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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION  
         [0001]    It is sometimes desirable to provide a walk-in, highly secured, lockable vault inside a building or habitat to protect property from damage or theft or to serve as a shelter from natural disaster or intruders.  
           [0002]    These walk-in vaults are often required to comply with various building codes and satisfy requirements set by regulatory bodies for security vaults. This has led to the walk-in vault being built in-place in a building by forming walls of substantial building material such as concrete, steel, or brick to form an enclosure which is fire-resistant and burglary-proof for a rated time.  
           [0003]    The fact that these walk-in vaults have to be built in-place makes them very expensive for the average person and prolongs construction time of the building. It also makes the addition of a vault to a building that is already constructed difficult. Thus it is desirable to have a fire-resistant, burglary-proof, walk-in security vault that can be built inexpensively and incorporated into a building quickly.  
         SUMMARY OF THE INVENTION  
         [0004]    In accordance with one aspect of the invention, a modular vault comprises a plurality of side, end, and roof panels. The panels are ore-cast from a durable material and connected together to define a walk-in enclosure. A floor slab forms the base of the walk-in enclosure. A door frame is molded in at least one of the side or end panels. A door which controls access to the walk-in enclosure is hingedly attached to the door frame. Joint means for engaging abutting panels are provided on the inner surfaces and peripheral edges of the panels. A plurality of metal plates are attached to the inner surfaces of the panels at a location proximate the peripheral edges. The edges of the metal plates contact when the panels are connected by the joint means. A plurality of metal connectors are welded to the metal plates adjoining at corners of the abutting panels. The metal connectors seal the corners of the abutting panels, thereby making the walk-in enclosure substantially vapor-tight.  
           [0005]    In accordance with another aspect of the present invention, a unitary vault includes a housing body made of a durable material. The housing body defines a substantially vapor-tight enclosure. A door frame is fixedly mounted to a side of the housing body. A door providing access to the enclosure is hingedly attached to the door frame. A plurality of hooks are mounted on the housing body. The hooks facilitate hoisting of the housing body. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0006]    [0006]FIG. 1 is a perspective view of one embodiment of the present invention.  
         [0007]    [0007]FIG. 2 is an exploded assembly view of the embodiment shown in FIG. 1.  
         [0008]    [0008]FIG. 3 is a side view of FIG. 1 in half section showing connections between adjoining walls and adjoining walls and roof.  
         [0009]    [0009]FIG. 4 is a perspective view of another embodiment of the present invention.  
         [0010]    [0010]FIG. 5 a  shows one embodiment of the present invention being transported to a construction site.  
         [0011]    [0011]FIG. 5 b  shows one embodiment of the present invention being set on the slab of a building with a crane.  
         [0012]    [0012]FIG. 6 shows how one of the embodiments of the present invention is incorporated into a building.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    Referring to the drawings wherein the reference characters are used for like parts throughout the several views, FIG. 1 depicts a walk-in vault  10  completely assembled and resting on a footing  15  at a construction site.  
         [0014]    As shown in FIG. 2, the walk-in vault  10  has a front wall  20 , rear wall  30 , side walls  40 , roof slab  50 , and floor slab  60 . While the walk-in vault  10  is illustrated as a four-wall embodiment, it should be understood that each wall may be constructed from a series of interlocking, pre-cast panels.  
         [0015]    The front wall  20  has a top edge  21 , a bottom edge  22 , an inner surface  23 , and an outer surface  24 . A pair of elongated grooves  25  run from the top edge  21  to the bottom edge  22 . The top edge  21  includes an outwardly extending ridge  26  integrally formed with the front wall  20 .  
         [0016]    A door frame  12  is integrally formed with the front wall  20 . A door  14  is attached to the door frame  12  in the front wall  20  by means of hinges  13 . The door  14  is preferably a fire-resistant, burglary-proof vault door with security locks and bolts.  
         [0017]    The rear wall  30  has a top edge  31 , a bottom edge  32 , an inner surface  33 , and an outer surface  34 . A pair of elongated grooves  35  run from the top edge  31  to the bottom edge  32 . The top edge  31  has an outwardly extending ridge  36  integrally formed with the rear wall  30 .  
         [0018]    The side walls  40  have top edges  41 , side edges  42 , bottom edges  43 , and an inner surface  44 . Each top edge  41  has an outwardly extending ridge  45  integrally formed with the side wall  40 . Each side edge  42  has an outwardly extending ridge  46  integrally formed with the side wall  40 .  
         [0019]    To form an interlocking walk-in space, the ridges  46  on the side edges  42  of the side walls  40  mate with the grooves  25  in the front wall  20  and the grooves  35  in the rear wall  30 .  
         [0020]    The roof slab  50  has a peripheral edge  52 , an inner surface  53 , and an outer surface  54 . Elongated grooves  55  and  56  are provided on the inner surface  53  of the roof  50 . The elongated grooves  55  and  56  run parallel to the peripheral edges  52  of the roof  50 . The elongated grooves  55  mate with ridge  26  on the front wall  20  and the ridge  36  on the rear wall  30 . The elongated grooves  56  mate with the ridges  45  on the side walls  40 .  
         [0021]    As shown in FIG. 3, apertures  70  are spaced along the perimeters of the front wall  20 , the rear wall  30 , and the roof slab  50 . The apertures  70  intercommunicate with the grooves  25 ,  35 , and  55  and  56  in the front wall  20 , rear wall  30 , and roof slab  50 , respectively. Each aperture  70  has an upper portion  72  and a lower portion  74 . The upper portion  72  has a key-way  76 .  
         [0022]    Metal rods  80  are molded into the front wall  20 , the rear wall,  30 , and the side walls  40 . The metal rods  80  protrude through the ridges  26 ,  36 , and  45  and  46  on the walls  20 ,  30 , and  40 , respectively. Portions of the metal rods  80  protruding from top edges  21 ,  31 , and  41  of the walls  20 ,  30 , and  40 , respectively, mate with the apertures  70  in the roof slab  50  when the ridges  26 ,  36 , and  45  on the top edges of the walls  20 ,  30 , and  40 , respectively, mate with the grooves in the roof slab  50 . Similarly, portions of the metal rods  80  protruding from the side edges  42  of the side walls  40  mate with the apertures  70  in the walls  20  and  30  when the ridges on the side edges  42  of the side walls  40  mate with the grooves  25  and  35  in the walls  20  and  30 , respectively.  
         [0023]    Washers  82  are welded to the metal rods  80  to keep the connected walls from pulling apart. The spaces in the upper portion  72  of the apertures  70  may be filled with grout to prevent access to the metal rods. The key-ways  86  prevent grouts inserted into the spaces in the upper portion  72  of the apertures  70  from falling out.  
         [0024]    Metal plates  84  are cast in the walls  20 ,  30 , and  40  and roof  50 . The metal plates  84  are held in place by means of studs  85 . The surfaces of the plates  84  are flushly arranged with the inner surfaces of the walls and roof flab. The plates  84  in the walls contact when the walls are fitted together. Contacting plates  84  are welded to metal connectors  86  using any suitable welding material.  
         [0025]    Advantageously, the double, fillet welds  88  formed by welding the plates  84  to the metal connectors  86  result in a stronger holding power than usually available if the plates  84  are directly welded together. Also, the continuity of the welds  88  provide a vapor-tight enclosure within the vault, thus protecting the contents of the vault from contaminants such as moisture and smoke and allowing the atmosphere in the vault to be controllable. The metal connectors  86  shield the fillet welds  88  from intruders, thus making it difficult for intruders to rupture the fillet welds  88  from outside the vault.  
         [0026]    The vault  10  is secured to the footing  15  by continuous, fillet welds  90 . The welds  90  help in providing a vapor-tight enclosure within the vault  10  and in preventing water from seeping into the vault to damage the property in the vault. The welds  90  may be covered by the floor slab  60 .  
         [0027]    Conduits may be provided in the walls to allow lighting and security systems and air passageways to be installed in the vault.  
         [0028]    The walls and roof are preferably pre-cast from monolithically poured concrete. The poured concrete may be reinforced with steel bars to prevent hairline cracking in the vault structure. Any other suitable material that satisfies requirements set by regulatory bodies for security vaults may also be used to pre-cast the walls, roof, and floor. The thickness of the walls, roof, and floor may be varied to suit the particular building in which the vault is to be used and to reduce the overall cost of the vault.  
         [0029]    The door frame  12  may be integrally formed in the front wall  20  by fitting the door frame  12  to an outer mold shell and pouring concrete monolithically into the mold cavity formed between the outer mold shell and an inner mold core. The concrete snugly holds the door frame  12  in place and eliminates the need for special fasteners to hold the door frame  12  to the front wall  20 .  
         [0030]    The floor slab  60  may be pre-cast at a manufacturing plant or formed at the construction site by pouring concrete onto the portion of footing  15  within the walk-in space defined by interlocking the walls  20 ,  30 , and  40 .  
         [0031]    The vault  10  is generally assembled at a construction site as follows. The bottom edge  21  of the front wall  20  is positioned on a footing at the construction site. The bottom edges  43  of the side walls  40  are positioned on the footing and connected to the front wall  20  by mating the ridges  46  on the side edges  42  of the side walls  40  with the grooves  25  in the front wall  20 . The rear wall  30  is positioned on the footing and connected to the side walls  40  by mating the grooves  35  in the rear wall  30  with the ridges  46  on the side edges  42  of the side walls  40 .  
         [0032]    The walls  20 ,  30 , and  40  are welded to the footing. A pre-cast floor slab  60  may be lowered into the walk-in enclosure defined by the interlocking walls  20 ,  30 , and  40 . Alternately, concrete may be poured onto the portion of the footing within the walk-in enclosure formed by the walls. The poured concrete becomes the floor slab  60 .  
         [0033]    The roof slab  50  is placed on top of the walls  20 ,  30 , and  40  by matching the grooves  55  and  56  on the roof  50  with the ridges  26 ,  36 , and  45  on the top edges of the walls  20 ,  30 , and  40 , respectively. Metal connectors  86  are welded to the metal plates  84  in the corners formed between adjoining walls and between the walls and the roof.  
         [0034]    An alternate embodiment replaces the front wall  20 , the rear wall  30 , the side walls  40 , the roof slab  50 , and the floor slab  60  with a unitary housing body  100  as shown in FIG. 4. The unitary housing body has a front portion  102 , a rear portion  104 , a first side portion  106 , a second side portion  108 , a roof portion  110 , and a floor portion  112 .  
         [0035]    The housing body is pre-cast from reinforced concrete by pouring concrete into a cavity defined by an inner mold core and an outer surrounding mold shell. A door frame  116  is integrally formed with the housing body  100 . A door  118  is mounted on the door frame  116  by means of hinges  120 . The door  14  is preferably a fire-resistant, burglary-proof vault door.  
         [0036]    Advantageously, the housing body  100  does not have seams that are prone to penetration by intruders. The enclosure defined within the housing body is also vapor-tight.  
         [0037]    To facilitate transporting of the housing body  100 , the roof portion  110  of the housing body  100  is provided with hooks  124 . The hooks  124  provide anchors for a crane to hoist the housing body  100  onto a truck or position the housing body  100  on a footing at a construction site. FIG. 5 a  shows the housing body  100  being transported to a construction site on a truck  126 . FIG. 5 b  shows a crane  128  engaging the hooks  124  of the housing body  100  and lowering the housing body  100  to a footing  130  at a construction site. FIG. 6 shows how the housing body  100  is incorporated into a building  132  at a construction site.  
         [0038]    The weight of a housing body pre-cast from reinforced concrete with strength of 3000 psi or greater may become quite substantial. To reduce the overall weight of the housing body  100 , the floor portion  112  of the housing body  100  may be omitted. If the floor portion  112  is omitted, a floor can be added to the housing body  100  at the construction site. This is done by molding a frame into the bottom of the housing body  100  and welding this frame to a similar frame at a footing in a construction site. Concrete is monolithically poured into the cavity defined by the frame attached to the bottom of the housing body  100  to form a floor.  
         [0039]    While the present invention has been described with respect to a limited number of preferred embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. The appended claims are intended to cover all such modifications and variations which occur to one of ordinary skill in the art.

Summary:
An easily constructed, highly secure, walk-in vault uses pre-cast panels. A door frame is molded into one of the panels. The panels have interlocking joints with adjacent panels. The interlocking joints are protected with continuous, double burglary-proof seams situated in the interior of the vault. Abutting panels are securely held together by metal rods that penetrate the interlocking joints.