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CONTENTS
Volume 41, Number 6, March25 2012
 

Abstract
One of the most popular and commonly used strengthening techniques to protect against earthquakes is to infill the holes in reinforced concrete (RC) frames with fully reinforced concrete infills. In some cases, windows and door openings are left inside infill walls for architectural or functional reasons during the strengthening of reinforced concrete-framed buildings. However, the seismic performance of multistory, multibay, reinforced concrete frames that are strengthened by reinforced concrete wing walls is not well known. The main purpose of this study is to investigate the experimental behavior of vulnerable multistory, multibay, reinforced concrete frames that were strengthened by introducing wing walls under a lateral load. For this purpose, three 2-story, 2-bay, 1/3-scale test specimens were constructed and tested under reversed cyclic lateral loading. The total shear wall (including the column and wing walls) length and the location of the bent beam bars were the main parameters of the experimental study. According to the test results, the addition of wing walls to reinforced concrete frames provided significantly higher ultimate lateral load strength and higher initial stiffness than the bare frames did. While the total shear wall length was increased, the lateral load carrying capacity and stiffness increased significantly.

Key Words
seismic strengthening; reinforced concrete (RC); frame; wing wall; reversed cyclic load

Address
M. Yasar Kaltakcia and Gunnur Yavuz: Engineering and Architecture Faculty, Department of Civil Engineering, Selcuk University, Konya, Turkey

Abstract
The foundation of a tall building frame resting on settable soil mass undergoes differential settlements which alter the forces in the structural members significantly. For tall buildings it is essential to consider seismic forces in analysis. The building frame, foundation and soil mass are considered to act as single integral compatible structural unit. The stress-strain characteristics of the supporting soil play a vital role in the interaction analysis. The resulting differential settlements of the soil mass are responsible for the redistribution of forces in the superstructure. In the present work, the nonlinear interaction analysis of a two-bay ten-storey plane building frame- layered soil system under seismic loading has been carried out using the coupled finite-infinite elements. The frame has been considered to act in linear elastic manner while the soil mass to act as nonlinear elastic manner. The subsoil in reality exists in layered formation and consists of various soil layers having different properties. Each individual soil layer in reality can be considered to behave in nonlinear manner. The nonlinear layered system as a whole will undergo differential settlements. Thus, it becomes essential to study the structural behaviour of a structure resting on such nonlinear composite layered soil system. The nonlinear constitutive hyperbolic soil model available in the literature is adopted to model the nonlinear behaviour of the soil mass. The structural behaviour of the interaction system is investigated as the shear forces and bending moments in superstructure get significantly altered due to differential settlements of the soil mass.

Key Words
conventional frame analysis; finite element method; plane frame; soil-structure interaction; nonlinear analysis; hyperbolic soil model; differential settlement; decay pattern; infinite elements; truncation boundary

Address
Ramakant Agrawal: Department of Civil Engineering,TRUBA Institute of Engineering and Information Technology, Bhopal, India
M.S. Hora: Department of Applied Mechanics, Maulana Azad National Institute of Technology, Bhopal, India

Abstract
This paper presents a comparison between two different procedures to deal with the geometric nonlinear analysis of space trusses, considering its structural stability aspects. The first nonlinear formulation, called positional, uses nodal positions rather than nodal displacements to describe the finite elements kinematics. The strains are computed directly from the proposed position concept, using a Cartesian coordinate system fixed in space. The second formulation, called corotational, is based on the explicit separation between rigid body motion and deformed motion. The numerical examples demonstrate the performances and the convergence of the responses for both analyzed formulations. Two numerical examples were compared, including a lattice beam with postcritical behavior. Despite the two completely different approaches to deal with the geometrical nonlinear problem, the results present good agreement.

Key Words
nonlinear analysis; FEM; space trusses; positional formulation; corotational formulation

Address
M. Greco, I.P. Ferreira and F.B. Barros: Graduate Program in Structural Engineering, Department of Structural Engineering, School of Engineering, Federal University of Minas Gerais, Belo Horizonte, Brazil
R.C.G. Menin: Department of Civil and Environmental Engineering, Faculty of Technology, University of Brasilia,
Brasilia, Brazil

Abstract
We study thickness-shear (TSh) free vibrations of an unbounded, laminated elastic plate with three layers of different materials. One of the two interfaces is slightly weakened as described by the shear-lag model that allows the displacement to be discontinuous across the interface. A frequency equation is obtained from the linear theory of elasticity. A perturbation solution of the frequency equation is obtained from which the frequency shifts of TSh modes due to the weakened interface can be calculated. It is shown that the frequency shifts of TSh modes of different orders are different, and they satisfy different conditions when different interfaces are weakened. These conditions are obtained which can potentially be used as criteria for determining specifically which interface is weakened.

Key Words
locating; thickness-shear; laminated elastic plate; TSh modes; weakened interface; frequency shifts

Address
J. Zhu: Department of Civil Engineering, Zhejiang University, Zijingang Campus, Hangzhou 310058, China
J.S. Yang: Department of Engineering Mechanics, University of Nebraska, Lincoln, NE 68588-0526, USA
W.Q. Chen: State Key Lab of CAD & CG, Zhejiang University, Zijingang Campus, Hangzhou 310058, China; Department of Engineering Mechanics, Zhejiang University, Yuquan Campus, Hangzhou 310027, China

Abstract
The objective of this paper is to present an energy-based method for calculating target displacement of RC structures. The method, which uses the Newmark-Hall pseudo-velocity spectrum, is called the \"Pseudo-velocity Spectrum (PSVS) Method\". The method is based on the energy balance concept that uses the equality of energy demand and energy capacity of the structure. First, nonlinear static analyses are performed for five, eight and ten-story RC frame structures and pushover curves are obtained. Then the pushover curves are converted to energy capacity diagrams. Seven strong ground motions that were recorded at different soil sites in Turkey are used to obtain the pseudo-acceleration and the pseudo-velocity response spectra. Later, the response spectra are idealised with the Newmark-Hall approximation. Afterwards, energy demands for the RC structures are calculated using the idealised pseudo-velocity spectrum. The displacements, obtained from the energy capacity diagrams that fit to the energy demand values of the RC structures, are accepted as the energy-based performance point of the structures. Consequently, the target displacement values determined from the PSVS Method are checked using the displacement-based successive approach in the Turkish Seismic Design Code. The results show that the target displacements of RC frame structures obtained from the PSVS Method are very close to the values calculated by the approach given in the Turkish Seismic Design Code.

Key Words
Pseudo-velocity spectrum; energy demand; energy-based performance point; PSVS method; target displacement

Address
Taner Ucar: Faculty of Architecture, Dokuz Eylul University, Izmir, Turkey
Onur Merter and Mustafa Duzgun: Faculty of Engineering (Civil), Dokuz Eylul University, Izmir, Turkey

Abstract
This paper focuses on post-buckling analysis of functionally graded Timoshenko beam subjected to thermal loading by using the total Lagrangian Timoshenko beam element approximation. Material properties of the beam change in the thickness direction according to a power-law function. The beam is clamped at both ends. The considered highly non-linear problem is solved by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. As far as the authors know, there is no study on the post-buckling analysis of functionally graded Timoshenko beams under thermal loading considering full geometric non-linearity investigated by using finite element method. The convergence studies are made and the obtained results are compared with the published results. In the study, with the effects of material gradient property and thermal load, the relationships between deflections, end constraint forces, thermal buckling configuration and stress distributions through the thickness of the beams are illustrated in detail in post-buckling case.

Key Words
functionally graded materials; geometrical non-linearity; post-buckling analysis; total lagrangian finite element model; Timoshenko beam; temperature loading

Address
Turgut Kocaturk and Seref Doguscan Akbas: Department of Civil Engineering, Yildiz Technical University, Davutpasa Campus, 34210 Esenler- stanbul, Turkey

Abstract
Significant structural damages due to pounding between adjacent superstructures of multispan reinforced concrete (RC) highway bridges have been observed in past earthquakes. Different methods have been proposed in the literature to mitigate the adverse seismic pounding effects. This paper presents an analytical investigation on the use of magnetorheological (MR) dampers in reducing seismic pounding effects of base-isolated multi-span RC highway bridges. It has been observed that MR damper can effectively reduce the seismic pounding effect. Three control strategies (passive off, passive on, and bang bang control) of MR damper have been investigated. Although all the control strategies are found to be effective, bang bang control has been observed to be the most effective.

Key Words
MR damper; pounding; highway bridges; control strategies; earthquakes

Address
M.N. Sheikh and J. Xiong: School of Civil, Mining and Environmental Engineering, University of Wollongong, NSW 2522, Australia
W.H. Li: School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, NSW 2522, Australia

Abstract
Offshore pipelines have to withstand combined actions of tension and bending during deepwater installation, which can possibly lead to elliptical buckle and even catastrophic failure of whole pipeline. A 2D theoretical model initially proposed by Kyriakides and his co-workers which carried out buckling response analysis of elastic-plastic tubes under various load combinations, is further applied to investigate buckling behavior of offshore pipelines under combined tension and bending. In association with practical pipe-laying circumstances, two different types of loadings, i.e., bent over a rigid surface in the presence of tension, and bent freely in the presence of tension, are taken into account in present study. In order to verify the accuracy of the theoretical model, numerical simulations are implemented using a 3D finite element model within the framework of ABAQUS. Excellent agreement between the results validates the effectiveness of this theoretical method. Then, this theoretical model is used to study the effects of some important factors such as load type, loading path, geometric parameters and material properties etc. on buckling behavior of the pipes. Based upon parametric studies, a few significant conclusions are drawn, which offer a theoretical reference for design and installation monitoring of deepwater pipelines.

Key Words
offshore pipeline; deepwater; buckling; pipe-laying

Address
Shun-feng Gong, Xing-yue Ni, Lin Yuan and Wei-liang Jin: Institute of Structural Engineering, Zhejiang University, Hangzhou, 310058, China


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