US 2976875 A
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March 28, 1961 HOFFMAN 2,976,875
ANCHORING MEANS Filed June 16, 1958 F/G.] F/G.2
2 W INVENTOR ROBERT/MI CHA EL HOFFMAN BY Ca ds: W
ATTORNEY Elite AN CHORING MEANS Filed June 16, 1958, Ser. No. 742,208
1 Claim. (Cl. 135-1) This invention relates to a method of anchoring elements to the ground and more particularly to an improved method of anchoring inflated'housings and other three-dimensional structures to the ground to provide stability during periods of applied high stress such as in a Windstorm.
It is known that hemispherical domes made of film or substantially gas-tight fabrics may be inflated to serve as structures for housing equipmentor personnel and maintained in the inflated condition by continuously operating pumps; Even with an inside ground cloth sewn to the tent to prevent air leakage, however, there is a problem of securing-the structure to the ground to hold it in place during a wind. Also there is a natural tendency for an inflated structure to become spherical and this tendency causes the periphery of an unsecured hemispherical enclosure to lift from the ground. The anchorage 2,935,875 Patented Mar. 28, 1961 tion an inflatable structure anchored to a base such as the ground or other relatively immobile surface. Figure 8 illustrates how an object such as an airplane may be anchored to a ship deck or other suitable surface.
More specifically referring to Figure 1, inflatable struc ture 1 is in gas-tight attachment to anchoring member 3 at 2. Anchoring member 3, which in this preferred embodiment is a flexible sheet material, lies substantially flat on the surface of base 4 and forms a substantially gas-tight seal with base 4 along a line, indicated by point 7, running outside of the line of attachment between structure 1 and anchoring member 3 which is indicated in Figure 1 by point 2. Vacuum pump S'is connected toth'e compartment formed by sealing the periphery of anchoring member 3 to base 4 and is of suflicient capacity to remove gas from this compartment sufficiently faster than any leakage of gas into the compartment so that gas pressure within the compartment is maintained sufiiciently'below the gas pressure exterior to both the compartment and structure 1 to prevent anchoring member Iifrom being removed from base 4 by forces acting upon structure 1. Inflating pump 6 serves to maintain sufiicient gas pressure Within structure 1 to keep it inflated at the desired pressure notwithstanding any leakage of gas-from structure 1. t Figure 2 shows an inflated structure having reinforcing members 9 at the base thereof so that the walls of structure 1 may be maintained substantially vertical without exerting undue stress upon the point of attachment to anchoring member 3. Reinforcing members 9 which are attached to the bottom edges of structure 1 are subof inflated structures has been a very diflicult problem,
particularly for large structures, some of which may be 400 feet or more in diameter.
It isan'object of this, invention to provide structures which-are anchored to theground with sufficient tenacity to Withstand ordinary forces of nature tending toraise' or move said structures. A more specific object is to provide an improved method for anchoring gas inflated structures-and other objects to azbase. 'It is also an objectto provide apressure compensating means for creating and maintainingsubatmospheric pressure between an inflated structure and'the ground. Other obiectswill appear from the description of the invention given below.
This invention provides a structure comprising in com bination an object, a base to which said object is anchored, an anchoring member attached to the object and located intermediate the-object and the base, the anchoring member being in substantially gas tight sealing contact with said base, aconfined layer of gas at a pressure lower than atmospheric. pressure intermediate said anchoring member and said base, and pressure adjusting means-connected to the-confined layer of gas to continuously maintain the pressure of said confined layer of gas at less than atmospheric pressure. According to this invention an object is anchored to a base by attaching an anchoring member to said object, placing the anchoring member on the base to provide gas tight sealing contact with said base, and providing a confined gas layer of lower than atmospheric pressure gas intermediate said anchoring'memberand said base as by connecting a pressure stantially rigid members oriented athwart the edge of the base of structure- 1', as shown in the plan view of Figure 3, and are positioned beneath anchor member 3 so that the pull exerted by thewalls of inflated structure t on anchor member 3 is distributed transversely over a substantial portion of anchor 3 rather than being concentrated on the line of attachment 2. The dotted lines in Figure 2 show the assumed shape of an unsupported airfi'lle'dround balloon of the size of structure 1.
Figure 4 illustrates a particularly useful embodiment of the invention as applied to the anchoring of inflatable structures to earth. Anchormember 3 in this embodimerit-is a flat planar doughnut-shaped member having a mean diameter substantially equal to the diameter of structure 1 upon inflation and the structure 1 is sealed to;anchor member 3 along this line 2 as indicated in Figures 4-and 5. Anchor member 3 is sealed to base 4 both along its inner and outer circumference as indicated by the points'7. Upon evacuation ofthe compartment 8;f0rmed by sealing anchor member 3 to base 4, anchoring of great strength is obtained because the center line of-the doughnut-shaped compartment from which gas is evacuated'lies directly beneath the point of attachment of; structure 1 to anchor member 3 that is at seal 2, where the greatest stress is exerted on the anchor member.
Figure 5 shows a plan view of the anchored inflated structure of Figure 4 with the inner and outer diameters 0 of anchoring member 3 indicated at'7 and 7, r especadjusting means to said confined layer, and maintaining a pressure differential between said layer of confined gas and the atmosphere or other gas above the anchoring member and object suflicientlygreat to provide the'anchoring strength desired. The invention is particularly useful for anchoring inflated structures to the earth but is useful for anchoring any object, particularly objects of great weight or size suchas an airplane, building, etc., to the earth or other relatively stable base.
The drawings illustrate specific embodiments of the tively, and the seal between structure andanchoring invention. Figures 1 through 7 show in schematic.sec-' doughnut shaped andis attached at its base to anchoring member 3 in a gas-tight seal extending entirely about the periphery of the doughnut. .Roof member 12 is also attached to the doughnut-shaped structure 11 about its periphery to provide chamber 14. Pressure in chamber 11 will normally be greater than the pressure in chamber 14 and as in all structures of this invention pressure in compartment 8 intermediate anchoring member 3 and base 4 will be maintained at a pressure sufficiently less than the pressure exterior to the entire structure by an amount sufficient to provide the anchoring strength necessary to hold the anchoring member 3 to base 4. In the normal situation where the inflatable structure is anchored to the earth, pressure in compartment 8 will be maintained substantially below atmospheric pressure, at least one of compartments 11 and 14 being maintained at superatmospheric pressure.
Figure 8 shows how the anchoring device of this invention may be utilized to anchor an airplane to the deck of a ship.
The object which is anchored in accordance with this invention is preferably one or more inflatable housing structures which may be constructed of any flexible, substantially gas-impermeable material well known to the art. Examples of such flexible materials include rubber, neoprene, polyethylene, polyethylene terephthalate, polyamide, and other synthetic films, coated fabrics such as nylon fabric coated with neoprene, and the like. The housing structure may also be rigid and made of materials such as wood, metal, glass, ceramic, pressboard, plastic, paper, fabric, and the like, and may contain additional flooring, roofing, partitions, windows, doors, plumbing, lighting and the like, located usually but not necessarily above the anchoring member. The object to be anchored to the ground may also be non-inflatable, such as aircraft, buildings, towers, beacons, and other equipment. For greatest anchoring strength, each and everypoint of attachment of an object to the anchoring member should lie directly above a low pressure compartment intermediate the anchoring member and base.
The anchoring means will usually be a flexible sheet material such as a ground cloth or equivalent which should be attached to the bottom and/ or other suitable parts of the housing or other object to be anchored to provide, where necessary, a gas-tight seal between the two. This ground cloth may be attached by sewing, heat sealing, cementing, stapling, riveting, zippering, weaving, molding, laminating, or any other means of fastening depending upon the material of construction of the ground cloth and the housing. The ground cloth may be made of one or more various materials either similar to or diiferent from that of the housing; such as rubber, neoprene, nylon, polyethylene terephthalate, and other film or sheetings, woven, knitted, and non-woven fabrics, coat ed fabrics such as polyester impregnated glass fabrics, neoprene coated nylon fabrics, tarpaulins, aluminum foil, pressboard, composition flooring (e.g., linoleum), papers and the like, and may be of rigid construction if portability is unimportant. Obviously, this anchoring means must be substantially gas impermeable and is preferably completely gas impermeable.
The base to which the housing or other object is anchored will usually be the ground, which may be in the form of dirt, sand, snow, ice, rock, synthetic paving material, or other surfaces such as floorings, roofings, or vehicular platforms (e.g., ship decks, railroad flat cars, truck tops). The surface of the base may have a limited amount of vegetation thereon. In each case, the edges of the anchoring means must be in substantially gastight sealing contact with the base. By a substantially gas-tight seal as used in this specification is meant a seal sufliciently gas-impermeable so that the pressure adjusting means is able to maintain satisfactory pressure conditions. Customary adhesives, glues, cements, tar, putty, moldable compositions, gaskets, or conformable inflated balloons may be employed to seal the edges of the anchoring means to the base. In certain substances it is convenient to provide an annular ditch surrounding the structure to beanchored so that the edges of a ground cloth may be buried in this ditch and the edges covered over with dirt or other material to seal the ground cloth to the ground. Some conventional securing aids may be used as additional sealing means by positioning one or more of these upon or beneath and at the edges of the anchoring means. These aids, which may include materials such as stakes, pegs, cables, stones, guy wires, sand bags, sand, bricks, dirt, snow, water, or the like, may be desirable to provide a stronger seal between the anchoring means and the base, especially in the initial stages of inflating the housing and/or evacuating the compartment formed by the anchoring member and base. The base is preferably flat and level or substantially flat and level, but in some cases it may be desirable or necessary to assemble the housing on a curved base or on a base which is irregular, uneven, or not level.
The pressure adjusting means, which is essential in this invention to provide reduced pressure between the anchoring member and base and in the case of inflatable structure, a positive pressure for inflatation, may be conventional pumps, such as a vacuum or fluid pump, aspirator pump, bellows, fan, blower or turbine, said means being in one, two or more parts. There may be, for example, an inflating pump for continuously maintaining the higher than atmospheric pressure gas in the inflated housing. There may also be provided a vacuum pump for maintaining the lower than atmospheric pressure gas in the closed compartment between the base and anchoring means. A manifold with a multiplicity of connecting channels may be provided to accelerate the passage of the gas molecules throughout the compartment to a vacuum pump. The gas used for inflating the components of the inflatable housings will normally be air, but for some special purposes such as scientific experimentation or storage of fluids per se or storage of materials under gases other than air, any suitable gas, such as nitrogen, carbon dioxide, helium, oxygen, fuel gases, and the like, may be used.
The over-all principle involved in this invention is based on the creation of a relatively low pressure area between a structure and a base and a relatively higher pressure exterior to both structure and base but adjacent thereto which higher pressure presses the structure to the base. An anchored inflated structure of this invention is associated with at least three pressure zones, a superatmospheric pressure zone within the inflated structure, a subatmospheric pressure. zone between the base and anchoring member, and, of course, atmospheric pressure (which may be artificially created) outside the over-all structure. The pressure means may be adjusted to provide diflerent degrees of pressure between the atmosphere and the lower pressure space, and different pressure differentials between each of the higher and lower pressure spaces with respect to the atmosphere, in order to compensate for the size of the inflated housing, the velocity of the wind and other external forces in a given area, the porosity of the housing material and base, leaks, and other varia bles.
Various means may be provided for attaching an inflatable housing to an anchoring member, sealing an anchoring member to the base, providing different locations between the anchoring member and base for the compartment of lower pressure gas, and providing variations in pressure differential between each of the higher and lower pressure gases and the atmosphere. A typical inflated housing is described below to illustrate one of the preferred specific embodiments of the invention.
, The wei ht of the atmosphere pressing on the surface of the earth is approximately 15 pounds persquare inch,
or one ton per square foot. A 10 ft, x 10 ftrpiece of rubberized ground cloth sucked against the earth by a small continuously operating vacuum pump connected by a hose to the center of the cloth, is pressed down by a total pressure approaching a limit of 100 tons. On a circlular cloth 400 ft, in diameter the limit approached, neglecting leakage, is 120,000 tons. Not all of this total weight is available for use in anchoring a tent to the ground, since the wall of the tent will put the major stress on the circle representing the points of attachment of the tent to the ground cloth. This immediately indicates that an anchoring ground cloth should cover not only most of the inside floor area but should also extend outside the tent proper.
A large gas-impermeable round bag of coated nylon cloth, when placed on the ground and partially inflated, takes on the shape of an oblate spheroid (see dotted lines in Figure 2). The bag, upon being then filled with air at slightly higher than atmospheric pressure, for example, one pound per square inch gauge, has no tendency as a whole to rise because of the weight of the contained air. However, there is another less desirable feature of this internal air pressure, namely its tendency to round up the bag so that the walls (at ground level) are not vertical but contact the ground tangentially making .the inflated bag unsuitable as housing. If this rounding tendency is counteracted with guy wires to increase the inside floor area of the bag, these wires are under considerable tension and require a strong anchorage.
The minimum stress from the rounding-up tendency can he arrived at as follows: An inflated bag in the shape of an oblate spheroid will, depending on the inflation air pressure, contact the ground in an inner circle which will be less than the bags largest diameter. To anchor such a bag to the ground, in accordance with this invention, the anchoring member must be larger in area than this inner circle and preferably larger than the largest diameter of the bag. When the bag is sewn to the anchoring member along this inner circle, pulling tension upon the anchoring member from the rounding-up tendency is minimized.
For the purpose of obtaining more usable floor space inside an inflated bag (hereinafter called an inflated tent) the floor may be extended to include an area between that of the no-tension inner circle and the higher-tension outer circle corresponding to the true hemispherical In this compromise situation, the one ton per the tendency of the tent to round up and lift the ground cloth. If desired, rigid members such as bars may be placed under the ground cloth and fastened to it, as shown in Figures 2 and 3, to distribute the tension over a greater area.
One advantage of this invention is that it provides more stable, more convenient and more rapidly erected inflated air structures or other housings than that available heretofore. The inflated housings of this invention will withstand much higher wind forces and other external forces because of the novel anchoring method than will housings of the prior art which have been attached to the ground solely by stakes, pegs, guy wires, and the like. Another advantage is that the anchoring method of this invention does not require any additional novel or expensive equipment but merely conventional pumps for achieving the improved anchoring.
The novel method of this invention may be used to anchor various elements for a wide variety of purposes, both military and commercial. Examples of such elements which may be anchored include tents, radomes, balloons, aircraft, radio towers, beacons, markers, military equipment, tarpaulins, airplane hangers, garages, structures for housing personnel, animals, supplies, machinery and equipment, fences, wind breaks, barricades, reservoirs, rain collectors, solar stills, solar housings, greenhouses, and the like.
The claimed invention:
An inflated structure comprising an inflated tent attached along its bottom by a substantially air-impermeable seal to a substantially air-impermeable flexible sheet material larger in surface area than the largest plan projected area of the inflated tent, the sheet material lying flat upon the ground, a substantially air-tight compartment intermediate the sheet material and the ground containing air at a pressure sufiiciently less than atmospheric pressure to hold the entire structure firmly to the ground.
References Cited in the file of this patent UNITED STATES PATENTS