STRUCTURAL FILLER FILLED STEEL TUBE COLUMN

Abstract: A structural filler filled steel tube column (20) including: a steel tube (22) having an inner face and an outer face (28); a core (26) made from the structural filler disposed within the steel tube; a separating layer (24), interposed between the inner face (28b) of the steel tube and the core (26), for separating the core from the inner face of the steel tube so that the steel tube is not bonded to the core; and an inner flange (50, 51) circumferentially mounted on the inner face (34c) of the steel tube (34) to radially inwardly project for transmitting an axial load, applied on the steel tube (22, 34), to the core (26).

Description: Background of the Invention The present invention relates to a structural filler filled steel tube column which may be used for columns and piles of building structures. One of the inventors has proposed a mechanism for transmitting an axial force from a steel tube to a concrete core disposed within it in EP-A-0 195 552 entitled "CONCRETE FILLED STEEL TUBE COLUMN AND METHOD OF CONSTRUCTING SAME" and filed on March 5, 1986. The axial force transmitting mechanism has a stiffener welded to the inner face of the steel tube and disposed within the concrete core. The stiffener is composed of steel plates welded in a cross-shape. In this steel tube column, a separating layer is interposed between the steel tube and the concrete core so that the steel tube is not bonded to the core, and hence a large part of axial force exerted to the steel tube is transferred via the axial force transmitting mechanism to the concrete core, so that the steel tube is subjected to less axial force than the concrete core. Thus, the concrete filled steel tube column is capable of providing sufficient lateral confinement to the concrete core when the latter is compressed, thereby considerably enhancing compression strength thereof. However, in the axial force transmitting mechanism, there are the following points to be improved. The interior of the steel tube is divided into four separate spaces at its portion where the cross-shaped stiffener is provided, and hence it is rather hard to fill concrete uniformly into the four spaces with a tremie which is inserted into the steel tube erected on a base. To evenly distribute concrete four tremies may be inserted into respective separate spaces. However, use of four tremies is costly and reduces workability. Further, it is laborious to weld together crossing portions of the plates which constitute the stiffener in addition to welding of its outer ends to the inner wall of the steel tube. Summary of the Invention Accordingly, it is an object of the present invention to provide a structural filler filled steel tube column which enables filling of concrete uniformly in the steel tube with a single tremie and hence enhances workability in filling concrete. It is another object of the present invention to provide a structural filler filled steel tube column which is less laborious in constructing the axial force transmitting mechanism than the concrete filled steel tube column previously proposed. With these and other objects in view, the present invention provides a structural filler filled steel tube column including: a steel tube having an inner face and an outer face; a core made from the structural filler disposed within the steel tube; a separating layer, interposed between the inner face of the steel tube and the core, for separating the core from the inner face of the steel tube so that the steel tube is not bonded to the core; and an inner flange circumferentially mounted on the inner face of the steel tube to radially inwardly project for transmitting an axial load, applied on the steel tube, to the core. The inner flange may be mounted on the inner face of an upper portion of the steel tube. Preferably, the steel tube includes a tube body and a joint tube concentrically jointed to the tube body, and the inner flange is mounted on an inner face of the joint tube. The joint tube may have H steel beams jointed to the outer face thereof, each beam having a pair of flange portions and a web portion jointing the flange portions, and the joint tube may further have a pair of the inner flanges mounted on the inner face thereof at the same level as corresponding flange portions of the beams. A plurality of first ribs may be mounted on the inner face of the steel tube so that they are jointed to corresponding web portions of the beams through a wall of the steel tube. In the presence of the first ribs, the shearing force from the beams is efficiently transferred to the core and the inner flanges obtain greater strength against an axial force as compared to the axial force transferring mechanism without the ribs. The inner flange may be mounted on the inner face of the steel tube at an intermediate portion of the steel tube including an inflection point of moment of the steel tube. Each inner flange is preferably provided with means for preventing air from staying in lower side of the flange when the structural filler is filled into the steel tube. The air stay preventing means prevents any space not filled with concrete from being formed in the core, thus providing predetermined strength to the core. The air stay preventing means may include an air vent hole formed through the inner flange to extend in an axial direction of the steel tube. The inner flange may have a plurality of the air vent holes, in which case the air vent holes are circumferentially formed at substantially equal angular intervals. In another modified form, the inner flange is inclined to a plane perpendicular to an axis of the steel tube to converge toward an upper end of the steel tube. With such a construction, air is prevented to stay below the inner flange and hence any space not filled with the filler is prevented from being formed below the inner flange. The steel tube may include reinforcing means for reinforcing the inner flange against an axial load applied on the inner flange. In a preferred form, the reinforcing means includes a second rib jointing at least one of opposite faces of the flange to the inner face of the steel tube. With the second rib the strength of the flange is enhanced and axial force is hence efficiently transmitted from the second rib to the core. The steel tube may include means for absorbing an axial strain which develops in the steel tube when the steal tube is subjected to an axial load. Preferably, the axial strain absorbing means may include a circumferential groove, circumferentially formed in one of both the inner face and the outer face of the steel tube, for absorbing the axial strain of the steel tube by deforming the groove. In another preferred form, the axial strain absorbing means includes a bead portion radially outwardly protruding from the steel tube by radially outwardly projecting the inner face of the steel tube. The bead portion absorbs the axial strain by axial deformation thereof. Brief Description of the Drawings The invention will now be described by way of example with reference to the accompanying drawings in which: FIG. 1 is a partial view partially cutaway of a building framework having a plurality of structural filler filled steel tube columns according to the present invention; FIG. 2 is an enlarged fragmentary front view, partly in section, of the steel tube column in FIG.1; FIG. 3 is a view taken along the line III-III in FIG. 2; FIG. 4 is a partial view partly in section of the steel tube column in FIG. 2, illustrating filling of a steel tube with a concrete by means of a tremie; FIG. 5 is a cross-sectional view of a modified form of the steel tube column in FIG. 3; FIG. 6 is a fragmentary front view, partly in section, of another modified form of the steel tube column in FIG. 2; FIG. 7 is a view taken along the line VII-VII in FIG. 6; FIG. 8 is a fragmentary front view of still another modified form of the steel tube column in FIG. 2 showing how to fill it with concrete; FIG. 9 is a view taken along the line IX-IX in FIG. 8; FIG. 10 illustrates fragmentary axial section of a modified form of an inner flange in FIG. 8; FIG. 11 is a partial view partially cutaway of another building framework having another embodiment according to the present invention; FIG. 12 is an enlarged fragmentary front view, partly in section, of the steel tube column in FIG. 11; FIG. 13 is a view taken along the line XIII-XIII in FIG. 12; FIG. 14 is a fragmentary front view partially cutaway of a modified form of an axial strain absorbing mechanism in FIG. 2; FIG. 15 is a fragmentary front view partially cutaway of another modified form of the axial strain absorbing mechanism in FIG. 2; and FIG. 16 is a fragmentary front view partially cutaway of still another modified form of the axial strain absorbing mechanism in FIG. 2; Detailed Description of the Preferred Embodiments In the drawings, like reference characters designate corresponding parts throughout views, and descriptions of the corresponding parts are omitted after once given. FIG. 1 illustrates a part of a building framework according to the present invention which has a plurality of steel tube columns 20 concentrically jointed in series. Each column 20 includes, as illustrated in FIGS. 2 and 3, a steel tube 22 coated over its inner face 22a with a separating layer 24 and a core 26 disposed within the steel tube 22. The thickness of the steel tube 22 is generally in the range of about 1/500 to about 1/10 of the outer diameter of the steel tube 22. The separating layer 24 may be made of a separating material, such as asphalt, grease, paraffin wax, synthetic resin and paper. The core 26 is made of a structural filler, such as concrete, mortar, sand, glass particles, metal powder, and synthetic resin. The separate layer 24 serves to separate the steel tube 22 from the core 26 so that the core 26 is not bonded to the steel tube 22. In this embodiment, the steel tube 22 has a tube body 28 which is provided at its intermediate portion, i.e. inflection point of moment, with a through slot portion 30 having a plurality of rows of through slots 32. As shown in FIG. 2, through slots 32 in a row are circumferentially formed in the through slot portion 30 at equal spacings, and adjacent through slots 32 of adjacent two rows are shifted in their positions in a zigzag manner. The sum of vertical width W of vertically aligned through slots 32 of the through slot portion 30 (e.g., the through slots 32 on the phantom line VL in FIG. 2) is preferably in the range of a maximum axial strain of the steel tube 22 which is caused by overturning moment of the building. The width of each slot 32 is such that wall of each slot 32 has enough strength not to collapse by the axial compression during the framework construction and against stationary load. Instead of the through slots 32, openings of other configurations such elliptical openings, slits may be formed in the tube body 28. The steel tube 22 also has a relatively short joint tube 34 concentrically welded to upper end 28a of the tube body 28. To the upper edge 34a of the joint tube 34, another steel tube 22 is concentrically welded at its lower end. The joint tube 34 is welded at its outer face 34b to inner ends of four H steel beam joint members 36, 38, 40 and 42 (see FIG. 3) so that the beam joint members are disposed in a horizontal plane with adjacent beam members forming a right angle. Each of the beam joint members 36, 38, 40 and 42 has a pair of flange portions 44 and 45 and a web portion 46 which joints the flange portions 44 and 45. The outer end of each beam joint members 36, 38, 40 and 42 is welded to a beam 48 shown in FIG. 1. The joint tube 34 has a pair of inner flanges 50 and 51 circumferentially welded to the inner face 34c thereof at the same level as corresponding flange portions 44 and 45 of the beam joint members 36, 38, 40 and 42. The inner flanges 50 and 51 project radially inwardly into the core 26. The radial length L of each inner flange is generally in the range of about 1/40 to about 1/5 of the outer diameter of the joint tube 34. In this embodiment, each of the inner flanges 50 and 51 has a plurality of air vent holes 52. The vent holes 52 extend in an axial direction of the steel tube 22 and are circumferentially formed at substantially equal angular intervals. The inner diameter of each vent hole 52 is large enough to allow water and cement to go through it. The thickness of the inner flanges 50 and 52, number and diameter of the vent holes 52 are preferably designed to provide them with enough strength to transfer an axial force from the steel tube 22 to the core 26 even when the maximum axial strain is generated in the steel tube 22. In this construction, shearing force from the beams 48 is transferred via the beam joint members 36, 38, 40 and 42 and via the wall of the joint tube 34 to the inner flanges 50 and 51. Then, the shearing force is transferred from the inner flanges 50 and 51 to the core 26 as an axial force. Thus, the steel tube 22 is subjected to a rather smaller axial force from the beams 48 than the core 26. In the presence of the separating layer 24, the steel tube 22 is axially movable relative to the core 26 and hence when the core 26 undergoes axial compression, the steel tube 22 follows the core 26 with a much smaller degree of axial strain than the prior art steel tube bonded to its concrete core. Furthermore, the axial compression of the steel tube 22 reduces its axial length by axially deforming the through slots 32 of the through slot portion 30, thus dissipating the axial stress in the steel tube 22. In constructing the above described steel tube column 20, a structural filler, for example concrete, is filled into the steel tube 22 to form the core 26 by using, for example, a tremie which conveys concrete. In this filling process, the inner flanges 50 and 51 enable a tremie 54 to be inserted into the steel tube 22 along the axis thereof by allowing the tremie 54 to pass through the center openings 50a and 51a of inner flanges 50 and 51 as illustrated in FIG. 4. Thus, the concrete 26 is supplied to the center of the steel tube 22 and then evenly distributed over the whole cross-sectional area of the steel tube 22. When the top face 26a of the concrete 26 approaches from a level shown by the solid line in FIG. 4 to the phantom line, air goes through the center opening 50a of the flange 50 and vent holes 52, so that the ring shaped air space 56 under the inner flange 50 is filled with the concrete 26 and then the vent holes 52 and the center opening 50a of the inner flange 50 are also filled with the concrete. Any similar air space is prevented from being formed in the lower side 51b of the flange 51 in the same manner. As a result, a steel tube column having the joint portion with no air space not occupied with concrete is constructed. A modified form of the embodiment in FIG. 3 is illustrated in FIG. 5, in which a tube body not shown and a joint tube 58 have square cross-sections. A pair of inner flanges 60 and 60 each having a plurality of vent holes 52 are circumferentially welded to the inner face 58c of the joint tube 58 in the same manner as the inner flanges 50 and 51 although only one inner flange is shown in FIG. 5, and an octagonal center hole 60a is formed in the center of each inner flange 60. Another modified form of the column in FIGS. 2 and 3 is shown in FIGS. 6 and 7, in which the joint tube 34 has four ribs 62 welded to the inner face 34c thereof so that the ribs 62 are jointed to corresponding web portions 46 of the beam joint members 36, 38, 40 and 42 through a wall 34b of the joint tube 34. The ribs 62 project radially 'inwardly into the core 26 and join the inner flanges 50 and 51 at their opposite ends. In this modification, shearing force from the web portions 46 of the beam joint members 36, 38, 40 and 42 is transferred via the wall of the joint tube 34 mainly to the ribs 62. Then, the shearing force is transferred from the ribs 62 via the flanges 50 and 51 to the core 26. Thus, in the presence of the ribs 62, the shearing force from the beams 48 is efficiently transferred to the core 26 and the inner flanges 50 and 51 obtain greater strength against an axial force as compared to the inner flanges in FIGS. 2 and 3. Still another modified form of the column in FIGS. 2 and 3 is shown in FIGS. 8 and 9, in which steel tube 64 is provided at its upper end portion 64a with the four beam joint members 36, 38, 40 and 42. A pair of inner flanges 66 and 68 are circumferentially welded to the inner face 64b of the steel tube 64 at the same level as corresponding flange portions 44 and 45 of the joint members 36, 38, 40 and 42. The flanges 66 and 68 incline to a plane perpendicular to the axis of the steel tube 64 to converge toward the upper edge 64a. Another steel tube is concentrically welded at its lower end to the upper end 64a of the steel tube 64. The angle B of inclination of each flange 66 or 68 is generally in the range from 0° to about 60°. When the angle B is near 0°, spaces not filled with concrete may be produced below the outer peripheries of inner flanges 66 and 68. With the angle B more than about 60°, an axial force is not efficiently transmitted from each of the flanges 66 and 68 to the core 26. Preferably, the angle B of inclination, as shown in FIG. 8, is substantially equal to an angle of the slope of the top face 26a of the concrete 26 during filling thereof. The angle B of the top face 26a may be determined from a result of a slump test for concrete used. During the filling process in the above steel tube 64, air between the top face 26a of the concrete 26 and the flange 66 escapes along the lower face 66b of the flange 66 toward the center opening 66a of the flange 66 as the top face 26a of the concrete approaches to the lower face 66b of the flange and then goes through the opening 66a. In the flange 68, air passes the center opening 68a in the same manner. Thus, the concrete 26 fills the whole inner space of the steel tube 64 so that concrete core 26 with no air space is constructed. The angle of inclination B may be increased as far as it allows corresponding flanges 66 and 68 to transfer the shearing force to the core 26. It is also possible to set the angle B smaller than the inclined angle of the top face 26a of the concrete 26 in view of fluidity of the concrete during placing thereof. In place of the inner flanges 66 and 68, inner flanges having a trapezoidal vertical section with their upper faces not inclining but with their lower faces inclining to the plane perpendicular to the axis of the steel tube 64 may be welded to the inner face 64b of the steel tube 64. FIG. 10 shows a modified form of the inner flange 66 or 68 in which an inner flange 70 has a plurality of air vent holes circumferentially formed at approximately equal angular intervals as the inner flanges 50 and 51 in FIG. 2. The vent holes 52 extend in an axial direction of the steel tube 64. The vent holes 52 may be formed preferably in the outer peripheral portion of the flange 70 so as to prevent a space not filled with cement from being produced below the flange 70 by allowing air and cement to positively pass through them during the filling of the concrete. Air guiding grooves in communication with the vent holes 52 may be formed in the outer periphery of the lower face of the flange 70 so that air is led into the vent holes 52. FIGS. 11 to 13 show another embodiment of the invention. In FIG. 11, a plurality of steel tube columns 72 are jointed in series to form a building framework. Each column 72 has a steel tube 74 provided at its upper end with a joint portion 74a to which a plurality of beam joint members 76 are welded. As shown in FIG. 12, the steel tube 74 of every three columns 72 includes an upper tube piece 78 and a lower tube piece 80 concentrically welded at its upper end to the lower end of the upper tube piece 78. The upper tube piece 78 has a inner flange 82 circumferentially welded to the inner face 78a thereof at the lower end portion thereof. The flange 82 has a plurality of reinforcing ribs 84 welded at their lower edges to the upper face 82a thereof and the ribs 84 are welded at their radially outer edges to the inner face 78a of the tube piece 78 (see FIG. 13). That is, the ribs 84 joints the upper face 82a of the flange 82 to the inner face 78a of the tube piece so that the flange 82 is reinforced against an axial load. On the other hand, the lower tube piece 80 is provided at its upper end with the through slot portion 30. Thus, the steel tube 74 of every three column 72 is provided at its intermediate portion, including its inflection point of moment, with the flange 82 and the through slot portion 30. A modified form of the axial strain absorbing mechanism 30 in FIG. 2 is shown in FIG. 14, in which a plurality of ring-shaped grooves 86 are circumferentially formed in the outer face 22c of the steel tube 22 with equal axial spacings. Each groove 86 extends full circumference of steel tube 22. The number and the width C of the grooves 86 may be determined, as in the slots 32 in FIG. 2, according to design conditions of each column 20. The thickness D of the bottom wall of each groove 86 is such that the bottom wall has enough strength against the axial compression during the framework construction and against stationary load. Every groove 86 reduces its width C when the axial compression is given to the steel tube 22. Thus, the grooves 86 absorb the axial strain in the steel tube 22 and dissipate the stress. In place of the grooves 86, grooves 88 may be formed in the inner face 22a of the steel tube 22 as shown in FIG. 15. Another modified form of the axial strain absorbing mechanism 30 is illustrated in FIG. 16, in which the inner face 22a of a portion of the steel tube 22 is radially outwardly projected so that a bead portion 90 is formed to protrude from the steel tube 22. A ring-shaped partition member 94 fits into the bead portion 90 for sealing the inside of the bead portion 90 from the interior of the steel tube 22 so as to define a ring-shaped air space 92 between it and the inner face of the bead portion 90, thus preventing the concrete 26 to enter the air space 92. The partition member 94 may be made of a flexible material such as asphalt, rubber, lead and aluminum. The bead portion 90 is axially deformed when the axial compression is exerted to the steel tube 22, this dissipating the axial stress in the steel tube 22. It will be understood that although preferred embodiments of the present invention have been shown and described, various modifications thereof will be apparent to those skilled in the art, and, accordingly, the scope of the present invention should be defined only by the appended claims and equivalents thereof.

Claims: A structural filler filled steel tube column comprising: a steel tube (22) having an inner face and an outer face; a core (26) made from the structural filler disposed within the steel tube; a separating layer (24), interposed between the inner face of the steel tube and the core, for separating the core from the inner face of the steel tube so that the steel tube is not bonded to the core; and an inner flange (50, 51) circumferentially mounted on the inner face of the steel tube to radially inwardly project for transmitting an axial load, applied on the steel tube, to the core. A structural filler filled steel tube column as recited in Claim 1, wherein the steel tube comprises joint means for jointing beams to the steel tube, and wherein said inner flange is mounted on the joint means. A structural filler filled steel tube column as recited in Claim 2, wherein the steel tube comprises a tube body, wherein said joint means comprises a joint tube concentrically jointed to said tube body, and wherein said inner flange is mounted on an inner face of the joint tube. A structural filler filled steel tube column as recited in Claim 1, wherein the steel tube comprises an upper end portion, and wherein the inner flange is mounted on the inner face of said upper end portion of the steel tube. A structural filler filled steel tube column as recited in Claim 3, wherein said joint tube has H steel beams jointed to the outer face thereof, each beam having a pair of flange portions and a web portion jointing the flange portions, wherein the joint tube has a pair of said flanges mounted on the inner face thereof at the same level as corresponding flange portions of the beams, and wherein the joint tube has a plurality of first ribs mounted on the inner face thereof so that the first ribs are jointed to corresponding web portions of the beams through a wall of the steel tube. A structural filler filled steel tube column as recited in Claim 1, wherein said inner flange is mounted on the inner face of the steel tube at an intermediate portion of the steel tube including an inflection point of moment of the steel tube. A structural filler filled steel tube column as recited in Claim 1, 2, 3, 4, 5 or 6, wherein; said inner flange has an upper side and a lower side; and the inner flange is provided with means for preventing air from staying in lower side of the flange when the structural filler is filled into the steel tube. A structural filler filled steel tube column as recited in Claim 7, wherein said air stay preventing means is an air vent hole formed through said inner flange to extend in an axial direction of the steel tube. A structural filler filled steel tube column as recited in Claim 8, wherein the inner flange has a plurality of said air vent holes, and wherein the air vent holes are circumferentially formed at substantially equal angular intervals. A structural filler filled steel tube column as recited in Claim 7, wherein said steel tube comprises means for absorbing an axial strain which develops in the steel tube when the steal tube is subjected to an axial load. A structural filler filled steel tube column as recited in Claim 1, 2, 3, 4, 5 or 6, wherein the steel tube comprises an upper end, and wherein said inner flange is inclined to a plane perpendicular to an axis of the steel tube to converge toward said upper end. A structural filler filled steel tube column as recited in Claim 11, wherein said steel tube comprises means for absorbing an axial strain which develops in the steel tube when the steal tube is subjected to an axial load. A structural filler filled steel tube column as recited in Claim 1, 2, 3, 4, 5 or 6, further comprising reinforcing means for reinforcing said inner flange against an axial load applied on the inner flange. A structural filler filled steel tube column as recited in Claim 13, wherein said steel tube comprises means for absorbing an axial strain which develops in the steel tube when the steel tube is subjected to an axial load. A structural filler filled steel tube column as recited in Claim 13, wherein said steel tube has an upper end and a lower end, wherein said inner flange has an upper face and a lower face, and wherein said reinforcing means comprises a second rib jointing at least one of opposite faces of the flange to the inner face of the steel tube. A structural filler filled steel tube column as recited in Claim 1, 2, 3, 4, 5, 6, 8, 9 or 15, wherein said steel tube comprises means for absorbing an axial strain which develops in the steel tube when the steel tube is subjected to an axial load. A structural filler filled steel tube column as recited in Claim 16, wherein said axial strain absorbing means comprises a through slot section having a plurality of rows of through slots circumferentially formed therein at an equal spacing, adjacent through slots of adjacent two rows being shifted in positions thereof in a zigzag manner. A structural filler filled steel tube column as recited in Claim 16, wherein said axial strain absorbing means comprises a circumferential groove, circumferentially formed in one of both the inner face and the outer face of the steel tube, for absorbing the axial strain of the steel tube by deforming the groove. A structural filler filled steel tube column as recited in Claim 16, wherein said axial strain absorbing means comprises a bead portion radially outwardly protruding from the steel tube by radially outwardly projecting the inner face of the steel tube.

Inventors: HOSOKAWA, OSAMU, KITAGAWA, SEIHO, KOSHIDA, KAZUNORI, NAKAMURA, YASUKAZU, NAKASHIMA, HIDEO, SANO, TAKESHI, SATO, TAKANORI, SHIOKAWA, HIDEYO, WATANABE, YASUSHI
Applicants: SHIMIZU CONSTRUCTION CO. LTD.
Application year: 1986
Main classification: E04B1
IPC codes: E04B1, E04C3