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CONTENTS
Volume 52, Number 4, November25 2014
 

Abstract
The use of steel-concrete composite members has been significantly increased as they have the advantages of the reduction of cross sectional areas, excellent ductility against earthquake loadings and a longer life span than typical steel frame members. The increased use of composite members requires an intensive study on the shear resistance evaluation of stud connectors in high strength concrete. However, the applicability of currently available standards is limited to composite members with normal and lightweight strength concrete. In this paper, push-out tests were performed on 24 specimens to investigate the structural behavior and shear resistance of stud connectors in high strength concrete. Test parameters include the existence of shear studs, height to diameter ratio of a shear stud, its diameter and concrete cover thickness. A shear resistance equation of stud connectors is proposed through a linear regression analysis based on the test results. Its accuracy is compared with those of existing shear resistance equations for studs in normal and lightweight concrete.

Key Words
shear stud; composite members; shear resistance; high strength concrete; steel pipe

Address
Young Hak Lee, Min Sook Kim, Heecheul Kim and Dae-Jin Kim: Department of Architectural Engineering, Kyung Hee University, 1 Sochon-Dong, Kihung-Gu, Yongin, Kyunggi, 446-701, Republic of Korea

Abstract
This paper deals with free vibration analysis of bidirectional functionally graded annular plates resting on a two-parameter elastic foundation. The formulations are based on the three-dimensional elasticity theory. This study presents a novel 2-D six-parameter power-law distribution for ceramic volume fraction of 2-D functionally graded materials that gives designers a powerful tool for flexible designing of structures under multi-functional requirements. Various material profiles along the thickness and in the in-plane directions are illustrated by using the 2-D power-law distribution. The effective material properties at a point are determined in terms of the local volume fractions and the material properties by the Mori-Tanaka scheme. The 2-D differential quadrature method as an efficient and accurate numerical tool is used to discretize the governing equations and to implement the boundary conditions. The fast rate of convergence of the method is shown and the results are compared against existing results in literature. Some new results for natural frequencies of the plates are prepared, which include the effects of elastic coefficients of foundation, boundary conditions, material and geometrical parameters. The interesting results indicate that a graded ceramic volume fraction in two directions has a higher capability to reduce the natural frequency than conventional 1-D functionally graded materials.

Key Words
nonlinear distribution of material profiles; 3-D vibration analysis of plates; bidirectional functionally graded materials; two-parameter elastic foundations; differential quadrature method

Address
Vahid Tahouneh: Department of Mechanical Engineering, Islamshahr Branch, Islamic Azad University, Tehran, Iran

Abstract
Based on the energy method considering the second order effects, the natural frequencies of externally prestressed simply supported beam and the compression softening effect of external prestress force were analyzed. It is concluded that the compression softening effect depends on the loss of external tendon eccentricity. As the number of deviators increases from zero to a large number, the compression softening effect of external prestress force decreases from the effect of axial compression to almost zero, which is consistent with the conclusion mathematically rigorously proven. The frequencies calculated by the energy method conform well to the frequencies by FEM which can simulate the frictionless slide between the external tendon and deviator, the accuracy of the energy method is validated. The calculation results show that the compression softening effect of external prestress force is negligible for the beam with 2 or more deviators due to slight loss of external tendon eccentricity. As the eccentricity and area of tendon increase, the first natural frequency of the simply supported beams noticeably increases, however the effect of the external tendon on other frequencies is negligible.

Key Words
external prestress; simply supported beam; natural frequency; energy method; dynamic analysis

Address
De-Ping Fang: College of Civil Engineering, Huaqiao University, Xiamen, 361021, China

Abstract
In the assessment of existing RC buildings, the reliable appraisal of the compressive strength of in-situ concrete is a fundamental step. Unfortunately, the data that can be obtained by the available testing methods are typically affected by a high level of uncertainty. Moreover, in order to derive indications about the degradation and ageing of the materials by on site tests, it is necessary to have the proper terms of comparison, that is to say, to know the reference data measured during the construction phases, that are often unavailable when the building is old. In the cases when such a comparison can be done, the in situ strength values typically turn out to be lower than the reference strength values (tests performed on taken samples during the construction). At this point, it is crucial to discern and quantify the specific effect induced by different factors: ageing of the materials; poor quality of the placement, consolidation or cure of the concrete during the construction phases; damage due to drilling. This paper presents a procedure for correlating the destructive compressive tests and non-destructive tests (ultrasonic pulse velocity tests) with the data documenting the compressive strength tested during the construction phases. The research work is aimed at identifying the factors that induce the difference between the in-situ strength and cubes taken from the concrete casting, and providing, so, useful information for the assessment procedure of the building.

Key Words
existing RC buildings; in-situ strength of concrete; compressive strength; seismic assessment; core drilling; structural safety; compaction degree; concrete; ultrasonic pulse velocity method; concrete degradation

Address
Francesco Porco, Giuseppina Uva, Andrea Fiore and Mauro Mezzina: DICATECh, Politecnico di Bari, Via Orabona 4 – 70126 Bari, Italy

Abstract
Prestressing is the most commonly employed technique in bridges and long span beams in commercial buildings as prestressing results in slender section with higher load carrying capacities. This work is an attempt to study the performance of a minimum weight prestressed concrete beam adopting a non-prismatic section so that there will be a reduction in the volume of concrete which in turn reduces the self-weight of the structure. The effect of adopting a non-prismatic section on parameters like prestressing force, area of prestressing steel, bending stresses, shear stresses and percentage loss of prestress are established theoretically. The analysis of non-prismatic prestressed beams is based on the assumption of pure bending theory. Equations are derived for dead load bending moment, eccentricity, and depth at any required section. Based on these equations an algorithm is developed which does the stress checks for the given section for every 500 mm interval of the span. Limit state method is used for the design of beam and finite difference method is used for finding out the deflection of a non-prismatic beam. All the parameters of nonprismatic prestressed concrete beams are compared with that of the rectangular prestressed concrete members and observed that minimum weight design and economical design are not same. Minimum weight design results in the increase in required area of prestressing steel.

Key Words
prestressing; non-prismatic; deflection; finite difference method; eccentricity; loss of prestress; limit state method; economical design

Address
P. Markandeya Raju: Department of Civil Engineering, Maharaj Vijayram Gajapathi Raj College of Engineering, Vijayramnagar, Chintalavalasa, Vizianagaram - 535 005, A.P, India
K. Rajsekhar: Department of Civil Engineering, College of Engineering, Andhra University, Visakhapatnam - A.P, India
T. Raghuram Sandeep: Bhabha Atomic Research Centre, Visakhapatnam -A.P, India

Abstract
There have been many packages that can be employed to analyze plane frames. However, because most structural analysis packages suffer from closeness of system, it is very difficult to integrate it with an optimization package. To overcome the difficulty, we proposed a possible alternative, DAMDO, which integrate Design, Analysis, Modeling, Definition, and Optimization phases into an integrative environment. The DAMDO methodology employs neural networks to integrate structural analysis package and optimization package so as not to need directly to integrate these two packages. The key problem of the DAMDO approach is how to generate a set of reasonable random designs in the first phase. According to the characteristics of optimized plane frames, we proposed the ratio variable approach to generate them. The empirical results show that the ratio variable approach can greatly improve the accuracy of the neural networks, and the plane frame optimization problems can be solved by the DAMDO methodology.

Key Words
artificial neural networks; optimization; plane frame; ratio variable

Address
Chin-Sheng Kao and I-Cheng Yeh: Department of Civil Engineering, Tamkang University, No.151, Yingzhuan-ro, Tamsui-gu, New Taipei City, Taiwan,The Republic of China

Abstract
In this present work, Artificial Bee Colony Algorithm (ABCA) is used to optimize the stacking sequences of simply supported antisymmetric laminated composite plates with criticial buckling load as the objective functions. The fibre orientations of the layers are selected as the optimization design variables with the aim to find the optimal laminated plates. In order to perform the optimization based on the ABCA, a special code is written in MATLAB software environment. Several numerical examples are presented to illustrate this optimization algorithm for different plate aspect ratios, number of layers and load ratios.

Key Words
laminated plates; artificial bee colony algorithm; buckling; optimization

Address
Umut Topal and Hasan Tahsin Ozturk: Department of Civil Engineering, Faculty of Technology, Karadeniz Technical University, 61830, Trabzon, Turkey

Abstract
This paper presents the design of reinforced concrete circular footings subjected to axial load and bending in two directions using a new model. The new model considers the soil real pressure acting on contact surface of the circular footings and these are different, with a linear variation in the contact area, these pressures are presented in terms of the axial load, moments around the axis \"X\" and the axis \"Y\". The classical model takes into account only the maximum pressure of the soil for design of footings and it is considered uniform at all points of contact area. Also, a comparison is presented in terms of the materials used (steel and concrete) between the two models shown in table, being greater the classical model with respect the new model. Therefore, the new model is the most appropriate, since it is more economic and also is adjusted to real conditions.

Key Words
circular footings design; ground reaction; moments; bending shear; punching shear

Address
Arnulfo Luévanos Rojas: Faculty of Engineering, Science and Architecture, Juárez University of Durango State, Av. Universidad S/N, Fracc. Filadelfia, CP 35010, Gómez Palacio, Durango, México

Abstract
Starting with Hamilton\'s variational principle, the governing field equations for the steady state response of thin-walled beams under harmonic forces are derived. The formulation captures shear deformation effects due to bending and warping, translational and rotary inertia effects and as well as torsional flexural coupling effects due to the cross section mono-symmetry. The equations of motion consist of four coupled differential equations in the unknown displacement field variables. A general closed form solution is then developed for the coupled system of equations. The solution is subsequently used to develop a family of shape functions which exactly satisfy the homogeneous form of the governing field equations. A super-convergent finite element is then formulated based on the exact shape functions. Key features of the element developed include its ability to (a) isolate the steady state response component of the response to make the solution amenable to fatigue design, (b) capture coupling effects arising as a result of section mono-symmetry, (c) eliminate spatial discretization arising in commonly used finite elements, (d) avoiding shear locking phenomena, and (e) eliminate the need for time discretization. The results based on the present solution are found to be in excellent agreement with those based on finite element solutions at a small fraction of the computational and modelling cost involved.

Key Words
torsional-flexural response; monosymmetric section; harmonic forces; exact shape functions

Address
Mohammed A. Hjaji: Department of Mechanical and Industrial Engineering, University of Tripoli, Tripoli, Libya
Magdi Mohareb: Civil Engineering Department, University of Ottawa, 161 Louis Pasteur (A-025), Ottawa, Ontario, K1N 6N5, Canada

Abstract
Buckling optimization of laminated composite plates is significant as they fail because of buckling under in-plane compressive loading. The plate is usually modeled without cutout so that the buckling strength is found analytically using classical laminate plate theory (CLPT). However in real world applications, the composite plates are modeled with cutouts for getting them assembled and to offer the provisions like windows, doors and control system. Finite element analysis (FEA) is used to analyze the buckling strength of the plate with cutouts and it leads to high computational cost when the plate is optimized. In this article, a genetic algorithm based optimization technique is used to optimize the composite plate with cutout. The computational time is highly reduced by replacing FEA with artificial neural network (ANN). The effectiveness of the proposed method is explored with two numerical examples.

Key Words
sacking sequence optimization; artificial neural network; genetic algorithm; finite element analysis

Address
P. Emmanuel Nicholas and D. Vasudevan: 1Department of Mechanical Engineering, PSNA College of Engineering and Technology, Dindigul 624622, India
K.P. Padmanaban: 2Department of Mechanical Engineering, SBM College of Engineering and Technology, Dindigul 624005, India

Abstract
The main purpose of this study is to determine the effect of overlay on the crack propagation. In order to simplify the problem, a cement concrete pavement is modeled as an elastic plate on Winkler foundation. To derive the singular integral equations, the Fourier transform and dislocation density function are used. Lobatto-Chebyshev integration formula, as a numerical method, is used to solve the singular integral equations. The numerical solution of stress intensity factor at the crack tip is derived. In order to examine the effect of overlay for resisting crack propagation, numerical analyses are carried out for a cement concrete pavement with an embedded crack and a concrete pavement with an asphalt overlay. Results show the significant factors that influence the crack propagation.

Key Words
fourier transform; dislocation density function; singular integral equation; stress intensity factor; overlay

Address
Baofeng Pan and Yang Zhong: Faculty of Infrastructure Engineering, Dalian University of technology, Dalian Liaoning 116024, China
Yuanyuan Gao: College of Civil Engineering and Mechanics, Yan Shan University, Qinhuangdao Hebei 066004, China

Abstract
Concrete infill and reinforcement are one of the most well-known strengthening methods of structural elements. This study investigated flexural performance of concrete infill composite PHC pile (ICP pile) reinforced by infill concrete and longitudinal rebars in hollow PHC pile. A total four series of pile specimens were tested by four points bending method under simply supported conditions and investigated bending moment experimentally and analytically. From the test results, it was found that although reinforcement of infilled concrete on the pure bending moment of PHC pile was negligible, reinforcement of PHC pile using infilled concrete and longitudinal rebars increase the maximum bending moment with range from 1.95 to 2.31 times than that of conventional PHC pile. The error of bending moment between experimental results and predicted results by nonlinear sectional analysis on the basis of the conventional layered sectional approach was in the range of -2.54 % to 2.80 %. The axial compression and moment interaction analysis for ICP piles shows more significant strengthening effects of infilled concrete and longitudinal rebars.

Key Words
PHC pile; infilled concrete; longitudinal rebar; flexural performance

Address
Jin Wook Bang, Jung Hwan Hyun and Yun Yong Kim: Department of Civil Engineering, Chungnam National University, 99 Daehak-ro Yuseong-gu, Daejeon, 305-764, Republic of Korea
Bang Yeon Lee: School of Architecture, Chonnam National University, 300 Yongbong-dong, Buk-gu, Gwangju, 500-757, Republic of Korea
Byung Jae Lee: R&D Center, JNTINC Co., Ltd., Hyundaikia-ro 830beon-Gil, Bibong-Myeon, Hwaseong-City, Gyeonggi-Do
445-842, Republic of Korea


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