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Design Aid for Moment Strength of Built-up Crane Runway Girders
Wei T. Hsu,Dung M. Lue,Y. Frank Chen 한국강구조학회 2012 International Journal of Steel Structures Vol.12 No.3
The evaluation of elastic moment for built-up crane runway girders is not an easy task as the difficulty involves the calculation of torsional properties including warping constant, the coefficient of monosymmetry, and torsion constant. To date,all AISC specifications offer no specific formulas for determining the elastic critical moment for WC (W-shape with Cap channel) or SC (S-shape with Cap Channel) girders. They provide only the approximate formulas which were derived from singly symmetric I-sections. Based on this study, the AISC approximate formulas would underestimate the elastic critical moment of WC/SC girders by 6-25% depending upon the unbraced length. This paper first summarizes the theoretical and AISC formulas for WC/SC girders. Theoretical torsional properties and relevant design parameters for WC/SC girders are computed and arranged in tabular form for design purposes. With these design values made available, engineers can perform more rational evaluation of WC/SC girders more conveniently. Lastly, a simplified but rational design approach is proposed for all available WC and SC girders listed in the AISC design manuals.
Molecular Gas Feeding the Circumnuclear Disk of the Galactic Center
Hsieh, Pei-Ying,Koch, Patrick M.,Ho, Paul T. P.,Kim, Woong-Tae,Tang, Ya-Wen,Wang, Hsiang-Hsu,Yen, Hsi-Wei,Hwang, Chorng-Yuan American Astronomical Society 2017 The Astrophysical journal Vol.847 No.1
<P>The interaction between a supermassive black hole (SMBH) and the surrounding material is of primary importance in modern astrophysics. The detection of the molecular 2 pc circumnuclear disk (CND) immediately around the Milky Way SMBH, SgrA*, provides a unique opportunity to study SMBH accretion at subparsec scales. Our new wide-field CS(J = 2 - 1) map toward the Galactic center (GC) reveals multiple dense molecular streamers that originated from the ambient clouds 20 pc further out, and that are connected to the central 2 pc of the CND. These dense gas streamers appear to carry gas directly toward the nuclear region and might be captured by the central potential. Our phase-plot analysis indicates that these streamers show a signature of rotation and inward radial motion with progressively higher velocities as the gas approaches the CND and finally ends up corotating with the CND. Our results might suggest a possible mechanism of gas feeding the CND from 20 pc around 2 pc in the GC. In this paper, we discuss the morphology and the kinematics of these streamers. As the nearest observable Galactic nucleus, this feeding process may have implications for understanding the processes in extragalactic nuclei.</P>