SELF MATING BEAM SECTION
A self-mating beam section for constructing a box beam, the self-mating beam section having a substantially “C” shape comprising a web with a first flange and a second flange extending outwardly from the web. The flanges may extend substantially perpendicularly to the web. The self-mating beam section further includes a first longitudinal groove and a second longitudinal groove disposed proximate the intersection of the web and the flange. Each groove configured for receiving a free end of each flange of another identical self-mating beam section, wherein the difference between a width of a groove and the flange thickness is limited to prevent deflection of the free end of the flange when received into a corresponding flange so that the flange does not experience local buckling prior to the beam being loaded to a design stress corresponding to a similarly shaped tubular section.
This application claims the benefit of U.S. Provisional Patent Application No. 61/937,996 filed Feb. 10, 2014 and U.S. Provisional Patent Application No. 62/012,015 filed Jun. 13, 2014, the entire disclosures of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention is in the field of field-assembled box beams, particularly a beam comprised of two identical sections wherein a first section matingly engages with a second section to form a box or tubular structural member.
2. Description of Related Art
Existing two-piece box or tube beam sections have a substantial U-shape wherein the flange sections overlap and a fastener is then inserted or driven through the two overlapping flanges. Because the free end of each of the flanges is not laterally supported, the allowable design strength is significantly lower than the ultimate strength for the section and material of the section (even assuming a factor of safety) when compared to a conventional tubular section or two welded conventional channel sections. For example, in a two-piece box beam constructed of two overlapping C-shaped beam sections, the ultimate strength of aluminum is around thirty-eight (38) ksi and the allowable design strength of the resulting box beam from the overlap of two U-shaped sections is around eight (8) ksi. Thus, the allowable design stress for current field-constructed box beam made from overlapping C-sections is about 21% of the materials ultimate stress. While this configuration of a box beam section provides ease of construction in the field, it results in a very inefficient use of raw materials and restricts the working span lengths.
There are no known currently existing box beam sections that allow a designer to use an increased design stress associated with unitary box beams such as conventional tubular sections or welded channel sections. U.S. Patent Publication No. 2007/0074480 to Kleila, et al (the “'480 application”) discusses issues that pertain to the design of currently existing box beams which are constructed from two conventional C-shape sections (extrusions 212 and 214). In
The '480 application also discloses self-mating beam shapes that insufficiently encapsulates the unsupported edge to prevent a ripple type failure due to local buckling similar experienced in the embodiment shown in
An increase in allowable design stress allows more efficient use of the material as it allows the same box beam section to have an increased span or, alternatively, reduces the amount of material that must be used for the same span. Thus, there is a need in the art for a box beam section that maintains the ease of use and installation currently provided by the overlapping box beam sections, but also allows the designer of to use an increased design stress of a unitary box beam to improve the material efficiency experienced in the industry providing lower material costs for the contractor and the consumer.
The accompanying drawings form a part of the specification and are to be read in conjunction therewith, in which like reference numerals are employed to indicate like or similar parts in the various views.
The following detailed description of the present invention references the accompanying drawing figures that illustrate specific embodiments in which the invention can be practiced. The embodiments are intended to describe aspects of the present invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized and changes can be made without departing from the spirit and scope of the present invention. The present invention is defined by the appended claims and, therefore, the description is not to be taken in a limiting sense and shall not limit the scope of equivalents to which such claims are entitled.
As illustrated in
First flange 14 includes a first end 26 and a second end 28 that define a first flange length, and an outer surface 30 and an inner surface 32 that define a first flange thickness. First end 26 is coupled to web 12 proximate first end 18 of web 12. First flange 14 extends away from inner surface 24 of web 12 wherein second end 28 is generally, and may be referred to herein as, a free end. First flange 14 includes an overlapping portion 34 having one or more longitudinal ribs 36 disposed on its outer surface 30. Overlapping portion 34 is generally orientated substantially perpendicular to web 12, although, angular orientations are within the scope of the present invention. Self-mating beam section 10 and 10′ may also include a longitudinal groove 38 that is continuous along the length of self-mating beam section 10 and 10′. Groove 38 is positioned proximate the outer surface 30 of first flange 14 and proximate the intersection of the web 12 and flange 14. Longitudinal groove 38 may extend substantially perpendicular to overlapping portion 34 and self-mating beam section 10 may have a stiffening portion 40 disposed laterally adjacent to groove 38. As shown, stiffening portion 40 may comprise an outer portion 40a and an inner portion 40b. Stiffening portion 40 may extend substantially laterally and perpendicular to groove 38 and overlapping portion 34 as shown in
Turning back to
When the ends of the flanges 14 and 16 of both sections are received into the grooves 38 and 60 as shown in
Once the second ends of each flange 14 and 16 are received into a groove 38 or 60 in the mating engagement, the free second ends 28 or 50 are effectively restrained from lateral displacement in both directions. Tests have shown that this construction increases the allowable design strength of a conventional site-constructed box beam without the mating engagement of second ends 28 and 50 and grooves 38 and 60. In one embodiment of the present invention, the allowable design strength of an extruded aluminum section doubled from eight (8) ksi for a C-shape section to sixteen (16) ksi for a unitary box beam. Thus, substantial material efficiency may be realized using the present self-mating beam section 10 and 10′.
In order for a beam to meet the requirements of the Aluminum Design Manual, Part A1, for the section to be considered equivalent to a unitary box beam, the built-up beam section must act in a unitary manner Thus, it is imperative that the tolerance of lateral movement, and hence the amount of deflection that can be allowed, to prevent failure due to this local buckling mechanism is limited. Turning to
A novel approach to estimating the allowable clearance or tolerance of movement for the free end of a flange of a self-mating beam section is to analyze the buckling of a similarly dimensioned unitary tube shape. For example, a unitary rectangular tube shape that at is nominally two inches by four inches (2″×4″) having a wall thickness of fifteen-one-hundredths of an inch (0.15″) was used to model one embodiment of the present self-mating beam section. This analysis is based upon a calculation of allowable stress set for aluminum shapes the Aluminum Design Manual (“ADM”) produced by the Aluminum Association, 1525 Wilson Blvd., Arlington Va. 22209. The allowable stress per the Aluminum Design Manual (“ADM”) is approximately sixteen and eight tenths (16.8) ksi for a unitary box beam of these dimensions.
The engineering formulas that apply for the calculation of this deflection for various rectangular geometries, such as conventional tube sections, are as follows:
Mmax =(wmax)(l)/8.
Stressmax=Mmax/Sectional Modulus.
fmax=Wmax×5×(1)3/384×(the Modulus of Elasticity)×(the Moment of Inertia).
In the above formulas, “Mmax” is the maximum moment applied to the beam, “w” is total uniformly distributed load in pounds/foot, “1” is the length of the beam between supports and is used in several of the formulas below, Stressmax equals the maximum stress experienced by the beam when the M. is applied; fmax is the maximum deflection; max=the total load, “Sectional Modulus” and “Moment of Inertia” are properties specific to the geometry of the shape under consideration, “Modulus of Elasticity” is a property of the specific material being used.
In addition, formula 3.4−3−14 of the ADM for normal slenderness limits for a box-beam is: LbSc/0.5Cb(Iy)5, with “Lb” being the unbraced length of the beam, “Sc” being the Sectional Modulus of the beam—compression side, “Cb” being a coefficient depending on moment gradient that comes from the ADM, and “Iy” being the moment of inertia of the beam section.
In the example of a unitary rectangular tube shape that at is nominally two inches by four inches (2″×4″) having a wall thickness of fifteen-one-hundredths of an inch (0.15″) and an allowable design stress of 16.8 ksi, the maximum deflection cannot exceed plus or minus twelve-one-thousandths of an inch (+/−0.012″) in order for the member not to experience a stress level above 16.8 ksi. Thus, for a mated shape of similar net dimensions to function substantially equivalent to the box, it was posited that the maximum deflection of the free ends of a flange of a section 10 or 10′ must not exceed plus or minus twelve-one-thousandths of an inch (+/−0.012″). Thus, in the embodiment of
Thus, it was unexpected that the maximum clearance between the flange and the groove can be estimated by the above formulas. These formulas result in one embodiment having the maximum clearance being one-one-hundredth of an inch (0.01″). In other words, if the difference between the groove width Wg and the flange thickness Tf as shown in
The present self-mating beam section 10 and 10′ may be made from extruded metal or polymer, with common metals being aluminum, stainless steel, copper, steel, or any other known extruded metal. Any substantially rigid polymer, PVC, or plastic may also be within the scope of the present invention. The present self-mating beam section 10 and 10′ may also be cast or injection molded in defined lengths. In one embodiment, the present self-mating beam section 10 and 10′ may be made from 6000 series aluminum alloys including 6005, 6066 and 6070, or 5000 series aluminum alloys, including 5050. Any of the materials may have a “brushed” finish that would eliminate or mask cosmetic issues due to fabrication.
As is evident from the foregoing description, certain aspects of the present invention are not limited to the particular details of the examples illustrated herein. It is therefore contemplated that other modifications and applications using other similar or related features or techniques will occur to those skilled in the art. It is accordingly intended that all such modifications, variations, and other uses and applications which do not depart from the spirit and scope of the present invention are deemed to be covered by the present invention.
Other aspects, objects, and advantages of the present invention can be obtained from a study of the drawings, the disclosures, and the appended claims.
Claims
1. A box beam section comprising:
- a web;
- a first flange extending away from said web proximate a first end of said web, said first flange having a first flange thickness;
- a second flange extending away from said web proximate a second end of said web, said second flange having a second flange thickness; and
- a first longitudinal groove orientated parallel to and disposed outward of said first flange, said first longitudinal groove having a first groove width; and
- a second longitudinal groove orientated parallel to and disposed inward of said second flange, said second longitudinal groove having a second groove width;
- wherein first flange thickness is less than said second groove width and a difference between said first flange thickness and said second groove width is a first allowable clearance;
- wherein second flange thickness is less than said first groove width and a difference between said second flange thickness and said first groove width is a second allowable clearance; and
- wherein said first allowable clearance is less than a deflection of said first flange under a first loading that causes local buckling of said first flange, and said second allowable clearance is less than a deflection of said second flange under a second loading that causes a local buckling of said second flange.
2. The box beam section of claim 1 wherein the first allowable clearance is less than or equal to 0.01 inches and the second allowable clearance is less than or equal to 0.01 inches.
3. A box beam comprising:
- A first beam section and a second beam section coupled by a plurality of fasteners;
- Said first and second beam sections being substantially identical, each identical beam section comprising:
- a web;
- a first flange extending away from said web proximate a first end of said web, said first flange having a first flange thickness;
- a second flange extending away from said web proximate a second end of said web, said second flange having a second flange thickness; and
- a first longitudinal groove orientated parallel to and disposed outward of said first flange, said first longitudinal groove having a first groove width; and
- a second longitudinal groove orientated parallel to and disposed inward of said second flange, said second longitudinal groove having a second groove width;
- wherein first flange thickness is less than said second groove width and a difference between said first flange thickness and said second groove width is a first allowable clearance;
- wherein second flange thickness is less than said first groove width and a difference between said second flange thickness and said first groove width is a second allowable clearance; and
- wherein said first allowable clearance is less than a deflection of said first flange under a first loading that causes local buckling of said first flange, and said second allowable clearance is less than a deflection of said second flange under a second loading that causes a local buckling of said second flange; and
- wherein each of said first and second flanges of said first and second beam sections have a free end, and said free ends of said flanges of said first beam section are received into said grooves of said second beam section and, wherein said free ends of said flanges of said second beam section are received into said grooves of said first beam section.
4. The box beam section of claim 3 wherein the first allowable clearance is less than or equal to 0.01 inches and the second allowable clearance is less than or equal to 0.01 inches.
Type: Application
Filed: Feb 10, 2015
Publication Date: Aug 13, 2015
Inventors: William Dorman (Umatilla, FL), Keith Burnett (Seminole, FL)
Application Number: 14/618,108