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CONTENTS
Volume 54, Number 6, June25 2015
 

Abstract
Form-finding for cable-membrane structures is a delicate operation. During the last decades, the force density method (FDM) was considered to be an efficient method to address the problem. Many researchers were devoted to improving this method and proposed many methods such as natural force density method (NFDM), improved nonlinear force density method (INFDM), et al. In this paper, a modified nonlinear force density method (MNFDM) is proposed. In this method, the stresses of membrane elements were transformed to the force-densities of cable nets by an equivalent relationship, and then they can be used as initial conditions. By comparing with the forming finding results by using the FDM, NFDM, INFDM and MNFDM, it had demonstrated that the MNFDM presented in this paper is the most efficient and precise.

Key Words
form-finding; cable-membrane structure; force density method (FDM); equivalent transform relationship

Address
Rui Xu, DongXu Li, Wang Liu, JianPing Jiang, YiHuan Liao
and Jie Wang: College of Aerospace Science and Engineering, National University of Defense Technology, Changsha, Hunan, 410073, People

Abstract
This paper presents a nonlocal sinusoidal shear deformation beam theory (SDBT) for the nonlinear vibration of single walled carbon nanotubes (CNTs). The present model is capable of capturing both small scale effect and transverse shear deformation effects of CNTs, and does not require shear correction factors. The surrounding elastic medium is simulated based on Pasternak foundation. Based on the nonlocal differential constitutive relations of Eringen, the equations of motion of the CNTs are derived using Hamilton\'s principle. Differential quadrature method (DQM) for the natural frequency is presented for different boundary conditions, and the obtained results are compared with those predicted by the nonlocal Timoshenko beam theory (TBT). The effects of nonlocal parameter, boundary condition, aspect ratio on the frequency of CNTs are considered. The compar¬ison firmly establishes that the present beam theory can accurately predict the vibration responses of CNTs.

Key Words
nonlinear vibration; sinusoidal shear deformation theory; DQM; Eringen theory

Address
Hasan Rahimi Pour: Young Researchers and Elite Club, Khomeyni Shahr Branch, Islamic Azad University, Khomeyni Shahr, Iran
Hossein Vossough, Mohammad Mehdi Heydari: Department of Civil Engineering, Jasb Branch, Islamic Azad University, Jasb, Iran
Gholamhossein Beygipoor: Young Researchers and Elite Club, Bandarabbas Branch, Islamic Azad University, Bandarabbas, Iran
Alireza Azimzadeh: Department of Mechanical Engineering, Kashan Branch, Islamic Azad University, Kashan, Iran

Abstract
The use of acoustic emission (AE) technique for detecting and monitoring damages and the progress on damages in different structures is widely used and has earned a reputation as one of the most reliable and well-established technique in non-destructive testing (NDT). Acoustic Emission is a very efficient and effective technology used for fracture behavior and fatigue detection in metals, fiberglass, wood, composites, ceramics, concrete and plastics. It can also be used for detecting faults and pressure leaks in vessels, tanks, pipes, as well as for monitoring the progression of corrosion in welding. This paper reviews major research developments over the past few years in application of acoustic emission in numerous engineering fields, including manufacturing, civil, aerospace and material engineering.

Key Words
application of AE; acoustic emission; non-destructive testing; NDT applications

Address
S. Gholizadeh, Z. Leman and B.T.H.T. Baharudin: Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia

Abstract
A novel optimization approach for reinforced concrete (RC) biaxially loaded columns is proposed. Since there are several design constraints and influences, a new computation methodology using iterative analyses for several stages is proposed. In the proposed methodology random iterations are combined with music inspired metaheuristic algorithm called harmony search by modifying the classical rules of the employed algorithm for the problem. Differently from previous approaches, a detailed and practical optimum reinforcement design is done in addition to optimization of dimensions. The main objective of the optimization is the total material cost and the optimization is important for RC members since steel and concrete are very different materials in cost and properties. The methodology was applied for 12 cases of flexural moment combinations. Also, the optimum results are found by using 3 different axial forces for all cases. According to the results, the proposed method is effective to find a detailed optimum result with different number of bars and various sizes which can be only found by 2000 trial of an engineer. Thus, the cost economy is provided by using optimum bars with different sizes.

Key Words
reinforced concrete; biaxially loaded columns; optimization; metaheuristic algorithms; harmony search algorithm

Address
Sinan Melih Nigdeli, Gebrail Bekdaş: Department of Civil Engineering, Istanbul University, 34320 Avcilar, Istanbul, Turkey
Sanghun Kim: Department of Civil and Environmental Engineering, Temple University, Philadelphia 19122, USA
Zong Woo Geem: Department of Energy IT, Gachon University, Seongnam 461-701, South Korea

Abstract
Rebar corrosion in concrete is one of the main causes of reduction of service life of reinforced concrete buildings. This paper presents the influence of rebar corrosion on the structural behavior of reinforced concrete (RC) buildings subjected to strong earthquake ground motion. Different levels of rebar corrosion scenarios were applied on a typical four story RC frame. The deteriorated conditions as a result of these scenarios include loss in cross-sectional area and loss of mechanical properties of the reinforcement bars, loss in bond strength, and loss in concrete strength and its modulus of elasticity. Dynamic analyses of the frame with different corrosion scenarios are performed with selected strong earthquake ground motion records. The influences of degradation in both concrete and reinforcement on structural behavior are investigated by comparing the various parameters of the frame under different corrosion scenarios with respect to each other. The results show that the progressive deterioration of the frame due to rebar corrosion causes serious structural behavior changes such as change in failure mode. The intensity, propagation time, and extensity of rebar corrosion have very important effects on the level of degradation of steel and concrete, as well as on the earthquake behavior of the structure.

Key Words
earthquake; frame; rebar corrosion; reinforced concrete

Address
Isa Yuksel: Department of Civil Engineering, Bursa Technical University, Yildirim Campus, 16330 Bursa, Turkey

Abstract
Most of current bridge decks are made of reinforced concrete and often deteriorate at a relatively rapid rate in operational environments. The quick deterioration of the deck often impacts other critical components of the bridge. Another disadvantage of the concrete deck is its high weight in long-span bridges. Therefore, it is essential to examine new materials and innovative designs using hybrid system consisting conventional materials such as concrete and steel with FRP plates which is also known as composite deck. Since these decks are relatively new, so it would be useful to evaluate their performances in more details. The present study is dedicated to Hat-Shape composite girder with concrete slab. The structural performance of girder was evaluated with nonlinear finite element method by using ABAQUS and numerical results have been compared with experimental results of other researches. After ensuring the validity of numerical modeling of composite deck, parametric studies have been conducted; such as investigating the effects of constituent properties by changing the compressive strength of concrete slab and Elasticity modulus of GFRP materials. The efficacy of the GFRP box girders has been studied by changing GFRP material to steel and aluminum. In addition, the effect of Cross-Sectional Configuration has been evaluated. It was found that the behavior of this type of composite girders can be studied with numerical methods without carrying out costly experiments. The material properties can be modified to improve ultimate load capacity of the composite girder. strength-to-weight ratio of the girder increased by changing the GFRP material to aluminum and ultimate load capacity enhanced by deformation of composite girder cross-section.

Key Words
composite girders; GFRP; hat-shape section; nonlinear finite element analysis; ABAQUS

Address
Elham Alizadeh and Mehdi Dehestani: Faculty of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran

Abstract
Deployable structures have gained more and more applications in space and civil structures, while it takes a large amount of computational resources to analyze this kind of multibody systems using common analysis methods. This paper presents a new approach for dynamic analysis of multibody systems consisting of both rigid bars and arbitrarily shaped rigid bodies. The bars and rigid bodies are connected through their nodes by ideal pin joints, which are usually fundamental components of deployable structures. Utilizing the Moore-Penrose generalized inverse matrix, equations of motion and constraint equations of the bars and rigid bodies are formulated with nodal Cartesian coordinates as unknowns. Based on the constraint equations, the nodal displacements are expressed as linear combination of the independent modes of the rigid body displacements, i.e., the null space orthogonal basis of the constraint matrix. The proposed method has less unknowns and a simple formulation compared with common multibody dynamic methods. An analysis program for the proposed method is developed, and its validity and efficiency are investigated by analyses of several representative numerical examples, where good accuracy and efficiency are demonstrated through comparison with commercial software package ADAMS.

Key Words
multibody system; deployable structure; dynamic analysis; constraint equations; equations of motion; generalized inverse matrix

Address
Ping Xiang: Department of Architecture, Waseda University, 3-4-1 Okubo, Tokyo 169-8555, Japan
Minger Wu: Department of Building Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China
Rui Q. Zhou: Shanghai Institute of Mechanical & Electrical Engineering Co., Ltd, 1287 West Beijing Road, Shanghai 200040, China

Abstract
This paper investigates the fundamental period of vibration of RC buildings by means of finite element macro-modelling and modal eigenvalue analysis. As a base study, a number of 14-storey RC buildings have been considered \"according to code designed\" and \"according to code non-designed\". Several parameters have been studied including the number of spans; the span length in the direction of motion; the stiffness of the infills; the percentage openings of the infills and; the location of the soft storeys. The computed values of the fundamental period are compared against those obtained from seismic code and equations proposed by various researchers in the literature. From the analysis of the results it has been found that the span length, the stiffness of the infill wall panels and the location of the soft storeys are crucial parameters influencing the fundamental period of RC buildings.

Key Words
fundamental period; infilled frames; masonry; modal analysis; reinforced concrete buildings

Address
Panagiotis G. Asteris: Computational Mechanics Laboratory, School of Pedagogical and Technological Education, Heraklion, GR 14121, Athens, Greece
Constantinos C. Repapis: Department of Civil Engineering, Technological Education Institute of Piraeus, 250 Thivon and Petrou Ralli Str., Aigaleo 122 44, Athens, Greece
Liborio Cavaleri: Dipartimento di Ingegneria Civile, Ambientale, Aerospaziale e dei Materiali (DICAM), University of Palermo, Italy
Vasilis Sarhosis: School of Engineering, Cardiff University, Queen`s Building, Newport Road, Cardiff CF24 3AA, UK
Adamantia Athanasopoulou: Computational Mechanics Laboratory, School of Pedagogical and Technological Education, Heraklion, GR 14121, Athens, Greece

Abstract
This paper presents the details of size independent fracture energy and bi-linear tension softening relation for nano modified high strength concrete. Nano silica in powder form has been used as partial replacement of cement by 2 wt%. Two popular methods, namely, simplified boundary effect method of Karihaloo et al. (2003) and RILEM (1985) fracture energy with P-8 tail correction have been employed for estimation of size independent fracture energy for nano modified high strength concrete (compressive strength ranges from 55 MPa to 72 MPa). It is found that both the methods gave nearly same values, which is an additional evidence that either of them can be employed for determination of size independent fracture energy. Bi-linear tension softening relation corresponding to their size independent fracture energy has been constructed in an inverse manner based on the concept of non-linear hinge from the load-crack mouth opening plots of notched three-point bend beams.

Key Words
high strength concrete; nano-silica; size dependent fracture energy; size independent fracture energy; tension softening relation

Address
A. Ramachandra Murthy, P. Ganesh, S. Sundar Kumar and Nagesh R. Iyer: CSIR, Structural Engineering Research Centre, Chennai 600113, India

Abstract
In this research a theoretical and numerical study on a bridge damage detection procedure is presented based on vibration measurements collected from a set of accelerometers. This method, referred to as \"Adjoint Variable Method\", is a sensitivity-based finite element model updating method. The approach relies on minimizing a penalty function, which usually consists of the errors between the measured quantities and the corresponding predictions attained from the model. Moving mass is an interactive model and includes inertia effects between the model and mass. This interactive model is a time varying system and the proposed method is capable of detecting damage in this variable system. Robustness of the proposed method is illustrated by correct detection of the location and extension of predetermined single, multiple and random damages in all ranges of speed and mass ratio of moving vehicle. A comparative study on common sensitivity and the proposed method confirms its efficiency and performance improvement in sensitivity-based damage detection methods. In addition various possible sources of error, including the effects of measurement noise and initial assumption error in stability of method are also discussed.

Key Words
damage detection; sensitivity; moving mass; finite element model updating; Ill posed problem; inverse problem; regularization; noise

Address
Akbar Mirzaee, Mohsenali Shayanfar and Reza Abbasnia: Department of Civil Engineering, Iran University of Science and Technology, Narmak, Tehran, Islamic Republic of Iran

Abstract
In this research, the cylindrical absorber made of expanded metal sheets under impact loading has been examined. Expanded metal sheets due to their low weight, effective collapse mechanism has a high energy absorption capacity. Two types of absorbers with different cells angle were examined. First, the absorber with cell angle a=0 and then the absorber with angle cell a=90. Experimental Study is done by drop Hammer device and numerical investigation is done by finite element of ABAQUS software. The output of device is acceleration- time Diagram which is shown by Accelerometer that is located on the picky mass. Also the output of ABAQUS software is shown by force-displacement diagram. In this research, the numerical and experimental study of the collapse type, force-displacement diagrams and effective parameters has been investigated. Similarly, the comparison between numerical and experimental results has been observed that these results are matched well with each other. From the obtained results it was observed that the absorber with cell angle a=0, have symmetric collapse and had high energy absorption capacity but the absorber with cell angle a=90, had global buckling and the energy absorption value was not suitable.

Key Words
expanded metal sheet; energy absorption capacity; energy absorbers; dynamic axial loading; impact force; finite element

Address
M. Damghani Nouri, H. Hatamiand A. Ghodsbin Jahromi: Faculty of Mechanical Engineering, Semnan University, Iran

Abstract
Carbon steel plate girders have been used on a large scale in the building industry. Nowadays, Lean Duplex Stainless Steel (LDSS) plate girders are gaining popularity as they possess greater strength and are more impervious to corrosion than those that are constructed from carbon steel. Regardless of their popularity, there is very limited information with regards to their shear behavior. In this paper, the non-linear finite element analysis was employed to investigate the shear behavior of LDSS plate girders. Parameters considered were the web thickness, the flange width, and the girders aspect ratio. The analysis revealed that although the shear behavior of the LDSS girders was no different from that of carbon steel plate girders, it had obviously been affected by the non-linearity of the material. Furthermore, the selected parameters were found to pronounce effect on the shear capacity of the LDSS girders. That is, the shear capacity increased considerably with web thickness, and increased slightly with flange width. However, it was reduced as the aspect ratio increased. Comparisons between the finite element analysis failure loads and those predicted by the current European Code of Practice revealed that the latter underestimated the shear strength of the LDSS plate girders.

Key Words
lean duplex stainless steel (LDSS); shear response; ultimate shear capacity; finite element analysis; Welded I-sections

Address
Salam R. Armoosh, A.R. Khalim: Department of Civil and Structural Engineering, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia
Akram Sh. Mahmood: Department of Civil Engineering, University of Al-Anbar, Ramadi, Anbar, Iraq


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