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CONTENTS
Volume 37, Number 6, December25 2020
 


Abstract
This paper aims to study the seismic performance of external diaphragm connection between SST (square steel tube) column and H-shaped beam through experimental and analytical study involving finite element (FE) method and theoretical analysis. In the experimental study, three external diaphragm connection specimens with weak panel zone were tested under axial pressure on the top of the column and antisymmetric cyclic loads at the beam end to investigate the seismic performance of the panel zone. The hysteretic behavior, failure mode, stiffness and ductility of the specimens were discussed. Key point to be explored was the influence of the thickness of the steel tube flange on the shear capacity of the specimens. In the analytical study, three simplified FE models were developed to simulate the seismic behavior of the specimens for further analysis on the influence of steel tube flange. Finally, four existing calculation formulas for the shear capacity of the external diaphragm connection were evaluated through comparisons with the results of experiments and FE analysis, and application suggestions were put forward.

Key Words
external diaphragm connection; panel zone; seismic performance; steel tube flange; shear capacity; finite element; calculation formula evaluation

Address
Bin Rong: Department of Civil Engineering, Tianjin University, Tianjin, 300072, China;
Key Laboratory of Coast Civil Structure Safety, Tianjin University, Tianjin, 300072, China
Shuhao Yin, Ruoyu Zhang, Lei Wang, Ziheng Yang, Hongtao Li and Wenyu Wan: Department of Civil Engineering, Tianjin University, Tianjin, 300072, China



Abstract
Although several types of rigid shear connectors have been developed particularly to increase load-carrying capacity, application is limited due to the complicated details of such connection. In this study, push-out tests were performed for specimens with hybrid shear connectors using headed studs and shear plates to identify the effects of each parameter on the structural performance of such shear connection. The test parameters included steel ratios of headed stud to shear plate, connection length, and embedded depth of shear plates. The peak strength and residual strength were estimated using various shear transfer mechanisms such as stud shear, concrete bearing, and shear friction. The hybrid shear connectors using shear plates and headed studs showed large load-carrying capacity and deformation capacity. The peak strength was predicted by the concrete bearing strength of the shear plates. The residual strength was sufficiently predicted by the stud shear strength of headed studs or by shear friction strength of dowel reinforcing bars. Further, the finite element analysis was performed to verify the shear transfer mechanism of the connection with hybrid shear connector.

Key Words
hybrid shear connection; shear connector; shear plate; headed shear stud; composite steel-concrete structure

Address
Jang-Woon Baek:Department of Civil Engineering and Environmental Sciences, Korea Military Academy, Seoul, 06978, Republic of Korea
Hyeon-Keun Yang and Hong-Gun Park: Department of Architecture and Architectural Engineering, Seoul National University, Seoul, 08826, Republic of Korea
Tae-Sung Eom: Department of Architectural Engineering, Dankook University, Gyeonggi-do, 16891, Republic of Korea
Hyeon-Jong Hwang: School of Architecture, Konkuk University, Seoul, 05029, Republic of Korea

Abstract
This paper proposes a novel topology optimization method generating multiple materials for external linear plane crack structures based on the combination of IsoGeometric Analysis (IGA) and eXtended Finite Element Method (X-FEM). A so-called eXtended IsoGeometric Analysis (X-IGA) is derived for a mechanical description of a strong discontinuity state's continuous boundaries through the inherited special properties of X-FEM. In X-IGA, control points and patches play the same role with nodes and sub-domains in the finite element method. While being similar to X-FEM, enrichment functions are added to finite element approximation without any mesh generation. The geometry of structures based on basic functions of Non-Uniform Rational B-Splines (NURBS) provides accurate and reliable results. Moreover, the basis function to define the geometry becomes a systematic p-refinement to control the field approximation order without altering the geometry or its parameterization. The accuracy of analytical solutions of X-IGA for the crack problem, which is superior to a conventional X-FEM, guarantees the reliability of the optimal multi-material retrofitting against external cracks through using topology optimization. Topology optimization is applied to the minimal compliance design of two-dimensional plane linear cracked structures retrofitted by multiple distinct materials to prevent the propagation of the present crack pattern. The alternating active-phase algorithm with optimality criteria-based algorithms is employed to update design variables of element densities. Numerical results under different lengths, positions, and angles of given cracks verify the proposed method's efficiency and feasibility in using X-IGA compared to a conventional X-FEM.

Key Words
multi-material; topology optimization; crack problem; X-IGA; IGA; X-FEM; Non-Unifrom Rational B-spline

Address
Thanh T. Banh, Jaehong Lee and Dongkyu Lee: Department of Architectural Engineering, Sejong University, Seoul 05006, Korea
Joowon Kang: Department of Architecture, Yeungnam University, Gyeongsan 38541, Korea

Abstract
This paper investigates the seismic response of buildings equipped with Self-Centering Energy Dissipating (SCED) braces. Two-dimensional models of 3, 6, 12 and 16-story SCED buildings considering both material and geometric nonlinearities are investigated by carrying out pushover and nonlinear time-history analyses. The response indicators of the buildings are studied for weight-scaled ground motions to represent the Design Basis Earthquake (DBE) level and the Maximum Considered Earthquake (MCE) event. The fragility curves of the buildings for two Immediate Occupancy (IO) and Life Safety (LS) performance levels are developed using Incremental Dynamic Analysis (IDA). Results of the nonlinear response history analyses indicate that the maximum inter-story drift occurs at the taller buildings. The mean peak inter-story drift is less than 2% in both hazard levels. High floor acceleration peaks are observed in all the SCED frames regardless of the building height. The overall ductility and ductility demand increase when the number of stories reduces. The results also showed the residual displacement is negligible for all of case study buildings. The 3 and 6-story buildings exhibit desirable performance in IO and LS performance levels according to fragility curves results, while 12 and 16-story frames show poor performance especially in IO level. The results indicated the SCED braces performance is generally better in lower-rise buildings.

Key Words
seismic assessment; self-centering; energy dissipating braces; fragility curves

Address
Hossein Kharrazi: School of Civil Engineering, College of Engineering, University of Tehran, Iran
Seyed Mehdi Zahrai: School of Civil Engineering, College of Engineering, University of Tehran, Iran;
Department of Civil Engineering, University of Ottawa, Canada


Abstract
The buckling properties of a single-layered graphene sheet (SLGS) are examined using nonlocal integral first shear deformation theory (FSDT) by incorporating the influence of visco-Pasternaks medium. This model contains only four variables, which is even less than the conventional FSDT. The visco-Pasternak's medium is introduced by considering the damping influence to the conventional foundation model which modeled by the linear Winkler's coefficient and Pasternak's (shear) foundation coefficient. The nanoplate under consideration is subjected to compressive in- plane edge loads per unit length. The impacts of many parameters such as scale parameter, aspect ratio, the visco-Pasternak' s coefficients, damping parameter, and mode numbers on the stability investigation of the SLGSs are examined in detail. The obtained results are compared with the corresponding available in the literature.

Key Words
nonuniform stability; Integral FSDT; nonlocal shear deformation model; visco-Pasternak's medium

Address
Abdelkrim Rouabhia, Abdelmoumen Anis Bousahla and Houari Heireche: Laboratoire de Modelisation et Simulation Multi-echelle, Universite de Sidi Bel Abbes, Algeria
Abdelbaki Chikh: Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria;
Universite Ibn Khaldoun, BP 78 Zaaroura, 14000 Tiaret, Algerie
Fouad Bourada: Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria; Département des Sciences et de la Technologie, centre universitaire de Tissemsilt, BP 38004 Ben Hamouda, Algeria
Abdeldjebbar Tounsi: Laboratoire de Modélisation et Simulation Multi-échelle, Université de Sidi Bel Abbés, Algeria;
Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria
Kouider Halim Benrahou: Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria
Abdelouahed Tounsi:Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria;
YFL (Yonsei Frontier Lab), Yonsei University, Seoul, Korea;
Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran,
Eastern Province, Saudi Arabia
Mesfer Mohammad Al-Zahrani: Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran,
Eastern Province, Saudi Arabia







Abstract
This paper deals with free vibration of FG sandwich annular sector plates on Pasternak elastic foundation with different boundary conditions, based on the three-dimensional theory of elasticity. The plates with simply supported radial edges and arbitrary boundary conditions on their circular edges are considered. The influence of carbon nanotubes (CNTs) waviness, aspect ratio, internal pores and graphene platelets (GPLs) on the vibrational behavior of functionally graded nanocomposite sandwich plates is investigated in this research work. The distributions of CNTs are considered functionally graded (FG) or uniform along the thickness of upper and bottom layers of the sandwich sectorial plates and their mechanical properties are estimated by an extended rule of mixture. In this study, the classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. The core of structure is porous and the internal pores and graphene platelets (GPLs) are distributed in the matrix of core either uniformly or non-uniformly according to three different patterns. The elastic properties of the nanocomposite are obtained by employing Halpin-Tsai micromechanics model. A semi-analytic approach composed of 2D-Generalized Differential Quadrature Method (2D-GDQM) and series solution is adopted to solve the equations of motion. The fast rate of convergence and accuracy of the method are investigated through the different solved examples. Some new results for the natural frequencies of the plate are prepared, which include the effects of elastic coefficients of foundation, boundary conditions, material and geometrical parameters. The new results can be used as benchmark solutions for future researches.

Key Words
CNTs waviness and aspect ratio; sandwich sectorial plates; vibration; rule of mixture; two-parameter elastic foundations; Graphene Platelets (GPLs); 2D-Generalized Differential Quadrature Method (GDQM)

Address
Hongwei Feng and Daoming Shen: School of Civil Engineering and Architecture, Xinxiang University, Xinxiang, 453000, China
Vahid Tahouneh: Young Researchers and Elite Club, Islamshahr Branch, Islamic Azad University, Islamshahr, Iran

Abstract
The subject of the paper pertains to simply supported beams with bisymmetrical cross sections under three-point bending with consideration of the shear effect. The deformation of a planar cross section of the beam is described taking into account the assumed nonlinear hypothesis-theory. Two differential equations of equilibrium are obtained based on the principle of stationary potential energy. This system is analytically solved and the shear coefficients and deflections of the beams are derived. Moreover, the Young's modules of the materials and deflections of the beams are experimentally determined on a test stand. The results of the studies are specified in tables and compared.

Key Words
mechanical properties; analytical modelling; mechanical testing; nonlinear hypothesis-theory

Address
Krzysztof Magnucki:Lukasiewicz Research Network – Institute of Rail Vehicles TABOR, ul. Warszawska 181, 61-055 Poznan, Poland
Piotr Paczos and Radostaw Wichniarek: Poznan University of Technology, ul. Piotrowo 3, 60-965 Poznan, Poland


Abstract
Steel plate-concrete composite slabs provide attractive features, such as more effective loading transfer, and more cost-effective stay-in-place forms, thereby enabling engineers to design more high-performance light structures. Although significant studies in the literatures have been directed toward designing and implementing the steel plate-concrete composite beams, there are limited data available for understanding of the composite slabs. To fill this gap, nine the composite slabs with different variables in this study were tested to unveil the impacts of the critical factors on the ultimate strength behavior. The key information of the findings included sample failure modes, crack pattern, and ultimate strength behavior of the composite slabs under either four-point or three-point loading. Test results showed that the failure modes varied from delamination to shear failures under different design factors. Particularly, the shear stud spacing and thicknesses of the concrete slabs significantly affected their ultimate load-carrying capacities. Moreover, an analytical model of the composite slabs was derived for determining their ultimate load-carrying capacity and was well verified by the experimental data. Further extensive parametric study using the proposed analytical methods was conducted for a more comprehensive investigation of those critical factors in their performance. These findings are expected to help engineers to better understand the structural behavior of the steel plate-concrete composite slabs and to ensure reliability of design and performance throughout their service life.

Key Words
steel plate-concrete composite slab; shear studs; ultimate capacity; failure mode; interface slip effect; experimental study

Address
Lili Wu and Hui Wang: School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing,
Ding No.11 Xueyuan Road, Haidian District, China
Zhibin Lin: Department of Civil and Environmental Engineering, North Dakota State University,
1340 Administration Ave., Fargo, USA




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