Static structures (e.g. – buildings) – Machine or implement
Reexamination Certificate
2000-09-29
2002-07-09
Stephan, Beth A. (Department: 3635)
Static structures (e.g., buildings)
Machine or implement
C052S745190
Reexamination Certificate
active
06415577
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the fields of metal working and building construction. More particularly, the invention concerns structural beams, such as I-beams, having a web that may be corrugated, interposed between two hollow plates, resulting in beams that are relatively light weight, yet strong compared to other building materials.
2. Description of Related Art
In the construction industry, beams and girders are often utilized to provide the structural strength for a variety of buildings. These beams and girders may be manufactured from metal, such as steel. It is known to utilize steel beams to construct a variety of structures like buildings, bridges, fences, ship bulkheads, truck bodies, aircraft, and mobile homes frames, to name a few.
Often, it is desired to reduce the weight and cost of manufacture of these metal beams, while concomitantly improving the strength of these metal beams. One method of increasing the strength of the metal beams is through the use of high strength steels. Use of high-strength steels allows for smaller beams to carry greater loads. However, these high-strength steels do not necessarily reduce the weight of the beams and often increase manufacturing costs.
Another method of decreasing the weight of the beam without reducing its strength is by using an I-beam. An I-beam is generally comprised of two solid metal flanges supported by a slender connecting piece or web. Thus, the beam is formed in the shape of an I. For a given strength of the beam, it is known that the I-beam is much lighter than a metal beam with a solid cross section.
To reduce the weight of beams and girders, it is customary to decrease the thickness of the webs. The thin web is connected to the solid metal flanges in a variety of ways. For instance, the web may be welded to flanges. The web may be welded on one side or both sides. Or, if a very thin web is utilized, angle iron may be used to support the connection of the web to the flanges. However, thin webs—while reducing the overall weight of the beam—are susceptible to fatigue and may buckle laterally when loaded.
Multiple attempts have been made to increase the fatigue strength and lateral stability of these I-beams with thin webs. For instance, it is standard practice to place stiffeners strategically along the length of the I-beam to laterally support the web. While the strength of such a beam is improved, and its weight remains relatively light, manufacturing costs associated with the attachments of the stiffeners makes the use of stiffeners less attractive. Further, it is known that I-beams having thin webs with stiffeners experience decreased fatigue life compared to other beams. Attachment of stiffeners may cause severe stress concentrations thus further reducing the fatigue strength of welded beams and girders.
Another method of improving the strength of these I-beams is to increase the web thickness. However, this increase in thickness is accompanied by an increase in weight.
Another method of reducing this buckling problem and increasing the strength of the I-beam is through the use of corrugated webs. It is known to provide a web that is corrugated, i.e. having alternating ridges and grooves. The corrugation may be symmetrical or asymmetrical, and may have straight or curved profiles. For example, corrugations of the shape of a sine wave are known for use with solid flanges, as are corrugations having a trapezoidal or rectangular profile for use with the solid flanges.
In general, corrugations greatly increase fatigue strength of the I-beam compared to flat webs. Further, it is known that the use of corrugations decreases the weight of the beam required to support a given load. Thus, it is known that the web thickness can be reduced by using a corrugated web while maintaining beam strength. For practical reasons and for thermal stress relief, the corrugated web may be attached to the solid flange at discrete points: e.g. bolts.
Another attempt to provide strong, yet relatively light metal beams or girders is described in U.S. Pat. No. 5,079,884 entitled “Extendible Interconnected Z-studs” to Menchetti. This patent describes the formation of Z-form metal sections having opposed flanges, and a method of interconnecting two Z-studs.
Thus, there is a need for providing girders or beams that, compared to other beams, are relatively strong and relatively light in weight. The desired beams would have a high strength-to-weight ratio, while providing lateral structural stability and resistance to bending and fatigue. There is also a need to provide structural beams that do not have sharp edges. Further, there is a need for producing these beams in a cost efficient manner, which does not necessarily include the use of stiffeners, flange braces, or difficult-to-deform materials.
SUMMARY OF THE INVENTION
A structural beam is described having a top tube, a bottom tube, and a web having a first end and a second end. The web is interposed between the top tube and the bottom tube. The first end of the web is connected to the top tube, and the second end of the web is connected to the bottom tube. In some embodiments, the top tube has a first rectangular cross section. In others, the bottom tube has a second rectangular cross section.
In some aspects, the first and second rectangular cross sections each have a wall thickness of between about ⅛ inch and about ⅞ inch. In other aspects, the first and second rectangular cross sections each have a width of between about four inches to about twelve inches and a height of between one inch and eight inches. In other embodiments, a structural beam is described in which the web comprises a corrugated web having a trapezoidal profile.
In other embodiments, a method of constructing a structural beam is described having the following steps: providing a rectangular top tube, providing a rectangular bottom tube, providing a web having a first end and a second end, attaching the first end of the web to the rectangular top tube, and attaching the second end of the web to the rectangular bottom tube such that the web is interposed between the rectangular top tube and the rectangular bottom tube.
REFERENCES:
patent: 1523106 (1925-01-01), Dornier
patent: 2007898 (1935-07-01), Ragsdale
patent: 2108795 (1938-02-01), Budd
patent: 2514607 (1950-07-01), McLean
patent: 3686819 (1972-08-01), Atkinson
patent: 4490958 (1985-01-01), Lowe
patent: 5079884 (1992-01-01), Menchetti
patent: 5417022 (1995-05-01), Ritchie
patent: 5553437 (1996-09-01), Navon
patent: 5787559 (1998-08-01), Dean
patent: 5842318 (1998-12-01), Bass et al.
Two (2) drawings dated Feb. 1998, showing prior EagleSpan Steel Structure, Inc. beam sold in 1998.
Arsicault, M. and Lalleman, J.P., “Joint Tracking with Self-Teaching System,”Welding Journal, Dec., 1990.
Peterson, J.M. and Cord, M.E., “Investigation of the Buckling Strength of Corrugated Webs in Shear,”Technical Note D-424, Washington, D.C. 1960.
Rothwell, A., “The Shear Stiffness o Flat Side Corrugated Webs,”Aeronautical Quarterly, vol. 19, Pt.3, 1968, pp. 224-234.
Sherman, D. and Fisher, J., “Beams With Corrugated Webs,”Proceedings of the First Specialty Conference on Cold-Formed Steel Structures, University of Missouri-Rolla, 1971, pp. 198-204.
Libove, C., “On the Stiffness, Stress, and Buckling of Corrugated Shear Webs,”Proceedings of the Second Specialty Conference on Cold Formed Steel Structures, University of Missouri-Rolla, 1973, pp. 259-301.
Easley, J.T., “Buckling Formulas for Corrugated Metal Shear Diaphragms,”Journal of the Structural Division, ASCE, St. 7, 1975, pp. 1403-1417.
Wu, L.H. and Libove C., “Curvilinearly Corrugated Plates in Shear,”Journal of the structural Division, ASCE, St. 11, 1975, pp. 2205-2222.
Hussain, M.I. and Libove, C., “Stiffness tests of Trapezoidal Corrugated Shear Webs,”Journal of the Structural Division, ASCE, St. 5, 1977, pp. 971-987.
Harrison, J.D., “Exploratory Fatigue Tests of Two Girders with Corrugated Webs,”British Welding Journal, 12, No. 3, 1965, pp. 12
EagleSpan Steel Structures, Inc.
Howrey Simon Arnold & White , LLP
Slack Naoko
Stephan Beth A.
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