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CONTENTS
Volume 57, Number 6, March25 2016
 

Abstract
Vibration analysis of the beams on elastic foundation has gained the great interest of many researchers. In the literature, there are many studies that focus on the free vibration analysis of the beams on one or two parameter elastic foundations. On the other hand, there are no sufficient studies especially focus on the comparison of dynamic response including the bending moment and shear force of the beams resting on Winkler and two parameter foundations. In this study, dynamic response of the axially loaded Timoshenko beams resting on modified Vlasov type elastic soil was investigated by using the separation of variables method. Governing equations were obtained by assuming that the material had linear elastic behaviour and mass of the beam was distributed along its length. Numerical analysis were provided and presented in figures to find out the differences between the modified Vlasov model and conventional Winkler type foundation. Furthermore, the effect of shear deformation of elastic soil on the dynamic response of the beam was investigated.

Key Words
Vlasov type foundation; Timoshenko beam; forced vibration; separation of variables method

Address
Caglayan Hizal: Department of Civil Engineering, Engineering Faculty of Izmir Institute of Technology, 35430, Urla, Izmir, Turkey
Hikmet Huseyin Ctal: Department of Civil Engineering, Engineering Faculty of Dokuz Eylul University, 35160, Buca, Izmir, Turkey

Abstract
This paper deals with the analysis of the natural frequencies, mode shapes of an axially loaded beam system carrying ends consisting of non-concentrated tip masses and three spring-two mass subsystems. The influence of system design and sub-system parameters on the combined system characteristics is the major part of this investigation. The effect of material properties, rotary inertia and shear deformation of the beam system is included. The end masses are elastically supported against rotation and translation at an offset point from the point of attachment. Sub-systems are attached to center of gravity eccentric points out of the beam span. The boundary conditions of the ordinary differential equation governing the lateral deflections and slope due to bending of the beam system including developed shear force frequency dependent terms, due to the sub–system suspension, have been formulated. Exact formulae for the modal frequencies and the modal shapes have been derived. Based on these formulae, detailed parametric studies are carried out. The geometrical and mechanical parameters of the system under study have been presented in non-dimensional analysis. The applied mathematical model is presented to cover wide range of mechanical, naval and structural engineering applications.

Key Words
vibration frequencies; exact solution; Timoshenko beam; eccentric mass; sub-system; combined system

Address
Tamer A. El-Sayed and Said H. Farghaly:Department of Mechanical Design, Faculty of Engineering, Mataria, Helwan University, P.O. Box 11718, Helmeiat-El zaton, Cairo, Egypt

Abstract
In the current research an advanced criterion with non-associated flow rule (non-AFR) for depicting the behavior of anisotropic sheet metals is presented to consider the strength differential effects (SDEs) for these materials. Owing to the fact that Lou et al. (2013) yield function is dependent on structure of an anisotropic material (BCC, FCC and HCP), an advanced yield function with inspiring of Yoon et al. (2014) yield function is proposed which is dependent upon anisotropic structures. Furthermore, to compute Lankford coefficients, a new pressure sensitive plastic potential function which would be dependent to anisotropic structure is presented and coupled with the proposed yield function with employing a non-AFR in a novel criterion which is called here \'advanced criterion\'. Totally eighteen experimental data are required to calibrate the criterion contained of directional tensile and compressive yield stresses for the yield function and directional Lankford coefficients for the plastic potential function. To verify the criterion, three anisotropic sheet metals with different structures are taken as case studies such as Al 2008-T4 (a BCC material), Al 2090-T3 (a FCC material) and AZ31 (a HCP material).

Key Words
advanced criterion; asymmetric anisotropic sheet metals; non-AFR; tensile yield stresses; compressive yield stresses; Lankford coefficients

Address
Farzad Moayyedian: Department of Mechanical Engineering, Eqbal Lahoori Institute of Higher Education (ELIHE), Mashhad, Iran
Mehran Kadkhodayan: Department of Mechanical Engineering, Ferdowsi University of Mashhad (FUM), Mashhad, Iran

Abstract
In this research, an approximate analytical solution has been presented for nonlinear problems of vibratory systems in mechanical engineering. The new method is called Variational Approach (VA) which is applied in two different high nonlinear cases. It has been shown that the presented approach leads us to an accurate approximate analytical solution. The results of variational approach are compared with numerical solutions. The full procedure of the numerical solution is also presented. The results are shown that the variatioanl approach can be an efficient and practical mathematical tool in field of nonlinear vibration.

Key Words
variational approach method; nonlinear vibration; numerical method

Address
Seyyed A.Edalati: Department of Civil and Environmental Engineering, Tarbiat Modares University, Tehran, Iran
Mahmoud Bayat: Department of Civil Engineering, College of Engineering, Bandar Abbas Branch, Islamic Azad University, Bandar Abbas, Iran
Iman Pakar: Young Researchers and Elite Club, Mashhad Branch, Islamic Azad University, Mashhad, Iran
Mahdi Bayat: Young Researchers and Elite Club, Mashhad Branch, Islamic Azad University, Mashhad, Iran

Abstract
Link-to-column connections in Eccentrically Braced Frames (EBFs) have critical role in their safety and seismic performance. Accordingly, in this study, contribution of supplemental stiffeners on hysteretic behavior of the link-to-column connection is investigated. Considered stiffeners are placed on both sides and parallel to the link web between the column face and the first stiffener of the link. Hysteretic behaviors of the link beams with supplemental stiffeners are numerically investigated using a pre-validated numerical model in ANSYS. It turned out that supplemental stiffeners can change energy dissipation mechanism of intermediate links from shear-flexure to shear. Both rectangular and trapezoidal supplemental stiffeners are studied. Moreover, optimal placement of the supplemental stiffeners is also investigated. Obtained results indicate a discrepancy of less than 9% in maximum link shear of the numerical and experimental specimens. This indicates that the numerical results are in good agreement with those obtained from the test. Trapezoidal supplemental stiffeners improve rotational capacity of the link. Moreover, use of two supplemental stiffeners at both ends of the link can more effectively improve hysteretic behavior of intermediate links. Supplemental stiffeners would also alleviate the imposed demands on the connections. This latter feature is more pronounced in the case of two supplemental stiffeners at both ends of the link.

Key Words
link-to-column connections; supplemental stiffeners; cyclic behavior; plastic hinges; trapezoidal supplemental stiffeners

Address
Saman Zarsav: Islamic Azad University, Takestan Branch, Takestan, Iran
Seyed Mehdi Zahrai: School of Civil Engineering, The University of Tehran, Tehran, Iran
Asghar Vatani Oskouei: Shahid Rajaee Teacher Training University, Tehran, Iran

Abstract
The analysis and design of skeletal structures is greatly influenced by the behaviour of beamto- column connections, where patented designs have led to a wide range of types with differing structural quantities. The behaviour of beam-to-column connections plays an important role in the analysis and design of framed structures. This paper presents an overview of the influence of connection behaviour on structural stability, in the in-plane (bending) mode of sway. A computer-based method is presented for geometrically nonlinear plane frames with semi-rigid connections accounting for shear deformations. The analytical procedure employs transcendental modified stability functions to model the effect of axial force on the stiffness of members. The member stiffness matrix were found. The critical load has been searched as a suitable load parameter for the loss of stability of the system. Several examples are presented to demonstrate the validity of the analysis procedure. The method is readily implemented on a computer using matrix structural analysis techniques and is applicable for the efficient nonlinear analysis of frameworks. Combined with a parametric column effective length study, connection and frame stiffness are used to propose a method for the analysis of semi-rigid frames where column effective lengths are greatly reduced and second order (deflection induced) bending moments in the column may be distributed via the connectors to the beams, leading to significant economies.

Key Words
stability, nonlinear analysis; semi-rigid connection; effective length; shear deformation

Address
Halil Gorgun: Department of Civil Engineering, Dicle University, 21280, Diyarbakir, Turkey

Abstract
The drainage problem in bifurcations causes pecuniary losses when hydropower stations are undergoing periodic overhaul. A new design philosophy for Y-typed bifurcations that are flat-bottomed is proposed. The bottoms of all pipe sections are located at the same level, making drainage due to gravity possible and shortening the draining time. All fundamental curves were determined, and contrastive analysis with a crescent-rib reinforced bifurcation in an actual project was conducted. Feasibility demonstrations were researched including structural characteristics based on finite element modeling and hydraulic characteristics based on computational fluid dynamics. The new bifurcation provided a well-balanced shape and reasonable stress state. It did not worsen the flow characteristics, and the head loss was considered acceptable. The proposed Y-typed bifurcation was shown to be suitable for pumped storage power stations.

Key Words
hydropower; bifurcation; flat-bottomed; design philosophy; finite element modeling; computational fluid dynamics

Address
Yang Wang, Chang-zheng Shi and He-gao Wu: State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan, Hubei 430072, China
Qi-ling Zhang: Changjiang River Scientific Research Institute, Wuhan, Hubei 430010, China
Kai Su: State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan, Hubei 430072, China

Abstract
Consistent finite strain Plate constitutive relations are derived based on a hyperelastic formulation for an isotropic material. Plate equilibrium equations under finite strain are derived following a static kinematic approach. Three Euler angles and four shear angles, based on Timoshenko beam theory, represent the kinematics of the deformations in the plate cross section. The Green deformation tensor has been expressed in term of a deformation tensor associated with the deformation and stretches of an embedded plate element. Buckling formulation includes the in-plane axial deformation prior to buckling and transverse as well as in-plane shear deformations. Numerical results for a simply supported thick plate under uni-axial compression force are presented.

Key Words
plate; buckling; shear deformations; hyperelasticity

Address
Idris A. Musa: Department of Civil Engineering, University of Duhok, 38 Zakho Street, Duhok City, 1006AJ, Duhok Governorate, Kurdistan Region, Iraq

Abstract
Tunneling is one of the challenging tasks in civil engineering because it involves a variety of decision making and engineering judgment based on knowledge and experience. One of the challenges is to construct tunnels in risky areas under shallow overburden. In order to prevent the collapse of ceilings and walls of a large tunnels, in such conditions, either a sequential excavation method (SEM) or ground reinforcing method, or a combination of both, can be utilized. This research deals with the numerical modeling of L-profiles and pipe fore-poling pre-support systems in the adit tunnel in northwestern Iran. The first part of the adit tunnel has been drilled in alluvial material with very weak geotechnical parameters. Despite applying an SEM in constructing this tunnel, analyzing the results of numerical modeling done using FLAC3D, as well as observations during drilling, indicate the tunnel instability. To improve operational safety and to prevent collapse, pre-support systems, including pipe fore-poling and L-profiles were designed and implemented. The results of the numerical modeling coupled with monitoring during operation, as well as the results of instrumentation, indicate the efficacy of both these methods in tunnel collapse prevention. Moreover, the results of modeling using FLAC3D and SECTION BUILDER suggest a double angle with equal legs (2L100x100x10 mm) in both box profile and tee array as an alternative section to pipe fore-poling system while neither L80x80x8 mm nor 2L80x80x8 mm can sustain the axial and shear stresses exerted on pipe fore-poling system.

Key Words
sequential excavation method; alluvial material; numerical modeling; L-profiles; pipe forepoling; monitoring

Address
Ayub Elyasi: Department of Mining Engineering, Tarbiat Modares University, Tehran, Iran
Taher Moradi, Javad Moharrami, Saeid Parnian: Consultant Engineering Institute of Iman Sazan, Tehran, Iran
Akbar Mousazadeh: Department of Civil Engineering, Islamic Azad University of Naghadeh, Naghadeh, Iran
Sepideh Nasseh: Department of Geology, Ferdowsi University of Mashhad, Mashhad, Iran

Abstract
This paper presents a comparative study of finite element method (FEM) and analytical method for the plane problem of a layered composite containing an internal perpendicular crack in literature. The layered composite consists of two elastic layers having different elastic constants and heights. External load is applied to the upper elastic layer by means o a rigid punch and the lower elastic layer rests on two simple supports. Numerical simulations are realized by the world wide code ANYS software. Two dimensional analysis of the problem is carried out and the results are verified by comparison with solutions reported in literature. Main goal of the numerical simulation is to investigate the normal stress ex(0,y), stress intensity factors at the crack factor and the crack opening displacements.

Key Words
fracture mechanics; crack; stress intensity factor; FEM

Address
Murat Yaylac: Department of Civil Engineering, Recep Tayyip Erdoğan University, 53100, Rize, Turkey


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