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CONTENTS
Volume 20, Number 5, April10 2016
 

Abstract
A nonlocal trigonometric shear deformation beam theory based on neutral surface position is developed for bending, buckling, and vibration of functionally graded (FG) nanobeams using the nonlocal differential constitutive relations of Eringen. The present model is capable of capturing both small scale effect and transverse shear deformation effects of FG nanobeams, and does not require shear correction factors. The material properties of the FG nanobeam are assumed to vary in the thickness direction. The equations of motion are derived by employing Hamilton\'s principle, and the physical neutral surface concept. Analytical solutions are presented for a simply supported FG nanobeam, and the obtained results compare well with those predicted by the nonlocal Timoshenko beam theory.

Key Words
nanobeam; nonlocal elasticity theory; bending; buckling; vibration; functionally graded materials; neutral surface position

Address
(1) Mama Ahouel, Mohammed Sid Ahmed Houari, E.A. Adda Bedia and Abdelouahed Tounsi:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
(2) Mohammed Sid Ahmed Houari:
Département de génie civil, Université de Mascara, Algeria;
(3) Abdelouahed Tounsi:
Laboratoire des Structures et Matériaux Avancés dans le Génie Civil et Travaux Publics, Université de Sidi Bel Abbes, Faculté de Technologie, Département de génie civil, Algeria;
(4) Abdelouahed Tounsi:
Laboratoire de Modélisation et Simulation Multi-échelle, Département de Physique, Faculté des Sciences Exactes, Département de Physique, Université de Sidi Bel Abbés, Algeria.

Abstract
The aim of this study is to investigate the impact behavior and impact-induced damage of sandwich composites made of E-glass/epoxy face sheets and PVC foam. The studies were carried out on square flat and curved sandwich panels with two different radius of curvatures. Impact tests were performed under impact energies of 10 J, 25 J and 80 J using an instrumented drop-weight machine. Contact force and displacement versus time and contact force- displacement graphs of sandwich panels were presented to determine the panel response. Through these graphs, the energy absorbing capacity of the sandwich panels was determined. The impact responses and failure modes of flat and curved sandwich panels were compared and the effect of curvature on sandwich composite panel was demonstrated. Testing has shown that the maximum contact force decrease while displacement increases with increasing of panel curvature and curved panels exhibits mixed failure mode, with cylindrical and cone cracking.

Key Words
sandwich composite; curved panel; impact; foam core

Address
Department of Mechanical Engineering, Celal Bayar University, Engineering Faculty, Muradiye, Manisa, 45140, Turkey.


Abstract
The use of Carbon Fiber Reinforced Polymer (CFRP) to strengthen steel structures has attracted the attention of researchers greatly. Previous studies demonstrated bonding of CFRP plates to the steel sections has been a successful method to increase the mechanical properties. However, the main limitation to popular use of steel/CFRP strengthening system is the concern on durability of bonding between steel and CFRP in various environmental conditions. The paper evaluates the performance of I-section steel beams strengthened with pultruded CFRP plate on the bottom flange after exposure to diverse conditions including natural tropical climate, wet/dry cycles, plain water, salt water and acidic solution. Four-point bending tests were performed at specific intervals and the mechanical properties were compared to the control beam. Besides, the ductility of the strengthened beams and distribution of shear stress in adhesive layer were investigated thoroughly. The study found the adhesive layer was the critical part and the performance of the system related directly to its behavior. The highest strength degradation was observed for the beams immersed in salt water around 18% after 8 months exposure. Besides, the ductility of all strengthened beams increased after exposure. A theoretical procedure was employed to model the degradation of epoxy adhesive.

Key Words
steel strengthening; steel/CFRP; environmental performance

Address
(1) M. Gholami:
Road, Housing and Urban Development Research Center, Tehran, Iran;
(2) A.R. Mohd Sam, A.K. Marsono:
Faculty of Civil Engineering, Universiti Teknologi Malaysia, Skudai, Malaysia;
(3) M.M. Tahir, I. Faridmehr:
UTM Construction Research Centre (CRC), Institute of Smart Infrastructures and Innovative Construction, Universiti Teknologi Malaysia (UTM), Skudai, Malaysia.

Abstract
Based on Hamilton's principle, the flexural vibration differential equations and boundary conditions of the steel-concrete composite beam (SCCB) with comprehensive consideration of the influences of the shear deformation, interface slip and longitudinal inertia of motion were derived. The analytical natural frequencies of flexural vibration were compared with available results previously observed by the experiments, the results calculated by the FE model and the other similar beam theories available in the open literatures. The comparison results showed that, the calculation results of the analytical and Timoshenko models had a good agreement with the results of the experimental test and FE model. Finally, the influences of shear deformation and interface slip on the flexural natural frequencies of the SCCB were discussed. The shear deformation effect increases with the increase of the mode orders of flexural natural vibration, and the flexural natural frequencies of the higher mode orders ignoring the influence of shear deformations effect would be overestimated. The interface slip effect decrease with the increase of the mode orders of flexural natural vibration, and the influence of the interface slip effect on flexural natural frequencies of the low mode orders is significant. The influence of the degree of shear connection on shear deformation effect is insignificant, and the low order modes of flexural natural vibration are mainly composed of the rotational displacement of cross sections.

Key Words
steel-concrete composite beam; shear deformation; interfacial slip; flexural natural vibration; degree of shear connection; Hamilton's principle

Address
(1) Wangbao Zhou:
School of Civil Engineering, Guangzhou University, Guangzhou, 510006, China;
(2) Wangbao Zhou, Shujin Li:
School of Civil Engineering and Architecture, Wuhan University of Technology, Wuhan, 430070, China;
(3) Lizhong Jiang, Zhi Huang:
School of Civil Engineering, Central South University, Changsha, 410075, China.

Abstract
A new analytical solution based on a third order shear deformation theory for the problem of static analysis of cross-ply doubly-curved shells is presented. The boundary-discontinuous generalized double Fourier series method is used to solve highly coupled linear partial differential equations with the mixed type simply supported boundary conditions prescribed on the edges. The complementary boundary constraints are introduced through boundary discontinuities generated by the selected boundary conditions for the derivation of the complementary solution. The numerical accuracy of the solution is compared by studying the comparisons of deflections, stresses and moments of symmetric and anti-symmetric laminated shells with finite element results using commercially available software under uniformly distributed load. Results are in good agreement with finite element counterparts. Additional results of the symmetric and anti-symmetric laminated and sandwich shells under single point load at the center and pressure load, are presented to provide data for the unsolved boundary conditions, benchmark comparisons and verifications.

Key Words
analytical solution; cross-ply shells; sandwich shells; boundary discontinuous Fourier analysis; higher order shear deformation theory; mixed simply supported

Address
(1) Veysel Alankaya:
Department of Naval Architecture, Turkish Naval Academy, Tuzla 34942, Istanbul, Turkey;
(2) Ahmet Sinan Oktem:
Department of Mechanical Engineering, Gebze Technical University, Gebze 41400, Kocaeli, Turkey.

Abstract
Recent research on steel moment-resisting connection between steel beams and concrete filled steel tubes has shown that there are considerable advantages to be obtained by anchoring the connection to the concrete infill within the tube using anchors in blind bolts. In the research reported here, extensive experimental tests and numerical analyses have been performed to study the anchorage behaviour of cogged deformed reinforcing bars within concrete filled circular steel tubes. This data in essential knowledge for the design of the steel connections that use anchored blind bolts, both for strength and stiffness. A series of pull-out tests were conducted using steel tubes with different diameter to thickness ratios under monotonic and cyclic loading. Both hoop strains and longitudinal strains in the tubes were measured together with applied load and slip. Various lead-in lengths before the bend and length of tailed extension after the bend were examined. These dimensions were limited by the dimensions of the steel tube and did not meet the requirements for

Key Words
anchorage; cogged bar; blind-bolt; concrete filled steel tube; finite element analysis

Address
(1) Tilak Pokharel, Huang Yao, Helen M. Goldsworthy:
Infrastructure Department, University of Melbourne, Parkville, VIC 3010, Australia;
(2) Emad F. Gad:
Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, VIC 3122, Australia.

Abstract
The paper proposes to characterize the free vibration behaviour of non-uniform cylindrical shells using spline approximation under first order shear deformation theory. The system of coupled differential equations in terms of displacement and rotational functions are obtained. These functions are approximated by cubic splines. A generalized eigenvalue problem is obtained and solved numerically for an eigenfrequency parameter and an associated eigenvector which are spline coefficients. Four and two layered cylindrical shells consisting of two different lamination materials and plies comprising of same as well as different materials under two different boundary conditions are analyzed. The effect of length parameter, circumferential node number, material properties, ply orientation, number of lay ups, and coefficients of thickness variations on the frequency parameter is investigated.

Key Words
free vibration; anti-symmetric; non-uniform thickness; shear deformation; spline approximation; frequency parameter

Address
(1) UTM Centre for Industrial and Applied Mathematics (UTM-CIAM), Ibnu SIna Institiute for Scientific & Industrial Research, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia;
(2) Department of Mathematical Sciences, Faculty of Science, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia.


Abstract
The present investigation is to study the plane problem in initially stressed thermoelastic half-space with voids due to thermal source. Lord-Shulman (Lord and Shulman 1967) theory of thermoelasticity with one relaxation time has been used to investigate the problem. A particular type of thermal source has been taken as an application of the approach. Finite element technique has been used to solve the problem. The components of displacement, stress, temperature change and volume fraction field are computed numerically. The resulting quantities are depicted graphically for different values of initial stress parameter. The relaxation time and the initial stress parameter have a significant effect on all distributions.

Key Words
thermoelastic half-space; voids; initially stressed; thermal sources finite element

Address
(1) Ibrahim A. Abbas:
Department of Mathematics, Faculty of Science and Arts - Khulais, University Of Jeddah, Saudi Arabia;
(2) Ibrahim A. Abbas:
Nonlinear Analysis and Applied Mathematics Research Group (NAAM), Department of Mathematics, King Abdulaziz University, Jeddah, Saudi Arabia;
(3) Ibrahim A. Abbas:
Department of mathematics, Faculty of Science, Sohag University, Sohag, Egypt;
(4) Rajneesh Kumar:
Department of Mathematics, Kurukshetra University, Kurukshetra-136 119, India.

Abstract
As a first attempt, an inverse hybrid numerical method for small scale parameter estimation of functionally graded (FG) nanobeams using measured frequencies is presented. The governing equations are obtained with the Eringen's nonlocal elasticity assumptions and the first-order shear deformation theory (FSDT). The equations are discretized by using the differential quadrature method (DQM). The discretized equations are transferred from temporal domain to frequency domain and frequencies of the nanobeam are obtained. By applying random error to these frequencies, measured frequencies are generated. The measured frequencies are considered as input data and inversely, the small scale parameter of the beam is obtained by minimizing a defined functional. The functional is defined as root mean square error between the measured frequencies and calculated frequencies by the DQM. Then, the conjugate gradient (CG) optimization method is employed to minimize the functional and the small scale parameter is obtained. Efficiency, convergence and accuracy of the presented hybrid method for small scale parameter estimation of the beams for different applied random error, boundary conditions, length-to-thickness ratio and volume fraction coefficients are demonstrated.

Key Words
small scale parameter estimation; nanobeams; hybrid numerical method

Address
Department of Civil and Environmental Engineering, School of Engineering Shiraz University, Shiraz, Iran.

Abstract
In this article, an additive performance ratio method using structural analysis of both 2D and 3D is introduced to mitigate the complexity of work evaluating structural performances of numerous steel outrigger alternatives in multi-story buildings, especially high-rise buildings. The combined structural analysis process enables to be the design of economic, safe, and as constructional demanding structures by exploiting the advantages of steel, namely: excellent energy dissipation and ductility. First the approach decides the alternative of numerous steel outriggers by a simple 2D analysis module and then the alternative is evaluated by 3D analysis module. Initial structural analyses of outrigger types are carried out through MIDAS Gen 2D modeling, approximately, and then the results appeal structural performance and lead to decide some alternative of outrigger types. ETABS 3D modeling is used with respect to realization and evaluation of exact structural behaviors. The approach reduces computational burden in compared to existing concepts such as full 3D analysis methods. The combined 2D and 3D tools are verified by cycle and displacement tests including comprehensive nonlinear dynamic simulations. The advantages and limitations of the Additive Performance Ratio Approach are highlighted in a case study on a high rise steelcomposite building, which targets at designing the optimized alternative to the existing original outrigger for lateral load resisting system.

Key Words
additive performance ratio method; structural analysis; steel outrigger; high-rise building; alternative; lateral load resisting system

Address
Department of Architectural Engineering, Sejong University, Seoul, 143-747, Korea.

Abstract
Post-tensioned (PT) steel moment resisting frames (MRFs) with semi-rigid connections (SRC) can be used to control the hysteretic energy demands and to reduce the maximum inter-story drift (γ). In this study the seismic behavior of steel MRFs with PT connections is estimated by incremental nonlinear dynamic analysis in terms of dissipated hysteretic energy (EH) demands. For this aim, five PT steel MRFs are subjected to 30 long duration earthquake ground motions recorded on soft soil sites. To assess the energy dissipated in the frames with PT connections, a new expression is proposed for the hysteretic behavior of semi-rigid connections validated by experimental tests. The performance was estimated not only for the global EH demands in the steel frames; but also for, the distribution and demands of hysteretic energy in beams, columns and connections considering several levels of deformation. The results show that EH varies with γ, and that most of EH is dissipated by the connections. It is observed in all the cases a log-normal distribution of EH through the building height. The largest demand of EH occurs between 0.25 and 0.5 of the height. Finally, an equation is proposed to calculate the distribution of EH in terms of the normalized height of the stories (h/H) and the inter-story drift.

Key Words
steel frames, self-centering, semi-rigid connections, hysteretic energy, inter-story drift, time history analysis

Address
(1) Arturo López-Barraza, Alfredo Reyes-Salazar, Edén Bojórquez:
Facultad de Ingeniería, Universidad Autónoma de Sinaloa, Culiacán, Sinaloa, México;
(2) Sonia E. Ruiz:
Instituto de Ingeniería, Universidad Nacional Autónoma de México, México city, México.


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