BACKGROUND ART In general, there are two kinds of structures for joining a head of a steel pipe pile and a concrete foundation as follows.

A first structure is made in a such a manner that the head of a steel pipe pile is driven into the concrete foundation more deeply than a diameter of the steel pipe pile, and a driven portion of the steel pipe pile supports a driving force or a drawing force applied to the head of the steel pipe pile.

A second structure is made in such a manner that the head of the steel pipe pile is driven into the concrete foundation as deep as just about 10cm and the head of the steel pipe pile and the concrete foundation are connected by using a reinforcing steel, thereby supporting a load applied to the head of the steel pipe pile from the concrete foundation.

The first structure has a problem of requiring more complex steel arrangement and greater volume of steels compared with the second structure since a main reinforcing steel arranged on a bottom of the concrete foundation is sheared due to interference of the steel pipe pile driven into the concrete

foundation. Therefore, the second structure is more popular in use.

As shown in FIG. 6 illustrating an exemplary view of the second structure, after a cross reinforcing plate 6 is inserted into and welded to an inside of a steel pipe pile 1, a circular covering plate 5 is installed on and welded to an upper part of the steel pipe pile 1, and a reinforcing steel 3 is welded to a side surface of the steel pipe pile 1. Such a structure has drawbacks in that the covering plate 5 is ineffectual and the cross reinforcing plate 6 is difficult to be installed due to its heavy weight, requiring more installation cost. Particularly, the welding needs labor-intensive work and high cost since the reinforcing steel should be welded to the side surface of the steel pipe pile 1.

Korea Patent No. 229166 was suggested to solve the problems but failed to ultimately cure the problems since the patent also employs the cross reinforcing plate and the covering pate which are integrally jointed on the upper part of the steel pipe pile.

After then, as shown in FIG. 7, there has been developed a structure, which fills an inside of the steel pipe pile with concrete. A slide preventing jaw 101 and a lower plate flange 102 are respectively welded to a side wall inside the steel pipe pile 1, and then a lower plate 103 is installed on the lower plate flange 102 to close the section of the steel pipe pile 1. The reinforcing steel 3 is installed over an upper part of the lower plate 103 and the concrete is cast.

However, this conventional technology requires that the slide preventing jaw 101 and the lower plate flange 102 should be installed on the inside wall-of the steel pipe pile 1 by welding, whereby the narrow inside of the steel pipe pile 1 makes the jaw and the flange very difficult to be installed and possibility of poor welding increased.

In order to obviate the conventional problems, the inventor has developed such a structure as illustrated in FIG. 8 and assigned Korea Patent Application No.

2000-12472. In this structure, a cylindrical joining apparatus 200 integrally provided with a lower plate flange 202 on a lower part is completely inserted into an inside of a steel pipe pile 1. The joining apparatus 200 is integrally joined with a side surface of the steel pipe pile 1 by using bolts 201. The reinforcing steel 3, which put into the concrete foundation 2, is vertically arranged on an upper side surface of the joining apparatus 200. A lower plate 203 is disposed on the lower plate flange 202 to close a section of the steel pipe pile. When the concrete foundation is formed, the inside of the steel pipe pile 1 formed on the upper part of the lower plate 203 is also filled with concrete.

This conventional technology should support an axial force, such as the driving force and drawing force, applied to the head of the steel pipe pile by a friction force between a surface of the steel pipe pile and the concrete and a load of the bolts for joining the steel pipe pile and the joining apparatus. Here, the friction force is affected by condition of the surface of the steel pipe pile during construction, in other words, how severely the surface of the steel pipe pile is stained with earth, water or other substances. In consequence, design should be directed to securing of sufficient safety factor in consideration of the above.

In 140 tons that is the standard load of the steel pipe pile of 9mm in thickness and 508mm in diameter, 129 tons excluding 11 tons which is an allowable friction force should be supported by the bolts for joining the steel pipe pile and the joining apparatus. For this, approximately 28 bolts are needed. To install the bolts is costly, thereby decreasing economical efficiency.

Further, the joining apparatus should be located more deeply than a diameter

of the steel pipe pile from the upper part of the steel pipe pile in order to secure the friction force between the concrete and the steel pipe pile. As a result, the bolts are located under the ground and accordingly severe difficulty occurs in forming bolt holes and joining the bolts.

In general, the steel pipe pile has a compressive load much higher than a tensile load which should be supported by the steel pipe pile in the axial force from the concrete foundation. Perceiving such characteristics of the steel pipe pile, the inventor has developed the structure wherein the inside of the head of the steel pipe pile is filled with concrete, and the joining apparatus effectively supports the axial force which needs support by the steel pipe pile.

DISCLOSURE OF INVENTION Accordingly, the present invention is directed an apparatus and a structure for joining a head of a steel pipe pile and a concrete foundation that substantially obviates one or more problems due to limitations and disadvantages of the related prior arts.

An object of the present invention is to provide an apparatus and a structure for joining a head of a steel pipe pile and a concrete foundation which can improve construction efficiency and economical efficiency by enabling a load of a welding part or a bolt for joining the steel pipe pile and the joining apparatus to support a tensile load applied to a steel pipe pile, and enabling a load of a horizontal part or a flange of the joining apparatus to support most of a relatively higher compressive load.

Another object of the present invention is to provide an apparatus and a structure for joining a head of a steel pipe pile and a concrete foundation which

can support a greater bending moment by increasing a bending strength of the head of the steel pipe pile and support a greater compressive load by reducing a bearing stress generated on the concrete foundation on an upper part of the steel pipe pile.

Still another object of the present invention is to provide an apparatus and a structure for joining a head of a steel pipe pile and a concrete foundation which can achieve a superior performance by inserting the joining apparatus manufactured in a factory into the head of the steel pipe pile and then filling concrete to secure a joining strength between the concrete and the joining apparatus.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, an apparatus for joining a steel pipe pile, comprising: a circular vertical part including a plurality of bolt holes which are formed on an upper side surface of the vertical part at predetermined intervals to be bolt-joined with the steel pipe pile, a slide preventing jaw which is protruded on an inside of the vertical pat-to be mechanically engaged with concrete, and taking an external diameter corresponding to an internal diameter of the steel pipe pile to be inserted into a head of the steel pipe pile; a flange being outwardly protruded from an upper end

part of the vertical part to enable the joining apparatus to be put on the steel pipe pile and transfer a compressive load applied to the joining apparatus to the steel pipe pile when the joining apparatus is inserted into the head of the. steel pipe pile; and a bottom plate being integrally provided on a lower part of the vertical part to close a section of the steel pipe pile and allowing a plurality of steel mounting holes on which reinforcing steels are secured to be formed thereon.

In the joining apparatus, a central opening may be formed at the center of the bottom plate, and a covering plate may cover the central opening to close the central opening. In this case, a volume of steel used can be reduced in forming the bottom plate.

In another aspect of the present invention, an apparatus for joining a steel pipe pile, comprising; a joining apparatus body including a circular vertical part which has an external diameter corresponding to an internal diameter of the steel pipe pile to be inserted into a head of the steel pipe pile, and a horizontal part which is provided on an upper part of the vertical part in a circular outer frame of a predetermined width, has a flange outwardly protruded from the upper part of the vertical part to enable the joining apparatus to be put on the steel pipe pile when the joining apparatus is inserted into an inside of the steel pipe pile, and also has vertical rod holding holes formed at predetermined intervals along a circumference thereof; a plurality of vertical rods being inserted into and secured to the vertical rod holding holes which are formed on the horizontal part on one end part thereof and being vertically and downwardly extended; and Lbottom plate being connected to other end part of the vertical rods to close a section of the steel pipe pile.

In the joining apparatus, a plurality of bolt holes may be formed on a side

surface of the vertical part such that the joining apparatus body are joined with the steel pipe pile by means of bolts when the vertical part is inserted into the head of the steel pipe pile. A lower part of the flange of the horizontal part and an upper end part of the steel pipe pile may be welded together such that the joining apparatus body are integrally joined with the steel pipe pile. A plurality of vertical ribs may be provided between the horizontal part and the vertical part to support the horizontal part and the vertical part.

Further, in the joining apparatus, a plurality of reinforcing steel holding holes into which an end part of the respective reinforcing steels driven into a concrete foundation is inserted may be formed at predetermined intervals along a circumference of the horizontal part. A protrusion and a slide preventing jaw may be protruded on an inside wall of the vertical part to be mechanically engaged with concrete which is filled inside.

In further another aspect of the present invention, an apparatus for joining a steel pipe pile, comprising a body including a circular vertical part having an external diameter corresponding to an internal diameter of the steel pipe pile to be inserted into a head of the steel pipe pile, a horizontal part being provided on a lower end part of the vertical part in a form of a circular outer frame of a predetermined width and allowing vertical rod holding holes to be formed at predetermined intervals along a circumference thereof, and a flange being outwardly protruded from an upper end part of the vertical part to be put on an upper end part of the steel pipe pile; a plurality of vertical rods being inserted and secured to the vertical rod holding holes which are formed on the horizontal part of the body on one end part thereof and being vertically and downwardly extended; and a bottom plate being connected to other end part of the vertical

rods to close a section of the steel pipe In the joining apparatus, the body may be bolt-joined with the steel pipe pile.

Otherwise, the body may be integrally joined with the steel pipe pile by welding a lower part of the flange of the horizontal part and an upper end part of the steel pipe pile. A plurality of vertical ribs may be provided between the horizontal part and the vertical part of the joining apparatus to support the horizontal part and the vertical part. Meantime, a plurality of reinforcing steel holding holes, on which an end part of respective reinforcing steels driven into a concrete foundation is installed, may be formed on the horizontal part at predetermined intervals along the circumference of the horizontal part.

It is to be understood that both the, foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF DRAWINGS FIG. la is an exploded perspective view of a joining apparatus according to a preferred embodiment of the present invention; FIG. lb is a perspective view of a section taken through a line A-A of FIG. la wherein the joining apparatus of FIG. la is joined ; FIG. lc is a sectional view of a state where the joining apparatus of FIG. la is joined with a concrete foundation; FIG. 2a is an exploded perspective view of a joining apparatus according to another preferred embodiment of the present invention; FIG. 2b is a perspective view of a section taken through a line A-A of FIG.

2a wherein the joining apparatus of FIG. 2a is joined; FIG. 2c is a sectional view of a state where the joining apparatus of FIG. 2a is joined with a concrete foundation; FIG. 2d is a perspective view of a section wherein the joining apparatus of FIG. 2a is joined according to a modified embodiment of the joining apparatus of FIG. 2a; FIG. 3 a is an exploded perspective view of a joining apparatus according to further another preferred embodiment of the present invention; FIG. 3b is a perspective view of a section taken through a line A-A wherein the joining apparatus of FIG. 3a is joined; FIG. 3c is a sectional view of a state where the joining apparatus of FIG. 3a is joined with a concrete foundation; FIG. 3d is a perspective view of a section wherein the joining apparatus of FIG. 3a is joined according to a modified embodiment of the joining apparatus of FIG. 3a ; FIG. 3e is a sectional view of a state where the joining apparatus of FIG. 3d is joined with a concrete foundation; FIG. 4a is a perspective view of a section wherein the joining apparatus of FIG. 3a is joined according to another modified embodiment of the joining apparatus of FIG. 3a ; FIG. 4b is a sectional view of a state where the joining apparatus of FIG. 4a is joined with a concrete foundation; FIG. 5a is a perspective view of a section wherein the joining apparatus of FIG. 3a is joined according to still another modified embodiment of the joining apparatus of FIG. 3a;

FIG. 5b is a sectional view of a state where the joining apparatus of FIG. 5a is joined with a concrete foundation; FIG. 6 is a perspective view of a conventional joining apparatus; and FIG. 7 and FIG. 8 are a sectional view of a conventional structure for joining a concrete foundation and a steel pipe pile.

BEST MODE FOR CARRYING OUT THE INVENTION Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Initially, FIG. la to FIG. Ic will be explained with respect to a preferred embodiment of the present invention. FIG. la is an exploded perspective view of a joining apparatus according to the preferred embodiment of the present invention. FIG. lb is a perspective view of a section taken through a line A-A of FIG. la wherein the joining apparatus of FIG. la is joined. FIG. lc is a sectional view of a state where the joining apparatus of FIG. la is joined with a concrete foundation.

The joining apparatus 10 includes a circular vertical part 12 which has an external diameter corresponding to an internal diameter of a steel pipe pile 1 to be inserted into a head of the steel pipe pile, a flange 14 which is outwardly protruded in a radial direction from an upper end part of the vertical part and integrally formed with the vertical part 12 to enable the joining apparatus 10 to be <BR> <BR> put on the steel pipe pile 1 when the joining apparatus 10 is inserted into the head<BR> *"t of the steel pipe pile 1, and a bottom plate 15 which is integrally formed with a lower part of the vertical part 12 to close a section of the steel pipe pile 1. The flange 14 functions to transfer a compressive load applied to the joining apparatus

10 to the steel pipe pile 1.

Referring to FIG. la and FIG. lb, a plurality of bolt holes 16 are formed on an upper side surface of the vertical part 12 at predetermined intervals. The steel pipe pile 1 and the joining apparatus 10 are integrally formed by bolts 17 through corresponding bolt holes formed on a side of the steel pipe pile 1 and the bolt holes 16 of the vertical part 12, when the vertical part 12 is inserted into the head of the steel pipe pile 1. A tensile load applied to the joining apparatus 10 from the concrete foundation is transferred to the steel pipe pile 1 through the bolts 17.

A conventional joining apparatus of FIG. 8 requires a great number of bolts since the bolts for joining the joining apparatus and the steel pipe pile support most of the compressive load. However, according to the present invention, the bolts 17 for joining the joining apparatus 10 and the steel pipe pile 1 mostly support the tensile load, thereby reducing the number of the necessary bolts 17.

A plurality of a slide preventing jaw 18 are inwardly protruded on a side surface of the vertical part 12. The slide preventing jaws 18 transfer an axial force including the compressive load or the tensile load sent from the concrete foundation to the steel pipe pile 1 by being mechanically engaged with concrete when the concrete is filled in a space defined by the vertical part 12 and the bottom plate 15. Since the slide preventing jaws 18 are formed inside the vertical part 12 and its expansion is limited by the vertical part 12, there is considerably increased a supporting strength of the concrete which is filled in the space defined by the vertical part 12 an the bottom plate 15. As a result, the slide preventing jaws 18 get to support a considerable amount of compressive load applied to the joining apparatus 10 while the compressive load transferred to the bottom plate 15 is decreased. Thus, it is possible to make the bottom plate

15 thinner and the vertical part 12 shorter. This leads to reduction in a volume of steel used for the joining apparatus 10 and also a weight of the joining apparatus 10, resulting in improvement of construction efficiency and economical efficiency of the joining apparatus 10.

Reinforcing steel holding holes 19 are formed at predetermined intervals along a circumference of the bottom plate 15. An end part of each vertical reinforcing steel 3 is inserted into the reinforcing steel holding hole 19. Other end part of the reinforcing steel holding hole 19 is driven into the concrete foundation 2 (see FIG. lc). A shear resistance generated when the end parts of the reinforcing steels 3 and the reinforcing steel holding holes 19 are joined with screws can be additionally used, whereby a development length of the reinforcing steels 3 in the concrete foundation can be reduced.

For the purpose of reducing the weight of the joining apparatus 10, a thickness in a central portion of the bottom plate 15 may be different from that in edge portions of the bottom plate 15. According to the preferred embodiment, a central opening 8 is formed at the center of the bottom plate 15, and such a thin covering plate 9 as a steel plate, a wooden plate or the likes covers an upper part of the central opening 8 so as to close the central opening 8.

Meanwhile, a plurality of reinforcing ribs 7 may be installed between the bottom plate 15 and the vertical part 12 to firmly support the bottom plate 15.

Hereinafter will be explained a structure and a method for installing the joining apparatus according to the preferred embodiment of the present invention described above.

As shown in FIG. lc, after the vertical part 12 of the joining apparatus 10 is inserted into the upper part of the steel pipe pile 1, the upper part of the steel pipe

pile 1 and the vertical part 12 are joined by using the bolts 17. The end part of the reinforcing steel 3 is inserted into the reinforcing steel holding hole 19 of the bottom plate 15 to be secured to. In the event that screw parts are respectively formed on the reinforcing steel holding hole 19 and the reinforcing steel 3 to join together the reinforcing steel holding hole 19 and the reinforcing steel 3 with screws, the shear resistance may be additionally usable by virtue of the threaded engagement.

A steel bar 4 of the concrete foundation 2 is arranged over the steel pipe pile 1. Concrete is filled and cured in the inside of the vertical part 12 and in the concrete foundation 2.

In the conventional joining apparatus of FIG. 8, an adhesive strength between the concrete and the steel pipe pile is deteriorated because of alien substances, e. g., earth, water, etc., on an inside wall of the steel pipe pile. The joining apparatus according to the present invention, however, has no concern of deteriorating the adhesive strength between the concrete and the joining apparatus when the concrete is cast since the joining apparatus is manufactured in a factory.

Herein below will be explained a joining apparatus according to another preferred embodiment of the present invention with reference to FIG. 2a to FIG.

2c.

FIG. 2a is an exploded perspective view of the joining apparatus 20 according to another preferred embodiment of the present invention. FIG. 2b is a perspective view of a section of the joining apparatus taken through a line A-A of the FIG. 2a wherein the joining apparatus of the FIG. 2a is joined. FIG. 2c is a sectional view of a state where the joining apparatus 20 is joined with the concrete foundation.

The joining apparatus 20 includes a body 21 having a circular vertical part 22 which has an external diameter corresponding to an internal diameter of the steel pipe pile 1 to be inserted into the head of the steel pipe pile 1 and a horizontal part 23 which has is provided on an upper part of the vertical part 22 in a form of a circular outer frame with a predetermined width and allows a flange 24 being outwardly protruded to be put on an upper end part of the steel pipe pile 1 ; vertical rods 30 being secured on an end part of the horizontal part 23 and vertically and downwardly extended; and a bottom plate 25 being secured on other end part of the vertical rods 30 to close a section of the steel pipe pile 1.

Vertical rod holding holes 31 are formed on the horizontal part 23 at predetermined intervals to allow the end parts of the vertical rods 30 to be inserted thereinto. The vertical part 22 is inwardly and vertically formed from the end part of the horizontal part 23 as inside as a thickness of the steel pipe pile 1 or more, such that edge portions of the horizontal part 23 are outwardly protruded from the vertical part 22 so as to form the flange 24. The flange 24 is put on the upper end part of the steel pipe pile 1 and transfers a compressive load applied to the joining apparatus 20 to the steel pipe pile 1.

Reinforcing steel holding holes 29 may be provided on the horizontal part 23 to allow the reinforcing steels 3 driven into the concrete foundation 2 to be secured thereto. Screw parts may be respectively formed on the reinforcing steels 3 and the reinforcing steel holding holes 29 to join the reinforcing steels 3 and the reinforcing steel holding holes 29 with screws. If the reinforcing steels 3 are joined with the reinforcing steel holding holes 29 through the screws, a joining force is improved and thus a development length of the reinforcing steels 3 inside the steel pipe pile 1 is reduced, leading to reduction in cost and

enhancement in work efficiency.

A plurality of bolt holes 26 are formed on a side surface of the vertical part 22 at predetermined intervals. When the vertical part 22 is inserted into the head of the steel pipe pile 1, the steel pipe pile 1 and the joining apparatus 20 are integrally joined together by bolts 27 through corresponding bolt holes formed on a side surface of the steel pipe pile and inserting the bolts 27 into the bolt holes 26.

A tensile load applied to the joining apparatus 20 is transferred to the steel pipe pile 1 through the bolts 27.

A plurality of vertical ribs 37 may be provided between the horizontal part 23 and the vertical part 22 to support the vertically joined horizontal part 23 and vertical part 22. Eight to twelve ribs 3 7, are preferable but it is not limited to a certain number.

In contrast to the preferred embodiment illustrated in FIG. la to FIG. I c, the bottom plate 25 is separated from the vertical part 22. Since the bottom plate 25 is separated from the vertical part 22, when concrete is placed on the bottom plate 25, a friction force between the concrete and the side surface of the steel pipe pile supports an axial force, such as a compressive load or a tensile load, whereby a volume of steel used can be reduced and economical efficiency and construction efficiency can be improved.

The bottom plate 25 is formed of a circular plate having a diameter smaller than the internal diameter of the steel pipe pile 1. The bottom plate 25 closes the inside section of the steel pipe pile 1 by being connected with the horizontal part 23 by means of the vertical rods 30. When the concrete is filled into an inside space of the steel pipe pile 1, which is closed by the bottom plate 25 and formed on an upper part of the bottom plate 1, a sealing member (not shown) may be

provided on an external peripheral surface of the bottom plate so as not to leak the concrete. Once the sealing member is installed, underground water is prevented from flowing from a lower part of the steel pipe pile to an upper part of the steel pipe pile.

The one end part of the vertical rod 30 is inserted into and secured on the vertical rod holding hole 31 of the horizontal part 23. The vertical rod holding hole 32 is also formed on the bottom plate 25, such that the other end part of the vertical rod 30 is inserted into and secured on the vertical rod holding hole 32 formed on the bottom plate 25. The end part of the vertical part 30 is secured on the bottom plate 25 and/or the horizontal part in a manner that each vertical rod 30 is inserted into the holding holes 31 and 32, and then a nut is installed on an end part. Otherwise, the end part of the vertical part 30 is secured in a manner that a screw part is formed on an end part of the vertical rod 30, a corresponding screw part is formed on the holding holes 31 and 32, and a threaded engagement is performed. The number of vertical rods 30 is determined by structural calculation, preferably 8-12. However, it is not limited to a certain number.

A structure and a method for installing the joining apparatus 20 according to the another preferred embodiment of the present invention will be explained hereinafter.

The joining apparatus 20 is made by assembling the body 21 which includes the horizontal part 23 and the vertical part 22, the horizontal rods 30 and the bottom plate 25. That is to say, the end part of the vertical rod 30 is secured on the vertical rod holding hole 32 of the bottom plate 25, and the other end part of the vertical rod 30 is joined with the vertical rod holding hole 31 of the horizontal part 23. However, an order of assembling the vertical rod 30 is not restricted to

the above. The assembled joining apparatus 20 is inserted into the upper part of the steel pipe pile 1 and the flange 24 of the horizontal part 23 is put on the upper part of the steel pipe pile 1. The joining apparatus 20 is joined, with the steel pipe pile 1 by making the bolt holes formed on the upper side surface of the steel pipe pile 1 coinciding with the bolt holes 26 of the vertical part 22, and then inserting the bolts 27.

The reinforcing steel 3 driven into the concrete foundation is mounted on the joining apparatus 20. As drawn in FIG. 2b and FIG. 2c, the reinforcing steel holding hole 29 is formed on the horizontal part 23 of the body 21 and the reinforcing steel 3 is vertically secured to the reinforcing steel holding hole 29.

After the reinforcing steel 3 is installed, the steel 4 for the concrete foundation is arranged over the upper part of the steel pipe pile 1, and the concrete is filled into and cured in the inside of the steel pipe pile 1 which is closed by the bottom plate 25, and the concrete foundation.

FIG. 2d is a view of a modified embodiment of the aforesaid another preferred embodiment. FIG. 2d is a perspective view of a section wherein the joining apparatus 20 is assembled.

Referring to FIG. 2d, instead of the bolt-joining between the side surface of the vertical part 22 and the steel pipe pile 1, the joining apparatus 20 may be integrally joined with the steel pipe pile 1 by forming a chamfer 33 on the flange 24 of the horizontal part 23 and welding the chamfer 33 with the upper part of the steel pipe pile 1. In case that the joining apparatus 20 and the steel pipe.. pile 1 are joined with the bolts 27, the side surface of the steel pipe pile 1 should also be perforated in a construction site to form the bolt holes on the side surface of the steel pipe pile 1, corresponding to the bolt holes 26 of the joining apparatus 20.

In case that the joining apparatus 20 is joined with the steel pipe pile by welding, however, the process for forming the bolt holes becomes unnecessary, thereby enhancing work efficiency. Further, the load of the steel pipe pile is sufficiently usable since there doesn't occur a sectional loss of the steel pipe pile and the joining apparatus 20, the sectional loss which would be caused when the bolt holes 26 are formed.

In addition, it is also possible that the reinforcing steels 3 are inserted into an opening formed at the center of the horizontal part 23, vertically positioned on the bottom plate 25 at predetermined intervals, and the concrete is cast, without joining the reinforcing steels 3 with the horizontal part 23, The following is an explanation about a further another embodiment of the present invention illustrated in FIG. 3a to FIG. 3c.

FIG. 3a is an exploded perspective view of a joining apparatus 40 according to the further another preferred embodiment of the present invention. FIG. 3b is a perspective view of a section of the joining apparatus taken through a line A-A of FIG. 3a wherein the joining apparatus of FIG. 3a is joined. FIG. 3c is a sectional view of a state where the joining apparatus 40 is joined with the concrete foundation 2. FIG. 3d is a perspective view of a section wherein the joining apparatus 40 of FIG. 3a is joined with the steel pipe pile 1 by welding, and the end part of the reinforcing steel 3 is placed on the bottom plate without being joined with the horizontal part 23 according to a modified embodiment of the joining apparatus of FIG. 3a. FIG. 3e is sectional view of a state where the joining apparatus of FIG. 3d is joined with the concrete foundation 2.

The embodiments of FIG. 3a to FIG. 3e are modified embodiments of FIG.

2a to FIG. 2d, showing that the horizontal part is formed on a lower part of the

vertical part.

To be specific, the joining apparatus 40 includes a body 41 having a vertical part 43 which takes an external diameter corresponding to an internal diameter of the steel pipe pile 1 to be inserted into the inside of the steel pipe pile 1, a horizontal part 43 which is provided on a lower part of the vertical part 42 in a form of a circular outer frame of a predetermined width, and a flange 44 which is upwardly protruded on an upper part of the vertical part 42 to be put on the upper part of the steel pipe pile 1; vertical rods 50 each being secured to the horizontal part 43 on one end part thereof and vertically and downwardly extended; and a bottom plate 45 being secured on other end part of the vertical rods 50 to close a section of the steel pipe pile 1.

According to another preferred embodiment of FIG. 2a to FIG. 2e, the horizontal part 23 is formed on the uppermost part of the vertical part 22, and the flange 24 is formed by permitting the horizontal part 23 to be outwardly protruded farther than the external diameter of the vertical part 22. In contrast, according to the further another preferred embodiment of FIG. 3a to FIG. 3e, the horizontal part 43 is formed on a lower end part of the vertical part 42 and the flange 44 is separately formed on an upper end part of the horizontal part 42.

In the further preferred embodiment of FIG. 3a to FIG. 3e, the horizontal part 43 is formed on the lower part of the vertical part 42, whereby a plurality of vertical ribs 57 are formed on the upper part of the horizontal part 43, in contrast to the ribs 37 of FIG. 2a to FIG. 2e which are provided on the lower pat of the horizontal part. Other explanation about the further preferred embodiment of FIG. 3a to FIG. 3e would be omitted because it is identical with that about another preferred embodiment of FIG. 2a to FIG. 2d.

According to this embodiment, the reinforcing steel is connected to the joining apparatus on the inside of the steel pipe pile and reinforced with the concrete, so that a portion where the reinforcing steel and the joining apparatus are connected can be further reinforced.

Meantime, even in case of the embodiment of FIG. 3a to FIG. 3c, it is possible that the reinforcing steels 3 are inserted into holes formed at the center of the horizontal part 43 and vertically positioned on the bottom plate 34 at predetermined intervals, and then the concrete is cast (see FIG. 3d and FIG. 3e), without joining the reinforcing steel 3 with the horizontal part 23.

FIG. 4a and FIG. 4b show another modified embodiment of the embodiment of FIG. 3a to FIG. 3e. FIG. 4a is a sectional perspective view of a section wherein the joining apparatus 40 is mounted on the head of the steel pipe pile 1.

FIG. 4b is a sectional view of a state where the joining apparatus is joined with the concrete foundation 2.

Referring to this another modified embodiment, instead of bolt-joining between the side surface of the vertical part 42 and the steel pipe pile 1, the joining apparatus 40 is integrally formed with the steel pipe pile 1 by forming the chamfer on the flange 44 of the horizontal part 43 and welding the chamfer 33 with the upper part of the steel pipe pile 1.

FIG. 5a and FIG. 5b are a sectional perspective view and a sectional view, respectively, of the joining apparatus of FIG. 3a to FIG. 3c wherein a protrusion 58 and a slide preventing jaw 59 are additionally formed inside the vertical part according to a still modified embodiment of the embedment of FIG. 3a and FIG.

3c. The protrusion 58 and the slide preventing jaw 59 prevent the concrete filled in the inside of the vertical part from being separated from the vertical part due to

drying shrinkage, and reduce the load applied to the bottom plate by supporting the tensile load and the compressive load transferred from the concrete by virtue of mechanical engagement with the concrete. The protrusion 58 and the slide preventing jaw 59 may be provided in the previously described embodiments.

Further explanation of the embodiments of FIGS. 4a, 4b, 5a and 5b would be omitted because it is redundant. In all the embodiments explained, the reinforcing steel may be reinforced by being wound with a hoop tie.

The forgoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teachings can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art.

As stated above, a joining apparatus according to the present invention has an advantage of drastically reducing the number of bolts necessary for joining a joining apparatus and a steel pipe pile and accordingly improving construction efficiency and economical efficiency, if being compared with a conventional joining apparatus, since the bolts or welding parts for joining the joining apparatus and the steel pipe pile support a tensile load transferred from a concrete foundation to the steel pipe pile, and a load of a horizontal part and/or a flange of the joining apparatus supports most of a compressive load which is relatively greater.

The joining apparatus according to the present invention has another advantage of well supporting a bending moment and a compressive load applied to a head of the steel pipe pile, since the head of the steel pipe pile is formed into

a reinforced concrete.

Moreover, the joining apparatus according to the present invention has yet another advantage of reducing a depth of a vertical part of the joining apparatus which is inserted into an inside of the steel pipe pile, since the joining apparatus manufactured in a factory in advance is inserted into the inside of the steel pipe pile, and then concrete is filled between the joining apparatus and the steel pipe pile so as to enhance an adhesive strength between the concrete and the joining apparatus. As a consequence, manufacturing cost of the joining apparatus is reduced, since a volume of steel used for the joining apparatus is accordingly reduced.