Static structures (e.g. – buildings) – Openwork; e.g. – truss – trellis – grille – screen – frame – or... – Three-dimensional space-defining
Reexamination Certificate
1999-03-26
2003-02-11
Mai, Lanna (Department: 3637)
Static structures (e.g., buildings)
Openwork; e.g., truss, trellis, grille, screen, frame, or...
Three-dimensional space-defining
C052S167300, C052S638000, C052S749100, C052S653100
Reexamination Certificate
active
06516583
ABSTRACT:
This invention relates to structural connections between braces, beams and columns, using parallel gusset plate technology. As taught herein, gusset plates may be used to connect a brace, column and beam or, also, to connect a brace to a beam or a column. The use of gusset plates to connect beams to columns was taught in patent U.S. Pat. No. 5,660,017, mentioned above. This invention improves upon the structural connections taught in that patent, by reconfiguring the parallel gusset plates to receive diagonal braces. Thus, wherein the brace, column and beam are connected by parallel gusset plate, the system is a “dual” system because it uses gusset plates to attach both beams and braces to columns, thereby combining, interactively, a structurally braced lateral load resisting connection system with a structural moment resisting frame connection system. Similarly, wherein the brace and column only are connected by parallel gusset plates, the system is a special braced system because it acts alone to resist lateral loads.
The most commonly used braces, in this invention, are those known as wide-flanged “H” braces. Such braces have two wide flanges connected to each other by a web. The beams and columns most commonly used are “H” beams and columns, having two flanges and a web interconnecting them. However, other shapes may be used for brace, beam or column, or any combination thereof. Tube shapes and built-up box shapes are commonly known and used. It is to be appreciated that a box shape may be considered to have two flanges and two webs, acting in any principal direction, with the flanges in one principal direction acting as webs in the other principal direction, when loaded biaxially. Similarly, a built-up cruciform column may be used. Such cruciform column has four flanges and two webs which cross each other, described and discussed hereinafter, which flanges combine to provide significant stiffness and strength in each principal direction.
This invention is most useful in construction of single and multiple story buildings having a framework of structural steel. It is useful in either new construction or in retrofit construction of steel frame buildings to create a structure with both increased ductility and lateral stiffness.
It is to be appreciated that such joint connections would be useful in bridges and other structures using steel beams.
BACKGROUND OF THE INVENTION
It has been found that substantial improvement is needed in the moment-resisting capabilities of beam-to-column connections in prior, structural steel buildings. Continuing and similar experience has been recently gained from both laboratory testing and from earthquakes, high winds, hurricanes, tornadoes, blasts, explosions and various other severe loading conditions which have happened, and which will continue to happen when using prior brace-to-column and prior brace-to-beam structural connections. Such loading conditions place similar demands on braced structural connection systems as they do on moment-resisting frame structural connection systems, which severe loading conditions in the past, have resulted in brittle fracture of both connection weld metal and base metal.
It is now common knowledge that prior beam-to-column connections and brace-to-column and brace-to-beam connections, which often used complete penetration welded joints between beam flange and column flange, and between the brace flange and the column flange and between the brace flange and the beam flange are not adequate and are susceptible to brittle fracture of the connection elements and the base metal, under severe loading conditions. The old, traditional, connection technology simply does not provide the needed strength and ductility required to withstand extreme loading conditions.
The prior art teaches numerous ways to connect beams and braces to columns. Previously, the common brace-to-beam and brace-to-column connection has been through the use of a single gusset plate welded or bolted to brace, beam and column. Other common brace-to-beam and brace-to-column connections used previously, involve welding at a skewed angle, the brace flanges directly to the faces of the column and beam flanges, respectively, using large, highly-restrained, full-penetration, single-bevel groove welds. This connection may actually be more vulnerable to brittle fracture than its common previously used moment-resisting frame beam-to-column connection counterpart, in part due to a more restricted access for welding.
In the prior beam-to-column connection, the beam has often had the ends of its top and bottom flanges welded to one flange, or face, of the column by large, highly-restrained, full-penetration, single bevel groove welds.
There has been partial or complete failure of the highly-restrained welds between the beam flange and the column flange, either by a crack in the weld itself or a crack along the heat affected zone of the column flange, and/or a crack in the column flange base metal, pulling a divot of column steel from the face of the column flange.
In addition, failures between the beam flange and column flange have resulted in shear failure of the high strength bolts connecting the shear tabs to the web of the beam for the support of the gravity loads. Vertical loads, that is, the weight of the floors and gravity loads acting on the floors, are commonly carried by vertical shear tabs. Each such shear tab is vertically disposed and is welded to the face of the column and bolted or welded to the web of the beam, at the end of the beam which is nearest the column, using high-strength bolts.
Subsequent attempts by the building industry to improve beam-to-column connections and brace-to-column and brace-to-beam connections still rely on post-yield straining of large, highly-restrained, full-penetration, single-bevel grooves welded under field conditions. Such highly-restrained welds do not provide a reliable mechanism for dissipation of earthquake energy, explosion or blast energy, or other large forces, and can lead to brittle fracture of the weld and the column. Such brittle fracture shows that the design violates the ductile design intent of the Uniform Building Code, for both moment-resisting frame connection systems and special braced frame connection systems.
Of course, there are other requirements to be met, some of which are set forth in AISC (American Institute of Steel Construction) publications, including, but not limited to, the LRFD (Load and Resistance Factor Design) specifications and ASTM (American Society for Testing and Materials) publications, as well as ASME (American Society of Mechanical Engineers).
Skilled in the art structural engineers, designing strengthened structural steel buildings are familiar with the various design requirements set forth in those publications and the various State and local building codes which may be involved.
Contrary to prior beam-to-column structural joint connections, and brace-to-column and brace-to-beam structural joint connections, the present invention, by taking advantage of parallel gusset plate technology, does not rely heavily on post-yield straining of the joint connection.
In the case of earthquakes and explosions, greater strength and ductility are particularly desirable in resisting sizeable loads in both the lateral and the vertical directions.
Parallel gusset plate technology, or, simply, gusset plate technology, as taught in the patent mentioned above, has been a substantial step forward in strengthening the beam-to-column connections in a building comprised of structural steel beams and columns. Two parallel gusset plates are attached on opposite sides of a column and attached on opposite sides of a beam, to connect the beam to the column.
Engineering analysis, design and testing have determined that the advancement provided by the parallel gusset plate technology can be further advanced and improved by using gusset plate technology to add braces in the form of a dual structural system, or to connect a brace to either a column or a beam without a moment connected beam-to-c
Humphries L. Lee
Mai Lanna
Yip Winnie
LandOfFree
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