Severe storm shelter

Abstract

This invention is related to the development of and installation of a shelter structure suitable for severe storm safety. The shelter is a composite structure constructed of precast and post tensioned structural elements or shells, the tendon post-tensioning is designed to maximize strength and minimize material costs by implementing a specific geometric shape, the inverted catenary, in three dimensions. The shelter is easily constructed and then assembled from readily available structural materials that are both economic and mechanically efficient.

1 . An above ground severe storm shelter having a geometrically-shaped structure, comprising:
 a plurality of structural shells connected to each other;   a plurality of support anchors;   a plurality of post tensioning tendons;   an access assembly for entry and exit;   a protective structural skirt surrounding base of the shelter;   a means for anchoring the structural shells;   a means for connecting the structural shells; and   a means for post tensioning the structural shells.   
   
   
       2 . The severe storm shelter of  claim 1 , wherein the shelter is made in the form of
 a catenoid or a three dimensional volume equivalent to a surface of revolution of an inverted catenary.   
   
   
       3 . The severe storm shelter of  claim 1 , wherein the structural shell is in the shape of an inverted catenary comprising:
 a surface with equation of the curve y=a cosh (kx) where “a” and “k” are constants and,   y is the vertical dimension and,   x is the horizontal direction.   
   
   
       4 . The severe storm shelter of  claim 3 , wherein the structural shell being a catenoid comprises a minimum surface area. 
   
   
       5 . The severe storm shelter of  claim 1 , wherein the one or more structural shells have openings to allow a person to enter the severe storm shelter. 
   
   
       6 . The severe storm shelter of  claim 1 , wherein the structural shells are post tensioned by use of one or more circumferentially located high strength tendons which are implemented in a bonded mode or unbonded mode. 
   
   
       7 . The severe storm shelter of  claim 1 , wherein the post tensioned tendons are strands of high tensile strength steel wire conforming to the requirements of ASTM standards. 
   
   
       8 . The severe storm shelter of  claim 1 , wherein the post tensioned tendons are high strength thread bar conforming to the requirements of ASTM Standards. 
   
   
       9 . The severe storm shelter of  claim 1 , further comprising a waterproof seal between contiguous shells to waterproof the bond between the structural shells. 
   
   
       10 . The severe storm shelter of  claim 1 , wherein walls and roof of the severe storm shelter form a continuously reinforced integral unit. 
   
   
       11 . The severe storm shelter of  claim 1 , wherein the means for connecting the consecutive structural shells comprises bolts passing through flanges on these shells. 
   
   
       12 . The severe storm shelter of  claim 6 , wherein the means for post tensioning the structural shells comprises applying tension to the tendon by stretching the tendon to a prescribed limit of stress. 
   
   
       13 . The severe storm shelter of  claim 6 , wherein the post tensioning stress on the tendons is at least 30 percent of the maximum allowable stress of the tendon. 
   
   
       14 . The severe storm shelter of  claim 1 , wherein the means for anchoring the structural shells define a cylindrical space for receiving a pipe. 
   
   
       15 . The severe storm shelter of  claim 14 , wherein the means for anchoring the structural shells comprises a plurality of pipes firmly anchored by cement in ground to a specified depth. 
   
   
       16 . The severe storm shelter of  claim 1 , wherein the means for fastening the structural shell to the support anchoring system comprises at least one bolt. 
   
   
       17 . The severe storm shelter of  claim 1 , wherein compressive and lateral forces on the structure are balanced in the catenary structural nature of the structural shells providing maximum stability. 
   
   
       18 . The severe storm shelter of  claim 1 , wherein the means for connecting adjacent shells includes a groove and tongue system. 
   
   
       19 . The severe storm shelter of  claim 1 , wherein the means for connecting adjacent shells includes an interlocking groove and a recesses system. 
   
   
       20 . The severe storm shelter of  claim 1 , wherein the means for connecting adjacent structural shells includes a male pin and a corresponding female socket to allow firm connection of shells. 
   
   
       21 . The severe storm shelter of  claim 1 , wherein the access assembly structure comprises layers of reinforced material and steel or other highly impact resistant protective material. 
   
   
       22 . The severe storm shelter of  claim 1 , wherein said access assembly is configured to allow the assembly to slide laterally across the face of the shell wall. 
   
   
       23 . The severe storm shelter of  claim 1 , wherein said access assembly has a multi-point locking mechanism securing the door in a closed position. 
   
   
       24 . The severe storm shelter of  claim 1 , wherein the shelter is constructed outdoors. 
   
   
       25 . The severe storm shelter of  claim 1 , wherein the shelter is constructed indoors in an enclosed space. 
   
   
       26 . The severe storm shelter of  claim 1 , wherein the primary support anchor is a high-strength circular or polygonal shaped structural element at the top of the shells viably disposed and connected to provide integral strength for the connected shell structure. 
   
   
       27 . The severe storm shelter of  claim 26 , wherein the structural shells are securely bolted to the high-strength circular or polygonal shaped element at the top by fasteners. 
   
   
       28 . The severe storm shelter of  claim 1 , wherein the structural shell is a composite structural member comprising: a concrete matrix with reinforcing rods called rebar, the shell being formed by pouring said concrete in an uncured state into a hollow form containing the reinforcing metal disposed to form a reinforcing grid and allowing the concrete to harden. 
   
   
       29 . The severe storm shelter of  claim 1 , wherein the structural shell is a composite structural member comprising a concrete matrix with reinforcing rods called rebar wherein the shell element concrete matrix is at least 3 inches thick. 
   
   
       30 . The severe storm shelter of  claim 28 , wherein the structural shells are constructed with the rebar rods disposed in a grid network with a maximum distance between rod elements in the horizontal and vertical directions is less than 12 inches. 
   
   
       31 . The severe storm shelter of  claim 28 , wherein the structural shells are manufactured at remote locations and transported to the assembly site. 
   
   
       32 . The severe storm shelter of  claim 1 , wherein the structural shells are constructed of a reinforced polymer laminate cured to a prescribed hardness. 
   
   
       33 . The severe storm shelter of  claim 1 , wherein the structural shells are constructed of a reinforced frame covered with an impact resistant material like Kevlar™. 
   
   
       34 . The severe storm shelter of  claim 1 , wherein the shelter is provided with a seating arrangement for the occupants comprises a plurality of seats integrally juxtaposed to the periphery of the base of the shelter. 
   
   
       35 . A method of constructing the severe storm structure of  claim 1  comprising the steps of:
 installing the primary and secondary anchors in holes disposed at the correct location and depth in the substratum by filling the holes with concrete and allowing the concrete to harden thus fixing the anchors in place;   mounting and attaching each previously manufactured structural shell to its respective secondary anchor with the required fasteners;   aligning each shell in sequence with its respective shell partner using the tongue and groove system and connecting the shells with fasteners and emplacing a chemical waterproof bond between respective shells;   attaching the tops of the shells to either the primary central anchor in one embodiment or in the other embodiment or the central circular structural element with fasteners;   inserting and aligning the post-tensioning tendons through each of the shell elements;   tightening all fasteners on the structural shells and the anchoring systems;   post tensioning the tendons circumferentially by using the post-tensioning mechanism which imparts a stress on the cable to the required design limit;   locking the tendons in place;   installing a floor and seating arrangements for the occupants of the structure.   
   
   
       36 . The severe storm shelter of  claim 3 , wherein the shape of the structural shell and shelter cross-section is modified by changing the values of the constants “a” and “k” in the catenary equation. 
   
   
       37 . The severe storm shelter of  claim 1 , wherein the number of structural shells is at least 2. 
   
   
       38 . The severe storm shelter of  claim 1 , wherein the means for connecting and reinforcing adjacent shells includes a keystone system in which the outer shell perimeter is larger than the inside shell perimeter.