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1

Buckling resistance of quasi-straight H-section beam-columns under unequal end moments

Giżejowski Marian Antoni, Szczerba Radosław Bronisław, Stachura Zbigniew, Gajewski Marcin Daniel

Archives of Civil Engineering

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2021

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Vol. 67, nr 1

323--349

EN

Steel prismatic elements of equal flanges double-tee section subject to major axis bending and compression, unrestrained in the out-of-plane direction between the supports, are vulnerable to buckling modes associated with minor axis flexural and torsional deformations. When end bending moments are acting alone on the quasi-straight member, the sensitivity to lateral-torsional buckling (LTB) is very much dependent upon the ratio of section minor axis to major axis moments of inertia, and additionally visibly dependent upon the major axis moment gradient ratio. In the case of major axis bending with the presence of a compressive axial force, even of rather small value in relation to the section squash resistance, there is a drastic reduction of structural elements in their realistic lengths to maintain a tendency to fail in the out-of-plane mode, governed by the large twist rotation. Increasing the load effects ratio of dimensionless axial force to dimensionless maximum major axis bending moment, the buckling mode goes away from that of lateral-torsional one, starting to become that closer to the minor axis flexural buckling (FBZ) mode. Different aspects of the flexural-torsional buckling (FTB) resistance of the typical rolled H-section beam-column with regard to the General Method (GM) formulation, developed by the authors elsewhere and based on the parametric finite element analysis, are dealt with in this paper. Investigations are concerned with different member slender ratio, different moment gradient ratios and different load effects ratio. Final conclusions are related to practical applications of the proposed format of General Method in relation to the effect of large displacements on the FTB resistance reduction factor described through the dimensionless measure of action effects and the FTB relative slenderness ratio of quasi-straight beam-columns.

PL

Dwuteowniki stalowe o przekroju bisymetrycznym, poddawane ściskaniu i zginaniu względem głównej osi bezwładności przekroju, są wrażliwe na wyboczenie względem osi mniejszej bezwładności, przy jednoczesnej podatności na deformacje zgięciowe i skręcenie względem tej osi bezwładności. Analizy numeryczne wykazały, że w sytuacji, kiedy na końcach elementu quasi-idealnego występuje obciążenie podporowymi momentami zginającymi, wrażliwość na wyboczenie giętno-skrętne zależy w głównej mierze od stosunku momentów bezwładności analizowanego przekroju oraz dodatkowo zależy, i to w sposób istotny, od gradientu momentu względem głównej osi bezwładności przekroju. W przypadku zginania względem przekrojowej głównej osi bezwładności (osi y-y) z udziałem siły ściskającej, nawet o bardzo małej wartości w porównaniu z siłą powodującą uplastycznienie (równą nośności przekroju klasy 1 na ściskanie), następuje drastyczna redukcja nośności elementów o typowo konstrukcyjnych długościach. Na podstawie przeprowadzonych obliczeń można zaobserwować, że wyboczenie następuje wskutek zginania w płaszczyźnie mniejszej bezwładności przekroju, któremu towarzyszą znaczne skręcenia przekroju. W miarę wzrostu wartości współczynnika obciążenia, który definiujemy jako stosunek bezwymiarowej siły osiowej do bezwymiarowego maksymalnego momentu zginania względem osi większej bezwładności, następuje oddalanie się krzywej wyboczeniowej od tej dla wyboczenia giętno-skrętnego i zbliżenie się do krzywej dla wyboczenia względem osi mniejszej bezwładności. W niniejszej pracy przeanalizowano wpływ wybranych czynników na nośność przy wyboczeniu giętno-skrętnym typowego elementu stalowego, definiowaną w ujęciu tzw. eurokodowej metody ogólnej, rozwijanej przez autorów w innych pracach. Do analiz parametrycznych wykonywano metodę elementów skończonych (MES).

2

Design and test of a compact compliant gripper using the Scott–Russell mechanism

Zhu Jiaxiang, Hao Guangbo

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 3

254--265

EN

This paper presents the design, modeling, fabrication, and test of a monolithic compliant gripper for micro-manipulation applications. A compact compliant mechanism that enables in-principle straight-line parallel jaw motion is obtained, by combining the Scott–Russell mechanism and the parallelogram mechanism. The right-circular corner-filleted (RCCF) flexure hinge is adopted to achieve a large displacement of lumped-compliance joints. A pseudo-rigid-body model (PRBM) method with the help of the virtual work principle is performed to obtain parametric analytical models including the amplification coefficient and kinetostatics. Finite element analysis (FEA) is conducted to validate the analytical model and capture adverse parasitic motions of jaws. A monolithic prototype was fabricated, the test results of which show satisfactory performances.

3

Design and study of floating roofs for oil storage tanks

El-Samanody M., Ghorab A., Noaman A. S.

Mechanics and Mechanical Engineering

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2017

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Vol. 21, nr 1

117--136

EN

Floating roofs are widely used to store petroleum products with high volatility. This is to prevent the product loss and to ensure safe environment around the storage tanks. However, small number of researches were accomplished. These researches aim at study the design of the floating roof and the associated risks that it faces during operation. In an effort to compensate the lack of knowledge for this issue and to investigate the behavior of the floating roof during operation, this paper studies the design of deck plate and roof pontoons of the floating roof with especial features. In this research and in order to study deck plate design, a comparative work was performed of the stress and deflection analyses of deck plate for the floating roofs under the load of accumulated rainfall. Five different loads were applied on the deck plate by using three different analysis methods to study the deflection and stresses. The results show that the nonlinear finite element analysis is the most accurate and applicable one to be used in the design of the floating roof deck, since it simulates the exact loading cases that happen in reality. However, using Roark’s Formulas gives higher results but it can be used as a reliable and fast method in the analysis of the deck plate. To study roof pontoons design, a buoyancy analysis of the floating roof was established with punctured pontoons. In this study, three cases were applied to analyze the buoyancy of the floating roof in each case. The obeyed methodology of this study is by calculating the center of gravity and moment of inertia of the floating roof in each case. Then, to determine the submergence height due to weight and tilt and ensure that the floating roof will keep floating under each case. The results show that the floating roof will remain floating after the puncture of two adjacent pontoons and deck plate according to the design of the physical model; but it will sink if the number of punctured pontoons is increased to three.

4

An ironless large displacement flat piston loudspeaker

Remy M., Lemarquand G., Guyader G.

Archives of Acoustics

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2009

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Vol. 34, No. 4

591-599

EN

This paper presents a small wide-band loudspeaker. Particular efforts have been made to reduce the nonlinearities of the loudspeaker as much as possible. The motor structure is completely ironless, the elastomer suspensions are replaced by ferrofluid seals and a monobloc carbon foam piston substitutes the traditional conic membrane. The circular radiating surface, which is flat, has a diameter equal to only 2 cm. Therefore, in order to obtain a sufficient sound pressure level at low frequencies, large displacements of the piston are necessary. After a detailed description of each part of the loudspeaker, theoretical results of the expected performances of this transducer are given.