Techno Press
Tp_Editing System.E (TES.E)
Login Search


sem
 
CONTENTS
Volume 73, Number 3, February10 2020
 

Abstract
This work treats the axisymmetric buckling of functionally graded (FG) porous annular/circular nanoplates based on modified couple stress theory (MCST). The nanoplate is located at the elastic medium which is simulated by Kerr foundation with two spring and one shear layer. The material properties of the porous FG nanostructure are assumed to vary through the nanoplate thickness based on power-law rule. Based on two variables refined plate theory, the governing equations are derived by utilizing Hamilton\'s principle. Applying generalized differential quadrature method (GDQM), the buckling load of the annular/circular nanoplates is obtained for different boundary conditions. The influences of different involved parameters such as boundary conditions, Kerr medium, material length scale parameter, geometrical parameters of the nanoplate, FG power index and porosity are demonstrated on the nonlinear buckling load of the annular/circular nanoplates. The results indicate that with increasing the porosity of the nanoplate, the nonlinear buckling load is decreased. In addition, with increasing the material length scale parameter to thickness ratio, the effect of spring constant of Kerr foundation on the buckling load becomes more prominent. The present results are compared with those available in the literature to validate the accuracy and reliability. A good agreement is observed between the two sets of the results.

Key Words
nonlinear buckling; annular/circular nanoplates; FGM; porosity; Kerr medium

Address
Amirmahmoud Sadoughifar: Department of Civil Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Isfahan, Iran
Fatemeh Farhatnia,Amirmahmoud Sadoughifar: Department of Mechanical Engineering, Khomeinishahr Branch, Islamic Azad University, Khomeinishahr, Isfahan, Iran
Amirmahmoud Sadoughifar, Mohsen Izadinia: Department of Civil Engineering, Khomeinishahr Branch, Islamic Azad University, Khomeinishahr, Isfahan, Iran

Abstract
In the present study, an innovative steel bracket and haunch hybrid scheme is devised, for retrofitting of earthquake damaged deficient beam-column sub-assemblages. Formulations are presented for evaluating haunch force factor under combined load case of lateral and gravity loads for the design of double haunch retrofit. The strength hierarchies of control and retrofitted beam-column sub-assemblages are established to showcase the efficacy of the retrofit in reversing the undesirable strength hierarchy. Further, the efficacy of the proposed retrofit scheme is demonstrated through experimental investigations carried out on gravity load designed (GLD), non-ductile and ductile detailed beam-column sub-assemblages which were damaged under reverse cyclic loading. The maximum load carried by repaired and retrofitted GLD specimen in positive and negative cycle is 12% and 28% respectively higher than that of the control GLD specimen. Further, the retrofitted GLD specimen sustained load up to drift ratio of 5.88% compared with 2.94% drift sustained by control GLD specimen. Repaired and retrofitted non-ductile specimen, could attain the displacement ductility of three during positive cycle of loading and showed improved ductility well above the expected displacement ductility of three during negative cycle. The hybrid haunch retrofit restored the load carrying capacity of damaged ductile specimen to the original level of control specimen and improved the ductility closer to the expected displacement ductility of five. The total cumulative energy dissipated by repaired and retrofitted GLD, non-ductile and ductile specimens are respectively 6.5 times, 2.31 times, 1.21 times that of the corresponding undamaged control specimens. Further, the damage indices of the repaired and retrofitted specimens are found to be lower than that of the corresponding control specimens. The novel and innovative steel bracket and haunch hybrid retrofit scheme proposed in the present study demonstrated its effectiveness by attaining the required displacement ductility and load carrying capacity and would be an excellent candidate for post-earthquake retrofit of damaged existing RC structures designed according to different design evolutions.

Key Words
beam-column sub-assemblage, steel bracket and haunch hybrid retrofit, energy dissipation, ductility, damage index, load-displacement hysteresis, strength degradation, post-earthquake retrofit

Address
1CSIR-Structural Engineering Research Centre, Chennai, Tamil Nadu, India
2Academy of Scientific and Innovative Research (AcSIR), India

Abstract
In this paper, bending-stretching analysis of thick functionally graded piezoelectric rectangular plates is studied using the higher-order shear and normal deformable plate theory. On the basis of this theory, Legendre polynomials are used for approximating the components of displacement field. Also, the effects of both normal and shear deformations are encountered in the theory. The governing equations are derived using the principle of virtual work and variational approach. It is assumed that plate is made of piezoelectric materials with functionally graded distribution of material properties. Hence, exponential function is used to modify mechanical and electrical properties through the thickness of the plate. Finally, the effect of material properties, electrical boundary conditions and dimensions are investigated on the static response of plate. Also, it is shown that results of the presented model are close to the three dimensional elasticity solutions.

Key Words
bending analysis; functionally graded; piezoelectric material; higher-order shear and normal deformable theory

Address
M. Lori Dehsaraji and M. Mohammadi:Department of Mechanical Engineering, Vali-e-Asr University of Rafsanjan, Rafsanjan, Iran
A.R. Saidi: Department of Mechanical Engineering, Shahid Bahonar University of Kerman, Kerman, Iran

Abstract
Passive control technologies are commonly used in several areas to suppress structural vibrations by the addition of supplementary damping, and some modal damping may be heavy beyond critical damping even for regular structures with energy dissipation devices. The design of passive control structures is typically based on (complex) mode superposition approaches. However, the conventional mode superposition approach is predominantly applied to cases of under-critical damping. Moreover, when any modal damping ratio is equal or close to 1.0, the system becomes defective, i.e., a complete set of eigenvectors cannot be obtained such that some well-known algorithms for the quadratic eigenvalue problem are invalid. In this paper, a generalized complex mode superposition method that is suitable for under-critical, critical and over-critical damping is proposed and expressed in a unified form for structural displacement, velocity and acceleration responses. In the new method, the conventional algorithm for the eigenvalue problem is still valid, even though the system becomes defective due to critical modal damping. Based on the modal truncation error analysis, modal corrected methods for displacement and acceleration responses are developed to approximately consider the contribution of the truncated higher modes. Finally, the implementation of the proposed methods is presented through two numerical examples, and the effectiveness is investigated. The results also show that over-critically damped modes have a significant impact on structural responses. This study is a development of the original complex mode superposition method and can be applied well to dynamic analyses of non-classically damped systems.

Key Words
non-classical damping; complex mode superposition approach; critical damping; overcritical damping; modal corrected method

Address
1Guangdong Provincial Key Laboratory of Earthquake Engineering and Applied Technology, Guangzhou University,
Guangzhou, 510006, China
2Key Laboratory of Earthquake Resistance, Earthquake Mitigation and Structural Safety, Ministry of Education, Guangzhou University,
Guangzhou, 510405, China

Abstract
This investigation deals with a size-dependent coupled thermoelasticity analysis based on Green-Naghdi (GN) theory in nano scale using a new modified nonlocal model of heat conduction, which is based on the GN theory and nonlocal Eringen theory of elasticity. In the analysis based on the proposed model, the nonlocality is taken into account in both heat conduction and elasticity. The governing equations including the equations of motion and the energy balance equation are derived using the proposed model in a nano beam resonator. An analytical solution is proposed for the problem using the Laplace transform technique and Talbot technique for inversion to time domain. It is assumed that the nano beam is subjected to sinusoidal thermal shock loading, which is applied on the one of beam ends. The transient behaviors of fields\' quantities such as lateral deflection and temperature are studied in detail. Also, the effects of small scale parameter on the dynamic behaviors of lateral deflection and temperature are obtained and assessed for the problem. The proposed GN-based model, analytical solution and data are verified and also compared with reported data obtained from GN coupled thermoelasticity analysis without considering the nonlocality in heat conduction in a nano beam.

Key Words
nano-sized resonator; nonlocal heat conduction; Green-Naghdi theory; analytical solution; nonlocal coupled thermoelasticity; energy dissipation

Address
Industrial Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad, PO Box: 91775-1111, Mashhad, Iran

Abstract
In this study an innovative rocking zipper braced frame (RZBF) is proposed to overcome the deficiencies of common concentrically braced frames. RZBF is an improved rocking concentrically braced frame which is based on combination of rocking behavior and zipper columns. The base rocking joints and post-tensioned bars provide rocking response and restoring force, respectively. Also, zipper columns distribute the unbalance force over the frame height and reduce the damage concentration. To evaluate seismic performance of RZBF, a comparison study is carried out considering concentrically braced frame, zipper braced frame, rocking concentrically braced frame and RZBF. Thereby, a suite of non-linear time history analyses had been performed on four different types of archetypes with four, six, eight, ten and twelve stories. Frames were designed and non-linear time history analyses were conducted in OpenSees. To compare the seismic behavior of the archetypes, roof drifts, residual roof drifts, story drifts, the forces of first and top story braces, PT bars forces, column uplift and base shears were taken in to consideration. Results illustrate that using RZBF, can reduce the damage due to reduced residual drifts. Zipper columns enhance the seismic performance of rocking systems. As the number of stories increase in the RZBF systems, larger top story braces were needed. So the RZBF system is applicable on low and midrise buildings.

Key Words
seismic performance; rocking system; zipper column; self-centering; nonlinear time history analysis

Address
Nasim Irani Sarand: Structural Engineering Department, School of Civil Engineering, University of Tabriz, Tabriz, Iran
Abdolrahim Jalali: Department of Civil Engineering, Faculty of Engineering, University of Kyrenia, Girne, Mersin 10, Turkey

Abstract
This paper investigates the free vibrations of cylindrical shells made of time-dependent materials for different viscoelastic models under various boundary conditions. During the extraction of equations, the displacement field is estimated through the first-order shear deformation theory taking into account the transverse normal strain effect. The constitutive equations follow Hooke\'s Law, and the kinematic relations are linear. The assumption of axisymmetric is included in the problem. The governing equations of thick viscoelastic cylindrical shell are determined for Maxwell, Kelvin-Voigt and the first and second types of Zener\'s models based on Hamilton\'s principle. The motion equations involve four coupled partial differential equations and an analytical method based on the elementary theory of differential equations is used for its solution. Relying on the results, the natural frequencies and mode shapes of viscoelastic shells are identified. Conducting a parametric study, we examine the effects of geometric and mechanical properties and boundary conditions, as well as the effect of transverse normal strain on natural frequencies. The results in this paper are compared against the results obtained from the finite elements analysis. The results suggest that solutions achieved from the two methods are ideally consistent in a special range.

Key Words
thick cylindrical shell; viscoelastic models; frequency analysis; first-order shear deformation theory; analytical solution; boundary conditions

Address
Faculty of Mechanical and Mechatronics Engineering, Shahrood University of Technology, Shahrood, Iran

Abstract
This paper proposes a new approximate analytical solution for highly nonlinear vibration of mechanical systems called Hamiltonian Approach (HA) that can be widely use for structural health monitoring systems. The complete procedure of the HA approach is studied, and the precise application of the presented approach is surveyed by two familiar nonlinear partial differential problems. The nonlinear frequency of the considered systems is obtained. The results of the HA are verified with the numerical solution using Runge-Kutta\'s [RK] algorithm. It is established the only one iteration of the HA leads us to the high accurateness of the solution.

Key Words
Hamiltonian Approach (HA); nonlinear vibration; analytical solution; Runge-Kutta\'s algorithm

Address
M. Bayat: Department of Civil and Environmental Engineering, University of Pittsburgh,
3700 O\'Hara Street, 729 Benedum Hall, Pittsburgh, PA 15261, USA
I. Pakar: Department of Civil Engineering, Faculty of Engineering, Shomal University, Amol, Mazandaran, Iran
H.R. Ahmadi: Department of Civil Engineering, Faculty of Engineering, University of Maragheh, Maragheh P.O. Box 55136-553, Iran
M. Cao: Jiangxi Provincial Key Laboratory of Environmental Geotechnical Engineering and Disaster Control, Jiangxi University of Science and Technology, Ganzhou, Jiangxi, 341000, People\'s Republic of China ; Department of Engineering Mechanics, Hohai University, 210098 Nanjing, Jiangsu, People\'s Republic of China
A.H. Alavi: Department of Civil and Environmental Engineering, University of Pittsburgh,
3700 O\'Hara Street, 729 Benedum Hall, Pittsburgh, PA 15261, USA; Department of Computer Science and Information Engineering, Asia University, Taichung, Taiwan

Abstract
Earthquakes are natural disasters that cause serious social disruptions and economic losses. In particular, they have a significant impact on critical lifeline infrastructure such as urban water transmission networks. Therefore, it is important to predict network performance and provide an alternative that minimizes the damage by considering the factors affecting lifeline structures. This paper proposes a probabilistic reliability approach for post-hazard flow analysis of a water transmission network according to earthquake magnitude, pipeline deterioration, and interdependency between pumping plants and 154 kV substations. The model is composed of the following three phases: (1) generation of input ground motion considering spatial correlation, (2) updating the revised nodal demands, and (3) calculation of available nodal demands. Accordingly, a computer code was developed to perform the hydraulic analysis and numerical modelling of water facilities. For numerical simulation, an actual water transmission network was considered and the epicenter was determined from historical earthquake data. To evaluate the network performance, flow-based performance indicators such as system serviceability, nodal serviceability, and mean normal status rate were introduced. The results from the proposed approach quantitatively show that the water network is significantly affected by not only the magnitude of the earthquake but the interdependency and pipeline deterioration.

Key Words
water transmission network; flow-based network simulation; seismic risk analysis; water network interdependency; buried pipeline deterioration

Address
Sungsik Yoon, Hyung-Jo Jung: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, 291
Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea
Young-Joo Lee: School of Urban and Environmental Engineering, Ulsan National Institute of Science and Technology, 50 UNIST-gil,
Eonyang-eup, Ulju-gun, Ulsan 44919, Republic of Korea

Abstract
In the previous studies, the authors proposed the use of laminated veneer lumber – carbon fiber reinforced polymer (LVL-CFRP) composite beams for structural application. Bond strength of the LVL-to-CFRP interface and flexural strengthening schemes to increase the bending capacity subjected to positive and negative moment were discussed in the previous works. In this article, theoretical models are proposed to predict the moment capacity when the LVL-CFRP beams are subjected to negative moment. Two common failure modes – CFRP fracture and debonding of CFRP are considered. The non-linear model proposed for positive moment is modified for negative moment to determine the section moment capacity. For the debonding based failure, previously developed bond strength model for CFRP-to-LVL interface is implemented. The theoretical models are validated against the experimental results and then use to determine the moment-rotation behaviour and rotational rigidity to compare the efficacy of various strengthening techniques. It is found that combined use of bi- and uni-directional CFRP U-wrap at the joint performs well in terms of both moment capacity and rotational rigidity.

Key Words
CFRP, LVL; negative moment; composites; analytical modelling; moment-rotation

Address
Mahbube Subhani: School of Engineering, Deakin University, Waurn Ponds, VIC 3216, Australia
Anastasia Globa: School of Architecture, Design and Planning, University of Sydney, NSW 2008, Australia
Jules Moloney: School of Design, RMIT University, Melbourne 3001, Australia


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2020 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-42-828-7996, Fax : +82-2-736-6801, Email: info@techno-press.com