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CONTENTS
Volume 62, Number 6, June25 2017
 

Abstract
This paper presents an approach for evaluating performance of prestressed concrete (PC) bridge girders exposed to fire. A finite element based numerical model for tracing the response of fire exposed T girders is developed in ANSYS. The analysis is carried out in three stages, namely, fire temperature calculation, cross sectional temperature evaluation, and then strength, deformation and effective prestress analysis on girders exposed to elevated temperatures. The applicability of the computer program in tracing the response of PC bridge girders from the initial preloading stage to failure stage, due to combined effects of fire and structure loading, is demonstrated through a case study, and validated by test data of a scaled PC box girder under ISO834 fire condition. Results from the case study show that fire severity has a significant influence on the fire resistance of PC T girders and hydrocarbon fire is most dangerous for the girder. The prestress loss caused by elevated temperature is about 10% under hydrocarbon fire till the girder failure, which can lead to the increase in deflection of the PC girder. The rate of deflection failure criterion is suggested to determine the failure of PC T girder under fire.

Key Words
bridge fires; fire resistance; PC girders; FEM analysis; failure criterion; fire scenario

Address
Gang Zhang, Wei Hou and Shuanhai He: School of Highway, Chang´an University, Xi´an, Shaanxi 710064, China

Venkatesh Kodur: Department of Civil and Environmental Engineering, Michigan State University, East Lansing, MI 48864, USA

Abstract
In this paper, based on the first-order shear deformation plate theory, buckling analysis of piezoelectric coupled transversely isotropic rectangular plates is investigated. By assuming the transverse distribution of electric potential to be a combination of a parabolic and a linear function of thickness coordinate, the equilibrium equations for buckling analysis of plate with surface bonded piezoelectric layers are established. The Maxwell

Key Words
buckling; piezoelectric; rectangular plate; transversely isotropic; analytical solution

Address
M.A. Ghasemabadian: Department of Mechanical Engineering, Ferdowsi University of Mashhad, Mashhad, Iran

A.R. Saidi: Department of Mechanical Engineering, Shahid Bahonar University of Kerman, Kerman, Iran


Abstract
In this work, a nonlocal zeroth-order shear deformation theory is developed for the nonlinear postbuckling behavior of nanoscale beams. The beauty of this formulation is that, in addition to including the nonlocal effect according to the nonlocal elasticity theory of Eringen, the shear deformation effect is considered in the axial displacement within the use of shear forces instead of rotational displacement like in existing shear deformation theories. The principle of virtual work together of the nonlocal differential constitutive relations of Eringen, are considered to obtain the equations of equilibrium. Closed-form solutions for the critical buckling load and the amplitude of the static nonlinear response in the postbuckling state for simply supported and clamped clamped nanoscale beams are determined.

Key Words
nanobeams; postbuckling; nonlocal elasticity

Address
Hichem Bellifa, Kouider Halim Benrahou, Abdelmoumen Anis Bousahla, Abdelouahed Tounsi: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria

Abdelmoumen Anis Bousahla, Abdelouahed Tounsi: Laboratoire de Modelisation et Simulation Multi-echelle, Universite de Sidi Bel Abbes, Algeria

Abdelmoumen Anis Bousahla: Centre Universitaire de Relizane, Algerie

S.R. Mahmoud: Department of Mathematics, Faculty of Science, King Abdulaziz University, Saudi Arabia

S.R. Mahmoud: Mathematics Department, Faculty of Science, University of Sohag, Egypt

Abstract
The goal of this study is to evaluate behavior uncertainties of structures by using interval finite element analysis based on interval factor method as a specific non-stochastic tool. The interval finite element method, i.e., interval FEM, is a finite element method that uses interval parameters in situations where it is not possible to get reliable probabilistic characteristics of the structure. The present method solves the uncertainty problems of a 2D solid structure, in which structural characteristics are assumed to be represented as interval parameters. An interval analysis method using interval factors is applied to obtain the solution. Numerical applications verify the intuitive effectiveness of the present method to investigate structural uncertainties such as displacement and stress without the application of probability theory.

Key Words
interval parameters; interval factor method; interval finite element analysis; structural behavior; uncertainty; non-stochastic

Address
Dongkyu Lee: Department of Architectural Engineering, Sejong University, Seoul, 143-747, Korea

Soomi Shin: Research Institute of Industrial Technology, Pusan National University, Busan, 609-735, Korea


Abstract
This paper develops a two-stage method for structural damage identification by using modal data. First, the Residual Force Vector (RFV) is introduced to detect any potentially damaged elements of structures. Second, data of the frequency domain are used to build up the objective function, and then the Imperialist Competitive Algorithm (ICA) is utilized to estimate damaged extents. ICA is a heuristic algorithm with simple structure, which is easy to be implemented and it is effective to deal with high-dimension nonlinear optimization problem. The advantages of this present method are: (1) Calculation complexity can be decreased greatly after eliminating many intact elements in the first step. (2) Robustness, ICA ensures the robustness of the proposed method. Various damaged cases and different structures are investigated in numerical simulations. From these results, anyone can point out that the present algorithm is effective and robust for structural damage identification and is also better than many other heuristic algorithms.

Key Words
structural damage identification; residual force vector; optimization problem; ICA; heuristic algorithm

Address
Z.H. Ding, R.Z. Yao, J.L. Huang, M. Huang and Z.R. Lu: School of Engineering, Sun Yat-sen University, Guangzhou, Guangdong Province, 510006, P.R. China

Z.H. Ding: Center for Infrastructural Monitoring and Protection, Curtin University, Bentley, WA6102, Australia

Abstract
We consider an elastic isotropic plate reinforced by stringers and weakened by a periodic system of rectilinear slots of variable width. The variable width of the slots is comparable with elastic deformations. We study the case when the slots faces get in contact at some area. Determination of parameters characterizing the partial closure of variable width slots is reduced to the solution of a singular integral equation. The action of the stringers is replaced with unknown equivalent concentrated forces at the points of their connection with the plate. The contact stresses and contact zone sizes are found from the solution of the singular integral equation.

Key Words
stringer plate; periodic system of variable width slots; contacting of slot faces; contact zone; contact stresses

Address
Department of Creep Theory, Institute of Mathematics and Mechanics of NAS of Azerbaijan, AZ1141, B. Vahabzade 9, Baku, Azerbaijan


Abstract
An analytical method considering axial equilibrium is proposed for the short- and long-term analyses of shear lag effect in reinforced concrete (RC) box girders. The axial equilibrium of box girders is taken into account by using an additional generalized displacement, referred to as the longitudinal displacement of the web. Three independent shear lag functions are introduced to describe different shear lag intensities of the top, bottom, and cantilever plates. The time-dependent material properties of the concrete are simulated by the age-adjusted effective modulus method (AEMM), while the reinforcement is assumed to behave in a linear-elastic fashion. The differential equations are derived based on the longitudinal displacement of the web, the vertical displacement of the cross section, and the shear lag functions of the flanges. The time-dependent expressions of the generalized displacements are then deduced for box girders subjected to uniformly distributed loads. The accuracy of the proposed method is validated against the finite element results regarding the short- and long-term responses of a simply-supported RC box girder. Furthermore, creep analyses considering and neglecting shrinkage are performed to quantify the time effects on the long-term behavior of a continuous RC box girder. The results show that the proposed method can well evaluate both the short- and long-term behavior of box girders, and that concrete shrinkage has a considerable impact on the concrete stresses and internal forces, while concrete creep can remarkably affect the long-term deflections.

Key Words
RC box girder; shear lag; creep; shrinkage; axial equilibrium; generalized displacement

Address
Department of Civil Engineering, Zhejiang University, Hangzhou 310058, China

Abstract
Notches such as slots are typical geometric features on mechanical components that promote fatigue crack initiation. Unlike for components with open hole type notches, there are no conventional treatments to enhance fatigue behavior of components with slots. In this work we evaluate the viability of applying laser shock peening (LSP) to extend the fatigue life of 6061-T6 aluminum components with slots. The feasibility of using LSP is evaluated not only on damage free notched specimens, but also on samples with previous fatigue damage. For the LSP treatment a convergent lens was used to deliver 0.85 J and 6 ns laser pulses 1.5 mm in diameter by a Q-switch Nd: YAG laser, operating at 10 Hz with 1064 nm of wavelength. Residual stress distribution was assessed by the hole drilling method. A fatigue analysis of the notched specimens was conducted using the commercial code FE-Safe and different multiaxial fatigue criteria to predict fatigue lives of samples with and without LSP. The residual stress field produced by the LSP process was estimated by a finite element simulation of the process. A good comparison of the predicted and experimental fatigue lives was observed. The beneficial effect of LSP in extending fatigue life of notched components with and without previous damage is demonstrated.

Key Words
laser shock processing; fatigue damage; fatigue life; residual stress

Address
Vignaud Granados-Alejo, Carlos Rubio-Gonzalez, Yazmin Parra-Torres, J. Antonio Banderas: Centro de Ingeniería y Desarrollo Industrial, Pie de la Cuesta. 702, Desarrollo San Pablo, Queretaro, Qro.,76125, Mexico

Gilberto Gomez-Rosas: Universidad de Guadalajara, Guadalajara, Jal. Mexico


Abstract
In structural mechanics, traditional analyses methods usually employ matrix operations for obtaining displacement and internal forces of the structure under the external effects, such as distributed loads, earthquake or wind excitations, and temperature changing inter alia. These matrices are derived from the well-known principle of mechanics called minimum potential energy. According to this principle, a system can be in the equilibrium state only in case when the total potential energy of system is minimum. A close examination of the expression of the well-known equilibrium condition for linear problems, P=K

Key Words
cable structures; TPO/MA method; minimum potential energy; structural analyses; geometric nonlinearity; metaheuristic algorithms; harmony search

Address
Yusuf Cengiz Toklu: Department of Civil Engineering, Okan University, Turkey

Gebrail Bekdas and Rasim Temur: Department of Civil Engineering, Istanbul University, Turkey


Abstract
The effect of central axial load on natural frequencies of various thin-walled beams, are investigated by some researchers using different methods such as finite element, transfer matrix and dynamic stiffness matrix methods. However, there are situations that the load will be off centre. This type of loading is called eccentric load. The effect of the eccentricity of axial load on the natural frequencies of asymmetric thin-walled beams is a subject that has not been investigated so far. In this paper, the mentioned effect is studied using exact dynamic stiffness matrix method. Flexure and torsion of the aforesaid thin-walled beam is based on the Bernoulli-Euler and Vlasov theories, respectively. Therefore, the intended thin-walled beam has flexural rigidity, saint-venant torsional rigidity and warping rigidity. In this paper, the Hamilton

Key Words
thin-walled beam; exact dynamic stiffness matrix; eccentric axial load; Wittrick-Williams algorithm; triply coupled vibration

Address
Faculty of Technical and Engineering, University of Mohaghegh Ardabili, Ardabil, Iran

Abstract
In this study, free vibration and damping behaviors of multilayered symmetric sandwich beams and single layered beams made of Functionally Graded Materials were investigated, experimentally and numerically. The beams were composed of Aluminum and Silicon Carbide powders and they were produced by powder metallurgy. Three beam models were used in the experiments. The first model was isotropic, homogeneous beams produced by using different mixing ratios. In the second model, the pure metal layers were taken in the middle of the beam and the weight fraction of the ceramic powder of each layer was increased towards to the surfaces of the beam in the thickness direction. In the third model, the pure metal layers were taken in the surfaces of the beam and the weight fraction of the ceramic powder of each layer was increased towards to middle of the beam. Then the vibration tests were performed. Consequently, the effects of stacking sequence and mixing ratio on the natural frequencies and damping responses of functionally graded beams were discussed from the results obtained. Furthermore, the results obtained from the tests were supported with a finite-element-based commercial program, and it was found to be in harmony.

Key Words
functionally graded; experimental investigation; dynamic analysis; frequency/modal analysis; finite element method (FEM)

Address
Department of Mechatronics Engineering, Pamukkale University, Kinikli Campus, 20070 Denizli, Turkey

Abstract
In this paper, a stress wave model is established to describe the three states (separate, contact and impact) of clearance joints. Based on this stress wave model, the propagation characteristics of stress wave generated in clearance joints is revealed. First, the stress wave model of clearance joints is established based on the viscoelastic theory. Then, the reflection and transmission characteristics of stress wave with different boundaries are studied, and the propagation of stress wave in viscoelastic rods is described by the characteristics method. Finally, the stress wave propagation in clearance joints with three states is analyzed to validate the proposed model and method. The results show the clearance sizes, initial axial speeds and material parameters have important influences on the stress wave propagation, and the new stress waves will generate when the clearance joint in contact and impact states, and there exist some high stress region near contact area of clearance joints when the incident waves are superposed with reflection waves, which may speed up the damage of joints.

Key Words
clearance joint; stress wave; characteristics method; collision; viscoelastic; propagation

Address
School of Mechano-Electronic Engineering, Xidian University, Xi


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