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TECHNICAL FIELD  
         [0001]    The present invention relates to floor structures, and more specifically to a floor assembly having removable access panels supported on a grid that is supported on a plurality of primary and secondary structural supports.  
         BACKGROUND OF THE INVENTION  
         [0002]    The increase in the use of computers, communication devices, and other electronic hardware has placed new demands on building designers. Users desire a large number of outlets for access to electrical power and communication signals, and they need the ability to change the location of such outlets on a regular, sometimes weekly basis. Power and data outlets have been located in, or under, a floor, typically in removable floor sections elevated above the original floor by supports. Two typical types of elevated floors are the pedestal floor and the low-profile floor.  
           [0003]    The pedestal access floor has pedestals that consist of metal rods with a base plate at one end and a supporting plate on the other that supports removable horizontal panels, thus forming a raised floor structure. The metal rods are height adjustable and rest on a conventional solid floor deck. The solid floor deck may be made of wood, concrete, or a combination of metal deck and a concrete topping slab. The rods are arranged in a grid, typically square. The rods and plates support removable floor sections. The height of the rods is typically about 18 inches and can be adjusted to a desired height prior to installing the floor sections. Electrical power and data cables are laid between the solid floor deck and the underside of the floor sections. The cables penetrate the floor sections at a desired location to suit the user&#39;s needs. The penetrations may consist only of cables, or may be a junction box, similar to a common electrical wall outlet. The penetrations may accommodate power wires, or signal cables such as cable television, speaker wire, computer networks, etc. In some designs, the space between the floor deck and the elevated floor sections is enough to enable the distribution of conditioned air through grilles and/or registers located in selected floor sections. Because it is relatively expensive, this system is generally used where accommodation must be made for changes in elevation of the floor.  
           [0004]    There is a labor premium involved in having to locate and install the foregoing pedestal system. The pedestals must be braced to meet seismic code, further increasing labor and cost. Moreover, the pedestals increase ceiling height requirements, and ultimately the height of the building, which increases the area of the exterior envelope, thereby increasing not only construction costs but also operating costs due to heat loss. If the pedestal access floor is only used in parts of a building, ramps or structural accommodations must be made for the changes in floor elevation. As users re-route electrical cables below the access floor, the pedestals may present an impediment in pulling cables to a new location. The access floor also represents another step in the construction schedule. The acoustical properties of this system are poor. The floor sections are usually relatively thin and rigid and transmit sound both horizontally and vertically.  
           [0005]    The second type of elevated floor is a low-profile design, which may be roughly 2½ inches to 4 inches high. This design does not use pedestals to raise and support the floor sections, but rather relies on “feet” at the corners of the sections to create the space above the solid floor deck and below the underside of the panel. The panels, with low “feet,” rest directly on the floor deck. This low-profile design is less costly than the pedestal floor, but still impacts the cost of a traditionally designed floor in a building because it requires the use of a solid floor deck. The problem of elevation changes between the existing conventional floor and accessible floor also remains.  
           [0006]    There are also disadvantages to the low-profile floor compared to the pedestal floor. The space below the low-profile sections is not deep enough to be used to supply air. The resulting floor is not as stable, in either the horizontal or vertical dimension, as the pedestal access floor described above. Since the sections are not fastened to the floor deck, they can move when cable is being pulled and re-routed. It also increases the floor-to-floor height of the building, and thus the construction and operating costs. In general, the smaller distance between the solid floor deck and the surface of the floor sections decreases the flexibility of the low-profile floor. Both types require an underlying solid floor deck for support and to provide structural stability to the exterior building.  
           [0007]    In addition, the acoustical characteristics of both common types of elevated floors are typically very poor. They tend to transmit noise to a degree that makes them impractical for use in many environments.  
         SUMMARY OF THE INVENTION  
         [0008]    In accordance with one embodiment of the invention, a floor assembly for a building is provided, the floor assembly having a plurality of primary structural building members, a plurality of spaced-apart secondary structural building members spanning the primary building members, a support grid on the top surfaces of the secondary building members, and a plurality of panels mounted on the support grid to form the floor, with each of the panels individually removable from the support grid to provide access to the space beneath.  
           [0009]    According to an alternative embodiment of the invention, a floor assembly is provided that includes a plurality of longitudinal structural supports, a grid assembly, an attachment system attaching the grid assembly to the upper surface of each of the longitudinal structural supports and configured to enable adjustment in the position of the grid assembly relative to the longitudinal structural supports, and a plurality of panels, the bottom portion of the panels configured to be received into openings in the grid, and the top portion configured to bear against a top surface of the grid assembly.  
           [0010]    In accordance with another embodiment of the invention, a building is provided that includes a plurality of primary structural building members, a plurality of spaced-apart secondary structural building members spanning the primary building members, a support grid affixed to the top surfaces of the secondary building members and configured to receive panels, an attachment system attaching the support grid to the top surface of each of the secondary structural building members and configured to enable adjustment in the position of the support grid relative to the secondary structural building members, and a plurality of panels received in the support grid to form a floor, each of the panels individually detachable from the support grid to provide access to the space between the secondary structural building members. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 shows an isometric view of a section of the floor system formed in accordance with one embodiment of the present invention;  
         [0012]    [0012]FIG. 2 shows a detail of a structural support grid element of a floor system formed in accordance with another embodiment of the present invention;  
         [0013]    [0013]FIG. 3 is a cross-sectional view taken along line III-III of a portion of the floor system of FIG. 1;  
         [0014]    [0014]FIG. 4 is a cross-sectional illustration of an alternative embodiment of the floor system of FIG. 3 taken along line IV-IV;  
         [0015]    [0015]FIG. 5 is a plan view of a floor system according to another embodiment of the invention;  
         [0016]    [0016]FIG. 6 is a plan view of a floor system according to an alternative embodiment of the invention;  
         [0017]    [0017]FIG. 7 is an isometric view of a further embodiment of a floor system of the present invention; and  
         [0018]    [0018]FIG. 8 is an isometric view of a floor system illustrating an alternative embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    The structurally integrated accessible floor system, hereinafter referred to as the floor system, is designated generally as  100 , and is shown isometrically in FIG. 1.  
         [0020]    Primary framing members  102  are provided, which can be formed as integral parts of metal frame type buildings. Secondary framing members, such as joists  104  are connected to the primary framing members  102 . According to one embodiment of the invention, a structural support grid  106  is then formed over the secondary framing members  104 . The grid  106  is configured to receive removable floor panels  108  in the openings  110  formed by the grid  106 . The removable floor panels  108  are of a uniform size to allow interchangeability, and they may be provided with terminals or hookups  112  for electrical power and communication access, and with vents or registers  114  for ventilation.  
         [0021]    For the sake of convenience and clarity, one type of power terminal  112  is shown in FIG. 1. However, it will be obvious to those skilled in the art that a wide variety of terminals may be used, including standard 110 volt sockets, coaxial cable terminals, fiber optical connections, heavy duty power terminals, T 2  connectors, etc. A user may further choose to provide an opening in the panel to enable the passage of cable without the use of a terminal. These and other options are considered to be within the scope of the invention.  
         [0022]    By the same token, a wide variety of means to transmit air and gas may be used in place of the vent  114 , including compressed air hookups, vacuum lines, fans, directionally adjustable vents, filters, emergency gas evacuation systems, compressed oxygen, CO 2 , propane, nitrogen, etc.  
         [0023]    [0023]FIG. 1 also shows optional panels  116  attached to metal channels  118 , which are in turn affixed to the underside of the secondary framing members. These panels  116  are ideally constructed of material that resists fire, thus forming a fire block. The panels  116  isolate one story of a building from the next, establishing fire protection, which may required by many building codes. The panels  116  attached to the underside of the secondary framing members enclose the space between the secondary framing members. This enclosed space may be employed as a plenum for HVAC. This can result in a financial savings, because ductwork is reduced or eliminated. Partitions may be used within this space to permit discreet sections of the floor system to pressurize for use as a plenum.  
         [0024]    Referring next to FIG. 2, shown therein is a section of one embodiment of the structural support grid  106 . According to this embodiment, the structural support grid comprises L-shaped rail members  202  affixed in back-to-back relationship to T-shaped joint nodes  200  to form supports for the removable floor panels. The nodes and rail members are standardized to permit interchangeability.  
         [0025]    It is to be understood that the rail members may have many different cross-sectional shapes and node configurations. For example, some alternative cross-sectional shapes include channel, “T”, and square.  
         [0026]    [0026]FIG. 3 shows the floor system  100  in cross-section taken along lines III-III in FIG. 1. The removable floor panel  108  has a plurality of layers, including a top layer  300 , which is configured according to the requirements of the particular application and may have a carpeted surface or a tile surface. Alternatively, the top layer may be formed using chemically resistive materials for use in a lab or other caustic environments. The top layer  300  and a bottom layer  306  are designed to provide structural stiffness to the panel  108  and are configured according to the structural and weight bearing requirements of the particular application. Fire retardant layers  304  are composed of fire resistant materials such as gypsum, or other appropriate material, and serve to inhibit the passage of fire from one side of the panel  108  to the other. An insulation layer  302  provides thermal and acoustic insulation, as well as additional stiffness.  
         [0027]    It will be understood that the composition of the removable floor panels will vary according to the requirements of a particular application and will in part be dictated by the anticipated environment, the required load carrying capacity, the desired appearance, the anticipated degree of noise control, local building and fire codes, and other factors.  
         [0028]    Although the removable floor panels  108  bear against the structural support grid  106 , panel fasteners  310  may be used to positively attach the panels  108  to the structural support grid  106 . In the embodiment shown in FIG. 3, the panel fasteners  310  comprise threaded fasteners that pass from a lower surface of the structural support grid  106  into an opening in a lower surface of the removable panel  108  via an opening  311  in the rail member  202  of the structural support grid  106 . The opening  311  is oversized in relation to the threaded fastener  310  to enable adjustment in the position of the removable panel  108  relative to the structural support grid  106 . The threads of the threaded fastener  310  engage the removable panel and a hexagonal head of the fastener  310  bears against the lower surface  324  of the support grid  106 , drawing the removable panel tight against the structural support grid  106 . Thus, in this embodiment access to the panel fasteners  310  is from beneath the structural support grid  106 .  
         [0029]    A leveling unit  308  is provided to control a vertical distance  320  between the structural support grid  106  and the secondary framing members  104 . FIG. 3 shows one of a plurality of similar units that comprise the leveling system, which functions as described below.  
         [0030]    As shown in FIG. 3, the leveling unit  308  includes a threaded rod  312  attached to a support plate  314  that bears against an upper surface  322  of the secondary framing member  104 . The threaded rod  312  passes through a lift plate  316  via an opening in the lift plate  316 , with the lift plate  316  bearing upward against the lower surface  324  of the structural support grid  106 . The rod  312  is slideably received in an opening  307  formed in the grid  106 . A pair of jam nuts  318  on the threaded rod supports the lift plate  316 . The position of the jam nuts  318  on the threaded rod determines the distance  320  between the upper surface  322  of the secondary framing member  104  and the lower surface  324  of the structural support grid  106 .  
         [0031]    By adjusting each of the plurality of units of the leveling system, the bearing surface  326  of the floor system  100  can be leveled, even if the upper surfaces  322  of the secondary framing members are not level.  
         [0032]    In another embodiment of the invention, leveling devices that are functionally similar to the leveling unit  308  described above may be employed between an upper surface  120  (shown in FIG. 1) of the primary framing members  102  and the part  105  of the secondary framing members  104  that bears against the primary framing members. By adjusting the vertical distance between the primary and secondary framing members, the level of the structural support grid  106  can be controlled.  
         [0033]    Other methods of controlling the vertical distance (not shown) between the primary and secondary framing members  102 ,  104 , or between the structural support grid  106  and the secondary framing members  104  will be obvious to those skilled in the art. These methods include the use of wedges, shims, threaded devices that are accessed from above the floor system, automatic or remotely adjustable devices, etc., all of which are deemed to be within the scope of the invention.  
         [0034]    [0034]FIG. 4 is a cross-sectional view of a floor system  100 , taken along line IV-IV, and shows an alternative embodiment of the removable panel  108 . In this embodiment, a flexible gasket  400  is affixed to the top edge  412  of each panel  108 ,  109 . The gaskets  400  of adjoining panels  108 ,  109  press against each other, providing a seal between the removable panels  108 ,  109 . The seal may be employed to prevent spills from leaking through the floor system. In applications where spills of caustic or dangerous fluids might be anticipated, the composition of the gasket  400  is chosen to be resistant to the particular classes of substances in use. Multiple or interlocking gaskets may also be employed to provide a more secure seal. Alternatively, a single gasket may be wedged between the adjoining panels  108 ,  109  after they are installed on the structural support grid  106 . The gasket  400  may also be used in applications where it is desirable to control the movement of air or other gasses from one side of the floor system to the other.  
         [0035]    [0035]FIG. 4 also shows an alternative embodiment of the panel fasteners. Here, the panel fastener  410  is accessed with a tool (not shown) that is inserted from above the surface of the floor system into the center of the joint node  200 . The panel fastener  410  is rotated approximately 45°. Fastener blades  408  rotate from positions in slots (not shown) in the joint node  200  into slots in the corners of the removable panels  406 , locking them in place.  
         [0036]    Other locking devices and systems will be evident to those skilled in the art and are considered to be within the scope of the invention. Such devices include those employing cam-type fasteners, devices that are accessible from the surface of the removable floor panels, devices that latch automatically when the removable floor panels are emplaced, etc.  
         [0037]    Depending upon the height and local requirements, some buildings include devices or methods of construction that provide earthquake resistance. In conventional construction methods a solid floor deck functions as a diaphragm, which is resistant to dimensional stresses.  
         [0038]    According to one embodiment of the invention, and as illustrated in FIG. 5, the structural support grid  106  is attached orthogonally, relative to the primary  102  and secondary  104  framing members. Diagonal stays  500  are employed to brace and provide the requisite stability to the structure. The stays  500  are attached directly to the primary columns  502  of a building and pass underneath the floor structure  100 .  
         [0039]    [0039]FIG. 6 shows an alternative embodiment of the invention, in which the structural support grid  106  is oriented diagonally, relative to the primary  102  and secondary  104  framing members. In this embodiment, the structural support grid  106  itself forms the diagonal bracing that reinforces the building structure.  
         [0040]    In a further embodiment of the invention, and as shown in FIG. 7, repositionable walls  700  may be employed as part of the structurally integrated accessible floor system. These repositionable walls may consist of floor to ceiling room dividers, which may be assembled on site, as shown in FIG. 7, or prefabricated and installed as individual units, or alternatively they may be prefabricated cubicle dividers of the type common in office environments. The repositionable walls  700  are affixed directly to the structural support grid  104 . Partial floor panels  1   08 a may be cut to the necessary size at the site, using conventional methods, or may be manufactured in common dimensions. By affixing the walls  700  to the grid  106  and employing partial floor panels, acoustical isolation is enhanced and the structural stability of the walls  700  is improved.  
         [0041]    Electrical components in the walls  700 , such as light switches, thermostats, power connections etc, may be wired directly through the bottom of the walls via harnesses (not shown) that can be connected to cables and connectors underneath the floor panels  108 . This is a significant advantage, especially in the case of cubicle dividers, over the methods currently in use, because conventional cubicle dividers must bring power into open areas and may involve complex interconnections between the dividers, and power drops from ceilings. Other methods include the use of wireless technology for switches and controls. Such technology has the advantage that it doesn&#39;t require any wiring connections in the walls.  
         [0042]    [0042]FIG. 8 illustrates an alternative embodiment of the invention in which structural support rails  800  are employed. The rails  800  span the secondary framing members  104  and support the removable floor panels  108  on two sides. The floor panels  108  of this embodiment are configured to span the structural support rails  800 .  
         [0043]    In a conventional building, an elevated floor system of the type described in the background section of this document is installed on top of an existing floor. The elevated floor occupies a space above the floor, and is not part of the building structure. The accessible space provided by such an elevated floor is that space between the panels that form the surface of the elevated floor and the upper surface of the solid floor deck. In the structurally integrated accessible floor system of the embodiments of the invention described herein the solid floor deck is not needed. The removable panels provide access to the space beneath the grid and between the individual secondary framing members. In prior floor structures, this space is inaccessible and wasted. Because the structural support grid of the present invention spans the secondary framing members, the space beneath is unobstructed, providing simplified access for pulling cables, laying conduit, ducting, and pipe.  
         [0044]    The cost of the floor system disclosed herein is significantly mitigated by several factors. A conventional structural floor is not required, and the floor system is essentially the same height as a conventional structural floor, obviating the need for ramps in areas where conventional floors adjoin the floor system. Because the floor system does not add height per story to the final building structure, there will be a savings in building materials, and a savings in operating costs over those of a similar building using accessible floors according to the prior art. Also, because the space under the floor system is unencumbered by pedestals, feet, or other support devices, the floor system has improved flexibility and changeability. Pulling cable, laying conduit and pipe, and installing ducting are all simplified. The labor costs and down time costs are reduced during changeovers.  
         [0045]    From the foregoing it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims and the equivalents thereof.

Summary:
A floor system for a building that includes primary and secondary structural supports, a grid attached to the supports, and a plurality of panels removably mounted in the grid to provide access to the space below the panels and the grid. The floor system replaces conventional permanent structural floors, and provides ready access to the underlying space which would otherwise be inaccessible in a conventional floor.