Structural floor system
A structural floor system is provided comprising: a plurality of I-joists; a plurality of composite wood panels attached to the plurality of I-joists, each panel having parallel first and second longitudinal edges, each panel containing a binder resin; and an adhesive composition containing the binder resin, the adhesive composition applied between on the first and second longitudinal edges.
A structural, weight-bearing floor system is constructed by lying a floor deck across a number of underlying, supporting I-joists. The deck may be made of a variety of different materials, such as wood as well as concrete although for the present invention, which is directed primarily at residential home construction, the flooring deck will most typically be constructed of wood, such as wood panels set to lie across a series of underlying wood joists.
One of the most important design parameters of a structural floors system is the distance that separates adjacent joists. The greater the distance, the fewer the joists that support the deck of the structural floor system. Increasing the span distance provides a number of advantages such as decreasing the cost and the amount of time that is necessary to install a floor, as well as give builders and architects more choice in the way homes are designed, arranged and built. Closely related to the span distance is the stiffness of the structural floor system: generally the closer the joists the stronger and stiffer the flooring system. And the stronger, and more stiff the floor is, the less likely that unwanted “squeaks” will develop. It is particularly desired to avoid producing these squeaks in a floor, because fixing them is often very difficult, time consuming and invariably expensive. Thus, it is desirable to have the structural flooring system composed of a material that allows for broad span distances while at the same time ensuring good stiffness and strength.
Many different techniques have been developed by which the distance and stiffness can be increased. For example, U.S. Pat. No. 5,220,761 discloses a structural flooring system constructed from concrete and structural steel, in which longer span distances are obtained by composite action of the concrete and cold formed structural steel together, with the shear transfer effectuated by the use of a bond bar attached to the structural steel and embedded in the concrete slab itself.
While this structural floor system has the advantage of increasing span distances and reducing the thickness of the cast concrete floor, it is not really suitable for widespread use in home construction. Much the same may be said about other techniques developed to increase the span distance of structural floors. For example, U.S. Pat. No. 5,168,681 discloses a prestressed flooring system. In this system, the underlying joists are maintained in laterally directed compressive stress by the use of a cable anchored at one end to the outermost joist, and the other end to a spring which is in turn connected to the outermost joist. The individual joists themselves are kept in place in their relative positions by use of blocking elements. The result is a structure that, according to the '681 patent, increases “vertical stiffness and reduces the amount of deflection, vibration, and noise experienced during loading.” While those are desirable benefits, the expense and difficulty of installing this pretensioning system makes it impractical for widespread residential use.
Accordingly, there is a need in the art for a structural flooring system construction that can be easily installed, is relatively inexpensive, shows excellent strength and stiffness, and increases the span distance between adjacent joists.
Wood-based composite material may be particularly suitable for use in a structural flooring system. Wood-based composites include such materials as plywood, particle board and oriented strand board (“OSB”). These wood-based composites are alternatives to natural solid wood lumber and have replaced wood lumber in many structural applications in the last seventy-five years because of both the cost of high-grade timber wood as well as a heightened emphasis on conserving natural resources. These wood-based composites not only use the available supply of timber wood more efficiently, but they can also be formed from lower-grade wood species, and even from wood wastes.
[This paragraph can be deleted if you'd like, it is a little too subtle. The point was to show that OSBs are a particularly good solution here because one of their admitted deficiencies is appearance, but appearance is irrelevant if the material is buried under a floor.] While these wood-based composite materials do offer a highly efficient way to use available wood material, because they typically consist of small particles (particle board), wood strands (OSB), flat pieces of low-grade wood species or some similar such material, products made from them do not have an attractive, grained appearance, but rather tend to have unsatisfactory aesthetic finishes. However, this poor aesthetic finish is irrelevant to their use in a structural flooring system, because the structural flooring system is typically not visible in a finished residential home. And while portions of the structural floor system may at times be visible (such as to those who are viewing the floor from beneath, in the basement of a house), the aesthetics of the structural flooring system would be irrelevant to almost every home dweller.
Accordingly there is a particular need in the art for a structural flooring system having desirable qualities such as being inexpensive, easy to install, and producing wide span distances, and that can additionally be constructed from a wood-composite material.
BRIEF SUMMARY OF THE INVENTIONThe present invention includes a structural floor system that contains: a plurality of I-joists; and a plurality of composite wood panels attached to the plurality of I-joists. Each panel has parallel first and second longitudinal edges, and each panel contains a binder resin. Also included is an adhesive composition containing the binder resin, the adhesive composition applied between on the first and second longitudinal edges.
The present invention also includes a structural floor system containing: a plurality of I-joists; and a plurality of OSB wood panels attached to the plurality of I-joists. Each panel has parallel first and second longitudinal edges, wherein a groove is formed along the second longitudinal edge, and a complementary shaped tongue formed along the first longitudinal edge; each panel further containing a binder resin, the binder resin being selected from the group comprising polyurethane resin, and isocyanate resin. And finally including an adhesive composition comprising containing the binder resin, the adhesive composition applied between on the first and second longitudinal edges.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGSThe foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawing figure,
All parts, percentages and ratios used herein are expressed by weight unless otherwise specified. All documents cited herein are incorporated by reference.
As used herein, “wood” is intended to mean a cellular structure, having cell walls composed of cellulose and hemicellulose fibers bonded together by lignin polymer.
By “laminated”, it is meant material composed of layers and bonded together using resin binders.
By “wood composite material” or “wood composite component” it is meant a composite material that comprises wood and one or more other additives, such as adhesives or waxes. Non-limiting examples of wood composite materials include oriented strand board (“OSB”), structural composite lumber (“SCL”), waferboard, particle board, chipboard, medium-density fiberboard, plywood, and boards that are a composite of strands and ply veneers. As used herein, “flakes”, “strands”, and “wafers” are considered equivalent to one another and are used interchangeably. A non-exclusive description of wood composite materials may be found in the Supplement Volume to the Kirk-Othmer Encyclopedia of Chemical Technology, pp 765-810, 6th Edition, which is hereby incorporated by reference.
In residential construction a structural floor system is built upon a generally conventional foundation (for the first story), which supports a floor system that is comprised of a series of parallel, spaced apart floor I-joists, with a wood decking fasten upon them.
The following describes preferred embodiments of the present invention, which provides a structural floor system comprising wood composite floor panels, supporting wood I-joists, and a polyurethane or isocyanate subfloor adhesive composition. The wood composite floor panels preferably have matching tongue and groove finishes along their longitudinal edges that allows adjacent panels to be easily connected to each other to form tongue and groove joints. Additionally, the aforementioned polyurethane or isocyanate subfloor adhesive is applied to the tongue and groove finishes on the longitudinal sides of the panels to improve bonding to one another. This structural floor system has the advantage of significantly improved stiffness over prior art wood composite structural floor systems, which allows for even greater span distances or shallower I-joists at the same span. While not intended to be limited by theory, it is believed that in the present invention improved surface stiffness has been achieved by a synergistic adhesive interaction between the polyurethane or isocyanate subfloor adhesive and the polyurethane or isocyanate binders in the wood composite panels. The result of this synergistic interaction is a strong bond between adjacent panels leading to an enhanced composite action effect, where the individual panels and I-joists are allowed to act as a single part, and the structural floor system shows greater strength and stiffness than the sum of its individual parts (the panels and joists) would indicate.
Wood Composite Floor Panels
The first component of the present invention is the wood composite floor panels. Preferably, the wood composite panels are made from OSB material. The wood composite panels have parallel first and second longitudinal edges. Preferably, a groove is formed along a first longitudinal edge and a complementary shaped tongue formed along the second longitudinal edge. Suitable tongue and groove arrangements are disclosed in greater detail in U.S. Pat. No. 6,675,544 B1, to Ou et al; and U.S. Pat. No. 6,772,569 B1, to Bennett; both of which are hereby incorporated by reference.
The oriented strand board is derived from a starting material that is naturally occurring hard or soft woods, singularly or mixed, whether such wood is dry (having a moisture content of between 2 wt % and 12 wt %) or green (having a moisture content of between 30 wt % and 200 wt %). Typically, the raw wood starting materials, either virgin or reclaimed, are cut into strands, wafers or flakes of desired size and shape, which are well known to one of ordinary skill in the art.
After the strands are cut they are dried in an oven and then coated with a special formulation of one or more polymeric thermosetting binder resins, waxes and other additives. The binder resin and the other various additives that are applied to the wood materials are referred to herein as a coating, even though the binder and additives may be in the form of small particles, such as atomized particles or solid particles, which do not form a continuous coating upon the wood material. Conventionally, the binder, wax and any other additives are applied to the wood materials by one or more spraying, blending or mixing techniques, a preferred technique is to spray the wax, resin and other additives upon the wood strands as the strands are tumbled in a drum blender.
After being coated and treated with the desired coating and treatment chemicals, these coated strands are used to form a multi-layered mat, preferably a three layered mat. This layering may be done in the following fashion. The coated flakes are spread on a conveyor belt to provide a first ply or layer having flakes oriented substantially in line, or parallel, to the conveyor belt, then a second ply is deposited on the first ply, with the flakes of the second ply oriented substantially perpendicular to the conveyor belt. Finally, a third ply having flakes oriented substantially in line with the conveyor belt, similar to the first ply, is deposited on the second ply such that plies built-up in this manner have flakes oriented generally perpendicular to a neighboring ply. Alternatively, but less preferably, all plies can have strands oriented in random directions. The multiple plies or layers can be deposited using generally known multi-pass techniques and strand orienter equipment. In the case of a three ply or three layered mat, the first and third plys are surface layers, while the second ply is a core layer. The surface layers each have an exterior face.
The above example may also be done in different relative directions, so that the first ply has flakes oriented substantially perpendicular to conveyor belt, then a second ply is deposited on the first ply, with the flakes of the second ply oriented substantially parallel to the conveyor belt. Finally, a third ply having flakes oriented substantially perpendicular with the conveyor belt, similar to the first ply, is deposited on the second ply.
Various polymeric resins, preferably thermosetting resins, may be employed as binders for the wood flakes or strands. Suitable polymeric binders include isocyanate resin, urea-formaldehyde, polyvinyl acetate (“PVA”), phenol formaldehyde (“PF”), melamine formaldehyde, melamine urea formaldehyde (“MUF”) and the co-polymers thereof. Isocyanates are the preferred binders, and preferably the isocyanates are selected from the diphenylmethane-p,p′-diisocyanate group of polymers, which have NCO— functional groups that can react with other organic groups to form polymer groups such as polyurea, —NCON—, and polyurethane, —NCOO—; a binder with about 50 wt % 4,4-diphenyl-methane diisocyanate (“MDI”) or in a mixture with other isocyanate oligomers (“pMDI”) is preferred. A suitable commercial pMDI product is Rubinate 1840 available from Huntsman, Salt Lake City, Utah, and Mondur 541 available from Bayer Corporation, North America, of Pittsburgh, Pa. Suitable commercial MUF binders are the LS 2358 and LS 2250 products from the Dynea corporation.
The binder concentration is preferably in the range of about 3 wt % to about 8 wt %. A wax additive is commonly employed to enhance the resistance of the OSB panels to moisture penetration. Preferred waxes are slack wax or an emulsion wax. The wax solids loading level is preferably in the range of about 0.1 wt % to about 3.0 wt % (based on the weight of the wood).
It is preferable that the surface layers in the present invention make use of the following enhanced resin composition. This resin composition involves the simultaneous application of an isocyanate resin and a powdered aromatic phenol-aldehyde thermoset material in the same blender in the preparation of the surface layers of the OSB. The powdered aromatic aldehyde thermoset effectively replaces a fraction of the MDI resin that otherwise would be needed. Preferably, a powdered phenol-formaldehyde is used that penetrates very well inside curled flakes of the surface layer(s) of the OSB. It also enhances resin distribution inside the curled flakes in the surface layer of OSB to improve the board product quality by reducing curled flake failures without increasing resin costs. The MDI binder ingredient renders the OSB structurally strong and durable and generally improves the water resistance, while the phenol-formaldehyde ingredient prevents flake popping and improves strength of the OSB among other things. The resin binder system used for one or both the OSB surface layers, as initially reacted, preferably is non-aqueous and contains no water or, at most, only nominal impurity levels (viz., less than 1 wt. % and preferably less than 0.5 wt. % water based on the total weight of the binder system). This resin composition and its methods for use are described in greater detail in U.S. Pat. No. 6,479,127.
After the multi-layered mats are formed according to the process discussed above, they are compressed under a hot press machine that fuses and binds together the wood materials, binder, and other additives to form consolidated OSB panels of various thickness and sizes. The high temperature also acts to cure the binder material. Preferably, the panels of the invention are pressed for 2-15 minutes at a temperature of about 175° C. to about 240° C. The resulting composite panels will have a density in the range of about 35 lbs/ft3 to about 48 lbs/ft (as measured by ASTM standard D1037-98). The density ranges from 40 lbs/ft to 48 lbs/ft for southern pine, and 35 lbs lbs/ft to 42 lbs/ft for Aspen. The thickness of the OSB panels will be from about 0.6 cm (about ¼″) to about 5 cm (about 2″), such as about 1.25 cm to about 6 cm, such as about 2.8 cm to about 3.8 cm.
I-Joists
The Wood I-joists consist typically of three sections: two flange members that are interconnected by a webstock member. Typically the flanges have dimensions in the range of 2 inches-4 inches×1 inch-2 inch. The most common thickness dimension for the webstock is ⅜ inch. Most typically the flanges are made from solid wood lumber, while wood composites have become the most typical material from which to form the webstock. Joints are formed between the opposing ends of each webstock member and grooves located in the wider face of each flange piece to receive the webstock. Typically, these joints will be glued to hold the the I-joist together. Typically, a phenol-resorcinol-formaldehyde or isocyanate/urethane adhesive is used. These adhesives are designed to cure at room temperature, but at least a small amount of heat is preferably used to speed cure. The wood composite panels are then placed in their final position on the I-joists, and the installation is completed by nails or some similar fasteners, which are driven through the wood composite panels into the I-joist.
Some suitable materials for I-joists include Advantech® 1-89 I-joists. These Advantech I-joists are available from Huber Engineered Woods, LLC, Charlotte, N.C. The Advantech® I-89 I-joists consist of flange sections made from 2100 fb machine stress rated solid wood lumber and measuring 3.5 inch×1.5 inch. The webstock is ⅜ inch Advantech OSB. Also suitable is Advantech® I-64 I-joists, whcich consist of flange sections made from 1950 fb machine stress rated lumber and measuring 2.5 inch×1.5 inch. The webstock is ⅜ inch Advantech® OSB. Another material particularly suitable as the flange sections in a wood composite I-joist is laminated veneer lumber (“LVL”), which is a wood composite material that includes several plys (typically between 11 and 20) laminated together.
Adhesive Composition
The adhesive composition of the present invention is applied, using a caulk gun in a continuous bead between the along longitudinal edges of the wood panel, preferably along the tongue and grooves formed thereon. The result of applying this adhesive is the creation of a strong bond between adjacent panels leading to an enhanced composite action effect, i.e., the structural floor system shows greater strength and stiffness than the sum of its individual parts. As mentioned above this can be achieved through the combined use of a polyurethane and/or isocyanate resin in both the adhesive composition and in the binder resin included in the wood composite floor panels. The aforementioned construction adhesive is also applied to the top of the I-joist so that the lower surface of the panel and the I-joist are adhesively bonded as well.
Another suitable combination of adhesive composition and wood composite floor panel is the combination of a phenolic-resorcinol-formaldehyde resin and PF-containing wood composite floor panel.
While the present application specifically mentions polyurethane and the scope of this invention is not limited to those materials. Indeed it is believed that the enhanced composite action effects can be obtained whenever the resin binder in the wood composite panels includes some or all of the same adhesive resins and materials that is found in the adhesive composition applied between adjacent wood panels along the longitudinal edge.
The invention will now be described in more detail with respect to the following, specific, non-limiting examples.
EXAMPLESStructural floor systems were prepared both according to the prior art processes and as disclosed in the present invention to show that the presently disclosed structural floor system provides better strength and stiffness performance than the prior art. The structural floor systems were tested according to a protocol and design guidelines devised by the Wood I-Joist Manufacturers Association.
The first step in this testing method was to determine a baseline by measuring the EI of the I-joist component of the structural floor systems. The EI is a measure of the stiffness and strength of the material, where ‘E’ is the modulus of elasticity and ‘I’ is the moment of inertia. In the present case, the EI was measured according to the method disclosed in ASTM D5055. In order to gain a comprehensive understanding of the presently inventive structural floor systems, the new floor systems as well as existing prior art floor systems were tested by incorporating a wide variety of different I-joist constructions, rather than just using the same I-joist material. The I-joist used was varied between the following three constructions was selected from one of the following materials:
(1) Laminated Veneer Lumber. These materials consists of flange sections made from laminated veneer lumber measuring 1.5 inch by 1.75 inch and being rated as having a modulus of elasticity of 2.2 million.
(2) Advantech® I-89 I-joists.
(3) Advantech® I-64 I-joists.
After measuring the EI of these I-joists, structural floor systems both of the present invention and according to the present invention were assembled incorporating these I-joists and composite wood panels. The precise construction and adhesive use of each of the floor systems were varied as follows:
1PL Premium ® adhesive, available from OSI Sealants, Inc., Mentor, Ohio
2PL 300 ® Foam Adhesive form OSI Sealants, Inc.
3For this floor construction, the adhesive was applied in successive sequences of 8 inch continuous bead adhesive, 8 inch skipped, no adhesive.
Then the EI of the prior art structural flooring systems and structural flooring systems prepared according to the present invention were measured by the use of a three point bending test per ASTM D198 and D5055, with the following experimental parameters:
(1) 11⅞ inch depth I-joist,
(2) 22/32 inch panel thickness
(3) 19.2 inches panel width
(4) 213.8 inches test span or both the prior art and the floor structure systems of the present invention, the EI was measured for each the five different floor system configurations with each of the three different joist materials. Then, these results were compared to the EI for the I-joists (as measured above). The mean % increase of the prior art floor structure system and the floor structure system of the present invention compared to the I-joist alone were then calculated and then graphically plotted in
As can be seen in
Using the same data as discussed above, additional advantages of the floor structure systems of the present invention may be noted. Based on geometry calculations of the Moment of Inertia of a composite cross-section, the panel component of the prior art structural flooring systems would have to be 0.93″ thick instead of 23/32″ in order to obtain the same Moment of Inertia of that of the 23/32″ thick AdvanTech panel in the floor structure systems of the present invention. Similarly, the AdvanTech panel could be reduced to a thickness of 0.6″ with a similar performance to the prior art structural flooring systems as stated above. This would allow the wood panel component to be 16% lighter—a savings of 13 lbs. The reduced weight would mean lower transportation costs per panel and the panel would be easier to install due to lighter weight in handling. Another way of reducing the Moment of Inertia by 25% would be to reduce the depth of the I-Joist from 11⅞″ to 10.5″, which would result in savings for material costs, shipping costs, and easier installation. Yet another way of reducing the cost of the floor would be by changing the joist spacing of 16″ to 19.2″. For a floor that is made with 11⅞″ I-Joists, that is 20 feet long, the difference in stiffness from 16″ spacing to 19.2″ spacing is 17%. Therefore, the stiffness increase of 25% by using AdvanTech panels in the floor structure systems of the present invention would make up for the stiffness difference, allowing the use of 20% fewer joists.
It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.
Claims
1. A structural floor system comprising:
- a plurality of I-joists;
- a plurality of composite wood panels attached to the plurality of I-joists, each panel having parallel first and second longitudinal edges, each panel containing a binder resin; and
- an adhesive composition containing the binder resin, the adhesive composition applied between on the first and second longitudinal edges.
2. The structural floor system according to claim 1, wherein a groove is formed along the second longitudinal edge, and a complementary shaped tongue formed along the first longitudinal edge.
3. The structural floor system according to claim 1, wherein the plurality of composite wood panels are formed from OSB.
4. The structural floor system according to claim 1 wherein the binder resin is selected from the group comprising polyurethane resin, and isocyanate resin.
5. The structural floor system according to claim 1 wherein the I-joists comprise:
- (a) a first flange and a second flange, at least the first flange being made from solid wood lumber; and
- (b) a webstock, interconnecting the first and second flange, the webstock being composed of a wood composite material.
6. The structural floor system according to claim 1 wherein the wood composite wood panels isocyanate resin and a powdered aromatic phenol-aldehyde thermoset material
7. A structural floor system comprising:
- a plurality of I-joists;
- a plurality of OSB wood panels attached to the plurality of I-joists, each panel having parallel first and second longitudinal edges, wherein a groove is formed along the second longitudinal edge, and a complementary shaped tongue formed along the first longitudinal edge; each panel further containing a binder resin, the binder resin being selected from the group comprising polyurethane resin, and isocyanate resin; and
- an adhesive composition comprising containing the binder resin, the adhesive composition applied between on the first and second longitudinal edges.
8. The structural floor system according to claim 7, wherein a groove is formed along the second longitudinal edge, and a complementary shaped tongue formed along the first longitudinal edge.
Type: Application
Filed: Dec 29, 2004
Publication Date: Jul 13, 2006
Inventors: Christopher Scoville (Carnesville, GA), Brian Peek (Cornelia, GA)
Application Number: 11/025,258
International Classification: E04B 1/00 (20060101);
