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CONTENTS
Volume 19, Number 4, October 2015
 

Abstract
This paper presents experimental and numerical studies into the structural behavior of a high performance corbel type composite connection adopted in Raffles City of Hangzhou, China. Physical tests under both monotonic and quasi-static cyclic loads were conducted to investigate the load carrying capacities and deformation characteristics of this new type of composite connection. A variety of structural responses are examined in detail, including load-deformation characteristics, the development of sectional direct and shear strains, and the history of cumulative plastic deformation and energy. A three-dimensional finite element model built up with solid elements was also proposed for the verification against test results. The studies demonstrate the high rigidity, strength and rotation capacities of the corbel type composite connections, and give detailed structural understanding for engineering design and practice. Structural engineers are encouraged to adopt the proposed corbel type composite connections in mega high-rise buildings to achieve an economical and buildable and architectural friendly engineering solution.

Key Words
composite structures; physical test; composite connection; high-rise building; finite element modelling

Address
(1) G.B. Lou:
State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, P.R. China;
(2) A.J. Wang:
Corporate Technical Management, CapitaLand Management (China) Co., Ltd., Shanghai, P.R. China.

Abstract
This paper presents a probabilistic investigation of American and European specifications (i.e., AISC and Eurocode 4) for square concrete-filled steel tubular (CFT) stub columns. The study is based on experimental results of 100 axially loaded square CFT stub columns from the literature. By comparing experimental results for ultimate loads with code-predicted column resistances, the uncertainty of resistance models is analyzed and it is found that the modeling uncertainty parameter can be described using random variables of lognormal distribution. Reliability analyses were then performed with/without considering the modeling uncertainty parameter and the safety level of the specifications is evaluated in terms of sufficient and uniform reliability criteria. Results show that: (1) The AISC design code provided slightly conservative results of square CFT stub columns with reliability indices larger than 3.25 and the uniformness of reliability indices is no better because of the quality of the resistance model; (2) The uniformness of reliability indices for the Eurocode 4 was better than that of AISC, but the reliability indices of columns designed following the Eurocode 4 were found to be quite below the target reliability level of Eurocode 4.

Key Words
composites column; concrete; steel; square tubes; specifications; modeling uncertainty parameter; reliability analys

Address
(1) Zhao-Hui Lu, Yan-Gang Zhao, Zhi-Wu Yu:
National Engineering Laboratory for High Speed Railway Construction, School of Civil Engineering, Central South University, Changsha 410075, China;
(2) Yan-Gang Zhao:
Department of Architecture and Building Engineering, Kanagawa University, Yokohama 221-8686, Japan;
(3) Cheng Chen:
Department of Civil Engineering, San Francisco State University, San Francisco 94132, USA.

Abstract
In this paper, a refined exponential shear deformation beam theory is developed for bending analysis of functionally graded beams. The theory account for parabolic variation of transverse shear strain through the depth of the beam and satisfies the zero traction boundary conditions on the surfaces of the beam without using shear correction factors. Contrary to the others refined theories elaborated, where the stretching effect is neglected, in the current investigation this so-called "stretching effect" is taken into consideration. The material properties of the functionally graded beam are assumed to vary according to power law distribution of the volume fraction of the constituents. Based on the present shear deformation beam theory, the equilibrium equations are derived from the principle of virtual displacements. Analytical solutions for static are obtained. Numerical examples are presented to verify the accuracy of the present theory.

Key Words
beam; static; shear deformation theory; strain; stretching effect

Address
(1) Benoumrane Sallai, Lazreg Hadji, T. Hassaine Daouadji and E.A. Adda Bedia:
Laboratoire des Matériaux & Hydrologie, Université de Sidi Bel Abbes, 22000 Sidi Bel Abbes, Algeria;
(2) Lazreg Hadji, T. Hassaine Daouadji:
Université Ibn Khaldoun, BP 78 Zaaroura, 14000 Tiaret, Algeria.

Abstract
Recycled tire rubber-filled concrete (RRFC) is employed into the steel-concrete composite structures due to its good ductility and crack resistance. Push-out tests were conducted to investigate the static behavior of steel and rubber-filled concrete composite beam with different rubber mixed concrete and studs. The results of the experimental investigations show that large studs lead a higher ultimate strength but worse ductility in normal concrete. Rubber particles in RRFC were shown to have little effect on shear strength when the compressive strength was equal to that of normal concrete, but can have a better ductility for studs in rubber-filled concrete. This improvement is more obvious for the composite beam with large stud to make good use of the high strength. Besides that the uplift of concrete slabs can be increased and the quantity and width of cracks can be reduced by RRFC efficiently. Based on the test result, a modified empirical equation of ultimate slip was proposed to take not only the compressive strength, but also the ductility of the concrete into consideration.

Key Words
recycled tire rubber-filled concrete; steel-concrete composite beam; push-out test; large studs

Address
(1) Qing-Hua Han, Jie Xu, Ying Xing, Zi-Lin Li:
School of Civil Engineering, Tianjin University, Tianjin 300072, China;
(2) Qing-Hua Han, Jie Xu:
Key Laboratory of Coast Civil Structure Safety, Tianjin University, Ministry of Education, Tianjin 300072, China;
(3) Zi-Lin Li:
School of Civil Engineering, Tianjin Chengjian University, Tianjin 300384, China.

Abstract
Composite sections design consists on checking that the point defined by axial load and bending moment keeps included within the surface enclosed by the section interaction curve. Eurocode 4 suggests a method for tracing this diagram based on the plastic stress distribution method. However curves obtained according to this criterion overvalue concrete encased sections bearing capacity, especially when axial force comes with high bending moment values, so a correction factor is required. This article proposes a method for tracing this diagram based on the strain compatibility method. When stresses on the section are integrated by considering the Navier hypothesis, the use of the materials nonlinear constitutive equations provides curves much more adjusted to reality. This process requires the use of rather complex software which might reveal as too complex for practitioners. Preserving the same criteria of an elastic-plastic stress distribution, this article presents alternative expressions to obtain the failure internal forces in five significant points of the interaction diagram having considered five different positions of the neutral axis. These expressions are simply enough for their practical application. Concordance of curves traced strictly relying on these five points with those obtained by computer assisted stress integration considering the strain compatibility method and even with Eurocode 4 weighted curves will be presented for three different cross-sections and two different concrete strengths, revealing very good results.

Key Words
concrete encased sections; interaction diagrams; Eurocode 4; plastic; elastic-plastic

Address
(1) Ernesto Fenollosa, Enrique Gil, Ivan Cabrera:
Department of Continuum Mechanics and Theory of Structures, Polytechnic University of Valencia, Cno. de Vera s/n 46022 Valencia, Spain;
(2) Jose Vercher:
Department of Architectural Constructions, Polytechnic University of Valencia, Cno. de Vera s/n 46022 Valencia, Spain.

Abstract
Connections to circular hollow steel sections (CHS) are considered one of the most complex and time consuming connections in steel construction. Such connections are usually composed of gusset plates welded to the outside of the steel tube or penetrating the steel tube. Design guides, accounting for the effect of connection configuration on the strength of the connection, are not present. This study aims to investigate, through experimental testing and a parametric study, the influence of connection configuration on the strength of one sided branch plate-to-CHS members. A notable effect was observed on the behavior of the connections due to its detailing changes with respect to capacity, failure mode, ductility, and stress distribution. A parametric study is performed using the calibrated analytical model to include a wider range of parameters. The study involves 26 numerical analyses of finite element models including parameters of the diameter-to-thickness (D/t) ratio, length of gusset plate, and connection configuration. Accordingly, a modification to the formulas provided by the current design recommendations was suggested to include connection configuration effects for the one sided branch plate-to-CHS members.

Key Words
branch plate; circular hollow section; connection; steel structure; tube

Address
Department of Structural Engineering, Cairo University, Gamaa Street, Giza, Egypt.

Abstract
A procedure for critical buckling moment of a tapered beam is proposed with the application of potential energy calculations using Ritz method. Respective solution allows to obtain critical moments initiating lateral buckling of the simply supported, modestly tapered steel I-beams. In particular, lateral-torsional buckling of beams with simultaneously tapered flanges and the web are considered. Detailed, numerical, parametric analyses are carried out. Typical engineering, uniformly distributed design loads are considered for three cases of the load, applied to the top flange, shear centre, as well as to the bottom flange. In addition simply supported beam under gradient moments is investigated. The parametric analysis of simultaneously tapered beam flanges and the web, demonstrates that tapering of flanges influences much more the critical moments than tapering of the web.

Key Words
tapered I-beam; stability; lateral-torsional buckling; critical buckling moments

Address
Faculty of Civil Engineering, Opole University of Technology, 45-758 Opole, Prószkowska Street 76, Poland.

Abstract
During a seismic event, a considerable amount of energy is input into a structure. The law of energy conservation imposes the restriction that energy must either be absorbed or dissipated by the structure. Recent earthquakes have shown that the use of concentric bracing system with their low ductility and low energy dissipation capacity, causes permanent damage to structures during intense earthquakes. Hence, engineers are looking at bracing system with higher ductility, such as chevron and eccentric braces. However, braced frame would not be easily repaired if serious damage has occured during a strong earthquake. In order to solve this problem, a new bracing system an off-centre bracing system with higher ductility and higher energy dissipation capacity, is considered. In this paper, some numerical studies have been performed using ANSYS software on a frame with off-centre bracing system with optimum eccentricity and circular element created, called OBS_C_O model. In addition, other steel frame with diagonal bracing system and the same circular element is created, called DBS_C model. Furthermore, linear and nonlinear behavior of these steel frames are compared in order to introduce a new way of optimum performance for these dissipating elements. The obtained results revealed that using a ductile element or circular dissipater for increasing the ductility of off-centre bracing system and centric bracing system is useful. Finally, higher ductility and more energy dissipation led to more appropriate behavior in the OBS_C_O model compared to DBS_C model.

Key Words
finite elements; numerical analysis; braced frame; damping; building; knee brace; steel structure

Address
Faculty of Civil Engineering, Semnan University, Semnan, Iran.

Abstract
In this paper, brake pad performance of two organic matrix composites namely, Sample 1 (contains no brass filler) and Sample 2 (contains 1.5% brass filler), is studied based on tribological and squeal noise behavior. In the first stage, a pin-on-disc tribometer is used to evaluate the frictional behavior of the two pads. On the following stage, these pads are tested on squeal noise occurrence using a drag-type brake dynamometer. From the two type of tests, the results show that; (i) brass fillers play a dual role; firstly as reinforcing element of the brake pad providing primary contact sites, and secondly as solid lubricant by contributing to the formation of a layer of granular material providing velocity accommodation between the pad and the disc; (ii) brass fillers contribute to friction force stabilization and smooth sliding behavior; (iii) the presence of small weight quantity of brass filler strongly contributes to squeal occurrences; (iv) there is close correlation between pin-on-disc tribometer and brake dynamometer tests in terms of tribological aspect.

Key Words
friction materials; tribological behavior; brass filler; squeal noise; rubbed surface

Address
(1) Mohamed Kchaou, Amira Sellami, Riadh Elleuch:
University of Sfax - ENIS — LASEM - BP 3038 Sfax — Tunisia;
(2) Abd. Rahim Abu Bakar, Ahmad Razimi Mat Lazim:
Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor, Malaysia;
(3) Senthil Kumar:
Department of Mechanical Engineering, P.A. College of Engineering and Technology, Pollachi 642002, Tamilnadu, India.

Abstract
Carbonation depth was verified in 40 points of two 57 years old concrete viaducts. Field testing (phenolphthalein spraying) was performed on the structures. Data obtained were statistically analyzed by the Kolmogrov-Smirnov's test, one-way analysis of variance (ANOVA's test), and Fisher's method. The results revealed significant differences between maximum carbonation depths of different elements of the same concrete structure. Significant differences were also found in the carbonation of different concrete structures inserted in the same macroclimate. Microclimatic factors such as temperature and local humidity, sunshine, wind, wetting and drying cycles, among others, may have been responsible by the behavior of carbonation in concrete.

Key Words
concrete structures; environment; field testing; viaducts; statistical

Address
(1) Ronaldo A. Medeiros-Junior, Marcelo H.F. Medeiros:
Department of Civil Construction, Federal University of Parana (UFPR), Jardim das Americas - Curitiba, Parana, Brazil;
(2) Maryangela G. Lima, Ricardo Yazigi:
Department of Civil Engineering, Aeronautics Institute of Technology (ITA), Marechal Eduardo Gomes, 50, Sao Jose dos Campos, Sao Paulo, Brazil.

Abstract
The aim of this paper is to investigate the appropriateness of current codes of practice for predicting the axial load capacity of high-strength Concrete Filled Steel Tubular Columns (CFSTCs). Australian/New Zealand standards and other international codes of practice for composite bridges and buildings are currently being revised and will allow for the use of high-strength CFSTCs. It is therefore important to assess and modify the suitability of the section and ultimate buckling capacities models. For this purpose, available experimental results on high-strength composite columns have been assessed. The collected experimental results are compared with eight current codes of practice for rectangular CFSTCs and seven current codes of practice for circular CFSTCs. Furthermore, based on the statistical studies carried out, simplified relationships are developed to predict the section and ultimate buckling capacities of normal and high-strength short and slender rectangular and circular CFSTCs subjected to concentric loading.

Key Words
composite structures; concrete filled steel tubular columns; high-strength; axial load capacity

Address
(1) Farhad Aslani, Brian Uy:
Centre for Infrastructure Engineering and Safety, The University of New South Wales, Sydney NSW 2052, Australia;
(2) Zhong Tao, Fidelis Mashiri:
Institute for Infrastructure Engineering, Western Sydney University, Penrith NSW 2751, Australia.

Abstract
This study presents design optimization of spot welded structures to attain maximum strength by using the Nelder-Mead (Simplex) method. It is the main idea of the algorithm that the simulation run is executed several times to satisfy predefined convergence criteria and every run uses the starting points of the previous configurations. The material and size of the sheet plates are the pre-assigned parameters which do not change in the optimization cycle. Locations of the spot welds, on the other hand, are chosen to be design variables. In order to calculate the objective function, which is the maximum equivalent stress, ANSYS, general purpose finite element analysis software, is used. To obtain global optimum locations of spot welds a methodology is proposed by modifying the Nelder-Mead (Simplex) method. The procedure is applied to a number of representative problems to demonstrate the validity and effectiveness of the proposed method. It is shown that it is possible to obtain the global optimum values without stacking local minimum ones by using proposed methodology.

Key Words
optimal design; spot weld; Finite Element Analysis (FEA); modified Nelder-Mead (Simplex) method; mechanical strength

Address
Department of Biomedical Engineering, Karabuk University, Karabuk 78050, Turkey.


Abstract
In this article, large amplitude bending behaviour of laminated composite flat panel under combined effect of moisture, temperature and mechanical loading is investigated. The laminated composite panel model has been developed mathematically by introducing the geometrical nonlinearity in Green-Lagrange sense in the framework of higher-order shear deformation theory. The present study includes the degraded composite material properties at elevated temperature and moisture concentration. In order to achieve any general case, all the nonlinear higher order terms have been included in the present formulation and the material property variations are introduced through the micromechanical model. The nonlinear governing equation is obtained using the variational principle and discretised using finite element steps. The convergence behaviour of the present numerical model has been checked. The present proposed model has been validated by comparing the responses with those available published results. Some new numerical examples have been solved to show the effect of various parameters on the bending behaviour of laminated composite flat panel under hygro-thermo-mechanical loading.

Key Words
laminated composite flat panel; hygro-thermo-mechanical bending; HSDT; Green-Lagrange nonlinearity; Nonlinear FEM; flexural analysis

Address
(1) Vishesh R. Kar, Subrata K. Panda:
Department of Mechanical Engineering, National Institute of Technology, Rourkela, India;
(2) Trupti R. Mahapatra:
School of Mechanical Engineering, KIIT University, Bhubaneswar, India.

Abstract
A genetic algorithm-based minimum weight design method is presented for steel frames containing composite beams, semi-rigid connections and column bases. Genetic Algorithms carry out optimum steel frames by selecting suitable profile sections from a specified list including 128 W sections taken from American Institute of Steel Construction (AISC). The displacement and stress constraints obeying AISC Allowable Stress Design (ASD) specification and geometric (size) constraints are incorporated in the optimization process. Optimum designs of three different plane frames with semi-rigid beam-to-column and column-to-base plate connections are carried out first without considering concrete slab effects on floor beams in finite element analyses. The same optimization procedures are then repeated for the case of frames with composite beams. A program is coded in MATLAB for all optimization procedures. Results obtained from the examples show the applicability and robustness of the method. Moreover, it is proved that consideration of the contribution of concrete on the behavior of the floor beams enables a lighter and more economical design for steel frames with semi-rigid connections and column bases.

Key Words
AISC-ASD; genetic algorithm; weight optimization; composite beams; semi-rigid connection

Address
(1) Musa Artar:
Department of Civil Engineering, Bayburt University, Bayburt 69000, Turkey;
(2) Ayşe T. Daloğlu:
Department of Civil Engineering, Karadeniz Technical University, Trabzon 61000, Turkey.


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