Patent Grant
8561373
The invention relates to beam type construction materials; and, more particularly to I-beams constructed of bamboo.
The use of engineered I-beams in western style construction has become common place particularly for use as a component in floors, joists and beams, as they are both lighter and less prone to warping than solid wood joists. Conventional wood based I-beams typically are constructed from an oriented strand board or fiberboard web bound by top and bottom flange sections also typically constructed of high quality fir or laminated veneer lumber. I-beams are capable of supporting higher loads than an equivalent sized dimensional lumber beam and are therefore an economic means of construction. In a typical application the I-beams are intended to span a distance wherein the ends of the I-beam are supported and a load is applied along the length of the beam. In this configuration, the top flange is longitudinally in compression whilst the bottom flange is in tension. The web material maintains the distance between the top and bottom flanges and is in shear when the beam is under load, very much like the cross members in a truss. Because the load is largely borne by the top and bottom flanges, the flanges must be of high quality material. Ideally the flanges should be constructed from a single continuous piece of lumber or an engineered laminated veneer lumber; however, in practice seams are required to achieve length. Consequently seams must also be designed to bear the required loads.
I-beams constructed of wood have a number of advantages; however, there has been some concern as to their rapid loss of strength in a fire if unprotected. Also, wood as a construction material is general becoming a scarcer commodity, thus increasingly expensive, and the harvesting of wood is coming under increased environmental scrutiny. Various alternate renewable materials have been proposed to replace wood in engineered I-beams; however, ideally one would prefer the use of renewable and sustainable materials that impose a low environmental impact to harvest and process. Bamboo is such a material.
Bamboo is a prolific woody grass that has long been used in various forms as a construction material. Bamboo possesses numerous properties advantageous to the construction industry. Of particular utility is the high compression and tensile strength when used in pole form, also referred to as bamboo cane, as a support member or load bearing element in a structure. However use of bamboo in traditional western construction practices has been problematic as the tubular bamboo culm must be processed into a construction material having western style standardized dimensions, durability and strength characteristics. These difficulties are particularly pronounced as demonstrated by prior art attempts to utilize bamboo in I-beam structures wherein the bamboo is typically shredded, chipped, stranded, flaked and reconstituted into an oriented strand board; or, ripped and milled longitudinally along the culm into solid small narrow strips assembled into stacks and bonded into board form.
Use of bamboo culm in an I-beam component, without compromising the beneficial characteristics of a tubular cane, provides numerous advantages over wood including higher overall strength for the same volume of material content, higher fire resistance, lower weight, and high durability and flexibility.
Bamboo is generally lower cost than wood. Bamboo is fast growing requiring only three to four years before harvesting an individual timber grade bamboo culm, a growth time significantly less than wood. As compared to wood, bamboo has a higher rot resistance and resistance to insect infestation than most woods. Further, bamboo has a higher level of carbon sequestration than most woods. Therefore, what is needed is an I-beam construction component principally utilizing bamboo while maintaining the bamboo culm beneficial structural characteristics largely in tact thereby capitalizing on the advantageous characteristics of bamboo timber while providing a material with substantially consistent and predictable dimensions and structural characteristics such as timber or other load bearing structural components.
Accordingly, the present invention is directed to an improved load bearing construction material, and, more specifically, to a bamboo based engineered I-beam, and a manufacturing process thereof, having a laminated bamboo web and laminated bamboo flange sections providing light weight construction, high load capacity, low material and manufacturing costs, and high durability, thereby substantially obviating one or more of the problems due to the limitations and disadvantages of the related art.
The bamboo I-beam, according to the present invention, is similar in appearance and dimension to conventional wood or steal I-beams having a central web vertically oriented with top and bottom flange sections each arranged perpendicular to the vertical web and fixed horizontally along the entire top and bottom length of the web section thus forming an I shape. The flanges comprise two flange elements each respectively positioned on opposing sides of the top and bottom edges of the web such that the web is disposed between the flange elements with the edge of the web flush with the outer surface of the flange elements. The flange elements are bonded to the web with construction grade adhesive. The web portion is constructed from prepared bamboo boards with the bamboo grain direction arranged to exploit the high compression and tensile characteristics of bamboo cane so as to maximize the load bearing properties of the I-beam and minimize material content. Similarly, the flange elements comprise laminated prepared bamboo strips also so arranged. The flange elements are constructed such that the bamboo grain direction is arranged parallel to the top and bottom of the beam. Embodiments of the invention are directed towards variations in grain orientation of the various elements and the structure of the web section.
Preparation of the bamboo boards and strips so as to maximize the preservation of the bamboo cane structural characteristics is central to the present invention. The boards and strips are prepared from contiguous portions of bamboo culm by splaying bamboo cane longitudinally and then pressing the culm portions flat in a manner such that damage to the dominant vertical fibers of the culm is minimized. The resulting pressed bamboo is planed to a desired thickness preferentially removing material from the pith surface of the board thereby leaving the high fiber content cortex largely in tact. The process transforms bamboo cane into a flat bamboo board element wherein the liginin binder is randomly fractured allowing the fibers to separate from one another longitudinally with minimal or no damage to the fiber itself. All components of the I-beam, including the bamboo boards and strips, are fashioned from the process bamboo board elements. The I-beam components are laminated together to form the finished beam.
Many objectives of the present invention are achieved principally through the use of and exploitation of bamboo, accordingly prepared and arranged, including, but not limited to, an I-beam having substantially improved load bearing characteristics, for a given material content, as compared to traditional and conventional wooden I-beams generally constructed with oriented strand board webs and dimensional lumber flanges. Generally, bamboo possesses higher tensile and compression properties as compared to wood. The bamboo I-beam, according to the present invention, provides substantially lower deflection than traditional wood based I-beams. Bamboo, being a grass, is high in silicate content improving the fire resistance of the material over wood products. Yet further, the bamboo, being a fast growing plant, is a rapidly renewable resource wherein timber bamboo culm, suitable for constructing the present invention, may be harvested from the same plant each year. The bamboo content required to yield a dimensionally equivalent sized wood based I-beam provides an I-beam of substantially higher strength and improved performance. Timber bamboo, the constituent material, is readily available, low cost, renewable, and has high carbon sequestration properties.
The accompanying drawings, which are incorporated in and constitute a part of this specification illustrate embodiments of the invention and, together with the description, serve to explain the features, advantages, and principles of the invention.
In the drawings:
Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. As used herein, the term “wood” refers to tree based material as distinguished from bamboo, which is grass based. Where examples are presented to illustrate aspects of the invention, these should not be taken as limiting the invention in any respect. Referring now in greater detail to the various figures of the drawings wherein like reference characters refer to like parts, there is shown in a perspective view at 10 in
Referring to
All components of the I-beam 10 are formed by laminating splayed, pressed and planed bamboo stock trimmed into bamboo boards and strips that are specifically arranged and bonded with adhesive so as to maximize the strength and provide the dimensional requirements of a specific size of I-beam. The bamboo is harvested from preferably from timber bamboo. The bamboo cane is then splayed longitudinally. The splaying, pressing and planning process produces flat bamboo board stock having widths of typically 8 to 10 inches depending upon the culm diameter, a length dependent upon the cane length and a thickness defined by the thickness of the culm wall less material sacrificed during processing so as to achieve a specified thickness. The bamboo board stock is trimmed into bamboo boards and strips each having opposing sides parallel to each other, adjacent sides perpendicular to each other, a length, a width and thickness with longitudinally oriented grain. In trimming the boards to width, the maximum width should be trimmed from the stock whilst also keeping the longitudinal edges parallel. Variations in board widths are tolerated in the design. Maximizing the width also maximizes the use of the bamboo. The grain direction is maintained parallel to the longitudinal dimension of the trimmed boards and strips. Being fabricated from a contiguous portion of the bamboo culm, the bamboo board stock has a high fiber cortex face and a softer opposing pith face. The pith face is therefore preferentially planned to achieve the finished thickness to maximize preservation of the high fiber cortex face. The cutaneous surface of the cortex need only be planned to provide a uniformly level the surface and to remove the waxy surface layer of the culm.
In one embodiment of the invention, the web portion of the I-beam comprises a plurality of splayed, pressed and planed bamboo boards, typified at 30, arranged contiguously and adjacent to each other with the longitudinal edges contacting a forming a single bamboo board layer being the web. The contact regions between the bamboo boards, being the seams, typified in another embodiment at 56 may optionally be fixed with adhesive. This assemblage of bamboo boards forming the single bamboo board layer, is trimmed to the height required for the I-beam such that the seams 56 between the bamboo boards are either perpendicular or at an angle to the top and bottom of the I-beam. The web is disposed between flange elements along the top and bottom longitudinal edges of the web to form top and bottom flanges. The flanges elements comprise laminated bamboo strips with grain direction alike and parallel to the longitudinal dimension of the beam.
In another embodiment, as illustrated in the figures, the web comprises a plurality of bamboo board layers wherein the each layer is arranged relative to the adjacent layer with the seams of each layer at differing angles such that the layer seams do not coincide with each other along the longitudinal length. Referring to
Referring now to
The embodiment illustrated in
Proper lamination of the elements of the bamboo I-beam is essential to achieve maximum performance. A non-formaldehyde adhesive is preferred so as not to degrade the environmental benefits the bamboo based beam. Further, minimizing the glue lines also necessarily reduces the material costs of the finished product particularly as non-formaldehyde adhesives are presently more costly. In cross section of the top flange section of the I-beam of
Referring further to the structural characteristics of the component bamboo boards, the bamboo culm contains fiber and tubular vascular components positioned axially along the length of the culm. The fiber and vascular components are intraspaced with a natural polymer lignin that acts, in part, as a binder. The density of fibers and vascular components increases towards the cortex of the bamboo culm. Conversely, the density of fiber and vascular components is lowest near the inner diameter, or pith surface, of the culm where the structure is dominated by lignin. Higher density fiber and vascular components provide higher strength. The cortex of the culm also comprises, amongst other elements and irregular features, a waxy cutaneous material that interferes with the efficient binding of adhesives with the bamboo culm. Therefore, the outside surface of the bamboo board is, more specifically, planned to remove the outer nodes, flatten and disrupt or remove the cortex only to the extent as to provide adequate surface area for keying adhesives required for binding the bamboo with adjacent laminate layers.
Consequently, the orientation of the higher fiber density side of the bamboo boards and strips relative to adjacent I-beam elements influences the performance of the beam. The bamboo board layers of the web, according to the present invention, may be arranged such that the cortex sides of the boards are positioned uniformly outwardly or inwardly as required to achieve a desired performance of the beam. The web portion may therefore be assembled with both layers having the cortex side facing outwardly or inwardly. Configurations having the cortex face outwards yield a stiff web element. In embodiments utilizing a web having a single bamboo board layer, the cortex face is direction is preferably alternated in each adjacent board. It will be appreciated that the various possible combinations of arrangement of the cortex side of the individual boards are optional embodiments.
Similarly, the flange element strips of the flanges may be assembled with various orientations of the cortex side of the flange element strips relative to each other. A strip having higher stiffness is achieved by assembling the flange element strips such that the cortex face is positioned outwardly on the assembled flange element. Tests show that the orientation of cortex face of the strips when more than two strips are utilized does not have a significant impact to the overall stiffness of the flange element.
Referring to
A further embodiment of the present invention is illustrated in
In
A further embodiment of the present invention is illustrated in
In
| Number | Name | Date | Kind |
|---|---|---|---|
| 1377891 | Knight | May 1921 | A |
| 2230628 | Sahlberg | Feb 1941 | A |
| 2886857 | Brosenius | May 1959 | A |
| 3271917 | Rubenstein | Sep 1966 | A |
| 4336678 | Peters | Jun 1982 | A |
| 5664393 | Veilleux et al. | Sep 1997 | A |
| 5972467 | Washo | Oct 1999 | A |
| 5976644 | Sanaee et al. | Nov 1999 | A |
| 6281148 | Dagher et al. | Aug 2001 | B1 |
| 7921621 | Krestel | Apr 2011 | B2 |
| 7981233 | Wellwood et al. | Jul 2011 | B2 |
| Number | Date | Country | |
|---|---|---|---|
| 61228570 | Jul 2009 | US |
