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CONTENTS
Volume 21, Number 5, August10 2016
 

Abstract
The jib system with middle strut is widely used to achieve the large arm length in the large scale tower crane and the deployability in the mobile construction crane. In this paper, an analytical solution for the out-of-plane buckling of the jib system with middle strut is proposed. To obtain the analytical expression of the buckling characteristic equation, the method of differential equation was adopted by establishing the bending and torsional differential equation of the jib system under the instability critical state. Compared with the numerical solutions of the finite element software ANSYS, the analytical results in this work agree well with them. Therefore, the correctness of the results in this work can be confirmed. Then the influences of the lateral stiffness of the cable fixed joint, the dip angle of the strut, the inertia moment of the strut, and the horizontal position of the cable fixed joint on the out-of-plane buckling behavior of the jib system were investigated.

Key Words
tower crane; jib system with middle strut; out-of-plane buckling; analytical solution; method of differential equation

Address
School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, P.R. China.


Abstract
To avoid the cracks of cast-in-place concrete in shear pockets and seams in the traditional composite beam with precast decks, this paper proposed a new type of prefabricated steel truss-concrete composite beam (ab. PSTC beam) with pre-embedded shear studs (ab. PSS connector). To study the initial cracking load of concrete deck, the development and distribution laws of the cracks, 3 PSTC beams were tested under hogging moment. And the crack behavior of the deck was compared with traditional precast composite beam, which was assembled by shear pockets and cast-in-place joints. Results show that: (i) the initial crack appears on the deck, thus avoid the appearance of the cracks in the traditional shear pockets; (ii) the crack of the seam appears later than that of the deck, which verifies the reliability of epoxy cement mortar seam, thus solves the complex structure and easily crack behavior of the traditional cast-in-place joints; (iii) the development and the distribution laws of the cracks in PSTC beam are different from the conventional composite beam. Therefore, in the deduction of crack calculation theory, all the above factors should be considered.

Key Words
Prefabricated Steel Truss-Concrete Composite Beam (PSTC beam); precast deck; Preembedded Shear Studs (PSS Connector); epoxy cement mortar seam; deck crack test

Address
(1) Yanmei Gao, Zhixiang Zhou:
State Key Laboratory Cultivation Base of Mountain Bridge and Tunnel Engineering, Chongqing Jiaotong University, 400074, China;
(2) Yanmei Gao, Zhixiang Zhou, Dong Liu:
College of Civil Engineering, Chongqing Jiaotong University, 400074, China;
(3) Yinhui Wang:
Ningbo Institute of Technology, Zhejiang University, School of Civil Engineering and Architecture, 315100, China.

Abstract
This study presents free vibration of beam made of porous material. The mechanical properties of the beam is variable in the thickness direction and the beam is investigated in three situations: poro/nonlinear nonsymmetric distribution, poro/nonlinear symmetric distribution, and poro/monotonous distribution. First, the governing equations of porous beam are derived using principle of virtual work based on Euler-Bernoulli theory. Then, the effect of pores compressibility on natural frequencies of the beam is studied by considering clampedclamped, clamped-free and hinged-hinged boundary conditions. Moreover, the results are compared with homogeneous beam with the same boundary conditions. Finally, the effects of poroelastic parameters such as pores compressibility, coefficients of porosity and mass on natural frequencies has been considered separately and simultaneously.

Key Words
free vibration; Euler-Bernoulli theory; functionally graded beam; porous material

Address
(1) M.R. Galeban:
Young Researchers and Elite Club Behbahan Branch, Islamic Azad University, Behbahan, Iran;
(2) A. Mojahedin, M. Jabbari:
Department of Mechanical Engineering, South Tehran Branch, Islamic Azad University, Tehran, Iran;
(3) Y. Taghavi:
Department of Biomedical Engineering, Tehran Medical Sciences Branch, Islamic Azad University, Tehran, Iran.

Abstract
When a welded circular hollow section (CHS) tubular joint is subjected to brace axial loading, failure position is located usually at the weld toe on the chord surface due to the weak flexural stiffness of the thin-walled chord. The failure mode is local yielding or buckling in most cases for a tubular joint subjected to axial load at the brace end. Especially when a cyclic axial load is applied, fracture failure at the weld toe may occur because both high stress concentration and welding residual stress along the brace/chord intersection cause the material in this region to become brittle. To improve the ductility as well as to increase the static strength, a tubular joint can be reinforced by increasing the chord thickness locally near the brace/chord intersection. Both experimental investigation and finite element analysis have been carried out to study the hysteretic behaviour of the reinforced tubular joint. In the experimental study, the hysteretic performance of two full-scale circular tubular T-joints subjected to cyclic load in the axial direction of the brace was investigated. The two specimens include a reinforced specimen by increasing the wall thickness of the chord locally at the brace/chord intersection and a corresponding un-reinforced specimen. The hysteretic loops are obtained from the measured load-displacement curves. Based on the hysteretic curves, it is found that the reinforced specimen is more ductile than the un-reinforced one because no fracture failure is observed after experiencing similar loading cycles. The area enclosed by the hysteretic curves of the reinforced specimen is much bigger, which shows that more energy can be dissipated by the reinforced specimen to indicate the advantage of the reinforcing method in resisting seismic action. Additionally, finite element analysis is carried out to study the effect of the thickness and the length of the reinforced chord segment on the hysteretic behaviour of CHS tubular T-joints. The optimized reinforcing method is recommended for design purposes.

Key Words
Circular hollow section (CHS) tubular T-joints; hysteretic behaviour; local chord reinforcement; failure mode; energy dissipation

Address
(1) Y.B. Shao, Y.M. Wang:
School of Mechatronic Engineering, Southwest Petroleum University, Chengdu, P.R. China;
(2) D.P. Yang:
Technology Inspection Center, China Petroleum & Chemical Corporation, Dongying, P.R. China.

Abstract
Optimization of the construction scheme of the cable-strut tensile structure based on error sensitivity analysis is studied in this paper. First, the element length was extracted as a fundamental variable, and the relationship between element length change and element internal force was established. By setting all pre-stresses in active cables to zero, the equation between the pre-stress deviation in the passive cables and the element length error was obtained to analyze and evaluate the error effects under different construction schemes. Afterwards, based on the probability statistics theory, the mathematical model of element length error is set up. The statistical features of the pre-stress deviation were achieved. Finally, a cable-strut tensile structure model with a diameter of 5.0 m was fabricated. The element length errors are simulated by adjusting the element length, and each member in one symmetrical unit was elongated by 3 mm to explore the error sensitivity of each type of element. The numerical analysis of error sensitivity was also carried out by the FEA model in ANSYS software, where the element length change was simulated by implementing appropriate temperature changes. The theoretical analysis and experimental results both indicated that different elements had different error sensitivities. Likewise, different construction schemes had different construction precisions, and the optimal construction scheme should be chosen for the real construction projects to achieve lower error effects, lower cost and greater convenience.

Key Words
cable-strut tensile structures; error sensitivity analysis; construction scheme; statistical analysis; model experiment

Address
(1) Lian-meng Chen. Dong Hu:
College of Civil Engineering and Architecture, Wenzhou University, Wenzhou, 325035, China;
(2) Hua Deng:
Space Structures Research Center, Zhejiang University, Hangzhou 310027, China;
(3) Yu-hong Cui:
Sanjian Construction Group, Wenzhou, 325000, China;
(4) Yi-yi Zhou:
School of Civil Engineering and Architecture, Changzhou Institute of Technology, Changzhou 213002, China.

Abstract
Concrete bridges with corrugated steel webs and prestressed by both internal and external tendons have emerged as one of the promising bridge forms. In view of the different behaviour of components and the large shear deformation of webs with negligible flexural stiffness, the assumption that plane sections remain plane may no longer be valid, and therefore the classical Euler-Bernoulli and Timoshenko beam models may not be applicable. In the design of this type of bridges, both the ultimate load and ductility should be examined, which requires the estimation of full-range behaviour. An analytical sandwich beam model and its corresponding beam finite element model for geometric and material nonlinear analysis are developed for this type of bridges considering the diaphragm effects. Different rotations are assigned to the flanges and corrugated steel webs to describe the displacements. The model accounts for the interaction between the axial and flexural deformations of the beam, and uses the actual stress-strain curves of materials considering their stress path-dependence. With a nonlinear kinematical theory, complete description of the nonlinear interaction between the external tendons and the beam is obtained. The numerical model proposed is verified by experiments.

Key Words
corrugated steel webs; full-range behaviour; geometric nonlinearity; material nonlinearity; prestressed concrete bridges; sandwich beam theory

Address
(1) Xia-chun Chen, Zhi-zhou Bai, Yu Zeng, Rui-juan Jiang, Francis T.K. Au:
Department of Civil Engineering, The University of Hong Kong, Hong Kong, China;
(2) Zhi-zhou Bai:
Department of Bridge Engineering, Tongji University, Shanghai, 200092, China;
(3) Rui-juan Jiang:
Research Center, Shenzhen Municipal Engineering Design and Research Institute, Shenzhen, 518029, China.

Abstract
This paper introduces a new and effective design amplification factor-based approach for reliable optimum design of trusses. This paper may be categorized as in the family of decoupled methods that aiming for a reliable optimum design based on a Design Amplification Factor (DAF). To reduce the computational expenses of reliability analysis, an improved version of Response Surface Method (RSM) was used. Having applied this approach to two planar and one spatial truss problems, it exhibited a satisfactory performance.

Key Words
design amplification factor; reliable; optimum; trusses

Address
(1) Babak Dizangian:
Department of Civil Engineering, Velayat University, Iranshahr, Iran;
(2) Mohammad Reza Ghasemi:
Department of Civil Engineering, University of Sistan and Baluchestan, Zahedan, Iran.

Abstract
The present paper is aimed to evaluate and compare the effective elastic properties of CNT- and graphene-based nanocomposites using 3-D nanoscale representative volume element (RVE) based on continuum mechanics using finite element method (FEM). Different periodic displacement boundary conditions are applied to the FEM model of the RVE to evaluate various elastic constants. The effects of the matrix material, the volume fraction and the length of reinforcements on the elastic properties are also studied. Results predicted are validated with the analytical and/or semiempirical results and the available results in the literature. Although all elastic stiffness properties of CNT- and graphene-based nanocomposites are found to be improved compared to the matrix material, but out-of-plane and in-plane stiffness properties are better improved in CNT- and graphene-based nanocomposites, respectively. It is also concluded that long nanofillers (graphene as well as CNT) are more effective in increasing the normal elastic moduli of the resulting nanocomposites as compared to the short length, but the values of shear moduli, except G23 of CNT nanocomposite, of nanocomposites are slightly improved in the case of short length nanofillers (i.e., CNT and graphene).

Key Words
carbon nanotubes (CNT); graphene; representative volume element (RVE), nanocomposites; homogenization; elastic properties

Address
Mechanical Engineering Department, Malaviya National Institute of Technology, Jaipur 302017, India.


Abstract
In this study, it is presented that a new developed approach for equivalent area-distributed loading (EADL) induced from a single concentrated force. For the purpose, a full scale 3D steel formwork system was constructed in laboratory conditions. A developed load transmission platform was put on the formwork system and loaded step by step on the mass center. After each load increment, displacement was measured in several crictical points of the system. The developed platform which was put in to slab of formwork to equivalently distribute the load from a point to the whole slab was constituted using I profiles. A 3D finite element model of the formwork system was analyzed to compare numerical displacement results with experimental ones. In experimental tests,difference among the displacements obtained from reference numerical model (model applied EADL) and main numerical model (model applied single load using a load cell via load transmission platform) is about %13 in avarage. Difference among the displacements obtained from experimental results and main numerical model under 30 kN single load is about %11 in avarage. The results revealed that the displacements obtained experimentally and numerically are dramatically closed to each other. It is highlighted from the study that the developed approach is reliable and useful to get EDL.

Key Words
3D steel formwork system; equivalent area distributed loading; laboratory model; load transmission plafform

Address
Yıldız Technical University, Department of Civil Engineering, 34220, Ístanbul, Turkey.


Abstract
This paper presents a displacement-based finite element procedure for second-order distributed plasticity analysis of planar steel frames with semi-rigid beam-to-column connections under static loadings. A partially strain-hardening elastic-plastic beam-column element, which directly takes into account geometric nonlinearity, gradual yielding of material, and flexibility of semi-rigid connections, is proposed. The second-order effects and distributed plasticity are considered by dividing the member into several sub-elements and meshing the cross-section into several fibers. A new nonlinear solution procedure based on the combination of the Newton-Raphson equilibrium iterative algorithm and the constant work method for adjusting the incremental load factor is proposed for solving nonlinear equilibrium equations. The nonlinear inelastic behavior predicted by the proposed program compares well with previous studies. Coupling effects of three primary sources of nonlinearity, geometric imperfections, and residual stress are investigated and discussed in this paper.

Key Words
distributed plasticity; nonlinear inelastic analysis; second-order effects; semi-rigid connections; steel frames

Address
Department of Civil and Environmental Engineering, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul 143-747, South Korea.


Abstract
To study the effects of foam core density and face-sheet thickness on the mechanical properties and failure modes of aluminum foam sandwich (AFS) beam, especially when the aluminum foam core is made in aluminum alloy and the face sheet thickness is less than 1.5 mm, three-point bending tests were investigated experimentally by using WDW-50E electronic universal tensile testing machine. Load.displacement curves were recorded to understand the mechanical response and photographs were taken to capture the deformation process of the composite structures. Results demonstrated that when foam core was combined with face-sheet thickness of 0.8 mm, its carrying capacity improved with the increase of core density. But when the thickness of face-sheet increased from 0.8 mm to 1.2 mm, result was opposite. For AFS with the same core density, their carrying capacity increased with the face-sheet thickness, but failure modes of thin face-sheet AFS were completely different from the thick face-sheet AFS. There were three failure modes in the present research: yield damage of both core and bottom face-sheet (Failure mode I), yield damage of foam core (Failure mode II), debonding between the adhesive interface (Failure mode III).

Key Words
aluminum foam sandwich; three-point bending; mechanical properties; deformation; failure mode

Address
Key Laboratory of Road Construction Technology & Equipment of Chang\'an University, MOE, Xi\'an, Shaanxi 710064, China.


Abstract
A newly puzzle shape of crestbond rib shear connector is a type of ductile perfobond rib shear connector. This shear connector has some advantages, including relatively easy rebar installation and cutting, as well as the higher shear resistance strength. Thus, this study proposed a newly puzzle shape of crestbond rib with a \"Ʊ\" shape, and its shear resistance behaviors and shear strengths were examined using push-out tests. Five main parameters were considered in the push-out specimens to evaluate the effects of shear resistance parameters such as the dimensions of the crestbond rib, transverse rebars in the crestbond dowel, concrete strength, rebar strength, and dowel action on the shear strength. The shear loading test results were used to compare the changes in the shear behaviors, failure modes, and shear strengths. It was found that the concrete strength and number of transverse rebars in the crestbond rib were significantly related to its shear resistance. After the initial bearing resistance behavior of the concrete dowel, a relative slip occurred in all the specimens. However, its rigid behavior to shear loading decreased the ductility of the shear connection. The cross-sectional area of the crestbond rib was also shown to have a minor effect on the shear resistance of the crestbond rib shear connector. The failure mechanism of the crestbond rib shear connector was complex, and included compression, shear, and tension. As a failure mode, a crack was initiated in the middle of the concrete slab in a vertical direction, and propagated with increasing shear load. Then, horizontal cracks occurred and propagated to the front and rear faces of the specimens. Based on the results of this study, a design shear strength equation was proposed and compared with previously suggested equations.

Key Words
crestbond rib; composite dowel; push-out test; shear connector; shear resistance; puzzle shape; equation of crestbond

Address
(1) Thi Hai Vinh Chu:
Faculty of Civil Engineering, MienTrung University of Civil Engineering, 24 Nguyen Du Street, Ward 7, Tuy Hoa City, Phu Yen, Vietnam;
(2) Duc Vinh Bui, Van Phuoc Nhan Le:
Department of Civil Engineering, Ho Chi Minh City University of Technology, 68 Ly Thuong Kiet Street, Ward 14, District 10, Ho Chi Minh City, Vietnam;
(3) In-Tae Kim, Duy Kien Dao:
Department of Civil Engineering, Pusan National University, 30 Jangjoen-dong, Geumjeong-gu, Busan 609-735, Korea;
(4) Jin-Hee Ahn:
Department of Civil Engineering, Gyeongnam National University of Science and Technology, Korea / 30 Donghin-Ro, Jinju, Gyeongnam 660-758, South Korea.


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