Patent Grant
8484915
This invention relates to concrete-filled steel tubular columns for high load carrying capacity and more particularly to concrete-filled steel tubular columns which are resistant to fire.
Concrete-filled steel tubular columns are today a preferred choice of designers for high load carrying capacity per unit area of cross section of columns. Such columns provide faster construction and no requirement for framework. Patents are available giving descriptions of the methods of construction of such columns and cantilevers. However, the problem associated with this type of construction is in the escape of gases during exposure to relatively intense fires especially when the columns are massive.
This problem is exacerbated with the use of high strength concrete because of the reduced porosity thus providing fewer escape routes for gases during fire exposure. The mixing of polypropelene fibers in the concrete of such members helps to provide passage because of the fibers melting during the fire produce porosity for the escape of gases from inside the concrete mass. However, the mixing of polypropelene fibers in concrete will not be that effective because of the requirement of a large number of vents required in the steel tube which is not structurally feasible.
The exposure of such columns to fire may even lead to its bursting in the case of insufficient vents for the escape of gases. Most of the currently available studies use vents in the outer steel column for the escape of gases. A patent search on concrete filled steel tube columns disclosed the following patents.
A U.S. Patent of Sato U.S. Pat. No. 4,722,156 is entitled CONCRETE FILLED STEEL TUBE COLUMN AND METHOD OF CONSTRUCTING THE SAME. As disclosed, a concrete filled steel tube column includes a steel tube having an inner face; a concrete core disposed within the steel tube; and a separating layer interposed between the inner face of the steel tube and the concrete core for separating the concrete core from the inner face of the steel tube. Therefore, the steel tube is not bonded to the concrete core. After the separating layer is formed on the inner face of the steel tube, the concrete is charged into the steel tube to form a concrete core.
A further U.S. Patent of Schleich et al. U.S. Pat. No. 4,779,395 discloses a COMPOSITE CONCRETE/STEEL FIREPROOF COLUMN. As disclosed, a fireproof construction element has a plurality of integrally interconnected and parallel profile beams each having a longitudinally extending outer flange defining an outer surface and a longitudinally extending web extending inwardly from the flange. The webs are each formed adjacent the flange with a row of at least generally longitudinally extending, elongated, and laterally throughgoing slots. The beams form a plurality of outwardly open channels laterally bounded by the flanges. Respective masses of concrete substantially fill the channels between the webs and inward of the flanges and have outer surfaces contiguous with the outer surfaces of the beam flanges. The slots can be provided in two rows with the slots of one row overlapping and staggered with the rows of the other.
Finally, a U.S. Patent of Vincent U.S. Pat. No. 6,061,992 discloses a Composite Steel/Concrete Column comprising a longitudinally extending H-shaped steel assembly having a pair of parallel flange plates and a web plate interconnecting the flange plates and defining two opposite channel-shaped spaces. A plurality of spaced-apart transversal tie bars are disposed along the steel assembly on each side of the web plate for interconnecting the flange plates. A mass of concrete fills the channel-shaped spaces. The steel concrete column is characterized in that the ratio of the cross-sectional surface area of the steel assembly with respect to the total surface area of the composite steel/concrete column is less than 9%, preferably 2% to 5%. The column is principally to be utilized in structural steel high-rise buildings which have the advantage of shop prefabrication resulting in rapid on site construction. The column shows a steel to concrete ratio greatly reduced as compared to prior art composite columns, thereby greatly reducing the production cost and the size of the columns.
Notwithstanding the above, it is presently believed that there is a need and a potentially large commercial market for improved concrete-filled tubular steel columns for high load carrying capacity. It is also believed that the steel tubular columns for high load carrying capacity in accordance with the present invention can be produced at a competitive cost and yet possess the physical properties required in the building industry. Further, it is believed that if a fire is encountered, there are methods for retrofitting the columns at a reasonable cost.
In essence, the present invention comprises or consists of an outer longitudinally extending vertical tubular steel shell and an inner steel member disposed within the outer longitudinally extending vertical tubular shell. In a preferred embodiment of the invention, the inner steel member is a perforated tubular element that is considerably smaller than the outer steel shell and is centrally disposed within the longitudinally outwardly vertical tubular shell. The column also includes a plurality of equally or unequally spaced transverse flanges extending outwardly from the inner steel member and a plurality of horizontally disposed perforated pipes adjacent each of the flanges at regularly vertical spacings between the outer shell and the inner steel member for the escape of gases in the event of fire.
In a preferred embodiment of the invention, the concrete-filled steel tubular column in accordance with the invention comprises an outer longitudinally extending vertical tubular steel shell and an inner perforated tubular steel member having a plurality of openings therein centrally disposed within the outer longitudinally extending tubular steel shell. In addition, a plurality preferably four radially extending vertical flanges extend outwardly from said inner tubular steel member between the inner steel member and the outer longitudinally extending vertical tubular steel shell. In addition, a plurality of horizontal perforated pipes having a plurality of openings therein are disposed at regular vertical spacings between the inner perforated steel member and the outer longitudinally extending vertical tubular steel shell for the escape of gases in the event of fire. A mass of concrete engulfs the flanges and pipes and fills the void between the outer longitudinally extending vertical tubular steel shell and the inner perforated tubular steel member. In a preferred embodiment of the invention, a mass of concrete is high strength concrete.
The invention will now be described in connection with the following figures wherein like reference numerals have been used to identify like parts.
As
In a preferred embodiment of the invention, as shown in
It should be recognized that the main source of casualties during fires is the inhalation of noxious gases and smoke which are reduced by the novel system disclosed herein. Such systems can channel the gases upwardly through the tubular member 22 from the concrete filled steel tubular column 10 to the outside of the building.
The inner steel pipes 26 and inner steel tubular member 22 also provide better means for the dissipation of heat of hydration of concrete particularly when high strength concrete is used. The inner pipes may also be used for passing chilled water for the purpose of dissipation of heat of hydration. Further, the inner vertical tubular member 22 and the perforated inner pipes 26 may be subsequently used for injecting cement grout through the perforations for strengthening the post fire damaged concrete.
One of the main advantages of the novel system of strengthening as compared to several other conventional methods is that it does not alter the size of the column and hence its esthetic appearance. The filling of space inside the inner steel pipe with cement grout would also provide additional strength after a fire with damage to the column 10.
A preferred embodiment of the invention will now be described with references to
The concrete-filled tubular steel column 10 also includes a perforated tubular steel member 22 that is centrally disposed within the outer longitudinally extending vertical steel shell 20 that is made of low carbon steel with a diameter that is suitable for grouting with a minimum of about 100 mm. The inner tubular steel member 22 based on the structural design of the column considering its load carrying capacity and may be kept as low as 12 gauge steel has a diameter of between about ⅛th and ⅓rd of the diameter of the outer longitudinally extending vertical steel shell 20.
The inner tubular steel member 22 also adds reinforcement to the column 10. Additionally reinforcement is provided by four flange like steel vertical plates 24 that extend outwardly from the inner tubular member 22. These plates 24 have a thickness based on the structural design of the column considering its load carrying capacity and may be kept as low as 12 gauge steel and are made of low carbon steel. The plates 24 are attached to the inner tubular member 22 by welding or other suitable means and extend outwardly nearly to but are at least spaced from the inner surface of the outer longitudinally extending vertical tubular shell 20.
In addition to the above, the column 10 also includes a plurality of horizontally disposed perforated pipes 26 disposed at regular vertical spacings. Each of the perforated pipes 26 include a plurality of openings with a diameter of about 40 mm and open inner and outer ends. The plurality of openings i.e. openings in the pipes have a diameter of about 20 mm. An inner end of each pipe is welded or otherwise fixed to the inner tubular steel member 22 with the open end aligned with an opening in the inner tubular steel member to allow gases generated during a fire to exit upwardly through the inner tube or member 22. The pipes 26 may also be welded or otherwise fixed to the vertical steel flange like plates 24.
For example, the perforated horizontal pipes 26 may be fixed to the vertical flanges 24 by one or more clips 31 as shown in
A plurality of meltable plastic or adhesive tape or polymer caps of polyethylene, PVC or the like close each of the openings in the pipes 26 as well as the open outer ends of pipes 26 and the openings in the inner tubular steel member 22. These caps prevent water and concrete from entering the pipes through the openings when the concrete is in a plastic state and allows gases to escape in the event of fire when the plastic caps are melted due to heat from the fire.
A mass of concrete preferably high strength or ultra high strength fills the void between the outer longitudinally extending vertical tubular steel shell 20 and the inner tubular steel member 22 and engulfs the plates 24 and pipes 26. In the preferred embodiment of the invention the concrete is high strength or ultra high strength concrete.
As illustrated in
Another embodiment of the invention is shown in
A still further embodiment of the invention is shown in
While the invention has been disclosed in connection with its preferred embodiments it should be recognized that changes and modifications may be made therein without departing from the scope of the claims.
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