Concrete filled steel tube column and method of constructing same

Claims

What is claimed is:

1. In a concrete filled steel tube column which constitutes a part of the framework of a structure, the steel tube column including: a steel tube connected to beams of the structure so that an axial compressive load is transferred from the beams and applied to the steel tube; and a concrete core, disposed within the steel tube, for bearing an axial compressive load transferred from the beams via the steel tube to the concrete core, the improvement wherein the steel tube comprises a plurality of prestressed tube pieces concentrically joined in series, each tube piece having an axial tensile prestress introduced thereinto to counteract a compressive stress resulting from said compressive load applied to the steel tube, whereby substantially no axial stress is induced in the steel tube, and wherein the concrete core is held under an axial compression, in addition to said axial compressive load, said axial compression of the core applying said prestress to each of the tube pieces.

2. A concrete filled steel tube column as recited in claim 1, wherein each of the tube pieces has load transfer means, mounted on an inner face thereof, for transferring the axial load between the steel tube and the concrete core.

3. A concrete filled steel tube column as recited in claim 2, wherein the load transfer means comprises a plurality of projection members, each projecting radially inward from the inner face of the corresponding tube piece.

4. A concrete filled steel tube column as recited in claim 2, wherein each of the tube pieces has a joint portion to which the beams of the structure are joined, and wherein the load transfer means comprises an inner flange circumferentially formed on the inner face of the joint portion, the inner flange projecting radially inward.

5. A concrete filled steel tube column as recited in claim 4, further comprising a separating layer interposed between the steel tube and the concrete core, for separating the core from the steel tube so that the steel tube is not bonded to the core.

6. A concrete filled steel tube piece for use in a structural column, comprising: a steel tube piece having an axial tensile prestress introduced thereinto; and a concrete core disposed within the tube piece so that an axial load is transferred between the tube piece and the concrete core, the concrete core being under an axial compression to maintain the prestress in the tube piece, said axial compression being a reaction to the introduction of the prestress into the tube piece.

7. A concrete filled steel tube piece as recited in claim 6, wherein the tube piece has load transfer means, mounted on an inner face thereof, for transferring the axial load between the tube piece and the concrete core.

8. A concrete filled steel tube piece as recited in claim 7, wherein the load transfer means comprises a plurality of projection members, each projecting radially inward from the inner face of the tube piece.

9. A method of constructing a concrete filled steel tube column comprising the steps:

(a) preparing a steel tube piece;

(b) erecting the tube piece;

(c) after the erecting step, joining beams to the tube piece;

(d) applying an axial tensile load to the tube piece so that an axial stress is induced in the tube piece;

(e) after the load applying step, charging concrete into the tube piece to form a concrete core within the tube piece;

(f) after the charged concrete is cured, releasing the tensile load from the tube piece so that the concrete core is subjected to an axial compression as a reaction to the application of an axial tension to the tube piece, whereby the stress induced in the tube piece remains in the tube piece as an axial prestress;

(g) preparing another steel tube piece;

(h) coaxially joining said another tube piece to an upper end of the concrete filled tube piece; and thereafter

(i) repeating the steps (c) to (i), whereby the prestress in each of the tube pieces counteracts a stress resulting from a compressive load exerted on the tube piece by the joined tube pieces, resulting in the construction of a concrete filled steel tube column in which the steel tube has substantially no axial stress.

10. A method as recited in claim 9, wherein each of the steps (a) and (g) comprises the step:

(j) mounting a load transfer means on an inner face of the tube piece for transferring the axial load between the steel tube and the concrete core.

11. A method of constructing a concrete filled steel tube column comprising the steps in the order described:

(k) preparing a plurality of concrete filled steel tube pieces, each including a steel tube piece having an axial prestress introduced thereinto, and a concrete core disposed within the tube piece, the concrete core being under an axial compression as a reaction to the application of an axial tension to the tube piece to introduce the prestress into the tube piece;

(l) erecting one of the concrete filled tube pieces;

(m) joining beams to the concrete filled tube piece;

(n) coaxially joining another concrete filled tube piece to an upper end of the concrete filled tube piece to which the beams are joined; and

(o) repeating the steps (m) to (o), whereby the prestress in each of the tube pieces counteracts a stress resulting from a compressive load exerted on the tube piece by the joined concrete filled steel tubes, resulting in the construction of a concrete filled steel tube column in which the steel tube has substantially no axial stress.

12. A method as recited in claim 11, wherein the step (k) comprises the steps in the order described:

(p) preparing a steel tube piece;

(q) applying an axial tensile load to the tube piece so that an axial stress is induced in the tube piece;

(r) charging concrete into the tube piece to form a concrete core within the tube piece; and

(s) after the charged concrete is cured, releasing the tensile load from the tube piece so that the concrete core is subjected to an axial compression as a reaction to the application of an axial tension to the tube piece, whereby the stress induced in the tube piece remains in the tube piece as an axial prestress.

13. A method as recited in claim 12, wherein the step (p) comprises the step:

(t) mounting a load transfer means on an inner face of the tube piece for transferring the axial load between the steel tube and the concrete core.

14. A method of constructing a concrete filled steel tube column comprising the steps:

(A) preparing a steel tube piece;

(B) forming a separating layer on an inner face of the tube piece so that the tube piece is not bonded to concrete that is to be charged into the tube piece;

(C) erecting the tube piece;

(D) after the step (C), joining beams to the tube piece;

(E) forming a ring-shaped gap in the tube piece so that an upper portion of the tube piece is separated from a lower portion of the tube piece;

(F) after the steps (B) and (C), charging said concrete into the tube piece having the separating layer to form a concrete core within the tube piece, whereby the tube piece is axially slidable relative to the concrete core;

(G) preparing another steel tube piece;

(H) forming a separating layer on an inner face of said another tube piece so that the tube piece is not bonded to concrete that is to be charged into the tube piece;

(I) after the charged concrete is cured, coaxially joining said another tube piece to an upper end of the concrete filled tube piece;

(J) repeating the steps (D) to (J), whereby the concrete core is subjected to an axial compressive load, thereby reducing its axial length, resulting in a downward sliding movement of the tube pieces which eliminates the ring-shaped gaps in the tube pieces; and

(K) finally, joining the upper portion of each of the tube pieces together with the lower portion of the corresponding tube piece, whereby there is constructed a concrete filled steel tube column in which the steel tube has substantially no axial stress.

15. A method as recited in claim 14, wherein each of the steps (A) and (G) comprises the step:

(L) mounting load transfer means on an inner face of the upper end portion of the tube piece for transferring the axial load between the steel tube and the concrete core.

16. A method of constructing a concrete filled steel tube column comprising the steps:

(M) preparing a steel tube piece;

(N) forming a separating layer on an inner face of the tube piece so that the tube piece is not bonded to concrete that is to be charged into the tube piece;

(O) erecting the tube piece on a foundation with a lower end of the tube piece spaced apart from the foundation so that a ring-shaped gap is formed between the lower end of the tube piece and the foundation;

(P) after the step (O), joining beams to the tube piece;

(Q) after the steps (N) and (O), charging said concrete into the tube piece having the separating layer to form a concrete core within the tube piece, whereby the tube piece is axially slidable relative to the concrete core;

(R) preparing another steel tube piece;

(S) forming a separating layer on an inner face of said another tube piece so that the tube piece is not bonded to concrete that is to be charged into the tube piece;

(T) after the charged concrete is cured, coaxially placing said another tube piece on the concrete filled tube piece with the adjacent ends of both the tube pieces spaced apart so that a ring-shaped gap is formed between their adjacent ends;

(U) after the step (T), repeating the steps (P) to (U), whereby the concrete core is subjected to an axial compressive load, thereby reducing its axial length, resulting in a downward sliding movement of the tube pieces which eliminates the ring-shaped gaps; and

(V) finally, joining all the tube pieces in series and the lowermost tube piece together with the foundation, whereby there is constructed a concrete filled steel tube column in which the steel tube has substantially no axial stress.

17. A method as recited in claim 16, wherein each of the steps (M) and (R) comprises the step:

(W) mounting load transfer means on an inner face of the upper end portion of the tube piece for transferring the axial load between the steel tube and the concrete core.

18. A method of constructing a concrete filled steel tube column comprising the steps:

(i) preparing a steel tube piece;

(ii) forming a separating layer on an inner face of the tube piece so that the tube piece is not bonded to concrete that is to be charged in to the tube piece;

(iii) erecting the tube piece;

(iv) after the step (iii), joining beams to the tube piece;

(v) forming a ring-shaped gap in the tube piece so that an upper portion of the tube piece is separated from a lower portion of the tube piece;

(vi) after the steps (ii) and (iii), charging said concrete into the tube piece having the separating layer to form a concrete core within the tube piece, whereby the tube piece is axially slidable relative to the concrete core;

(vii) after the charged concrete is cured, applying an axial tensile load to the tube piece by pulling both the upper and lower portions of the tube piece toward each other to eliminate the ring-shaped gap, whereby an axial stress is induced in the tube piece;

(viii) after the step (vii), joining the upper portion of the tube piece together with the lower portion of the tube piece so that the stress induced in the tube piece remains in the tube piece as an axial prestress;

(ix) preparing another steel tube piece;

(x) forming a separating layer on an inner face of said another tube piece so that the tube piece is not bonded to concrete that is to be charged in to the tube piece;

(xi) after the step (viii), coaxially joining said another tube piece to an upper end of the concrete filled tube piece; and

(xii) repeating the steps (iv) to (xii), whereby the prestress in each of the tube pieces counteracts a stress resulting from a compressive load exerted to the tube piece by the joined tube pieces, resulting in the construction of a concrete filled steel tube column in which the steel tube has substantially no axial stress.

19. A method as recited in claim 18, wherein each of the steps (i) and (ix) comprises the step:

(xiii) mounting load transfer means on an inner face of the upper end portion of the tube piece for transferring the axial load between the steel tube and the concrete core.

20. A method of constructing a concrete filled steel tube column comprising the steps:

(I) preparing a steel tube piece;

(II) forming a separating layer on an inner face of the tube piece so that the tube piece is not bonded to concrete that is to be charged in to the tube piece;

(III) erecting the tube piece on a foundation with a lower end of the tube piece spaced apart from the foundation so that a ring-shaped gap is formed between the lower end of the tube piece and the foundation;

(IV) after the step (III), joining beams to the tube piece;

(V) after the steps (II) and (III), charging said concrete into the tube piece having the separating layer to form a concrete core within the tube piece, whereby the tube piece is axially slidable relative to the concrete core;

(VI) after the charged concrete is cured, applying an axial tensile load to the tube piece by pulling the tube piece downward to eliminate the ring-shaped gap, whereby an axial stress is induced in the tube piece;

(VII) after the load applying step, joining the lower end of the tube piece with the foundation so that the stress induced in the tube piece remains in the tube piece as an axial prestress;

(VIII) preparing another steel tube piece;

(IX) forming a separating layer on an inner face of said another tube piece so that the tube piece is not bonded to concrete that is to be charged in to the tube piece;

(X) after the lower end joining step, coaxially placing said another tube piece on the concrete filled tube piece with their adjacent ends spaced apart so that a ring-shaped gap is formed between their adjacent ends;

(XI) after the step (X), repeating the steps (V) to (VI);

(XII) subsequently, joining the lower end of the tube piece with an upper end of the lower adjoined tube piece so that the stress induced in the tube piece remains in the tube piece as an axial prestress; and

(XIII) repeating the steps (VIII) to (XIII), whereby the prestress in each of the tube pieces counteracts a stress resulting from a compressive load exerted on the tube piece by the joined tube pieces, resulting in the construction of a concrete filled steel tube column in which the steel tube has substantially no axial stress.

21. A method as recite in claim 20, wherein each of the steps (I) and (VIII) comprises the step:

(XIV) mounting load transfer means on an inner face of the upper end portion of the tube piece for transferring the axial load between the steel tube and the concrete core.

BACKGROUND OF THE INVENTION

This invention relates to a concrete filled steel tube column and the method of constructing the same, the concrete filled steel tube column constituting, for example, a part of a building structure such as a column and a pile.

A conventional concrete filled steel tube column is a structural column made of a steel tube having a concrete core within it. In this type of column, it is expected that the steel tube enhances the concrete core in axial compressive strength by its lateral confinement.

The above-mentioned type of steel tube column is constructed by carrying out following steps:

First, a steel tube piece is erected at a construction site;

Second, beams are joined to the erected tube piece at a predetermined level;

Third, concrete is charged into the tube piece to form a core within the tube piece;

After the charged concrete is cured, another tube piece is concentrically joined to the upper end of the tube piece having the core in it; and

Thereafter, the fore-mentioned steps are repeated in the same order.

In a column constructed according to the above steps, the tube pieces, which are joined in series, i.e., a steel tube is bonded to the concrete core. Therefore, the steel tube and the core move in singular alignment when axial compression is applied to the column. When the concrete column is subjected to an axial compression beyond a predetermined compressive strength, excess strains develop in the steel tube and the concrete core, resulting in a local buckling in the steel tube or in that the steel tube reaches an yield area under Mieses's yield condition. Thus, the steel tube does not provide the concrete core with sufficient confinement even though the steel tube still has enough circumferential tensile strength, which causes the concrete core to reach a downward directed area of the stress-strain curve at a load applied considerably lower than a predetermined load. For this reason, it cannot be expected to efficiently enhance the concrete core in compressive strength by the lateral confinement of the steel tube hence, a relatively large cross-sectional area must be given to the concrete filled steel tube column to provide sufficient strength for it.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a concrete filled steel tube column and a method of constructing same which efficiently enhance the compressive strength of the core thereby enabling a considerable reduction in the cross-section thereof in comparison with the prior art column.

Another object of the present invention is to provide a concrete filled steel tube column and a method of constructing same which enable the column itself to have axial compressive and tensile strength resistant to a short-time loading caused, for example, by an earthquake, and thus effectively enhancing the building in rigidity.

With these and other objects in view, one aspect of the present invention is directed to a concrete filled steel tube column including: a steel tube connected to beams of a structure so that an axial compressive load is transferred from the beams to the steel tube; and a concrete core, disposed within the steel tube, for bearing an axial compressive load transferred from the beams via the steel tube to the concrete core. The steel tube comprises a plurality of prestressed tube pieces concentrically joined in series. Each of these tube pieces has an axial prestress introduced into it to counteract a stress resulting from the compressive load applied to the steel tube. With this arrangement, substantially no axial stress is induced in the steel tube.

It is preferred that each of the tube pieces has load transfer means, mounted on its inner face, for transferring the axial load between the steel tube and the concrete core. It is also preferable that in order to introduce the prestress into the tube pieces, the concrete core is under an axial compression as a reaction to the application of an axial tension to the tube pieces.

The load transfer means may consist of a plurality of projection members which project radially inward from the inner face of the corresponding tube piece. Also, the load transfer means may comprise an inner flange circumferentially formed on the inner face of the tube piece. In this case, it is preferable that each of the tube pieces has a joint portion to which the beams of the structure are joined and that the inner flange is formed at the joint portion. The column may have a separating layer interposed between the steel tube and the concrete core, for separating the core from the steel tube so that the steel tube is not bonded to the core.

Another aspect of the present invention is directed to a concrete filled steel tube piece for use in structural columns, the concrete filled steel tube piece comprising a steel tube piece having an axial prestress introduced into it, and a concrete core disposed within the tube piece. The concrete core is under an axial compression as a reaction to the application of an axial tension to the tube piece to introduce the prestress into the tube piece.

Preferably, the tube piece has load transfer means, mounted on its inner face, for transferring the axial load between the tube piece and the concrete core. The load transfer means may be a plurality of projection members which project radially inward from the inner face of the tube piece.

A further aspect of the present invention is directed to a method of constructing a concrete filled steel tube column. A steel tube piece is prepared. The tube piece is erected. After the erecting of the tube piece, beams are joined to the tube piece. An axial tensile load is applied to the tube piece so that an axial stress is induced in the tube piece. After the application of the load, concrete is charged into the tube piece to form a concrete core within the tube piece. After the charged concrete is cured, the tensile load is released from the tube piece so that the concrete core is subjected to an axial compression as a reaction to the application of an axial tension to the tube piece, whereby the stress induced in the tube piece remains in the tube piece as an axial prestress. Another steel tube piece is prepared. Said another tube piece is coaxially joined to an upper end of the concrete filled tube piece. Thereafter, the above-mentioned steps from the beam-joining step to the tube piece-joining step are repeated a plurality of times, whereby the prestress in each of the tube pieces counteracts a stress resulting from a compressive load exerted on the tube piece by the joined tube pieces, this resulting in the construction of a concrete filled steel tube column in which the steel tube has substantially no axial stress.

A still further aspect of the present invention is directed to another method of constructing a concrete filled steel tube column. A plurality of concrete filled steel tube pieces, each including a steel tube piece having an axial prestress introduced into it, and a concrete core disposed within the tube piece, are prepared. One of the concrete filled tube pieces are erected. Beams of the structure are joined to the erected concrete filled tube piece. Subsequently, another concrete filled tube piece is coaxially joined to an upper end of the concrete filled tube piece to which the beams are joined. Then, the fore-mentioned steps from the beam-joining step to the tube piece-joining step are repeated a plurality of times, whereby the prestress in each of the tube pieces counteracts a stress resulting from a compressive load exerted on the tube piece by the joined concrete filled steel tubes, resulting in the construction of a concrete filled steel tube column in which the steel tube has substantially no axial stress.

A still further aspect of the present invention is directed to another method of constructing a concrete filled steel tube column. A steel tube piece is prepared. A separating layer is formed on an inner face of the tube piece so that the tube piece is not bonded to concrete that is to be charged into the tube piece. The tube piece is erected. After the erecting of the tube piece, beams of the structure are joined to the tube piece. A ring-shaped gap is formed in the tube piece so that an upper portion of the tube piece is separated from a lower portion of the tube piece. After the formation of the separating layer and the erecting of the tube piece, the concrete is charged into the tube piece to form a concrete core within the tube piece, whereby the tube piece is axially slidable relative to the concrete core. Another steel tube piece is prepared. A separating layer is formed on an inner face of said another tube piece so that the tube piece is not bonded to concrete that is to be charged into the tube piece. After the charged concrete is cured, said another tube piece is coaxially joined to an upper end of the concrete filled tube piece. The fore-mentioned steps from the beam joining step to the tube joining step are repeated a plurality of times, whereby the concrete core is subjected to an axial compressive load, thereby reducing its axial length, resulting in a downward sliding movement of the tube pieces that eliminates the ring-shaped gaps in the tube pieces. Finally, the upper portion of each of the tube pieces is joined together with the lower portion of the corresponding tube piece, whereby there is constructed a concrete filled steel tube column in which the steel tube has substantially no axial stress.

A still further aspect of the present invention is directed to another method of constructing a concrete filled steel tube column. A steel tube piece is prepared. A separating layer is formed on an inner face of the tube piece so that the tube piece is not bonded to concrete that is to be charged into the tube piece. The tube piece is erected on a foundation with its lower end spaced apart from the foundation so that a ring-shaped gap is formed between the lower end of the tube piece and the foundation. After the erecting of the tube piece, beams of the structure are joined to the tube piece. After the formation of the separating layer and the erecting of the tube piece, the concrete is charged into the tube piece to form a concrete core within the tube piece, whereby the tube piece is axially slidable relative to the concrete core. Another steel tube piece is prepared. A separating layer is formed on an inner face of said another tube piece so that the tube piece is not bonded to concrete that is to be charged into the tube piece. After the charged concrete is cured, said another tube piece is coaxially placed on the concrete filled tube piece with the adjacent ends of both the tubes spaced apart so that a ring-shaped gap is formed between their adjacent ends. After the placement of said another tube piece, the above-mentioned steps from the beam joining step to the tube placement step are repeated a plurality of times, whereby the concrete core is subjected to an axial compressive load, thereby reducing its axial length, resulting in a downward sliding movement of the tube pieces which eliminates the ring-shaped gaps. Finally, all the tube pieces are joined in series and the lowermost tube piece is joined with the foundation, whereby there is constructed a concrete filled steel tube column in which the steel tube has substantially no axial stress.

A still further aspect of the present invention is directed to another method of constructing a concrete filled steel tube column. A steel tube piece is prepared. A separating layer is formed on an inner face of the tube piece so that the tube piece is not bonded to concrete that is to be charged in to the tube piece. The tube piece is erected. After the erecting of the tube piece, beams of the structure are joined to the tube piece. A ring-shaped gap is formed in the tube piece so that the upper portion of the tube piece is separated from the lower portion of the tube piece. After the formation of the separating layer and the erecting of the tube piece, the concrete is charged into the tube piece to form a concrete core within the tube piece, whereby the tube piece is axially slidable relative to the concrete core. After the charged concrete is cured, an axial tensile load is applied to the tube piece by pulling both the upper and lower portions of the tube piece toward each other to eliminate the ring-shaped gap, whereby an axial stress is induced in the tube piece. After the application of the tensile load, the upper portion of the tube piece is joined with the lower portion of the tube piece so that the stress induced in the tube piece remains in the tube piece as an axial prestress. Another steel tube piece is prepared. A separating layer is formed on an inner face of said another tube piece so that the tube piece is not bonded to concrete that is to be charged in to the tube piece. After the joining of the upper and lower portion, said another tube piece is coaxially joined to an upper end of the concrete filled tube piece. The above-mentioned steps from the beam joining step to the tube piece joining step are repeated a plurality of times, whereby the pr