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CONTENTS
Volume 33, Number 5, December10 2019
 

Abstract
This paper presents a theoretical and finite element (FE) study on the stress intensity factors of double-edged cracked steel beams strengthened with carbon fiber reinforced polymer (CFRP) plates. By simplifying the tension flange of the steel beam using a steel plate in tension, the solutions obtained for the stress intensity factors of the double-edged cracked steel plate strengthened with CFRP plates were used to evaluate those of the steel beam specimens. The correction factor α1 was modified based on the transformed section method, and an additional correction factor φ was introduced into the expressions. Threedimensional FE modeling was conducted to calculate the stress intensity factors. Numerous combinations of the specimen geometry, crack length, CFRP thickness and Young's modulus, adhesive thickness and shear modulus were analyzed. The numerical results were used to investigate the variations in the stress intensity factor and the additional correction factor φ. The proposed expressions are a function of applied stress, crack length, the ratio between the crack length and half the width of the tension flange, the stiffness ratio between the CFRP plate and tension flange, adhesive shear modulus and thickness. Finally, the proposed expressions were verified by comparing the theoretical and numerical results.

Key Words
stress intensity factor; carbon fiber reinforced polymer (CFRP); strengthening; cracked steel beam; finite element models

Address
(1) Hai-Tao Wang, Habeeb M. Zakari:
College of Civil and Transportation Engineering, Hohai University, Nanjing, China;
(2) Gang Wu, Yu-Yang Pang:
Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, Southeast University, Nanjing, China.

Abstract
This paper investigates the effect of aftershocks on the seismic performance of self-centering (SC) prestressed concrete frames using the probabilistic seismic demand analysis methodology. For this purpose, a 4-story SC concrete frame and a conventional reinforced concrete (RC) frame are designed and numerically analyzed through nonlinear dynamic analyses based on a set of as-recorded mainshock-aftershock seismic sequences. The peak and residual story drifts are selected as the demand parameters. The probabilistic seismic demand models of the SC and RC frames are compared, and the SC frame is found to have less dispersion of peak and residual story drifts. The results of drift demand hazard analyses reveal that the SC frame experiences lower peak story drift hazards and significantly reduced residual story drift hazards than the RC frame when subjected to the mainshocks only or the mainshock-aftershock sequences, which demonstrates the advantages of the SC frame over the RC frame. For both the SC and RC frames, the influence of as-recorded aftershocks on the drift demand hazards is small. It is shown that artificial aftershocks can produce notably increased drift demand hazards of the RC frame, while the incremental effect of artificial aftershocks on the drift demand hazards of the SC frame is much smaller. It is also found that aftershock polarity does not influence the drift demand hazards of both the SC and RC frames.

Key Words
self-centering; concrete frame; aftershocks; probabilistic seismic demand analysis; residual drift

Address
(1) Long L. Song:
College of Civil and Transportation Engineering, Hohai University, Nanjing, 210098, P.R. China;
(2) Tong Guo, Xin Shi:
Key Laboratory of Concrete and Prestressed Concrete Structures of the Ministry of Education, Southeast University, Nanjing, 210096, P.R. China.

Abstract
In this paper aeroelastic behavior of 3-phase nano-composite beam-plate with double delaminations is investigated. It is tried to study the effect of carbon nano-tubes (CNTs) on critical flutter pressure of reinforced damaged nano-composite structures. In this case, the CNTs are appending to the polymer matrix uniformly. The Eshelby-Mori-Tanaka model is used to obtain the effective material properties of 3-phase nano-composite beam-plate. To investigate the aeroelastic behavior of delaminated beam-plate subjected to supersonic flow, it is assumed that the damaged segments are forced to vibrate together. The boundary conditions and auxiliary conditions at edges of delaminated segments are used to predict critical flutter pressure. The influence of CNTs and different delamination parameters such as delamination length, axial position and its position through thickness are investigated on critical flutter pressure.

Key Words
carbon nano-tubes; double delaminations; nano-composite; flutter

Address
Departement of Mechanical Engineering, Quchan University of Technology, P.O. Box 94717-84686, Quchan, Iran.


Abstract
In this work, a simple four-variable trigonometric shear deformation model with undetermined integral terms to consider the influences of transverse shear deformation is applied for the dynamic analysis of anti-symmetric laminated composite and soft core sandwich plates. Unlike the existing higher order theories, the current one contains only four unknowns. The equations of motion are obtained using the principle of virtual work. The analytical solution is determined by solving the eigenvalue problem. The influences of geometric ratio, modular ratio and fibre angle are critically evaluated for different problems of laminated composite and sandwich plates. The eigenfrequencies obtained using the current theory are verified by comparing the results with those of other theories and with the exact elasticity solution, if any.

Key Words
shear deformation; antisymmetric; laminated; sandwich; natural frequencies

Address
(1) Meriem Sahla, Hayat Saidi, Kada Draiche, Abdelmoumen Anis Bousahla, Fouad Bourada, Abdelouahed Tounsi:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
(2) Kada Draiche:
Département de Génie Civil, Université Ibn Khaldoun Tiaret, BP 78 Zaaroura, 14000 Tiaret, Algérie;
(3) Fouad Bourada:
Département des Sciences et de la Technologie, centre universitaire de Tissemsilt, BP 38004 Ben Hamouda, Algeria;
(4) Abdelmoumen Anis Bousahla, Abdelouahed Tounsi:
Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia.

Abstract
This paper numerically assesses the initial stiffness and moment capacity of stainless steel composite bolted joints with concrete-filled circular tubular (CFCT) columns. By comparing with existing design codes including EN 1993-1-8 and AS/NZS 2327, a modified component method was proposed to better predict the flexural performance of joints involving circular columns and curved endplates. The modification was verified with independent experimental results. A wide range of finite element models were then developed to investigate the elastic deformations of column face in bending which contribute to the corresponding stiffness coefficient. A new design formula defining the stiffness coefficient of circular column face in bending was proposed through regression analysis. Results suggest that a factor for the stiffness coefficient of endplate in bending should be reduced to 0.68, and more contribution of prying forces needs to be considered. The modified component method and proposed formula are able to estimate the structural behaviour with reasonable accuracy. They are expected to be incorporated into the current design provisions as supplementary for beam-to-CFCT column joints.

Key Words
stainless steel; circular column; beam-to-column joint; component method; initial stiffness; moment capacity

Address
School of Civil Engineering, The University of Sydney, Sydney, NSW, 2006, Australia.


Abstract
In this paper, wave propagations in sigmoid functionally graded (S-FG) plates are studied using new Higher Shear Deformation Theory (HSDT) based on two-dimensional (2D) elasticity theory. The current higher order theory has only four unknowns, which mean that few numbers of unknowns, compared with first shear deformations and others higher shear deformations theories and without needing shear corrector. The material properties of sigmoid functionally graded are assumed to vary through thickness according sigmoid model. The S-FG plates are supposed to be imperfect, which means that they have a porous distribution (even and uneven) through the thickness of these plates. The governing equations of S-FG plates are derived employed Hamilton's principle. Using technique of Navier, differential equations of S-FG in terms displacements are solved. Extensive results are presented to check the efficient of present methods to predict wave dispersion and velocity wave in S-FG plates.

Key Words
wave propagation; S-FG; porosity; higher shear deformations theories

Address
(1) Belaid Batou, Riadh Bennai, Hassen Ait Atmane, Abdeldjebbar Tounsi, Mohammed Bouremana:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
(2) Mokhtar Nebab, Riadh Bennai, Hassen Ait Atmane:
Department of civil engineering, Faculty of civil engineering and architecture, University Hassiba Benbouali of Chlef, Algeria.

Abstract
This paper is motivated by the lack of studies in the technical literature concerning to vibration analysis of a singlelayered graphene sheet (SLGS) with corner cutout based on the nonlocal elasticity model framework of classical Kirchhoff thin plate. An isogeometric analysis (IGA) based upon non-uniform rational B-spline (NURBS) is employed for approximation of the Lshape SLGS deflection field. Trimming technique is employed to create the cutout in geometry of L-shape plate. The L-shape plate is assumed to be Free (F) in the straight edges of cutout while any arbitrary boundary conditions are applied to the other four straight edges including Simply supported (S), Clamped (C) and Free (F). The Numerical studies are carried out to express the influences of the nonlocal parameter, cutout dimensions, boundary conditions and mode numbers on the variations of the natural frequencies of SLGS. It is precisely shown that these parameters have considerable effects on the free vibration behavior of the system. In addition, numerical results are validated and compared with those achieved using other analysis, where an excellent agreement is found. The effectiveness and the accuracy of the present IGA approach have been demonstrated and it is shown that the IGA is efficient, robust and accurate in terms of nanoplate problems. This study serves as a benchmark for assessing the validity of numerical methods used to analyze the single-layered graphene sheet with corner cutout.

Key Words
single-layered graphene sheet; free vibration; isogeometric analysis; trimming technique; NURBS; L-shape structure

Address
School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran.


Abstract
The nonlinear behavior of single- and multi-story steel plate shear walls (SPSWs) strengthened with three different patterns of fiber reinforced polymer (FRP) laminates (including single-strip, multi-strip and fully FRP-strengthened models) is studied using the finite element analysis. In the research, the effects of orientation, width, thickness and type (glass or carbon) of FRP sheets as well as the system aspect ratio and height are investigated. Results show that, despite an increase in the system strength using FRP sheets, ductility of reinforced SPSWs is decreased due to the delay in the initiation of yielding in the infill wall, while their initial stiffness does not change significantly. The content/type/reinforcement pattern of FRPs does affect the nonlinear behavior characteristics and also the mode and pattern of failure. In the case of multi-strip and fully FRP-strengthened models, the use of FPR sheets almost along the direction of the infill wall tension fields can maximize the effectiveness of reinforcement. In the case of single-strip pattern, the effectiveness of reinforcement is decreased for larger aspect ratios. Moreover, a relatively simplified and approximate theoretical procedure for estimating the strength of SPSWs reinforced with different patterns of FRP laminates is presented and compared with the analytical results.

Key Words
composite steel plate shear walls; FRP; reinforcement pattern; ultimate strength; initial stiffness; ductility; energy dissipation

Address
(1) Mehdi Seddighi, Mohammad A. Barkhordari:
Department of Civil Engineering, Faculty of Engineering, Iran University of Science and Technology, Narmak Ave, Tehran, 16846-13114, Iran;
(2) S.A.A. Hosseinzadeh:
Department of Civil Engineering, Faculty of Engineering, Golestan University, Al-ghadir Ave, Golestan, 49188-88369, Iran.

Abstract
Metaheuristic algorithm is used to solve the weight minimization problem of truss structures considering shape, and sizing design variables. The cross-sectional areas of the line element in trusses are the design variables for size optimization and the changeable joint coordinates are the shape optimization used in this study. The design of plane and spatial truss structures are optimized by metaheuristic technique named Teaching-Learning-Based Optimization (TLBO). Finite element analyses of structures and optimization process are carried out by the computer program visually developed by the authors coded in MATLAB. The four benchmark problems (trusses 2D ten-bar, 3D thirty-seven-bar, 3D seventy-two-bar and 2D two-hundred-bar) taken from literature are optimized and the optimal solution compared the results given by previous studies.

Key Words
truss structures; shape and size optimization; TLBO algorithm; dynamic constraints

Address
(1) Maksym Grzywiński, Jacek Selejdak:
Czestochowa University of Technology, Faculty of Civil Engineering, Czestochowa, Poland;
(2) Tayfun Dede:
Karadeniz Technical University, Department of Civil Engineering, Trabzon, Turkey.

Abstract
This study examined geometric and physical nonlinear analyses of beams and arches specifically from rolled profiles used in mining and underground constructions. These profiles possess the ability to create plastic hinges owing to their robustness. It was assumed that displacements in beams and arches fabricated from these profiles were comparable with the size of the structure. It also considered changes in the shape of a rod cross-section and the nonlinearities of the structure. The analyses were based on virtual unit moments, effective flexural rigidity of used open sections, and a secant method. The use of the approach led to a solution for the "after-critical" condition in which deformation increased with decreases in loads. The solution was derived for static determinate beams and static indeterminate arches. The results were compared with results obtained in other experimental tests and methods.

Key Words
steel structure; arch; beam; large displacement; geometrical nonlinearity; physical nonlinearity; virtual unit moments; effective flexural rigidity; open section; secant method

Address
(1) Lenka Koubova, Petr Janas, Martin Krejsa:
Department of Applied Mathematics, IT4Innovations, VSB - Technical University of Ostrava, Studentska 1, 708 33 Ostrava-Poruba, Czech Republic;
(2) Alexandros Markopoulos:
Department of Applied Mathematics, IT4Innovations, VSB - Technical University of Ostrava, Studentska 1, 708 33 Ostrava-Poruba, Czech Republic.


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