Equivalent viscous damping for steel eccentrically braced frame structures with buckling restraint braces

With increasing need for high-speed, high-temperature, and oil-free turbomachinery, gas foil bearings (GFBs) have been considered to be the best substitutes for traditional oil-lubricated bearings. A multi-cantilever foil bearing (MCFB), a novel GFB with multi-cantilever foil strips serving as the compliant underlying structure, was designed, fabricated, and tested. A series of static and dynamic load tests were conducted to measure the structural stiffness and equivalent viscous damping of the prototype MCFB. Experiments of static load versus deflection showed that the proposed bearing has a large mechanical energy dissipation capability and a pronounced nonlinear static stiffness that can prevents overly large motion amplitude of journal. Dynamic load tests evaluated the influence of motion amplitude, loading orientation and misalignment on the dynamic stiffness and equivalent viscous damping with respect to excitation frequency. The test results demonstrated that the dynamic stiffness and damping are strongly dependent on the excitation frequency. Three motion amplitudes were applied to the bearing housing to investigate the effects of motion amplitude on the dynamic characteristics. It is noted that the bearing dynamic stiffness and damping decreases with incrementally increasing motion amplitudes. A high level of misalignment can lead to larger static and dynamic bearing stiffness as well as to larger equivalent viscous damping. With dynamic loads applied to two orientations in the bearing midplane separately, the dynamic stiffness increases rapidly and the equivalent viscous damping declines slightly. These results indicate that the loading orientation is a non-negligible factor on the dynamic characteristics of MCFBs.

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Equivalent viscous damping of steel members for direct displacement based design

Structures ◽

10.1016/j.istruc.2021.07.056 ◽

2021 ◽

Vol 33 ◽

pp. 4781-4790

Author(s):

Ahmad Tarawneh ◽

Sereen Majdalaweyh ◽

Hazim Dwairi

Keyword(s):

Viscous Damping ◽

Equivalent Viscous Damping ◽

Direct Displacement Based Design ◽

Steel Members ◽

Displacement Based

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Experimental Evaluation of the Structure Characterization of a Novel Hybrid Bump-Metal Mesh Foil Bearing

Journal of Tribology ◽

10.1115/1.4031496 ◽

2015 ◽

Vol 138 (2) ◽

Cited By ~ 14

Author(s):

Kai Feng ◽

Yuman Liu ◽

Xueyuan Zhao ◽

Wanhui Liu

Keyword(s):

Excitation Frequency ◽

Structure Characterization ◽

Viscous Damping ◽

Metal Mesh ◽

Equivalent Viscous Damping ◽

Foil Bearings ◽

Damping Characteristics ◽

Foil Bearing ◽

Mesh Density ◽

Load Tests

Rotors supported by gas foil bearings (GFBs) experience stability problem caused by subsynchronous vibrations. To obtain a GFB with satisfactory damping characteristics, this study presented a novel hybrid bump-metal mesh foil bearing (HB-MMFB) that consists of a bump foil and metal mesh blocks in an underlying supporting structure, which takes advantage of both bump-type foil bearings (BFBs) and MMFBs. A test rig with a nonrotating shaft was designed to estimate structure characterization. Results from the static load tests show that the proposed HB-MFBs exhibit an excellent damping level compared with the BFBs with a similar size because of the countless microslips in the metal mesh blocks. In the dynamic load tests, the HB-MFB with a metal mesh density of 36% presents a viscous damping coefficient that is approximately twice that of the test BFB. The dynamics structural coefficients of HB-MFBs, including structural stiffness, equivalent viscous damping, and structural loss factor, are all dependent on excitation frequency and motion amplitude. Moreover, they exhibit an obvious decrease with the decline in metal mesh density.

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COMPARATIVE STUDY OF THE BEHAVIOUR OF BUILDING STRUCTURE OF HOTEL DAFAM LOTUS JEMBER BY USING MOMENT RESISTING FRAME AND ECCENTRICALLY BRACED FRAME

Jurnal Rekayasa Sipil dan Lingkungan ◽

10.19184/jrsl.v2i01.7435 ◽

2018 ◽

Vol 2 (01) ◽

pp. 13

Author(s):

Reza Kurniawan ◽

Dwi Nurtanto ◽

Gati Annisa Hayu

Keyword(s):

Axial Force ◽

Shear Force ◽

Steel Structure ◽

System Structure ◽

Braced Frame ◽

Eccentrically Braced Frame ◽

Moment Resisting Frame ◽

Concentrically Braced Frame ◽

Moment Resisting ◽

Short Link

Eccentrically Braced Frame (EBF) is one of several types of braces that can be used in steel building. EBF has a good stiffness and ductility to withstand earthquake load. In EBF itself there are 3 types of links, namely: Long Link, Intermediate Link, and Short Link. Meanwhile, MRF of Moment resisting Frame is a structural system where the beams and columns are connected rigidly. MRF has a good ductility in accepting load even it has no lateral braces installed. In this research the Dafam Lotus Jember hotel consisting of 10 floors with total height of 33,6 m is modeled as a MRF system structure and steel structure equipped with EBF short link. The objective of this research is to compare the effectiveness of EBF and MRF in terms of displacement, axial force, shear force, and moment occurring in buildings. The modeling results show that EBF with short link has smaller displacement value compared to MRF. The difference between the two is 86,99%. In terms of axial force, shear force, and moment, EBF has smaller values than MRF. The differences are 79,76%, 53,91%, and 10,48% respectively. These results indicate that EBF has better capacity compared to MRF. Indonesia merupakan negara yang memiliki tingkat intensitas kegempaan yang tinggi. Ini menjadikan Indonesia tidak terhindarkan dari dampak negatif yang akan ditimbulkan oleh gempa bumi, yaitu menyebabkan kerusakan insfrastruktur fisik. Peraturan gempa SNI 03-1726-2012 membahas mengenai bresing sebagai salah satu alternatif yang dapat digunakan untuk menangani masalah gempa. Eccentrically Braced Frame (EBF) adalah salah satu jenis bresing yang memiliki kekakuan dan daktilitas yang baik jika dibandingkan dengan Concentrically Braced Frame (CBF) yang hanya memiliki kekakuan yang baik. Selain itu terdapat pula Moment Resisting Frame (MRF) yaitu salah satu sistem struktur yang memiliki sifat daktail. Melihat permasalahan yang ada, maka pembahasan ini bertujuan untuk membandingkan efektivitas dari EBF menggunakan short link dengan MRF apabila diaplikasikan pada bangunan Hotel Dafam Lotus Jember 10 lantai yang memiliki tinggi 33,6 m. Adapun efektivitas yang dibadingkan disini adalah nilai story displacement dan gaya dalam (momen, gaya geser, dan gaya aksial) yang terjadi. Hasil analisa dengan bantuan program analisa struktur menunjukkan bahwa EBF menggunakan short link memiliki nilai yang lebih kecil dibandingkan dengan MRF dalam menerima beban yang bekerja. Dari segi story displacement, selisih prosentasenya adalah 86,99% sedangkan untuk gaya dalam yang meliputi momen, gaya geser, dan gaya aksial, selisihnya secara berturut-urut adalah 79,76%, 53,91% dan 10,48%. Hal ini menunjukkan bahwa EBF menggunakan short link lebih efektif jika dibandingkan dengan MRF.

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Energy-Based Design Criterion of Dissipative Bracing Systems for Seismic Retrofit of Frame Structures

10.20944/preprints201801.0086.v1 ◽

2018 ◽

Author(s):

Gloria Terenzi

Keyword(s):

Damping Ratio ◽

Dissipative System ◽

Design Criterion ◽

Frame Structures ◽

Element Analysis ◽

Equivalent Viscous Damping ◽

Linear Behaviour ◽

Energy Based Design ◽

Equivalent Viscous Damping Ratio ◽

Reduction Factors

Direct sizing criteria represent useful tools in the design of dissipative bracing systems for the advanced seismic protection of existing frame structures, especially when incorporated dampers feature a markedly non-linear behaviour. An energy-based procedure is proposed herein to this aim, focusing attention on systems including fluid viscous devices. The procedure starts by assuming prefixed reduction factors of the most critical response parameters in current conditions, which are evaluated by means of a conventional elastic finite element analysis. Simple formulas relating the reduction factors to the equivalent viscous damping ratio of the dissipaters, ξeq, are proposed. These formulas allow calculating the ξeq values that guarantee the achievement of target factors. Finally, the energy dissipation capacity of the devices is deduced from ξeq, finalizing their sizing process. A detailed description of the procedure is presented in the article, by distinguishing the cases where the prevailing structural deficiencies are represented by poor strength of the constituting members, from the cases having excessive horizontal displacements. A demonstrative application to the retrofit design of a reinforced concrete gym building is then offered to explicate the steps of the sizing criterion in practice, as well as to evaluate the enhancement of seismic response capacities generated by the installation of the dissipative system.

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