Static structures (e.g. – buildings) – Window or window sash – sill – mullion – or glazing – Panel or panel edging – directly clamped or adhered to wall
Reexamination Certificate
2002-04-03
2004-04-06
Glessner, Brian E. (Department: 3635)
Static structures (e.g., buildings)
Window or window sash, sill, mullion, or glazing
Panel or panel edging, directly clamped or adhered to wall
C052S204530, C052S204591, C052S204620, C052S455000
Reexamination Certificate
active
06715245
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the impact resistant structures for transparent, translucent and similar panes, for example in or around doors and windows.
According to the invention, a pane structure comprises a laminate with a flexible plastic sheet that protrudes beyond a rigid body, for example the flexible plastic center sheet of a glass-plastic-glass laminate. The protruding sheet of plastic remains in a plane and is spaced from one or both of the facing surfaces of the pane, e.g., by a thickness of glass. The pane fits in an inset in a wall or panel, which can be formed by a stepped cutout, or can be limited by an affixed molding or strip. The inset is substantially as deep as the spacing, such that the plastic sheet is positioned to protrude for a distance adjacent to the inset where the pane is fitted. The protruding plastic is coplanar with the integral portion of the plastic in the laminate and is clamped by molding elements to the surface adjacent to the inset. In this way the pane is rigidly fixed in the inset so long as the pane remains intact, is resiliently fixed in the opening in any event, and can be replaced readily if broken.
2. Prior Art
Efforts have been made for some years to improve the structural strength of elements of buildings, particularly in coastal areas and most particularly in the state of Florida after unexpectedly heavy damage was caused by a hurricane in 1992. Standards were developed for determining the merits of structures for withstanding damage in storms characterized by high winds, such as hurricanes and tornadoes. In such storms, wind pressure imposes static and also dynamic or cyclic loads on structures. Strong winds also entrain debris that may strike structures with considerable force.
An impact from fast moving debris can cause a structure such as a window or door to fail. Failure of a window or door potentially weakens the structure as a whole, and at least increases the likelihood of further damage by permitting wind, rain and possibly additional debris to enter the building. Conventional window glass is readily frangible (i.e., not tempered or laminated safety glass). Thus breaking the glass may leave an unobstructed opening.
After incidents of hurricane damage, more stringent building code standards were applied in coastal areas to deal with this danger. Among other requirements, windows, doors and other similar openings were required to be capable of surviving certain impacts without failing to the extent that the opening that they occupy becomes breached. Thus for example, the glass in a window or door might fracture and the window (etc.) could still meet the code, provided that the manner of breakage kept intact the envelope of the building structure.
Preventing any fracture of the glass might require glass that is very strong. Glass can be made strong enough even to be “bulletproof,” but there are drawbacks. The glass might be very thick and aesthetically undesirable, noticeably refractive, less-than transparent, unduly heavy, expensive, etc. The code requirement to keep intact the building envelope in the event of impact is usually met instead by using laminated safety glass, similar to glass used in automobiles. The glass is a sandwich of frangible glass attached to a flexible plastic sheet. The glass can fracture but remains affixed to the flexible sheet. The flexible sheet and the pieces of glass that remain adhered to the plastic, maintain a barrier across the opening, even if the glass becomes fractured. The pane may have to be replaced if the glass fractures, but hurricanes and associate breakage are rare, so the cost/benefit mix is right.
The specific standards applicable in South Florida and other jurisdictions are different in different counties, but typically divide a building into zones of different elevation. At low elevation up to 10 m (30 ft) of building elevation, relatively large wind-borne debris might be expected, e.g., trashcans, lawn furniture, vegetation, fencing and building elements, etc. At higher elevation, smaller debris is more likely to be carried in a high wind, such as roof gravel or ballast. Either type of debris could easily break a window pane.
An exemplary standard for the “large missile zone,” or low elevation zone, may require a door or window to survive test firing of a 4-kg, 0.06 m diameter×1.2 m timber (substantially equal to a 9-lb framing stud) endwise at the test specimen, at a missile speed of 15 m/s (55 km/h or 50 ft/sec or 35 mph). Each test specimen is struck twice, once in the center and once in a corner. After the large missile impact tests, which may fracture the glass as discussed above, the test specimens are subjected to an extended series of many positive and negative wind pressure cycles.
Door and window structures that can routinely survive such tests are available. Some are characterized by a transparent or translucent pane that is inherently strong enough to survive an impact and is mounted rigidly in a door or wall or other structurally sound panel via a rigid mounting structure that likewise can survive the impact. Others are laminates of materials and may have layers of glass and flexible plastic, metal or fibrous mesh reinforcement, etc.
U.S. Pat. No. 5,765,325—DeBlock teaches a multiple layer hurricane door light construction. (A door “light” refers to a light transmissive pane or window installation in an otherwise opaque door or entryway or similar structure.) In DeBlock, a polycarbonate sheet having peripheral screw holes is mounted between two glass panels and is spaced from each of the glass panels. The polycarbonate sheet is rigid and relatively clear, but is much less easily shattered than glass. The door light is mounted in an opening in a door frame by means of molding members that are screwed together to clamp the door between them, and according to this patent the screws are passed through the holes around the rigid polycarbonate sheet so as to improve the structural connection between the window pane structure and the door frame. If a missile breaks the glass, the polycarbonate is likely to remain intact.
The DeBlock door light construction is less easily breached than plain glass, but the polycarbonate sheet is not attached to the glass in the manner of safety glass and instead forms only a means for improving the mechanical connection with the door via the clamping moldings. The relatively hard plain glass spaced on either side of the polycarbonate sheet normally isolates and protects the softer polycarbonate against scratches. Thus the door light appears much like a familiar glass structure. However, the multiple spaced layers of glass and polycarbonate make the door light or window relatively thick and reminiscent of bulletproof glass. The polycarbonate sheet is structurally complicated by the need for pre-formed peripheral holes, which makes the construction somewhat complicated and expensive. Safety glass can be used in the outer glass panes, but if so the safety glass does not contribute structurally to the mounting of the door light, which relies on the opposed clamping moldings and the polycarbonate sheet.
Instead of, or in addition to making a door light or window pane very durable and similar to bulletproof glass in a heavy frame, the pane can be mounted in a manner intended to absorb impact stress. Even assuming the breakage of a frangible glass portion of the door light or window, the envelope that is defined by the window can be arranged to remain intact if a flexible barrier remains in place. A partly compliant mounting reduces shock on the glass during an impact, as compared to a very rigid mounting, and reduces the incidence of breakage.
U.S. Pat. Nos. 6,101,783, Howes and 5,560,149—Lefevre use resilient mounting techniques that might be considered similar to mounting a rigid pane against cushioned glazing pads placed at the perimeter of the pane. In U.S. Pat. No. 5,960,606—Dlubak, a very heavy pane is mounted rigidly in a channel forming structure and is faced with a floating pan
Duane Morris LLP
Glessner Brian E.
McDermott Kevin
Signature Door Co. Inc.
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