Stock material or miscellaneous articles – Structurally defined web or sheet – Edge feature
Reexamination Certificate
2000-11-21
2003-09-16
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Edge feature
C428S060000, C106S735000
Reexamination Certificate
active
06620487
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to panels that are applied to framing in residential and other types of light construction. More particularly, the invention relates to panels that are able to resist lateral forces imposed by high wind and earthquake loads in regions where they are required by building codes. Such panels, commonly known as shear walls or diaphragms, must demonstrate shear resistance as shown in recognized tests, such as ASTM E72.
If one considers a simple box structure having panels fastened to framing, it can be seen that a strong lateral force acting against one side of the box (e.g., wind pressure) will tend to force the side walls resisting that force from a rectangular shape into a parallelogram. Not all sheathing panels are capable of resisting such forces, nor are they very resilient, and some will fail, particularly at points where the panel is fastened to the framing. Where it is necessary to demonstrate shear resistance, the sheathing panels are measured to determine the load which the panel can resist within the allowed deflection without failure.
The shear rating is generally based on testing of three identical 8×8 ft (2.44×2.44 m) assemblies, i.e., panels fastened to framing. One edge is fixed in place while a lateral force is applied to a free end of the assembly until the load is no longer carried and the assembly fails. The measured shear strength will vary, depending upon the thickness of the panel and the size and spacing of the nails used in the assembly. For example, a typical assembly, e.g., a nominal ½ inch (12.7 mm) thick plywood fastened with 8d nails (see the nail description below) to nominal 2×4 inch (50.8×101.6 mm) wood studs spaced 16 inches (406.4 mm) apart (on centers), the nails being spaced 6 inches (152.4 mm) apart on the perimeter and 12 inches (304.8 mm) apart within the perimeter, would be expected to show a shear strength of 720 lbs/ft (1072 kg/m) before failure occurs. (Note that the measured strength will vary as the nail size and spacing is changed, as the ASTM E72 test provides.) This ultimate strength will be reduced by a safety factor, e.g., a factor of three, to set the design shear strength for the panel.
Sheathing panels used where a shear rating must be met usually are plywood or oriented strand board (OSB), which consist of pieces of wood that are glued together. These panels can provide the needed shear strength, but each is combustible and neither is durable when exposed to water. A panel made of hydraulic cement will resist water, but is much heavier than the wood panels and has insufficient shear strength. It is believed that there is no panel currently available which can provide the necessary shear strength, while avoiding the deficiencies of plywood or OSB panels.
As the thickness of the board affects its physical and mechanical properties, e.g., weight, load carrying capacity, racking strength and the like, the desired properties vary according to the thickness of the board. Thus, the desired properties which a shear rated panel with a nominal thickness of 0.5 inches (12.7 mm) should meet include the following.
The panel when tested according to ASTM 661 and American Plywood Association (APA) Test Method S-1 over a span of 16 inches (406.4 mm) on centers, should have an ultimate load capacity greater than 550 lbs (250 kg) under static loading, an ultimate load capacity greater than 400 lbs (182 kg) under impact loading and a deflection of less than 0.078 inches (1.98 mm) under both static and impact loading with a 200 lb (90.9 kg) load.
The racking shear strength of a 0.5 inch (12.7 mm) thick panel measured by the ASTM E72 test using the nail size and spacing described above should be at least 720 lbs/ft (1072 kg/m).
A 4×8 ft, ½ inch thick panel (1.22×2.4 m, 12.7 mm thick) should weigh no more than 99 lbs (44.9 kg) and preferably no more than 85 lbs (38.6 kg).
The panel should be capable of being cut with the circular saws used to cut wood.
The panel should be capable of being fastened to framing with nails or screws.
The panel should be machinable so that tongue and groove edges can be produced in the panel.
The panel should be dimensionally stable when exposed to water, i.e., it should expand as little as possible, preferably less than 0.1% as measured by ASTM C 1185.
The panel should not be biodegradable or subject to attack by insects or rot.
The panel should provide a bondable substrate for exterior finish systems.
The panel should be non-combustible as determined by ASTM E136.
After curing for 28 days, the flexural strength of a 0.5 inch (12.7 mm) thick panel having a dry density of no more than 65 lb/ft
3
(1041 kg/m
3
) after being soaked in water for 48 hours should be at least 1700 psi (11.7 MPa), preferably at least 2500 psi (17.2 MPa), as measured by ASTM C 947. The panel should retain at least 75% of its dry strength.
It should be evident that plywood and OSB panels meet some, but not all, of the above performance characteristics. Thus, there is a need for improved panels which can meet the shear rating required in certain locations and which exceed the capability of the currently-used wood-based panels by providing non-combustibility and water durability.
Prior art hydraulic cement-based panels and structures also have not possessed the combination of low density, nailability and cuttability required to enable the panel to be cut or fastened (either nailed or screwed) with conventional carpentry tools.
The panels of the invention may generally be described as gypsum-cement compositions reinforced with glass fibers and, with the addition of microspheres, having reduced weight compared with hydraulic cement panels. The panels will satisfy performance requirements listed above and may be distinguished from other compositions to be discussed below which contain similar components, but are not capable of meeting the desired performance.
Gypsum-cement compositions are disclosed generally in U.S. Pat. Nos. 685,903; 5,858,083 and 5,958,131. In each patent, pozzolans are added, silica fume in the '903 and '803 patents and metakaolin in the '131 patent. Aggregates and fiber additions are suggested, but panels meeting the requirements of the invention are not described.
Although glass fibers have been used to reinforce cement, they are known to lose strength with time since the glass is attacked by the lime present in cured cement. This may be offset, to some extent, by coating the glass fibers or by using a special alkali-resistant glass. Other fibers have been suggested to reinforce cement, such as metal fibers, wood or other cellulose fibers, carbon fibers, or polymer fibers.
Cement-based panels and structures have also contained lightweight particles of glass, ceramics and polymers in order to reduce weight, but at the expense of reduced strength. Other aggregates have been suggested, but they will not have the advantages of the lightweight particles.
In U.S. Pat. No. 4,379,729, three layers are used in panels intended to replace wood for concrete forms. The outer two layers are glass fiber reinforced cement, while the middle layer is cement containing hollow spheres. While such panels are subject to static loading, they are not required to meet the building code requirements where wind and earthquake loads are expected.
In Russian Patent No. SU 1815462, three layers are also used in making pipe, rather than panels. Again, the outer layers are made of glass fiber reinforced cement, while the middle layer contains both glass fiber and glass spheres.
A thick modular wall section, rather than a shear rated panel, is discussed in U.S. Pat. No. 4,259,824. Various aggregates, including glass fibers, are suggested to be useful.
In U.S. Pat. No. 5,154,874, a gypsum board including paper fibers is disclosed.
A gypsum-cement panel is discussed in Canadian Patent No. CA 2,192,724. The panel contains 10 to 35 wt. % of wood or paper fibers, rather than glass fibers. Similarly, in U.S. Pat. No. 5,371,989, a gypsum boar
Bonen David M.
Dubey Ashish
Natesaiyer Kumar C.
Tonyan Timothy D.
Janci David F.
Jenkens & Gilchrist
Lorenzen John M.
Pyon Harold
Rhee Jane
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