US3031800A

US3031800A - Metal storage tank

Info

Publication number: US3031800A
Application number: US15718A
Authority: US
Inventors: John H Wiggins
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-03-17
Filing date: 1960-03-17
Publication date: 1962-05-01
Anticipated expiration: 1979-05-01

Description

May 1, 1962 J. H. WIGGINS 3,031,800

METAL STORAGE TANK Filed March 17, 1960 r 4 Sheets-Sheet l INVEN TOR. JOHN H. W/GG/NS A 7' TOP/VEV:

May 1, 1962 J. H. WIGGINS METAL STORAGE TANK 4 Sheets-Sheet 2 Filed March 17, 1960 5 .w G mm W w m M N Wm M N J m V. M G? B g AKEVAEWWAE May 1, 1962 J. H. WIGGINS METAL STORAGE TANK 4 Sheets-Sheet 3 Filed March 17, 1960 INVENTOR. JOHN H. W/GG/NS A 7' TO/PNE VS y 1962 J. H. WIGGINS 3,031,800

METAL STORAGE TANK Filed March 17, 1960 4 Sheets-Sheet 4 INVENTOR. JOHN H. W/GG/NS ,4 7'TORNEVS United States Patent ()fifice Fatented May 1, 1962 3,tl3l,ilil METAL STfilti-hGE TANK John H. Wiggins, 2M tlosselyn lime, Woodside, Calif. Filed Mar. 17, 196% Ser. No. 15,718 13 (Ilaims. (Ci. 5054) The present invention relates to load-dividing, double suspension type roofs for metal storage tanks, commonly employed for the storage of petroleum products, grain and the like, and is concerned more particularly with the provision of a new roof structure having an improved con struction for drainage purpose which is of fail-safe character, particularly for water loads. This roof is the type shown in my co-pending application, Serial No. 726,515, filed April 4, 1953, for Metal Storage Tanks.

There are two principal types of downwardly directed live loading to which a roof of a metal storage tank for petroleum products is subjected, the first of which is a load which by its nature is substantially evenly distributed over the whole area of the roof and which will remain evenly distributed, regardless of slight changes in shape or sag of the roofs surface, and this type of load is imposed by a partial vacuum inside the gas tank or by a snow load. The roofs are commonly provided with a preferred or normal slope throughout the periphery in order to provide satisfactory handling of this character of load. The other type of downwardly directed live load to which the roof may be subjected is the type which will concentrate in a low area which may be built into the roof by design of a sloping curb or uneven sagging of a collection surface, and water is illustrative of this type of load. There is no problem if the water is drained off substantially as fast as rain falls or snow melts which can easily be done under normal conditions. However, with this type of load there is a hazard because of freezing, because an operator carelessly or accidentally closes the drainage spouts, or because of sabotage when someone purposely closes off the drainage. A solution to this problem by increasing the strength of the roof structure including increasing the size of the entire curb member is prohobitive in cost.

It is the principal object of this invention to provide a double suspension roof constructed to minimize or reduce the maximum possible cumulative water load to an amount that will be negligible, and without complicating the design of the roof and without diminishing the slice tiveness of the optimum design insofar as the first type of load is concerned.

it is another object of the invention to provide a double suspension roof of the type described herein wherein the socalled normal slope of the outer deck is maintained through a major part of the circumference of the curb or root, so as to maintain the effectiveness of the roof in withstanding a static load, and to provide a small portion of the roofs periphery with a notch or depression forming a weir which controls the amount of water which can collect in the trough.

A further object of the invention is to provide a double suspension roof having in one portion of its periphery a depression in the outer deck providing a weir to control the maximum level of water to be collected in the trough of the roof.

Other objects and advantages of the invention will be apparent from the following description of a preferred embodiment thereof, made with reference to the attached drawings, in which:

FIG. 1 is a partial plan view of a tank having a double suspension roof embodying the present invention.

FIG. 2 is a transverse sectional view taken in a plane indicated by the line 22. in FIG. 1.

FIG. 3 is a sectional view, partially in elevation, taken along the line 3-3 of H6. 2.

FIG. 4 is a fragmentary elevational view of a partly developed periphery of the tank adjacent its curb, the View being indicated by the line 44 in FIG. 2.

FIG. 5 is a fragmentary sectional view taken as indicated by the line 5-5 in PEG. 4 where the outer deck has a normal slope.

' FIG. 6 is another fragmentary sectional view taken as indicated by the line 6-6 in PEG. 4 where the outer deck has a'reduced slope.

FIG. 7 is a fragmentary plan view illustrating another form of the invention.

FIG. 8 is a transverse sectional view taken in the plane indicated in the line 88 in FIG. 7.

FIG. 9 is a radial projection of a sectional view taken along the circular section line 9-9 of FIG. 8.

Referring to the drawings, and particularly to FIG. 2, the storage tank includes a bottom wall it a cylindrical side wall ll, having a circular compression member or angle 12 secured to the upper edge thereof and forming a curb, and a center support 13 mounted on a foundation M on the bottom wall 16. The construction of the center support 13 is generally conventional and includes at its upper end a circular frame 16 to which the inner edge of the roof is attached. The roof is composed of an outwardly and downwardly sloping inner deck 18 and an inwardly and downwardly sloping outer deck 19 which are formed of metal plates and which meet at the lowest circle 23 of a gutter area 21. The angle between the inner deck and the outer deck 19 is generally ll-shaped and is less than 180 degrees. From the gutter area one or more drainage pipes 22 extend.

The inner deck 18 is a built-in shape or structure of double curvature by virtue of the welding of the joints between the metal plates after they have assumed their positions in a catenary shape which is suspended from the center support 13 and extends to the gutter line 20. The inner deck, therefore, resists deformation Within the limits of its strength. The outer deck 19 throughout the majority of its periphery is a surface of single curvature and also has a built-in shape which is approximately a frustum of a cone. The outer deck P9 is attached to the curb member 12 at its outer periphery and to the inner deck 18 at the lowest circle 20 of the gutter area at its inner periphery. The downwardly and inwardly sloping surface of the outer deck, having a shape substantially that of a conical frustum, namely, a shape of single curvature, is free to respond advantageously to conditions imposed by a large live load. Such response is the bending downwardly to substantially increase the angle of approach of the outer deck to the curb, as the curb moves bodily inwardly as compression increases. That angle of approach is thus steepened relative to the horizontal. The result of this steepening for any given live load is to thereby increase the efficiency of the outer-deck-pluscurb-combination as a load carrying structure with the following results (as compared to no steepening of the above described angle of approach): (1) The tension of the roof plates is decreased, and (2) the curb compression is decreased. This increase in efliciency can be such that the weight of the curb member can be halved to carry a given maximum live load.

To solve the water load problem efiectively the outer deck and curb is provided with a notch or depression along which a curb 12a descends gradually from the full height of the curb 12 to a central low point 25. Assuming a -foot diameter tank to be shown, a proper normal slope for the outer deck would provide a height of 12 inches from the trough 20 to the level of the curb 12, and at the central point 25 of the notch in the curb and the outer deck, the height of the effective curb at this point is lowered 8 inches so that a weir 25 is pro vided which operates when there is only a maximum of a 4-inch depth of water at the center line or lowest circle 29 will be provided. The maximum water load is indicated in FIG. 1 by the boundary lines 21, and its level 21a is indicated in FIG. 2. The slanting curb member 12a slopes upwardly in either direction from its low point 25 until it joins at points 26 the full height curb member 12 which is level throughout the remainder of the length of the circumference. The slope of the outer deck at the lowest point of the notched curb portion. 12a is 4 inches as compared with the normal slope of 12 inches from the curb 12 to the lowest circle 29. The surface of the outer deck is warped from this slope of 4 inches to the selected normal slope of 12 inches.

. The warped surface 24, which extends about 30 feet along the curb and is flatter than the remainder of the outer deck, provides increased tension on the curb between the points 26 for a given load as compared to the tension on the curb for that same load at a point on the trough which is located where the curb is at normal height. This locally accumulated increased tension may be compensated for by increasing the size and weight of the curb member 12a in comparison with the curb member 12., but I prefer to stabilize the warped surface 24 adjacent its center point and reduce the live load that has to be carried by the curb 1261. For this purpose l preferably provide an overhead support for the warped surface 24 adjacent to the central point, and this overhead support includes a channel member 41 extending along the line of the lowest circle and being either straight or curved, and being welded or otherwise secured to the deck plates of the inner deck 18. This channel 41 provides a means for suspending the roof at its lowest circle 2% at a desired height. This channel 41 has a central adjustable support 43 in the form of a turnbuckle connected thereto and extending upwardly to the lower channel as of a radial beam or truss 4d. The truss 4! also includes an upper angle 47 which is connected to the lower angle by a series of vertical angles 43, suitable diagonal braces 49 being provided. The upper angle 47 of the truss idis also connected by diagonal turnbuckle sections 42 which extend from adjacent the ends of the channel dfl to the upper angle 47. This truss 4% is provided at either end with supports which rest freely on the inner deck 13 and the curb portion i211, respectively, these supports comprising a pair of inclined post supports 44 at the inner end of the beam as and resting freely on the deck 13, and a pair of inclined post supports 45 at the outer end resting freely adjacent the low point of the curb section 1211. In this way the warped surface 2d is supported from two vertically stable portions of the tank, namely the inner deck 18 and the curb 12. At the time of installation the beam or truss ill is so set and its height so selected so that the warped surface 24 will carry the weight of the roof plates in suspension from the curb, but any tendency of the warped surface 24 to be lowered due to a live load will be resisted by the beam and the force on the beam will be transmitted to the inner deck 18 and to the curb 12a.

In another preferred manner of supporting the warped surface 2 I provide a support post 29 carrying a channel 3% at the top extending generally horizontally and in the direction of a tangent to the lowest circle. The post 29 rests on a lower platform or base 31 which is on the bottom wall ltl of the tank. This support post 2) may be attached to the roof or it may be held in place by guy wires. The support post 29 and the channel 3% assure that the roof portion resting thereon will remain at a fixed elevation under the application of a live load to the roof, so that any increased load will result only in a slight sagging between the channel 3% and the curb 12a so that the lowest effective point of that part of the outer deck moves outward to a. point between the support and the curb. This results in reducing the amount of live load carried by the curb and hence the amount of compression in the curb member 12a.

At the time of installation the support 29, 36 is so set and the height is determined so that the warped surface 24 will carry the weight of the roof plates in suspension from the curb. Thus there will be clean drainage to the drainage pipe leading from the tank. The

support

29, 30 will start to pick up the load as soon as any live load is applied to the Warped surface 24.

While I have shown and described certain preferred forms of the invention, it will be apparent that the invention is capable of variation and modification from the forms shown so that the scope thereof should be limited only by the scope of the claims appended hereto.

What I claim is:

1. A load-dividing double suspension type roof for a metal storage tank having a bottom wall, a stationary ide wall of uniform height, a circular compression ring attached to said side wall adjacent the top thereof and forming a curb, a center support mounted on said bottom wall and stationary relative to and higher than said curb, said load-dividing double suspension type roof being composed of metal plates joined to each other and comprising an outer deck sloping up to said curb and an inner deck sloping upward to said center support adjacent the top thereof, said inner and outer decks meeting and joining at the lowest circle of the roof, said curb and said outer deck at one portion of their periphery having built-in notch means said notch providing an overflow region for said roof, said overflow region and a corresponding region of said lowest circle being radially aligned and the vertical distance of said overflow region above the said corresponding region of the lowest circle being substantially less than the vertical distance between any two similar points on any other region of said roof providing a lower level thereof to decrease the maximum water load that can be imposed on said roof.

2. In a load-dividing double suspension type roof as recited in claim 1 in which means is provided adjacent said notch means to effectively stabilize the elevation of the lowest circle of the roof adjacent said notch means and to resist deformation of said roof adjacent said notch under a load.

3. A load-dividing double suspension type roof as recited in claim 2 in which said last-named means comprises a support on the bottom wall of the tank and engaging underneath said roof at the lowest circle thereof and adjacent said notch means.

4. A load-dividing double suspension type roof as re cited in claim 3 in which said support comprises a vertical post and a horizontal roof-engaging member thereon.

5. A load-dividing double suspension type roof as recited in claim 2 in which said stabilizing means comprises a load-supporting member attached to the roof along a portion of the lowest circle thereof adjacent said notch means, and means is provided for supporting said load-supporting member.

6. A load-dividing double suspension type roof as recited in claim 5 in which said member supporting means comprises an overhead truss disposed radially of the roof having connections to said member and having supporting means extend downwardly therefrom to the inner deck of the roof at one end and to the curb at the other end.

7. A load-dividing double suspension type roof as recited in claim 6 in which said connections from the membet to the truss comprises a vertically extending turnbuckle mcmber, and a pair of divergent turnbuckle members extending from the truss to the ends of the horizontal load supporting member.

8. A load-dividing double suspension type roof for a metal storage tank having a bottom wall, a stationary side wall of uniform height, a circular compression ring attached to said side wall adjacent the top thereof and forming a curb, a center support mounted on said bottom wall and stationary relative to and higher than said curb, said load-dividing double suspension type roof being composed of metal plates joined to each other and comprising an outer deck sloping up to said curb and an inner deck sloping up to said center support adjacent the top thereof, said inner and outer decks meeting and joining at an annular drain area including the lowest circle of the roof, said curb being spaced vertically with respect to said circle, a uniform height throughout a major portion of its periphery, said curb at one portion of its periphery descending from either side to a low point providing a shorter vertical dimension from said curb to said circle than said uniform height and said outer deck adjacent said one curb portion having a warped shape to mate with said curb portion, the height of curb portion at its low point limiting the volume of water that can collect in said drain area.

9. In a load-dividing double suspension type roof of the type recited in claim 8 in which means is provided adjacent said one curb portion to effectively stabilize the elevation of the lowest circle of the roof adjacent said portion and to resist deformation of said roof.

10. A load-dividing double suspension type roof as recited in claim 9 in which said last-named means comprises a support on the bottom wall of the tank and engaging underneath said roof at the lowest circle thereof.

11. A load-dividing double suspension type roof as recited in claim 10 in which said support comprises a vertical part and a horizontal roof-engaging member thereon.

12. In a load-dividing double suspension type roof of the type recited in claim 9 in which said stabilizing means comprises an overhead structure extending between the outer curb and the inner deck and across said lowest circle, said structure having means connecting it to the lowest circle of the roof to resist downward movement thereof.

13. In a load-dividing double suspension type roof of the type recited in claim 12 in which connecting means to the curb and to the inner deck comprise downwardly extending adjustable members connected to the structure and to the roof.

References Cited in the file of this patent UNITED STATES PATENTS 2,327,084 Wiggins Aug. 17, 1943 2,425,771 Wiggins Aug. 19, 1947 2,804,028 Wiggins Aug. 27, 1957 2,805,631 Wiggins Sept. 10, 1957 FOREIGN PATENTS 210,083 Australia Mar. 1, 1956