The present invention relates, generally, to materials used in construction. More specifically, the present invention relates to steel joist structures used in building construction.
Steel joists have been used to structurally support building roofs and floors throughout the United States for the better part of a century. An exemplary array of conventional joists forming a support for a deck or roof is depicted in
The conventional steel joist used today consists of a top chord, a bottom chord, and multiple diagonals. As
The top chord of today's conventional steel joist consists of a pair of steel angles, parallel to one another, and positioned in a “back-to-back” orientation. See
Well known problems associated with present conventional steel joist constructions include: 1.) the need for erection bracing, also known as erection bridging as defined by OSHA; 2.) poor aesthetics; 3.) potential for corrosion of untreated areas; 4.) proclivity to top and/or bottom chord local bending; 5.) poor power actuated fastener penetration due to top chord local bending; 6.) inability to properly support/distribute and/or aesthetically conceal electrical and plumbing lines and HVAC ductwork. A need, therefore, exists for a steel joist assembly which resolves or greatly reduces these known problems.
The present invention is a substantially hollow tubular joist structure, a joist assembly including a plurality of aligned repetitive tubular joist structures, and a method of constructing this joist assembly. The tubular joists are preferably steel. Tubular joists offer several advantages over conventional steel joists. The tubular joists of the present disclosure are designed to fully comply with OSHA 29 C.F.R. §1926.757(a)(3), incorporated fully herein by reference.
Steel joists have never been fabricated exclusively from hollow steel tubes. These hollow steel tubes may include, by way of example and without limitation, a square, rectangular, round, oval, diamond shape, or hexagonal cross-section, however, it is understood that any suitable geometry could be employed as may be suitable for a particular application or known or developed by one of skill in the art. Preferred geometries may include round, square (including substantially square such as square with rounded or truncated corners), or rectangular (also perhaps with rounded or truncated corners) with rectangular or substantially rectangular being the most preferred cross-section. These hollow tubes (most preferably steel but may be constructed of any suitable material) shall be referred to herein as “tubular.” Joists constructed using tubular chords which may also include tubular diagonals shall be referred to herein as “tubular joists”.
The joist structure of the present disclosure includes a tubular top chord; a tubular bottom chord; and, a plurality of diagonals extending between the tubular top chord and the tubular bottom chord. The diagonals are also, in a preferred arrangement, tubular in construction. The diagonals are preferably arranged in a zig-zag formation between the tubular top chord and the tubular bottom chord.
The tubular top chord may be capable of receiving a power actuated fastener (PAF). The tubular top chord and the tubular bottom chord are capable of receiving a utility conduit. A utility conduit may include an electrical conduit or cable, a plumbing conduit, or it may receive a HVAC duct or may even itself act as an HVAC duct to convey conditioned air.
A method of constructing a tubular joist includes arranging a tubular top cord and a tubular bottom chord in a nearly or substantially parallel relationship. The tubular top chord and tubular bottom chord support one another through a plurality of diagonals which extend between the tubular top chord and tubular bottom chord in a preferred, substantially zig-zag manner. The diagonal are fastened to the tubular top chord and the tubular bottom chord preferably by welding or using fasteners or by any other means or as known in the art.
A method of constructing a tubular joist assembly of the present disclosure includes assembling a plurality of tubular joist structures each including a top chord, a bottom chord, and a plurality of diagonals extending between the top chord and bottom chord; and, wherein a plurality of the joist structures include a tubular top chord and a tubular bottom chord. This method of construction allows for the joist to be set in place with a substantially reduced requirement and in many instances without requiring a crane to support the joist while the erection bridging is installed since in most practical cases the erection bracing can be eliminated. By way of example, however, a tubular joist structure, as disclosed herein, could also be fabricated so as to be longer than conventional joists. In such longer structures, it is contemplated that erection bracing or the use of a crane for support during installation of the erection bracing may be preferred.
The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processes and manufacturing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the invention herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the claimed invention.
With reference to
Bottom chord 22 is a horizontal member that is beneath and parallel (or nearly parallel) to top chord 20. With reference to
The diagonals 24 (
Bottom chord 104 includes a length of tubular steel the same construction as top chord 102 and positioned parallel to top chord 102 and separated by diagonals 106. In the preferred arrangement depicted in
Diagonals 106 connect tubular top chord 102 and tubular bottom chord 104. In the preferred arrangement, diagonals 106 are also steel tubular construction also with a rectangular cross section but of a smaller size than tubular top chord 102 and tubular bottom chord 104. However, it is understood that diagonals 106 could be constructed of any suitable geometry. Alternatively, diagonals 106 could be of a conventional construction and not tubular. Diagonals 106 in the preferred arrangement are oriented in a zig-zag pattern to join tubular top chord 102 and tubular bottom chord 104. Diagonals 106 are welded to top chord 102 and bottom chord 104, thus forming a rigid open web tubular joist design. Tubular top chord 102, tubular bottom chord 104 and diagonals 106, when constructed lie in, or nearly in, a common vertical plane.
Tubular joists offer several advantages over conventional steel joists. Specifically, nine such advantages have been identified and are set forth herein. For example, with regard to fabrication, tubular joists have several advantages. Tubular joists have half the number of chord pieces, and one-third fewer web member pieces (no verticals) to handle and cut in the shop. Tubular joists will have less than half the surface area that must be coated. All web-to-chord tubular connections are simple gapped joints with small fillet welds made on the flat area of the HSS tube wall.
Advantage 1: Erection Bracing:
With reference to
The torsional constant “J”, which is a property of the member cross section, directly impacts the member's effectiveness in resisting torsion: the greater “J”, the greater the resistance against torsion. The following comparison contrasts a conventional top chord 20 (
Hence, the tubular chord 118 (
According to the erection stability equation that is behind the OSHA erection bridging span tables, an unbraced conventional design (32LH06) joist performs unfavorably compared to an unbraced tubular joist of the present disclosure of equivalent weight & load carrying capacity:
This is because the torsional constant of the tubular joist is 130 times greater than that of the conventional joist. As a result, the tubular joist design of the present disclosure would be the first joist to be manufactured in compliance with OSHA 29 C.F.R. §1926.757(a)(3).
The cost benefits are also two-fold:
Example Crane Savings from Eliminating Bolted X Bridging (BXB):
Advantage 2: Aesthetics:
Conventional steel joists 10 (
Advantage 3: Corrosion Reduction:
Conventional steel joist fabrication utilizing a pair 28, 30 and 32, 34 (
Advantage 4: Top Chord Local Bending:
With reference to
Hence, an equivalent square tubular chord 118 offers a 21% increase in bending strength over the conventional chord 20. This efficiency offers two cost benefits:
Advantage 5: Bottom Chord Local Bending:
With reference to
Similar to the top chord comparison, the additional bending strength of an equivalent tubular bottom chord 120 (
Advantage 6: Local Bending Preventing PAF Penetration:
Attention is next directed to
Referring to
Advantage 7; Wall Penetrations:
Reference is next made to
Advantage 8: Electrical and Plumbing Lines:
When electrical and plumbing lines run parallel to the conventional joists that support them, clips and hangers must be used to attach those lines to the joist chord(s). A tubular joist chord provides a ready conduit for these lines 128, 130 (
Advantage 9: Conditioned Air Delivery
Similar to electrical and plumbing lines 128 and 130 (
An example calculation of estimated cost savings for the different one-story “Big Box” type buildings resulting from the use of the tubular steel joists of the present disclosure over a conventional steel joists are set forth in Table I.
Thus, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those skilled in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the appended claims.
This application claims the benefit of U.S. Provisional Application No. 61/784,615 filed Mar. 14, 2013, herein incorporated by reference in its entirety for all purposes.
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Entry |
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OSHA 29 CFR 1926.751 https://www.osha.gov/pls/oshaweb/owadisp.show—document?p—table=STANDARDS&p—id=10787. |
Number | Date | Country | |
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20140338279 A1 | Nov 2014 | US |
Number | Date | Country | |
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61784615 | Mar 2013 | US |