US2282772A - Pontoon type floating roof for liquid storage tanks - Google Patents

Description

May 12, 1942. .1. H. wlGGlNs PONTOON TYPE FLOATING ROOFS FOR LIQUID STORAGE TANKS Filed April l5, 1939 3 Sheets-Sheet 1 -'-O if 2 [NVE/vrom ATTORNEY u u u m. N.. N m um v u. u mm. J r1 v f( fm u ,u w uw UN Q m. `v n N m. `M v m. u GN f 1, 12.1/ 1 1 mlm 1111 .1 1 llll 11 1111111 l 11 111 -uw f f w q b. 2, m m, 9 s w k1 1. Q1 1 r 11 z .Wdh 1 l|1 l 1111 11111 11| 1r w l. QN hm .www 1o L 1 1- 1 1 1 1 1 1.1-1

May 12, 1942.

FIG. 5.

3 Sheets-Sheet 2 v INVENTOR; JoH/v H. W/GG/Ns BY/WM HT TUHNE Y May 12, l942- J. H. wlGGlNs PoNTooN TYPE FLOATING RooFs FOR `LIQUIlJ STORAGE TANKS Filed April l5, 1939 3 Sheets-Sheet 3 NVENTOH;

A TTORNE Y Patented May l2, 1942 7 ortica ATING ROOF FR (CE. 22o-26) This invention relates to oating roofs for l Claim.

liquid storage tanks, and particularly floating roofs of the type that are equipped with one or more pontoons for increasing the buoyancy of the roof.

One object of my invention is to provide a iioating roof whose component parts are constructed and arranged in a novel manner that attains the following results: (a) decreases the weight of the roof; (b) reduces the number of parts used in the construction of the roof; (c) increases the stability of the roof under all conditions; (d) insures eilcient drainage of water from the top side of the roof and eliminates the possibility of an excessive quantity of rain water collecting and remaining on the roof; and (e) reduces the cost of manufacturing and erecting the roof.

Another object is to provide a oating roof which is equipped with a novel means for preventing the approximate shape of the deck of the roof from being substantially changed or altered by flexing c displacement, resulting from accumulation of gases on the underside of the roof.

Another object of my invention is to provide a oating roof that is equipped with a novel means for preventing the central portion of 'the roof from sagging disproportionately to the rest of the roof, in the event an abnormally heavy load of rain water or snow is imposed on said 5 central portion.

Another object is to provide a oating roof of the pontoon type, in which the deck and the pontoons are of such construction and arrangement that the roof is capable of successfully carrying a much greater load than pontoon roofs of conventional design, and also has a safety factor far in excess of that required-for a commercially acceptable floating roof.

Another object is to provide a floating roof roof is being erected; and which is easy to comthe deck from one side to the other. Othm objects and desirable features of my invention will be hereinafter pointed out.

To this end I have devised a floating roof that comprises a deck, preferably formed from a metal diaphragm or substantially limber metal sheet structure that constitutes the top surface of the roof, a stii annular compression member arranged at the periphery of the roof and constructed in the form of a pontoon that projects downwardly from the underside of the deck, a. stiil compression member at the center of the roof constructed or arranged so as to comprise a downwardly-projecting portion, and radiallydisposed tension members rigidly attached to or combined with said center compression member and said peripheral compression member, for maintaining said compression members in the positions they are intended to occupy relatively to each other, or, in other words, for preventing, or tending to prevent, either of said compression members from moving vertically relatively to the other under the loads or forces which the roof is liable to be subjected to in normal use. To state it in another way, my improved roof is constructedv on the same general principle as the conventional wire spoked Wheel and comprises two sti compression elements at the center and at the periphery of the structure that correspond to the hub portion and the rim of the wheel, plus radially-disposed tension members, corresponding to the spokes of the wheel, that cause vertical loads, strains, or forces exerted on the center compression element (either upward or downward forces) to be transmitted to the peripheral compression element in substantially the same way that the side thrusts on a wheel hub are transmitted by the spokes to the rim when the wheel is traveling around a curve.

The number of pontoons with which the roof is equipped may be varied, and the construction and arrangement of the pontoons may be varied, without departing from the spirit of my invention, but in all instances, the roof Will be provided with a buoyant means, such as a pontoon or pontoons, that project downwardly from the underside of the deck and which are combined with the deck in such a way as to support and maintain the deck out of contact with the liquid in the tank. Preferably, the roof comprises a substantially annular-shaped, stii pontoon that constitutes a compression member located at the periphery of the deck and said deck and said peripheral pontoon are designed or arranged 2 ,aeavra so that under normal conditions the peripheral portion of the deck will be spaced higher above the surface of the liquid than the central portion of the deck, thereby producing a floating roof of substantially dish shape or inverted cone form, who top surface slopes downwardly to a drain outlet at the center of the deck. Ihe peripheral pontoon above referred to, or any other pontoon of the roof that is of annular form or substantially annular form, is preferably made up of a number of sections or units that can be easily manufactured and tested in a factory and then shipped to the place where the roof is to be erected. The particular crosssectional shape of said annular pontoon or pontoons is not essential, and may be square, oblong, round, oval, or a modification of any of said shapes. In/addition to the peripheral pontoon above mentioned,` the roof may also comprise (a) a stifl.' center pontoon that functions as a compression member; (b) an intermediate pontoon of substantially annular form, arranged between the center of the roof and the peripheral pontoon; or (c) a center pontoon and one or more substantially annular pontoons arranged between the center `pontoon and the peripheral pontoon.

'lhe tension members preferably consist of rav dially-disposcd members attached at their inner surface of the liquid. The meansthat is used to prevent distortion of the deck is herein illustrated as consisting of tension members which. in

addition to maintaining the approximate form or shape of the deck, effectively carry eccentric loads from one side of the peripheral pontoon to the other. In Figure 1 I have illustrated my improved roof as being equipped with a set of radially-disposed, inclined tension members 2, attached at their inner ends to a strut 3, which constitutes a rigid compression member that depends from the center of the underside of the deck," and connected at their outer ends to the top edge of the annular compression member or pontoon A, and a 1'5 separate set of oppositely inclined, radially-disof the pontoon A. The tension members 2 which extend radially from the center compression element of the roofto the peripheral compression element, effectively prevent the central portion of the deck from sagging disproportionately tov the rest of the deck, in the event an 4abnormally heavy load of rain or snow is imposed upon the roof, and the tension members 4, which lead inwardly from the peripheral compression element, and are attached to the center compression eleends` to a stiff compression element comprising ment, hold the deck down, and prevent the cena part or member depending from the center of the roof, and attached at their outer ends to the annular compression member formed by the peripheral pontoon, said tension members being so disposed that they act to hold down the central $5 portion of the roof and prevent said central portion from ilexing upwardly, due to the accumulation of gases on the underside of the roof, and said tension members also act to prevent the central portion of the roof from sagging disproportionately to the rest of the roof when an abnormally heavy load of snow or rain water is imposed on said central portion.

The roof is preferably equipped with a drainage apparatus that may comprise a 'center drain,

either of the inverted syphon type, or any other preferred type, and one or more annular rows of auxiliary drains arranged between the center drain and the periphery of the roof.

Figures 1 to "I, inclusive, of the drawings are vertical transverse sectional views, illustrating various ways of constructing the floating roof which constitutes my present invention; and

Figure 8 is a fragmentary top plan view of said roof, illustrating the preferable way of constructing the annular pontoons.

The roof illustrated in Figure 1 comprises a still.' annular compression member formed by an annular pontoon A, arranged at the peripheral edge of the roof, a deck I, constructed from metal plates, and preferably designed so that when the roof is completed, it will be dish-shaped or of substantially inverted coneform, and a means for maintaining the approximate shape of the deck and preventing it from being displaced by upward and downward forces exerted on same, such, for example, as an upward force resulting .from accumulation of gases on the underside of' the roof, or a downward force caused by an ab- 1y from the underside of same and is so designed and combined with the deck as to always maintral portion of same from flexing upwardly when the gas pressure on the underside of the roof increases. Usually, the tension members 2 and 4 will be formed from metal rods.

Water that falls onto the top surface of the deck I is conveyed away from said surface by drains that discharge the drain water downwardly into the body of liquid in the tank on which the roof floats. Preferably, the roof is provided u with a primary center drain and a plurality of v'emergency drains arranged between the center drain and the periphery of the roof. 'Ihe said drains may be of the inverted syphon type. commonly used in floating tank roofs, or may con- -m sist simply of vertically-disposed, tubular members, whose open upper ends terminate in the top surface of the deck. In the roof shown in Figure 1 the tubular member 3 at the center of the roof is used to form the primary drain of the roof, and the emergency drama are formed by an annular row or rows of tubular members.

I arranged between the center drain and the annular pontoon A. Some or all of the drains Just mentioned may be made of such length that u when the tank is empty, said drains will serve as supporting legs for the center and intermediate portions of the roof. The peripheral portion of the roof may be supported during the operation of erecting the roof, or when the tank is empty, either by supporting legs attached to the peripheral pontoon A, or by roof supports t attached to the -bottom 'I of the tank in which the floating roof is used.

.The floating roof shown in Figure 2 embodies lroof shown in Figure 1, and is composed of parts of quite similar construction and arrangement. However, the roof shown in Figure 2 Is provided with a stiff or rigid center pontoon B that functions as a compression member, and the tension members 2 and 4 are attached to said center pontoon B. In Figure 2 the reference character I designates a center drain that extends upwardly through the center pontoon B, and the tain the deck at a point considerably above the reference character l* designates depending legs the desirable characteristics and features-of the or roof supports attached to the peripheral pontoon A. I

.The-'roof illustrated. in Figure, 3 is provided with an intermediate annular pontoon C arranged between the center of the roof and the peripheral pontoon A. OppositeLv- inclined tension rods 2 and 4 are combined with a depending rigid center member 3, and with the intermediate annular pontoon C, and additional sets of oppositely inclined, radially-disposed tension members 2a and 6B are combined with the intermediate pontoon C and the annular compression member A at the periphery of the roof.

Figure 4 illustrates an additional feature that may be incorporated in a roof of the kind shown inFigure 3, to wit, radially-disposed deck beams 8 attached to the underside of the portion of the deck I which bridges the space between the annular pontoon A and the intermediate pontoon C, so as to impart stiffness to the peripheral portion of the deck.

The roof shown in Figure is similar to the .one shown in Figure 4, except that it is provided with a stii or rigid center pontoon` B', to which the inner ends of the tension rods 2 and 4 ,are attached, the center pontoon B being equipped with a center drain 38 that also acts as a roof support under certain conditions.

Figure 6 illustrates a roof that differs from the one shown in Figure 5, in that the trussing means arranged between the intermediate pontoon C and the annular pontoon A that constitutes the peripheral compression member, is composed of a plurality of sets of oppositely-inclined, crossed braces II combined with vertical struts I0 and I.

with horizontal top and bottom beams 8 and 9 in such a way as to co-act with the tension members 2 and d between the center of the roof and the intermediate pontoon C to effectively hold the roof in shape and cause loads or forces thereon to be distributed in the manner previously explained.

It is not essential that all of the tension members be arranged on the underside of the deck. In some instances it may be desirable to arrange some of the tension members on the top side of the deck. Thus, as shown in Figure 7, the roof may comprise a stii annular compression member formed by a peripheral pontoon A, an intermediate annular pontoon C, a depending center strut 3, and sets of oppositely- inclined tension rods 2, 2a, 4 and Il, some or all of which may extend through the deck and be attached to struts I2 and I3 that project upwardly from the top side of the deck, said struts I2 and I3 being l located intermediate the center of the roof and the peripheral pontoon A. The tension rods 2B that lead upwardly and outwardly from the bottom edge of the intermediate pontoon C extend through the deck, and after passing over the upper ends of the struts I 2, are attached to the outer top edge of the peripheral pontoon A. Similarly, the tension rods 2 that extend outwardly and upwardly from the center strut 3 pass through the deck and are attached to the upper end of the struts I3 on the top side of the deck. The tension rods Ila that lead inwardly from the bottom edge of the peripheral pontoon A pass upwardly through the deck and are attached to the struts I3. If desired, said rods 4a may be extended inwardly towards the center of the roof, as shown in broken lines inFigure 7, and can be attached to a strut ld shown in broken lines, that projects upwarc'ly from the top side of the center of the deck.

Y In order to reduce the cost of manufacture and erection of the ro'of, I prefer to construct each of the annular pontoons from a plurality of sections or units thatcan be manufactured and inspected at a factory and then shipped to the place where the roof is to be erected. This feature of my invention is illustrated in Figure 8 of the drawings, wherein it will be noted that the peripheral pontoon A and the intermediate pontoon C are each made up of a number of small hollow members I5. Said hollow members may be oi any preferred cross sectional shape, but each of said members consists of a complete hermetically sealed member provided with a top wall, a bottom wall, side walls, and end walls, joined together by tight joints. Said members I5 are of .such form that when a plurality of members are arranged end to end, they cooperatc-with each other to form a pontoon of substantially annular form. 'Ihe pontoon sections I5 can be hermetically sealed, because they are of such shape and size that they will stand any possible pressure or vacuum. Also, they are small enough so that they may be shop-welded and tested for leaks under high pressure, and then shipped in lengths of 30 ft. or 40 ft., or more, to the place where the roof is to be installed. By constructing the annular pontoons in the way above described, the cost of fabricating same is materially reduced. As previously explained, the particular cross-sectional shape of the annular pontoons is immaterial, but I prefer to use a peripheral pontoon of such shape and size and combine the deck of the roof with the pontoons in such a way that the roof, after completion, will have a sloping top surface that pitches downwardly to a drain outlet at the center of the roof. The emergency drains, although highly desirable, are not essential to the successful operation of the roof. They are so disposed or located on the surface of the roof that if the center drain becomes stopped up, water can collect on the roof only until it reaches the first row of emergency drains. Preferably, the roof is so designed that the center portion of the deck is normally a lfew inches (2 inches or 3 inches) above the liquid line, so that with avery small load of water or snow, on the roof, the center of the roof is submerged inthe liquid on which the roof floats, and hence, becomes a buoyant means of itself. makes the roof as an entirety capable of carrying a very large snow load, and also decreases the stress in the tension rods that are used to prevent the central portion of the roof from sagging disproportionately to the rest of the roof, in the event of an abnormally heavy load. Whereas, the center of the roof normally may be only 2 or 3 inches above the liquid, the peripheral portion of the roof deck may be from 10 to 18 inches above the liquid line. Thus, an emergency load, which would bring the upper openings of the emergency drains down to the liquid line, would be the complete displacement of all the pontoons, plus thedisplacement of the cone formed by the roof deck. To submerge the pontoons alone would require a snow load of from 15 inches to 25 inches. To further submerge the deck (assuming that it is constructed inthe shape of a cone with a 9 inch pitch to center) would require an additional load of 21 inches of snow. Consequently, a roof constructed inaccordance with my invention can be designed to carry from 36 inches to 46 inches of snow, without liability of the-liquid stored in the tank nding its Way to the top surface of the roof. It

This fact will also be noted that. it would be impossible for a rain load of equivalent magnitude to collect on the roof, due to the fact that the roof is provided at numerous points throughout its area with emergency drains arranged in one or more annular rows between the center of the roof and the periphery of the roof. i

Ordinarily, when erecting a ioatingVV roof, whose co-operating parts are Joined together inside of the tank in which. the roof is used, it is necessary to build a frame over the whole area of the tank bottom upon which to erect the roof.

With a roof of the design herein illustrated the pontoon sections can be set in place on their xed supports and welded together so as to form complete pontoons. If the roof is provided with a peripheral pontoon and an intermediate pontoon, said pontoons are joined together by roof beams 8, thus forming a. supporting framework that constitutes part of the roof, and which overcomes the necessity of building a temporary framework. In most instances the pontoons will have a depth of about 3 ft. Consequently, if the ing the operation of illing the tank, the roof is effective as a floating roof as soon as the bottom of the peripheral pontoon is sealed by the liquid in the tank. Thus, adjustable legs are eliminated and more of the tank height is used as a floating roof than has been the custom with prior designs of floating roofs. This decreases the cost of the roof and increases the efiiciency of the entire structure.

Having thus described my' invention, what I claim as new and desire to secure by Letters Patent of the United States is:

l A oating roof for liquid storage tanks, comprising a stiff annular peripheral pontoon, a single deck portion constructed in the form of a flexible diaphragm, attached to the said pontoon pontoons are provided with depending portions adjacent the upper edge thereof, and sloped downwardly towards the center of the roof, d radially-arranged tension members, each havi g one end attached to said single deck portion t a point inwardly spaced from said pontoon and having the other end attached to said pontoon, at a point substantially at the bottom. of said pontoon, for maintaining said deck portion in a downwardly sloped position, under all conditions of pressure in the gas space between the roof and the liquid in the tank.

JOHN H. WIGGINS.

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