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CONTENTS
Volume 50, Number 6, June25 2014
 

Abstract
Ultra-High Performance Concrete (UHPC) is an innovative new material that, in comparison to conventional concretes, has high compressive strength and excellent ductility properties achieved through the addition of randomly dispersed short fibers to the concrete mix. This study presents the results of an experimental investigation on the behavior of axially loaded UHPC short circular columns wrapped with Carbon-FRP (CFRP), Glass-FRP (GFRP), and Aramid-FRP (AFRP) sheets. Six plain and 36 different types of FRP-wrapped UHPC columns with a diameter of 100 mm and a length of 200 mm were tested under monotonic axial compression. To predict the ultimate strength of the FRP-wrapped UHPC columns, a simple confinement model is presented and compared with four selected confinement models from the literature that have been developed for low and normal strength concrete columns. The results show that the FRP sheets can significantly enhance the ultimate strength and strain capacity of the UHPC columns. The average greatest increase in the ultimate strength and strain for the CFRP- and GFRP-wrapped UHPC columns was 48% and 128%, respectively, compared to that of their unconfined counterparts. All the selected confinement models overestimated the ultimate strength of the FRP-wrapped UHPC columns.

Key Words
ultra high performance concrete with steel fibers; fiber reinforced polymer; ultimate strength; ultimate strain; confinement model

Address
Soner Guler : Faculty of Civil Engineering University of Yuzuncu Y

Abstract
A fracture criterion based on the strain energy density (SED) over a control volume, which embraces the notch edge, is employed in the present paper to assess the fracture loads of some U-notched Brazilian disk (UNBD) specimens. The specimens are made of commercial graphite and have been tested under pure mode I, pure mode II and mixed mode I/II loading. The results show that the SED criterion allows to successfully assess the fracture loads of graphite specimens for different notch tip radii and various mode mixity conditions with discrepancies that fall inside the scatter band of +-20%.

Key Words
Strain Energy Density (SED); U-notch; brittle fracture; mixed mode loading; graphite; UNotched Brazilian disk (UNBD)

Address
A.R. Torabi : Fracture Research Laboratory, Faculty of New Science and Technologies, University of Tehran, P.O. Box 13741-4395, Tehran, Iran
F. Berto : Department of Management and Engineering, University of Padova, Stradella, S. Nicola 3-36100 Vicenza, Italy

Abstract
The conventional PHC pile-footing connection is the weak part because the surface area and stiffness are sharply changed. The Composite PHC pile reinforced with the transverse shear reinforcing bars and infilled-concrete, hereafter ICP pile, has been developed for improving the flexural and shear performance. This paper investigates the cyclic behavior and performance of the ICP pile-footing connection. To investigate the behavior of the connection, one PHC and two ICP specimens were manufactured and then a series of cyclic loading tests were performed. From the test results, it was found that the ICP pile-footing connection exhibited higher cyclic behavior and connection performance compared to the conventional PHC pile-footing connection in terms of ductility ratio, stiffness degradation and energy dissipation capacity.

Key Words
PHC pile; transverse shear reinforcing bar; cyclic behavior; pile-footing connection

Address
Jin-Wook Bang, Jung Hwan Hyun and Yun Yong Kim : Department of Civil Engineering, Chungnam National University, 220 Gung-dong 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

Abstract
A simplistic approach towards evaluation of complete load deflection response of Reinforced Concrete (RC) flexural members under post fire (residual) scenario is presented in this paper. The crosssection of the RC flexural member is divided into a number of sectors. Thermal analysis is performed to determine the temperature distribution across the section, for given fire duration. Temperature-dependent stress-strain curves for concrete and steel are then utilized to perform a moment-curvature analysis. The moment-curvature relationships are obtained for beams exposed to different fire durations. These are then utilized to obtain the load-deflection plots following pushover analysis. Moreover one of the important issues of modeling the initial stiffness giving due consideration to stiffness degradation due to material degradation and thermal cracking has also been addressed in a rational manner. The approach is straightforward and can be easily programmed in spreadsheets. The presented approach has been validated against the experiments, available in literature, on RC beam subjected to different fire durations viz. 1hr, 1.5hrs and 2hrs. Complete load-deflection curves have been obtained and compared with experimentally reported counterparts. The results also show a good match with the results obtained using more complicated approaches such as those involving Finite element (FE) modeling and conducting a transient thermal stress analysis. Further evaluation of the beams during fire (at elevated temperatures) was performed and a comparison of the mechanical behavior of RC beams under post fire and during fire scenarios is made. Detailed formulations, assumptions and step by step approach are reported in the paper. Due to the simplicity and ease of implementation, this approach can be used for evaluation of global performance of fire affected structures.

Key Words
fire; residual capacity; load deflection; simplistic numerical approach

Address
Hitesh Lakhani, Tarvinder Singh, G.R. Reddy and R.K. Singh : Reactor Safety Division, Bhabha Atomic Research Centre, Mumbai, 400085, India
Akanshu Sharma : Institute of Construction Materials, University of Stuttgart, 70569 Stuttgart, Germany

Abstract
This paper deals with free vibration analysis of continuous grading fiber reinforced (CGFR) and bi-directional FG annular sector plates on two-parameter elastic foundations under various boundary conditions, based on the three-dimensional theory of elasticity. The plates with simply supported radial edges and arbitrary boundary conditions on their circular edges are considered. A semi-analytical approach composed of differential quadrature method (DQM) and series solution is adopted to solve the equations of motion. Some new results for the natural frequencies of the plate are prepared, which include the effects of elastic coefficients of foundation, boundary conditions, material and geometrical parameters. Results indicate that the non-dimensional natural frequency parameter of a functionally graded fiber volume fraction is larger than that of a discrete laminated and close to that of a 2-layer. It results that the CGFR plate attains natural frequency higher than those of traditional discretely laminated composite ones and this can be a benefit when higher stiffness of the plate is the goal and that is due to the reduction in spatial mismatch of material properties. Moreover, it is shown that a graded ceramic volume fraction in two directions has a higher capability to reduce the natural frequency than conventional one-dimensional functionally graded material. The multidirectional graded material can likely be designed according to the actual requirement and it is a potential alternative to the unidirectional functionally graded material. The new results can be used as benchmark solutions for future researches.

Key Words
free vibration; continuous grading fiber reinforcement; bi-directional FG plates; thick annular sector plates; pasternak elastic foundations; three-dimensional elasticity

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

Abstract
Cooling tower is analyzed as an assembly of layered nonlinear shell elements. Geometric representation of the shell is enabled through layered nonlinear shell elements to define the different layers of reinforcements and concrete by considering the material nonlinearity of each layer for the cooling tower shell. Modal analysis using Ritz vector analysis and nonlinear time history analysis by direct integration method have been carried out to study the effects of the inclination of the supporting columns of the cooling tower shell on its dynamic characteristics. The cooling tower is supported by I-type columns and ᴧ-type columns supports having the different inclination angles. Relevant comparisons of the dynamic response of the structural system at the base level (at the junction of the column and shell), throat level and at the top of the tower have been made. Dynamic response of the cooling tower is found to be significantly sensitive to the change of the inclination of the supporting columns. It is also found that the stiffness of the structure system increases with increase in inclination angle of the supporting columns, resulting in decrease of the period of the structural system. The participation of the stiffness of the tower in structural response of the cooling tower is fund to be dependent of the change in the inclination angle and even in the types of the supporting columns.

Key Words
cooling tower; hyperbolic shell; finite element analysis; dynamic response; layered shell; modal analysis; nonlinear time history analysis; support inclination

Address
Esmaeil Asadzadeh, Mehtab Alam : Department of Civil Engineering, Jamia Millia Islamia University, 110025 Maulana Mohammed Ali Jauhar Marg, New Delhi, India
Sahebali Asadzadeh : Department of Civil Engineering, Islamic Azad University of Maragheh, Maragheh, Iran

Abstract
An experimental program was designed in the current work to examine the structural behavior of ferrocement beams reinforced with composite materials under three point loadings up to failure. The experimental program comprised casting and testing of twelve ferrocement beams having the dimensions of 120 mm width, 200 mm depth and 1600 mm length. The twelve beams were different in the type of reinforcements; steel bars, traditional wire meshes (welded and expanded wire meshes) and composite materials (fiberglass wire meshes and polypropylene wire meshes). The flexural performances of the all tested beams in terms of strength, ductility, cracking behavior and energy absorption were investigated. Also all the tested beams were simulated using ANSYS program. The results of the experimental tests concluded that the beam with fiber glass meshes gives the lowest first crack load and ultimate load. The ferrocement beam reinforced with four layers of welded wire meshes has better structural behavior than those beams reinforced with other types of wire meshes. Also the beams reinforced with metal wire meshes give smaller cracks width in comparing with those reinforced with non-metal wire meshes. Also the Finite Element (FE) simulations gave good results comparing with the experimental results.

Key Words
ferrocement; fiberglass mesh; polyethylene mesh; finite element method; nonlinear analysis

Address
Yousry B.I. Shaheen, Boshra A. Eltaly and Samer G. Abdul-Fataha : Civil Engineering Department, Faculty of Engineering, Minoufia University, Gamal Abdul-Nasser Street, Minufiya, Egypt

Abstract
Despite the availability of other transport methods such as land and air transportations, marine transportation is the most preferred and widely used transportation method in the world because of its economical advantages. In service, ships experience cyclic loading. Hence, it can be said that fatigue fracture, which occurs due to cyclic loading, is one of the most critical failure modes for vessels. Accordingly, this makes fatigue failure prevention an important design requirement in naval architecture. In general, a ship structure contains many structural components. Because of this, structural modeling typically relies on Finite Element Analysis (FEA) techniques. It is possible to increase fatigue performance of the ship structures by using FEA in computer aided engineering environment. Even if literature papers as well as rules of classification societies are available to assess effect of fatigue cracks onto the whole ship structure, analytical studies are relatively scarce because of the difficulties of modeling the whole structure and obtaining reliable fatigue life predictions. As a consequence, the objective of this study is to improve fatigue strength of a mercantile vessel against fatigue loads via analytical method. For this purpose, the fatigue life of the mercantile vessel has been investigated. Two different type of fatigue assessment models, namely Coffin-Manson and Morrow Mean stress approaches, were used and the results were compared. In order to accurately determine the fatigue life of the ship, a nonlinear finite element analysis was conducted considering plastic deformations and residual stresses. The results of this study will provide the designer with some guidelines in designing mercantile vessels.

Key Words
ANSYS; fatigue strength; Finite Element Analysis (FEA); mercantile vessel

Address
Ahmet H. Ertas : Department of Biomedical Engineering, Karabuk University, Karabuk 78050, Turkey
Ahmet F. Yilmaz : Department of Naval Architecture, Bartin University, Bartin 74100, Turkey / Department of Mechanical Engineering, Karabuk University, Karabuk 78050, Turkey

Abstract
In this paper, two approximate analytical methods have been applied to forced nonlinear vibration problems to assess a high accurate analytical solution. Variational Iteration Method (VIM) and Perturbation Method (PM) are proposed and their applications are presented. The main objective of this paper is to introduce an alternative method, which do not require small parameters and avoid linearization and physically unrealistic assumptions. Some patterns are illustrated and compared with numerical solutions to show their accuracy. The results show the proposed methods are very efficient and simple and also very accurate for solving nonlinear vibration equations.

Key Words
Variational Iteration Method (VIM); Perturbation Method (PM); nonlinear oscillators; nonlinear spring

Address
Mahmoud Bayat, Mahdi Bayat : Department of Civil Engineering, College of Engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran
Iman Pakar : Young Researchers and Elites Club, Mashhad Branch, Islamic Azad University, Mashhad, Iran


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