Eccentricities

There are two forces acting on foundations of the type under consideration the dead load, acting in a vertical direction and the wind load, acting in a horizontal direction. The combined action of these two forces has the same effect as an eccentric vertical load. It is not necessary to calculate the eccentricity to determine the stability of the foundation. However, because there are definite relationships between eccentricity and stability, they will be explained as a matter of interest. 

Note The value of e calculated by the above equation is the maximum value, as the dead load, is minimum. The eccentricity for other conditions of dead loading may be obtained by substituting the proper weight in place of Wt. 

It has been shown by previous discussion that the following relationships exist  

Substituting values of S2 from the preceeding equations and values for,  

Area a of side to Extreme Section Gyration r 

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On Line Eccentricity Measurement during Fabrication of Aluminium Tubes. 

A tube manufacturer wanted to investigate the possibility for on-line measurement, calculation and presentation of eccentricity values on aluminum tubes when drawn at high velocities. Based on our experience from development of tube inspection systems [1, 2] for off-line inspection of precision tubes, a project was formulated. The main specifications for the tube manufacturing are summarized below ... 

A prototype system was manufactured to measure eccentricity values for such tubes in a production line. 

With four transducers the coordinates for the eccentricity can be calculated using X=Vi X- minus X+) and Y=>/2 (Y- minus Y+)... 

These initial considerations were promising for an eccentricity measuring system. To investigate the practical possibilities a series of problems had to be examined, such as transducers and equipment, demand to tube guidance, coupling and measurement velocity. 

Higher measuring density for the eccentricity measurement pulse could be obtained... 

The project demonstrated that it is possible to measure and evaluate eccentricity of aluminum tubes at drawing velocities around 25 km per hour. Not all demands regarding small diameter tubes and thin walls were tested, and the calibration procedures were not finalized. Optimizing the system should make it possible to expand the limits... 

When the ID and OD of a tube are not on the same ceiitre, the tube wall will have an eccentric shape with one part of the wall thinner than the other. This is the definition of eccentricity. 

In several generating banks inspected, a number of tubes have been found with eccentricity exceeding 1,0 mm and in one extreme case 2,0 mm, or 40 % of the nominal wall thickness was noted. A conceptual diagram of tire cross section of a concentric tube and a simulated plot of the wall thickness scan is presented in figure 3. The scan presented in figure 2 is a relatively concentric tube less than 0,2 mm of wall variation. 

Figure 5 is a photo of a sectioned tube removed from a tube sheet. Within the tube sheet the wall thickness of the tube is 3,35 mm on the left and 4,37 mm on the right (elevation A). Immediately above the tube sheet (elevation B), but still within the roll, the left wall is 2,74 mm and the right 4,67 mm. Immediately above the roll mark (elevation C), there is a significant reduction in the tubes eccentricity, as the left wall is 4,67 mm and the right 4,83 mm. 

Fig. 5 Tube eccentricity Fig. 6 Concentric tube with Fig.7 Expanded scan plot of an caused during fabrication internal rilling pattern. eccentric lube with rifling,...

Wastage does not have to be dramatic to be easily observed on a full coverage scan. Figure 14 and 15 show a tube with 0,2 ram of eccentricity that has been in service for two years and has 0,15 mm of wastage near the drum. New tubes are good indicators to determine wastage rates as the scans are very clean without noise of uneven rough corrosion. 

Depending upon the random orientation of en eccentric tube relative to the wastage zone, the tube may have to be replaced years sooner than it normally would have, had the tube conformed to a concentric specification. 

Fig. 16 Wastage on the thick side of an Fig. 17 Two sided wastage on the thick side eccentric tube. of an eccentric tube.

When wastage is located on the thin side of an eccentric tube, the life of the lube may be dramatically shortened because the material loss is subtracted from the thinnest part of the tube. 

Tile detection of this type of wastage is very straight forward as there is an exaggerated increase in the amplitude of lube w all eccentricity. The amount of wastage can be estimated by visualising the original wave shape and subtracting the measured minimum value. 

Wastage will also occur on that part of an eccentric tube that represents the nominal thickness of the tube. 

A number of refinements and applications are in the literature. Corrections may be made for discreteness of charge [36] or the excluded volume of the hydrated ions [19, 37]. The effects of surface roughness on the electrical double layer have been treated by several groups [38-41] by means of perturbative expansions and numerical analysis. Several geometries have been treated, including two eccentric spheres such as found in encapsulated proteins or drugs [42], and biconcave disks with elastic membranes to model red blood cells [43]. The double-layer repulsion between two spheres has been a topic of much attention due to its importance in colloidal stability. A new numeri-... 

Poor performance can result from fan inlet eccentric or spinning dow, and discharge ductwork that does not permit development of hiU fan pressure. Sometimes inlet restrictions starve a fan and limit performance. To obtain rated performance, the air must enter the fan uniformly over the inlet area without rotation or unusual turbulence. This allows all portions of the fan wheel to do equal work. If more air is distributed to one side of the wheel, such as with an elbow on the inlet, the work performed by the lightiy loaded portions of the wheel is reduced and capacity is decreased by 5—10%. The use of an inlet box duct on a fan can reduce capacity by as much as 25% unless there are turning vanes in the duct. Use of the vanes reduces the capacity loss to around 5%. 

Other elastomeric-type fibers iaclude the biconstituents, which usually combine a polyamide or polyester with a segmented polyurethane-based fiber. These two constituents ate melt-extmded simultaneously through the same spinneret hole and may be arranged either side by side or ia an eccentric sheath—cote configuration. As these fibers ate drawn, a differential shrinkage of the two components develops to produce a hehcal fiber configuration with elastic properties. An appHed tensile force pulls out the helix and is resisted by the elastomeric component. Kanebo Ltd. has iatroduced a nylon—spandex sheath—cote biconstituent fiber for hosiery with the trade name Sidetia (6). 

Bicomponent fibers have also provided a route to self-texturing (self-crimping) fibers. The crimp results from the length differential developed during processing caused by differential shrinkage in the two polymers in side-by-side or eccentric core—sheath configurations (50). 

Fig. 6. Orifice plates (a) concentric, (b) eccentric, (c) segmental, (d) universal, and (e) quadrant-edge.

Fig. 1. A cut-away schematic of a typical a-c open-arc, steelmaking, eccentric bottom tapping (EBT) furnace.

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