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CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of provisional patent application Ser. No. 60/785,113, filed with the USPTO on Mar. 23, 2006, which is incorporated by reference. 
     
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISK 
       [0003]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of the Invention 
         [0005]    The present invention generally relates to the field of construction, and more particularly to a modular building unit that may be utilized to construct a protective shelter for enclosing the interior of a pre-existing room during a high-wind incident. 
         [0006]    2. Background Art 
         [0007]    High wind storms can cause significant structural damage resulting in substantial economic loss, significant injuries, and loss of life as was evident from hurricanes striking the coastal regions of Louisiana, Texas and Florida in recent years. Structural failure in high wind conditions is a significant factor contributing to economic loss, injuries and fatalities sustained by affected home and business owners. 
         [0008]    The Federal Emergency Management Agency (FEMA) has established criteria for in-residence shelters to protect the inhabitants of buildings from natural disasters. These shelters are “to provide a high degree of occupant protection during severe windstorms (hurricanes and tornadoes).” In-Residence Shelter, October, 1998. This FEMA publication provides construction plans and drawings for several different types of shelters including an in-ground shelter, a basement lean-to, a corner location basement shelter, a Concrete Masonry Unit (CMU), a CMU/concrete shelter, and a wood-frame shelter with plywood sheathing or steel wall sheathing. 
         [0009]    There is also a published pamphlet sponsored by FEMA and written by the Wind Engineering Research Center of Texas Tech University entitled, “Taking Shelter from the Storm: Building a Safe Room Inside Your House” (Second Ed., March 2004), listed as publication FEMA  320 . The publication states that the basis of the design of a shelter “is to provide a space where you and your family can survive a tornado or hurricane with little or no injury . . . To protect the occupants during extreme windstorms, the shelter must be adequately anchored to the house foundation to resist overturning and uplift. The connections between all parts of the shelter must be strong enough to resist failure, and the walls, roof, and door must resist penetration by windborne missiles.” However, the pamphlet further states that extensive testing has shown that “walls, ceilings, and doors commonly used in house construction cannot withstand the impact of missiles carried by extreme winds.” The publication then describes shelter designs that meet the design criteria. 
         [0010]    All of the shelters in the FEMA publication involve permanent construction using concrete as the primary material or as the foundation material. The installation of these shelters thus cannot be performed by the average homeowner and requires the use of a professional builder. For example, the wall construction recommended for a typical frame shelter plan with plywood and steel wall sheathing includes two layers of three-quarter inch plywood panels on the outside, a 14 gauge steel sheathing on the inside and double 2×4 studs at 16 inches on center. 
         [0011]    FEMA shelters have the following design criteria: they will withstand wind pressures developed from 250-MPH, 3-second gusts in accordance with ASCE 7-95; they will withstand windborne debris (missile) impact loads created by a 15 pound 2×4 traveling horizontally along the board&#39;s longitudinal axis at 100 mph, traveling vertically at 67 mph, and impacting perpendicular to the wall surface. This missile speed corresponds to a 250 mph wind. The tornado missile test criteria were established by the Wind Engineering Research Center (WERC) at the Texas Tech University. FEMA set another criterion for in-ground shelters wherein there must be a minimum of five square feet per person. 
         [0012]    The shelter design criteria have contradictory requirements: on the one hand the shelters must be physically strong so they can withstand high wind and earthquake forces; and the shelters must also be able to withstand the penetration of windborne articles. If the shelter is constructed pursuant to the plans in the aforementioned FEMA publication, it can easily meet both of these contradictory criteria. However, such a shelter must be constructed by a professional building contractor having a number of different professional workers, each with one of the requisite construction skills such as masonry, carpentry, and iron work. 
         [0013]    There are many U.S. patents that disclose a multitude of shelters. Invariably, all of these shelters have the primary goal of providing structural integrity and protecting against collapse, ignoring the protection against the penetration of windborne articles. One issued patent, U.S. Pat. No. 5,813,174 to Waller, discloses a light-weight steel structure that can be packaged and shipped as loose tubular and bent-plate channel modules and can be assembled by the user. Its disclosure states that the structure can be assembled entirely from within the structure as it is being built, and thus it can be installed in a pre-existing enclosure. It appears that an embodiment of this patent is presently being marketed by the Remagen Corporation of Monteagle, Tenn. However, the intent of this patent is to produce a structure comprised of a plurality of metal panels bolted together to produce extremely rigid walls that provide a solid enclosure. The construction features set forth in the patent clearly describe an I-beam configuration between adjacent panels that are connected to a rigid frame. For example,  FIG. 5  of the patent discloses a rigid frame that is comprised of square, hollow steel tubes that defines the parallelepiped shape of the structure. Each end of each wall panel has a rigid metal cap that is fixedly connected to the frame to provide increased rigidity. 
         [0014]    The difficulty with very rigid and solid structures is that they will not pass the FEMA penetration test due to their high rigidity. Such structures are designed to protect against building collapse. The walls have virtually no “give” or “play”, and thus no means for absorbing and distributing the striking force of a propelled object (e.g. a 2×4 beam traveling at over 100 miles per hour). Page 12 of the publication FEMA  320  states, “[d]amage can also be caused by flying debris (referred to as windborne missiles). If wind speeds are high enough, missiles can be thrown at a building with enough force to penetrate windows, walls, or the roof . . . Even a reinforced masonry wall will be penetrated unless it has been designed and constructed to resist debris impact during extreme winds. Because missiles can severely damage and even penetrate walls and roofs, they threaten not only buildings but the occupants as well.” 
         [0015]    Thus, there is a need for a protective shelter that will not only meet the aforementioned FEMA criteria, but can also be assembled by the consumer without the need for professional builders. Further, there is also a need for a shelter that can be installed within a pre-existing structure and does not require installation prior to construction of the structure. Still further, there is a need for a shelter that can be economically purchased and easily assembled with common hand tools. It is thus clear that well recognized need exists for an economical protective shelter that can be assembled by everyday consumers, from prefabricated components with readily available hand tools in a short period of time, and when assembled can pass both FEMA&#39;s structural integrity test and missile penetration test. 
         [0016]    Thus, it would be useful to provide a protective shelter capable of installation within a pre-existing structure, using common hand tools, and not requiring an extensive structural foundation. 
       BRIEF SUMMARY OF THE INVENTION 
       [0017]    In accordance with one embodiment, a composite panel assembly is disclosed comprising at least one modular building unit that comprises: a first tube; a second tube aligned immediately adjacent and parallel to the first tube; and at least one integral connection between the outer circumference of the first tube and the outer circumference of the second tube. 
         [0018]    Such composite panel assemblies may be further utilized in the construction of a protective shelter that protects an inner space. The protective shelter comprises: a front wall, the front wall having a door frame assembly therein and a door attached to the door frame assembly; a rear wall; two side walls; and a ceiling panel; wherein the walls and the ceiling panel each comprise a composite panel assembly, the composite panel assembly comprises a plurality of modular building units, each of the modular building units comprises a first tube, a second tube aligned immediately adjacent and parallel to the first tube, and at least one integral connection between the outer circumference of the first tube and the outer circumference of the second tube. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0020]      FIG. 1  is a top view of an embodiment of a modular building unit in accordance with the present invention. 
           [0021]      FIG. 2  is a top view of an embodiment of a modular building unit coated with structural material in accordance with the present invention. 
           [0022]      FIG. 3  is a side view of an embodiment of a modular building unit in accordance with the present invention. 
           [0023]      FIG. 4  is a top view of one embodiment of a composite panel assembly in accordance with the present invention. 
           [0024]      FIG. 5  is a top view of one embodiment of a modular building corner unit in accordance with the present invention. 
           [0025]      FIG. 6  is a top view of one embodiment of a modular building corner unit coated with structural material in accordance with the present invention. 
           [0026]      FIG. 7  is an elevated perspective view of one embodiment of a protective shelter in accordance with the present invention. 
           [0027]      FIG. 8  is an elevated perspective view of one embodiment of a front wall composite panel assembly further comprising a door frame assembly and a door in accordance with the present invention. 
           [0028]      FIG. 9  is a top view of one embodiment of a composite panel assembly in accordance with the present invention depicting a connecting means secured to the modular building units by typical bolts and receiving nuts. 
           [0029]      FIG. 10  is a top view and side view of one embodiment of a receiving nut disposed within the lower portion of the modular building unit in accordance with the present invention. 
           [0030]      FIG. 11  is a top view and side view of one embodiment of a receiving nut disposed within the upper portion of the modular building unit in accordance with the present invention. 
           [0031]      FIG. 12  is a cut away side view of one embodiment of a connecting means securing modular building units to both the base and ceiling panel in accordance with the present invention. 
           [0032]      FIG. 13  is a top view of one embodiment of a protective shelter in accordance with the present invention, having the ceiling panel removed for clarification purposes. 
           [0033]      FIG. 14  is an elevated perspective view of one embodiment of a door frame assembly in accordance with the present invention. 
           [0034]      FIG. 15  is an elevated perspective view of one embodiment of a door in accordance with the present invention. 
           [0035]      FIG. 16  is a top view of one embodiment of a modular building unit in accordance with the present invention. 
           [0036]      FIG. 17  is an elevated perspective view of one embodiment of a composite panel assembly in accordance with the present invention. 
           [0037]      FIG. 18  is a top view of one embodiment of a modular building corner unit in accordance with the present invention. 
           [0038]      FIG. 19  is an elevated perspective view of one embodiment of a modular building corner unit and adjacent modular building unit in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. Unless otherwise defined, technical and scientific terms herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Suitable methods and materials are described below; additionally however, methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. In addition, the materials, methods and examples given are illustrative in nature only and not intended to be limiting. Accordingly, this invention may be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these illustrated embodiments are provided solely for exemplary purposes so that this disclosure will be thorough and complete, and will convey the scope of the invention to those skilled in the art. Other features and advantages of the invention will be apparent from the following detailed description. 
         [0040]    Referring now to  FIGS. 1-6 , a composite panel assembly  10  in accordance with the present invention will be described. The composite panel assembly  10  comprises at least one modular building unit  20 , preferably a composite panel assembly  10  comprises a plurality of modular building units  20  attached to each other. 
         [0041]    As depicted in  FIG. 1 , the modular building unit  20  is formed from a first tube  22  and a second tube  24  having at least one integral connection  26  between the outer circumference of the first tube  22  and the outer circumference of the second tube  24 . Tubes  22 ,  24  are preferably composed of readily available steel, however, tube  22 ,  24  composition material may include, but is not limited to, other metals, composite materials, polymeric materials, any combination thereof, and any other structural materials known within the art. 
         [0042]    The integral connection  26  may be provided for in a wide variety of configurations including, but not limited to, a single connection point, one continuous connection along the majority of the lengths of tubes  22 ,  24 , connections at approximately the midpoint and both ends of the tubes  22 ,  24 , uniformly spaced connections along the length of the tubes  22 ,  24  (depicted in  FIG. 3 ), and any other connection configurations known within the art. Further, integral connection  26  may be provided for via a variety of methods including, but not limited to, a welded connection, a laminate bond, an epoxy bond, a polyurethane bond, an acrylic bond, a cyanoacrylate bond, a silicone bond, and any other connection methods known within the art for each particular tube  22 ,  24  material. 
         [0043]    As depicted in  FIG. 2 , a structural material  28  may be deposited onto the exterior surface of the modular building unit  20 . Structural material  28  may serve to enhance the function and/or characteristics of the underlying tube  22 ,  24  materials. Beneficial attributes of the structural material may include, but are not limited to, protecting modular building unit  20 , strengthening modular building unit  20 , improving the durability of modular building unit  20 , improving impact resistance of modular building unit  20 , improving the connection strength between at least two modular building units  20 , and any other beneficial coating attributes known within the art. Suitable structural materials  28  that may impart such characteristics include, but are not limited to, polymeric materials (e.g., polyvinyl chloride, polyurethane, etc.), rubberized materials, composite materials (e.g. KEVLAR®, which comprises fibers formed from long molecular chains produced from poly-paraphenylene terephthalamide), cement materials, and any other materials known within the art. 
         [0044]    As depicted in  FIG. 4 , a composite panel assembly  10  may be formed from a plurality of attached modular building units  20  disposed within the same plane. The attachments  29  between adjacent modular building units  20  may be similar to the integral connections  26  between tubes  22 ,  24 . Such attachments  29  between the abutting tubes of immediately adjacent modular building units  20  may include, but are not limited to, a welded connection, a laminate bond, an epoxy bond, a polyurethane bond, an acrylic bond, a cyanoacrylate bond, a silicone bond, and any other connection methods known within the art for the selected tubular material. The configuration for attachment  29  may be selected from the same wide variety as described for the integral connection  26 . In a preferred embodiment, integral connection  26  is a welded connection and attachment  29  is an epoxy bond. 
         [0045]    The modular building units  20  of composite panel assembly  10  may have an optional coating of structural material  28 , as described above, disposed about the outer circumference of tubes  22 ,  24 . In a preferred embodiment depicted in  FIG. 2 , the structural material  28  is disposed about the modular building unit  20  such that the external surface of the coated modular building unit  20  has a rectangular cross section. In one configuration, a portion of said outer circumference of tubes  22 ,  24  that is diametric to the integral connection  26  remains uncovered by the structural material  28 . Such a configuration, as shown in  FIG. 2  and  FIG. 4 , allows for the direct attachment  29  of abutting tubes  22 ,  24  in immediately adjacent modular building units  20 . Additionally, abutting structural material  28  portions of immediately adjacent modular building units  20  may be bonded together to provide a contiguous outer surface to the composite panel assembly  10 . Such structural material  28  to structural material  28  bonding may also serve to further strengthen and reinforce the attachment  29  junctions between adjacent modular building units  20 . 
         [0046]    A modular building corner unit  30  may be used in connecting two composite panel assemblies  10 .  FIG. 5  depicts a modular building corner unit  30  comprising a corner tube  32 , a first side tube  34  and a second side tube  36 , wherein said side tubes  34 ,  36  are attached to corner tube  32  by respective integral connections  26 .  FIG. 5  depicts side tubes  34 ,  36  connected to corner tube  32  forming an orthogonal modular building corner unit  30 . Such an orthogonal configuration is a preferred embodiment, however, the scope of the present invention includes all possible corner angles desired by a user, subject only to the abutment of constituent side tube  34 ,  36  material. Structural material  28 , as described above and depicted in  FIG. 6 , may be deposited onto the exterior surface of the modular building corner unit  30 . 
         [0047]    Filler material may optionally be disposed within the tubes  22 ,  24  of each modular building unit  20  and modular building corner unit  30 . Filler materials enable a dramatic increase in the strength and impact resistance of the modular building units  20 . Appropriate filler material may include, but is not limited to, cement, steel (e.g. steel rods disposed within tubes  22 ,  24 ), foam (e.g. high density foam), polymers (e.g. polyurethane), any combinations thereof, and any other filler materials known within the art. Use of such strengthening filler material allows the possibility of using a more economical material for tubes  22 ,  24  of the modular building units  20 . As an example, with use of an appropriate filler material a user may opt for a lower grade standard metal fence post instead of ¼ inch steel pipe as the chosen material for pipes  22 ,  24 . 
         [0048]    Composite panel assemblies  10 , as described above, are capable of use in a wide variety of construction functions. Such utility includes, but is not limited to, vertical structures such as walls and barriers, and horizontal structures such as decks, floors, roofs, and the like. Use of a plurality of strong and impact resistant composite panel assemblies together allows a user to construct a very safe definable space. Examples include safe rooms or storm rooms to protect people from harmful outside actions and forces. As an example, such a protective shelter would be highly advantageous in providing protection from tornadoes in the Midwest and hurricanes in the Southeast. 
         [0049]      FIGS. 7-15  depicts a protective shelter  100  and its constituent elements. As viewed in  FIG. 7 , shelter  100  comprises a front wall  40 , a rear wall  42 , a left side wall  44 , a right side wall  46 , and a roof panel  48 . A door frame assembly  50  may be disposed within the front wall  40 . A movable door  52  may be attached to door frame assembly  50  through which access to shelter  100  can be gained. Movable door  52  may swing into shelter  100 , swing out of shelter  100 , slide parallel to front wall  40 , or perform any other movable door function known in the art to allow access to the protective shelter  100 . Shelter  100  rests on a base, wherein the base may be a floor constructed of any conventional building material, preferably being a concrete slab or cement floor. 
         [0050]    A preferred embodiment of the protective shelter  100  of the present invention is depicted in  FIG. 7 . The walls  40 ,  42 ,  44 ,  46  and roof panel  48  may comprise a plurality of modular building units  20 , each wall  40 ,  42 ,  44 ,  46  extending the height of the room walls and attached to adjacent modular building units  20  down the length of each room wall or to a modular building corner unit  30  at a room corner. 
         [0051]    After determining the dimensions of the room to be retrofitted, an appropriate number of modular building units  20  are joined along the length of each interior wall of the pre-existing structure via an attachment  29 . Similarly each modular building corner unit  30  is joined to adjacent tubes  22 ,  24  of modular building units  20  via attachment  29 . The combined length of adjacent modular building units  20  and joined modular building corner units  30  at each corner along a wall may equal the length of each room wall. The length of a modular building corner unit  30  may approximately equal that of a modular building unit  20 . Walls  40 ,  42 ,  44 ,  46  incident to a corner without a modular building corner unit  30  from the orthogonal adjacent wall  40 ,  42 ,  44 ,  46  will include an attached modular building corner unit  30 . Alternatively, the modular building units  20  and modular building corner units  30  may be sized during the manufacturing process so that the appropriate number of modular building units  20  extends the length of the inner surface of each room wall. 
         [0052]    After room wall interior surfaces are fitted with adjacent modular building units  20  and room corners include modular building corner units  30 , connecting means  54  may be used to further secure each modular building unit  20  to adjacent unit(s)  20  or corner unit(s)  30  along a wall  40 ,  42 ,  44 ,  46  or roof panel  48  (see  FIG. 9 ). The connecting means  54  for further securing modular building units  20  of a wall  40 ,  42 ,  44 ,  46  or ceiling panel  48  to each other may comprise a flat bracket or any other connecting means known within the art. The function of connecting means  54  may further include securing the walls  40 ,  42 ,  44 ,  46  to both the ceiling panel  48  and the base (e.g. floor or slab), as shown in  FIG. 12 . In a preferred embodiment depicted in  FIGS. 8 ,  9 ,  12  and  13 , connecting means  54  may comprise an L-bracket as is commonly used in the art. Connecting means  54  may also comprise any other connectors known to one of ordinary skill in the art. 
         [0053]    Connecting means  54  may be attached to walls  40 ,  42 ,  44 ,  46  in any manner known within the arts including, but not limited to, welding, conventional bonding, and the use of typical nuts, bolts and/or screws. A preferred embodiment comprises typical bolt(s)  56  and complementary receiving nut(s)  58 , as shown in  FIGS. 9-12 . Receiving nuts  58  may comprise individual components or may be provided in the form of a nut plate if more than one bolt  56  is to be used per tube  22 ,  24 . As depicted in the preferred embodiment, at least one hole in connecting means  54  is aligned with at least one fastening hole  60  formed within the upper and lower ends of tubes  22 ,  24  of the modular building unit(s)  20 . The fastening hole(s)  60  may be centered on the exposed circumference of the respective tubes  22 ,  24  of the modular building units  50  (see  FIGS. 9 and 10 ). In such an embodiment, the bolts  56  and nuts  58  secure connecting means  54  to the modular building units  20  further securing the modular building units  20  of a composite panel assembly  10  to each other. Although this embodiment depicts the use of L-brackets as the connecting means  54  positioned at the top and bottom of adjacent modular building units  20 , any number of clamps or other connecting means  54  may be used at any respective position. In addition, any method appreciated by one of skill in the art may be used to effectively secure the adjacent modular building units  20  of the room walls  40 ,  42 ,  44 ,  46  to each other, and to the roof panel  48  and base, respectively. 
         [0054]    A roof panel  48  is composed of adjacent modular building units  20  similar to the units  20  used in composing the room walls  40 ,  42 ,  44 ,  46 , as discussed above. As shown in  FIG. 7 , the tubes  22 ,  24  of the roof panel  48  may extend the width or length of the room as opposed to the height of the room in any pre-existing structure. A plurality of modular building units  20  are attached to one another, as described above, to form the roof panel  48  that is set atop the walls  40 ,  42 ,  44 ,  46  of the protective shelter  100 . Similar to the wall  40 ,  42 ,  44 ,  46  constructions, a connecting means  54  may be used to further attach the modular building units  20  of the roof panel  48  to each other, and may further serve to secure the roof panel  48  to the upper portion of the walls  40 ,  42 ,  44 ,  46 . Tubes  22 ,  24  comprising the modular building units  20  of the roof panel  48  may have at least one fastening hole  60  at each end of the respective tubes  22 ,  24 . Such at least one fastening holes  60  may align with holes within a connecting means  54  attached to the upper portion of each wall  40 ,  42 ,  44 ,  46 . The connecting means  54  may then be secured to the roof panel  48  by any means known within the art, with a preferred embodiment comprising typical bolts  56  and receiving nuts  58  depicted in  FIG. 12 . Additionally, a tube  22 ,  24  of the last modular building unit  20  on both ends of roof panel  48  may have fastening holes  60  along the length of the tube  22 ,  24  for attachment of connecting means  54  capable of securing roof panel  48  to the upper tube  22 ,  24  ends of the respective walls  40 ,  42 ,  44 ,  46  (e.g. see specifically front wall  40 , back wall  42 , and roof panel  48  of  FIG. 7 ). In a preferred embodiment, the connecting means  54  is an L-bracket abutted into the intersection corner between the roof panel  48  and a wall  40 ,  42 ,  44 ,  46 . 
         [0055]    The modular building units  20  of the walls  40 ,  42 ,  44 ,  46  can be secured to the base or floor via connecting means  54  in the same method in which they were secured to the roof panel  58  above. Connecting means  54  may include a portion for securing to the lower end of tubes  22 ,  24  of walls  40 ,  42 ,  44 ,  46  and another portion for securing to the base. As with the roof panel  48  above, any other method known to one of skill in the art may be used in securing the walls  40 ,  42 ,  44 ,  46  of the protective shelter  100  to the base. The base or flooring may include pre-drilled holed coinciding with holes within connecting means  54 , into which screws are passed thereby securing the shelter  100  to the floor. All means of securing the connecting means  54  to the roof panel  48 , walls  40 ,  42 ,  44 ,  46 , and base may be accessible from the inside of the shelter to permit its construction from within the protected space. 
         [0056]    As depicted in  FIG. 8 , any room door may be retrofitted or replaced with a door  50  formed of adjacent modular building units  20 , as disclosed above. An appropriate door hinge or door slide is preferably capable of withstanding the torque and forces for storm room requirements disclosed by FEMA.  FIG. 14  shows one embodiment of a door frame assembly  52  to which an appropriate door hinge or slide may be attached. Similar to the wall  40 ,  42 ,  44 ,  46  and roof panel  48  constructions, the door  50  (see  FIG. 15 ) may comprise adjacently attached modular building units  20  that may be further secured to one another using a connecting means  54 , as discussed above. The movable door  50  may be utilized in place of or retrofitted over the door of the pre-existing structure. 
         [0057]    Another embodiment of a modular building unit  20  and protective shelter  100  in accordance with the present invention will now be described in reference to  FIGS. 16-19 . Means of construction are similar to those disclosed above, with some minor differences discussed herein. 
         [0058]      FIG. 16  depicts another embodiment of a modular building unit  70 . The modular building unit  70  comprises an I-beam  72  and a tubular member  74 . I-beam  72  may comprise a first flange  76  disposed parallel to a second flange  78 , wherein the first flange  76  and the second flange  78  are connected by a web  80 . The web  80  is disposed perpendicular to both the first flange  76  and the second flange  78 . Tubular member  74  may be disposed parallel to the longitudinal axis of the I-beam  72 , wherein half of the outer circumference of the tubular member  74  is positioned within the I-beam  72  between the first flange  76  and the second flange  78 , as depicted in  FIG. 16 . Modular building unit  70  may further comprise positioning material  82  disposed within the I-beam  72  between the first flange  76  and the second flange  78  for maintaining approximately half of the outer circumference of the tubular member  74  within the I-beam  72  between its first flange  76  and its second flange  78 . 
         [0059]    The positioning material  82  serves to hold the tubular member  74  at the weakest part of the I-beam  72 . Positioning material  82  may include, but is not limited to, polyurethane, other polymers, cement, foams, composite materials, and any other materials known within the art. The exposed surface of positioning material  82  may be formed in a concave shape that is complimentary to the external circumference of the tubular member  74 , as shown in  FIG. 16 . The concave shape may be obtained during the manufacture of the I-beam  72  or during the retrofit procedure. Further, the exposed surface of positioning material  82  may have an adhesive disposed thereon to assist in maintaining the position of tubular member  74 . 
         [0060]      FIG. 17  depicts a plurality of modular building units  70  disposed within the same plane and in an alternating arrangement of I-beams  72  and tubular members  74 . In such a configuration, the tubular members  74  serve to reinforce and support the weakest portion of the I-beams  72 . With each modular building unit  70  comprising an I-beam  72  and a tubular member  74 , a tubular member  74  of a first modular building unit  70  may be disposed within the open side of an I-beam  72  of a second modular building unit  70  in a repeating manner, as seen in  FIG. 17 . Similar to the disclosure above, to further secure the modular building units  70  to each other, a connecting means  54  may be disposed across the junctions of the modular building units  70 .  FIG. 17  depicts at least one fastening hole  84  on each modular building unit by which a connecting means  54  may be secured. Such a connecting means  54  may be attach to the modular building units  70  at any position and in any number desired across the secured panel. The method for securing the connecting means  54  to the panel of modular building units  70  may be any means known within the art, with a preferred embodiment being a typical bolt and receiving nut. 
         [0061]    Another embodiment of a protective shelter  100  may comprise a plurality of modular building units  70  combined in a manner similar to the above disclosed shelter  100  constructions using modular building units  20 . Walls, a roof panel and a door may be constructed from a panelized plurality of modular building units  70 , as depicted in  FIG. 17 .  FIGS. 18 and 19  depict an embodiment of a modular building corner unit  90 . As shown in  FIG. 18 , two I-beams may be combined into a modular building corner unit  90 . By cutting away one leg of a flange on both I-beams, the cut legs and normal legs may, respectively, abut and may be fixedly attached to each other by any means known within the art. In a preferred embodiment, the two I-beams may be welded together to form the modular building corner unit  90  in  FIG. 18 . The I-beams  72  and tubular members  74  of the modular building units  70  are cut to lengths equal to the height of the room to be retrofitted. Similarly, an appropriate number of modular building units  70  may be incorporated in forming walls that match the dimensions of the room within the pre-existing structure. Modular building corner units  90  may be utilized to connect panelized wall portions at the corners of the pre-existing room. Adjacent modular building units  70  may be secured together via connecting means  54 , as done with modular building units  20 , fastening holes  60 , with the preferred method using nuts and bolts, as described above. 
         [0062]    The I-beams  72  and tubular members  74  of each modular building panel  70  of the roof panel extends the length or width of the room to be retrofitted, as discussed above with the modular building units  20 . Similarly, the walls of the shelter  100  may be fixedly connected to both the base and the roof panel via connecting means  54 , which may be secured at both the upper and lower portion of each adjacent I-beam  72  constituent of the shelter  100  walls. Attachment of connecting means  54  to the roofs, walls, and base can be in any manner known in the art. A preferred means of attaching the connecting means is via typical nuts and bolts, as discussed above for the first embodiment of the protective shelter  100 . 
         [0063]    In the drawings and specification, there have been disclosed typical preferred embodiments of the invention, and all though specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The invention has been described in considerable detail with specific references to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the invention as described in the forgoing specification. 
         [0064]    While the above description contains many specificities, these should not be construed as limitations on the scope of any embodiment, but as exemplifications of the presently preferred embodiments thereof. Many other ramifications and variations are possible within the teachings of the various embodiments. 
         [0065]    Thus the scope of the invention should be determined by the appended claims and their legal equivalents, and not by the examples given.

Summary:
A composite panel assembly comprising at least one modular building unit. The modular building unit of the present invention may comprise two tubes aligned immediately adjacent, oriented parallel to each other, and having an integral connection over at least one portion of their outer circumferences. The volume surrounding the integrated tubes may be coated with a wide variety of function specific structural materials, and yet further, the inner diameter of the tubes may be filled with a wide variety of function specific filler materials. The composite panel assembly may be used in a wide variety of construction applications including, but not limited to, load bearing and impact resistant structures. One such application is a protective shelter that can be assembled in a pre-existing structure using common hand tools. The shelter may be assembled from the inside, and is resistant to both high winds and airborne missiles.