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CONTENTS
Volume 54, Number 3, May10 2015
 

Abstract
In this paper an 8-node quadrilateral assumed stress hybrid Mindlin plate element with 39B is presented. The formulation is based on complementary energy principle. The proposed element is free of shear locking and is capable of passing all the patch tests, especially the non-zero constant shear enhanced patch test. To accomplish this purpose, special attention is devoted to selecting boundary displacement interpolation and stress approximation in domain. The arbitrary order Timoshenko beam function is successfully used to derive the boundary displacement interpolation. According to the equilibrium equations, an appropriate stress approximation is rationally derived. Particularly, in order to improve element\'s accuracy, the assumed stress field is derived by employing 39B rather than conventional 21B. The resulting element can be adopted to analyze both moderately thick and thin plates, and the convergence for the very thin case can be ensured theoretically. Excellent element performance is demonstrated by a wide of experimental evaluations.

Key Words
hybrid stress element; Mindlin plate; arbitrary order Timoshenko beam function; enhanced patch test

Address
Tan Li, Zhaohui Qi, Xu Ma: 1State Key Laboratory for Structural Analysis of Industrial Equipment, Department of Engineering Mechanics, Dalian University of Technology, Dalian, 116023, China
Wanji Chen: 2Key Laboratory of Liaoning Province for Composite Structural Analysis of Aero craft and Simulation, Shenyang Aerospace University, Shenyang 110136, China

Abstract
The free vibration of rotating Euler-Bernoulli beams with the thickness and/or width of the cross-section vary linearly along the length is investigated by using the Adomian modified decomposition method (AMDM). Based on the AMDM, the governing differential equation for the rotating tapered beam becomes a recursive algebraic equation. By using the boundary condition equations, the dimensionless natural frequencies and the closed form series solution of the corresponding mode shapes can be easily obtained simultaneously. The computed results for different taper ratios as well as different offset length and rotational speeds are presented in several tables and figures. The accuracy is assured from the convergence and comparison with the previous published results. It is shown that the AMDM provides an accurate and straightforward method of free vibration analysis of rotating tapered beams.

Key Words
adomian modified decomposition method; rotating tapered beam; taper ratio; natural frequency; mode shape

Address
Qibo Mao: School of Aircraft Engineering, Nanchang HangKong University, 696 South Fenghe Avenue, Nanchang, CN-330063, P.R. China

Abstract
This paper focuses on large deflection static behavior of edge cracked simple supported beams subjected to a non-follower transversal point load at the midpoint of the beam by using the total Lagrangian Timoshenko beam element approximation. The cross section of the beam is circular. The cracked beam is modeled as an assembly of two sub-beams connected through a massless elastic rotational spring. It is known that large deflection problems are geometrically nonlinear problems. The considered highly nonlinear problem is solved considering full geometric non-linearity by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. There is no restriction on the magnitudes of deflections and rotations in contradistinction to von-Karman strain displacement relations of the beam. The beams considered in numerical examples are made of Aluminum. In the study, the effects of the location of crack and the depth of the crack on the non-linear static response of the beam are investigated in detail. The relationships between deflections, end rotational angles, end constraint forces, deflection configuration, Cauchy stresses of the edge- cracked beams and load rising are illustrated in detail in nonlinear case. Also, the difference between the geometrically linear and nonlinear analysis of edge-cracked beam is investigated in detail.

Key Words
open edge crack; total Lagrangian finite element model; circular beams; timoshenko beam; large displacements; large rotations

Address
Seref Doguşcan Akbas: Department of Civil Engineering, Bursa Technical University,152 Evler Mah., Eğitim Cad., 1. Damla Sok., No: 2/10, 16330 Y

Abstract
A hybrid approach of Particle Swarm Optimization (PSO) and Swallow Swarm Optimization algorithm (SSO) namely Hybrid Particle Swallow Swarm Optimization algorithm (HPSSO), is presented as a new variant of PSO algorithm for the highly nonlinear dynamic truss shape and size optimization with multiple natural frequency constraints. Experimentally validation of HPSSO on four benchmark trusses results in high performance in comparison to PSO variants and to those of different optimization techniques. The simulation results clearly show a good balance between global and local exploration abilities and consequently results in good optimum solution.

Key Words
hybrid meta-heuristics; Hybrid Particle Swallow Swarm Optimization algorithm; truss optimization; frequency constraints

Address
A. Kaveh, T. Bakhshpoori and E. Afshari: Centre of Excellence for Fundamental Studies in Structural Engineering, School of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran-16, Iran

Abstract
This study presents the validation of a numerical model developed for dynamic analysis of buildings with roller seismic isolation bearings. Experimental methods allowed validation of the motion equations of a physical model of a building with and without roller bearings under base excitation. The results are presented in terms of modal parameters, frequency response functions (FRFs) and acceleration response. The agreement between numerical and experimental results proves the accuracy of the developed numerical model. Finally, the performance of the constructed seismic protection system is assessed through a parametric study.

Key Words
base isolation systems; seismic protection systems; frequency response functions; roller seismic isolation bearings

Address
Nelson A. Ortiz, Carlos Magluta and Ney Roitman: Department of Civil Engineering, COPPE/UFRJ Centro de Tecnologia, Bloco I2000, Sala I116, Cidade Universitária, Ilha do Fundão, Rio de Janeiro, CEP21945-970, Brazil

Abstract
Under seismic loading, underground station structures behave differently from above ground structures. Underground structures do not require designated energy dissipation system for seismic loads. These structures are traditionally designed with shear or racking deformation capacity to accommodate the movement of the soil caused by shear waves. The free-field shear deformation method may not be suitable for the design of shallowly buried station structures with complex structural configurations. Alternatively, a station structure can develop rocking mechanisms either as a whole rigid body or as a portion of the structure with plastic hinges. With a rocking mechanism, station structures can be tilted to accommodate lateral shear deformation from the soil. If required, plastic hinges can be implemented to develop rocking mechanism. Generally, rocking structures do not expect significant seismic loads from surrounding soils, although the mechanism may result in significant internal forces and localized soil bearing pressures. This method may produce a reliable and robust design of station structures.

Key Words
underground structures; seismic analysis; seismic design; rocking mechanism; soil-structure interactions; plastic hinges

Address
Jianzhong Gu: Architectural and Engineering Technology, Thompson Rivers University, 900 McGill Rd, Kamloops, British Columbia, Canada

Abstract
Presence of torsional loadings can significantly affect the flow of internal forces and deformation capacity of reinforced concrete (RC) columns. It increases the possibility of brittle shear failure leading to catastrophic collapse of structural members. This necessitates accurate prediction of the torsional behaviour of RC members for their safe design. However, a review of previously published studies indicates that the torsional behaviour of RC members has not been studied in as much depth as the behaviour under flexure and shear in spite of its frequent occurrence in bridge columns. Very few analytical models are available to predict the response of RC members under torsional loads. Softened truss model (STM) developed in the University of Houston is one of them, which is widely used for this purpose. The present study shows that STM prediction is not sufficiently accurate particularly in the post cracking region when compared to test results. An improved analytical model for RC square columns subjected to torsion with and without axial compression is developed. Since concrete is weak in tension, its contribution to torsional capacity of RC members was neglected in the original STM. The present investigation revealed that, disregard to tensile strength of concrete is the main reason behind the discrepancies in the STM predictions. The existing STM is extended in this paper to include the effect of tension stiffening for better prediction of behaviour of square RC columns under torsion. Three different tension stiffening models comprising a linear, a quadratic and an exponential relationship have been considered in this study. The predictions of these models are validated through comparison with test data on local and global behaviour. It was observed that tension stiffening has significant influence on torsional behaviour of square RC members. The exponential and parabolic tension stiffening models were found to yield the most accurate predictions.

Key Words
square column; tension stiffening; softened truss model; torque; twist, compression

Address
T. Ghosh Mondal and S. Suriya Prakash: Department of Civil Engineering, Indian Institute of Technology Hyderabad, India

Abstract
Depending on the damage type as well as the level of damage observed after the earthquake, certain measures should be taken for the damaged buildings. In this study, structural repairing of two different types of damaged RC beam-column assembly by carbon fiber-reinforced polymer sheets is investigated in detail as a member repairing technique. Two types of 1:1 scale test specimens, which represent the exterior RC beam-column connection taken from inflection points of the frame, are utilized. The first specimen is designed according to the current Turkish Earthquake Code, whereas the second one represents a deficient RC beam-column assembly. Both of the specimens were subjected to cyclic quasistatic loading in the laboratory and different levels of structural damage were observed. The first specimen displayed a ductile response with the damage concentrated in the beam. However, in the second specimen, the beam-column joint was severely damaged while the rest of the members did not attain their capacities. Depending on the damage type of the specimens, the damaged members were repaired by CFRP wrapping with different configurations. After testing the repaired specimens, it is found that former capacities of the damaged members were mostly recovered by the application of CFRPs on the damaged members.

Key Words
CFRP; beam-column joint; reinforced concrete; structural repair

Address
Ozgur Yurdakul: Jan Perner Transport Faculty, University of Pardubice, Pardubice, 53009, Czech Republic
Ozgur Avsar: Department of Civil Engineering, Anadolu University, Eskişehir, 26555, Turkey

Abstract
In this paper, blast-induced vibration effects on buildings located in rural areas were investigated. Damages to reinforced concrete, adobe and masonry buildings were evaluated in Çatakköprü and Susuz villages in Silvan district of Diyarbak, Turkey. Blasting of stiff rocks to construct highway at vicinity of the villages damaged the buildings seriously. The most important reason of the damages is lack of engineering services and improper constructed buildings according to the current building design codes. Also, it is determined that, inappropriate blast method and soft soil class increased the damages to the buildings. The study focuses on four points: Blast effect on buildings, soil conditions in villages, building damages and evaluation of damage reasons according to the current Turkish Earthquake Code (TEC).

Key Words
structural damages; blast-induced ground vibration effect; rural buildings

Address
Mehmet Emin Oncu, Burak Yon, Taha Taskiran: Civil Engineering Department, Dicle University, 21280, Diyarbak

Abstract
The main objective of this paper is to study the dynamic load allowance (DLA) calculation methods for bridges according to the dynamic response curve. A simply-supported concrete bridge with a smooth road surface was taken as an example. A half-vehicle model was employed to calculate the dynamic response of deflection and bending moment in the mid-span section under different vehicle speeds using the vehicle-bridge coupling method. Firstly, DLAs from the conventional methods and code provisions were analyzed and critically evaluated. Then, two improved computing approaches for DLA were proposed. In the first approach, the maximum dynamic response and its corresponding static response or its corresponding minimum response were selected to calculate DLA. The second approach utilized weighted average method to take account of multi-local DLAs. Finally, the DLAs from two approaches were compared with those from other methods. The results show that DLAs obtained from the proposed approaches are greater than those from the conventional methods, which indicate that the current conventional methods underestimate the dynamic response of the structure. The authors recommend that the weighted average method based on experiments be used to compute DLAs because it can reflect the vehicle\'s whole impact on the bridge.

Key Words
dynamic load allowance (DLA); vehicle-bridge coupling; vehicle oscillation; weighted average method; bridges

Address
Yongjun Zhou: Department of Highway School, Chang\'an University, Middle Section of Nan Erhuan Road, Xi\'an, 710064, China
Zhongguo John Ma: Department of Civil and Environmental Engineering, University of Tennessee Knoxville,
313 John D. Tickle Building, Knoxville, TN 37996-2313, USA
Yu Zhao: Department of Highway School, Chang\'an University, Middle Section of Nan Erhuan Road, Xi\'an, 710064, China
Xiongwei Shi: Xi\'an Highway Research Institute, South Wenyi Road, Xi\'an, 710054, China
Shuanhai He: Department of Highway School, Chang\'an University, Middle Section of Nan Erhuan Road, Xi\'an, 710064, China

Abstract
A general geometrically non-linear model for lateral-torsional buckling of thick and thin-walled FGM box beams is presented. In this model primary and secondary torsional warping and shear effects are taken into account. The coupled equilibrium equations obtained from Galerkin\'s method are derived and the corresponding tangent matrix is used to compute the critical moments. General expression is derived for the lateral-torsional buckling load of unshearable FGM beams. The results are validated by comparison with a 3D finite element simulation using the code ABAQUS. The influences of the geometrical characteristics and the shear effects on the buckling loads are demonstrated through several case studies.

Key Words
lateral torsional buckling; box beam; FGM; non-linear; Galerkin\'s method

Address
Noureddine Ziane, Sid Ahmed Meftah: Laboratoire des Structures et Materiaux Avances dans le Genie Civil et Travaux Publics, Universite de Djillali Liabes, Sidi Bel Abbes, Algeria
Giuseppe Ruta: Department of Structural & Geotechnical Engineering. Faculty of Civil & Industrial Engineering, Sapienza University, Rome, Italy
Abdelouahed Tounsi and El Abbas Adda Bedia: Laboratoire des Materiaux et Hydrologie, Universite de Sidi Bel Abbes, Algerie

Abstract
In this study, linear vibrations of an axially moving beam under non-ideal support conditions have been investigated. The main difference of this study from the other studies; the non-ideal clamped support allow minimal rotations and non-ideal simple support carry moment in minimal orders. Axially moving Euler-Bernoulli beam has simple and clamped support conditions that are discussed as combination of ideal and non-ideal boundary with weighting factor (k). Equations of the motion and boundary conditions have been obtained using Hamilton\'s Principle. Method of Multiple Scales, a perturbation technique, has been employed for solving the linear equations of motion. Linear equations of motion are solved and effects of different parameters on natural frequencies are investigated.

Key Words
axially moving; vibration; non-ideal support; perturbation methods

Address
Suleyman M. Bagdatli and Bilal Uslu: Faculty of Engineering, Department of Mechanical Engineering, Celal Bayar University, 45140, Yunusemre, Manisa, Turkey


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