Analysis of light gage steel shear diaphragms

INTRODUCTION It has long been recognized by structural engineers, that light gage steel cladding floor and roof decking systems have a considerable stiffening and strengthening effect on building frameworks. The beneficial contribution of these diaphragm systems is most pronounced when the structure as a whole is subjected to loads which result in an in-plane shear action of the cladding. This occurs, for example, when the rigidity of a floor or roof diaphragm acting as a membrane is utilized to transmit lateral forces to stiff end walls. Another example of diaphragm action is found in pitched roof portal sheds under vertical and lateral loads. In such cases the membrane strength and rigidity of the cladding can be used to restrict the tendency of intermediate frames to sway, by transfering the load to end walls and resulting in substantial economy in the design of the frames. Specific utilization of the in-plane shear strength and stiffness of panelling was suggested more than 18 years ago, but unless this effect could be calculated in advance no practical use could be made. In order to take this contribution to stiffness and strength into account in engineering design, it was necessary to develop means for predicting the effective shear rigidity and ultimate strength in shear of the steel panel diaphragm. Because of the complexity of such diaphragm systems, up to now, engineers have relied upon tests of full-scale-panel assemblies, in which the performance of specific combinations of panels, marginal framing members and connections have been studied on a strictly ad hoc basis. While much has been learned using this approach, and valuable design information was obtained, no rational theory to describe and predict structural behavior has resulted. On the other hand, testing of large full scale diaphragm installations is expensive and time consuming, and tests results are applicable only to identical assembly using the same panels as tested, with directly equivalent fastening systems. The need for a general method of analysis is clear

Analysis of light gage steel shear diaphragms

INTRODUCTION: It has long been recognized by structural engineers, that light gage steel cladding floor and roof decking systems have a considerable stiffening and strengthening effect on building frameworks. The beneficial contribution of these diaphragm systems is most pronounced when the structure as a whole is subjected to loads which result in an in-plane shear action of the cladding. This occurs, for example, when the rigidity of a floor or roof diaphragm acting as a membrane is utilized to transmit lateral forces to stiff end walls. Another example of diaphragm action is found in pitched roof portal sheds under vertical and lateral loads. In such cases the membrane strength and rigidity of the cladding can be used to restrict the tendency of intermediate frames to sway, by transfering the load to end walls and resulting in substantial economy in the design of the frames. Specific utilization of the in-plane shear strength and stiffness of panelling was suggested more than 18 years ago, but unless this effect could be calculated in advance no practical use could be made. In order to take this contribution to stiffness and strength into account in engineering design, it was necessary to develop means for predicting the effective shear rigidity and ultimate strength in shear of the steel panel diaphragm. Because of the complexity of such diaphragm systems, up to now, engineers have relied upon tests of full-scale-panel assemblies, in which the performance of specific combinations of panels, marginal framing members and connections have been studied on a strictly ad hoc basis. While much has been learned using this approach, and valuable design information was obtained, no rational theory to describe and predict structural behavior has resulted. On the other hand, testing of large full scale diaphragm installations is expensive and time consuming, and tests results are applicable only to identical assembly using the same panels as tested, with directly equivalent fastening systems. The need for a general method of analysis is clear

Analysis of light gage steel shear diaphragms

INTRODUCTION: It has long been recognized by structural engineers, that light gage steel cladding floor and roof decking systems have a considerable stiffening and strengthening effect on building frameworks. The beneficial contribution of these diaphragm systems is most pronounced when the structure as a whole is subjected to loads which result in an in-plane shear action of the cladding. This occurs, for example, when the rigidity of a floor or roof diaphragm acting as a membrane is utilized to transmit lateral forces to stiff end walls. Another example of diaphragm action is found in pitched roof portal sheds under vertical and lateral loads. In such cases the membrane strength and rigidity of the cladding can be used to restrict the tendency of intermediate frames to sway, by transfering the load to end walls and resulting in substantial economy in the design of the frames. Specific utilization of the in-plane shear strength and stiffness of panelling was suggested more than 18 years ago, but unless this effect could be calculated in advance no practical use could be made. In order to take this contribution to stiffness and strength into account in engineering design, it was necessary to develop means for predicting the effective shear rigidity and ultimate strength in shear of the steel panel diaphragm. Because of the complexity of such diaphragm systems, up to now, engineers have relied upon tests of full-scale-panel assemblies, in which the performance of specific combinations of panels, marginal framing members and connections have been studied on a strictly ad hoc basis. While much has been learned using this approach, and valuable design information was obtained, no rational theory to describe and predict structural behavior has resulted. On the other hand, testing of large full scale diaphragm installations is expensive and time consuming, and tests results are applicable only to identical assembly using the same panels as tested, with directly equivalent fastening systems. The need for a general method of analysis is clear

Anisotropy of the space orientation of radio sources. I: The catalog

A catalog of the extended extragalactic radio sources consisting of 10461 objects is compiled based on the list of radio sources of the FIRST survey. A total of 1801 objects are identified with galaxies and quasars of the SDSS survey and the Veron-Veron catalog. The distribution of the position angles of the axes of radio sources from the catalog is determined, and the probability that this distribution is equiprobable is shown to be less then 10^(-7). This result implies that at Z equal to or smaller then 0.5, spatial orientation of the axes of radio sources is anisotropic at a statistically significant level.Comment: 8 pages, 7 figure

Optimum conditions for composites fiber coating by chemical vapor infiltration

A combined analytical and numerical method is employed to optimize process conditions for composites fiber coating by chemical vapor infiltration (CVI). For a first-order deposition reaction, the optimum pressure yielding the maximum deposition rate at a preform center is obtained in closed form and is found to depend only on the activation energy of the deposition reaction, the characteristic pore size, and properties of the reactant and product gases. It does not depend on the preform specific surface area, effective diffusivity or preform thickness, nor on the gas-phase yield of the deposition reaction. Further, this optimum pressure is unaltered by the additional constraint of a prescribed deposition uniformity. Optimum temperatures are obtained using an analytical expression for the optimum value along with numerical solutions to the governing transport equations. These solutions account for both diffusive and advective transport, as well as both ordinary and Knudsen diffusion. Sample calculations are presented for coating preform fibers with boron nitride

A locally analytic density functional theory describing adsorption and condensation in microporous materials

The fluid density distribution within microscopic pores is determined by solving integral equations relating to the local chemical potential to the Van der Waals attractions and hard sphere repulsions of surrounding material. To avoid resolving the density distribution on sub-molecular scales, the governing equations are averaged over zones of molecular size using analytic functions to represent local density variations within each zone. These local density profiles range form singularities to uniform distributions depending on the local variation of the potential field. Sample calculations indicate that this integral approach yields results in very good agreement with those based on traditional density functional theory (DFT), while reducing computing times by factors of 10{sup 3} to 10{sup 4} for one- dimensional geometries

Deposition uniformity, particle nucleation and the optimum conditions for CVD in multi-wafer furnaces

A second-order perturbation solution describing the radial transport of a reactive species and concurrent deposition on wafer surfaces is derived for use in optimizing CVD process conditions. The result is applicable to a variety of deposition reactions and accounts for both diffusive and advective transport, as well as both ordinary and Knudsen diffusion. Based on the first-order approximation, the deposition rate is maximized subject to a constraint on the radial uniformity of the deposition rate. For a fixed reactant mole fraction, the optimum pressure and optimum temperature are obtained using the method of Lagrange multipliers. This yields a weak one-sided maximum; deposition rates fall as pressures are reduced but remain nearly constant at all pressures above the optimum value. The deposition rate is also maximized subject to dual constraints on the uniformity and particle nucleation rate. In this case, the optimum pressure, optimum temperature and optimum reactant fraction are similarly obtained, and the resulting maximum deposition rate is well defined. These results are also applicable to CVI processes used in composites manufacturing

In situ bioremediation: A network model of diffusion and flow in granular porous media

In situ bioremediation is a potentially expedient, permanent and cost- effective means of waste site decontamination. However, permeability reductions due to the transport and deposition of native fines or due to excessive microorganism populations may severely inhibit the injection of supplemental oxygen in the contamination zone. To help understand this phenomenon, we have developed a micro-mechanical network model of flow, diffusion and particle transport in granular porous materials. The model differs from most similar models in that the network is defined by particle positions in a numerically-generated particle array. The model is thus widely applicable to computing effective transport properties for both ordered and realistic random porous media. A laboratory-scale apparatus to measure permeability reductions has also been designed, built and tested

On the Relation Between Peak Luminosity and Parent Population of Type Ia Supernovae: A New Tool for Probing the Ages of Distant Galaxies

We study the properties of Type Ia Supernovae (SNe Ia) as functions of the radial distance from their host galaxy centers. Using a sample of 62 SNe Ia with reliable luminosity, reddening, and decline rate determinations, we find no significant radial gradients of SNe Ia peak absolute magnitudes or decline rates in elliptical+S0 galaxies, suggesting that the diversity of SN properties is not related to the metallicity of their progenitors. We do find that the range in brightness and light curve width of supernovae in spiral galaxies extends to brighter, broader values. These results are interpreted as support for an age, but not metallicity, related origin of the diversity in SNe Ia. If confirmed with a larger and more accurate sample of data, the age-luminosity relation would offer a new and powerful tool to probe the ages and age gradients of stellar populations in galaxies at redshift as high as $z\sim1-2$. The absence of significant radial gradients in the peak $\rm (B-V)_0$ and $\rm (V-I)_0$ colors of SNe Ia supports the redding correction method of Phillips et al (1999). We find no radial gradient in residuals from the SN Ia luminosity-width relation, suggesting that the relation is not affected by properties of the progenitor populations and supporting the reliability of cosmological results based upon the use of SNe Ia as distance indicators.Comment: 19 pages, incl. 3 tables & 3 figures; to appear in Nov 2000 issue of Ap

Double Bars, Inner Disks, and Nuclear Rings in Early-Type Disk Galaxies

We present results from an imaging survey of an unbiased sample of thirty-eight early-type (S0--Sa), low-inclination, optically barred galaxies in the field. Our goal was to find and characterize central stellar and gaseous structures: secondary bars, inner disks, and nuclear rings. Bars inside bars are surprisingly common: at least one quarter of the sample galaxies (possibly as many as 40%) are double-barred, with no preference for Hubble type or the strength of the primary bar. A typical secondary bar is ~12% of the size of its primary bar and 240--750 pc in radius. We see no significant effect of secondary bars on nuclear activity. We also find kiloparsec-scale inner disks in at least 20% of our sample, almost exclusively in S0 galaxies. These disks are on average 20% the size of their host bar, and show a wider range of relative sizes than do secondary bars. Nuclear rings are present in about a third of our sample. Most are dusty, sites of current or recent star formation, or both; such rings are preferentially found in Sa galaxies. Three S0 galaxies (15% of the S0's) appear to have purely stellar nuclear rings, with no evidence for dust or recent star formation. The fact that these central stellar structures are so common indicates that the inner regions of early-type barred galaxies typically contain dynamically cool and disklike structures. This is especially true for S0 galaxies, where secondary bars, inner disks, and/or stellar nuclear rings are present at least two thirds of the time. (abridged)Comment: LaTeX, 15 pages, 7 EPS figures; to appear in The Astronomical Journal (July 2002