US20150259942A1

US20150259942A1 - Concrete shell construction method

Info

Publication number: US20150259942A1
Application number: US13/999,606
Authority: US
Inventors: Henry Crichlow
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-03-13
Filing date: 2014-03-13
Publication date: 2015-09-17

Abstract

A shell structure construction method utilizing a plurality of anchored and laterally connected pre-cast reinforced concrete shells, each of these subject shells has a specific shape in which the shell walls are defined by an inverted catenary shape or alternatively by other efficient geometric shapes. An improved joint support mechanic includes a combination of fastener elements and a plurality of post tensioned cable systems disposed between and connecting contiguous shell elements. This construction method is suitable for manufacturing and implementing severe storm shelters used during tornadoes and other severe weather events.

Description

BACKGROUND OF THE INVENTION

Tornadoes are a most destructive force of nature. Their measurement scale ranges from a low EF0 to EF5. EF0 storms have winds of 72 mph while EF5 storms have winds in excess of 318 mph. The combined effects of wind driven projectiles and wind forces are the destructive forces exerted by a tornado.
EF5 damage represents the upper limit of tornado power, and destruction is almost always total. An EF5 tornado pulls well-built homes off their foundations and into the air before shredding them, flinging the wreckage for miles and sweeping the foundation clean. Very little recognizable structural debris is generated by EF5 damage, with most materials reduced to a coarse mix of small, granular particles and dispersed evenly across the tornado's damage path. Large, multi-ton steel frame vehicles and farm equipment are often mangled beyond recognition and deposited miles away or reduced entirely to unrecognizable component parts. The official description of this damage highlights the extreme nature of the destruction, noting that “incredible phenomena will occur”; historically, this has included such awesome displays of power as twisting skyscrapers, leveling entire communities, and stripping asphalt from roadbeds. Despite their relative rarity, the damage caused by EF5 tornadoes represents a disproportionately extreme hazard to life and limb—since 1950 in the United States, only 58 tornadoes (0.1% of all reports) have been designated F5 or EF5, and yet these have been responsible for more than 1,300 deaths and 14,000 injuries (21.5% and 13.6%, respectively).
Any construction system made to survive in this hostile environment and to keep its occupants safe must provide a level of safety that is superior comparable to the existing structures and be available to a majority of the population at a reasonable cost. It should also provide for a secure personal feeling without increasing the individual anxiety and claustrophobic fear which some people develop in such trying and emotional circumstances. For instance many people have a primordial fear of going underground, especially during a time of severe duress. A shelter concept and means are needed to mitigate the fears of individuals when using these shelters.
On May 3, 1999 a tornado in Moore, Okla. was measured by Doppler radar at 302 mph. At this speed the damage to structures is intense. Life threatening flying projectiles present a clear and present danger to people. However, the projectiles do not actually fly at the measured wind speed but usually at about a maximum level equal to ⅓ of that measured wind velocity. Adequate protection is necessary to protect the individual from this debris and also to maintain the integrity of the structure in which the individual is waiting out the storm.

SPECIFICATION

Further compounding the challenge of the overall design and construction objectives of structures is the observation that cost, safety and psychological effects are very important to most homeowners. For example, an affordable cost combination with structural integrity is very high on the requirement list of many people. People need flexible alternatives to current shelter designs and which can still provide a sense of security and allow for ease of use by the typical individual. A design criterion as previously mentioned, the cost efficient use of shelter floor space is also an ever-growing concern, particularly as building costs continue to escalate. The circular floor concept embodied in this invention maximizes the person capacity number for a given floor space area.
Meeting these objectives often requires improved technology, improved design, and better understanding of the psychology of the human behavior in stressful situations. Conventional severe storm construction methods do not adequately address all the problems that need to be solved in the area of severe wind weather survival.
What is needed in the art is a shelter and a construction method that:

- 1. Utilizes better and more effective building technology to provide a demonstrably structurally stronger and lighter in design, also to minimize total material usage, and still produce an intrinsically safer shelter;
- 2. Provides a comparatively more economical use of available materials to more inexpensively design and install the shelter that meets the affordability criteria of the general public;
- 3. Allows the standardization of manufacture and construction procedures in order to use a wide range of workers of varying competency levels during the construction phase;
- 4. Can be used to rapidly deploy the structures across a wide range of regional locations: rural, urban or suburban;
- 5. Allows for easy transportation of the materials and sub-assemblies of the shelter structures by using existing trucks—large or small in size, or by rail or barge type transportation;
- 6. Meets the social and personal acceptability criteria of the populace, some of whom have had an individual phobias and fears of going below ground during the inclement weather that is associated with tornado-like events;
- 7. Meets the requirements of regulatory bodies and agencies like FEMA and state, municipal and regional bodies.
- 8. Provides for maximum person occupancy per unit area of floor space.

Thus, an improved shelter construction method that provides greater physical security to the occupants during critical and the very destructive tornadic events, allows more rapid, time efficient and more streamlined construction procedures, provides a more cost effective and a more occupant-friendly and user-preferable safety environment compared to conventional methods of shelter design and use is desired. The novel shelter construction method implements a plurality of specially designed and implemented pre-fabricated concrete shells along with the necessary structural and tensioning subassemblies to provide the stability and physical survivability of the construction unit during severe wind events even up to EF-5 tornado level in order to keep the occupants safe and with a minimum level of fear for their personal safety during the wind event.
Through the discussions, below, it shall be shown that the shelter and construction disclosed herein, said construction is well suited for a safe system in tornadic conditions and other severe wind events.

SUMMARY OF THE INVENTION

The present invention relates to the construction of a shelter that keeps occupants safe during a major wind event like a tornado, hurricane or a major weather disturbance.
Particularly, the present invention provides for the utilizing advanced building technology to design, develop and construct a shelter system that by virtue of its structural design with specialized reinforced concrete shells using inverted catenary models and the integration of compressive tensioned assemblies into the structure, allows for a lighter weight units which are as strong as existing storm shelters on a weight basis.
The shells which form the basic construction elements of the proposed invention are designed to maximize the structural integrity of the shelter. Each shell is designed and constructed with precision comparable to that of a manufactured article. It is a feature of this inventive process wherein remote offsite manufacturing of the shells provides for a level of standardization and quality control level that is difficult to obtain economically in a “built-onsite” system.
In another embodiment of the invention, the shells which form the basic construction elements of the proposed invention structure may be fabricated by preforming the shell members into desired configurations which are based on the inverted catenary shape. This shell configuration, when implemented in the preferred embodiments, allows load bearing and dissipation of external forces evenly throughout the shelter structure. During construction phase, the shell members are then sequentially connected and secured together.
In summary, the features of the above-described inventive embodiments are as follows:
Construction of Shells with Optimal Cross-Section Attributes.
Since the shell structure is built by a well-known industry and reliable forming process variations can be easily made in the construction process to vary the size and complexity of the final product. Different sized structures can be routinely produced based on varied shell sizes with the same nominal geometric factors based on the inverted catenary formulations discussed herein.

Structural Features of the Shell Structure.

A characteristic of the inventive shell structure is that the rigidity and strength of the individual shell members is great and the entire structure can be significantly reinforced by additional mechanical elements and processes available in the industry today. These available mechanical attributes involve steel connectors, post tensioned apparatuses and systems and anchored piers. Because of the combination of a concrete matrix and reinforced steel rebar, the shell members easily resist inward deformation from flying debris impact. Furthermore, the “edge-less” i.e. no sharp edges, nature of the outside shape of the shells with their smooth curves generate minimal wind interference by allowing wind flow past the structure without destructive flow vortices occurring on the leeward side of the structure which can destroy or weaken a structure. In addition, the structure is enhanced in these embodiments by additional mechanisms such as the post tensioned steel cables and specifically designed and buried anchor piers. The net resultant of these novel features illustrates a new invention that is capable of providing survivability and a level of safety to the people during a major weather event.
The inventive shell structure and the method of construction according to the present invention are ideally suited for the mass market since the simplicity of construction, economies of scale, and standardization of design allow construction by non-professional personnel in an environment where this type of construction is usually difficult, highly labor intensive and demanding of a higher level of personnel than the normal do-it-yourself individual.
The result is an aesthetically pleasing, socially acceptable, safe, strong, extremely protective, comfortable, lightweight, easily transportable and deployable system that can be implemented and installed by workers of average capability and intelligence level, without the need for a high level of professional education and training.
On-site assembly is simple and fast using simple tools compared to the construction of conventional shelters. Furthermore, by virtue of significant savings in labor and material costs, the shelter construction is also cost competitive relative to conventional shelter construction.
The features and advantages of subject invention will be further understood and appreciated by those skilled in the art by reference to the following written specification, appended drawings and attached claims.

PRIOR ART

Two categories of shelters exist. Underground and above ground. The underground shelters are basically excavations under grade level and lined with masonry blocks or concrete, or plastic enclosures placed in a hole in the ground and covered with earth. Above ground shelters are either internal to existing structures or built adjacent existing buildings. Underground plastic shells, like empty plastic swimming pools are prone to being expelled from the ground by water movement or shallow water tables.
Above ground shelters like the “Oz”, Ref.1, which is a massive monolithic cement structure which are poured around forms placed on location. A 5×5 foot structure weighs 21 tons or 42,000 lbs., and costs about $9,000; an 8×5 structure weighs 60,000 pounds and costs close to $12,000 or more. This is an extraordinarily large quantity of concrete for a simple structure. The total weight of the structures illustrated in the inventive process taught herein is about 12,000 lbs. This structure weight is less than 30% of the weight of comparable structures available commercially today. The material utilized in one currently available structure can presumably make three structures of the type illustrated herein.
Furthermore, an elaborate and costly construction operation is needed to implement the existing types of shelter on location, including the use of massive trucks and cranes and hydraulic systems to transport and install these structures. Fences are removed, backyards are destroyed, electrical lines are removed, replaced and re-routed to allow ingress and egress from the building site. Since the shells 1 in this subject invention weigh only several hundred pounds, they can easily be “man-handled” by two people at a given construction site with basic construction equipment. Underground systems are usually constructed by backhoe operations which excavate suitable sized holes in the ground into which the structure is dropped or manually installed. The structure is then covered with earth. A continuing danger in some underground systems is the possibility of collapse due to soil encroachment or water invasion is some active soils.
U.S. Pat. No. 4,676,035 teaches a wall construction formed from a plurality of pre-cast reinforced concrete building panels each of which includes interior and exterior faces defined peripherally by upper and lower end edges and opposed side edges extending there-between. With an improved welded joint provided between two adjacent side edges of two adjacent side-by-side panels.
U.S. Pat. No. 4,680,901 teaches a domed self-supporting frame-less building structure includes a plurality of concrete panels arranged such that the panels are under compressive loadings in both the longitudinal and lateral directions. A plurality of circumferential courses of such panels are provided with the panels of any one such course being in abutting end-to-end relation with the panels of the next adjacent course. A tension ring surrounds the lower extremity of such dome and the lowermost ends of the panels of the lowermost course are in abutting relation with the ring thereby to assist in securing the panels together in the abutting edge-to-edge relationship.
US20090025307 describes a composite severe storm structure utilizing preformed concrete shells and tensioning members.
U.S. Pat. No. 7,765,746 teaches a spheroid shaped dome house made up of a plurality of complicated spring loaded tiles, attached to the foundation and mutually connected by means of horizontally and vertically disposed elongate members extending through lumens in adjacent tiles.
U.S. Pat. No. 7,237,363 teaches a domed building or mold constructed with flexible, lightweight curved panels snapped together using grooves and ridges formed in the panels to form a building wall, a tension ring holding the panels in place and a top cap overlying and secured to upper edges of the panels.
U.S. Pat. No. 6,324,791 teaches a prefabricated but in modules, of the kind that has four sides, two similar sides, a lower one and an upper one, where the cross sections of the module, viewed from the inside, are concave in the areas close to the lower side and convex in the areas close to the upper side, with an intermediate area where there is a progressive change in curvature.
U.S. Pat. No. 5,146,719 teaches a space tension chord arch member dome reinforced with tension members and method of construction. Maximum building space is ensured by using tension chord members, which reduces the material costs and simplifies assembly of the dome. The system permits use of laminated wood for the arch members of the dome superstructure.
U.S. Pat. No. 4,313,902 teaches a prestressed concrete pressure-containment vessel having one or more cavities within its external shell. The cavities, whether cylindrical or other shape, are totally contained by prestressing tendons, which apply forces to contain various pressures within the structure. The invention allows very high internal pressures to be contained therein.

FIGURES

FIG. 1: Generalized overview graphic of structure showing overall shape and major components.

FIG. 2 a: Vertical cross-section of structure.

FIG. 2 b: Vertical cross-section showing the inverted catenary form of the concrete shells of the structure.

FIG. 3 a: Horizontal cross section showing interlocking concrete shells, dovetailed fitting of adjacent shells, steel tensioned tendons and tendon anchor locations.

FIG. 3 b: Horizontal structural cross-section showing interlocking concrete shells and recesses in shells for connector flanges in adjacent concrete shells.

FIG. 4: Horizontal cross-section showing door location in a specific concrete shell.

FIG. 5: Schematic showing the steel matrix elements of rebar and the upper strengthened steel support flange, the connector flanges between adjacent concrete shells and the shell connections to the buried reinforced piers by an “L-shaped” steel connector.

FIG. 6: Schematic of the outside of structure showing the protective top cap and the hinged door.

FIG. 7 a: Top view of steel flange connecting two adjacent concrete shells.

FIG. 7 b: Front view of steel flange connecting two adjacent concrete shells, located in the recessed space between 2 adjacent concrete shells.

FIG. 7 c: Side view of steel flange in the recessed space between 2 concrete shells along with the connecting bolts in the flange.

FIG. 8: Torque sequencing diagram for nuts on the flanges in shell connections.

FIG. 9: Illustrates the optimal seating arrangement in the shelter.

	TABLE 1

	Item List	Description

	1	Concrete shell
	2	Structure cap
	3	Upper steel flange
	4	Reinforced metal bar - rebar
	5	Steel Flange
	6	Pier anchor metal flange
	7	Hole Excavated for Pier
	8	Earth
	9	Buried Pier
	9a	Pier rebar
	10	Floor
	11	Bench seat assembly
	12	Door
	12a	Door hinge
	13	Lower tension tendon
	14	Upper tension tendon
	15	Reinforced concrete matrix material
	16	Dovetail fitting
	17	Recess in Shell for flange assembly
	18	Tension Anchor in shell
	19	Steel connecting bolts
	20	Channel for tendon cable

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The present invention utilizes pier anchored reinforced concrete shells comprised of high strength cement with reinforced steel bars called rebar and tensioned structural elements as a means of imparting post tensioning stress into the structure. Typically, the reinforced concrete shells are prefabricated at an offsite location with conventional forming processes optimized for maximum cost efficiency and structural strength. The dimensions of the reinforced concrete shells can be varied depending on the height of the structure. Each shell is designed to simultaneously withstand all expected load stresses made by flying debris impacting the structure and the forecasted wind load effects on the structure during the severe storm weather events.
In the preferred embodiment, the generalized shape of the reinforced concrete shell is an inverted catenary curve. These reinforced concrete shells are designed with a plurality of connector means such that the concrete shells can be firmly anchored to each other laterally and additionally; connecting means to anchor the shells at ground level; and also further additionally to a reinforcing means at the top portion of the concrete shells thereby forming an integral assembly. This integral assembly is then later post tensioned.
In the present invention the reinforced concrete shells are generally manufactured in a factory-like setting by methods well known in the industry. These methods customarily involve placing cementitious material into forms containing a steel rebar matrix which makes up the internal tensile support, and allowing the cement to reach its maximum cured strength before the shells are removed and are installed on location.
Referring to FIG. 1 which shows the generalized view of a preferred embodiment of the invention; a plurality of specially designed reinforced concrete shells 1 are disposed and connected circumferentially to each other and vertically to a plurality of buried reinforced concrete piers 9. These piers 9 can be implemented in practice with or without footings depending on the soil type and soil properties. The shells 1 which are shown in FIG. 2 a are constructed with a pre-determined cross-section which follows an inverted catenary shape. This preferred embodiment construction process of utilizing a catenary shape in the shells 1 allows for maximum structural strength, minimum structural wind load effects along with minimum material use in construction. By minimizing material usage, the cost of implementation and construction of this type invention can be minimized. These shells 1 are connected to the piers 9 physically by connector devices 6 which are attached by secure means that are well known in the construction art.
The piers 9 comprise reinforced concrete elements with multiple steel rebar elements buried at sufficient depths in the earth 8 to withstand all expected overturning wind loads. As shown in FIGS. 3 a, 3 b, these shells 1 “dovetail” or fit conformably into each other laterally by a plurality of means such that a strong unobstructed surface connection is made between adjacent shells 1. The “dovetail” fitting 16 is represented vertically in FIG. 3 b.
Referring to FIGS. 2 a, 2 b, a plurality of tensioning devices 13,14 are disposed internally in each shell 1 to circumferentially provide a means for post-tensioning the structure by exerting tensioning forces which are applied to the shells 1 by means of these tendons 13,14. In a preferred embodiment, the suggested tensioning means are steel tendons 13,14 which are anchored in preferred locations 18 which are recessed in specifically selected origin and anchor shells 1. These tendons 13, 14 extended inside the shells 1 from an origin point to the endpoint of the subject tendons 13, 14.
Also shown in FIG. 2 a is a major reinforced support element in the form of a circular steel flange 3 which is bolted to and connects the top sections of each shell 1 to provide integral rigidity, stiffness and increased strength to the overall structure. A protective structural cap 2 is attached by securing means to the top of the flange 3.
By referring to FIGS. 3 a, 3 b the preferred embodiment illustrates the tapered nature of the edges of the shells 1. This tapered design which comprises a wider dimension at the outer shell surface compared to the inner shell surface allows the shells 1 to not only resist the external forces on the shells 1 but each shell 1 behaves as a “key stone” in the structure since compresses forces are transferred laterally and uniformly across all the shells 1 in the structure. This “keystone” effect further strengthens the structure.
By referring to FIG. 2 a, the inverted catenary shape of the shells 1 is illustrated. Each of these shells 1 is constructed over a frame of steel rebar 4 herein called a steel matrix, which is surrounded by concrete material 15 in a manner that is standard in the industry for reinforced concrete shell construction. By referring to FIG. 3 a, the preferred embodiment illustrates a plurality of shells 1 which fit together to form the structure and it also shows the tension anchors 18 in the recess 17 in the selected shells for the tensioning tendons 13, 14. The necessary hardware for anchoring the tendons 18 is positioned in these recesses 17. The edges of the shells 1 are tapered inwards as shown in the illustrations 3 a, 3 b to allow a better fit and more uniform loading laterally. In a departure from typical existing shelter technology, the present invention with the preferred embodiment implements a plurality of internally disposed steel tendons 13, 14 which provide considerable supplementary additional forces acting circumferentially to strengthen the structure. These tendons also shown graphically in FIG. 1 are standard industry devices which have been used in bridge construction and in large concrete dome structures worldwide. These tendons are internally disposed in each shell 1. It is contemplated that the multiple tendons 13, 14 are inserted in pre-installed plastic or metal channels 20 in each shell during the fabrication process of shells 1. The tendons 13, 14 in the preferred embodiment are tensioned in excess of 20,000 psi stress.
In the preferred embodiment, FIGS. 7 a, 7 b, 7 c, illustrate the implementation of the connections between adjoining shells 1. FIG. 7 a illustrates a recessed space 17 in the wall of the shell 1. In this recessed space 17, the flange elements 5 are housed. Constructively, a major rebar element 4 which extends laterally in the shell 1 has a metal flange element 5 welded to the rebar and is nominally at right angles to the rebar 4. Each rebar 4 has a flange element 5 at each section end. These flange elements 5 are mechanically connected as shown in FIG. 7 b by industry standard methods including welding or by flanged nuts and bolts. FIG. 7 c shows a cross-sectional side view of the recessed space 17 wherein the flange 5, the horizontally located rebar 4, the connecting bolts 19 and the concrete matrix 15 of the shell 1 is fully illustrated. A plurality of the flanges 5 are implemented in the design and construction to increase the strength of the structure.
FIG. 5 illustrates a preferred embodiment of the invention, in this preferred embodiment the steel matrix of the shell 1 comprising horizontal and vertical rebar elements 4, steel flanges 5, upper circular flange 3, steel pier connector 6 and steel pier rebar 9 are all integrally connected to form a stiff system which contributes to the overall tensile strength and rigidity of the structure.
FIG. 6 is a graphical illustration showing the location of the entry and exit door 12 to the structure. This door 12 which has attachment means, shown by hinges 12 a in this embodiment, comprises a laminated structure which has a steel framework and a puncture resistant layer such as Kevlar-like fabric or similar resistive material which has been developed in the protective industries for personnel safety during explosions. These fabrics are lightweight, widely available with such names as “Dragonshield” and are able to resist puncture by flying debris during a severe weather event.
FIG. 8 illustrates the preferred embodiment of the tightening sequence of the flange 5 bolts which maintains maximum structural integrity of the subject structure.
It is well known in the lifeboat, rescue and survival industry that a circular shape permits the maximum seating capacity for a given surface area. The interior of the structure is shown schematically in FIG. 2 a. A nominally circular bench-like structure 11 is implemented inside the structure to accommodate a maximum number of people in the given ground space. FIG. 9 illustrates a typical seating arrangement which allows for maximum capacity with a suitable comfort level in the embodiment of the invention. The proposed circular design of the subject embodiment allows for the most effective use of the available seating space. Federal agencies mandate a specific number of square feet per person within the shelter. For seated individuals 6 square feet are mandated, for standing individuals 5 square feet of space is required.
As shown in FIG. 9, a typical seating embodiment of this application is shown. For an 8 foot diameter structure with an 8 inch wall thickness it is shown that the outside perimeter is 29.32 feet. The inside area of the structure is approximately 50 square ft. Using the area mandated per seated person the subject structure can seat 8 people comfortably. By calculating the width provided per individual in this specific structure the seat width is 42 inches. This number is very comfortable, almost luxurious, compared to the published seating in average airline seats of 17.2 inches, in office chairs 20 inches and theater seats 19 inches. It is therefore, theoretically possible to seat almost 18 people inside this inventive structure if typical airline seating width are used.
The floor 10 of the structure is covered by any type of durable material suitable for outdoor use. Cement floors or wood floors can be used in practice.
The implementation of this construction method at a given site location is illustrated by the following sequence of steps. Those familiar with construction processes today, can see that modifications can be made without departing from the inventive intent of the subject invention.

- 1. The selected site location for installation of the structure is made and the holes for the anchor piers 9 are excavated in the ground and the steel anchors 9 a are installed with cement. In some instances pier footings are implemented in the piers 9 under the requisite soil conditions as needed.
- 2. The cement is allowed to cure to maximum strength or for at least 2 days.
- 3. The structure shelter as illustrated in FIG. 1 is then assembled by connecting each shell 1 to its pier 9 by the pier steel connectors 6 and then sequentially aligning the shells 1 by making the flanges 5 fit their neighbor shells 1 correctly.
- 4. After each shell 1 is em-placed on its pier 9, the steel tendons 13, 14 are connected with the tendon hardware 18 attached to each specific shell 1 by threading the tendon 13,14 inside the shells 1 circumferentially around the structure. The tendons 13, 14 are inserted in channels 20 which are pre-built into the shells 1 during forming process. Incrementally, the tendons 13, 14 are thus inserted into the shells 1.
- 5. The adjacent concrete shells 1 are aligned, connected and bolted together, but their nuts are not fully torqued after this initial assembly. All connections shall be fully torqued later in a specific sequence.
- 6. The structure shells 1 are torqued in a specific sequence depending on the total number of shells 1. In the preferred embodiment shown, 8 concrete shells are illustrated.
- 7. After the initial structure assembly in which all nuts are tightened by hand. The flange 5 bolt nuts are then tightened as shown by the numbered sequence in FIG. 8. The nuts are tightened several times by cycling through all shells 1 increasing the torque incrementally until the recommended torque is achieved.
- 8. For example, the first time around tighten the nuts with a hand wrench. Second time around tighten the nuts firmly. Third time around apply approximately 25% recommended torque. Fourth time apply approximately 75% of recommended torque. Fifth time around, apply 100% of recommended torque. Continue tightening nuts all around until nuts do not move under 100% recommended torque. If possible, re-torque after 24 hours.
- 9. The torque sequence of the shells 1 is designed to allow maximum load bearing within the structure without creating additional unbalanced load stresses in the structure which can be deleterious to its structural integrity.
- 10. The shells 1 are then post tensioned by stressing the tendons 13, 14 and to their required level of stress. The stress level is at least 30% of the maximum allowable strength of the tendon. The post tensioning process is standard for the industry using hydraulic devices and industry standard anchoring systems. The anchor systems are recessed into the shells 1 to allow for a smooth outer surface devoid of debris retention obstructions.
- 11. The door 12 is installed on its specific shell 1 and anchored to the shell frame.

Further modifications and alternative embodiments of various aspects of the invention may be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments.

REFERENCES

1. Oz Safe rooms, Del City, Okla.

Claims

I claim:

1. A storm shelter comprising:

a plurality of shells having a first surface with a recess to house a flange, a second surface and a third surface, said shells connected to each other by a connecting mechanism having a member on the shells to strengthen said storm shelter;

a structure connected to the second surface of said shells to anchor said shells to the earth to enable said storm shelter to withstand wind load; and

a supporter connected to the third surface of the shells to support the shells to provide integral rigidity, stiffness and strength to said storm shelter;

wherein said connecting mechanism connects said shells to each other by connecting said member on said shells to the flange housed in said recess at an angle to strengthen said shells by allowing load bearing.

2. The storm shelter according to claim 1, wherein said member of the connecting mechanism is connected perpendicular to the flange housed in said recess.

3. The storm shelter according to claim 1, wherein a connecting edge of said shells connected to each other is covered by a substance to provide adhesion between said shells.

4. The storm shelter according to claim 2, wherein the member and the flange are connected by a method selected from any one of welding and bolting.

5. The storm shelter according to claim 1, wherein said shells are circumferentially connected to each other by the connecting mechanism.

6. The storm shelter according to claim 1, wherein said structure comprises reinforced concrete with plurality of rebar buried at a depth in the earth.

7. The storm shelter according to claim 1, wherein the structure and the second surface of said shells are connected by a connecting device.

8. The storm shelter according to claim 1, wherein said member is a rebar.

9. The storm shelter according to claim 1, wherein said supporter is a circular flange.

10. The storm shelter according to claim 1, wherein a covering device covers an opening of said supporter.

11. The storm shelter according to claim 1, wherein said shells comprise a channel.

12. The storm shelter according to claim 11, wherein said shells are post tensioned by a tensioning device to strengthen the shells.

13. The storm shelter according to claim 12, wherein said tensioning device is circumferentially coupled to said shells.

14. The storm shelter according to claim 13, wherein said tensioning device is housed in the channel of said shells.

15. The storm shelter according to claim 14, wherein at least one of said shells are provided with a cavity to anchor said tensioning device.

16. The storm shelter according to claim 1, wherein one of said shells comprises a door to allow access into said storm shelter.

17. The storm shelter according to claim 16, wherein said door has a resistive layer to enable said door to resist puncture by flying debris during weather event.

18. The storm shelter according to claim 1, wherein said storm shelter houses a sitting arrangement to enable a user to sit.

19. A method of constructing a storm shelter comprising the steps of:

Installing a structure on the earth to enable anchoring of said storm shelter;

Assembling a plurality of shells having a first surface with a recess, second surface and a third surface by connecting the shells to each other by a connecting mechanism by connecting a member on the shells to a flange housed in the recess of said first surface at an angle to strengthen said shells by allowing load bearing;

Anchoring said shells to the structure by connecting said second surface of the shells with the structure by a connecting device; and

Supporting the shells by a supporter by connecting the third surface of the shell to the supporter.

20. The method according to claim 19, including assembling the shells by connecting the member perpendicularly to the flange.

21. The method according to claim 19, including assembling the shells by covering a connecting edge of the shells by a substance to provide adhesion between said shells.

22. The method according to claim 19, including connecting said shells circumferentially to each other by the connecting mechanism.

23. The method according to claim 19, including installing reinforced concrete with a plurality of rebar as the structure to enable anchoring of said storm shelter.

24. The method according to claim 19, including covering an opening of the supporter by a covering device.

25. The method according to claim 19, including post tensioning said shells having a channel by a tensioning device housed in the channel.

26. The method according to claim 25, including coupling said tensioning device circumferentially to the shells.

27. The method according to claim 26, including anchoring said tensioning device in a cavity on at least any on of said shells.

28. The method according to claim 19, including installing a door on any one of said shells to allow access into the storm shelter.

29. The method according to claim 28, including installing a door with a resistive layer to enable the door to resist puncture by flying debris during weather event.

30. The method according to claim 19, including housing sitting arrangement to enable the user to sit.