US3786606A

US3786606A - Supporting apparatus for vessels

Info

Publication number: US3786606A
Application number: US00137640A
Authority: US
Inventors: M Greaves; T Werner
Original assignee: MCKEE A AND CO
Current assignee: MCKEE A AND CO
Priority date: 1966-01-17
Filing date: 1971-04-26
Publication date: 1974-01-22
Anticipated expiration: 1991-01-22

Abstract

Apparatus for supporting a vessel, such as a blast furnace having a shell, comprising a main frame that surrounds the shell and is connected to and at least partially supports the shell. The supporting apparatus for the vessel also includes diverging legs rigidly connected to the main frame; during construction the lower ends of these legs are supported off-center from the centers of the legs to enable the lower ends of the legs to deflect outwardly by amounts corresponding to the amounts that they would deflect when loaded with the vessel. The legs are thus prestressed before loading.

Description

United States Patent [191 Greaves et al. 7

[451 Jan. 22, 1974 SUPPORTING APPARATUS FOR VESSELS [73] Assignee: Arthur G. McKee & Company,

Cleveland, Ohio [22] Filed: Apr. 26, 1971 [21] Appl. N0.: 137,640

Related U.S. Application Data [60] Division of Ser. No. 811,527, March 28, 1969, Pat. No. 3,630,507, which is a continuation-in-part of Ser. No. 778,883, Aug. 29, 1968, Pat. No. 3,559,972,

which is a division of Ser. No. 520,945, Jan. 17, 1

1966, Pat. No. 3,431,691.

[52] U.S. Cl. 52/223, 248/146 [51] Int. Cl. E046 3/10 [58] Field of Search 248/146, 2, DIG. l, 13;

[56] References Cited UNITED STATES PATENTS 3,431,691 3/1969 Greaves et a1. 52/223 R 6/1952 Franks 248/13 3/ 1956 Rougemont 248/13 Primary Examiner-Edward C. Allen Attorney, Agent, or Firm-Bosworth, Sessions, Herrstrom and Cain [5 7] ABSTRACT Apparatus for supporting a vessel, such as a blast furnace-having a shell, comprising a main frame that surrounds the shell and is connected to and at least partially supports the shell. The supporting apparatus for the vessel also includes diverging legs rigidly connected to the main frame; during construction the lower ends of these legs are supported off-center from the centers of the legs to enable the lower ends of the legs to deflect outwardly by amounts corresponding to the amounts that they would deflect when loaded with the vessel. The legs are thus prestressed before loadmg.

7 Claims, 13 Drawing Figures PATENTEU JAN? 91374 3. 7 86 6 O8 SHEET 1 OF 5 1 SUPPORTING APPARATUS FOR VESSELS CROSS REFERENCE TORELATED APPLICATIONS This application is a division of application Ser. No. 811,527, filed Mar. 28, 1969, now U.S. Pat. No. 3,630,507, which is a continuation-in-part of copending application Ser. No. 778,883 filed Aug. 29, 1968, now U.S. Pat. No. 3,559,972 which is a division of application Ser. No. 520,945, now U.S. Pat.v No. 3,431,691.

BACKGROUND OFTHE INVENTION The present invention relates to improved supporting structures for upright or upstanding vessels, and more particularly to supporting structures for vessels capable columns surrounding the lower portion of the furnace in close proximity to each other and to the lower portion ofthefurnace.

, Such furnace structures have certain advantages in that the upper part of the furnace including the shaft and top supported by the mantle havebeen free to expand. thermally as a unit on heating of the furnace. The downcomer attached to the furnace top also becomes heated during operation of the furnace, so it also expands and contracts with the portion of the furnace above the mantle, thus minimizing difficulties that might otherwise arise from thermal expansion.

However, in such furnacestructures there have been substantial difficulties arising from the differences in the thermal expansions of the supporting columns and the lower portion of the furnace below the mantle. The mantle-supporting columns themselves are not subjected to sufficient heat to cause them to expand appreciably, but the lower portion of the furnace is subjected to high temperature heat; therefore, the lower portion of the furnace tends to expand substantially on heating of the furnace until it bears substantially all of the weight of the furnace above the mantle and the apparatus supported by such portion of the furnace. On cooling, the lower portion of the furnace contracts and the entire load again is transferred to the columns. It, therefore, has necessarily been the practice to make the columns strong enough to support the upper portion of the furnace and apparatus supported thereby, and also to make the lower portion of the furnace strong enough to support the upper furnace portion and such apparatus; this has involved substantial added costs. Furthnmore, the lining of the furnace in the vicinity of the mantle has been susceptible to excessive deterioration because of localized expansion and contraction arising from transfer of the load from the columns to the lower portion of the furnace and vice versa. The expansion joint often provided at this loca- 2 tionto minimize this problemhas, itself, been a source of trouble.

In conventional European blast furnace structures, the lower portion of the furnace including the hearth and bosh, and the upper portion of the furnace including the shaft but not the furnace top, are supported from a massive foundation set into the earth. The furnace top, including the load equipment and downcomers, is supported from this foundation by long posts or columns. This design tends to overcome the above described disadvantage of American-type structures, but

introduces new problems. The bosh jacket is a structural element that supports the shaft of the furnace; consequently, a hot spot in the bosh can impair the support for the shaft; furthermore, the necessity for maintaining the bosh jacket as a structural supporting member increases the difficulties of relining the bosh. This design also makes it difficult to maintain a satisfactory tight joint between the furnace top and the portion of the furnace below the top. Since such portion tends to expand on heating, whereas the columns supporting the top do not expand appreciably if at all, this problem is accentuated when high top pressures are used according to modern practice.

Other problems arise because the downcomer, supported from the columns, expands due to heat while the columns themselves do not expand, and because portion of the charge-distributing apparatus is usually supported by the furnace top and moves as the furnace expands, and a portion is supported from the posts and does not move from thermal expansion, consequently, jamming of distributor parts or gas leakage at the distributor may occur.

As a result of dimensional changes in furnace parts during operation, as due to expansion and contraction of the furnace shell from changing temperatures or pressures, the supporting members in conventional blast furnaces can be subjected to diverse and varying forces. Such forces can cause frequent stress reversals in furnace supporting members. For example, a member may be in tension at one stage of the operation of a blast furnace but put into compression as an adjacent furnace part changes dimension due to a change in heat and/or pressure. Such repeating reversals from tension stress through zero stress to compression stress followed by succeeding reversals through zero stress back to tension stress can promote fatigue failure in the support member. As is well known, a member can fail due to fatigue long before it might otherwise fail due to stress-induced causes.

Furthermore, in conventional American furnace structures, as well as in most European structures, the columns or posts that support the upper portions of the furnaces are so closely spaced in relation to the lower portions of the furnaces, as well as to each other, that they impair access to the lower portions of the furnaces for operations such as tapping, closing the tap holes and removing slag or spilled metal. They particularly impair access to these portions of the furnace by automatic machinery for perfonning these functions. Moreover, since the legs are closely disposed relative to the furnace, they can be damaged by molten metal in the event of break-outs. Furthermore, in both American and Eurpoean furnace structures, it is very difiicult, time-consuming and expensive to line the furnace, particularly the bosh and lower inwall portions which most frequently require lining, primarily because of the difficulties of access to the furnace caused by the closely spaced columns and by the construction of the bosh and hearth portions which must act as supports for the upper furnace portions.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome as many of these problems and disadvantages as are desired. Another object is the provision of support means for an upright vessel, such as a blast furnace, in which stress in a support member can fluctuate but never pass through zero stress. Such a member is always maintained either in tension or compression in accordance with the present invention. Failure due to fatigue in such member may be eliminated.

A further object is to provide an improved system of stabilizing members which, in one form, embrace an upstanding vessel at substantially the same elevation to steady it.

A further object is the provision of gussets to support and reinforce a furnace shell or the like having a refractory lining, by having the gussets extend on the interior of the shell into the refractory.

A further object is to provide a process and structure for prestressing support legs or columns for carrying an upright vessel and its attendant parts, so that the legs are deflected during construction when not supporting the vessel and essentially undeflected while supporting the vessel.

DESCRIPTION OF THE DRAWINGS These and other objects of the invention will be apparent from the following description of the invention in connection with the accompanying drawings in which:

FIG. 1 is a side elevation, partly in section, of a blast furnace embodying the present support means, parts not necessary for the disclosure being omitted for clearness;

FIG. 2 is a transverse section of FIG. 1 on the line 22 to an enlarged scale;

FIGS. 3 and 4 are partial sections generally along lines 3-3 and 44, respectively of FIG. 2, to a still larger scale;

FIG. 5 is a section on line 55 of FIG. 1 and to the same scale as FIG. 2;

FIGS. 6, 7, 8 and 9 are detail sections on lines 6-6, 77, 8-8 and 99 respectively of FIG. 5;

FIG. 10 is a somewhat diagrammatic side elevation of the supporting leg structure, illustrating prestressing of such structure before a load is applied, the deflections of the legs being greatly exaggerated for the sake of clearness;

FIG. 11 is an enlarged, fragmentary vertical section of the bottom end of one of the legs of FIGS. 1 and 10;

FIG. 12 is a section along line 1212 of FIG. 11 and to the same scale; and

FIG. 13 is a fragmentary view, partly in section along line 1313 of FIG. 1 and to the same scale.

GENERAL ARRANGEMENT In the illustrated apparatus, a supporting structure 9 supports a furnace 10. I

The furnace 10 comprises a shaft 11, bosh l2, and hearth portion 13, all enclosed in a continuous steel shell 14 free of sharp bends and lined with suitable refractory material. The hearth portion may be supported by an underlying foundation 16 indicated in FIG. 1, set into the earth, or it may be wholly or substantially unsupported by being suspended, as disclosed by the above-identified related applications. A conventional bustle pipe 22 surrounds the bosh l2 and communicates with conventional tuyeres 23 leading into the furnace. Conventional uptakes 24 are connected to the top of the furnace, which may also house or connect to other conventional equipment, not shown, such as a burden distributor, bell hopper, bells, downcomer, etc.

The structure 9 comprises a generally horizontal main frame, generally indicated at 25, and widely spaced legs 26 that are rigidly secured to frame 25 and supported by base 27 set into the earth. There may also be a working or cast house floor, not shown, at the lower end of the furnace. Frame 25 also rigidly carries an upper auxiliary structure comprising upstanding posts 28 connected to frame 25 and supporting several horizontal-disposed working platforms 29 as well as superstructure 30 and other equipment usually associated with the top of a blast furnace.

FRAME STRUCTURE Main frame 25 surrounds and is spaced from the shaft 1 1 above and adjacent a ring member 31 adjacent the lower portion of the shaft between the shaft and bosh in essentially the same vertical relationship on the furnace as a mantle in a conventional blast furnace. The frame 25 is polygonal in plan and, as illustrated, preferably comprises (FIGS. 1, 2, 3 and 5) four deep horizontal steel beams 32 that are rigidly welded or bolted together at their ends to form a square in plan. Each beam 32, which may be about 10 feet deep on a large furnace, is an l-section girder having (FIG. 3) a wide vertical web 33, generally horizontal top and

bottom flanges

34 and 35, and generally vertical reinforcing stiffeners 36. The top flange 34 of each beam carries two internally laterally projecting portions 37 (FIG. 5) substantially equally spaced along the length of each beam 32 essentially at its third points. Beams 32 may be conventionally fabricated, as by welding from steel plates.

At each of several locations of essentially equal deflection on frame 25, which are essentially at the third points of beams 32 in the illustrative embodiment to provide eight symmetrically spaced locations, there is a relatively large inwardly projecting plate connector member 38 (FIGS. 1, 2, 3, 5) essentially vertically and radially disposed with respect to the axis A of shaft 11, about which frame 25 is essentially symmetrical. Each member 38 is welded at its upper edge to a projection 37, and at its outer edge to web 33, of a beam 32. The inner edge of each member 38 slants downwardly and outwardly from shaft 11.

At the juncture of the shaft 11 and the bosh l2, supporting gussets 39 in the form of upstanding thick steel plates extend between and are welded to the top of ring member 31 and the outside of the shell 14 at the lower portion of the shaft. Preferably the ring member 31 is fixed to the shell of the furnace at a location such that when the furnace is empty or filled, the center of gravity of the furnace is below a horizontal plane containing the center of gravity of frame 25. stiffening

gussets

40 and 41, essentially radial with respect to the shaft 11, also are welded to and extend from the outside of the shaft shell and the top of ring member 31. Lateral stiffeners 42 and 43 (FIGS. 2, 3, 4) are fixed to gussets at their upper and outer edges. Thus, lateral stifi'eners 42 are welded to the outside of the furnace shell and to the upper ends of each gusset 39 and its adjacent gusset 40, while lateral stiffener 43 takes the form of a strip welded to the outer edges of all gussets and the ring member 31.

The outer edge of the ring member is polygonal in plan having straight edges that extend between the gussets 39 (FIG. 2). Gussets 39 therefore extend radially from the furnace shell a greater distance than

gussets

40 and 41. These shapes andrelationshipsof ring member 31 and the gussets provide desirable maximum strengths at the locations of gussets 39 by which the shell is supported.

Connecting means, generally indicated at 44 (FIGS. 1, 2, 3, 5) connectthe members 38 on frame 25 with the gussets 39 on the furnace shell 14. In the embodiment illustrated, means 44 comprises duplicate pairs of elongated connecting members 45. Members 45 of each pair are shown as relatively thick steel struts fixed to the opposite sides of members 38 by bolts 46 extending through both members 45 and member 38, and to the opposite sides of gussets 39 on the furnace shell by bolts 47 extending through the lower portions of the members 45 and the gussets. Members 45 extend diagonally downwardly and inwardly from frame 25 toward the furnace shell and are located at the points of maximum deflection of the frame in essentially vertical planes thatextend substantially radially to the furnace shaft 11, and essentially pass through and are essentially equiangularly spaced about vertical axis A of the furnace.

In such supporting structure, during changes in dimensions of the shell 14 occuring during normal operations, such as expansion or contraction of the shell due to increases or decreases in temperature or internal pressure, the magnitude of the longitudinal stresses on the members 45 fluctuate, butwithout reaching zero stress or undergoing reversal of such longitudinal stress. By longitudinal stress is meant the stress in the members 45 between the locations where such members are attached to the

members

38 and 39. Preferably the members .45 are always in tension; they may be substantially rigid members as shown that are capable of withstanding substantial compressive stresses such as might occur in unusual circumstances such as explosions. As illustrated by FIG. 3, connector members 45 provide substantially the only direct connection between frame 25 and ring member 31 on the furnace shell. Because of their inclination, they cause vertical and horizontal components of tension forces acting on member 31. The parts are so designed, moreover, that the forces to which ring member 31 is subjected by members 45 during normal changes in dimensions of the shell may vary substantially, but they are always in one direction and do not reverse direction.

Additional means for resisting varying forces exerted on the furnace shell at the juncture of the shaft and bosh, and on the ring member 31, due to variations in temperatures of pressures and weights of the furnace due to changing loads include

companion portions

39a, 40a and 41a to

gussets

39, 40 and 41, fixed to and radially extending from the inside of the furnace shell and fixed to the portion of ring member 31 inside the shell.

These inwardly projecting portions are embedded 1 within the refractory lining 14 (FIGS. 2 and 3) which may also have conventional coolers 48. Preferably

portions

39a, 40a and 41a have openings 49 that remove sufiicient area of metal to weaken these projections sufiiciently so that during expansion and contraction of the shell these internally projecting portions can upset or change dimension due to compressive stresses without overstressing the outer gussets. Moreover, any upsetting of these internal projecting portions does not appreciably reduce their reinforcing effects.

COMPRESSION RING MEMBER A compression ring member generally indicated by 51 and shown in the illustrated embodiment as octagonal with sides of equal length and equal angles between the sides, is fixed as by welding to the top flanges 34 of the beams 32 of the main frame 25. Member 51 resists tilting of the beams 32 about their longitudinal generally horizontal axes, from forces arising from the weight of the furnace or from expansion of the furnace shell on heating or from increased pressure. As the furnace shell increases in diameter for these reasons the lower ends of the connecting members 45 tend to move outwardly with the lower portion of the shell of shaft portion 11. This can tend to cause the upper ends of the connectors 45 to move inwardly so that they tend to cause the beams 32 to twist about their longitudinal axes so their upper flanges 34 tend to move closer to the furnace than their lower flanges 35. However, any tendency of the beams 32 thus to twist or tilt is resisted by the ring member 51 which is thus subjected to compressive forces. Since the ring member 51 is a symmetrical polygon with straight sides at the junctures of which connectors 45 are located, member 51 is exceptionally efficient in resisting the forces to which it is subjected. A polygonal member is less expansive to make than a circular one, and is less subject to distortions due to heat or other factors to which it is subjected. Member 51 may be fabricated from relatively thick steel plate welded to the underlying beams 32 of frame 25. The internal corners of the polygon defined by member 51 are enlarged at 52 to provide increased material and strength for connection to stabilizing ties to be described. As shown in FIG. 5, these enlarged interior portions 52 overlie the interior projecting portions 37 of the top flanges 34 of beams 32, which thereby provide further support for member 51 and the stabilizing tie means 53 and 54. Ring member 51 thus acts as an auxiliary frame.

Stabilizing tie means 53 and 54, connected to shell 14 of the furnace and compression ring member 51 around the shell, add lateral stability to the furnace in frame 25. Tie means 53 comprises a generally horizontally extending elongated fastening member 55 welded to the furnace shell 14 and two tie bars 56, each connected at one end. to an end of member'55 and the other end through a turnbuckle 57 to a connector member 58 pivotally connected by pin 59 passing through adjacent portion 52 of member 51 and portion 37 of beam 32. Each tie bar 56 is formed of two spaced

members

56a and 56b, (FIG. 6). Tie means 54 is similar, comprising an elongated fastening member 61' welded in an essentially horizontal position to the furnace shell; this member has its end portions forked at 62 to receive and be pivotally connected to one end of each of two tie bars 63. Each bar 63 passes between the members 56a and .56bof a crossing tie bar 56 of the adbuckle 64 to a connector member 65 that is pivotally connected by a pin 66 to adjacent portion 52 of member l and portions 37 of a beam 32. Preferably the stabilizing tie means 53 and 54 surround the furnace shaft 11 and are essentially at the same elevation, as is made possible by the crossing of tie bars 56 and 63, so that the lateral stabilizing forces acting between the frame 25 and the shell fall essentially in the same horizontal plane located above the center of gravity of the furnace and that of frame 25. Furthermore, each tie means 53 and 54 and their tie bars and associated turnbuckles and connector members extend essentially tangentially of the furnace shell, and the forces acting between the shell and frame 25 through the tie means are essentially tangential forces. The four tie means 53 shown essentially define a first square, while the other tie means 54 define another square intersecting the first square and displaced 45 angularly. Each square thus is a polygon of half the number of sides of the polygons defined by the member 51 and the supporting gussets 38. The lengths of the tie means can be adjusted as necessary by

turnbuckles

57 and 64, even while the tie means are in place.

LEG STRUCTURES According to another aspect of the present invention, the inclined legs 26 that carry the frame 25 of the supporting structure 9 are, prior to loading of the supporting structure, first prestressed by having the lower end of each leg moved outwardly from its initial unstressed position in a direction and by an amount essentially corresponding to the direction and amount that the lower end of the leg would move outwardly from its unstressed position if the supporting structure 9 of which the leg forms a part was subjected to a load corresponding to the furnace, so that the legs are deflected during prestressing as exaggeratedly indicated by the full lines in FIG. 10. The lower ends of the legs are then secured in such position. Supporting structure 9 is then loaded with the furnace so that the legs 26 assume positions in which they are essentially undeflected, as shown in broken lines in FIG. 10 and in full lines in FIG. 1. The legs may thereafter be filled with poured concrete which is allowed to solidify; the concrete after it has been hardened and cured stiffens the legs 26 and acts to maintain them in their undeflected conditions under load, in which conditions they have their maximum strength.

According to the present invention, this outward location of the lower portions of the legs to achieve the desired prestressing is facilitated by initially temporarily supporting each leg during construction, after the legs have been fixed rigidly to the frame 25, at a suitable location off-center from a line that is parallel to each leg at its lower end portion thereof and that passes through the point at the bottom of the leg at which the force resulting from the load on the leg would be concentrated; with a leg of circular or other symmetrical cross section about a center, as shown, such line is the centerline of the lower portion of the leg, and will for convenience be referred to as such below. The bottom of the leg is so supported off-center while the bottom of the leg is located outwardly the desired distance in the desired direction to put the desired prestress in the leg. The lower ends of the legs are then locked in such positions, and concrete or other supporting means is inserted under the bottom of the leg'to take most or all of the load that is carried by the leg and represented by its proportion of the weight of the supporting structure 9 and the furnace.

A shear and a bending moment is temporarily applied to the lower portion of each leg during such prestressing during construction, the shear being caused by the outward movement of the above described lower portion of the leg, and the bending moment being caused by locating the temporary support of the leg off-center from the center line of the leg. The direction and amount by which the bottom of the leg is supported offcenter is calculated so that such shear and bending moment are eliminated when the supporting structure 9 is fully loaded with the weight of the furnace.

More specifically, in the illustrated apparatus, the four legs 26 are rigidly connected to frame 25 at the four corners thereof as by welding or bolting, the legs extending and diverging equally in a downward radial direction from the vertical axis A of the furnace; the legs in a major portion of their lengths are of generally circular cross section and hollow, and quite limber until loaded and filled with concrete that hardens. FIG. 10 shows diagrammatically in full lines the bowed dispositions of the legs 26 when they are prestressed but not loaded, by having their lower ends displaced outwardly from the axis A of the furnace to the positions they are calculated to assume under full load. Under load, the horizontal beams 32 between the legs deflect and thus cause the rigidly attached upper ends of the legs to have an outwardly directed bending moment which essentially removes the prestress deflection in the legs, so that there is no appreciable deflection remaining in the legs after loading and the legs are straight and can develop their maximum strength, as shown by the broken lines in FIG. 10.

FIGS. 11 to 13 show preferable means according to the invention for supporting the lower ends of the legs 26 off center and moving them outwardly to prestress them as described. At the lower end of each leg there are internal reinforcing

plates

67 and 68 that extend upwardly from the bottom of the leg for a substantial distance. Plates 67 extend across the interior of each leg at each side of axis X of the leg, preferably being welded into slots in the leg wall 69 (FIG. 12) while cross plate 68 extends at right angles to plates 67, fitting and being welded in slots in plates 67 and in the leg wall.

The lower end of each leg 26 has a strong steel transverse flange 71 fixed to the bottoms of the leg wall and the plates. The flange has elongated openings 72 for anchor bolts 73, two such openings being located on the side of the flange nearest furnace axis A and six being located on the opposite side of the flange toward which the lower end of the leg is moved in prestressing. A ball portion 74 of hardened metal, somewhat greater than a hemisphere, is fixed to a base plate 75 welded on the underside of flange 71 at a location such that axis Y passing through the center of portion 74 is parallel to axis X of the leg 26 and displaced by a predetermined distance Z toward furnace axis A.

During erection, the ball portion of each leg seats in a mating socket 76 of a temporary adjustable base 77 located beneath flange 71 in the lower portion 78 of a recess 79 formed in permanent base 27. Temporary base 77 comprises a slidable member 80 carrying socket 76. Member 80 is slidably mounted in a guideway 81 on temporary fixed base member 82, defined by fixed side ribs 83 and adjustable shims 84 held in place by bolts 85, that properly laterally locates and guides member 80 for movement in the desired direction of movement of the lower end of the leg. Member 82 also has fixed end shoulders 86 and 87.

Member 82 is temporarily supported on three welded legs 91 that have threaded into them adjusting bolts 92 bearing against metal bases 93 resting on the bottom of recess 78, which has a suitably inclined and shaped bottom surface for the purpose. Bolts 92 and their bases 93 permit the member 82, before it supports its associated leg 26, to be mounted in recess 78 with considerable accuracy as to a predetermined lateral location, elevation and inclination.

During initial construction, the temporary base 77 for each leg is installed as accurately as possible utilizing the adjustability provided by the legs 91, bolts 92 and bases 93. Each base 77 is then grouted firmly in place by concrete 94 (FIGS. 11, 13). After hardening of this concrete, each member 80 is then installed, being accurately located in its lateral position by insertion of proper'shims 84; shims 88 are then installed adjacent shoulders 86 to limit properly the lateral outward'movement of the lower ends of legs 26. The legs 26 and the remainder of supporting structure 9 are then erected; at this time the ball portion 74 of each leg is seated in socket depression 76 of its member 80, the flange 71 being installed so the previously fixed anchor bolts extend through its slots 72. The direction and amount of the off-center distance Z, identical for each leg, has been calculated as discussed previously. The lower end of each leg is moved outwardly in guided movement of slidable member 80 in fixed member 82 for the full prestressing distance until limited by shims 88, such movement being assisted as necessary by forcing a movable wedge 95 into the space between slidable member 80 and stationary wedge 96 adjacent shoulder 87 of base 82. The temporary support of the legs on the ball and socket joints permits the lower ends of the legs to tiltor swivel as necessary.

.After the lower portions of the legs haveall been moved to the desired prestressing position indicated-in broken lines in FIG. 13, nuts 97 are partially tightened on anchor bolts 73 to hold the legs in proper position. The space under the flange 71 is then ompletely filled in with concrete grouting material 98 shown by broken lines; afterthis material has hardened, the nuts 97 are fully tightened to lock the lower ends of thelegs 26 in desired displaced position. The legs are thus largely and if desired completely supported by the flanges 71. After the supporting structure 9 is fully loaded, there is no prestress remaining in the legs 26, and no shear or bending moment at the lower portions of the legs.

If desired, before or after installing the furnace shell, the legs can be filled either fully or for a major portion of their lengths with concrete, preferably of a type that does not shrink, to stiffen the legs. Holes 99 (FIG. 2) may be used for this purpose.

in the illustrated application the parts are so designed that the ball portions 74 and slidable members 80 at the lower ends of the legs move in inclined paths essentially normal to the axes X of the legs during prestressing; this is made possible by the inclined position of the guideways 81. The flanges 71 are also essentially normal to the axis of the legs. Such inclined movements and inclined relationships of the flanges are preferable, since they provide less bending moments in the legs during prestressing than if the members 80 and ball portions 74 moved in horizontal paths, and since the positions of the flanges 71 normal to the axes X essentially eliminate shear and bending moments in the legs after the legs are largely or fully supported by flanges 71. Lateral forces could be present if the flanges were not normal to axes X.

The concrete in the legs, after it has hardened and cured, stifl'ens the legs 26 and acts to maintain them in their undeflected conditions, in which they have their maximum strength. This is particularly important since the frame structure as initially designed has deep, stiff cross beams 32, while the legs 26, while strong enough to support the load of the furnace even before the addition of the concrete, are relatively limber since they are made of steel and capable of being deflected in the prestressing operation. The addition and curing of concrete while the legs are in their straight or undeflected positions increases the stiffness of the legs and their resistance toward bending.

The concrete in the legs also adds substantial mass to the large legs. This large added mass and the resistance of the concrete to compressive forces provides added protection against damage from impacts on the legs, thus adding to the safety of the structure. The mass of the concrete also acts to substantially absorb and dissipate the energy of either steady or transient otherwise harmful vibrations to which the legs or the furnace structure as a whole could be subjected. Concrete thus set in each leg can also act as a high capacity heat sink that can absorb and transmit away from a point of localized exposure on the leg heat from hot metal, slag or coke that might approach or contact the legs.

While four legs of circular cross section are shown, one at each corner of a four-sided supporting frame, supporting frames of different shapes, preferably polygonal, supported by a different number of legs may be used, and the legs may be of cross sections other than circular, such as polygonal cross sections. In any event, the number and cross section of the legs should be such that adequate support and stability are provided. It appears that for most, if not all, uses four legs and a square-sided supporting frame are most advantageous from .the standpoints of stability, adequate support, economy and cost. While the illustrated legs are diagonally inclined for increased stability of the furnace structure, they may be vertically disposed, if desired.

According to the present invention, an upright vessel may be adequately and safely supported by a strong,

' stable supporting structure in which stresses are efficiently distributed. Studies have indicated that even if one of the legs of the illustrated embodiment should be damaged or eliminated, the three remaining legs can safely support the entire structure. Furthermore, studies also indicate that even if one of the illustrated eight sets of connecting members should be damaged or destroyed, the vessel would still remain safely supported in an upright position. These studies indicated that the redistribution of loads can result in stresses greater than normal, but still within safe margins. The use of thedescribed stabilizing ties was found to be particularly helpful in maintaining steady support of the vessel under such conditions.

Other modifications will be apparent to those skilled in the art. It is intended that the patent shall cover, by suitable expression in the appended claims, whatever features of patentable novelty reside in the invention.

What is claimed is:

1. Prestressed supporting structure for supporting an upright vessel comprising a generally horizontally disposed frame and spaced downwardly extending legs supporting the frame and rigidly connected at their upper ends to said frame, said legs being essentially straight when unstressed and when fully loaded, said legs being prestressed by being bent by displacement of their bottom ends; and means prestressing said legs before loading of said supporting structure with a load including said vessel so that the bottom of each leg is displaced and held in a direction and by an amount essentially corresponding to the direction and the amount said bottom of said leg would move if said supporting structure was fully loaded with a load including said vessel and so that the leg is bent, said means comprising means supporting each of said legs from the bottom of the leg, before loading of said supporting structure, at a location that is off-center of the point at the bottom of said leg at which the force resulting from the load supported by the leg would be concentrated, said location being off-center in a direction extending opposite to the direction at which the bottom of the leg is displaced and off-center by a distance such that after the supporting structure is fully loaded there is no prestress remaining in any of the previously prestressed legs and no shear or bending moment at the bottom of any such leg.

2. Apparatus of claim 1 in which each of said legs diverges outwardly from said frame in a direction radial to a generally vertical axis symmetrical to said frame.

3. The apparatus of claim 1 in which each of said means supporting said legs comprises a ball portion rigidly mounted on the bottom of each leg, and a socket portion that receives ball portion in mating contact and is supported from below.

4. The apparatus of claim 3 comprising means providing guided movement of said socket portion along the direction in which the bottom of said leg moves during said prestressing.

5. The apparatus of claim 4 comprising means for limiting movement of said socket portion to an amount predetermined to provide the desired prestressing of the leg.

6. The apparatus of claim 4 comprising means for locking the lower end of each leg in place after it has been moved in a direction and by said amount to cause an prestressing.

7. The apparatus of claim 4 comprising means for positively moving said socket portion in said direction.