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CONTENTS
Volume 53, Number 5, March10 2015
 

Abstract
This paper presents the application of a recently developed meta-heuristic algorithm, called Colliding Bodies Optimization (CBO), for size and topology optimization of steel trusses. This method is based on the one-dimensional collisions between two bodies, where each agent solution is considered as a body. The performance of the proposed algorithm is investigated through four benchmark trusses for minimum weight with static and dynamic constraints. A comparison of the numerical results of the CBO with those of other available algorithms indicates that the proposed technique is capable of locating promising solutions using lesser or identical computational effort, with no need for internal parameter tuning.

Key Words
Colliding Bodies Optimization; meta-heuristic algorithms; optimum design; size and topology optimization; truss structures

Address
A. Kaveh: Centre of Excellence for Fundamental Studies in Structural Engineering, Iran University of Science and Technology, Tehran, Iran
V.R. Mahdavi: School of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran-16, Iran

Abstract
Mechanical fastening is still one of the main methods used for joining components. Different techniques have been applied to reduce the effect of stress concentration of notches like fastener holes. In this work we evaluate the feasibility of combining laser shock peening (LSP) and cold expansion to improve fatigue crack initiation and propagation of open hole specimens made of 6061-T6 aluminum alloy. LSP is a new and competitive technique for strengthening metals, and like cold expansion, induces a compressive residual stress field that improves fatigue, wear and corrosion resistance. For LSP treatment, a Q-switched Nd:YAG laser with infrared radiation was used. Residual stress distribution as a function of depth was determined by the contour method. Compact tension specimens with a hole at the notch tip were subjected to LSP process and cold expansion and then tested under cyclic loading with R=0.1 generating fatigue cracks on the hole surface. Fatigue crack initiation and growth is analyzed and associated with the residual stress distribution generated by both treatments. It is observed that both methods are complementary; cold expansion increases fatigue crack initiation life, while LSP reduces fatigue crack growth rate.

Key Words
fatigue test; laser shock processing; residual stress

Address
Carlos Rubio-Gonzalez: Centro de Ingenieria y Desarrollo Industrial, Pie de la Cuesta. 702, Desarrollo San Pablo, Queretaro, Qro.,76130, Mexico
G. Gomez-Rosas: Universidad de Guadalajara, Guadalajara, Jal., Mexico
R. Ruiz: Instituto Tecnologico de Morelia, Morelia Mich., Mexico
M. Nait: Laboratorire de Mecanique de Lille, UMR CNRS 8107, IUT A GMP, Le recueil, Rue de la recherche BP 179, 59653 Villeneuve d\'Ascq, France
A. Amrouche: Laboratorire de Genie et Geo-Environnement LGCgE, EA 4515, Faculte des Sciences Appliquees Bethune, France

Abstract
In this study, a method for fatigue performance estimation of deepwater steel catenary riser (SCR) under short-term vortex-induced vibration was investigated for selected S-N curves. General tendency between S-N curve capacity and fatigue performance was analysed. SCRs are generally used to transport produced oil and gas or to export separated oil and gas, and are exposed to various environmental loads in terms of current, wave, wind and others. Current is closely related with VIV and it affects fatigue life of riser structures significantly. In this regards, the process of appropriate S-N curve selection was performed in the initial design stage based on the scale of fabrication-related initial imperfections such as welding, hot spot, crack, stress concentration factor, and others. To draw the general tendency, the effects of stress concentration factor (SCF), S-N curve type, current profile, and three different sizes of SCRs were considered, and the relationship between S-N curve capacity and short-term VIV fatigue performance of SCR was derived. In case of S-N curve selection, DNV (2012) guideline was adopted and four different current profiles of the Gulf of Mexico (normal condition and Hurricane condition) and Brazil (Amazon basin and Campos basin) were considered. The obtained results will be useful to select the S-N curve for deepwater SCRs and also to understand the relationship between S-N curve capacity and short-term VIV fatigue performance of deepwater SCRs.

Key Words
S-N curve; steel catenary riser (SCR); vortex-induced vibration (VIV); offshore riser engineering, riser fatigue

Address
D.K. Kim: Civil Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, Perak, Malaysia
H.S. Choi: Graduate School of Engineering Mastership, Pohang University of Science and Technology, Pohang, Republic of Korea
C.S. Shin: Graduate School of Engineering Mastership, Pohang University of Science and Technology, Pohang, Republic of Korea
M.S. Liew: Faculty of Geoscience and Petroleum Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, Perak, Malaysia
S.Y. Yu: Deepwater Technology Mission Oriented Research, Universiti Teknologi PETORNAS, Bandar Seri Iskandar, Perak, Malaysia
K.S. Park: Steel Business Division, POSCO, Seoul, Republic of Korea

Abstract
In this study, the effects of ground shocks due to explosive loads on the dynamic response of historical masonry bridges are investigated by using the multi-point shock response spectrum method. With this purpose, different charge weights and distances from the charge center are considered for the analyses of a masonry bridge and depending on these parameters frequency-varying shock spectra are determined and applied to each support of the two-span masonry bridge. The net blast induced ground motion consists of air-induced and direct-induced ground motions. Acceleration time histories of blast induced ground motions are obtained depending on a deterministic shape function and a stationary process. Shock response spectrums determined from the ground shock time histories are simulated using BlastGM software. The results obtained from uniform and multi-point response spectrum analyses cases show that significant differences take place between the uniform and multi-point blast-induced ground motions.

Key Words
historic masonry bridge; blast-induced ground motion; multi-point response spectrum method; charge weight; charge center

Address
Kemal Haciefendioglu: Department of Civil Engineering, Ondokuz Mayis University, 55139, Samsun, Turkey
Swagata Banerjee: Department of Civil and Environmental Engineering,The Pennsylvania State University, 16802-1408, USA
Kurtulus Soyluk: Department of Civil Engineering, Gazi University, Maltepe, 06570 Ankara, Turkey
Olgun Koksal: Vocational High School of Kavak, Ondokuz May

Abstract
Realistic prediction of concrete creep is of crucial importance for durability and long-term serviceability of concrete structures. To date, research about the behaviour of self-compacting concrete (SCC) members, especially concerning the long-term performance, is rather limited. SCC is quite different from conventional concrete (CC) in mixture proportions and applied materials, particularly in the presence of aggregate which is limited. Hence, the realistic prediction of creep strains in SCC is an important requirement for the design process of this type of concrete structures. This study reviews the accuracy of the conventional concrete (CC) creep prediction models proposed by the international codes of practice, including: CEB-FIP (1990), ACI 209R (1997), Eurocode 2 (2001), JSCE (2002), AASHTO (2004), AASHTO (2007), AS 3600 (2009). Also, SCC creep prediction models proposed by Poppe and De Schutter (2005), Larson (2007) and Cordoba (2007) are reviewed. Further, new creep prediction model based on the comprehensive analysis on both of the available models i.e. the CC and the SCC is proposed. The predicted creep strains are compared with the actual measured creep strains in 55 mixtures of SCC and 16 mixtures of CC.

Key Words
self-compacting concrete (SCC); conventional concrete (CC); creep; long-term behaviour

Address
Farhad Aslani: Centre for Infrastructure Engineering and Safety, School of Civil and Environmental Engineering, University of New South Wales, Australia

Abstract
In this study, in order to propose an efficient model to predict the torque capacity of steel fiber reinforced concrete (SFRC) beams, the existing experimental data related to torsional response of beams is reviewed. It is observed that existing data neglects the effects of some parameters on the variation of torque capacity. Thus, an experimental research was also conducted to obtain the effects of neglected parameters. In the experimental study, a total of seventeen SFRC beams are tested against torsion. The parameters considered in the experiments are concrete compressive strength, steel fiber aspect ratio, volumetric ratio of steel fibers and longitudinal reinforcement ratio. The effect of each parameter is discussed in terms of torque versus unit angle of twist graphs. The data obtained from this experimental research is also combined with the data got from previous studies and employed in artificial neural network (ANN) analysis to estimate the ultimate torque capacity of SFRC beams. In addition to parameters considered in the experiments, aspect ratio of beam cross-section, yield strengths of both transverse and longitudinal reinforcements, and transverse reinforcement ratio are also defined as parameters in ANN analysis due to their significant effects observed in previous studies. Assessment of the accuracy of ANN analysis in estimating the ultimate torque capacity of SFRC beams is performed by comparing the analytical and experimental results. Comparisons are conducted in terms of root mean square error (RMSE), mean absolute error (MAE) and coefficient of efficiency (Ef). The results of this study revealed that addition of steel fibers increases the ultimate torque capacity of reinforced concrete beams. It is also found that ANN is a powerful method and a feasible tool to estimate ultimate torque capacity of both normal and high strength concrete beams within the range of input parameters considered.

Key Words
reinforced concrete beam; torsion; steel fiber; artificial neural network

Address
Serkan Engin, Onur Ozturk and Fuad Okay: Department of Civil Engineering, Kocaeli University, 41380 Kocaeli, Turkey

Abstract
The present paper investigates the influence of the orientation of the ground-motion reference axes, the seismic incident angle and the seismic intensity level on the inelastic response of asymmetric reinforced concrete buildings. A single storey asymmetric building is analyzed by nonlinear dynamic analyses under twenty bi-directional ground motions. The analyses are performed for many angles of incidence and four seismic intensity levels. Moreover three different pairs of the horizontal accelerograms corresponding to the input seismic motion are considered: a) the recorded accelerograms, b) the corresponding uncorrelated accelerograms, and c) the completely correlated accelerograms. The nonlinear response is evaluated by the overall structural damage index. The results of this study demonstrate that the inelastic seismic response depends on the orientation of the ground-motion reference axes, since the three individual pairs of accelerograms corresponding to the same ground motion (recorded, uncorrelated and completely correlated) can cause different structural damage level for the same incident angle. Furthermore, the use of the recorded accelerograms as seismic input does not always lead to the critical case of study. It is also shown that there is not a particular seismic incident angle or range of angles that leads to the maximum values of damage index regardless of the seismic intensity level or the ground-motion reference axes.

Key Words
bi-directional excitation; ground-motion reference axes; seismic incident angle; inelastic response; intensity level; damage index; asymmetric single-story building

Address
Ioanna-Kleoniki M. Fontara, Konstantinos G. Kostinakis, Grigorios E. Manoukas and Asimina M. Athanatopoulou: Department of Civil Engineering, Aristotle University of Thessaloniki, University Campus, 54124, Thessaloniki, Greece

Abstract
This paper presents a finite element procedure for dynamic analysis of non-uniform Timoshenko beams made of axially Functionally Graded Material (FGM) under multiple moving point loads. The material properties are assumed to vary continuously in the longitudinal direction according to a predefined power law equation. A beam element, taking the effects of shear deformation and cross-sectional variation into account, is formulated by using exact polynomials derived from the governing differential equations of a uniform homogenous Timoshenko beam element. The dynamic responses of the beams are computed by using the implicit Newmark method. The numerical results show that the dynamic characteristics of the beams are greatly influenced by the number of moving point loads. The effects of the distance between the loads, material non-homogeneity, section profiles as well as aspect ratio on the dynamic responses of the beams are also investigated in detail and highlighted.

Key Words
axially FGM; non-uniform beam; FEM; multiple moving point load; dynamic response

Address
Buntara S. Gan, Thanh-Huong Trinh: Department of Architecture, College of Engineering, Nihon University, Koriyama, Fukushima-ken, 963-8642 Japan
Thi-Ha Le: Theoretical Group, Hanoi University of Transport and Communications, Cau Giay, Hanoi, Vietnam
Dinh-Kien Nguyen: Department of Solid Mechanics, Institute of Mechanics, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Vietnam

Abstract
The contribution of tensioned concrete between cracks (tension-stiffening) cannot be ignored when analysing deformation of reinforced concrete elements. The tension-stiffening effect is crucial when it comes to adequately estimating the load-deformation response of steel reinforced concrete and the more recently appeared fibre reinforced polymer (FRP) reinforced concrete. This paper presents a unified methodology for numerical modelling of the tension-stiffening effect in steel as well as FRP reinforced flexural members using the concept of equivalent deformation modulus and the smeared crack approach to obtain a modified stress-strain relation of the reinforcement. A closed-form solution for the equivalent secant modulus of deformation of the tensioned reinforcement is proposed for rectangular sections taking the Eurocode 2 curvature prediction technique as the reference. Using equations based on general principles of structural mechanics, the main influencing parameters are obtained. It is found that the ratio between the equivalent stiffness and the initial stiffness basically depends on the product of the modular ratio and reinforcement ratio (np), the effective-to-total depth ratio (d/h), and the level of loading. The proposed methodology is adequate for numerical modelling of tension-stiffening for different FRP and steel reinforcement, under both service and ultimate conditions. Comparison of the predicted and experimental data obtained by the authors indicates that the proposed methodology is capable to adequately model the tension-stiffening effect in beams reinforced with FRP or steel bars within wide range of loading.

Key Words
reinforced concrete; tension-stiffening; constitutive modelling; fibre reinforced polymer reinforcement; steel reinforcement; serviceability; numerical modelling

Address
Lluis Torres, Cristina Barris: Analysis and Advanced Materials for Structural Design (AMADE), Polytechnic School, University of Girona, Campus Montilivi s/n, 17071 Girona, Spain
Gintaris Kaklauskas: Department of Bridges and Special Structures, Vilnius Gediminas Technical University (VGTU), Sauletekio av. 11, 10223 Vilnius, Lithuania
Viktor Gribniak: Civil Engineering Research Centre, VGTU, Sauletekio av. 11, 10223 Vilnius, Lithuania

Abstract
In this study, the finite element method was used to analyze the distribution of the adhesive shear stresses in the single-lap bonded joint of two plates 2024-T3 aluminum with and without defects. The effects of the adhesive properties (shear modulus, the thickness and the length of the adhesive were highlighted. The results prove that the shear stresses are located on the free edges of the adhesively bonding region, and reach maximum values near the defect, because the concentration of high stress occurs near this area.

Key Words
finite element method (FEM); numerical methods; parametric analysis; quasi-static; simulation

Address
Aicha Benchiha and Kouider Madani: LMPM, Department of Mechanical Engineering, University of Sidi Bel Abbes, Algeria Cite Ben M\'hidi, Sidi Bel Abbes, Algeria

Abstract
This paper highlights the role of innovative vibration control system based on two promising properties in a parallel configuration. Hybrid device consists of two main components; recentering wires of shape memory alloy (SMA) and steel pipe section as an energy dissipater element. This approach concentrates damage in the steel pipe and prevents the main structural members from yielding. By regulation of the main adjustable design parameter, an optimum performance of the device is obtained. The effectiveness of the device in passive control of structures is evaluated through nonlinear time history analyses of a five-story steel frame with and without the hybrid device. Comparing the results proves that the hybrid device has a considerable potential to mitigate the residual drift ratio, peak absolute acceleration and peak interstory drift of the structure.

Key Words
shape memory alloy; recentering capability; energy dissipater component; nonlinear time history analysis; structural control

Address
Neda Salari and Behrouz Asgarian: Faculty of Civil Engineering, K. N. Toosi University of Technology, Tehran, Iran

Abstract
The study aims on the effect of material dependency in elastic- plastic contact models by contact analysis of sphere and flat contact model and wheel rail contact model by considering the material properties without friction. The various materials are selected for the analysis based on Young\'s modulus and yield strength ratio (E/Y). The simulation software \'ANSYS\' is employed for this study. The sphere and flat contact model is considered as a flattening model, the stress and strain for different materials are estimated. The simulation of wheel-rail contact model is also performed and the results are compared with the flattening model. The comparative study has also been extended for finding out the mean contact pressure for different materials the E/Y values between 150 and 660. The results show that the elastic-plastic contact analysis for materials up to E/Y=296.6 is depend on the nature of material properties and also for this material the mean contact pressure to yield strength reaches 2.65.

Key Words
contact analysis; E/Y ratio; stress; strain; mean contact pressure; yield strength

Address
V.C. Sathish Gandhi: Department of Mechanical Engineering, University College of Engineering Ariyalur (A constituent College of Anna University, Chennai), Ariyalur - 621 704, Tamilnadu, India
R. Kumaravelan: Department of Mechanical Engineering, Velalar College of Engineering and Technology, Erode - 638 012, Tamilnadu, India
S. Ramesh: Department of Mechanical Engineering,Vel Tech High Tech Dr.Rangarajan Dr.Sakunthala Engineering College, Chennai - 600 062, Tamilnadu, India
K. Sriram: Department of Mechanical Engineering, Amrita School of Engineering, Coimbatore - 641 112, Tamilnadu, India


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