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CONTENTS
Volume 32, Number 6, September25 2019
 

Abstract
Using first-order shear deformation theory (FSDT), a semi-analytical solution is employed to analyze creep damage and remaining life assessment of 304L austenitic stainless steel thick (304L ASS) cylindrical pressure vessels with variable thickness subjected to the temperature gradient and internal non-uniform pressure. Damages are obtained in thick cylinder using Robinson\'s linear life fraction damage rule, and time to rupture and remaining life assessment is determined by Larson-Miller Parameter (LMP). The thermo-elastic creep response of the material is described by Norton\'s law. The novelty of the present work is that it seeks to investigate creep damage and life assessment of the vessels with variable thickness made of 304L ASS using LMP based on first-order shear deformation theory. A numerical solution using finite element method (FEM) is also presented and good agreement is found. It is shown that temperature gradient and non-uniform pressure have significant influences on the creep damages and remaining life of the vessel.

Key Words
304L austenitic stainless steel (304L ASS); creep damage; life assessment; cylindrical pressure vessels; first-order shear deformation theory

Address
(1) Mosayeb Davoudi Kashkoli, Khosro Naderan Tahan:
Department of Mechanical Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran;
(2) Mohammad Zamani Nejad:
Department of Mechanical Engineering, Yasouj University, Yasouj, Iran.

Abstract
A horizontal cyclic test was carried out to study the seismic performance of lightweight aggregate concrete filled steel tube (LACFST). The constitutive and hysteretic model of core lightweight aggregate concrete (LAC) was proposed for finite element simulation. The stress and strain changes of the steel tube and concrete filled inside were measured in the experiment, and the failure mode, hysteresis curve, skeleton curve, and strain curve of the test specimens were obtained. The influence of axial compression ratio, diameter-thickness ratio and material strength were analysed based on finite element model. The results show that the hysteresis curve of LACFST indicated favourable ductility, energy dissipation, and seismic performance. The LACFST failed when the concrete in the bottom first crushed and the steel tube then bulged, thus axial force imposed by prestressing was proved to be feasible. The proposed constitutive model and hysteretic model of LAC under the constraint of its steel tube was reliable. The bearing capacity and ductility of the specimen increase significantly with increasing thickness of the steel tube. The bearing capacity of the member improves while the ductility and energy dissipation performance slightly decreased with the increasing strength of the steel and concrete.

Key Words
lightweight aggregate concrete filled steel tube; horizontal cyclic test; hysteretic behaviour; concrete constitutive model

Address
College of Civil and Transportation Engineering, Hohai University, No.1 Xikang Road, Nanjing, China.


Abstract
Shear deformation effects are neglected in most structural system identification methods. This assumption might lead to important errors in some structures like built up steel or composite deep beams. Recently, the observability techniques were presented as one of the first methods for the inverse analysis of structures including the shear effects. In this way, the mechanical properties of the structures could be obtained from the nodal movements measured on static tests. One of the main controversial features of this procedure is the fact that the measurement set must include rotations. This characteristic might be especially problematic in those structures where rotations cannot be measured. To solve this problem and to increase its applicability, this paper proposes an update of the observability method to enable the structural identification including shear effects by measuring only vertical deflections. This modification is based on the introduction of a numerical optimization method. With this aim, the inverse analysis of several examples of growing complexity are presented to illustrate the validity and potential of the updated method.

Key Words
structural system identification; observability; shear deformation; vertical deflection; composite structures

Address
(1) Seyyedbehrad Emadi, Gonzalo Ramos, Jose Turmo:
Department of Civil and Environmental Engineering, Universitat Polit?cnica de Catalunya (UPC) BarcelonaTECH, Barcelona, Spain;
(2) Jose A. Lozano-Galant:
Department of Civil Engineering, University of Castilla-La Mancha, Ciudad Real, Spain;
(3) Ye Xia:
Department of Bridge Engineering, Tongji University, Shanghai, China.

Abstract
Steel and concrete composite structures are commonly applied in multi-story buildings as they maximise the material strength through composite action. Despite the popularity of employing a trapezoidal deck slab, limited experimental data are available under elevated temperatures. The behaviour of the headed shear stud embedded in a transverse trapezoidal deck and solid slab was investigated at both ambient and fire conditions. Twelve push-out tests were conducted according to the ISO 834 standard fire utilising a customised electric furnace. A stud shearing failure was observed in the solid slab specimen, whereas the failure mode was changed from a concrete-dominated failure to the stud shearing in the transverse deck specimen with an increase in temperature. Comparisons between the experimental observations and design requirements are presented. The Eurocode design guidance on the transverse deck slab gives a highly conservative estimate for shear resistance. A new design formula was proposed to determine the capacity of the shear connection regardless of the slab type when the stud shearing occurs at high temperatures.

Key Words
composite beam; headed shear stud; push-out test; transverse deck; fire

Address
(1) Ohk Kun Lim:
R&D Laboratory, Korea Fire Institute, 331 Jisam-ro, Gyeonggi-do, 17088, Republic of Korea;
(2) Ohk Kun Lim, Sengkwan Choi:
School of the Built Environment, Ulster University, Newtownabbey, BT37 0QB, UK;
(3) Sungwook Kang, Minjae Kwon, J. Yoon Choi:
Fire Safety Centre, Korea Conformity Laboratories, 73 Yangcheong 3-gil, Cheongju, 28115, Republic of Korea.

Abstract
Vibration control in mechanical equipments is an important problem where unwanted vibrations are vanish or at least diminished. In this paper, free vibration active control of the porous sandwich piezoelectric polymeric nanocomposite microbeam with microsensor and microactuater layers are investigated. The aim of this research is to reduce amplitude of vibration in micro beam based on linear quadratic regulator (LQR). Modified couple stress theory (MCST) according to sinusoidal shear deformation theory is presented. The porous sandwich microbeam is rested on elastic foundation. The core and face sheet are made of porous and three-phase carbon nanotubes/resin/fiber nanocomposite materials. The equations of motion are extracted by Hamilton's principle and then Navier's type solution are employed for solving them. The governing equations of motion are written in space state form and linear quadratic regulator (LQR) is used for active control approach. The various parameters are conducted to investigate on the frequency response function (FRF) of the sandwich microbeam for vibration active control. The results indicate that the higher length scale to the thickness, the face sheet thickness to total thickness and the considering microsensor and microactutor significantly affect LQR and uncontrolled FRF. Also, the porosity coefficient increasing, Skempton coefficient and Winkler spring constant shift the frequency response to higher frequencies. The obtained results can be useful for micro-electro-mechanical (MEMS) and nano-electro-mechanical (NEMS) systems.

Key Words
active control; porous and polymeric materials; piezoelectric sandwich microbeam; free vibration; sinusoidal shear deformation theory; surface stress effects

Address
(1) B. Rousta Navi, M. Mohammadimehr, A. Ghorbanpour Arani:
Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, Kashan, Iran;
(2) A. Ghorbanpour Arani:
Institute of Nanoscience & Nanotechnology, University of Kashan, Kashan, Iran.

Abstract
The specially prefabricated steel moment connections with pyramid head is one of the significant innovations in the steel structures forms to improve the installation time and simplify the construction procedure. The beams in this structure form are supported by two top and bottom angles and web double angles. Such a configuration despite its advantages increases the welding operation and filed installation time and costs. In this paper, the effect of using beams with channel and I section in three classes of seismically compact, seismically non-compact, and slender section according to width-to-thickness ratio on the behavior of the connection was investigated under monotonic and cyclic loading. Modeling was performed by ABAQUS and verified by the results of an experimental specimen. The findings indicated that using I and channel section instead of angle section reduces the amount of welding materials as well as easing the installation procedure. However, it has no significant effect on the ultimate strength and ductility of the connection. Furthermore, if the beam section is seismically compact, this form is considered as a special moment frame that has a rotation capacity up to 0.04 radians without any reduction in connection moment resistance.

Key Words
new connection; modular pre-fabricated structural form; cyclic loading; monotonic loading; I and channel beam section

Address
(1) Seyed Morteza Kazemi:
Department of Civil Engineering, Kashmar Branch, Islamic Azad University, Kashmar, Iran;
(2) Mohammad Reza Sohrabi:
Civil Engineering Department, University of Sistan and Baluchestan, Zahedan, Iran;
(3) Hasan Haji Kazemi:
Civil Engineering Department, Ferdowsi University, Mashhad, Iran.

Abstract
The purpose of this research paper is to depict the thermomechanical interactions in transversely isotropic magneto thermoelastic solid with two temperatures and without energy dissipation in generalized LS theories of thermoelasticity. The Laplace and Fourier transform techniques have been used to find the solution of the problem. The displacement components, stress components, and conductive temperature distribution with the horizontal distance are computed in the transformed domain and further calculated in the physical domain numerically. The effect of two temperature and relaxation time are depicted graphically on the resulting quantities.

Key Words
transversely isotropic thermoelastic; magneto generalized thermoelastic solid; Laplace and Fourier transform; mechanical and thermal sources

Address
Department of Basic and Applied Sciences, Punjabi University, Patiala, Punjab, India.


Abstract
In this paper, free vibration of sandwich beam with flexible core resting on orthotropic Pasternak is investigated. The top and bottom layers are reinforced by carbon nanotubes (CNTs). This sandwich structural is modeled by Euler and Frostig theories. The effect of agglomeration using Mori-Tanaka model is considered. The Eringen's theory is applied for size effect. The structural damping is investigated by Kelvin-voigt model. The motion equations are calculated by Hamilton's principle and energy method. Using analytical method, the frequency of the structure is obtained. The effect of agglomeration and CNTs volume percent for different parameter such as damping of structure, thickens and spring constant of elastic medium are presented on the frequency of the composite structure. Results show that with increasing CNTs agglomeration, frequency is decreased.

Key Words
free vibration; sandwich beam; CNTs; agglomeration; orthotropic pasternak medium

Address
Faculty of Engineering, Shahrekourd University, Shahrekord, Iran.


Abstract
In recent earthquakes, the failure of ceiling systems has been one of the most widely reported damage and the major cause of functionality interruption in some buildings. In an effort to mitigate this damage, some scholars have studied a series of ceiling systems including plaster ceilings and mineral wool ceilings. But few studies have involved the backdrop metal ceiling used in some important constructions with higher rigidity and frequency such as the main control area of nuclear power plants. Therefore, in order to evaluate its seismic performance, a full-scale backdrop metal ceiling system, including steel runners and metal panels, was designed, fabricated and installed in a steel frame in this study. And the backdrop metal ceiling system with two perimeter attachments variants was tested: (i) the ends of the runners were connected with the angle steel to form an effective lateral constraint around the backdrop metal ceiling, (ii) the perimeter attachments of the main runner were retained, but the perimeter attachments of the cross runner were removed. In the experiments, different damage of the backdrop metal ceiling system was observed in detail under various earthquakes. Results showed that the backdrop metal ceiling had good integrity and excellent seismic performance. And the perimeter attachments of the cross runner had an adverse effect on the seismic performance of the backdrop metal ceiling under earthquakes. Meanwhile, a series of seismic construction measures and several suggestions that need to be paid attention were proposed in the text so that the backdrop metal ceiling can be better applied in the main control area of nuclear power plants and other important engineering projects.

Key Words
nuclear power plant; backdrop metal ceiling system; shaking table test; seismic design; seismic performance

Address
(1) Tie G. Zhou, Shuai S. Wei, Xiang Zhao, Yi M. Yuan, Zheng Luo:
School of Civil Engineering, Xi'an University of Architecture & Technology, Shaanxi, China;
(2) Le W. Ma
Key Lab of Structure Engineering and Earthquake Resistance, Ministry of Education (XAUAT), China.

Abstract
An analysis on thermal buckling and postbuckling of composite laminated plates reinforced with a low amount of graphene platelets is performed in the current investigation. It is assumed that graphaene platelets are randomly oriented and uniformly dispersed in each layer of the composite media. Elastic properties of the nanocomposite media are obtained by means of the modified Halpin-Tsai approach which takes into account the size effects of the graphene reinforcements. By means of the von Kármán type of geometrical nonlinearity, third order shear deformation theory and nonuniform rational B-spline (NURBS) based isogeometric finite element method, the governing equations for the thermal postbuckling of nanocomposite plates in rectangular shape are established. These equations are solved by means of a direct displacement control strategy. Numerical examples are given to study the effects of boundary conditions, weight fraction of graphene platelets and distribution pattern of graphene platelets. It is shown that, with introduction of a small amount of graphene platelets into the matrix of the composite media, the critical buckling temperature of the plate may be enhanced and thermal postbuckling deflection may be alleviated.

Key Words
thermal postbuckling; graphene platelets; NURBS-based isogeometric analysis; Halpin-Tsai rule; nanocomposite

Address
(1) Y. Kiani:
Faculty of Engineering, Shahrekord University, Shahrekord, Iran;
(2) M. Mirzaei:
Department of Mechanical Engineering, Faculty of Engineering,University of Qom, Qom, Iran.


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