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CONTENTS
Volume 27, Number 2, April25 2018
 

Abstract
Quasi-static three-point bending tests on sandwich beams with expanded metal sheets as core were conducted. Relationships between the force and displacement at the mid-span of the sandwich beams were obtained from the experiments. Numerical simulations were carried out using ABAQUS/EXPLCIT and the results were thoroughly compared with the experimental results. A parametric analysis was performed using a Box-Behnken design (BBD) for the design of experiments (DOE) techniques and a finite element modeling. Then, the influence of the core layers number, size of the cell and, thickness of the substrates was investigated. The results showed that the increase in the size of the expanded metal cell in a reasonable range was required to improve the performance of the structure under bending collapse. It was found that core layers number and size of the cell was key factors governing the quasi-static response of the sandwich beams with lattice cores.

Key Words
bending and shear strength; energy dissipation; quasi-static; steel/steel structure; numerical analysis

Address
Department of Mechanical Engineering, Semnan University, Semnan, P.O.B. 35131-19111, Semnan, Iran.


Abstract
Thermo-mechanical buckling of sandwich beams with a stiff core and face sheets made of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) within the framework of Timoshenko beam theory is presented. The material properties of FG-CNTRC are supposed to vary continuously in the thickness direction and are estimated through the rule of mixture. Also the properties of these materials should be considered temperature dependent. The governing equations and boundary conditions are derived by using Hamilton's principle and solved using an efficient technique called the Differential Transform Method (DTM) to achieve the critical buckling of the sandwich beam in uniform thermal environment. A detailed parametric study is guided to investigate the effects of carbon nanotube volume fraction, slenderness ratio, core-to-face sheet thickness ratio, and clamped-clamped, simply-simply and clamped-simply end supports on the critical buckling behavior of sandwich beams with FG-CNTRC face sheets. Numerical results for comparison of sandwich beams with uniformly distributed carbon nanotube-reinforced composite (UD-CNTRC) face sheets with those with FG-CNTRC face sheets are also presented.

Key Words
buckling analysis; sandwich beam; FG-CNTRC; thermal environment

Address
Department of Mechanical Engineering, Faculty of Engineering, Imam Khomeini International University, Qazvin, Iran.


Abstract
In this study, in-situ dynamic tests of the world\'s longest steel box tied-arch bridge over the Yangtze River, China, are reported. The double deck bridge supports highway and monorail systems at upper and lower levels, respectively. Strain, displacement, and acceleration responses were measured and used to investigate the vibration characteristics of the bridge when excited by running trains and/or trucks at a speed of 5-60 km/h, train braking, and truck bouncing. Impact factors were correlated with the running speed of trains and trucks. A three-dimensional finite element model of the coupled monorail-train-bridge vibration system accounting for track irregularities was established to understand the system behavior and validated by the experimental results. Truck bouncing was the dominant impact factor on bridge responses. The running speed of vehicles determined the riding comfort of traveling trains.

Key Words
straddle-type monorail; double-deck tied-arch bridge; in-situ dynamic test; finite element analysis; vibration; impact; riding comfort

Address
(1) Hongye Gou, Wen Zhou, Qianhui Pu:
Department of Bridge Engineering, School of Civil Engineering, Southwest Jiaotong University, Chengdu 610031, China;
(2) Hongye Gou:
Key Laboratory of High-Speed Railway Engineering, Ministry of Education, Southwest Jiaotong University, Chengdu 610031, China;
(3) Hongye Gou, Genda Chen, Yi Bao:
Department of Civil, Architectural, and Environmental Engineering, Missouri University of Science and Technology, Rolla, MO 65401, USA.

Abstract
This study contributes to evaluate multiphase topology optimization design of plate-like structures on elastic foundations by using classic plate theory. Multi-material optimal topology and shape are produced as an alternative to provide reasonable material assignments based on stress distributions. Multi-material topology optimization problem is solved through an alternative active-phase algorithm with Gauss-Seidel version as an optimization model of optimality criteria. Stiffness and adjoint sensitivity formulations linked to thin plate potential strain energy are derived in terms of multiphase design variables and Winkler-Pasternak parameters considering elastic foundation to apply to the current topology optimization. Numerical examples verify efficiency and diversity of the present topology optimization method of elastic thin plates depending on multiple materials and Winkler-Pasternak parameters with the same amount of volume fraction and total structural volume.

Key Words
topology optimization; multiphase; thin plate; adjoint sensitivity; elastic foundations; Winkler-Pasternak model

Address
(1) Thien Thanh Banh, Dongkyu Lee:
Department of Architectural Engineering, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul 05006, Republic of Korea;
(2) Soomi Shin:
Research Institute of Industrial Technology, Pusan National University, 2 Busandaehak-ro 63, Geumjeong-gu, Busan 46241, Republic of Korea.

Abstract
Fly ash can significantly improve concrete workability and performance, and recycling fly ash in concrete can contribute to a cleaner environment. Since fly ash influences pozzolanic reactions in concrete, mechanical behaviors of concrete containing fly ash differ from traditional concrete. Creep behaviors of fly ash concrete filled steel tube arch were experimentally investigated for 10% and 30% fly ash replacement. The axes of two arches are designed as circular arc with 2.1 m computed span, 0.24 m arch rise, and their cross-sections are all in circular section. Time dependent deflection and strain of loading and mid-span steel tube were measured, and long term deflection of the model arch with 10% fly ash replacement was significantly larger than with 30% replacement. Considering the steel tube strain, compressive zone height, cross section curvature, and internal force borne by the steel tube, the compressive zone height and structural internal forces increased gradually over time due to concrete creep. Increased fly ash content resulted in more significant neutral axis shift. Mechanisms for internal force effects on neutral axis height were analyzed and verified experimentally.

Key Words
creep; fly ash; concrete filled steel tubes; arch; experiment

Address
(1) Wu T. Yan, Bing Han, Hui B. Xie, Li Zhu:
School of Civil Engineering, Beijing Jiaotong University, Shangyuancun 3, Haidian District, Beijing 100044, P.R. China;
(2) Bing Han:
vKey Laboratory of Safety and Risk Management on Transport Infrastructures, Ministry of Transport, PRC, Beijing 100044, P.R. China;
(3) Jin Q. Zhang:
Research Institute of Highway Ministry of Transportation, West Tucheng Road 8, Haidian District, Beijing 100088, P.R. China;
(4) Zhong J. Xue:
Beijing Road Engineering Quality Supervision Station, Panjiamiao 222, Fengtai District, Beijing 100076, P.R. China.

Abstract
This paper presents an experimental work for short circular steel tube columns filled with normal concrete (NAC), recycled aggregate concrete (RAC), and RAC with silica fume and steel fiber. Ten specimens were tested under axial compression to research the effect of silica fume and steel fiber volume percentage on the behavior of recycled aggregate concrete-filled steel tube columns (RACFST). The failure modes, ultimate loads and axial load- strain relationships are presented. The test results indicate that silica fume and steel fiber would not change the failure mode of the RACFST column, but can increase the mechanical performances of the RACFST column because of the filling effect and pozzolanic action of silica fume and the confinement effect of steel fiber. The ultimate load, ductility and energy dissipation capacity of RACFST columns can exceed that of corresponding natural aggregate concrete-filled steel tube (NACFST) column. Design formulas EC4 for the load capacity NACFST and RACFST columns are proposed, and the predictions agree well with the experimental results from this study.

Key Words
recycled concrete-filled steel tube (RACFST); axial compression; steel fiber reinforced concrete; mechanical performance

Address
School of Urban Construction, Yangtze University, 1 Nanhuan Road,Jingzhou, Hubei, China.


Abstract
In this paper, three-dimensional (3D) elasticity theory in conjunction with nonlocal strain gradient theory (NSGT) is developed for mechanical analysis of anisotropic nanoparticles. The present model incorporates two scale coefficients to examine the mechanical characteristics much accurately. All the elastic constants are considered and assumed to be the functions of (r, θ, φ), so all kind of anisotropic structures can be modeled. Moreover, all types of functionally graded spherical structures can be investigated. To justify our model, our results for the radial vibration of spherical nanoparticles are compared with experimental results available in the literature and great agreement is achieved. Next, several examples of the radial vibration and wave propagation in spherical nanoparticles including nonlocal strain gradient parameters are presented for more than 10 different anisotropic nanoparticles. From the best knowledge of authors, it is the first time that 3D elasticity theory and NSGT are used together with no approximation to derive the governing equations in the spherical coordinate. Moreover, up to now, the NSGT has not been used for spherical anisotropic nanoparticles. It is also the first time that all the 36 elastic constants as functions of (r, θ, φ) are considered for anisotropic and functionally graded nanostructures including size effects. According to the lack of any common approximations in the displacement field or in elastic constant, present theory can be assumed as a benchmark for future works.

Key Words
three-dimensional elasticity theory; nonlocal strain gradient theory; spherical coordinate; anisotropic material; nanoparticles

Address
(1) Behrouz Karami, Maziar Janghorban:
Department of Mechanical Engineering, Marvdasht Branch, Islamic Azad University, Marvdasht, Iran;
(2) Abdelouahed Tounsi:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria.

Abstract
This paper utilizes 3D FEM to provide deeper insights about the structural behaviour of a 6.1 m span steel culvert, which was previously tested under extreme loading. The effect of different input parameters pertaining to the backfill soil has been investigated, where the structural response is compared to field measurements. The interface choice between the steel and soil materials was also studied. The results enabled to realize the major influence of the friction angle on the load effects. Moreover, the analyses showed some differences concerning the estimation of failure load, whereas reasons beyond this outcome were arguably presented and discussed.

Key Words
flexible culvert; soil-steel composite bridge; corrugated steel; finite element model; ultimate limit state; failure test

Address
(1) Amer Wadi, Raid Karoumi:
Division of Structural Engineering and Bridges, KTH Royal Institute of Technology, SE-100 44, Stockholm, Sweden;
(2) Lars Pettersson:
Skanska Sweden AB - Major Projects, SE-112 74, Stockholm, Sweden;
(3) Amer Wadi:
ViaCon AB, SE-531 02, Lidkoping, Sweden.

Abstract
High strength steel is widely used in industrial applications to improve the load-bearing capacity and reduce the overall weight and cost. To take advantage of the benefits of this type of steel in construction, an innovative hybrid fabricated member consisting of high strength steel tubes welded to mild steel plates has recently been developed. Component-scale uniaxial and multiaxial cyclic experiments have been conducted with simultaneous constant or varying axial compression loads using a multi-axial substructure testing facility. The structural interaction of high strength steel tubes with mild steel plates is investigated in terms of member capacity, strength and stiffness deterioration and the development of plastic hinges. The deterioration parameters of hybrid specimens are calibrated and compared against those of conventional steel specimens. Effect of varying axial force and loading direction on the hysteretic deterioration model, failure modes and axial shortening is also studied. Plate and tube elements in hybrid members interact such that the high strength steel is kept within its ultimate strain range to prevent sudden fracture due to its low ultimate to yield strain ratio while the ductile performance of plate governs the global failure mechanism. High strength material also significantly reduces the axial shortening in columns which prevents undesirable frame deformations.

Key Words
high strength steel tubes; hybrid fabricated members; lateral cyclic loading; varying axial force, hysteretic deterioration, ductile failure

Address
(1) Fatemeh Javidan, Amin Heidarpour, Xiao-Ling Zhao:
Department of Civil Engineering, Monash University, Melbourne, Australia;
(2) Riadh Al-Mahaidi:
Department of Civil and Construction Engineering, Swinburne University of Technology, Melbourne, Australia.

Abstract
In recent years, concrete-filled box or tubular columns have been commonly used in high-rise buildings. However, a number of fire test results show that there are significant differences between high strength concrete (HSC) and normal strength concrete (NSC) after being subjected to high temperatures. Therefore, this paper presents an investigation on the fire resistance of HSC filled steel tubular columns (CFTCs) under combined temperature and loading. Two groups of full-size specimens were fabricated to consider the effect of type of concrete infilling (plain and reinforced) and the load level on the fire resistance of CFTCs. Prior to fire test, a constant compressive load (i.e., load level for fire design) was applied to the column specimens. Thermal load was then applied on the column specimens in form of ISO 834 standard fire curve in a large-scale laboratory furnace until the set experiment termination condition was reached. The results demonstrate that the higher the axial load level, the worse the fire resistance. Moreover, in the bar-reinforced concrete-filled steel tubular columns, the presence of rebars not only decreased the spread of cracks and the sudden loss of strength, but also contributed to the load-carrying capacity of the concrete core.

Key Words
fire resistance; high strength concrete; concrete filled steel tubular columns

Address
Department of Civil Engineering & Geomatics, Cheng Shiu University, No. 840, Chengcing Rd.,Niaosong District, Kaohsiung City, Taiwan R.O.C.



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