US2849792A

US2849792A - Method of building metal storage tanks

Info

Publication number: US2849792A
Application number: US507887A
Authority: US
Inventors: John H Wiggins
Original assignee: Individual
Current assignee: Individual
Priority date: 1955-05-12
Filing date: 1955-05-12
Publication date: 1958-09-02
Anticipated expiration: 1975-09-02

Description

Sept.v 2,-1'958 J, AwlqlNs 4 2,8495792 l METHOD OF BUILDING METAL STORAGE TANKS Filed May 12, 1955 5 Sheets-Shea?l 1 ATTORNEY.'

Sept. 2, 1958 J. H. wlGGlNS METHOD oF BUILDING METAL STORAGE TANKS 5 Sheets-Sheer?l 2 Filed May l2, 1955 FIGA.

FIG.|O.

. INVENTOR,

JOHN H.WGGN$ BYYYMM ATTORNEY l SCPL 2, 1958 J. lli; wlGGlNs 2,849,792

`METHOD 0F BUILDING METAL` STORAGE TANKSz Filed May 12, 1955 y5 Sheets-*Sheet 3 FIG. 7.

L J INVENTOR,

4a oHN H.- w/ @INS F n E v BY )pi f.

' ATIORNEX United States Patent 42,849,792 METHOD or BUILDING METAL STORAGE TANKS John H. Wiggins, Woodside, Calif.

Application May 12, 1955, Serial No. 507,887

v 2 Claims. (Cl. 29--429) This invention relates to a novel method of building metal tanks that are used for holding liquid, grain and various other materials, and particularly storage tanks for petroleum products of the knd that are equipped with a stationary roof as distinguished from a roof which iloats on the liquid confined in the tank. i

One object of my invention is to reduce the quantity of steel required to built a metal tank roof, reduce the labory all of the work of fabricating or constructingv the roof ofy the tank to be performed at ground level, thereby overcoming the necessity of erecting expensive scaffolding for the workmen to stand on and making it safer and easier for the workmen to perform the tasks in whichy they are engaged. Other objects and desirable features of my invention will hereinafter be explained.

v To this end I have devised a method of building a metal tank which, briefly described, contemplates the following procedure: j

(a) Erecting a permanent, vertical roof support at the center of the tank,

(b) Building a complete and finished roof unit on the bottom of the tank composed of roof plates welded to each other and to stiff or rigid frame members so as to form a circular diaphragm provided at its periphery with a ring shaped beam and compression member and provided at its center with a ring shaped beam and tension member that surrounds the center roof support,

(c) After completion of the side wall of the tank, raising or hoisting'said roofl unit to Athe top edge of the tank side wall, and

(d) Thereafter combining said roof unit with the center roof support and with the tankwall so asto cause a certain proportion of the load of the roof to be carried by the center roof support and a certain proportion of the load of the roof to be carried by the tank side Wall. The above mentioned center and peripheral ring shaped frame members of the roof are arranged in concentric relation with each other and with the center roof support preparatory to -assembling the roof plates, and during the fabricating operation the roof plates are welded to each other and to said frame members while the platesrest upon and are supported by said frame members. During the operation of raising or hoisting the roof unit into operative position, said frame members impartsufiicient rigidity to the roof unit to maintain the shape and form of same, and in the nished structure said center and peripheral frame members coact with the center roof support and with the tank side wall toreinforce and phragm composed of roof plates and at least two circular' frame members at the center and periphery of the diaphragm, welded together while assembled on or adjacent, the bottom of the tank, and thereafter, after completion of the tank side wal1,.raised or hoisted into a positiony where the peripheral circular frame member of the diaphragm can be joined to the top edge portion of the tank wall and the center circular frame member of the diaphragm can be supported on or joined to a permanent, vertical roof support at the center of the tank.

Brieily described the roof illustrated in said companion application comprises two concentrically arranged, arced@ surfaces of dilerent' radii joined together at a circular orv substantially circular linewhich constitutes the lowest circle in the area of the roof, and disposed in such relationship with each other that the outer arced surface slopes upwardly and outwardly to the top ledge ofthe tank side Wall from which it is suspended, and the inner arced` surface slopes upwardly and inwardly to the center roof. support from which it is suspended. The outer arced surfaceA constitutes the peripheral' portion of the roof and'A the area of said portion is about one half, or less than yone half, of the tot-al area of the roof. Theradii of the arced elements of said peripheral portion are substantially shorter than the radii of the arced elements ofthe inner l arced surface which constitutes theicentral portion of the roof, with the result that the centers of thel radii of the two portions of the roof lie above and at opposite sides; (to the right `and left) of the circular line `whichvcon` stitutes the juncture of said rvtwo roof portionsran'dthe. lowest circle of the roof. By constructingtheroof in,v the manner above describedit is possible for the'ltank` side wall or the center roof support to settle a substantialy amount without shifting the lowest circle of the roof into such a position that the tank side wall will besubjected to a load in excess of the load it was designed Yto carryI or the center roof support will be subjectedto a load in. excess ofthe load it was designed to carry. t

Figure lfof the drawings is a fragmentary, verticalu proved method or procedure, the two portions ofthe tankA roof being broken away adjacent the lowest circle of theY roof so as to permit the use of certain lines and reference lcharacters mentioned in the description of the invention.

Figure 2 is a sectional View showing the two-portions of the roof connected together by a lap welded joint,v Figure 3 is a sectional view showing ,the two portions of the roof merging into each other and with a kink or.V sharp bend inthe roof plates at the lowest circle of theV roof.

Figures 4 to 10 inclusive illustrate another form of roof produced by my method wherein the kroof comprises an intermediate portion or connecting member of substantially V shape in cross section, disposed circumferentially of the roof between the center portion and peripheral portion of the roof and attached to said portions so as to join same together, said figures also illustrating the`procedure" of building the roof in the form of a complete unit onthe bottom of the tank and subsequently, after comple` tion of the tank side wall, raising or hoisting the roof into its operative position and joining it to the top edge portion of the tankside wall and to the upper end portion ofthe` vertical roof support a't'the center of the tank. In this group of figures, Figure 4 is a fragmentary, top, plan View showing the roof while it is being constructed or fabricated onthe bottom of the tank.

yFigure 5 is a vertical sectional view'takenon't'heline 5--5 or" Figure 4.

Figure 6 is a fragmentary, vertical'transverse'view showing how the'roof unitfismovedupwardly'toiits operative position by hoisting'rnechanism 'carried'by'thetcenter roof support andthe tank side wall.

Figure 7 is a similar View showing the'completed structure with the hoisting mechanism remo-ved, the center ring'member of the roof restingon the beams'at the upper end ofthe center yroof support 'and the center closure plate of the roof welded'to said center' ring member.

` Figure 8 is a fragmentary, vertical transverse sectional view showing ad'itferent kind of V-shaped connecting member that may be used at the circular line of juncture for joining the central portion and peripheral portion of the roof `to eachother.

Figure *i9 is av fragmentary, top plan view showing'a roof whose center and peripheral portions are joined together by a connecting member of the kind shown in Figure 8, and4 Figure l0 is a diagrammatic view, on an enlarged scale, illustrating theforces acting on the V-shaped connecting member'of the roof.

In Figuresl, A2, and 3 of the drawings, the reference character Lt designates the circular side "wall of the tank; 2 designates the bottom of the tank; F designates an irnivardlyl 'projecting flange 'at thetop edge of the vtank side wall, and C designates a vertical roof 'support at the center l'of lthe "tank, herein illustrated as being composed of av plurality ofvertical'uprights joined to eachother by horizontally disposed cross members i6 and inclined braces so as jtd form a tower that rests on a basepiece G on Athe `bottom of the tank. 'Ihe roof of the tankis formed 'by'ajmetal' diaphragm that comprises a central portion A which slopesdownwardly and outwardly from the'centerroof support C,` and a' peripheral portion B'thatl slopes `-downwardly'and linwardly fromvthe top edge of the tank 'side wall, said peripheral portion cons'tituting'about one h alff'o'r lessthan'o'nehalf, of the total area 'of the roof. Saidroof portion'sjAand B are joined together at ac ircular or substantially circular line a` which constitutes the lowest line 'orci'rrc'le in the area of the roof. At the center of saiddiap'hra'mthere is a stiring shaped tension member D and at'the periphery of saidrdiaphr'agm there is a stif ring shapedco'mpression member E.V Both of vsaidring shaped m'embers'jare rigidly attached to the roof platesof which the diaphragm is constructed and said ring shaped members are'used to suspend the diaphragm between the center roof support and the tank side wall, thetension member D'at the center ofthe diaphragm being attached to 'the center roof support C' in any pre ferred manner, as for example 'by horizontally disposed beamsA I2 on which said tension member rests, and the compression member E at the periphery of the'diaphragm beingjrigidly attached to theflange F at the top edge of the side wall 1 of the tank. After there-of has beeninstalled a cover plate'14 is welded to the top side` of 'the ring shaped tension member D so as to reinforce and strengthen same and close the hole in the center of the roof.

, Water that collects at the low point a of thereof is conducted away from same through one ormore drains 11 shown in Figures 2 and 3. y

As shown in Figure 2 the two roof portions maybe formed by twol separate, concentrically arrangedmembers connected together by a lap welded jointthat ex-` tendscircumferentially around the roof, or as shown in Figure 3 the roof portions A and B may constitute integral portions of a large diaphragm that has, a circular bend or kink formedfin same to constitute the lowest' circle-a of theroof, the portions of the diaphragm lying on the inside and on the outside yof said lowest circle a being 4 shaped so as to produce arced surfaces of different radii. So'far as my basic idea is concerned it is immaterial what method or procedure is used to fabricate or construct the roof diaphragm so long assaid diaphragm comprises a central portion and a peripheral portion of the kind above described.

For a better understanding of the basic idea of the roof, I will refer to Figure 1 of 'the drawings wherein the line b1 designates one element of an imaginary cylinder defined by the'lowest circle a of the roof, said cylinder having a radius R3. The central portion A of the roof has a surface which is formed by arced elements having radii r2 whose centerl lie'in a-circle IR2 located above and on the outside (to the left)`of the previously mentioned line b1 which designates one element of an imaginary cylinder defined by the lowest circle a of the roof, and the peripheral portion B of the roof has a surface which is formed by arced elements having radii r1 whose centers k lie in a circle R4 locatedI-above'and on thenside (to the right) of fthe 4line bl-designatingsaid cylinder. In Figure 1 the reference characterv R1 designates the radius of the tank side wall, c designates the point where the plates of the roof portion Bare joined to thecompression member E at the peripheral edge of the roof,R5 designates the radius of* the'inner edge of the central roof portion A and d designates the point where the plates ofy portion A are joinedto the fring shaped tension member D at the center of the roof. Preferably the two arced surfaces A and B of the rooffare disposedV in such relationship with each other :thatthey-form anangle of'less than 180 degrees at'the point where said arced'surfaces are joined together. 'If thev entire'lroof were built in- Ithe form of aV continuous arc or curvev lwhose lowest point or circle was tangential to a horizontal radial line, asubstantial settling or downward movement 4of the roof lsupport would cause the lowest line or circle of the roof to-move inwardly a substantialamonnt,v thereby decreasingfthe load on the center "tension vmember-D: carriedby the center roof support-'and-'increasing the load on" the peripheral compression 4member E carried by -the `vtank 'side Wall. Similarly a substantial settlingV or downward movement ofv the 'tank side wall would cause the lowest line or circle o f the roof to movev outwardly a -substantial amount, thereby Vdecreasing'the loadon Vthe compression member E onfthe t-a'nk'sidewall and increasing'the load on the tension member D carried by the center""roof support C. Inthe 'rioofherein shown the area of tbe roof is divided into two curved surfaces, each of whichhas' a different radiusfandV at'the pointl where fsaid curvedfsurfaces'meet or arew `joinedl together, Athe' tangents of said curved surf aces are disposed at lan `angle to a horizontal line as illustrated VinFigre 1 wherein h designates a horizontal line 'passingthroughthe lowest point a of the roof that is not tangential to'either ofthe roof portions A land B, andthe reference characters j and i designates tangents tothe roof portions 'A and B respectively at the klow point a ofthe roof. In Figure l'the' outside angle e between j and -less than 180 degrees-equals 180 degrees vminus f which is the Ainside angle between j and i, and saidinside anglej equals' the angle g between r1 and r2. In such a roof the loads on the two structures thatsupport the roof are etectively stabilized andthe compression 'forces set up in the compression member E bythev peripheral roofportion B are'reduced, thereby enabling a lighter` weight andless 'expensive structural element to 'be used to form the 'compression' member E. This: is clearly illustrated'in Figure 1 wherein it wll`be seen that making the peripheral portion B yofthe roof of considerably smaller radius than the central roof portion A and with the-centers k of the radii of said peripheral portiony locatedat the right of line b1, causes the roof portion B to be disposed at a much sharper downward pitch or 'slope than would b'e the case if the entire roof In Figure 1 the reference character m' `designates the tangent tothek arc of the' roof portion B at the point c where the roof plates of portion B are attached to the structure. Preferably it is of substantially V shape iny cross section and constitutes a substantial portion of the total area of the top surface of the roof. On a 120' diameter roof the member 4 will usually constitute about of the total area of the roof. It may be constructed from a heavy plate bent into the form of a wide V-shaped member whose side portions are sloped considerably steeper than the slope or curve of the top surfaces of the portions A and B of the roof, the circular line where the side portions of said V-shaped member 4 merge lor join -each other being the lowest point of the roof. By making the V of member 4 relatively wide, I obtain a satisfactory factor of safety for maintaining the lowest circle of the roof at the radius for which the roof is designed. For a 120 diameter roof where the radial dimension of the portion B of the roof is 14 feet, I would make each leg or side portion of the V about 2 feet and I would make the depth of the V about 3 inches. This would give aslope nearly the same as the slope where the peripheral portion B of the roof meets the ange F at the top edge of the side wall of the tank.

The plate from which the V-shaped member 4 is made would be 'about`4 feet wide. Figure 8 illustrates another another kind of member that may be used to join the portions A and B of the roof, said member consisting of a V-shaped plate 4a having transverselydisposed stilieners 4b attached to its underside and arranged in spaced relation around the circumference of said member as shown in Figure 9, said stiffeners 4b counteracting any tendency of the V to spread or open up due to the pull of the roof portions A and B on the. side legs of member 4a. Water that collects on the top surface of the roof in the zone of the V-shaped

member

4 or 4a is conducted to the exterior of the tank by one or more drains 11. 4

Any suitable means or mechanism may be used to move the roof diaphragm upwardly into its final position and for supporting it while it is being attached to the center roof support and to the tank side wall, but I prefer to use'hoisting devices that are removably mounted on'the center roof support C and on the tank side wall so that after they have performed their function they can be detached and used in building and erecting other tank roofs. The hoisting mechanism herein shown comprises a plurality of Winches 8 mounted on the lower end portion of the center roof support C and a group of cables 10 that lead upwardly from said winches over pulleys 9 removably mounted at the top of the center roof support and thence downwardly to the center tension ringrD of the roof diaphragm to which said cables are attached as shown in Figure 6. Said hoisting mechanism also comprises a plurality of Winches 8 arranged in spaced relation around the tank side Wall at the lower end of same, cables 7 leading upwardly from said Winches over pulleys 6 mounted in pulley supports 5 detachably connected to the top edge portion of the tank side wall, and thence downwardly from said pulleys to the peripheral compression frame member E of the diaphragm to which said cables are attached.

In practicing my method I prefer to first construct the bottom 2 of the tank and then weld the peripheral edge of the tank' bottom to the lowermost ring of the tank sidewall. The sidewallmay either by built at this time and join together the parts that form the peripheral com# pression ring E of the'roof diaphragm and the member 4V that joins the central and peripheral portions A and B of said diaphragm, the member 4 being arrangedin a level position on the bottom of the tank and the ring E being arranged a slight distance above the bottom of the tank preferably on temporary radially disposed rafters 21.'

supported by temporary blocks 22 as shown in Figure 5. Care must be taken to see that the member 4 is set inwardly a predetermined distance from the ring E and that the radial rafters 21 have the correct downward slope or pitch, in order that the peripheral portion B of the' roof will be of the correct area and will assume a curved' form of predetermined average radius when said periph? eral portion hangs suspended from the top edge of the tank side wall as shown in Figure 7. After said members 4 and E have been positioned correctly, radially disposed roof plates are laid on same with the longitudinal edges 18 of said plates in overlapped relation as shown in'Figure 3. Thereafter the longitudinal edges of the roof plates are welded to each other and the ends of said plates are Welded to the members 4 and E. In constructing the central portion A of the roof diaphragm, the segmental members that constitute the center tension' ring D are assembled and joined together so that the ring' Dsurrounds the roof support C; also a substantially cone shaped member 3 is attached to said ring D to form a portion on said ring to which the roof plates can easily be attached. At this time the ring D rests on supports on thebottom of the tank and is positioned a slight distance above the bottom of the tank as shown in broken lines in Figure 5 and designated by the reference character D. Subsequently radially disposed roof plates areA laid on the member 4 and center ring D in the manner shown in Figure 5 and designated by the reference character A in said ligure.- As each plate is laid, one end is tack welded at 20 to the member 4 and the other end of the plate is tack welded at 19 to the frustro-conical portion 3 of the center ring D as shown in Figure 4. As successive plates are laid with their longitudinal edges overlapping about two inches, these overlapped portions are slidably clamped together atintervals of three to four feet by clamps designated by the reference character 13 in Figure 4. When the complete circle of plates A has been thus assembled4 then the cables 10l of the center hoisting mechanism are used to raise the center ring D to the position shown in full lines in Figure 5 so as to give a properl curvature to the central portion A ofthe roof diaphragm. The top surface of this portion A will have a downward and outward slope from the center ring D, all the way to the member 4 that joins the central portion A to the peripheral portion B and each plate of por-Y tion A will take a sag as indicated by the arrows in Figure 5 between the cord Aa--Ab and the top surface of the plate. To get proper slope of roof portion A, especially near member 4, it is necessary to lift a portion of area B to get a load at Aa. This causes a fairly high compression in member 4. Depending on the surface radialrdimensions desired for area A, the center ring D will have been raised from three to six or even nine feet. As the horizontal radius of A increases, the height necessary to raise ring D increases. The plates of surface A are then securely welded to each other and to the member 4 and ring D and the clamps 13 are removed. The fabrication of the roof diaphragm on the bottom of the tank has now been completed and said diaphragm is now ready to be hoisted into its operative position at the top edge of the tank side wall. This operation is accomplished by turning the winches 8 mounted on the center roof support and r.7 on the tank side wall simultaneously. It is not necessary during this operation that the roof unit be maintainedin exactly the shape in which it was built. I find in practice that if it is so desired,-the"entire roof unit can be raised by using the tank side wall winches only until the periphery of theA roof unit is raised to its final position, WhereuponV the center winchescan be used to raisethe center ring D and set it in'such a position or at such an elevation that the two portions A and B of the roof and the member 4 that joins said portions together, will be disposed in a predetermined relationship with each other, which in the preferred form of my invention herein illustrated means that the central portion A of the roof will be a catenary of a predetermined average radius and the peripheral portion B ofthe roof will be of catenary like form 'but of a different predetermined average radius. If the roof plates of the peripheral portion B are welded while supported on donwwarrdly and inwardly sloping rafters 21 as previously explained, the said portion B will be of approximately frusto-conical shape at the completion of the fabricating operation, but in the operation of raising the roof unit said portion B will flex sufficiently to cause its shape to change to a catenary of a predetermined average radius which is less than the average radius of curvature of the central portion A of the roof whose plates were joined together while hanging in a curved form between the member 4 and the center ring D. After the roof unit has been raised to the top edge of the tank side wall, the peripheral ring E of said unit is welded to the overhanging portion F on the tank side wall. The center hoisting cables are then manipulated so as to adjust the center tensiony ring D of the roof unit at such a height or level that the two portions A and B of the roof will be in a predetermined relationship with each other and the V-shaped member 4 that joins said two portions together will constitute the lowest point of the area of the roof. Thereafter the horizontally disposed beams 12 lare installed on the center roof support C to form a bearing surface for lthe center ring D to rest on. Subsequently the portions of the center roof support that project above the center ring D are cut off and a cover plate 14 is welded to the top side of said ring D so as to reinforce and strengthen same and also close the hole in the center of the roof. Other fittings such as manholes, vent valves, etc. may now be installed in operative position onthe roof, and the hoisting mechanism is then removed and subsequently used in .building other tanks.

As previously explained, if roof portion B is considered an arc of a circle made up of very tine radially disposed elements, fsuch as line wires, reaching from E to member 4, it will be seen that all of these elements pull down throughout their entire length, because they slope downwardly and inwardly throughout` their entire length. These elements in this manner carry the load of the peripheral portion B of the roof. Similarly, conceive the surface A as being an -arc of a circle, similarly constructed of elements that slope downwardly and outwardly from center ring D to the member 4. These elements in this manner carry the load of the central portion A of the roof. The V-shaped member 4 is located in the circle where the slopes of elements composing roof portions A and B meet and hence the elements of said portions A and B lare here sloping in opposite directions. The two curved surfaces above referred to have different radii, and they meet vat an .angle of lessfthan 180 at approximately ythe bottom of the V-shaped member 4 which constitutes the lowest circle a of the roof.

The outer ring E is a continuous series of beams which carry the concentrated vertical loads created by the cables 7. At the same time the downwardly and inwardly directed tensions of the radial elements which' compose the portion B create an accumulated circumferential compression in E. Thus during the operation of raising the roof unit, the ring yE acts both as a series of 'beams and as a `circular compression member. The center ring D is `a continuousrseries: of beams which-carry the concentrated vertical loads .created by the cables 10. ,At-the same time, the downwardly and outwardly directed tensions of the radial elements which compose the portion A create an accumulated circumferential tension in ring D. Thus during this operationringy D actsboth as a series of-beams and a circular tension member.

After ring E has ybeen attached conitnuously to the top edgeL portion o-f the tank wall, E no longer acts as a series of beams to `carry concentrated loads. Hence E now acts as a circular compression member only. This is highly advantageous. While the roof unit is being raised, ring E has vto carry only the dead weight of the roof, about S# per square foot and hence I have strength to spare in E during this operation so that I can also use E as a series of beams as wellas a compression member, but in the completed roof, E must resist roof loads which are four or more times the total load during the hoistingv operation-about 38# or more persqaure foot. Thus by relieving E of doing duty as a series of beams in the completedroof, I greatly increases its strengthto act as a single duty member. This saves a great amount of steel required in E and hence the cost is much reduced. It should be noted that E is the longest circular member of the roof and hence .the saving `of a few pounds of steel per foot of circumference, in the aggregate, amounts to a large. amount. in addition to the above, when E is attached tothe ;tank-sidewall, such joining causes a substantial portion ofthe plate F .which forms the top edge of the tank wall to cooperate with, i. e., act as a unit with E to form .an even strongerscompression member at the top of the tank, which .againsaves more steel and further reduces the cost.

VSince all of the radial elements vwhich'compose peripheral portion B are in tension and sloping downwardly and inwardly from E, all these elements Yhave a vertical component. The summation of all .these vertical components constitutes the load of the roof for portion B. This portion B, of the roof load is, therefore, carried by the sidewall of the tank,.vertically downward as a circular column to the tank bottom or foundation. Since the center ring D `is supported yby beams 12, D continues to act as a `series of beams. This is no disadvantage, costwise, -for the simple reason that D is a member which is very short in circumferential length compared to the ring E. For example, on a -diameter tank, E is 376 long whereas D is only about 31 long. Thus it isseen that the extra steel required in ring- D in order to have it act while in service, simultaneously as a lseries of beams as well as a tensionmember, actually lnecessitates the use of only a comparatively few extra pounds of steel when the total weight of the roof is considered. Moreover, to support ring D from the center roof support C and eliminate the series of beam actions in D would cost much more money and weight of steel. Furthermore, the cover plate 14 co-acts `with ring D to help resist the center tensions of the central roof lportion A. This helps decrease the steel required in D. Thus we see that all parts of this roof are co-acting with other parts in such a way that not only reduces the amount of steel required to build the roof, but makes it a stronger roof at much less cost. Since all of the radial elements which compose portion A are in tension and sloping downwardly and outwardly from D, all these elements have a vertical component. The summation of all these vertical components constitutes the load of the roof for portion A. This portion A of the roof load is, therefore, carried by center ring D and hence by beams 12 tothe vertical posts of the center roof support C, and thence vertically downward to the base G 'upon which the center roof support rests.

In a roof of the type where the tank side vwalll and a center roof supportfcarry respectively certain percentages of the total roof load, it is necessary to hold the lowest circle of the roof at the same radius for all loadings to which .the roof will' besubjected in service, for if the ond, a slight difference of settlement of :,.zwall or of lowest circle of the roof under some live loading or for any other reason should move toward the tank side wall,

then said wall would take a smaller load than designed for it and the center roof support woud have to take a should move towardthe center roof support, then the Qtaukside wall compression member would have to take 1 more load than the one for w 'ch it was designed. In building a roofwhose tcp surface is vin the form o f a continuous, substantially tlat curve, it is almost impossible to predetermineexactly what radius the lowest circle of the roof will assume when erected, and one cannot be sure to what radius the lowest circle of the roof may move under various loadings for reasons such as, First, the variable shortening of the radius of the top edge portionof the tank side wall under live load; Secthe tank side the center roof support; or Third, uneven settling of thetank side wall. It is to guard against 'such contingencies that-I usev a"V-shaped member'4 or 4* of the kind herein shown to form the intermediate ,portion of the roof and to join or connect the two oppo- A sitely sloped center and peripheral portions of the roof, ias this is a positive way aswell as the cheapest way, `best way and easiest way of insuring that the tank side wall and the center roof support respectively, will carry their designed percentages of the total roof load, and 'o'allowances have to be made for unusual conditions. may arise as would be necessary in a roof where the percentages of the roof load could change a substan tial amount. In the tank herein shown the arcs of the top surfaces of the two roof portions A and B meet at an angle less than'180, and the point where said two roof portions meet constitutes the lowest circle of the l t .roof 'as designated by the reference character a in Figure 1 and in the diagrammatic view, Figure l0. ln said view, which is -intended to indicate the forces acting on the above mentioned intermediate lV-shaped connecting member, the horizontal component of tension in the roof portion A' is designated by the arrows S, the vertical component of tension in said roof portion A is designated by the arrow aa, the horizontal component of tension in the roof portion B is designated by the arrows t, and the vertical component of tension in said roof portion B is desigiated by the arrow bb. The 'outer edge of the roof portion A is designated by the reference character Aa and the inner edge of the roof portion B is designated by the reference character Ba. Said Figure l also shows how the tangents to the curves of A and B at Al and Bb meet at an angle which is less than 180. From tests I have made ot roofs of the construction above described, I have found that the V-shaped connecting member which constitutes the lowest circle of the roof, greatly improves the operation of the roof when the roof has a large water load, as said member is stiff radially as well as circumferentially and hence will not allow the roof plates to bend down before the water load reaches such a level that the water load will start running over the top edge of the tank side wall. 'In actual tests I have made of the tank roofs constructed in the manner shown in Figures 4 to 10 inclusive I have found that the stiff V-shaped member a or d, reaching well up on the curves of theA roof, will decrease. A

.substantial amount, the total water load capable of collecting on the roof. Thus it will be seen that in such a roof the Vshaped member which joins the two curved portions A and Bof the roof performs a number of func tions as follows:

(a) As a circular compression member when roof portion A is pulled up into shape ready for welding the plates -jrom which'said portion is constructed. (b) As an aid to the erector, making A- roof load.

v 0 sible to set the lowest circle a of the roof at the proper radius.

(c) As a means for maintaining the lowest circle of the roof at its proper radius for all loadings to which the roof will be subjected in service, thus assuring that the tank side wall and center roof support will carry their predetermined percentages of the total roof l0ad.`

(d) As a means for minimizing or decreasing the sag of the roof under a heavy water load.

(e) As a member' to take compression or excess tension under certain types of live loads on the roof when the roof is in service, and

(f) As a means for interrupting the roof surfaces A and B while said surfaces still have considerable downward pitch. ln other words, the connecting

member

4 or 4a due to its V form, effectively insures that the radius of. the lowest circle of the roof will remain constant and not shift one way or the other and thus maintain the designed percentages of load on the center roof support and tank side wall.

Thus we have the following with the roof in service:

(l) Ring E is in compression only and does not act as a series of beams.

(2) The sidewall of the tank carries its predetermined percentage of the roof load.

(3) Ring D is acting as a tension member and a series of beams simultaneously. l

(4) 'Ihe center roof support C carries its predetermined percentage of the roof load, and` (5) 'Ihe form 'of the element 4"or 4*' that joins the two roof portions A and B is such thatit insures that the tank side wall and the center roof support :will eectively carry their designed proportionate share of the The fact that the roof is assembled' and welded at ground level not only makes the man hours required for building the roof less than in the building of a roof whose plates are joined. together while arranged in an elevated position at the top 'edge of the tankside wall, butalso th following conditions decrease the man hours;

'(a) There is an extremely small amount of framing required .during erection of the truste-conical outer portion B.

(b) There is no framing at all required for assembly of the cepter portion A. v

(c) Men working on the ground work more eicieutly.

(d) Men are safer working on the ground.

(e) Much time is saved because men do not have to climb up and down.

At no point of the roof plates is the unit tension (lbs. per sq. in.) great. Assume a 120 diameter tank in which the radial dimension of peripheral portion B is 14 feet the .radial dimension from' V-shaped connecting member 4 to ring D is 4l feet, and the radial dimension of ring D is 5 feet, and that all of the roof plates for portions A and B are im" thick, except the very small frustoconical portion 3 of the center ring D which is V4" plt. The slope of said portion 3 is 4" in 12". Then the total load on ring D at 38# per square foot (8# dead plus 30# per square foot live) is about 250,000#. The tension then in the frusto-conical portion 3 where it joins ring D is about 2100# per circumferential inch 'of said portion 3. Tension per inch i s 'about 'L if 250,000# X316 equals 2100# per inch.

Since this frusto-conical portion 3 is V4" thick the unit stress is only about 8400# per square inch, compared to 20,000# per square inch allowable.

The tension in the roof plates decreases as the diameter increases since each successive circumference is greater. The tension of the roof plates where they join it easy and posthe tank wall is as follows: Roof plates g" thick; slope .11 2" invl2".;,maximum load on roof portion B177,00 0#. 'I'he tension per inch of plt. where it is welded to the tank wall isabout 240#. Thus the unit stress is about 1280# persquare inch. Tensionperinch is about equals 24.0#.per inch. 'j l Y The vertical load passing in to the top edge portion of the tank wall per inch of circumference .is calculated to be only about 4l# per inch, causing practically. no bending of the overhanging portion F of Athe tank wall to which the peripheralring E of the roof is attached. Usually the .overhanging -portion F .of the tank side wall would .be aM: thick plate.

.Having thus described my invention, what I claim as new and .desire to secure by Letters Patent is the followmg:

i l. A method of building a tank roof having predetermined portions of its area suspended from the tank side wall and a center support respectively, and also having a peripheral compression ring, a central tension n'ng, and roof plates, in which the peripheral compression ring includes a circular member forming a part of the tank side wall and the central tension ring includes a circular structure forming part of the center support; characterized by erecting a roof portion on the tankbottom by providing a plurality of ring shaped frame members Aon the bottom of the tank disposed in concentric relation with each other, and adapted .to form parts respectively ofthe peripheral compression ring of the completed roof 'and the central tension ringnof the completed roof, and; said members having suicient strength for lifting'of the roof portion from the bottom wall of the tank with theroof plates assembled therewith, combining roof plates with said frame members so as t forma roof portion comprising two concentrically arranged arced surfaces of different radii disposed in angular relationshipv with 'each other and attached to said frame members, subsequently after completion'of the side wall ofthe tank, raising said roof portion, thereafter attaching the frame member forming part ofthe compression ring to aportion of the side Wall of the tank to form therewith acdmpletedperipheral Y sion ring providing additional strength in the roof structure to carry Aboth the dead and pleted roof.

, 2. A method of building a tank roof having predetermined portions of its area suspended from the tank sideI wall and a center support respectively, and also having a peripheral compression ring, a central tension ring, andv roof plates, in which the peripheral compression ring in cludes a circular member forming a part of the tank side Wall and the central tension ring includes a circular stxucture forming part of the center support; characterized live loads of the com- -by fabricating a circular member to form a part of the compression ring at a slight elevation from the bottom of the tank, assembling roof plates of the outer roof portion on said circular member in a frusto-conical array extending downwardly and inwardly from said member, fabricating a second circular member about saidcenter support to form a part of the central tension ring with said second circular member positioned slightly above the bottom of the tank, assembling roof plates forming a part of the central portion of the roof by tacking the plates to the second circular member and to the outer roof portion with the plates supported at least in part by the bottom wall of the tank, then raising the 'second circular member a distance to lift the roof plates from the bottom of the tank and impart a sag thereto, thereafter attaching the roof plates permanently in place, and therafter raisingj the roof to its final position and attaching it to the tanky side wall and to the center support respectively.

.References Cited in the tile of this patent UNITED STATES PATENTS 2,221,133 Gladville Nov. 12, 1940; 2,304,354 `Harvey Dec. s, 19422 2,360,222 Gruening Oct. 10, l944 2,554,768 Auen Mayv29, 1951g 2,585,856- orr Feb. 26, 1952; 2,606,684 Wiggins Aug. 12, 1952-' 2,746,137 Wiggins May 22, 1956