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CONTENTS
Volume 52, Number 5, December10 2014
 

Abstract
Structural behaviors of a sustainable hybrid column with the ultra high performance cementitious composites (UHPCC) permanent form under compression and flexure were studied. Critical state and failure stage characters are analyzed for large and small eccentricity cases. A simplified theoretical model is proposed for engineering designs and unified formulas for loading capacity of the hybrid column under compression and flexure loads are derived, including axial force and moment. Non-linear numerical analysis is carried out to verify the theoretical predictions. The theoretical predictions agree well with the numerical results which are verified by the short hybrid column tests recursively. Compared with the traditional reinforced concrete (RC) column, the loading capacity of the sustainable hybrid column is improved significantly due to UHPCC confinements.

Key Words
sustainable design; hybrid column; loading capacity; ultra high performance cementitious composites

Address
Wu Xiang-Guo and Hu Qiong: Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education, Harbin Institute of Technology, Harbin, 150090, China; School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China
Zou Ruofei: Department of Civil and Environmental Engineering, University of Illinois, IL 61801-2352, USA
Zhao Xinyu and Yu Qun: School of Architecture Engineering, Harbin Engineering University, Harbin 150001, China


Abstract
The aim of the shaking table experiment is to verify the isolation effect of a storage liquid tank with multiple friction pendulum bearings. A 1:20 scale model of a real storage liquid tank that is widely used in the petroleum industry was examined by the shaking table test to compare its anchored base and isolated base. The seismic response of the tank was assessed by employing the time history input. The base acceleration, wave height and tank wall stress were used to evaluate the isolation effect. Finally, the influences of the bearing performance that characterizes the isolated tank, such as the friction force and residual displacement, were discussed.

Key Words
tank; shaking table test; base isolation; multiple friction pendulum bearing; liquid solid coupling

Address
Ruifu Zhang, Dagen Weng and Qingzi Ge: Research Institute of Structural Engineering and Disaster Reduction, Tongji University, 1239 Siping Road, Shanghai 200092, China

Abstract
Very long life fatigue tests were carried out on 16Mn steel base metal and its welded joint by using the ultrasonic fatigue testing technique. Specimen shapes (round and plate) were considered for both the base metal and welded joint. The results show that the specimens present different S-N curve characteristics in the region of 105-109 cycles. The round specimens showed continuously decreasing tendency while plate specimens showed a steep decreasing step and an asymptotic horizontal one. The fatigue strength of round specimen was found higher than plate specimen. The fatigue strength of as-welded joint was 45.0% of the base material for butt joint and 40% for cruciform as-welded joint. It was found that fracture can still occur in butt joint beyond 5x6 cycles. The cruciform joint has a fatigue limit in the very long life fatigue regime (107-109 cycles). Fatigue strength of butt as-welded joint was much higher as compared to cruciform as-welded joint. Improvement in fatigue strength of welded joint was found due to UPT. The observation of fracture surface showed crack mainly initiated from welded toe at fusion areas or geometric discontinuity sites at the surface in butt joint and from welded toe in cruciform joint.

Key Words
16 Mn; very high cycle fatigue; welded joint; S-N curve; crack initiation mechanism

Address
Yongjie Liu, Chao He, Chongxiang Huang, Muhammad K. Khan and Qingyuan Wang: Key Laboratory of Energy Engineering Safety and Disaster Mechanics, Ministry of Education, College of Architecture & Environment, Sichuan University, Chengdu, 610065, China

Abstract
Large space structures may have resonant low eigenvalues and often these appear with closely-spaced natural frequencies. Owing to the coupling among modes with closely-spaced natural frequencies, each eigenvector corresponding to closely-spaced eigenvalues is ill-conditioned that may cause structural instability. The subspace to an invariant subspace corresponding to closely-spaced eigenvalues is well-conditioned, so a method is presented to design the feedback control law of intelligent structures with closely-spaced eigenvalues in this paper. The main steps are as follows: firstly, the system with closely-spaced eigenvalues is transformed into that with repeated eigenvalues by the spectral decomposition method; secondly, the computation for the linear combination of eigenvectors corresponding to repeated eigenvalues is obtained; thirdly, the feedback control law is designed on the basis of the system with repeated eigenvalues; fourthly, the system with closely-spaced eigenvalues is regarded as perturbed system on the basis of the system with repeated eigenvalues; finally, the feedback control law is applied to the original system, the first order perturbations of eigenvalues are discussed when the parameter modifications of the system are introduced. Numerical examples are given to demonstrate the application of the present method.

Key Words
feedback control; closely-spaced eigenvalue; intelligent structure; perturbed analysis

Address
Zongjie Cao and Zhongxiang Lei: Aviation University of Air Force, Changchun city of Jilin Province, 130022, China

Abstract
In this study, the control of the shape of pre-stressed cable structures and the effective control element were examined. The process of deriving the displacement control equations using the force method was explained, and the concurrent control scheme (CCS) and the sequence control scheme (SCS) were proposed. To explain the control scheme process, the quadrilateral cable net model was adopted and classified into a regular model and an irregular model for the analysis of the control results. In the control analysis of the regular model, the CCS and SCS analysis results proved reliable. For the SCS, the errors occur in the control stage and varied according to the control sequence. In the control analysis of the irregular model, the CCS analysis result also proved relatively reliable, and the SCS analysis result with the correction of errors in each stage was found nearly consistent with the target shape after the control. Finally, to investigate an effective control element, the Geiger cable dome was adopted. A set of non-redundant elements was evaluated in the reduced row echelon form of a coefficient matrix of control equations. Important elements for shape control were also evaluated using overlapping elements in the element sets, which were selected based on cable adjustments.

Key Words
shape adjustment; pre-stressed cable structures; force method; concurrent control; sequence control; non-redundant element; reduced row echelon form

Address
Sudeok Shon: School of Architectural Engineering, Korea University of Technology and Education, Cheonan, Chungnam 330-708, Republic of Korea
Alan S. Kwan: Cardiff School of Engineering, Cardiff University, Parade, Cardiff CF24-3AA, UK
Seungjae Lee: School of Architectural Engineering, Korea University of Technology and Education, Cheonan, Chungnam 330-708, Republic of Korea

Abstract
The MEMS structures usually are made from silicon; consideration of the viscoelastic effect in microbeams duo to the phenomena of silicon creep is necessary. Application of the fractional model of microbeams made from viscoelastic materials is studied in this paper. Quasi-static and dynamical responses of an electrically actuated viscoelastic microbeam are investigated. For this purpose, a nonlinear finite element formulation of viscoelastic beams in combination with the fractional derivative constitutive equations is elucidated. The four-parameter fractional derivative model is used to describe the constitutive equations. The electric force acting on the microbeam is introduced and numerical methods for solving the nonlinear algebraic equation of quasi-static response and nonlinear equation of motion of dynamical response are described. The deflected configurations of a microbeam for different purely DC voltages and the tip displacement of the microbeam under a combined DC and AC voltages are presented. The validity of the present analysis is confirmed by comparing the results with those of the corresponding cases available in the literature.

Key Words
viscoelastic microbeam; fractional derivatives; finite element method; electrical actuation; AC and DC voltage

Address
Seyed Masoud Sotoodeh Bahraini: Department of Mechanical Engineering, Yazd University, Yazd, 89195-741, Iran
Mohammad Eghtesad, Mehrdad Farid and Esmaeal Ghavanloo: School of Mechanical Engineering, Shiraz University, Shiraz, Iran

Abstract
Among severe plastic deformation methods, groove pressing is one of the prominent techniques for producing ultra-fine grained sheet materials. This process consists of imposing repetitive severe plastic deformation on the plate or sheet metals through alternate pressing. In the current study, a 2 mm pure Cu sheet has been subjected to repetitive shear deformation up to two passes. Hardness and tensile yield and ultimate stress were obtained after groove pressing. Fracture toughness tests have been performed and compared for three conditions of sheet material namely as received (initial annealed state), after one and two passes of groove pressing. Results of experiments indicate that a decrease in the values of fracture toughness attains as the number of constrained groove pressing (CGP) passes increase.

Key Words
Constrained Groove Pressing (CGP); copper; fracture toughness

Address
Bijan Mohammadi, Marzieh Tavoli and Faramarz Djavanroodi: School of Mechanical Engineering, Iran University of Science & Technology, Narmak, Tehran, Iran

Abstract
The parts of semi-rigid connected and partially embedded piles in elastic soil, above the soil and embedded in the soil are called the first region and second region, respectively. The upper end of the pile in the first region is supported by linear-elastic rotational spring. The forth order differential equations of both region for critical buckling load of partially embedded and semi-rigid connected pile with shear deformation are established using small-displacement theory and Winkler hypothesis. These differential equations are solved by differential transform method (DTM) and analytical method and critical buckling loads of semirigid connected and partially embedded pile are obtained, results are given in tables and graphs are presented for investigating the effects of relative stiffness of the pile and flexibility of rotational spring.

Key Words
differential transform method, semi-rigid connected, partially embedded pile, non-trivial solution, buckling

Address
Seval Catal: Civil Engineering Department, Engineering Faculty, Dokuz Eylul University, 35160, Buca, Izmir, Turkey

Abstract
According to the structure characteristics of the non-uniform beam bridge, a practical model for calculating the vibration equation of the non-uniform beam bridge is given and the application scope of the model includes not only the beam bridge structure but also the non-uniform beam with added masses and elastic supports. Based on the Bernoulli-Euler beam theory, extending the application of the modal perturbation method and establishment of a semi-analytical method for solving the vibration equation of the non-uniform beam with added masses and elastic supports based is able to be made. In the modal subspace of the uniform beam with the elastic supports, the variable coefficient differential equation that describes the dynamic behavior of the non-uniform beam is converted to nonlinear algebraic equations. Extending the application of the modal perturbation method is suitable for solving the vibration equation of the simply supported and continuous non-uniform beam with its arbitrary added masses and elastic supports. The examples, that are analyzed, demonstrate the high precision and fast convergence speed of the method. Further study of the timesaving method for the dynamic characteristics of symmetrical beam and the symmetry of mode shape should be developed. Eventually, the effects of elastic supports and added masses on dynamic characteristics of the three-span non-uniform beam bridge are reported.

Key Words
modal perturbation method; analytic solution; non-uniform beam; elastic support; added mass; mode shape

Address
Lu-ning Shi, Wei-ming Yan and Hao-xiang He: Beijing Laboratory of Earthquake Engineering and Structure Retrofit, Beijing University of Technology, Beijing 100124, China

Abstract
Rails are key elements in railway superstructure since these elements receive directly the train load transmitted by the wheels. Simultaneously, rails must provide effective stress transference to the rest of the track elements. This track element often deteriorates as a consequence of the vehicle passing or manufacturing imperfections that cause in rail several defects. Among these rail defects, transverse cracks highlights and are considered a severe pathology because they can suddenly trigger the rail failure. This study is focused on UIC-60 rails with transverse cracks. A 3-D FEM model is developed in ANSYS for the flawless rail in which conditions simulating the crack presence are implemented. To account for the inertia loss of the rail as a consequence of the cracking, a reduction of the bending stiffness of the rail is considered. The numerical models have been calibrated using the first four bending vibration modes in terms of frequencies. These vibration frequencies have been obtained using the Experimental Modal Analysis technique, studying the changes in the modal parameters of the rails induced by the crack and comparing the results obtained by the model with experimental results. Finally, the calibrated and validated models for the single rail have been implemented in a complete railway ballasted track FEM model in order to study the static influence of the cracks on the rail deflection caused by a load passing.

Key Words
Experimental Modal Analysis (EMA); rail; transverse crack; finite element model (FEM)

Address
Laura Montalban Domingo, Beatriz Baydal Giner and Julia I. Real Herraiz: Department of Transportation Engineering and Infrastructures, School of Civil Engineering, Polytechnic University of Valencia, Camino de Vera 14, 46022 Valencia, Spain
Clara Zamorano Martín: Foundation for the Research and Engineering in Railways, 160 Serrano, 28002 Madrid, Spain

Abstract
The free vibration of functionally graded material (FGM) beams on an elastic foundation and spring supports is investigated. Young\'s modulus, mass density and width of the beam are assumed to vary in thickness and axial directions respectively following the exponential law. The spring supports are also taken into account at both ends of the beam. An analytical formulation is suggested to obtain eigen solutions of the FGM beams. Numerical analyses, based on finite element method by using a beam finite element developed in this study, are performed in order to show the legitimacy of the analytical solutions. Some results for the natural frequencies of the FGM beams are given considering the effect of various structural parameters. It is also shown that the spring supports show the greatest effect on the natural frequencies of FGM beams.

Key Words
FGM beam, free vibration, closed-form solution, spring support, elastic foundation, FEM

Address
Hien Ta Duy, Thuan Nguyen Van and Hyuk Chun Noh: Department of Civil and Environmental Engineering, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul 143-747, Republic of Korea

Abstract
The structures of concern in this study are subject to two types of forces: dead loads from the acceleration imposed on the structures as well as the installed operation machines and the additional adjustable forces. We wish to determine the critical values of the adjustable forces when buckling of the structures occurs. The mathematical statement of such a problem gives rise to a constrained eigenvalue problem (CEVP) in which the dominant eigenvalue is subject to an equality constraint. A numerical algorithm for solving the CEVP is proposed in which an iterative method is employed to identify an interval embracing the target eigenvalue. The algorithm is applied to four engineering application examples finding the critical loads of a fixed-free beam subject to its own body force, two plane structures and one wide-flange beam using shell elements when acceleration force is present. The accuracy is demonstrated using the first example whose classical solution exists. The significance of the equality constraint in the EVP is shown by comparing the solutions without the constraint on the eigenvalue. Effectiveness and accuracy of the numerical algorithm are presented.

Key Words
buckling; equality constraint; eigenvalue; acceleration; dead loads; participation factor; finite element; stability

Address
Wenjing Wang: School of Mechanical, Electric and Control Engineering, Beijing Jiaotong University, Beijing, 10004, China
Randy Gu: Department of Mechanical Engineering, Oakland University, Rochester, Michigan 48309, USA

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