Abstract:
Tanks for storing materials, especially liquid and semi-liquid materials. The tank wall is formed of a plurality of arcuate panels, each fabricated from vertically stacked precast concrete panel sections, which are joined by vertical pilasters, each pilaster formed from precast concrete pilaster sections. The wall is prestressed by tensioned tendons disposed on the periphery thereof. Each of the pilasters are supported by a separate footing and the ends of the arcuate panels are likewise supported on the footings. The footings are interconnected by a novel stabilizing structure to withstand seismic loading. These as well as numerous other novel structural features provide for a storage tank of modular construction, which is strong, stable and versatile; which may be constructed in a facile manner; and which may, if desired, be easily dismantled for relocation.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to storage tanks which may be used to store liquid or semi-liquid substances. Although a tank constructed according to the principles of the invention may be utilized for storing a wide variety of materials, it is particularly adaptable for use as a farm manure bank. As the price of artificial fertilizers rises, it has become increasingly advantageous for farmers to store manure for subsequent soil fertilization. A number of storage tank structures have been available for use as manuare banks; however, they have been found to be unsatisfactory for a variety of reasons, such as necessitating expensive equipment and/or skilled labor for construction; unsafe in seismically active locations; inability to enlarge the capacity of the tank or relocate the tank; susceptable to corrosion failure. 
     The preferred embodiment of the storage tank according to the present invention includes a plurality of arcuate wall panels, each formed of a plurality of superimposed precast concrete panel sections, joined end to end by vertically extending pilasters to form a cylindrical tank wall. The tank is versatile due to the modular construction thereof; i.e., the height of the tank wall is determined by the number of superimposed panel sections which are utilized. For example, if a fifteen foot high tank is desired, the wall may be constructed of panels comprised of three superimposed panel sections, each section of five foot height. Further, if it is subsequently desired to increase the capacity of the tank by increasing the height of the tank wall to, for example, twenty feet, this can be achieved by the simple addition of one five footh high section to each wall panel. The tank wall is supported in a novel fashion by a plurality of circumferently spaced concrete footings located beneath each vertical pilaster. The footings are formed separate from the tank floor but are interconnected through radially directed spokes to facilitate the capability of the tank to withstand a greater degree of seismic loading than was heretofore known. The tank floor may be formed from a poured-in-place concrete slab after construction of the tank wall, eliminating the need for the construction of a circular form, or the floor may be fabricated at least in part from precast concrete elements. 
     The cylindrical wall of the tank if prestressed in anticipation of the forces generated by the material to be stored by the provision of vertically spaced wires or tendons tensioned around the tank periphery. The vertical spacing of the tendons is varied according to the computed force load along the vertical extent of the wall and the tendons are secured to two diametrically opposite stressing pilasters. The possibility of progressive failure of the tank due to implosion forces in the event that a single panel section should fail is negated by the fact that the pilasters are post-tensioned vertically and capable of resisting implosion due to a sudden emptying of the tank due to failure of one of the sections. If such an event should occur the tank will be repairable rather than totally demolished. 
     It is therefore the primary object of the invention to provide a storage tank having a novel modular construction which is versatile in utilization, structurally sound, and is facile and economical in fabrication and relocation. 
    
    
     This as well as other objects and advantages will become more apparent upon a reading of the hereinbelow described preferred embodiment of the invention in conjunction with the drawings wherein: 
     FIG. 1 is a perspective view of a tank constructed according to the principles of the invention; 
     FIG. 2 is a top plan view of the tank; 
     FIG. 3 is an enlarged vertical cross section taken along line 3--3 of FIG. 2; 
     FIG. 4 is an enlarged vertical cross section taken along line 4--4 of FIG. 2; 
     FIG. 5 is an enlarged horizontal cross section of a portion of the tank wall, including a non-stressing pilaster; 
     FIG. 6 is a view similar to FIG. 5 showing a portion of the tank wall including a stressing pilaster; 
     FIG. 7 is an enlarged vertical cross section of a portion of one preferred embodiment of the tank floor taken on line 7--7 of FIG. 2; 
     FIG. 8 is an enlarged vertical cross section of the preferred embodiment of the tank floor taken on line 8--8 of FIG. 2; 
     FIG. 9 is an enlarged vertical cross section of the preferred embodiment of the tank floor taken on line 9--9 of FIG. 2; 
     FIG. 10 is a side elevation partly in section of an alternate footing structure; 
     FIG. 11 is a top plan view of the footing structure of FIG. 10; 
     FIG. 12 is a side elevation of the wall area adjacent to the tank outlet port; 
     FIG. 13 is a section taken along line 13--13 of FIG. 12; 
     FIG. 14 is a schematic plan view of an alternate embodiment of the floor structure; and, 
     FIG. 15 is a schematic bottom view of an alternate stabilizing substructure. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the drawings, the construction of a tank according to the teachings of the invention is illustrated. It is pointed out that while a tank of approximately 80 feet in diameter and approximately 20 feet in height is contemplated, the drawings do not reflect these proportions for the reason of clarity in description. 
     The tank 10 is comprised basically of a cylindrical wall 12, a floor 14 and a plurality of vertically spaced tensioned wires or tendons 16 around the entire periphery of the wall 12. Wall 12 is comprised of a plurality of wall panels 18, each identical in construction and fabricated from a plurality of vertically stacked precast concrete panel sections 18a, 18b, 18c, 18d (FIG. 3). Each of the panel sections 18a, 18b, 18c, 18d of each wall panel 18 is identical to the others and is sized to require a minimum of panel sections to complete the tank while being conducive to delivery and placement with only light duty contruction equipment. The panel sections each contain interior metal reinforcement 19 in accordance with well known engineering practices. 
     As shown in the drawings, the panels 18 are joined end to end by vertical concrete pilasters 20. The adjacent ends of panels 18 as well as each pilaster 20 are supported on an individual respective concrete footing 22. As shown in FIGS. 1 and 4, the footings and wall panels are buried beneath the surface of the earth a sufficient distance so that the ground beneath will not freeze and apply an upward force on the tank wall. Pilasters 20 are each constructed of vertically connected identical pilaster sections 20a, 20b, 20c, 20d (FIG. 4) which are each of precast concrete with metal reinforcement 21 (FIG. 5) and are each of equal height with the panel sections 18a, 18b, 18c, 18d. Each pilaster section is provided with a pair of radially spaced, vertical bores 22 therethrough, each of which contain a metal connecting rod 24 for securing the bottom pilaster section 20a to the subjacent footing 22 and the superimposed pilaster sections 20b, 20c, 20d to the respective adjacent ends thereof. Preferrably, the connecting rods 24 are of the type known as Dywidag threaded bars which may be coupled by internally threaded sleeve connectors schematically shown at 26. It is noted that the lowermost connectors 26 are connected to the exposed upper end of respective threaded bars 27 which are anchored in concrete footings 22. After assembly of the pilasters the connecting rods 24 are post-tensioned in a conventional manner. 
     The pilasters 20 all have a substantially I-beam cross section with an internal flange portion 28, an external flange portion 30 and a midportion 32 joining the internal and external portions. FIGS. 4 and 5 show a typical non-stressing pilaster including a plurality of equally vertically-spaced, metal-lined, horizontal cross bores 34. Cross bores 34 allow unencumbered passage therethrough of tendons 16 and are positioned flush with the external surface of wall panels 18. As shown in FIG. 4, the spacing of tendons 16 is progressively increased from the bottom of the tank to the top due to the greater load forces experienced by the wall at the bottom when the tank is in use. 
     FIG. 6 shows one of two diametrically opposed stressing pilasters 20s which have a slightly modified cross bore design for the purpose of tensioning and securing tendons 16 during construction. In stressing pilaster 20s there are provided two angled cross bores 34a and 34b at the approximate level of each of the flush cross bores 34 in the non-stressing pilasters. Cross bores 34a and 34b are angled in opposite directions with respect to the external surface of the wall panels 18 in order to accommodate the ends of tendons 16 as they are pulled outwardly by hydraulic jacks, or the like, during tensioning of tendons 16. After tendons 16 are tensioned with sufficient force serrated wedges 36 are inserted in the bores 34a, 34b and hydraulically seated to hold tendons 16 and thereby prevent the withdrawal thereof from the bores 34a, 34b. Thereafter, a common grouting material 38 may be applied as shown in FIG. 6 to protect the anchorage. Also, FIG. 6 illustrates that grouting 38 may be utilized to provide a liquid tight seal between wall panels 18 and pilasters 20 at all locations if desired. It is noted, however, that in the case of manure storage, the manure will harden to self-seal the crevices between the vertically stacked wall panel sections and other abutments, if leakage should begin. 
     In the embodiments of FIGS. 2, 7, 8 and 9, tank floor 14 is a poured-in-place concrete structure entirely formed within the confines of the tank wall 18. Floor 14 includes an integral stabilizing structure having radially-directed, elongated struts or spoke portions 40 which extend between a respective footing 22 and a depending central hub portion 42. Internal metal reinforcement 44 connects each footing 22 with the metal reinforcement 45 of hub portion 42. This construction provides for an extremely stable structure which is capable of withstanding greater seismic loading by helping to maintain the circular profile of footings 22 and which helps prevent the tank wall from deforming due to lateral loading. 
     FIG. 9 illustrates a tank bottom inlet port 46 having a thickened annular wall 48 integral with floor 14. Inlet port 46 includes annular metal reinforcement 49 and may be connected to an underground pipe in any conventional manner for the introduction of material into the tank. 
     FIGS. 10 and 11 show a modified form of footing structure 22a having four depending piers 50 for providing additional support in geophysically poor areas. Each of the piers is eighteen inches or less in diameter to facilitate the drilling of pier bore holes into the ground with standard, easily obtainable rural boring machinery. Also, FIG. 10 suggests an alternative reinforcing structure including an external anchoring member 51 for post tensioning metal bar 44a running through spoke 40 and footing 22a. 
     FIGS. 12 and 13 illustrate the structure of a tank outlet port 52 in the wall 18 of tank 10. Outlet port 52 includes a bore 54 in the tank wall 18 and a metal member 56 having a central passage 58 coaxially located with respect to bore 54. Member 56 includes a peripheral flange 60 which may be secured to the exterior surface of wall 18 in any well known manner and an outwardly extending lip 62 which acts to spread the tendons 16, which would normally pass across the bore 54, both above and below the bore 54. An outlet pipe (not shown) may be connected to the outlet port 52. Due to the fact that the outlet port must be located at the bottom of tank 10, it is necessary to provide a frost wall 64 below tank wall 18 at the location where the ground (shown in dotted line in FIG. 12) is recessed. Frost wall 64 extends deep enough beneath tank wall 18 to prevent surface ground freezing from applying an upward force to tank wall 18. 
     FIGS. 14 and 15 schematically illustrate other tank floor embodiments. In FIG. 14 the tank floor 14a is shown as constructed of precast concrete sections 66 of various trapezoidal configurations and a central octagonal precast concrete section 68; all sections 66 and 68 interfit to form the main portion of continuous floor 14a. The peripheral areas between sections 66 and tank wall 12 is filled with poured-in-place concrete. The sections 66 are post-tensioned to provide for a strengthened floor structure by means of tensioned rods 70 extending from peripherally alternate footings 22, for example, from footing 22x to footing 22y through passages in the precast concrete sections 66. It is noted that any combination of the section configurations 66 shown in FIG. 14 will produce a satisfactory tank floor. For example, the tank floor may be comprised entirely of sections having a configuration indicated by numeral 66a, or entirely of sections having a configuration indicated by numeral 66b, or any interfitting combination of the configurations illustrated. 
     FIG. 15 shows a stabilizing substructure for the floor embodiments taught by FIG. 14. The stabilizing substructure consists of a plurality of precast concrete spokes 40a extending between a respective footing 22 and a central annular reinforced concrete member 72. A metal reinforcing rod 74 running longitudinally through each of the spokes 40a is tensioned between a respective footing 22 and member 72 by means of a conventional anchoring nuts 74a and 74b placed on the ends thereof. 
     It is contemplated that the structures illustrated in FIG. 15 or FIG. 2 may also be utilized in conjunction with an overlying liquid-impervious sheet material (not shown) to produce another acceptable tank floor structure. If desired, the liquid-impervious sheet may extend up the tank wall to seal same and be supported by means on top of the tank wall. This would eliminate the necessity for a full concrete floor structure, and the precast spokes 40a will maintain dimensional stability and the tank&#39;s capacity to resist seismic loading. 
     It is evident that according to the application of the tank, it may be utilized with or without any of various roof or cover structures. In the case of a manure bank, the manure forms an upper dried crust which acts as a floating cover eliminating the need for a tank roof construction. 
     The fabrication of a tank according to the principles of the invention is relatively simple. After the footings 22, which may be precast or poured-in-place, are placed in a circular pattern, the desired number of pilaster sections 20a through 20d are secured to the respective footing and to each other by means of connecting rods 24 and sleeve connectors 26. An equal number of wall panel sections 18a through 18d are placed between peripherally adjacent pilasters 20, adjacent ends of wall panels 18 being supported on footings 22. Thereafter, tendons 16 are threaded horizontally through selected cross bores 34 of the non-stressing pilasters, and the ends of tendons 16 are tensioned simultaneously from both ends at any one level through bores 34a and 34b of diametrically opposed stressing pilasters 20s and secured therein. Thereafter, any of the various floor structures described hereinabove may be fabricated within the confines of the tank wall along with the appropriate stabilizing substructure. Again, it is stressed that the tank wall itself provides the form for the poured concrete of floor 14. If it is subsequently desired to increase the tank capacity, it is merely necessary to add one or more layers of pilaster and wall panel sections to the top of the tank and pre-stress the additional portion in like manner. It should also be understood that a tank may e constructed to a height equal to only a single pilaster and wall panel section. 
     If it is desired to relocate a constructed storage tank as hereinabove set forth, it is clear that after the tensioned tendons have been detension, the wall structure can easily be dismantled and the same modular concrete materials utilized to form the tank wall in the new location. 
     Due to the fact that only concrete is exposed to the material stored, the tank is not subject to corrosion and failure resulting therefrom. Also, if one wall panel should crack or otherwise fail, the majority of the remaining panels will remain intact as a result of the independent pilaster support structure, thus the tank is not subject to progressive failure. 
     It can thus be appreciated that the novel modular construction described hereinabove produces an economical tank which is structually engineered for maximum strength and stability while requiring a minimum of labor and equipment for construction; it can withstand seismic loading and is not subject to progressive failure; it is versatile in application since it is non-corrosive; it may be easily modified to increase the volume thereof and may be readily dismantled and relocated if desired. 
     Inasmuch as numerous modifications may be made to the construction of the present invention without departing from the spirit and scope thereof, it is requested that the scope of the invention be determined solely by the claims appended hereto.