-concrete composite continuous beams with different span-ratios (0.53, 0.73, 0.85, 1) and different shear connection stiffnesses on the interface are calculated. The influence pattern of interfacial stiffness on bending vibration frequency was found. With the decrease of shear connection stiffness on the interface, the flexural vibration frequencies decrease obviously. And the influence on low order modes is more obvious while the reduction degree of high order is more sizeable. The real natural frequencies of partial-interaction continuous beams commonly used could have a 20% to 40% reduction compared with the fully-interaction ones. Furthermore, the reduction-ratios of natural frequencies for different span-ratios two-span composite beams with uniform shear connection stiffnesses are totally the same. The span-ratio mainly impacts on the mode shape. Four kinds of shear connection stiffnesses of steel-concrete composite continuous beams are calculated and compared with the experimental data and the FEM results. The calculated results using the proposed method agree well with the experimental and FEM ones on the low order modes which mainly determine the vibration properties.

Key Words
partial-interaction; steel-concrete composite continuous beam; shear connection stiffness; mode stiffness matrix; dynamic analysis

(1) Genshen Fang:
State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, P.R. China;
(2) Jingquan Wang, Shuai Li:
Key Laboratory of Concrete and Prestressed Concrete Structure of Ministry of Education, School of Civil Engineering, Southeast University, Nanjing 210096, P.R. China;
(3) Shubin Zhang:
Jiangsu Province Communications Planning and Design Institute Co., Ltd., Nanjing 210005, P.R. China.

Five extended cylindrical reticulated shells are proposed by changing distribution rule of diagonal rods based on three fundamental types. Modeling programs for fundamental types and extended types of cylindrical reticulated shell are compiled by using the ANSYS Parametric Design Language (APDL). On this basis, conditional formulas are derived when the grid shape of cylindrical reticulated shells is equilateral triangle. Internal force analysis of cylindrical reticulated shells is carried out. The variation and distribution regularities of maximum displacement and stress are studied. A shape optimization program is proposed by adopting the sequence two-stage algorithm (RDQA) in FORTRAN environment based on the characteristics of cylindrical reticulated shells and the ideas of discrete variable optimization design. Shape optimization is achieved by considering the objective function of the minimum total steel consumption, global and locality constraints. The shape optimization for three fundamental types and five extended types is calculated with the span of 30 m~80 m and rise-span ratio of 1/7~1/3. The variations of the total steel consumption along with the span and rise-span ratio are analyzed with contrast to the results of shape optimization. The optimal combination of main design parameters for five extended cylindrical reticulated shells is investigated. The total steel consumption affected by distribution rule of diagonal rods is discussed. The results show that: (1) Parametric modeling method is simple, efficient and practical, which can quickly generate different types of cylindrical reticulated shells. (2) The mechanical properties of five extended cylindrical reticulated shells are better than their fundamental types. (3) The total steel consumption of cylindrical reticulated shells is optimized to be the least when rise-span ratio is 1/6. (4) The extended type of three-way grid cylindrical reticulated shell should be preferentially adopted in practical engineering. (5) The grid shape of reticulated shells should be designed to equilateral triangle as much as possible because of its reasonable stress and the lowest total steel consumption.

Key Words
extended cylindrical reticulated shell; APDL; parametric modeling; shape optimization

(1) J. Wu, S.C. Li, Z.H. Xu, L.P. Li, Y.G. Xue:
Geotechnical and Structural Engineering Research Center, Shandong University, Ji'nan 250061, Shandong, China;
(2) J. Wu, X.Y. Lu:
Institute of Engineering Mechanics, Shandong Jianzhu University, Ji'nan 250101, Shandong, China;
(3) Z.D. Wang:
Shantui Construction Machinery co., Ltd, Ji

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