WO2008016203A1

WO2008016203A1 - Tension cylinder for tension steel wire for use in public works

Info

Publication number: WO2008016203A1
Application number: PCT/KR2006/004798
Authority: WO
Inventors: Jong Duck Shin
Original assignee: Dae Young Co., Ltd.
Priority date: 2006-08-01
Filing date: 2006-11-15
Publication date: 2008-02-07
Also published as: KR100767708B1

Abstract

A tension cylinder for a tension steel wire for use in public works is disclosed. The tension cylinder of the present invention includes a cylinder body (110), a hollow tension steel wire guide pipe (130), which is provided through the cylinder body along a longitudinal center axis thereof, a piston (120), which is airtightly provided between the cylinder body (110) and the tension steel wire guide pipe (130) so as to be reciprocally movable using hydraulic pressure, and a tension steel wire holding means (160), which is provided on an end of the rod of the piston to hold the tension steel wire when the piston is extended from the cylinder body. Here, the cylinder body (110) and the piston (120) are made of aluminum alloy having a low specific gravity, and surfaces of portions of the cylinder body (110) and the piston (120) which require high abrasion resistance and surface hardness are anodized, thus ensuring lightness and sufficient strength.

Description

TENSION CYLINDER FOR TENSION STEEL WIRE FOR USE

IN PUBLIC WORKS

Technical Field

[1] The present invention relates, in general, to tension cylinders for tension steel wires for use in public works and, more particularly, to a tension cylinder for a tension steel wire for use in public works which is made of aluminum alloy, having a low specific gravity compared with that of a conventional tension cylinder, and in which the surfaces of portions which require superior abrasion resistance and surface hardness are anodized to ensure sufficient strength, thus reducing the weight of equipment used in civil engineering and construction work, drift work or tunneling work to 2/3, thereby accomplishing the lightness thereof, and which can be easily manufactured at a relatively low cost. Background Art

[2] Generally, in engineering work such as bracing work and engineering work for stabilizing a tunnel portal or for reinforcing a stone wall or a retaining wall, permanent ground anchors or removable tension steel wire type ground anchors are used to reinforce soft ground or base rock, thus ensuring the stability of various kinds of structures.

[3] As shown in FIG. 1, for the construction of such a ground anchor, a hole 40 is bored at a desired position in soft ground using a boring machine, and a load-carrying body 20, which includes a grout hose 23, a tension steel wire 22, and an internal fixer 21, is inserted into the bored hole 40. Subsequently, grout is injected through the grout hose 23. After the injected grout cures with the load-carrying body 20, an external fixer 30 is coupled to the other end of the tension steel wire 22, which is adjacent to the opening of the bored hole 40. Thereafter, the tension steel wire 22 is pulled by a tensioning machine (not shown), so that the grout and ground are tensioned, thus reinforcing the soft ground.

[4] In the ground anchor for public works, a center hole jack, which is an independent cylinder 10a, has been proposed and used to tension the tension steel wire. As shown in FIG. 2, a hollow piston 12a is installed in a cylinder body 11a, which serves as an outer casing of a cylinder, so as to be reciprocally movable along the longitudinal center axis thereof. A tension steel wire guide pipe 13a, which serves as an inner casing of the cylinder, extends an end of the cylinder body 1 Ia, is installed through the cylinder body 11a, and is disposed in the piston 120 such that airtightness is ensured between the tension steel wire guide pipe 130 and the piston 120. [5] In the independent cylinder having the above-mentioned construction, the cylinder body 1 Ia, the piston 12a and the tension steel wire guide pipe 13a have relatively large diameters. As shown in FIG. 1, several load-carrying bodies 20 are inserted into a hole 40 bored in the ground, and grout cures around the load-carrying bodies 20. After the curing process has been completed, ends of tension steel wires which are adjacent to the opening of the bored hole 40 are consecutively inserted through a ground pressure plate 18, an external fixer 30, a wedge removal preventing plate 19 and the tension steel wire guide pipe 13a of the independent cylinder 10a, and, finally, fitted into a separate tension steel wire holding means 16a, thus completing the cylinder assembly process.

[6] In this state, the piston 12a is extended such that the tension steel wire holding means 16a is moved rearwards along with the piston 12a. Then, the tension steel wire 22 is pulled out and is thus tensioned. Here, the wedge removal preventing plate 19 provided on the outer fixer 30 serves to prevent the wedge bodies from being moved out along with the tension steel wire 22 when the tension steel wire is tensioned.

[7] As such, in the state in which the tension steel wire 22 is tensioned, when the piston

12a is returned to the original position thereof, the wedge bodies, which are disposed around the tension steel wire and are lightly held by an O-ring, are inserted into and fixed to a wedge receiving body, which is the outer fixer 30, thus maintaining the tension steel wire in the tensioned state.

[8] After the piston 12a is retracted into the cylinder body 11a and returned to the original position thereof, a worker manually pushes the tension steel wire holding means 16a. Thereafter, the piston is again extended. Then, the tension steel wire 22 is further pulled, so that higher tension is applied to the tension steel wire 22. This process is repeated until a desired degree of tension is applied to the tension steel wire. Subsequently, the center hole jack, which is the independent cylinder 10a, and the tension steel wire holding means 16a are removed, thus completing the tensioning work.

[9] Meanwhile, in a tension cylinder disclosed in Korean Patent Registration No.

10-0329727, as shown in FIG. 3, several tension cylinders 10b are mounted to a circular base 17 at positions spaced apart from each other at the same angular intervals on the same circumferential line. Here, the tension cylinders 10b, mounted to the base 17, are evenly inclined outwards around the vertical center axis, thus forming a cone shape. Each tension cylinder 10b includes a hollow piston 12b, which is installed in a cylinder body 1 Ib so as to be reciprocally movable along the longitudinal center axis thereof, and a tension steel wire guide pipe 13b, which extends to an end of the cylinder body 1 Ib, is installed through the cylinder body 11a, and is disposed inside the piston 12b such that airtightness is ensured between the tension steel wire guide pipe 13b and the piston 12b. Furthermore, a tension steel wire holding means 16b, which selectively holds or releases a tension steel wire 22, is provided on an end of each piston 12b.

[10] In the tension cylinder of the registered Patent mentioned above, after several load- carrying bodies 20 are inserted into a hole 40 bored in the ground, and grout has cured with the load-carrying bodies 20, a ground pressure plate, an external fixer, a wedge inserting device and the tension cylinders 10b are consecutively fitted over ends of the tension steel wires which are adjacent to the opening of the bored hole 40.

[11] In this state, wedge bodies are pushed into wedge heads, which are tension steel wire holding means 16b, to hold the tension steel wire 22. Thereafter, the pistons 12b are extended. Then, the tension steel wire holding means 16b is moved backwards along with the pistons 12b, thus pulling out the tension steel wires. Thereby, the tension steel wires are tensioned. As such, after the tension steel wires have been tensioned, the wedge inserting device is operated to push and fix wedge bodies in and to wedge receiving bodies, which are the outer fixer, thus maintaining the tension steel wire in the tensioned state.

[12] When the pistons 12b are retracted into the respective cylinder bodies 1 Ib after the process of tensioning the tension steel wires has been completed, the wedge bodies slide with respect to the tension steel wires 22 without holding them. When each piston 12b is maximally retracted into the associated cylinder body 1 Ib, the wedge bodies are brought into contact with the end of the tension steel wire guide pipe 13b and pushed out, thus being separated in a diameter direction. After the wedge bodies have been separated in a diameter direction, the wedge inserting device and the tension cylinders 10b are removed, thus completing the tensioning work.

[13] Furthermore, in Korean Utility Model Registration No. 20-0154884, another cylinder is integrated with the end of the cylinder body of one cylinder, which is separated from the above-mentioned tension cylinder. The two cylinders are partitioned by a separate partition wall. In addition, a separate piston is provided in the cylinder, which is provided on the end of the cylinder body, so that, after a tension steel wire has been tensioned, wedge bodies are inserted into a wedge receiving body of an outer fixer by the piston to maintain the tension steel wire in the tensioned state.

[14] In a brief description, the cylinder and the piston, which are additionally provided on the end of the tension cylinder, serve as a wedge inserting device for insertion of wedge bodies of the external fixer.

[15] The registered Utility Model having the above-mentioned construction is mainly used in the case where a single tension steel wire constituting a load-carrying body is provided at the center in the bored hole. Furthermore, in a construction process, a ground pressure plate, the external fixer and the tension cylinder are fitted over the end of the tension steel wire, which is adjacent to the opening of the bored hole, in which grout has cured with the load-carrying body. Thereafter, the tension cylinder is operated, such that the tension steel wire 22 is tensioned to a desired degree. Subsequently, the wedge bodies are inserted into the wedge receiving body of the external fixer by operating the piston in the cylinder, which is additionally provided in the tension cylinder.

[16] The tension steel wire is maintained in the tensioned state by inserting the wedge bodies into the wedge receiving body. In this state, the tension cylinder is removed, thus completing the tensioning work. Disclosure of Invention Technical Problem

[17] However, in the above-mentioned conventional tension cylinders, all elements including the cylinder body and the piston are made of steel having a specific gravity of 7.8 g/cm , so that the tension cylinder is relatively heavy, having a weight of several tens of kg. Therefore, when a construction process, in which one or two strips of tension steel wires are inserted into a hole bored in the ground and are tensioned, is repeated, the worker is easily tired by the heavy tension cylinder, thus reducing work efficiency.

[18] Particularly, in the case where stronger ground reinforcement is required, three to six tension steel wires, which have different lengths, and each of which has an internal fixer, are inserted into the hole bored in the ground. In the case of the tensioning construction using the several tension steel wires, several tension cylinders, which are assembled into a single unit to tension the respective tension steel wires, or a center hole jack, which is an independent cylinder, are used.

[19] However, the cylinder unit, which is provided by assembling the several tension cylinders into a single unit, or the center hole jack, which is the independent cylinder, are heavier, so that a separate crane must be used to install the tension cylinder and to conduct the tensioning process, or a group of three workers must manually conduct work. Furthermore, in this case, a separate space for installation of the crane is required, and subsidiary workers as well as a driver are required. In the case where a group of three workers manually conducts work, there are problems in that the process of installing the tension cylinder is complicated, thus reducing work efficiency, and labor costs are increased.

[20] Moreover, in the case of the independent cylinder, because several tension steel wires are held by a single tension steel wire holding means and are tensioned by a single piston, tension loss rates of 20% or higher act between the tension steel wires. Hence, construction stability is markedly reduced. [21] As well, in the conventional tension cylinders, with respect to the cylinder body and the piston, because the piston is expendable, the cylinder head is also expendable, so that brass welded parts are provided on the outer and inner surfaces of the head part of the piston and on the inner surface of the cylinder head such that they is able to be worn.

[22] In detail, as shown in FIGS. 4 and 5, to form the brass welded parts on the outer and inner surfaces of the head part of the piston, the pistons 12a, 12b are machined such that the outer surface of the head part of the piston 12a, 12b, which contacts the inner surface of the cylinder body 1 Ia, 1 Ib, and the inner surface of the head part of the piston 12a, 12b, which contacts the extension steel wire guide pipe 13a, 13b, have diameters to have machining allowances. Thereafter, a depression 121 having a depth of 2mm is formed throughout the entire circumferential area of each of the outer and inner surfaces of the head part. After the head part is heated to the temperature at which brass melts, molten brass 122 is charged into the depressions and is solidified. Subsequently, the formed parts are machined to the desired diameters, thus forming the brass welded parts 123. However, this process is very complex and difficult. Furthermore, when molten brass 122 is poured, air bubbles may be generated, thus the defective proportion is relatively high.

[23] Meanwhile, brass 122, which is softer than the rod of the piston 12a, 12b, is welded to the inner surface of the cylinder head. The piston 12a, 12b, the inner surface of which contacts the outer surface of the rod of the piston 12a, 12b, is airtightly assembled with the cylinder head so as to be slidable with respect to the cylinder head. An O-ring is provided between the piston and the cylinder head to more reliably ensure airtightness. However, because there are lots of foreign substances, such as soil, sand and dust, at a construction site, foreign substances may enter into the cylinder head when the piston 12a, 12b reciprocally moves, thus causing damage to the brass welded parts 123 and the O-ring, thereby resulting in leakage of fluid from the cylinder body, and reducing the lifetime of the tension cylinder.

[24] In addition, the tension steel wire holding means 16b and the cylinder head are respectively coupled to the end of the piston 12b and the cylinder body 1 Ib in a right- handed thread coupling manner, and the tension steel wire 22 is formed by right- twisting seven steel wires. When the tension steel wire is held and tensioned by the tension steel wire holding means 16b through the tension steel wire guide pipe 13b, the tension steel wire holding means 16b is rotated to the left along with the piston 12b. Therefore, the above-mentioned screwed parts may undesirably become loosened. Particularly, in the case where the screwed parts of the tension steel wire holding means 16b are loosened, so that the tension steel wire holding means 16b is separated from the piston 12b, there is a probability of a safety hazard. Technical Solution

[25] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a tension cylinder for a tension steel wire for use in public works, in which at least a cylinder body and a piston are made of aluminum alloy, having a relatively low specific gravity, unlike a conventional tension cylinder, and the surfaces of portions which require superior abrasion resistance and surface hardness are anodized to ensure sufficient strength, thus reducing the weight of equipment used in civil engineering and construction works, drift work or tunneling work to 2/3, thereby realizing lightness thereof, and making it possible to conduct installation of the tension cylinder and a process of tensioning the tension steel wire without using heavy equipment, and to conduct the work for a long time without burden so that safety hazards are prevented, the construction period is reduced, and the work efficiency is enhanced.

[26] Another object of the present invention is to provide a tension cylinder for a tension steel wire for use in public works in which the thickness of the cylinder body is increased to reinforce the strength of the cylinder body made of aluminum alloy, and the outer surface of an end thereof is cut at an incline into a polygonal planar surface, so that several tension cylinders can be assembled into a single cylinder unit having a conical shape without interference, and a slim, compact and light cylinder unit can be obtained.

[27] A further object of the present invention is to provide a tension cylinder for a tension steel wire for use in public works in which, when several tension cylinders are assembled with each other into a single conical cylinder unit, upper and lower hydraulic pressure distributors are provided in respective spaces defined above and below the cylinder bodies, and the lower hydraulic pressure distributor is connected to hydraulic ports formed in the upper ends of the cylinder bodies through hydraulic hoses, while the upper hydraulic pressure distributor is connected to hydraulic ports formed in the lower ends of the cylinder bodies through hydraulic hoses, so that the pistons, which are provided in the respective cylinder bodies, can be extended upwards or retracted downwards at the same time, and the hydraulic hoses are prevented from sticking to other working tools while the tensioning work is conducted, thus preventing delays in work and safety hazards, and providing a simple and neat cylinder unit.

[28] Yet another object of the present invention is to provide a tension cylinder for a tension steel wire for use in public works in which the cylinder body, the rod of the piston and the outer surface of the cylinder head other than the inner and outer surfaces of the head part of the piston and the inner surface of the cylinder head are anodized, thus ensuring sufficient abrasion resistance and strength without a brass welding process, which is complex, so that the process of manufacturing the cylinder is simplified, thereby reducing the manufacturing costs. [29] Still another object of the present invention is to provide a tension cylinder for a tension steel wire for use in public works in which a foreign substance entry preventing ring is provided on the inner surface of the cylinder head, which airtightly contacts the rod of the piston, so that a foreign substance is prevented from entering into the gap between the cylinder head and the rod of the piston when the piston is reciprocally moved, thus fundamentally preventing the cylinder head and the piston rod from being damaged by the foreign substance, thereby enhancing the durability of the cylinder.

Advantageous Effects

[30] In a tension cylinder for a tension steel wire for use in public works according to the present invention, at least a cylinder body and a piston are made of aluminum alloy, which has a relatively low specific gravity, unlike a conventional tension cylinder, and the surfaces of portions which require superior abrasion resistance and surface hardness are anodized to ensure sufficient strength, thus reducing the weight of equipment used in civil engineering and construction work, drift work or tunneling work to 2/3, thereby accomplishing the lightness thereof, and making it possible to conduct installation of the tension cylinder and a process of tensioning the tension steel wire without using heavy equipment, and to conduct such work for a long time without burden. Hence, safety hazards are prevented, the construction period is reduced, and work efficiency is enhanced.

[31] Furthermore, in the present invention, the thickness of the cylinder body is increased to reinforce the strength of the cylinder body made of aluminum alloy, and the outer surface of an end thereof is cut at an incline into a polygonal planar surface. Therefore, several tension cylinders can be assembled into a single cylinder unit having a conical shape without interference, and a slim, compact and light cylinder unit can be accomplished.

[32] In addition, in the present invention, when several tension cylinders are assembled with each other into a single conical cylinder unit, upper and lower hydraulic pressure distributors are provided in respective spaces defined above and below the cylinder bodies, and the lower hydraulic pressure distributor is connected to hydraulic ports formed in the upper ends of the cylinder bodies through hydraulic hoses, while the upper hydraulic pressure distributor is connected to hydraulic ports formed in the lower ends of the cylinder bodies through hydraulic hoses. Hence, the pistons, which are provided in the respective cylinder bodies, can be extended upwards or retracted downwards at the same time. As well, the hydraulic hoses are prevented from being stuck to other working tools while the tensioning work is conducted, thus preventing delays in work and safety hazards, and providing a simple and neat cylinder unit.

[33] Particularly, because several tension steel wires can be tensioned at the same time at the same pressure, the tension loss rate of the tension steel wires is reduced to 1% or less. Even after a process of tensioning the tension steel wires has been completed, the tension applied to the tension steel wires is maintained constant, thus ensuring the stability of the work.

[34] In addition, in the present invention, the cylinder body, the rod of the piston and the outer surface of the cylinder head, other than the inner and outer surfaces of the head part of the piston and the inner surface of the cylinder head, are anodized, thus ensuring sufficient abrasion resistance and strength without a brass welding process, which is complex, so that the process of manufacturing the cylinder is simplified, thereby reducing the manufacturing costs.

[35] Moreover, a foreign substance entry preventing ring is provided on the inner surface of the cylinder head, which is in airtight contact with the rod of the piston. Therefore, foreign substances are prevented from entering the gap between the cylinder head and the rod of the piston when the piston is reciprocally moved, thus fundamentally preventing the cylinder head and the piston rod from being damaged by foreign substances, thereby enhancing the durability of the cylinder. Brief Description of the Drawings

[36] FIG. 1 is a view showing the construction of a typical ground reinforcing anchor;

[37] FIG. 2 is a sectional view showing a center hole jack, which is a conventional independent cylinder for a tension steel wire for use in public works;

[38] FIG. 3 is a sectional view showing a conventional tension cylinder for a tension steel wire for use in public works;

[39] FIGS. 4 and 5 are sectional views illustrating processes of manufacturing head parts of pistons of the cylinders of FIGS. 2 and 3, respectively;

[40] FIG. 6 is a perspective view of a tension cylinder for a tension steel wire for use in public works, according to an embodiment of the present invention;

[41] FIG. 7 is a longitudinal sectional view of FIG. 6;

[42] FIG. 8 is an exploded perspective view of the tension cylinder according to the present invention;

[43] FIG. 9 is a sectional view showing the tension steel wire, which is inserted into the tension cylinder and is in a state just before being held by the tension cylinder, according to the present invention;

[44] FIG. 10 is a sectional view showing the tension steel wire, which is inserted into and held by the tension cylinder and is in a state of being tensed, according to the present invention; [45] FIG. 11 is a perspective view showing another embodiment of a tension cylinder for a tension steel wire for use in public works according to the present invention;

[46] FIG. 12 is a longitudinal sectional view of FIG. 11;

[47] FIG. 13 is a plan view of FIG. 11 ; and

[48] FIG. 14 is a sectional view taken along line A-A of FIG. 12.

Best Mode for Carrying Out the Invention

[49] In order to accomplish the above objects, the present invention provides a tension cylinder for a tension steel wire for use in public works, including: a cylinder body; a hollow tension steel wire guide pipe provided through the cylinder body along a longitudinal center axis thereof; a piston airtightly provided between the cylinder body and the tension steel wire guide pipe so as to be reciprocally movable using hydraulic pressure, which is selectively supplied into upper and lower ends of the cylinder body, the piston having a rod coaxially extending in one direction; and tension steel wire holding means provided on an end of the rod of the piston to hold the tension steel wire only when the piston is extended from the cylinder body. The cylinder body and the piston are made of aluminum alloy, having a low specific gravity, and surfaces of portions of the cylinder body and the piston which require high abrasion resistance and surface hardness are anodized, thus ensuring lightness and sufficient strength.

[50] The term "anodizing" means that a protective layer made of oxidized material is applied to the surface of metal (aluminum and titanium) to enhance corrosion resistance and abrasion resistance. In the case of aluminum, because it actively reacts in the air, the anodizing process must be conducted to restrict the active reaction. To anodize aluminum, an aluminum substance is immersed into an acid solution and, thereafter, a relatively high electrical field is applied to the substance. Then, the aluminum is ionized into Al ions by the force of the electric field, and the Al ions are reacted with oxygen, thus forming aluminum oxide. In other words, the aluminum is ionized into Al , and this is reacted with O , so that A12O3, which is called aluminum oxide, is formed. The aluminum oxide has a structure similar to aramite, which is a kind of ceramic, and has superior corrosion resistance, abrasion resistance and electric insulation, thus overcoming disadvantages of aluminum. Furthermore, in the anodizing process, dyeing treatment is conducted just before sealing treatment is conducted, so that pigment penetrates into a porous structure similar to aramite. As such, because pigment penetrates into the oxidized layer, rather than painting the surface thereof, it is prevented from being discolored, that is, the peculiar gloss of aluminum can be maintained.

[51] Here, the anodized portion has a hardness ranging from 350 to 450 hv, and an anodizing layer thereof has a thickness ranging from 50 to 80 μm. Particularly, of the cylinder body and the piston, the piston is expendable, so that the inner and outer surface of the head part of the piston and the inner surface of the cylinder head, which contacts the rod of the piston, must be maintained in the state of untreated aluminum alloy. Here, the aluminum alloy is a relatively soft material having a hardness ranging from 140 to 170 hv.

[52] The reason for this is that, if the inner surface of the cylinder body, the head part of the piston, which contacts and slides with respect to the cylinder body, the rod of the piston and the inner surface of the cylinder head, which contacts and slides with respect to the piston rod, are anodized, both the piston and the cylinder body are damaged, so that the whole cylinder must be discarded.

[53] Preferably, a foreign substance entry preventing ring is provided on the inner surface of the cylinder head, which airtightly contacts the rod of the piston, in order to prevent a foreign substance from entering between the cylinder head and the rod when the piston is reciprocated.

[54] Furthermore, in the tension cylinder of the present invention, the tension steel wire holding means is coupled to an end of the rod of the piston by a left-handed thread, such that, when the tension steel wire holding means holds and tensions the tension steel wire, which is right-twisted, the tension steel wire holding means, which is rotated to the left (in a counterclockwise direction) when viewed on a longitudinal center axis of the tension steel wire, is further tightened and is thus prevented from being loosened. Preferably, the cylinder head is also fastened to the cylinder body through a left-handed thread to prevent the cylinder head from being loosed by frictional force generated by rotation of the piston.

[55] In addition, in the tension cylinder of the present invention, the thickness of the cylinder body is increased to reinforce the strength of the cylinder body made of aluminum alloy, and the outer surface of an end thereof is cut at an incline into a polygonal planar surface, so that several tension cylinders can be easily assembled into a single cylinder unit having a conical shape.

[56] Moreover, in the case where several tension cylinders are assembled with each other into a single cylinder unit, tension cylinders, each of which includes a cylinder fastening pipe having a predetermined length coupled to an end of a cylinder body thereof, may be provided. The tension cylinders are mounted to a circular base at positions spaced apart from each other at regular intervals on the same circumferential line. The tension cylinders are inclined outwards around a vertical center axis to have a cone shape. A casing, which surrounds the tension cylinders throughout upper and lower ends of the cylinder bodies to protect the tension cylinders, is coupled to the cylinder fastening pipes.

[57] Preferably, the circular base, the cylinder fastening pipes and the casing are made of aluminum alloy to reduce the weight of the cylinder unit. In the case where the circular base is made of aluminum alloy, a steel ring may be provided under the bottom of the circular base to prevent it from being worn or broken.

[58] Furthermore, the casing includes upper and lower ring-shaped protective members disposed around the upper and lower ends of the tension cylinders, and a plurality of coupling members, which couple the upper and lower protective members to each other. The lower protective member of the protective members is fastened to the cylinder fastening pipes.

[59] Preferably, the number of coupling members of the casing is equal to the number of tension cylinders, and the coupling members are disposed outside at positions adjacent to the respective tension cylinders, which are spaced apart from each other at regular angular intervals, so as to protect the respective tension cylinders. The tension cylinders are installed such that polygonal planar surfaces formed in the lower ends of the respective cylinder bodies are in contact with the respective coupling members of the casing.

[60] Furthermore, in the present invention, upper and lower hydraulic pressure distributors are respectively provided in upper and lower spaces defined above and below the cylinder bodies such that pistons, which are provided in the respective cylinder bodies, are extended upwards or retracted downwards at the same time. Upper hydraulic ports, which are formed in the upper ends of the respective cylinder bodies, are connected to the lower hydraulic pressure distributor through hydraulic hoses, while lower hydraulic ports, which are formed in the lower ends of the respective cylinder bodies, are connected to the upper hydraulic pressure distributor through hydraulic hoses. Mode for the Invention

[61] Hereinafter, a tension cylinder for a tension steel wire for use in public works according to the present invention will be described in detail with reference to the attached drawings. In the description of the present invention, the same reference numeral will be used for the tension steel wire and for the conventional art, because they have the same construction.

[62] As shown in FIGS. 6 through 10, in the tension cylinder for the tension steel wire for use in public works, a hollow piston 120 is installed in a cylinder body 110 so as to be reciprocally movable in the longitudinal axis of the cylinder body 110. A tension steel wire guide pipe 130 is provided through the cylinder body 110, extends to an end of the cylinder body 110, and is provided through the piston 120 such that airtightness is ensured between the tension steel wire guide pipe 130 and the piston 120. Furthermore, a tension steel wire holding means 160, which releases a tension steel wire 22 only when the piston 120 is maximally inserted into the cylinder body 110, is provided on an end of the piston 120.

[63] The tension steel wire guide pipe 130 is made of steel, and the cylinder body 110 and the piston 120 are made of aluminum alloy. The surfaces of the piston 120 other than the circumferential inner and outer surfaces of the head part 126 of the piston 120 are anodized in order to increase the surface hardness and abrasion resistance thereof.

[64] The circumferential inner and outer surfaces of the head part 126 of the piston 120 are maintained in an untreated aluminum alloy state. Therefore, when the circumferential inner surface of the cylinder body 110 and the circumferential outer surface of the tension steel wire guide pipe 130 slide with respect to each other while in contact with each other, the circumferential inner and outer surfaces of the head part 126 of the piston 120 become worn.

[65] As such, the reason why the present invention is constructed such that the circumferential inner and outer surfaces of the head part 126 of the piston 120 become worn is that the piston 120, rather than the cylinder body 110, is expendable. For this, the circumferential inner and outer surfaces of the head part 126 of the piston 120 must be maintained in an untreated aluminum alloy state. Such aluminum alloy is a relatively soft material having a hardness ranging from 140 to 170 hv.

[66] The anodizing treatment serves to apply a protective layer made of oxidized material to the surface of the metal (aluminum), thus increasing corrosion resistance and abrasion resistance. In the present invention, the anodized portion has a hardness ranging from 350 to 450 hv, and the anodizing layer thereof has a thickness ranging from 50 to 80 μm.

[67] The reason why the portion of the piston 120 other than the circumferential inner and outer surfaces of the head 126 is anodized is that, if both the head of the piston, which contacts and slides with respect to the inner surface of the cylinder body, and the inner surface of the cylinder head, which contacts and slides with respect to a rod of the piston, are anodized, both the cylinder body and the piston are damaged, and thus both must be discarded.

[68] The lower end of the cylinder body 110 is closed by the tension steel wire guide pipe 130. The tension steel wire guide pipe 130 is fixed by the tension steel wire guide head 140, which is coupled to the lower end of the cylinder body 110. An upper end of the cylinder body 110 is closed by the cylinder head 150, which has a ring shape. Because the inner surface of the tension steel wire guide pipe 130 is in close contact with the tension steel wire 22, it is preferable that the tension steel wire guide pipe 130 be made of steel. Furthermore, because it is important that the tension steel wire guide head 140 and the cylinder head 150, other than the tension steel wire guide pipe 130, be light and expendable, it is preferable that they be made of aluminum alloy. [69] Meanwhile, first and second hydraulic ports 111 and 112, though which hydraulic pressure is selectively supplied from a hydraulic pump into the cylinder body 110 in order to reciprocally move the piston 120 along the longitudinal axis of the cylinder body 110, are formed in the lower and upper ends of the cylinder body 110.

[70] As described above, the cylinder head 150 is made of aluminum alloy, and the inner surface thereof airtightly and slidably contacts the outer surface of the rod 125 of the piston 120. To ensure more reliable airtightness between the cylinder head 150 and the rod 125 of the piston 120, an O-ring 151 is provided in the cylinder head 150. Furthermore, a foreign substance entry preventing ring 152 is provided in the cylinder head 150 to prevent soil, sand or dust from entering the cylinder body at a construction site.

[71] Furthermore, the surface of the cylinder head 150 other than the inner surface is anodized to increase the surface hardness and abrasion resistance, thus having sufficient strength. Particularly, the inner surface of the cylinder head 150, made of the aluminum alloy, is not anodized, so that, when it contacts with and slides along the rod 125 of the piston 120, the inner surface of the cylinder head 150 is worn.

[72] The tension steel wire holding means 160 is coupled to the piston 120 through a left-handed thread formed on the end of the piston 120. The tension steel wire holding means 160 includes a wedge head 161, which has a conical wedge seating hole 162 in the central portion thereof, at least two evenly separated wedge bodies 163, which are provided in the wedge seating hole 162 of the wedge head 161, a wedge sleeve 164, which evenly contacts the separated wedge bodies 163, a spring 165, which elastically pushes the wedge sleeve 164, and a spring cap 166, which is coupled to the wedge head 161 and covers the wedge bodies 163 and the spring 165 such that the spring 165 elastically supports the wedge bodies 163 and the wedge sleeve 164.

[73] Among the elements of the tension steel wire holding means 160, the wedge head

161, the wedge sleeve 164 and the spring cap 166, other than the wedge bodies 163 and the spring 165, are preferably made of aluminum alloy to reduce the weight of the tension cylinder 100.

[74] The wedge head 161 is fastened to the left-handed thread formed on the end of the rod 125 of the piston 120. Thus, when the tension steel wire 22, which is right-twisted, is tensioned, even through the wedge head 161 including the wedge bodies 163 holding the tension steel wire 22 is rotated to the left (in a counterclockwise direction) when viewed from the longitudinal center axis of the tension steel wire 22, because the wedge head 161 is rotated in the direction in which it is tightened to the rod 125 of the piston 120, the wedge head 161 is prevented from being loosened.

[75] Here, the wedge bodies 163 are made of steel, and the remaining elements, that is, the wedge head 161, the wedge sleeve 164 and the spring cap 166, are anodized to increase the surface hardness and the abrasion resistance thereof. Therefore, the tension steel wire holding means is imparted with sufficient strength.

[76] In the drawings, reference numeral 170 denotes a ground pressure plate, which closes an opening of a bored hole 40, 172 denotes an external fixer, which maintains the state of the tension steel wire 22 tensioned by the tension cylinder 100, and 174 denotes a wedge inserting device, which inserts external wedge bodies 172b into the wedge receiving body 172a of the external fixer 172.

[77] In a construction process using the tension cylinder for the tension steel wire for use in public works according to the present invention, having the above-mentioned construction, a load-carrying body is first inserted into a hole bored in soft ground, and grout is injected into the hole and, thereafter, cures with the load-carrying body. At the site where the above-mentioned processes have been conducted, hydraulic hoses of the hydraulic pump (not shown) are connected to the first and second hydraulic ports 111 and 112 of the cylinder body 110 such that hydraulic pressure can be selectively supplied into the first and second hydraulic ports 111 and 112. Subsequently, fluid is supplied into the second hydraulic port 112 of the cylinder body 110 to place the piston 120 at the position at which the piston 120 is maximally retracted into the cylinder body 110 of the tension cylinder 100.

[78] In this state, the ground pressure plate 170, the external fixer 172 and the wedge inserting device 174 are fitted over the tension steel wire, forming the load-carrying body, such that the tension cylinder is supported on the opening of the bored hole. Thereafter, the tension steel wire is inserted through the tension steel wire guide head 140, the tension steel wire guide pipe 130 and the tension steel wire holding means 160, which constitute the tension cylinder 100. At this time, because the wedge bodies 163 in the wedge head 161 of the tension steel wire holding means 160 are pushed by the tension steel wire guide pipe 130 and thus are in a state of being separated in the diameter direction, the inserted tension steel wire 22 is not held by the wedge bodies 163.

[79] In this state, fluid is supplied into the first hydraulic port 111 of the cylinder body

110. Then, the piston 120 is pushed towards the second hydraulic port 112 of the cylinder body 110 and thus extended outwards. As such, when the piston 120 is pushed, because the wedge bodies 163 in the wedge head 161 of the tension steel wire holding means 160 are supported by the spring 165, the wedge bodies 163 are gradually inserted into the wedge seating hole 162 by the restoring force of the spring 165 while moving away from the end of the tension steel wire guide pipe 130, thus holding the tension steel wire 22.

[80] Even after the tension steel wire 22 has been held, the piston 120 is still pushed towards the second hydraulic port 112 of the cylinder body 110, so that the tension steel wire 22 is tensioned, thus reinforcing the soft ground. As such, after the tension steel wire 22 has been tensioned to a desired degree, the wedge inserting device 174 is operated. Then, the external wedge bodies 172b are pushed and inserted into the wedge receiving body 172a of the external fixer 172. Hence, the tension steel wire 22 is reliably held by the wedge receiving body 172a and the external wedge bodies 172b, so that the tension steel wire 22 maintains the tensioned state.

[81] As such, after the process of tensioning the tension steel wire has been completed, fluid is supplied into the second hydraulic port 112 of the cylinder body 110. Then, the piston 120 is retracted towards the first hydraulic port 111 into the cylinder body 110. At this time, although the wedge bodies 163 in the wedge head 161 are supported by the spring 165, because the wedge bodies 163 are in a state of moving along with the piston 120 towards the first hydraulic port 111 of the cylinder body 110, the wedge bodies 163 are pushed outwards and thus release the tension steel wire 22, and, thereafter, slide with respect to the tension steel wire 22.

[82] Subsequently, when the piston 120 is maximally retracted towards the first hydraulic port 111 into the cylinder body 110, the wedge bodies 163 in the wedge head 161 are brought into contact with the end of the tension steel wire guide pipe 130 and are thus pushed outwards, thus being separated in the diameter direction. After the wedge bodies 163 have been separated in the diameter direction, fluid, which has been supplied into the first and second hydraulic ports 111 and 112 of the cylinder body 110, is interrupted. Thereafter, the tension cylinder 100 is removed, thus completing the tensioning work.

[83] FIGS. 11 through 14 are views showing another embodiment of a tension cylinder for a tension steel wire for use in public works according to the present invention. In the case where more reliable reinforcement of the ground is required, several tension cylinders 100 are assembled into a single unit, such that several tension steel wires 22 can be tensioned at the same time.

[84] In this embodiment, the several tension cylinders 100, each of which is provided with a relatively long cylinder fastening pipe 142, in place of the tension steel wire guide head 140, coupled to an end of a cylinder body 110, are provided. The tension cylinders 100 are mounted to a circular base 176 at positions spaced apart from each other at the same angular intervals on the same circumferential line. Here, the tension cylinders 100, mounted to the base 176, are evenly inclined outwards around the vertical center axis, thus forming a cone shape. A casing 180, which surrounds the tension cylinders 100 throughout the upper and lower ends of the cylinder bodies in order to protect the tension cylinders 100, is coupled to the cylinder fastening pipes 142.

[85] The angle at which each tension cylinder 100 is mounted to the base is appropriate if, when the tension cylinder 100 is provided on the tension steel wire 22, the tension steel wire 22 is smoothly curved so that the process of tensioning the tension steel wire 22 can be normally conducted. Therefore, it is preferable that the angle at which each tension cylinder 100 is mounted to the base be within an angular range from 3° to 15°, at which, even though the tension steel wire 22 is bent, the tensioning process can be normally conducted.

[86] The casing 180 includes upper and lower ring-shaped protective members 181 and

182, which are disposed around the upper and lower ends of the tension cylinders 100, and a plurality of coupling members 183, which couple the protective members 181 and 182 to each other. The lower protective member 182 of the protective members 181 and 182 is fastened to the cylinder fastening pipes 142.

[87] Preferably, the number of coupling members 183 of the casing 180 is the same as the number of tension cylinders 100, and the coupling members 183 are disposed outside at positions adjacent to the respective tension cylinders 100, which are spaced apart from each other at regular angular intervals, so as to protect the respective tension cylinders 100. Here, the tension cylinders 100 are installed such that polygonal planar surfaces formed in the lower ends of the respective cylinder bodies 110 are in contact with the respective coupling members 183 of the casing 180. The reason for this is that a cylinder unit having a more well-organized structure can be provided.

[88] Furthermore, hydraulic pressure distributors 190 and 192 are provided among the tension cylinders 100 in upper and lower spaces defined above and below the cylinder bodies 110, which are arranged on the same circumferential positions. Second hydraulic ports 112, which are formed in the upper ends of the cylinder bodies 110, are connected to the lower hydraulic pressure distributor 192 through hydraulic hoses 194. First hydraulic ports 112, which are formed in the lower ends of the cylinder bodies 110, are connected to the upper hydraulic pressure distributor 190 through hydraulic hoses 193. Thus, pistons 120, which are provided in the respective cylinder bodies 110, can be extended upwards or retracted downwards at the same time.

[89] Because the circular base 176, the cylinder fastening pipes 142 and the casing 180 are made of aluminum alloy, the cylinder unit including the several tension cylinders is relatively light. Among these elements, the circular base 176 and the cylinder fastening pipes 142, which require relatively high surface hardness and abrasion resistance, are preferably anodized.

[90] As such, in the case where the circular base 176 is made of aluminum alloy, a steel plate or steel ring 178 may be provided under the lower surface of the circular base 176 to prevent it from being worn or broken by the tension steel wires.

[91] In a construction process using the tension cylinder unit for the tension steel wire for use in public works according to the present invention having the above-mentioned construction, as shown in FIG. 1, a load-carrying body 40 is first inserted into a hole 40 bored in soft ground, and grout is injected into the hole and, thereafter, cures with the load-carrying body 20. At the site where the above-mentioned processes have been conducted, hydraulic hoses of the hydraulic pump are connected to the hydraulic pressure distributor 190 and 192. Thereafter, fluid is supplied into the second hydraulic ports 112 of the cylinder bodies 110 of all of the tension cylinders 100 through the lower hydraulic pressure distributor 192 to place the pistons 120 at positions at which the pistons 120 are maximally retracted into the respective cylinder bodies 110.

[92] Subsequently, a ground pressure plate 170, an external fixer 172 and a wedge inserting device 174, which are shown in FIG. 9, are fitted over the tension steel wire, forming the load-carrying body, such that the tension cylinder unit is supported on the opening of the bored hole. Thereafter, the tension steel wires are inserted through the circular base 176, the respective cylinder fastening pipes 142, respective tension steel wire guide pipes 130 and respective tension steel wire holding means 160. At this time, because wedge bodies 163 in the wedge head 161 of each tension steel wire holding means 160 are pushed by the associated tension steel wire guide pipe 130 and thus are in a state of being separated in the diameter direction, the inserted tension steel wire 22 is not held by the wedge bodies 163.

[93] In this state, fluid is supplied into first hydraulic ports 111 of the cylinder bodies

110 through the upper hydraulic pressure distributor 190 of the tension cylinder unit 100. Then, the pistons 120 are pushed towards the second hydraulic ports 112 of the cylinder bodies 110 and thus extended outwards. At this time, because the wedge bodies 163 in the wedge head 161 of each tension steel wire holding means 160 are supported by the spring 165, when the wedge bodies 163 are moved away from the end of the tension steel wire guide pipe 130 while the pistons 120 are pushed and extended outwards, the wedge bodies 163 are inserted into the wedge seating hole 162 by the restoring force of the spring 165 while moving away from the end of the tension steel wire guide pipe 130, thus holding the tension steel wire 22.

[94] As such, after the tension steel wires 22 are held, as shown in FIG. 10, the pistons

120 are continuously moved towards the second hydraulic ports 112 of the cylinder bodies 110. Thus, tension proportional to the amount that the pistons 120 are extended is applied to the tension steel wires 22, thus reinforcing the soft ground. Here, although the tension steel wires 22 are pulled through the respective cylinder fastening pipes 142, which are coupled to the circular base 176 in the state of being inclined at a predetermined angle, the angle is sufficiently small to prevent the process of tensioning the tension steel wires 22 from being impeded.

[95] Furthermore, when the tension steel wires 22 are tensioned, although the tension steel wires 22 are bent at the circular base 176, because the rounded steel ring 178 is provided under the lower end of the circular base 176 at which the tension steel wires 22 are bent while passing therethrough, the circular base 176 is prevented from being worn or broken by the tension steel wires, and the tension steel wires are prevented from being excessively bent.

[96] As such, after the tension steel wire 22 has been tensioned to a desired degree, the wedge inserting device 174 is operated. Then, external wedge bodies 172b are pushed and inserted into a wedge receiving body 172a of the external fixer 172. Hence, the tension steel wires 22 are reliably held by the wedge receiving body 172a and the external wedge bodies 172b, so that the tension steel wires 22 maintain the tensioned state.

[97] After the process of tensioning the tension steel wire has been completed, fluid is supplied into the second hydraulic ports 112 of the cylinder bodies 110 through the lower hydraulic pressure distributor 192. Then, the pistons 120 are retracted towards the first hydraulic ports 111 into the respective cylinder bodies 110. At this time, although the wedge bodies 163 in each of the wedge heads 161 are supported by the associated springs 165, because the wedge bodies 163 are in a state of moving along with the piston 120 towards the first hydraulic port 111 of the cylinder body 110, the wedge bodies 163 are pushed outwards and thus release the associated tension steel wire 22, and, thereafter, slide with respect to the tension steel wire 22.

[98] Subsequently, when the pistons 120 are maximally retracted towards the first hydraulic ports 111 into the respective cylinder bodies 110, the wedge bodies 163 in each wedge head 161 are brought into contact with the end of the associated tension steel wire guide pipe 130 and are thus pushed outwards, thus being separated in the diameter direction. After the wedge bodies 163 have been separated in the diameter direction, fluid, which has been supplied into the first and second hydraulic ports 111 and 112 of the cylinder bodies 110, is interrupted. Thereafter, the tension cylinder 100 is removed, thus completing the tensioning work. Industrial Applicability

[99] As described above, a tension cylinder for a tension steel wire for use in public works according to the present invention is used to tension a tension steel wire for a permanent ground anchor or a removable tension steel wire type ground anchor, which is used in public works such as bracing work and public works for stabilizing a tunnel portal or for reinforcing a stone wall or a retaining wall. That is, the present invention is useful in industrial fields concerned with techniques of reinforcing the ground or base rock, in addition to a building, in order to ensure the stability of various structures.

Claims

[1] A tension cylinder for a tension steel wire for use in public works, comprising: a cylindrical cylinder body; a hollow tension steel wire guide pipe provided through the cylinder body along a longitudinal center axis thereof; a piston airtightly provided between the cylinder body and the tension steel wire guide pipe so as to be reciprocally movable using hydraulic pressure, which is selectively supplied into upper and lower ends of the cylinder body, the piston having a rod coaxially extending in one direction; and tension steel wire holding means provided on an end of the rod of the piston to hold the tension steel wire only when the piston is extended from the cylinder body, wherein the cylinder body and the piston are made of aluminum alloy, having a low specific gravity, and surfaces of portions of the cylinder body and the piston which require high abrasion resistance and surface hardness are anodized, thus ensuring lightness and sufficient strength.

[2] The tension cylinder for the tension steel wire for use in public works according to claim 1, wherein the cylinder body is made of aluminum alloy to increase strength thereof, a thickness of the cylinder body is increased, and an outer surface of an end thereof is cut at an incline to have a polygonal planar surface such that a plurality of tension cylinders is assemblable into a single cylinder unit.

[3] The tension cylinder for the tension steel wire for use in public works according to claim 1, wherein each anodized portion has a hardness ranging from 350 to 450 hv, and an anodizing layer thereof has a thickness ranging from 50 to 80 μm.

[4] The tension cylinder for the tension steel wire for use in public works according to claim 1, wherein outer and inner surfaces of a head part of the piston are maintained in an untreated aluminum alloy state.

[5] The tension cylinder for the tension steel wire for use in public works according to claim 1, wherein an inner surface of a cylinder head, which is provided in the cylinder body and is fitted over and is in contact with the rod of the piston, is maintained in an untreated aluminum alloy state.

[6] The tension cylinder for the tension steel wire for use in public works according to claim 5, wherein a foreign substance entry preventing ring is provided on the inner surface of the cylinder head to prevent a foreign substance from entering between the cylinder head and the rod when the piston is reciprocated.

[7] The tension cylinder for the tension steel wire for use in public works according to claim 1, wherein the tension steel wire holding means is coupled to an end of the rod of the piston through a left-handed thread, such that, when the tension steel wire holding means holds and tensions the tension steel wire, which is right- twisted, the tension steel wire holding means, which is rotated to a left (in a counterclockwise direction) when viewed from a longitudinal center axis of the tension steel wire, is tightened and prevented from being loosened.

[8] The tension cylinder for the tension steel wire for use in public works according to claim 1, wherein the cylinder head is fastened to the cylinder body through a left-handed thread to prevent the cylinder head from being loosened by frictional force generated by rotation of the piston.

[9] The tension cylinder for the tension steel wire for use in public works according to claim 1 or 2, comprising a plurality of tension cylinders, each of which includes a cylinder fastening pipe having a predetermined length coupled to an end of a cylinder body thereof, wherein the tension cylinders are mounted to a circular base at positions spaced apart from each other at regular intervals on a same circumferential line, the tension cylinders are inclined outwards around a vertical center axis to have a cone shape, and a casing, which surrounds the tension cylinders throughout upper and lower ends of the cylinder bodies to protect the tension cylinders, is coupled to the cylinder fastening pipes.

[10] The tension cylinder for the tension steel wire for use in public works according to claim 9, wherein the circular base, the cylinder fastening pipes and the casing are made of aluminum alloy to reduce a weight of the cylinder unit.

[11] The tension cylinder for the tension steel wire for use in public works according to claim 9, wherein the casing comprises upper and lower ring-shaped protective members disposed around the upper and lower ends of the tension cylinders, and a plurality of coupling members, which couple the upper and lower protective members to each other, wherein the lower protective member of the protective members is fastened to the cylinder fastening pipes.

[12] The tension cylinder for the tension steel wire for use in public works according to claim 11, wherein a number of the coupling members of the casing is equal to a number of the tension cylinders, and the coupling members are disposed outside at positions adjacent to the respective tension cylinders, which are spaced apart from each other at regular angular intervals, so as to protect the respective tension cylinders.

[13] The tension cylinder for the tension steel wire for use in public works according to claim 11 or 12, wherein the tension cylinders are installed such that polygonal planar surfaces formed in the lower ends of the respective cylinder bodies are in contact with the respective coupling members of the casing.

[14] The tension cylinder for the tension steel wire for use in public works according to claim 10, wherein, in a case where the circular base (176) is made of aluminum alloy, a steel ring (178) is provided under a lower surface of the circular base to prevent the circular base from being worn or broken by the tension steel wires.

[15] The tension cylinder for the tension steel wire for use in public works according to claim 9, wherein an angle at which each tension cylinder is mounted to the circular base is within an angular range from 3° to 15°, at which, even though the tension steel wire is bent, the tensioning process is normally conducted.

[16] The tension cylinder for the tension steel wire for use in public works according to claim 9, wherein upper and lower hydraulic pressure distributors are respectively provided in upper and lower spaces defined above and below the cylinder bodies such that pistons, which are provided in the respective cylinder bodies, are extended upwards or retracted downwards at the same time, and upper hydraulic ports, which are formed in the upper ends of the respective cylinder bodies, are connected to the lower hydraulic pressure distributor through hydraulic hoses, while lower hydraulic ports, which are formed in the lower ends of the respective cylinder bodies, are connected to the upper hydraulic pressure distributor through hydraulic hoses.