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CONTENTS
Volume 58, Number 6, June25 2016
 

Abstract
The second order analysis taking place due to non-linear behavior of the structures under the mechanical and geometric factors through implementing exact and approximate methods is an indispensible issue in the analysis of such structures. Among the exact methods is the slope-deflection method that due to its simplicity and efficiency of its relationships has always been in consideration. By solving the differential equations of the modified slope–deflection method in which the effect of axial compressive force is considered, the stiffness matrix including trigonometric entries would be obtained. The complexity of computations with trigonometric functions causes replacement with their Maclaurin expansion. In most cases only the first two terms of this expansion are used but to obtain more accurate results, more elements are needed. In this paper, the effect of utilizing higher order terms of Maclaurin expansion on reducing the number of required elements and attaining more rapid convergence with less error is investigated for the Bernoulli beam with various boundary conditions. The results indicate that when using only one element along the beam length, utilizing higher order terms in Maclaurin expansion would reduce the relative error in determining the critical buckling load and kinematic parameters in the second order analysis.

Key Words
non-linear behavior; slope-deflection method; axial compressive force; Maclaurin expansion; critical load; kinematic parameters

Address
Seyed Mehdi Zahrai, Mohamad Hosein Mortezagholi: Center of Excellence for Engineering and Management of Civil Infrastructures, School of Civil Engineering, The University of Tehran, P.O. Box 11155-4563, Tehran, Iran
Maryam Mirsalehi: Department of Civil Engineering, Isfahan University of Technology, Isfahan, Iran

Abstract
Due to the significant aerodynamic interference from sub-towers and surrounding tall buildings, the wind loads and dynamic responses on main tower of three-tower connected tall building typically change especially compared with those on the isolated single tall building. This paper addresses the wind load effects and equivalent static wind loads (ESWLs) of three-tower connected tall building based on measured synchronous surface pressures in a wind tunnel. The variations of the global shape coefficients and extremum wind loads of main tower structure with or without interference effect under different wind directions are studied, pointing out the deficiency of the traditional wind loads based on the load codes for the three-tower connected tall building. The ESWLs calculation method based on elastic restoring forces is proposed, which completely contains the quasi-static item, inertia item and the coupled effect between them. Then the wind-induced displacement and acceleration responses for main tower of three-tower connected tall building in the horizontal and torsional directions are investigated, subsequently the structural basal and floor ESWLs under different return periods, wind directions and damping ratios are studied. Finally, the action mechanism of interference effect on structural wind effects is investigated. Main conclusions can provide a sientific basis for the wind-resistant design of such three-tower connected tall building.

Key Words
three-tower connected tall building; wind tunnel test; equivalent static wind load; wind loads; wind effect; interference effect

Address
Shitang Ke, Hao Wang: Department of Civil Engineering, Nanjing University of Aeronautics and Astronautics, Yudao Road 29, Nanjing 210016,China
Yaojun Ge: State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Siping Road 1239, Shanghai 200092, China

Abstract
Moist curing of concrete is a time consuming procedure. It takes minimum 28 days of curing to obtain the characteristic strength of concrete. However, under certain situations such as shortage of time, weather conditions, on the spot changes in project and speedy construction, waiting for entire curing period becomes unaffordable. This situation demands early strength of concrete which can be met using accelerated curing methods. It becomes necessary to obtain early strength of concrete rather than waiting for entire period of curing which proves to be uneconomical. In India, accelerated curing methods are used to arrive upon the actual strength by resorting to the equations suggested by Bureau of Indian Standards\' (BIS). However, it has been observed that the results obtained using above equations are exaggerated. In the present experimental investigations, the results of the accelerated compressive strength of the concrete are used to develop the regression models for predicting the short term and long term compressive strength of concrete. The proposed regression models show better agreement with the actual compressive strength than the existing model suggested by BIS specification.

Key Words
ordinary portland cement; concrete; compressive strength; accelerated compressive strength; normal curing; accelerated curing

Address
N.L. Shelke: Department of Structural Engineering, Sardar Patel College of Engineering, Andheri (West), Mumbai-400058, India
Sangeeta Gadve: Department of Applied Mechanics, Visvesvaraya National Institute of Technology (VNIT), Nagpur-440010, India

Abstract
The study is to investigate the free vibration of antisymmetric angle-ply conical shells having non-uniform sinusoidal thickness variation. The arbitrarily varying thickness is considered in the axial direction of the shell. The vibrational behavior of shear deformable conical shells is analyzed for three different support conditions. The coupled differential equations in terms displacement and rotational functions are obtained. These displacement and rotational functions are invariantly approximated using cubic spline. A generalized eigenvalue problem is obtained and solved numerically for an eigenfrequency parameter and an associated eigenvector of spline coefficients. The vibration characteristic of the shells is examined for cone angle, aspect ratio, sinusoidal thickness variation, layer number, stacking sequence, and boundary conditions.

Key Words
vibration; anti-symmetric; conical shell; splines; thickness variation

Address
Saira Javed, K.K. Viswanathan, Z.A. Aziz: UTM Centre for Industrial and Applied Mathematics (UTM-CIAM), Ibnu SIna Institiute for Scientific & Industrial Research, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia; Department of Mathematical Sciences, Faculty of Science, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia
J.H. Lee: Department of Naval Architecture & Oceon Engineering, Division of Mechanical Engineering, Inha University, Incheon 22212, South Korea

Abstract
Different versions of a damage index (DI) along with a formulation to find the number of cycles at failure due to fatigue, applicable to reinforced concrete (RC) structures are presented. These are based on an energetic analysis method and applicable to both global and local levels. The required data can be found either from the numerical simulation of structures or from the experimental tests. A computer program has been developed to simulate numerically the nonlinear behavior of RC columns under cyclic loading. The proposed DI gives a regular distribution of structural damages up to failure and is validated by the results of the tests carried out on RC columns subjected to cyclic loading. In general, the local and global damage indices give approximately similar results, while each of them has its own advantages. The advantage of the implicit version of DI is that, it allows the comparison of the results with those of the monotonic loading case, while the explicit version makes it possible to estimate the number of loading cycles at failure due to fatigue, and the advantage of the simplified version is that; the monotonic loading data is not needed for the cyclic loading case.

Key Words
reinforced concrete; structures, earthquake, fatigue, damage, cyclic loading, failure

Address
Kabir Sadeghi and Fatemeh Nouban: Civil Engineering Department, Near East University, Near East Boulevard, ZIP: 99138, Nicosia, North Cyprus, Mersin 10, Turkey

Abstract
Shallow footings are one of the most common types of foundations used to support mid-rise buildings in high risk seismic zones. Recent findings have revealed that the dynamic interaction between the soil, foundation, and the superstructure can influence the seismic response of the building during earthquakes. Accordingly, the properties of a foundation can alter the dynamic characteristics (natural frequency and damping) of the soil-foundation-structure system. In this paper the influence that shallow foundations have on the seismic response of a mid-rise moment resisting building is investigated. For this purpose, a fifteen storey moment resisting frame sitting on shallow footings with different sizes was simulated numerically using ABAQUS software. By adopting a direct calculation method, the numerical model can perform a fully nonlinear time history dynamic analysis to realistically simulate the dynamic behaviour of soil, foundation, and structure under seismic excitations. This three-dimensional numerical model accounts for the nonlinear behaviour of the soil medium and structural elements. Infinite boundary conditions were assigned to the numerical model to simulate free field boundaries, and appropriate contact elements capable of modelling sliding and separation between the foundation and soil elements are also considered. The influence of foundation size on the natural frequency of the system and structural response spectrum was also studied. The numerical results for cases of soil-foundation-structure systems with different sized foundations and fixed base conditions (excluding soil-foundation-structure interaction) in terms of lateral deformations, inter-storey drifts, rocking, and shear force distribution of the structure were then compared. Due to natural period lengthening, there was a significant reduction in the base shears when the size of the foundation was reduced. It was concluded that the size of a shallow foundation influences the dynamic characteristics and the seismic response of the building due to interaction between the soil, foundation, and structure, and therefore design engineer should carefully consider these parameters in order to ensure a safe and cost effective seismic design.

Key Words
seismic soil-foundation-structure interaction; shallow foundation; footing; foundation size; ABAQUS

Address
Quoc Van Nguyen, Behzad Fatahi: School of Civil and Environmental Engineering, University of Technology Sydney (UTS), Sydney, Australia
Aslan S. Hokmabadi: Ove Arup & Partners, Hong Kong

Abstract
In the last few years, many structural monitoring studies have been performed using different techniques to measure structures of different scales such as buildings, dams or bridges. One of the mostly used tools are GPS instruments, which have been utilized in various combinations with accelerometers and some other conventional sensors. In the current study, observation series were recorded for 8 hours with GPS receivers (NovAtel) and Inclination Measurement Sensors mounted on a television tower in Istanbul, Turkey. Each series of observations collected from two different sensors were transformed into a single coordinate system (Local Topocentric Coordinates System). The positional changes of the tower were calculated from the GPS and the inclination data. These changes were plotted in two dimensions (2D) on the same graphic. Thus, the possibility of comparison and analysis were found using the data from both the GPS and the Inclinometer complement each other, in the real test area. The positional changes of the tower were modeled for further examination. As a result, the movement of the tower within an area of 1x1 cm2 was observed. Based on the results, it can be concluded that inclinometers can be used for monitoring the structural behavior of the tower.

Key Words
structural health monitoring; GPS; inclinometers; time series; measurement

Address
Huseyin Pehlivan: Department of Geodesy and Photogrametry Engineering, Gebze Technical University, P.K : 141 41400, Kocaeli, Turkey
Halim Ferit Bayata: Department of Civil Engineering, Erzincan University, P.K : 24 100, Erzincan, Turkey

Abstract
A method of damage detection based on the moving harmonic excitation and continuous wavelet transforms is presented. The applied excitation is used as a moving actuator and its frequency and speed parameters can be adjusted for an amplified response. The continuous wavelet transforms, CWT, is used for cracks detection based on the resulting amplified signal. It is demonstrated that this identification procedure is largely better than the classical ones based on eigenfrequencies or on the eigenmodes wavelet transformed. For vibration responses, free and forced vibration analyses of multi-cracked beams are investigated based on both analytical and numerical methodological approaches. Cracks are modeled through rotational springs whose compliances are evaluated using linear elastic fracture mechanics. Based on the obtained forced responses, multi-cracks positions are accurately identified and the CWT identification can be highly improved by adjusting the frequency and the speed excitation parameters.

Key Words
multi-cracks identification; wavelet transform; differential quadrature method; moving harmonic excitation; free and forced vibration

Address
Hajar Chouiyakh: Mathematical Modeling and Control, Faculty of Sciences and Techniques of Tangier, Abdelmalek Essaâdi University, Tangier, Morocco
Lahcen Azrar: Mathematical Modeling and Control, Faculty of Sciences and Techniques of Tangier, Abdelmalek Essaâdi University, Tangier, Morocco; LaMIPI, Higher School of Technical Education of Rabat (ENSET), Mohammed V University in Rabat, Morocco; Department of Mechanical Engineering, Faculty of Engineering, King Abdulaziz University, Jeddah, Saudi Arabia
Khaled Alnefaie: Department of Mechanical Engineering, Faculty of Engineering, King Abdulaziz University, Jeddah, Saudi Arabia
Omar Akourri: Mathematical Modeling and Control, Faculty of Sciences and Techniques of Tangier, Abdelmalek Essaâdi University, Tangier, Morocco

Abstract
The present paper focuses on size optimization of double layer barrel vaults considering nonlinear behavior. In order to tackle the optimization problem an improved colliding bodies optimization (ICBO) algorithm is proposed. The important task that should be achieved before optimization of structural systems is to determine the best form having the least cost. In this study, an attempt is done to find the best form then it is optimized considering linear and non-linear behaviors. In the optimization process based on nonlinear behavior, the geometrical and material nonlinearity effects are included. A large-scale double layer barrel vault is presented as the numerical example of this study and the obtained results indicate that the proposed ICBO has better computational performance compared with other algorithms.

Key Words
optimization; double layer barrel vault; nonlinear behavior; meta-heuristic

Address
Saeed Gholizadeh, Changiz Gheyratmand and Hamed Davoudi: Department of Civil Engineering, Urmia University, Urmia, West Azerbaijan Province, Iran

Abstract
The pounding phenomenon in adjacent structures happens in severing earthquakes that can cause great damages. Connecting neighboring structures with active and semi-active control devices is an effective method to avoid mutual colliding between neighboring buildings. One of the most important issues in control systems is applying online control force. There will be a time delay if the prose of producing control force does not perform on time. This paper proposed a time-delay compensation method in coupled structures control, with semi-active Magnetorheological (MR) damper. This method based on Newmark\'s integration is adopted to mitigate the time-delay effect. In this study, Lyapunov\'s direct approach is employed to compute demanded voltage for MR dampers. Using Lyapunov\'s direct algorithm guarantees the system stability to design a controller based on feedback. Because of the strong nonlinearity of MR dampers, the equation of motion of coupled structures becomes an involved equation, and it is impossible to solve it with the common time step methods. In present paper modified Newmark-Beta integration based on the instantaneous optimal control algorithm, used to solve the involved equation. In this method, the response of a coupled system estimated base on optimal control force. Two MDOF structures with different degrees of freedom are finally considered as a numeric example. The numerical results show, the Newmark compensation is an efficient method to decrease the negative effect of time delay in coupled systems; furthermore, instantaneous optimal control algorithm can estimate the response of structures suitable.

Key Words
coupled structures control; time delay; Newmark compensation; magneto rheological damper

Address
Javad Katebi and Samira Mohammady Zadeh: Department of Civil Engineering, University of Tabriz, Iran


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