Patent Application
20140174017
This invention relates generally to the field of heavy timber construction materials. More particularly, the present invention relates to trusses and truss and column structures, and related methods, that incorporate straight and branched natural round timbers to provide improved spanning and bracing with reduced consumption of energy and non-renewable materials compared to the prior art.
Buildings, large and small, must span space and resist axial and lateral forces, for example, forces caused by gravity, snow, wind or earthquakes. In residential construction this is most often accomplished by a series of triangular trusses in the attic space and wall and roof sheathing. Flat roofed and multi-story commercial buildings typically carry loads with walls or columns, and span spaces with combinations of girders, beams, and joists which are often trusses. Lateral bracing is accomplished with combinations of three bracing methods: a moment-resisting frame, diaphragm shear walls and floors or diagonal bracing. Moment-resisting frames are achieved through theoretically rigid joints, such as a welded steel connection or a continuously poured concrete intersection of column and beam. Diaphragm bracing (or shear walls) are able to rigidly resist forces in any direction. Diagonal bracing can take the form of knee braces (at frame corners) or floor-to-floor cross bracing.
The commercial construction industry is currently dominated by steel and concrete structural systems which are structurally functional but demand high inputs of energy and non-renewing natural resources. Wood is a much more environmentally friendly construction material due to its lower energy requirements, low emissions and renewable nature. However, dimensional wood framing cannot meet many commercial fire code requirements, and create the moment-resisting frame bracing possible in steel and concrete structures.
This leaves diagonal bracing as the bracing method available for timber construction. Dimensional wood framing typically employs plywood shear panels to provide lateral bracing. Heavy timber structures typically employ knee bracing—additional diagonal members attached to form triangles at each connecting corner of the column and beam frame. This system is functional but cumbersome—each knee brace requires additional member preparations and the fabrication of additional connections.
What is needed is a branched timber system for heavy timber construction that provides integrated lateral bracing and spanning in a post and beam structural system suitable for large buildings, with simplified construction and reduced cost.
Trusses comprising natural round timbers as top and bottom cords are provided. Also provided are truss and column assemblies comprising natural branched round timber columns connected to a truss.
One embodiment of a truss comprises: a top cord comprising a first natural round timber; a bottom cord comprising a second natural round timber, the first natural round timber and the second natural round timber being disposed in a substantially parallel arrangement; and a webbing structure comprising a plurality of web members, the web members connecting the first natural round timber and the second natural round timber.
One embodiment of a truss and column assembly comprises: a first column; a second column; and a truss connecting the first and second columns. The truss comprises: a top cord comprising a first natural round timber; a bottom cord comprising a second natural round timber, the first natural round timber and the second natural round timber being disposed in a substantially parallel arrangement; and a webbing structure comprising a plurality of web members, the web members connecting the first natural round timber and the second natural round timber.
In some embodiments of the truss and column assemblies, the first column comprises a first natural branched round timber having a trunk, a first branch and a second branch, the first and second branches being connected at a crook; the second column comprises a second natural branched round timber having a trunk, a first branch and a second branch, the first and second branches being connected at a crook. In these embodiments, the first natural round timber is connected to a branch of the first natural branched round timber and a branch of the second natural branched round timber; and the second natural round timber is connected to a branch of the first natural branched round timber and a branch of the second natural branched round timber.
Further objects, features, and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.
In the drawings:
Trusses comprising natural round timbers as top and bottom cords are provided. Also provided are truss and column assemblies comprising natural branched round timber columns connected to a truss. The truss and column assemblies can provide improved strength in spanning and lateral bracing and improved durability, relative to truss and column assemblies that use milled lumber, rather than natural round timber.
The use of natural round timbers in the present trusses and assemblies is advantageous because they are stronger than lumber, and are a relatively fast renewing resource that may be sourced locally from forest cullings that are typically viewed by the forest industry as waste or low-value products. As a result, natural round timber trusses and truss and column assemblies have the potential to improve strength and durability, while reducing the energy, pollution and waste required for processing the materials used to fabricate building structures.
For the purposes of this disclosure, the phrase “natural round timbers” refers to trees retaining their natural round cross-sections and the inherent natural taper along their longitudinal axis (i.e., along the length of the timber). The present natural round timbers can also be referred to as round wood logs. The natural round timbers may be branched, that is they may retain one or more of their branches. Unlike lumber, natural round timbers retain the densest and strongest portions of their wood, which forms toward their perimeters as they mature in uniformly-aged, and increasingly dense, conifer stands. As a result, natural round timbers can be 50% stronger in bending than equivalent-sized milled timbers. The wood fibers at the perimeter of natural round timber, which are the first to be milled away in the production of lumber, are also grown in tension, which increases a natural round timber's ability to span spaces and resist lateral loads in buildings. As a result, a piece of lumber will typically have less than a third of the bending strength of the natural round timber from which it is milled.
Natural branched round timbers, also referred to as branched natural timbers, are similarly stronger than their lumber counter-parts. In fact, the branched crook of a natural branched round timber provides a very strong natural rigid wooden connection, stronger even than the branches that it connects. In contrast, man-made joints between pieces of milled timber, such as mitered joints and knee braces, are generally the weakest point of an assembly constructed with such joints.
As perhaps best shown in
A truss and column assembly made with natural branched round timber further includes a webbed truss 30 with a top cord 32 and a bottom cord 36 connected together by a web 40. The web 40 may be formed of a web member 44 extending between a web top limit 42 at the top cord 32 and a web bottom limit 46 at the bottom cord 36. In this embodiment, the web member 44 is formed from a plurality of sections of steel section stock, such as C-channel or L-channel stock. The sections can comprise web tabs 48 disposed at their ends, the web tabs having a hole sized for a suitable fastener, such as a nail, screw or bolt.
The top cord 32 is a relatively straight and low-taper natural round timber. Top cord 32 can be formed as a unitary structure, or of multiple pieces, each piece comprising a natural round timber. In this embodiment, the top cord 32 is formed of at least two pieces, each having a top cord end 34. The top cord ends 34 of the natural round timbers can be fastened together using a cord-cord connection 70. The cord-cord connection 70 is preferably located between the first branch end 22 and the second branch end 26. The top cord 32 is fastened to the first branch end 22 and second branch end 26 by a top-cord-to-branch-connection 50. By locating cord-cord connection 70 between the branch ends, the span between cord-to-branch-connections 50 in neighboring columns along the truss is reduced relative to span between the cord-to-column-connections of a truss having the same design that uses unbranched columns. As a result, the spanning capacities of the present trusses are improved. In addition, the triangulated shape formed by the two top-cord-to-branch-connections 55 and crook 16 distribute axial, shear, and lateral loads to two points, thereby increasing the load bearing capacities of the present trusses relative to those of trusses having the same design that use unbranched columns, which distribute the loads to a single point. This triangulated assembly also provides lateral strength along its length.
By way of illustration, while spans between cord-to-branch connections having a variety of lengths could be used in the column-truss assembly, in some embodiments, the lengths of the spans are in the range from about 10 to 50 feet (10′ to 50′). This includes embodiments in which the spans have lengths in the range from about 10′ to 20′ and also includes embodiments in which the spans have lengths the range from about 20′-50′. Similarly, while a variety of column heights could be used, typical column heights are in the range from about 8′ to 30′. This includes embodiments in which the column heights are in the range from about 10′ to 30′ and also includes embodiment in which the column heights are in the range from about 16′-24′.
Like top cord 32, bottom cord 36 is a relatively straight and low-taper natural round timber. Bottom cord 36 has a bottom cord end 38 secured to the natural branched round timber 10 using a bottom-cord-to-timber-connection 60. The bottom-cord-to-timber-connection 60 may be made at a point above the crook 16, in other words, on one of the first branch 20 or second branch 24. Alternatively, the bottom-cord-to-timber-connection 60 can be made at a point below the crook 16, in other words, on the trunk 15.
The geometry of the natural branched round timber 10 can be characterized by several reference points and dimensions, including its height, base center 14, geometric crook center 18, and effective crook center 19. The first branch 20 terminates in a first branch end 22 and includes a first branch inter-cord section 21 between the top cord 32 and the bottom cord 36. The second branch 24 terminates in a second branch end 26 and includes a second branch inter-cord section 25 between the top cord 32 and the bottom cord 36. The midpoint between the first branch end 22 and the second branch end 26 is a geometric branch center 28, which may differ from the effective branch center 29.
As shown in
In the embodiment of
In the embodiment of
Plate 73 can be recessed into top cord 32 by scribing the parameters of plate 73 onto the surface of top cord 32 to determine an appropriate kerf, or slot, size and bolt hole locations. A kerf can then be cut into the surface of top cord 32 at top cord ends 34 to provide slot 72. The kerf should be cut longitudinally with the grain of the wood, and should be slightly larger than the length, width and thickness of plate 73. Bolt holes in alignment with holes in plate 73 are then drilled into top cord 32 and the plate is then inserted into the kerf, aligned with the holes and bolted across top cord ends 34.
In the embodiment of
In the embodiment of
In the embodiment of
Another embodiment of a truss and column assembly is shown in the schematic diagram of
Web members of truss web 506 include vertical members 526 and diagonal members 528, connected at regular intervals between top cord 502 and bottom cord 504. The diagonal and vertical members have an alternating arrangement, that is, an arrangement in which a vertical member is disposed between diagonal members. In some embodiments of the truss, the web members are comprised of natural round timbers, steel, milled timbers or a combination thereof. For example, vertical members 526 may be wood members comprising natural round timbers or lumber and diagonal members 528 may be steel members. The specific material, number, spacing and angles (relative orientations) of web members 526, 528 can be selected based on the specific spans, loads and other structural engineering requirements for the building structure into which the truss is to be incorporated. Advantageously, the truss design incorporating natural round timbers as cords reduces the number of web members and connecting points needed to resist loads relative to trusses having the same overall design that use steel or lumber cords. This can reduce the fabrication costs and can be attributed to natural round timber's larger section modulus, relative to common steel or milled lumber sections, which allows for increased spans between the bracing web members.
Top cord 502 and bottom cord 504 comprise long, straight natural round timbers with slight natural tapers along their lengths. The natural round timbers are desirably characterized by four or fewer growth rings per inch, particularly in the outer third of their radii. Such natural round timbers may be obtained, for example, from over-stocked tree stands where growth has been suppressed. Typical lengths for the natural round timbers are in the range from 20 to 50 feet and typical diameters for the natural round timbers are in the range from 3 to 14 inches (3″ to 14″). However, lengths and diameters outside these ranges can be used. The natural round timbers are desirably not cut from tree tops with juvenile growth and should be visually inspected to avoid timbers with rot, insect infestations or a high density of knots. Selected natural round timbers can be peeled and dried (for example, to an average of 15% moisture content or lower). Once peeled and dried the natural round timbers can be inspected for twisting, checks and other defects and then tested in a machine stress grader for grading scores.
The natural round timbers from which top cord 502 and bottom cord 504 are constructed should have similar lengths and diameters and should be oriented with their tapers reversed, such that the thick end 514 of one natural round timber is above or below the thin end 512 of the other natural round timber. The natural round timbers have a natural curve, or camber, along their longitudinal axis. The trusses can be constructed such that both cord cambers are oriented upward, as shown in
As illustrated in
It is understood that the invention is not confined to the embodiments set forth herein as illustrative, but embraces all such forms thereof that come within the scope of claims supported by this disclosure.
This application claims priority from U.S. provisional patent application No. 61/745,761, filed on Dec. 24, 2012, the entire disclosure of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61745761 | Dec 2012 | US |
