Patent Application
20160145862
This invention relates to concrete-filled steel columns for high load carrying capacity and fire resistance, usually required in tall buildings. More particularly the invention relates to concrete-filled steel tubular columns having a plurality of vertical tubular members for venting smoke and noxious gases from a fire and dissipating heat of hydration of concrete. Moreover the column can be easily and effectively strengthened after damage during fire without shape change.
The use of concrete-filled steel tubular (CFST) columns has increased in recent decades due to their excellent structural performance which takes advantage of the combined effect of steel and concrete working together. The steel tube provides confinement to the concrete core resulting in increased compressive strength whereas the concrete core restricts inward deformation of the steel tube thus enhancing local buckling resistance of steel tubes. In addition to these advantages, the steel tubes surrounding the concrete columns eliminates permanent formwork which reduces the construction time and costs. Moreover, CFST columns possess better fire resistance as compared to steel columns
The fire risk in high-rise buildings is significantly higher than a lower-rise building because of the potential for more fire locations and greater consequences of the fire itself (e.g. stack effect) and to a greater number of occupants. However, the fires in high-rise buildings generate large quantities of smoke that can spread vertically or horizontally through the building even if the fire is contained to only one room or unit. The smoke emitting from burning polypropylene fibers usually embedded in high strength concrete adds more toxicity to the smoke which is responsible for many of the fatalities in such incidents. Thus, there is higher potential risk to life from fire in high-rise buildings which demands greater fire safety in these buildings where CFST columns are commonly used for carrying heavy loads.
There are a number of approaches for the construction of such columns to overcome the problem with such construction as for example in the escape of smoke and gases during exposure to fire especially when the columns are massive. The problem gets aggravated 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 polypropylene fibers in the high-strength concrete of reinforced concrete members helps to provide passages by the melting of fibers during fire for the escape of gases from inside a concrete mass. But, the mixing of polypropylene fibers in concrete of CFST columns will not be that effective because of the requirement of a large number of vents required in the steel tube which is not structurally favorable. The exposure of such columns to fire may lead to more serious consequences in the case of insufficient vents. Therefore, most of the available studies use a plurality of vents in the outer steel column for the escape of gases.
A U.S. Pat. No. 8,484,915 of Abbas et al. entitled “System for Improving Fire Endurance of Concrete-Filled Steel Tubular Columns” is assigned to the same assignee as the present invention. As disclosed therein, a concrete filled tubular steel column includes a longitudinally extending outer vertical tubular steel shell and an inner perforated tubular steel shell disposed at the center of the outer steel shell to be coaxial therewith. A plurality of spaced vertically steel plates extend from the inner steel shell towards but not abutting the outer steel shell. In addition, a plurality of horizontally disposed perforated pipes extend outwardly from the inner member. All perforated inner tubular steel shell and pipes have a plurality of meltable polymer plugs or caps to prevent plastic cement from flowing into or closing the openings. In the event of fire, the plastic or polymer plugs or caps melt and allow gases and smoke to flow into the perforated pipes and up through the inner member and out therefrom to the top of the column
It is presently believed that there is a present need and a potential commercial market for an improved concrete-filled steel tubular column for high load carrying capacity and fire resistance. There should be a need and a potential commercial market for such products that dissipate smoke and toxic gases at the top of the column, eliminate to a large degree exit vents in the steel tubular column and to a larger degree reduce the smoke and toxic gases from areas adjacent to inhabited floors as well as reducing the costs while maintaining the load carrying capacity.
In essence, the present invention contemplates a concrete-filled steel tubular column for high load carrying capacity that may be relatively massive and/or more effective in dissipating smoke and toxic gases near the top of the column and away from human inhabitants in the upper floors of a building. The column comprises and/or consists of an outer longitudinally extending generally vertical tubular shell and an inner longitudinally extending perforated steel tubular shell disposed within said outer longitudinally extending vertical tubular shell and coaxially therewith. In addition, a plurality of relatively small diameter vertically extending perforated tubular steel members are disposed around the inner longitudinally extending tubular shell between the outer longitudinally extending tubular shell and the inner longitudinally extending steel shell with axes parallel to the coaxial axis. All perforated inner tubular steel shells and members have a plurality of meltable polymer plugs or caps to prevent plastic cement from flowing into or closing the openings. In the event of fire, the plastic or polymer plugs or caps melt and allow gases and smoke to flow into the inner perforated pipes and out therefrom to the top of the column
The invention will now be described in connection with the accompanying drawings wherein like elements are designated with like numbers.
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As shown, the steel tubular column 10 also includes a plurality of relatively small diameter vertically extending perforated tubular steel members 16 disposed around the inner longitudinally extending perforated tubular steel shell 14 between the outer tubular shell 12 and inner tubular shell 14. As presently contemplated, the outer steel shell 12 has a minimum diameter of about 500 mm while the inner shell will have a minimum diameter of about 150 mm as designed for structural consideration and loads. By contrast, the longitudinally extending steel tubular member 16 will have a minimum diameter of about 150 mm as designed for structural consideration and loads. The perforations of the inner longitudinally extending perforated tubular steel shell 14 and small diameter vertically extending perforated tubular steel members 16 are all closed with a plurality of water resistant polymer caps for preventing the escape of water or mortar through the openings when the cement is in the plastic state. Further, the plastic caps are melted during a fire thus providing passage for the escape of gases through the inner vertical tubular members 14 and 16 to the top.
It is also contemplated that the height of the column 10 will extend for full height of a building i.e. up to the roof top so that smoke and gases escape through the roof top.
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A further embodiment of the invention is illustrated in
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While the invention has been described in connection with its preferred embodiments, it should be recognized and understood that changes and modifications may be made therein without departing from the scope of the appended claims.
