Current designs for double row or larger polygonal arches present difficulties when applied to structures with spans above 40 feet (12 m) that need to meet public load safety standards, or that need to be dismantled easily and reused, or which are constructed without scaffolding, assembled without heavy equipment, and built with bamboo or other locally-available beam materials, or which need to be safely and reliably assembled by non-professionals.
What are needed are connectors that enable the construction of arch-shaped structures either individually or as parallel ribs of cylindrically-shaped structures such as supporting arches for bridges, tunnel linings, Quonset hut-type shelters and arbors. The need is for a connector that enables the construction of arches where the stringer beams are arranged in two or more parallel rows so that the ends of the beams in one row are opposite the midsection of the beams in an adjacent row. Arches constructed from straight beams are desirable because they use lower cost standard components but retain the strength, simplicity and extended span of arches constructed of specially engineered curved components.
The end-to-end alignment of beams in polygonal arches transfers the load placed on the arch to the abutments along the longitudinal axis of each beam. This end-to-end load transfer makes efficient use of the strength of most materials. Although a polygonal arch makes good use of materials, the end-to-end alignment of the beams is unstable. Adding enough bracing to make a single row of beams rigid increases costs and lowers the strength-to-weight ratio. The instability problem is solved by joining at least two parallel, end-to-end aligned rows of beams so that the point where the beams meet in one row is braced by the mid-point of a beam in the adjacent row. The resulting arch is strong, light-weight and uses readily available standard materials.
For most civil engineering projects, the trusses and curved-component arches that can be made of aluminum or steel are more efficient in their use of materials than the double row polygonal arch. However, for many remote, emergency response, environmentally-sensitive or limited-funding situations, the double row or multi-row polygonal arch would be a superior support structure for bridges and larger shelters due to its simplicity, strength and ability to span greater distances with small, human-portable components assembled by unskilled labor. To meet the requirements of these demanding situations, the structure needs to be improved so it can be built quickly and safely out of standard modules in difficult terrain, be constructed of bamboo or other local materials like small diameter timber, and be easily disassembled, transported and reused.
Various designs exist for building arches using straight beams both with and without connectors between the beams, e.g., U.S. Pat. No. 4,412,405, J. J. Tucker; U.S. Pat. No. 1,727,022, T. Ahlborn; U.S. Pat. No. 3,004,302, W. W. Nightingale; U.S. Pat. No. 3,091,002, L. E. Nicholson. Historical arch designs also provide examples, e.g., the ‘self-supporting bridge’ of Leonardo Da Vinci, bridges in rural China such as Meichong Bridge, Yunhe County, and Xidong Bridge, Taishun County, both in Zhejiang Province, and the Moon Bridge at Huntington Gardens in Pasadena, Calif. Some designs provide modularity, reusability and safety, but the benefits are limited primarily to one material, or to very small structures. A single design which addresses the combined requirements of cantilevering, allowing a wide range of beam materials, and reducing construction time, which can be scaled up to build structures with spans of 20 meters or more, is lacking.
The present invention is a structural connector for creating a double row or multi-row polygonal arch using straight beams. The connector joins three straight beams in a triangular union that forms one node of the structure. A series of ‘nodes’ creates an arch, or a complete circle if enough ‘nodes’ are added. All the ‘nodes’ of the arch are established by the connector, all connectors in a single arch can be identical connectors of the type described in the invention, and no other types of connectors are required to assemble the beams into an arch structure. The connector according to the present invention is typically made of sheet metal or steel plate.
The connector is a ‘Y’-shaped device with three brackets that bind the ends or middle of beams to the connector. One bracket is located on each arm of the ‘Y’. The two brackets at the top of the ‘Y’ are on the opposite longitudinal face of the connector from the bracket at the bottom of the ‘Y’ so that the connector joins two beams from one row of beams together end-to-end, and joins the two separate rows of beams in the arch to each other.
The beams inserted into the two brackets at the top of the ‘Y’-shape must slope downward at an angle of 1 or more degrees from horizontal in a completed arch. To establish the required slope, the top brackets may be fixed in relation to each other and the bottom bracket at the specific angle required, or allowed to swivel through a range of angles so that the final angle is determined by the length of the beams used and the basic rules of geometry. The bottom bracket is aligned at roughly 90 degrees to the vertical centerline of the connector so that the beam in the bottom bracket is the base of the isosceles-triangle-shaped union and the beams in the top brackets are the sides of the union.
The connector establishes a modular ‘building block’ for double row or multi-row polygonal arches. One beam with one connector attached to the beam's midsection by the bottom bracket of the connector is the basic construction unit. Each of these ‘building blocks’ interlocks with other identical blocks turned in the opposite direction. The ends of the beams in opposite-facing ‘building blocks’ fit into the top brackets of the connectors of its neighboring ‘building blocks’ creating an interlocking structure.
The connector allows an arch to be assembled in-place, without scaffolding, by creating a series of cantilevers from the arch's abutments to the center of the span. Each ‘building block’ cantilevers from the next lower block by hanging from its own connector and using the connector of the next lower building block as a counter-balance. At the center of the span, the final ‘building block’ acts as a ‘keystone’ joining the two cantilevered half-arches.
Once an arch is complete, the connectors direct the load forces around the arch to the abutments in the same way as the stones in a keystone arch. Each connector also maintains the alignment of the beams in the double row structure of the arch. The brackets of the connector can simply hook over the beams, holding the beams in place by balancing the opposing forces in the top brackets against the bottom bracket. Fasteners holding beams to the brackets are not required but can be used to add convenience during construction, or structural durability. Top brackets may be constructed to fully enclose the ends of the beams, allowing the use of beams made of bundles of smaller elements, like bamboo poles and small diameter timber.
The brackets of the connector can simply hook over the beams, holding the beams in place by balancing the opposing forces in the top brackets against the bottom bracket. Fasteners holding beams to the brackets are not required but can be used to add convenience during construction, or structural durability. top brackets may be constructed to fully enclose the ends of the beams, allowing the use of beams made of bundles of smaller elements, like bamboo poles and small diameter timber.
A transverse beam may be added through the optional transverse notch between the top brackets to connect a single arch to other parallel arches in a multi-arch structure.
The bottom bracket can be configured with a flange, called a “Chaining Hook”, which connects the bracket to the adjacent connector in a structure with multiple, closely adjacent parallel arches.
Construction-grade connectors are applicable to bridges, shelters, culverts, tunnels and arbor-like structures. Smaller embodiments of the connector made of thin-gauge metal, plastics, fabric or composites can be used in furniture, toys and small devices. The number, type, composition and size of fasteners required used to assemble the connector and attach beams to the brackets of the connector are application-specific.
Referring to
In the
As shown in
Elements of the Invention
Top Brackets: Each Y-shaped connector has two top brackets 1L, 1R, as illustrated in
Any method of attaching the end of a stringer beam to a node of a double row polygonal arch that does not require joinery which interlocks or overlaps the beam with either the end of the stringer beam in the opposite top bracket or the transverse beam is considered a top bracket. All top brackets allow disassembly of the attachment between the stringer beam and the top bracket, and reuse of the bracket and beam.
Each top bracket holds the stringer beam at a downward sloping angle relative to the upper transverse plane 43 of the connector (as seen in
Each top bracket can have holes 4, as shown in
Transverse Notch: Referring to
Bottom Bracket: Each connector has one bottom bracket 2. The bottom bracket is constructed to attach the connector to the midsection of a stringer beam. In operation, bottom bracket applies an upward force on the stringer beam. The upward force is generated by the outward thrust produced by loads on the arch or by the weight of the cantilevered portion of the arch which is transferred to the connector through the top brackets and countered by the stringer beam in the bottom bracket.
The bottom bracket may be configured as “L-shaped”, “U-shaped”, “Fully-enclosed” or simply as a flat plate of material extending down from the top brackets with one or more bolts used to attach the plate to the stringer beam.
Central Structure: As shown in
The central structure is a general term for the elements of the connector which are not included in the top brackets or bottom bracket. The central structure:
As illustrated in
The sliding bottom bracket allows one connector to be used with beams of different lengths creating different spans for the arch.
The central structure 12 with one or more slots or tracks can be constructed to extend up to the top of the top brackets or beyond, extending both above and below the top brackets. Sliding the bottom bracket from below to above hinged top brackets causes the arch to first collapse to a straight row of beams and then curve up rather than down.
One or more embodiments of the invention may form the central structure part as part of the top or bottom brackets. In these embodiments, a portion of a top bracket or bottom bracket element performs the function of the central structure.
Top Bracket Mounting Using Hinges, Pivots or Flexible Material: The invention, as illustrated in
The pivot can be located anywhere along the top, bottom or transverse-notch-facing end of the top bracket.
Chaining Hook: One embodiment of the invention includes a ‘chaining hook’ 20, as illustrated in
In structures with two immediately adjacent double-row polygonal arches, the ‘chaining hook’ 20 acts to counteract the torque that can develop at each node under load. Each Y-shaped connector tends to rotate toward the bottom bracket under load as outward thrust in the top bracket 1R is resisted by the bottom bracket. The ‘chaining hook’ both stops that rotation for its own connector and counters the rotation in the adjacent connector with the force it applies. Braces 13 can increase the value of the ‘chaining hook’ by making the central structure and bottom bracket 2 more rigid.
The ‘chaining hook’ can also fasten two adjacent double-row arches together by adding holes for fasteners to the ‘chaining hooks’ 20 and ‘notch floor plates’ 21.
Building Blocks: The invention, as illustrated in
Additionally, arches can be constructed using non-identical ‘building blocks’ which are designed to interlock with just the adjacent blocks of the structure. Non-identical ‘Building blocks’ can be asymmetrical to create parabolic and non-semi-circular arches. To create a parabolic or other non-circular arch, the length of the beams and the angles of the top brackets can be unique to every ‘building block’. Each ‘building block’ may also be unique with respect to the location at which the bottom bracket is attached to the beam: exactly at the midpoint or offset from the midpoint toward one end of the beam.
Referring to
The ‘stub beam’ 24 of the ‘abutment connection bracket’ is a solid or tubular duplicate of the end of a stringer beam. The stub beam is welded or fastened to the ‘abutment connection plate’ 26 at an angle matching the angle of the top bracket of the springer ‘building block’.
The ‘locking angle’ 23 is attached to the ‘abutment connection plate’ 26 by a hinge 27 with the axis of rotation parallel to the ground. The hinge is mounted such that the lower wall 28 of the ‘locking angle’ is flush with the ‘abutment connection plate’ 26 at one end of the range of travel and at 90 degrees to the plate at the other end of the range of travel. The lower wall of the ‘locking angle’ is as tall as the depth of the springer ‘building block beam’ and at least as wide as the beam.
The ‘cantilever support brace’ 25 is located immediately below the ‘locking angle’ and extends at 90 degrees from the ‘abutment connection plate’ 26. The ‘cantilever support brace’ is only used when the arch is constructed by cantilevering. The ‘cantilever support brace’ supports the springer ‘building block’ whose beam is the sole support for the entire cantilevered portion of one side of the arch during cantilevered construction.
The ‘cantilever support brace’ 25 has a notch 29 in the upper face of the brace to allow room for the ‘bottom wall’ of the bottom bracket of the springer ‘building block’. The length of the ‘cantilever support brace’ is application-specific. The ‘cantilever support brace’ is welded or bolted to the metal plate. The ‘cantilever support brace’ can be removed and reused once the ‘keystone building block’ is in place.
Referring to
The abutment-facing end of the beam of each springer ‘building block’ is shortened to fit the ‘abutment connection bracket’. The beam is cutoff at 90 degrees. The position of the cutoff is calculated so that the cutoff face of the beam end will rest squarely on the lower wall of the ‘locking angle’ 28 when the ‘stub beam’ 24 is fully inserted into the ‘top bracket’ of the springer ‘building block’ 30 and the arch is loaded.
The ‘abutment connection bracket’ may have multiple ‘stub beam’ and a ‘locking angle’ pairs so that multiple parallel arches to be connected to the abutment with one bracket.
Cantilevered Construction:
The invention enables a double-row polygonal arch to be assembled in its final location and vertical orientation from the abutments without any other scaffolding or support as illustrated in
Assembly Procedure:
Tied Beam Connection for Tied Arches: The connector supports creating a tied arch, as illustrated in
Multi-Rib Arch Structures: The invention enables multiple double-row polygonal arches to be connected into larger, multi-rib structures by transverse beams 10 inserted in the ‘transverse notch’ 3 of the inventive connectors in each arch, as seen in
Symmetrical Connectors: A variant of the double-row polygonal arch which has 3 rows of beams can be created by combining two standard connectors into one connector. Two combinations are possible: ‘front-to-front’ and tack-to-back′. ‘Front-to-front’ connectors, as shown in
The 3-row arch has value as a decorative structure. The 3-row arch can be used for structures if the beams in the center row are increased in size to be equal in load-bearing capacity of the two outer rows.
Hinges and Pivots: The hinges and pivots described and illustrated represent generic, off-the-shelf components or application-specific engineered connections that have the axis of rotation indicated and perform the function described. The illustrations are not necessarily drawn to scale. Flexible material such as fabric can serve as a hinge in some applications. Custom engineered solutions and integration of the hinge function into elements of the connector are include as options where hinges or pivots are included in the invention
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/323 553, filed Apr. 15, 2016, the entirety of which is hereby incorporated by reference.
Number | Name | Date | Kind |
---|---|---|---|
1840041 | Kellogg | Jan 1932 | A |
4009543 | Smrt | Mar 1977 | A |
4117636 | Smith | Oct 1978 | A |
4194851 | Littlefield | Mar 1980 | A |
4729197 | Miller | Mar 1988 | A |
4876828 | Brill | Oct 1989 | A |
6647683 | Thomsen | Nov 2003 | B1 |
7017307 | Jones | Mar 2006 | B2 |
9328513 | Maguire | May 2016 | B2 |
Number | Date | Country | |
---|---|---|---|
20170298612 A1 | Oct 2017 | US |
Number | Date | Country | |
---|---|---|---|
62323553 | Apr 2016 | US |