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RISS 인기검색어
- 검색키워드
- 저자 : Ashraf Ayoub (검색결과 5 건)
- 무료
- 기관 내 무료
- 유료
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Analysis of composite frame structures with mixed elements - state of the art
Ayoub, Ashraf Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.41 No.2
The paper presents a review of the application of the newly proposed mixed finite element model for seismic simulation of different types of composite frame structures. To evaluate the performance of the element, a comparison with displacement-based and force-based models is conducted. The study revealed that the mixed model is superior to the others in terms of both speed of convergence and numerical stability, and is therefore considered the most practical approach for modeling of composite structures. In this model, the element is derived using independent force and displacement shape functions. The nonlinear response of the frame element is based on the section discretization into fibers with uniaxial material models. The interfacial behavior is modeled using an inelastic interface element. Numerical examples to clarify the advantages of the model are presented for the following structural applications: anchored reinforcing bar problems, composite steel-concrete girders with deformable shear connectors, beam on elastic foundation elements, R/C girders strengthened with FRP sheets, R/C beam-columns with bond-slip, and prestressed concrete girders. These studies confirmed that the model represents a major advancement over existing elements in simulating the inelastic behavior of composite structures.
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Analysis of composite frame structures with mixed elements – state of the art
Ashraf Ayoub 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.41 No.2
The paper presents a review of the application of the newly proposed mixed finite element model for seismic simulation of different types of composite frame structures. To evaluate the performance of the element, a comparison with displacement-based and force-based models is conducted. The study revealed that the mixed model is superior to the others in terms of both speed of convergence and numerical stability, and is therefore considered the most practical approach for modeling of composite structures. In this model, the element is derived using independent force and displacement shape functions. The nonlinear response of the frame element is based on the section discretization into fibers with uniaxial material models. The interfacial behavior is modeled using an inelastic interface element. Numerical examples to clarify the advantages of the model are presented for the following structural applications: anchored reinforcing bar problems, composite steel-concrete girders with deformable shear connectors, beam on elastic foundation elements, R/C girders strengthened with FRP sheets, R/C beam-columns with bond-slip, and prestressed concrete girders. These studies confirmed that the model represents a major advancement over existing elements in simulating the inelastic behavior of composite structures.
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Eff ect of Boundary Conditions on the Behavior of Stiff ened and Un-Stiff ened Cylindrical Shells
Oussama Temami,Ashraf Ayoub,Djamal Hamadi,Imed Bennoui 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.3
The eff ect of boundary conditions is very important in the analysis of cylindrical shells, and is rarely studied in the literature due to its diffi cult experimental simulation. For large structures such as shell roofs, the type of boundary supports is among the major factors that can minimize the stresses and defl ections. In this study, experimental and numerical investigations of the eff ect of diff erent boundary supports for stiff ened and un-stiff ened cylindrical shells were conducted. Two diff erent models of the stiff ened and un-stiff ened cylindrical shells with diff erent boundary conditions, “pinned and with rigid diaphragms”, were studied. It was shown that by using rigid diaphragms for cylindrical shells, the defl ections are minimized by 80%, and by (45–50) % for the stiff ened cylindrical shells. From the experimental investigations and the numerical results obtained, the effi ciency of the proposed boundary support types for cylindrical shells is confi rmed, which can result in economic benefi ts.
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Fiber Beam Analysis of Reinforced Concrete Members with Cyclic Constitutive and Material Laws
T. Ravi Mullapudi,Ashraf Ayoub 한국콘크리트학회 2018 International Journal of Concrete Structures and M Vol.12 No.6
This paper presents a non-linear Timoshenko beam element with axial, bending, and shear force interaction for nonlinear analysis of reinforced concrete structures. The structural material tangent stiffness matrix, which relates the increments of load to corresponding increments of displacement, is properly formulated. Appropriate simplified cyclic uniaxial constitutive laws are developed for cracked concrete in compression and tension. The model also includes the softening effect of the concrete due to lateral tensile strain. To establish the validity of the proposed model, correlation studies with experimentally-tested concrete specimens have been conducted.
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Ahmed Esmat,Fahad A. Al-Abbasi,Mardi M. Algandaby,Ashaimaa Y. Moussa,Rola M. Labib,Nahla A. Ayoub,Ashraf B. Abdel-Naim 한국식품영양과학회 2012 Journal of medicinal food Vol.15 No.3
The present study aimed at isolating and elucidating the structure of the main components of Pistacia khinjuk L. and exploring its potential anti-inflammatory effect in different experimental models. The extract was evaluated for antiinflammatory activity by measuring paw volume in three experimental models. Then, prostaglandin E2 (PGE2) level, ear edema, tissue myeloperoxidase (MPO) activity, histopathology, nitric oxide (NO) level, and tumor necrosis factor-a (TNF-a) level were assessed. Seven phenolic compounds, mainly flavonoids and galloylated compounds, were isolated from the aqueous methanol extract: gallic acid (1), methyl gallate (2), quercetin-3-O-b-d-4C1-galactopyranoside (hyperin) (3), myricetin- 3-O-a-l-1C4-rhamnopyranoside (myricitrin) (4), 1,6-digalloyl-b-d-glucose (5), 1,4-digalloyl-b-d-glucopyranoside (6), and 2,3-di-O-galloyl-(a/b)-4C1-glucopyranose (nilocitin) (7). The anti-inflammatory activity was evidenced by decreased carrageenan-induced rat paw edema and PGE2 elevation. In the croton oil–induced ear edema model, MPO activity was significantly inhibited, and inflammatory histopathological changes were ameliorated. In the rat air pouch model, NO generation and TNF-a release were significantly inhibited. The isolation and nuclear magnetic resonance spectral data of compound 6 from the genus Pistacia are revealed for the first time. Also, P. khinjuk L. aqueous methanol extract possesses anti-inflammatory activity in several experimental models.
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