Abstract:
A composite I-beam is presented. The inventive I-beam includes a first flange and a second flange, with a web extending between the first and second flanges. At least one of the flanges of the inventive I-beam has a reinforcing layer of a supporting material thereon or therein.

Description:
TECHNICAL FIELD 
     The present invention relates to an I-beam made from engineered lumber, and having improved properties. More particularly, the present invention relates to a composite I-beam formed from a pair of parallel flanges with a web of oriented strandboard extending therebetween. At least one of the flanges is reinforced, thereby providing more desirable failure characteristics. 
     BACKGROUND OF THE INVENTION 
     In residential and commercial construction, conventional solid sawn lumber joists used for floor supports (such as 2″×12″ lumber joists), usually made from spruce, fir or pine, are often being replaced by I-beams. An I-beam is a structural member having upper and lower flanges corresponding to the top and bottom horizontal portions of the “I” and what is referred to as a web therebetween. Of course, the strength of the I-beam depends on the materials of construction, where, for instance, a steel I-beam is structurally stronger (albeit much heavier) than a wood I-beam, as well as the dimensions of the component parts, where, for instance, an I-beam having a tall web is generally stronger than an I-beam with a short web (assuming the same thickness of web and size of the flanges). That said, wood I-beams can be stronger and lighter, as well as less expensive, than similar sizes of solid sawn lumber. 
     Although steel I-beams may be most desirable in terms of strength, the weight and cost of steel I-beams make them prohibitive. Although wood I-beams are far more desirable than steel I-beams in terms of weight and cost, for applications such as residential construction, the behavior of the wood I-beam in case of fire is an important consideration. More specifically, regardless of the strength and other characteristics of a wood I-beam, without having fire endurance and related properties equivalent to or better than solid sawn lumber joists, wood I-beam are of limited practicality in most applications. Included in the desirable characteristics is time-to-failure and failure mode (i.e., whether the failure is catastrophic, or sudden, or whether there is bowing/deflection and other effects usually observed with solid sawn lumber) of solid sawn lumber in a fire. 
     As noted, a wood I-beam, also often referred to as a composite I-beam, typically has two flanges, an upper flange (i.e., the flange which is that nearest the floor of the building in which the I-beam is used) and a lower flange (i.e., the flange sitting furthest away from (and below) the floor of the building in which the I-beam is used), with a web therebetween. The web is often, but not always, formed of plywood, oriented strandboard (“OSB”) or other form of engineered lumber, and inserted into the flanges by means of a groove routed into the flanges. Engineered lumber refers to a lumber product made from natural wood, but that has been processed or engineered such that it is no longer in its original form. For instance, a laminate of strips of wood (from which the flanges of a wood I-beam are often formed), commonly referred to as laminated veneer lumber (“LVL”), would be considered engineered lumber. Likewise, OSB is another form of engineered lumber, formed by bonding wood particles with a resin system to form a relatively continuous sheet or web. 
     What is desirable, therefore, is a wood I-beam comprising two flanges with a generally continuous web arranged therebetween, where the I-beam has a time-to-failure and/or failure mode at least equivalent to solid sawn lumber. 
     SUMMARY OF INVENTION 
     It is an object of the present invention to provide an I-beam useful as a floor joist for residential or commercial construction. 
     It is another object of the present invention to provide an I-beam lighter in weight and less expensive to manufacture than a steel I-beam of corresponding dimensions. 
     It is still another object of the present invention to provide an I-beam stronger and lighter in weight than an equivalent length of solid sawn lumber joists. 
     It is a further object of the present invention to provide an I-beam having time-to-failure and failure mode at least equivalent to solid sawn lumber joists. 
     These objects and others that will become apparent to the artisan upon review of the following description can be accomplished by providing a composite I-beam having a first flange and a second flange, with a generally continuous web extending between the flanges. At least one of the flanges includes a reinforcing layer of a supporting material either thereon or therein. In particular, at least one of the flanges of the I-beam (and possibly both of the flanges) is a laminated flange having a plurality of wood members adhesively joined together into a generally rectangular cross-section, wherein a reinforcing layer of a supporting material is disposed between at least two of the plurality of wood members. The reinforcing layer is preferably a sheet of fibrous material having a thickness of no more than about 0.030 inch and can be a sheet of fiberglass, aramid fibers, para-aramid fibers, polymetaphenylene diamine fibers, polytetrafluoroethylene fibers, high modulus polyethylene, graphite fibers, carbon fibers, or mixtures thereof. The reinforcing layer of supporting material can also be disposed between more than two of the plurality of wood members in one or both of the laminated flanges or in the groove routed into one or both of the flanges. 
     In another embodiment of the claimed invention, at least one (and possibly both) of the flanges of the I-beam is made from a length of solid sawn lumber having a generally rectangular cross-section having two major and two minor surfaces, wherein a reinforcing layer of a supporting material is disposed on at least one of the major surfaces of the flange, and possible both of the major surfaces of the flange, or in the groove routed into the flanges. Again, the reinforcing layer can be a sheet or bundle of fibrous material having a thickness of no more than about 0.030 inch, formed from a sheet of fiberglass, aramid fibers, para-aramid fibers, polymetaphenylene diamine fibers, polytetrafluoroethylene fibers, high modulus polyethylene, graphite fibers, carbon fibers, or mixtures thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood and its advantages more apparent in view of the following detailed description, especially when read with reference to the appended drawings, wherein: 
     FIG. 1 is a side perspective view of a wood I-beam in accordance with the present invention; 
     FIG. 2 is a partially broken-away side perspective view of an alternative embodiment of a wood I-beam in accordance with the present invention; and 
     FIG. 3 is a side cross-sectional view of the wood I-beam of FIG. 2 in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings in detail, a wood I-beam prepared in accordance with the present invention is shown and generally designated by the reference numeral  10 . It should be noted that for the sake of clarity not all the components and elements of wood I-beam  10  may be shown and/or marked in all the drawings. Also, as used herein, the terms “top,” “bottom,” “upper,” “lower,” etc. refer to wood I-beam  10  when in the orientation shown in FIG.  1 . However, the artisan will recognize that wood I-beam  10  can adopt any particular orientation when in use. 
     Wood I-beam  10  can be used as a floor joist in residential or commercial construction. Alternatively, wood I-beam  10  can be used in any other application in which a solid sawn lumber floor joist can be used, including as a ceiling or roofing joist, etc. Wood I-beam  10  has as its major components two flanges, and upper flange  20  an a lower flange  30  and a web  40  therebetween. Flanges  20  and  30  of wood I-beam  10  can be said to include an upper flange  20  and a lower flange  30 . Flanges  20  and  30  can be formed of a length of solid sawn lumber, such as spruce, fir or pine, or other appropriate woods, or they can be formed of as a laminate of a plurality of wood members adhesively joined together into a generally rectangular cross-section (for the purposes of simplicity, flanges  20  and  30  are illustrated as each being a laminate of two wood members adhesively joined together; however, flanges  20  and  30  can be formed of solid sawn lumber, as noted above, or as a laminate of more than two, and up to about  20  or more wood members adhesively joined together). 
     Each of flanges  20  and  30  have two major surfaces  22   a  and  22   b , and  32   a  and  32   b , respectively and two minor surfaces  24   a  and  24   b , and  34   a  and  34   b , respectively, as shown in FIGS. 1 and 3. In most cases major surfaces  22   a ,  22   b ,  32   a ,  32   b  of flanges  20  and  30  are longer than minor surfaces  24   a ,  24   b ,  34   a ,  34   b ; however, that is not necessarily the case. As used herein, the terms “major surfaces” and “minor surfaces” are used to distinguish the upper and lower surfaces of flanges  20  and  30  (major surfaces) and the side surfaces of flanges  20  and  30  (minor surfaces) when in the orientation of FIG.  1 . 
     In most cases, upper flange  20  and lower flange  30  are similar in construction and materials, but this is not necessary. For instance, upper flange  20  can be made from a laminated flange comprising a plurality of wood members adhesively joined together into a generally rectangular cross-section, and lower flange  30  can be formed from a length of solid sawn lumber having a generally rectangular cross-section  32 , and vice versa. Most commonly, however, upper flange  20  and lower flange  30  are each made from the same material, either each being a laminated flange comprising a plurality of wood members adhesively joined together into a generally rectangular cross-section  22  or each being a length of solid sawn lumber having a generally rectangular cross-section  32 . 
     The length of flanges  20  and  30  will depend on the particular application; however, for most residential and commercial floor joist uses, flanges  20  and  30  will be from about 10 feet to about 50 feet in length. The other dimensions of flanges  20  and  30  will again depend on the particular application, and desired characteristics such as strength and flexibility; typically, flanges  20  and  30  are each about 2 inches to about 5 inches along their major surfaces  22   a ,  22   b ,  32   a ,  32   b  and about 0.5 inches to about 3 inches along their minor surfaces  24   a ,  24   b ,  34   a ,  34   b  (provided that major surfaces  22   a ,  22   b ,  32   a ,  32   b  are longer than minor surfaces  24   a ,  24   b ,  34   a ,  34   b ). Generally, a web receiving groove  26 ,  36  is formed in one of the major surfaces of each of flanges  20  and  30 , as illustrated in FIGS. 1 and 2. More particularly, groove  26  is formed in the major surface of flange  20  (such as major surface  22   b ) that faces towards flange  30 , and groove  36  is formed in the major surface of flange  30  (such as major surface  32   a ) that faces towards flange  20 . In this way, web  40  can be received in grooves  26  and  36  and maintained in place between flanges  20  and  30  more stably. 
     When either or both flange  20  or flange  30  is formed as a laminate of a plurality of wood members adhesively joined together into a generally rectangular cross-section, a reinforcing layer of a supporting material  50  is disposed between two of the wood members  28   a ,  28   b  of at least one of flange  20  or  30  formed as a laminate. Most preferably, upper flange  20  is formed as a laminate and has reinforcing layer  50  disposed between two of the wood members  28   a ,  28   b . Advantageously, reinforcing layer  50  is disposed between wood members located at or near the middle of flange  20  or  30  (as opposed to being located near the upper or lower major surface  22   a ,  22   b  of laminate  22 ), as illustrated in FIGS. 1-3. In this way, reinforcing layer  50  will be protected the longest in case of burning of flange  20  or  30 . Although in most cases, the laminate comprises several wood members  28   a ,  28   b , etc., each of which is relatively thin (on the order of no more than about 0.25 inches in thickness), wood members  28   a ,  28   b  can also comprise lengths of oriented strand board, as described in U.S. Pat. No. 6,012,262, the disclosure of which is incorporated herein by reference. 
     Reinforcing layer  50  is preferably a sheet of fibrous material having a thickness of no more than about 0.030 inch (and typically no less than about 0.003 inch) and can be a sheet of fiberglass; aramid fibers; para-aramid fibers, like poly-paraphenylene terephthalamide fibers commercially available from E.I. du Pont de Nemours and Company as KEVLAR® fibers; polymetaphenylene diamine fibers commercially available from E.I. du Pont de Nemours and Company as NOMEX® fibers; fluorocarbon fibers like polytetrafluoroethylene (PTFE) fibers commercially available from E.I. du Pont de Nemours and Company as TEFLON® fibers; high modulus polyethylene; graphite fibers; carbon fibers; or mixtures thereof. If desired, reinforcing layer  50  can be adhered in place using the same adhesive as is used to form laminate  22 , or a different adhesive, like an epoxy or a phenolic adhesive. Advantageously, reinforcing layer  50  is disposed between more than two of the wood members  28   a ,  28   b ,  28   c  of the laminate, for increased support, as shown in FIG.  2 . Most advantageously, each of flanges  20  and  30  are formed from the laminate and have reinforcing layer  50  disposed between at least two of its constituent wood members. 
     When either or both flange  20  or flange  30  is formed from a length of solid sawn lumber having a generally rectangular cross-section  32 , a reinforcing layer of a supporting material  60  is disposed on at least one of the major surfaces  24   a ,  24   b ,  34   a ,  34   b  of at least one of flange  20  and flange  30 . Preferably, reinforcing layer  60  is adhered in place using an adhesive that can be used to form a wood laminate, or a different adhesive, like an epoxy or phenolic adhesive. Advantageously, reinforcing layer is disposed on the major surface of flange  20  or  30  (and preferably both flange  20  and flange  30 ) in which groove  26  or  36  is formed. Reinforcing layer  60  is preferably a sheet of fibrous material having a thickness of no more than about 0.030 inch and can be a sheet of fiberglass; aramid fibers; para-aramid fibers; polymetaphenylene diamine fibers; fluorocarbon fibers; high modulus polyethylene; graphite fibers; carbon fibers; or mixtures thereof In other words, reinforcing layer  60  can be made in the same manner and from the same materials as reinforcing layer  50 . 
     Web  40 , disposed between flanges  20  and  30 , can be formed of any appropriate generally continuous material, such as plywood. Preferably, however, web  40  is formed of oriented strand board (OSB), sometimes referred to as oriented strand lumber (OSL). Oriented strand board, as used herein and as generally understood by the artisan, refers to an engineered lumber product which incorporates oriented strands of wood fiber bonded with an adhesive and cured in a hot platen press. Web  40  should most preferably have a length approximately equal to the length of flanges  20  and  30  (i.e., from about 10 to about 50 feet), a height (i.e., the distance between flanges  20  and  30  when web  40  is disposed therebetween) of about 7 inches to about 30 inches, and a width of about 0.15 to about 1.5 inches. Correspondingly, grooves  26 ,  36  should be sized so as to receive web  40 , or a tapered portion  42  of web  40 , and thereby maintain it stably in place between flanges  20  and  30 . A suitable adhesive can also be used to maintain web  40  in grooves  26 ,  36 . 
     By incorporating reinforcing layer  50  in flange  20  or  30 , or reinforcing layer  60  on flange  20  or  30 , increased support is provided to the flange, and thus to I-beam  10 . In this manner, the time-to-failure of I-beam  10  in case of fire can be improved, as compared to a similar wood I-beam without reinforcing layer  50  or reinforcing layer  60 . Indeed, time-to-failure can approach or even exceed the solid sawn lumber joists currently being used in residential and/or commercial construction. Moreover, the mode of failure of I-beam  10  can also be improved, so as to more closely resemble solid sawn lumber joists, rather than the sudden and catastrophic failure often seen with wood I-beams not employing reinforcing layer  50  or reinforcing layer  60 . Another potential advantage is that the strength of wood I-beam  10  per se, as opposed to under extraordinary conditions like a fire, can be improved so as to be superior to solid sawn lumber. In this way, wood I-beam  10  can be used to provide a stronger weight-bearing surface. 
     In order to provide even further flame retardancy to wood I-beam  10 , wood I-beam  10  (or at least one of flanges  20 ,  30  or web  40 ) can also be coated or otherwise treated with an intumescent composition, especially one that contains particles of expandable graphite. By “treated with” is meant that wood I-beam  10  is formed using the intumescent composition during formation, such as in the resin system used in OSB web  40 . Expandable graphite is graphite that has been intercalated with intercalants such as sulfuric and nitric acids under conditions to render the graphite expandable when exposed to high temperatures, such as a flame. Expansion of the graphite can delay or prevent spread of the flame to the substrate on which the composition is coated or with which the composition is treated (i.e., wood I-beam  10 ). Suitable intumescent compositions containing particles of expandable graphite are described in, for instance, International Publication No. WO 99/35196 and U.S. Pat. No. 5,968,669, the disclosures of each of which are incorporated herein by reference. 
     More particularly, a common method for manufacturing expandable graphite is described by Shane et al. in U.S. Pat. No. 3,404,061, the disclosure of which is incorporated herein by reference. In the typical practice of the Shane et al. method, graphite flakes are intercalated by dispersing the flakes in a solution containing e.g., a mixture of nitric and sulfuric acid. The intercalation solution contains oxidizing and other intercalating agents known in the art. Examples include those containing oxidizing agents and oxidizing mixtures, such as solutions containing nitric acid, potassium chlorate, chromic acid, potassium permanganate, potassium chromate, potassium dichromate, perchloric acid, and the like, or mixtures, such as for example, concentrated nitric acid and chlorate, chromic acid and phosphoric acid, sulfuric acid and nitric acid, or mixtures of a strong organic acid, e.g. trifluoroacetic acid, and a strong oxidizing agent soluble in the organic acid. Alternatively, an electric potential can be used to bring about oxidation of the graphite. Chemical species that can be introduced into the graphite crystal using electrolytic oxidation include sulfuric acid as well as other acids. 
     In a preferred embodiment, the intercalating agent is a solution of a mixture of sulfuric acid, or sulfuric acid and phosphoric acid, and an oxidizing agent such as nitric acid, perchloric acid, chromic acid, potassium permanganate, hydrogen peroxide, iodic or periodic acids, or the like. Although less preferred, the intercalation solution may contain metal halides such as ferric chloride, and ferric chloride mixed with sulfuric acid, or a halide, such as bromine as a solution of bromine and sulfuric acid or bromine in an organic solvent. 
     After the flakes are intercalated, any excess solution is drained from the flakes and the flakes are water-washed. The quantity of intercalation solution retained on the flakes after draining may range from about 50 to 150 parts of solution by weight per 100 parts by weight of graphite flakes (pph) and more typically about 50 to 120 pph. Alternatively, the quantity of the intercalation solution may be limited to between 10 to 50 parts of solution per hundred parts of graphite by weight (pph) which permits the washing step to be eliminated as taught and described in U.S. Pat. No. 4,895,713, the disclosure of which is also herein incorporated by reference. 
     Upon exposure to high temperature, e.g. a fire, the particles of intercalated graphite expand as much as 80 to 1000 or more times their original volume in an accordion-like fashion in the c-direction (in the direction perpendicular to the crystalline planes of the constituent graphite particles) to form expanded graphite particles or worms, which can function to retard flame spread. 
     The above description is intended to enable the person skilled in the art to practice the invention. It is not intended to detail all of the possible variations and modifications that will become apparent to the skilled worker upon reading the description. It is intended, however, that all such modifications and variations be included within the scope of the invention that is defined by the following claims. The claims are intended to cover the indicated elements and steps in any arrangement or sequence that is effective to meet the objectives intended for the invention, unless the context specifically indicates the contrary.