US2349096A - Elevated tank - Google Patents

Description

May 16, 1944.

' J. O. JACKSON ELEVATED TAN-K Filed Aug. 4, 1941 5 Sl'xeeas-Sheetv l lNvENToR .A6/'4 ATTORNEYS May 36 l944- J. o. JACKSON 2,349,096

ELEVATED TANK Filed Aug.` 4, 1941 5' Sheets-Sheet 2 Si lNvENTor.

May 16; 1944 .1. o..JAc fKsoN x 2,349,096

ELEVATED TANK Filed Aug. 4, 1941 5 Sheets-Sheet 3 /A ATTORNEYS lMay 16, 1944 J.' '0. JAcKsoN -ELEVATED TANK Filed Aug. 4, 1941 Sheets-Sheet 4 MA ATTORNEYS May 16, 1944. v J. o. JACKSON ELEVATED TANK Filed Aug. 4Q 1941 5 Sheets-Sheet 5 m 55 lup *um INVENT-oR @I www? @0m M-,a ATTORNEYS Patented May 16, 1944 zama@ ELEVATED TANK .Eames D. `lackson, Grafton, Pa., assignor to Pittsharsh-Dea Moines Company, a. corporation oi' Pennsylvania Application August 4, 1941, Serial No. 405,287

(ci. zzo-ss) Claims.

This invention relates to elevated tanks for the storage of large quantities oi water and particularly to a tank of that character which has a low range of head between the upper and the lower capacity lines or water elevations.

Tanks of this general type have been built in the past, using various methods of supporting the relatively large bottom areas of such tanks,

on which, the weight of the stored water is im posed. Tanks with essentially ilat bottoms have been built in which the bottom surfaces have been supported by a system of grillage beams which in turn have been supported by girdrs and columns. This type of construction has the inherent disadvantage that the bottom plates must transfer the weight of the supported water to the underlying grillage beams by means of bending stresses, which requires either that the bottom plates be made relatively thick and, therefore, heavy and expensive or that the grillage beams be closely spaced so as to reduce the eect of the weight of the water on the bottom plates. Structures of this type are, therefore, uneconomical in design and excessive in cost.

More recently large shallow elevated tank designs have been developed in which the Weight of the contained water is transferred to the supporting members by means of tensional mem l brane stresses in the bottom plates. This has been accomplished either by the use of sag plates between girder-like members supporting the bottom or by combination forms such as a partially suspended and partially supported bottom as described in my Patent No. 2,086,131 issued on July 6, 1937.

One of the objects of the present invention is to provide a large elevated tank of the suspended bottom type in which the weight of Water is transferred by the bottom thereof to a supporting structure by means of tensional membrane stresses.

Another object of the invention resides in providing an elevated tank the bottom of which is composed of a central spherical portion and a peripheral toroidal portion connected at or adjacent their theoretical line of intersection to a girder assembly. Y

A still further object of the invention resides in providing a tank of relatively large size and in which the variation in water head from a substantially full to a substantially empty condition is comparatively small and in which the tank bottom has a spherical portion surrounded by a toroidal portion and connected in such manner that both portions slope downwardly away from the Vpoint of connection, the weight of water in such tank being distributed through suchportions to a system of supports.

Other and further objects and advantages will be understood by those skilled in this art or will be apparent or pointedout hereinafter.

In the .accompanying drawings:

vliig. 1 illustrates, partly in vertical elevation and partly in vertical section, an elevated tank responding to my present invention;

Fig. 2 is a fragmentary horizontal cross-sectional view taken along the line II-II of Fig. l and in the direction of the arrows thereof;

Fig. 3 is a fragmentary horizontal sectional view similar to Fig. 2 but of a modified form of the invention;

Fig. 4 is a fragmentary detail view taken along line IV-IV of Fig. 2 and in the direction of the arrows thereof;

Fig. 5 is a fragmentary view, partly in vertical elevation and partly in vertical section, of a further modified form of tank;

Fig. 6 is a fragmentary view partly in plan and partly in horizontal section taken along line VI-VI of Fig. 5 and in the direction of the arrows thereof;

Fig. 7 is a view similar to Fig. 5 but of a still further modified form of tank;

Fig. 8 is a view similar to Fig. 6 of the modication of Fig. 7 and taken along the line VIII-VIII of Fig. 7 and in the direction of the arrows thereof;

Fig. 9 is a. view similar to Fig. 5 of another modified formof tank; and

Fig. 10 is a view similar to Fig. 6 of the form of tank of Fig. 9 taken along the line X-X of Fig. 9 and in the direction of the arrows thereof.

Similar numerals designate corresponding parts throughout the various views.

In the form of my invention shown in Figs. 1 and 2 the tank bottom is composed of a central segmental substantially spherical sheet metal membrane surface 2l and an outer toroidal sheet metal surface 20. The surfaces 20 and 2l are connected to a. circular girder 24 which is disposed at or adjacent the theoretical line of interl section of members 2U and. 2l, the radii and configuration of the latter being such that both is disposed substantially vertically beneath the said circular girder 24 and thus is below the said circular line of intersection. Circular webs 25 and 21 lie between girders 24 and 26 and form a box-like assembly of such construction that it will properly and adequately support said membrane surfaces approximately at their common intersection, and receive from such membrane surfaces any vertical load or reaction which may be present at approximately such intersection the contacting surfaces. The radial girders are securely attached to the circular girder '26 in such manner that -they receive the loads and reactions present in the said circular girder and transmit the same, by virtue of their girder-like properties, to the riser pipe 30 and to the columnar members 29 which support the radial girders near their outer ends.

The membrane surfaces 20 and 2| are relatively very thin as compared to the principal dimensions of the tank structure. brane surfaces would usually be formed of, for example, sheet steel properly formed and united by means of welding, riveting or the like, to form a continuous water-tight surface. Now a relatively thin sheet metal membrane surface has considerable ability to resist tensional stresses but a very limited ability to resist compressive stresses or bending stresses. This property of a thin sheet metal membrane surface determines the distribution of the weight of the contained water over the new bottom structure.

It is apparent that the solid cylindrical column of water contained in the riser pipe 30 plus that directly above the riser which extends to the upper surface of the water in the elevated tank between the dotted lines A and B is supported directly by the riser pipe foundation 3|. The hollow cylindrical (annular) portion of water around column A-B and between the dotted lines Band C is supported substantially by the ring girder assembly above described. The hollow substantially cylindrical (annular) portion of water between line C and the outer shell 22 of the tank is supported substantially by the radial girders 28 at the outer ends thereof where they are connected to shell 22 and thence by supports 29. The location of the dotted line C is fixed by the point at which the curved portion of the bottom 20 is tangent to a horizontal plane. Since,

at this point, only horizontal loads are transferred in the bottom membrane it is apparent that the vertical weight of the contained water must be divided at this point. The column members 28 supporting the outer ends of the radial girders 28- may theoretically be placed at any point between the circular girder assembly and the outer ends of radial girders 28. However, I have found that the most economical design results when each column is so placed that the bending moment, caused by the load transmitted from the shell 22 to substantially the end of girder 28, about the end of supporting column 28 is substantially equal to the bending moment caused by the vertical load transmitted from the circular girder assembly to radial girder 28, the maximum value of which will occur directly under such circular girder assembly.

I have found that by a proper selection of the radii of curvature of members 20 and 2| and of their lneof intersection, with reference to a horizontal plane, it is practical to substantially Such memplied -by the cotangent of thev angle formed'be- 1 tween two lines lying in a plane normal to such connection, one such line being'horizontal and the other such line being tangent to the shell at the line of connection thereof to said support.

The vertical components of the tensional forces in members 28 and 2| are, however, additive and hence they load the ring girder assembly with a substantially downward force, which` is approximately uniform, around its periphery. Ring 26 is supported by a number of radial girders 23 but regardless of the number of such supporting girders ring girder 26, being a curved girder. is subjected to torsional stresses, which usually make a girder of this shape impractical. One of the important features of my design is based upon the manner in which this girder is inherently braced against lateral movement by the double curved membrane surfaces 20 and 2|. these surfaces being relatively quite `thin and capable of effectively resisting only tensional st resses. However, when such thin membrane surfaces are dished or curved in two directions they become very stiff and unyielding in lateral directions, for example, membrane surface 2| connected to circular girder 24 would very effectively restrain any part of member 24 from moving toward the outside of the tank, because in order for such movement to take place, the circumference of the exterior periphery of 2| would necessarily have to. be increased, which would cause tensional stresses to be set up in the circumferential direction, and which would oppose such movement of member 24. Likewise the inner periphery of member 20 would Iresist any tendency of member 24 to move toward the inside or central axis of the tank. This novel use of the double curved membrane surfaces to brace and restrain a curved circular girder thus makes it possible to use a construction which was formerly believed to be impractical and which resultsin a structure having a pleasing appearance and an economical design.

The foregoing will be understood and appreciated from a reference to Fig. 4 which illustrates a section through the box-like girder assembly showing adjacent parts of surfaces 20 and 2|. From this figure the theoretical line of intersection between members 26 and 2|, hereinabove referred to, will be seen to lie along the line Y-Y. The girder assembly is clearly positoned below but at such line. The assembly with surfaces 20 and 2| is made as follows: backing-,up circular strips 32 are welded along the under marginal edges of upper' circular girder 24; the supporting ledges thus produced support the individual sheets or sections which are then connected, as by welding, to form a permanent assembly and finally other segmental yportions are secured, as by welding, to the sheets or sections which adjoin the girder assembly thus forming the surfaces 20 and 2|.

In the modied form of the invention shown in Fig. 3 the construction is substantially the same as in Fig. 2 as is indicated by the choice of numerals. In Fig. 3, however, the box-like girder assembly is provided with polygonal web members 25' and 21'-, i. e., the web members are straight between succeeding radial girders 28. This I have found to simplify fabrication and thus to be a favorable cost factor.

In the modified form of tank illustrated in Figs. 5 and 6 I have provided a design of tank which dispenses with the radial girders 28, heretofore described, andwhich is therefore more economical to produce particularly for the larger tank sizes. Certain parts are the same as already described. as will be understood from the use of the same numerals. In this form of tank, however, each circular girder assembly is made up of circular top and bottom girders 24a and 26a which are vertically spaced from one another by the interposed' circular webs 25a and 21a which form al closed box-like arrangement. Each girder assembly is supported by a plurality of columns 29a which are substantially uniformly spaced around the underside of the side. A plurality of columns 29' is secured at spaced intervals to upright cylindrical shell 22, as by welding.

'The further modif-led tank construction of Figs. 7 and 8 is suitable for still larger tanks and is intended to be employed in designing the largest tank sizes. In this case the tank bottom is made up of a central spherical portion 2lb, a semi-circular intermediate portion h and an outer toroidal portion 20h. A plurality of circular box-like girder assemblies is provided which may. each be constructed in accordance with either Fig. l or Fig. 5. These girder assemblies are made up of circular top and bottom plates and circular webs and for convenience are designated only as a unit by the numerals 2lb and 21e. As will be clear from Fig. 7 the tank bottom. extends downwardly away :from the top plate of each girder assembly for a purpose which will be clear from what has preceded. Girder assemblies 21h and 21e are supported by a ring of columns 29D and 29e as shown. More than two ring girder assemblies can be employed and, for the largest tanks, three or even more are desirable. The number of tank bottom portions will increase correspondingly in such cases.

Since many standpipes, which have heretofore been built, have been outgrown due to Vpopulation increases and for other reasons, I'have designed a. modified form of my invention which incorporates such standpipes as in some cases this makes a very satisfactory and economical arrangement. Such a tank is illustrated in Figs. 9 and l0. To an old or existing standpipe 35 a circular metal bar 36 is secured, as by welding, on the upper edge. The sheet metal surfaces 20 and 2l are secured to bar 36. Column is provided at the center as before and surface 2| is secured thereto. This form of the invention is generally similar to that of Figs. 5 and 6. The old standpipe 35 supports a large proportion of the water in the tank and the columns 29 support that hollow cylindrical portion of the water which extends inwardly fromthe'upright tank portion 22 to the point at which surface 20 becomes tangent to the horizontal. 'Ihis will' be clear from the discussion of Fig. 1. Bar 36 is located at but under the theoretical line of intersection of surfaces 20 and 2| as will be clear by referring back to Fig. 4.

While I have described certain preferred forms of my invention, it is to be understood that the foregoing is intended as illustrative and not as limitative and that, within the terms and scope concentric relationship with the adjacent edges of two such shells secured to said support member and so formed and positioned with relation to each other that the load vertically above .the iirst such shell and included between the lines of connection with said support and the lowest level of the first such shell multiplied by the co-tangent of the` angle formed between two lines lying in a plane normal to such connection, one such linefbeing horizontal and the other being tangent to said shell at the line of connection thereof to said support is substantially equal to the product of the corresponding vertical load and the corresponding cotangent for the connection of the second curved bottom plate on the other sidof said support.

2. An elevated tank comprising a sheet metal upright portion, an arched roof portion and a composite bottom portion comprising a toroidal section attached to the lower edge of said upright portion along its outer periphery, a substantially circular girder-like member concentrically located with relation to said toroidal section and attached thereto throughout the circular extent thereof, a second toroidal section located con- Y centrically with relation to said circular member and having its outer edge secured thereto throughout the circular extent thereof, a second girder-like circular member located concentrically of said second toroidal section andr secured thereto along a circumferential edge thereof and a central section approximating a section of a sphere supported along its outer periphery by said second girder-like member, a central support secured to said central section and columns 'for supporting said upright lportion and said girder-like circular members.

3. An elevated tank comprising a. sheet metal upright portion, an arched roof portion and a composite bottom portion, said bottom portion being formed of a plurality of toroidal shells, the .outer of such shells `being attached to said upright portion, circular support means located between adjacenttoroidal shells and to which the adjacent circular edges of such shells are secured in iiuid tight relation, said toroidal shells having differentl radii of curvature and being so positioned with reference to each other that horizontal components of their normal tensional forces at the circular support means are substantially equal and opposite and thus substantially neutralize each other, and supporting means for said upright portion and said circular support means.-

4. An elevated tank construction as set forth in claim 3 in which said supporting means comprise a plurality of radial girders and acentral column supporting the inner ends of said radial girders, and a separate support column for each radial girder located intermediate the ends thereof and so positioned with relation thereto that the bending moment in each girder directly above said intermediate column and the bending moment directly below said circular support means are equal.

5. An elevated tank construction as set forth in claim 3 in which the circular support means is in the form of a built-up girder having a polygonal web member and at least one annular flange having circular edges to which the circular edges of two of said toroidal shells are i secured in fluid-tight relation.

l JAMES O. JACKSON.

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