Structural panels, generally consisting of a honeycomb core covered on the front and back with facings such as plywood are well known. The facings, both front and back, are nailed during the construction process to the vertical studs of the building structure. They are likewise nailed to the wood base plate and to upper plates which are installed during construction. The honeycomb core, usually made a resin impregnated heavy paper gives the panel structural strength and is commonly glued to the front and back sheets.
The core also provides thermal and acoustic insulation and may be utilized to support additional insulation. Insulating material, such as cellulose fiber, may be deposited in the cavities of the cellular core. Any type of insulation can be used including plastic foams and mineral fiber.
The honeycomb core gives strength to the panel by keeping the front and back facings parallel, thereby preventing them from flexing under the compressive forces of the weight they support.
Such structural panels lack the strength necessary to provide structural support to multi-story buildings. They are typically difficult to install properly and lack the flexibility required for on-site modification such as would be required to add windows or doors.
Also, the allowed capacities of such panels to withstand the structural loads imposed upon them is presently determined by the number of nails fastening the panels to the studs and plates of the building frame. Although panels which are both nailed and glued together consistently withstand vertical testing loads of 40,000 pounds (18,144 kilograms) per panel, the building codes will only allow the nailing schedule to determine the allowable vertical loading. With the maximum practical nailing schedule of 2 inches (5 centimeters) between nails around the perimeter of each panel, the allowed load is only 12% of the test load. The building codes recognize only the load limit of a panel with nails alone even though the assembly can utilize both glue and nails to attach the panels to the framing members. They will recognize the load values for glued assemblies only if no nails are used. This invention will allow the utilization of the full strength of the panel as given by actual experimental test results.
A prior art search did not disclose any patents for structural panels which provide increased strength, ease of installation, and flexibility in use, in the manner of this invention. The following U.S. patent documents were considered in the investigation and evaluation of the prior art relative to this invention.
______________________________________ U.S. Pat. No. INVENTOR ISSUE DATE ______________________________________ 2,809,403 Clements 15 October 1957 2,893,076 Herts 7 July 1959 3,616,139 Jones 26 October 1971 3,665,662 Timbrook 30 May 1972 3,970,502 Turner 20 July 1976 ______________________________________
The Clements patent discloses a structural panel primarily for use as a door. It utilizes a honeycomb core. It is concerned mainly with a method of obtaining maximum strength from the honeycomb core but is not particularly concerned with vertical loading. Specifically, it does not approach the problem of vertical stresses in the manner of the present invention.
The Herts patent discloses structural panels having a honeycomb core which are intended primarily as doors or table tops.
The Jones patent discloses multilayered thermal insulators which utilize multiple honeycomb structures and is primarily concerned with the insulating properties of the panel.
The Timbrook patent discloses a structural panel utilizing a honeycomb core. It is primarily concerned with providing a method of interconnecting the panels to facilitate on-site construction with prefabricated panels.
The Turner patent discloses a structural panel having a foam core. It is primarily concerned with preventing delamination of the outer coverings from the core and with providing an improved latching method for interconnecting panels.
All the above mentioned panels lack the structural strength required to withstand the vertical stresses of use in multi-story buildings. They do not lend themselves to easy on-site modification and they present a comparatively high degree of difficulty in their installation.