Patent Application
20080196341
1. Field of the Invention
The present invention relates, in general, to a modular column system constructed by stacking at least one precast unit between a foundation section and a coping section, as well as a method of constructing the same, in which the precast unit makes use of an internally confined hollow column unit fabricated in advance, and in which a joint section between the precast units is firmly formed. As a result, the modular column system realizes a short construction period and economy because reinforcement bars and forms are not used, and also realizes high resistance to bending moment and a reduction in cross section and self-weight of the precast unit, so that the modular column system enables easier and more economical assembly, and prevents brittle fracture of the joint section between the precast units.
2. Description of the Related Art
Generally, piers constructed in bridge work are cast-in-place concrete structures, in which, after foundation pit excavation work is carried out at the site, concrete is poured into formwork, in which reinforcement bars are arranged, and is cured for a predetermined period of time, and thereby a foundation section is formed.
After the foundation section is cured, the reinforcement bars and forms are arranged on the cured foundation section, and the concrete is poured into and cured in the formwork to form a pier. An upper portion of the pier, i.e. a coping section supporting a bridge deck, is formed by pouring concrete in a primary or secondary process after the forms are arranged in the state in which a staging is supported. Thereby, the pier is finished.
For this reason, a long construction period and great expense are required for the work of setting up the formwork and dismantling the formwork after curing the concrete. Further, problems with the pier can occur depending on the construction location. For example, in the case of constructing an elevated roadway, the pier creates a traffic jam around the construction site. Further, in the situation where the work environment is unfavorable, as in underwater work, the construction and management of the pier are difficult, and the possibility of faulty construction is increased.
In consideration of these aspects, piers have been constructed at sites in a method of constructing the foundation section including the foundation pit excavation under the ground, and then fabricating and assembling the pier as a unit structure.
To realize the advantages of construction of the modular pier, because a structure fabricated in a precast way in respective units, namely precast units, is fabricated in a factory, it is advantageous to control the quality of the concrete. Further, because the precast units are continuously fabricated, it is advantageous to manage manpower and the forms. In addition, because the precast units can be fabricated together with the construction of the foundation section, it is possible to reduce the construction period in comparison with the cast-in-place method.
In this manner, the modular pier constructed using the precast unit is disclosed in Korean Patent No. 10-99113 (titled “Modular Pier and Column Structure and Method of Constructing the Same”).
In the document, a plurality of precast units having a cross section of a spherical shape, a circular shape, or an oval shape is fabricated according to the height of a pier. Among the precast units, an upper precast unit has a convex shape at a lower end thereof, whereas a lower precast unit corresponding to the upper precast unit has a concave shape at an upper end thereof. Then, the upper and lower precast units are assembled. The convex and concave portions are provided with shear keys that are adapted to transmit compressive force, tensile force, axial force, and shear force when a bending moment is applied to the upper precast unit at five different positions. The shear keys are assembled in a construction method of injecting grout into shear key recesses of the middle thereof through an injection hole from the outside.
The above-described construction of the modular pier is characterized by directly assembling and constructing the pier structure as a unit structure at a site, and by the unit stably withstanding the fractional force transmitted thereto via the shear keys, installed in different directions, in conjunction with the injection of the grout.
However, when constructing this pier, it is difficult to set up the formwork for fabricating units having convex and concave shapes. Practically, due to its self-weight, the precast unit made of concrete has nothing but to be lifted by a crane, so that, when constructing a high pier, the number of precast units to be fabricated is excessively increased.
Meanwhile, the pier of the bridge serves to accept the load of its upper structure as the force to transmit it in a downward direction, and acts as a main member for resisting transverse loads, such as that of an earthquake. Hence, the pier should be designed such that it can resist vertical loading, transverse loading, bending moment, and so forth.
In consideration thereof, the design of the pier is based on the concept of a plastic hinge enabling core concrete to resist great compressive deformation and thus have the capability to dissipate energy. This means that the pier is endowed with ductile capability capable of causing plastic deformation against repeated load without remarkable reduction of stress resistance or rigidity.
The response modification factor taken into consideration in an earthquake-proof design is greatly influenced by this ductile capability. In the bridge, the ductile capability of the pier accounts for most of the ductile capability of the entire bridge.
Currently, the design criteria of roadway and railway bridges prescribe a transverse reinforcement ratio in order to secure the ductile capability of the plastic hinge section of the pier with respect to the earthquake and the transverse load. A reinforced concrete pier having a solid cross section is widely constructed on the basis of the transverse reinforcement ratio, and has good load supporting capacity.
However, the solid cross-section reinforced concrete pier has various disadvantages in that it is difficult to apply to a place where the foundation section encounters a structural problem due to the self-weight thereof, that it is economically unfavorable due to the increase in concrete material cost, and in that it encounters a chance of cracks occurring due to the generation of the heat of hydration when concrete is poured.
For this reason, attention is paid to a steel pier having advantages of good ductile capacity and a reduced construction period in spite of a certain disadvantage with respect to construction expenses.
However, the steel pier generally has a relatively greater width over the thickness of a deck constituting the pier, and thus has a problem in that it is vulnerable to local buckling when earthquakes occur.
Conventionally, in order to address this problem, a concrete filled steel tube (CFT) is used. CFT refers to a structure in which a steel tube having a circular or angular cross section is filled with concrete. Because the concrete is confined in the steel tube, CFT has advantages in that it is excellent in preventing the local buckling, has good ductile capability, and is reduced in cross section and self-weight due to an increase in resistance to the bending moment compared to the existing concrete pier.
However, CFT has a problem in that the material expense thereof is very high. Further, CFT still has a problem in that, when constructed as a high pier, it is increased in cross section and self-weight and thus is unsuitable for on-site conditions having restrictions on the ratio of width to thickness. In addition, CFT encounters a problem of maintenance for preventing corrosion thereof in on-site conditions, in which the corrosion becomes an issue, as in the underwater pier.
Further, in the case in which the pier of the bridge or the column of a building has a structural problem due to the excessive self-weight of concrete, or the material expense of the concrete is relatively high, a pier or a column having a hollow cross section is used, instead of one having a solid cross section.
Such a hollow cross-section pier or column is estimated to have high applicability because the resistance to the bending moment is not dynamically weaker compared to a usual pier or column.
Especially, as earthquake-proof design is currently becoming a hot issue, there is a necessity to design a pier or column capable of withstanding a greater bending moment, and furthermore, transverse displacement is required. Thus, when designing a pier or column capable of withstanding a great bending moment, a hollow cross-section pier or column, the self-weight of which is reduced because the inside thereof is hollow, can be more favorable according to the circumstances.
However, the ductile capacity of the hollow cross-section pier or column is doubtful, because it is difficult to expect a concrete confining effect therefrom. In other words, due to brittle fracture behavior caused in the inside of the hollow cross section because there is no concrete confining effect, the pier or column having a hollow cross-section evidences poor ductile capability in practice.
Nevertheless, in the case of modular piers proposed to date, no special study has been made of excessive self-weight in the case of using concrete for the precast unit, high material expense in the case of using CFT as a material for replacing concrete, whether to introduce the hollow cross section as an approach to resolve the increase in cross section and self-weight when constructing a high pier, the brittle fracture of the hollow cross section in the case of using the hollow cross section, and maintenance in the case of using CFT for, for example, an underwater pier.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a modular column system using at least one internally confined hollow column unit, in which the internally confined hollow column unit includes an outer pipe section formed of steel or fiber reinforced plastic (FRP), a concrete section filled with concrete and forming a hollow section inside the outer pipe section, and an inner pipe section installed in the hollow section of the concrete section and formed of steel or FRP, which confines the concrete section, thereby providing easy assembly of the units as well as economical construction due to the advantages derived from construction using a general modular column system, due to the hollow section, and due to a reduction in self-weight caused by reduction of a cross section, and improving corrosion resistance by means of the inner and outer pipe sections formed of FRP in the case of, for example, an underwater pier.
In order to achieve the above object, according to one aspect of the present invention, there is provided a modular column system using at least one internally confined hollow column unit. The modular column system includes at least one precast unit installed between a foundation section and a coping section, and means for fastening the precast unit to the foundation section, fastening the precast units to each other, and fastening the coping section to the precast unit. The precast unit is an internally confined hollow column unit which includes an outer pipe section formed of steel or fiber reinforced plastic (FRP), a concrete section filled with concrete and forming a hollow section inside the outer pipe section, and an inner pipe section installed in the hollow section of the concrete section and formed of steel or FRP confining the concrete section.
Therefore, the modular column system of the present invention is constructed in a manner such that the internally confined hollow column unit is attached to the upper portion of the foundation section by means of the fastening means, such that the internally confined hollow column units are stacked on and attached to the attached hollow column unit up to the designed height of the modular column system, and such that the coping section is attached to an upper portion of the uppermost one of the internally confined hollow column units.
The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:
Reference will now be made in greater detail to an exemplary embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts.
As illustrated in
When constructed for a general structure, the inner pipe section 13 and an outer pipe section 11 are preferably made of steel, thereby securing the resistance to bending moment.
However, when being constructed for use in a corrosive environment, such as for an underwater pier, the inner and outer pipe sections 13 and 11 can be made of fiber reinforced plastic (FRP) having corrosion resistance and ductility. More preferably, the FRP is selected from materials suitable for the conditions of on-site construction, for instance FRPs to which reinforcing materials have been added, such as carbon FRP (CFRP), aramid FRP (AFRP), glass FRP (GFRP), and so on. Further, the use of such an FRP incidentally reduces the self-weight of the structure, thereby serving to make assembly easy.
As illustrated in
The hollow section 14 is formed so as to run through the concrete section 12. Thus, as illustrated in
As illustrated in
In the case of using the cylindrical pipe 13a, there is an advantage in that it can exert resistance to axial compressive force and bending moment. In the case of using the corrugated pipe 13b, it has a good effect of confining the concrete section 12, and thus is suitable for preventing local buckling of the inner pipe section 13 as well as increasing the ductility of the precast unit, so that it can be properly selected according to the conditions at a construction site.
As illustrated in
Similarly, as illustrated in
The shear connectors 16 are formed of steel in the case in which the inner and outer pipe sections 13 and 11 are formed of steel. Thereby, the shear connectors 16 are preferably welded to the outer and inner surfaces of the inner and outer pipe sections 13 and 11, to which the concrete section 12 is attached. At this time, a weld zone between the inner or outer pipe section 13 or 11 and each shear connector 16 is preferably prevented from brittle fracture by maintaining strength greater than that of each of the inner and outer pipe sections 13 and 11 and the shear connectors 16.
Meanwhile, the shear connectors 16 are formed of FRP in the case in which the inner and outer pipe sections 13 and 11 are formed of FRP. Thereby, the shear connectors 16 are preferably bonded to the outer and inner surfaces of the inner and outer pipe sections 13 and 11, to which the concrete section 12 is attached. At this time, the bonding zone between the inner or outer pipe section 13 or 11 and each shear connector 16 is preferably prevented from brittle fracture by maintaining strength greater than that of each of the inner and outer pipe sections 13 and 11 and the shear connectors 16.
As illustrated in
Meanwhile, as illustrated in
Further, means for fastening a coping section 30 and the lowermost one of the internally confined hollow column units 10 includes a plurality of coping section anchoring holes 31 formed in the lower portion of the coping section 30, a plurality of upper anchoring holes 15a that are formed in the upper portion of the concrete section 12 and are opposite the coping section anchoring holes 31, a plurality of bar-like members 40 that are inserted between the upper anchoring holes 15a and the coping section anchoring holes 31, and grout 50 that fixes the bar-like members 40.
Also, means for fastening the two adjacent internally confined hollow column units 10 includes a plurality of upper anchoring holes 15a that are formed in the upper portion of the lower one of the internally confined hollow column units 10, a plurality of lower anchoring holes 15b that are formed in the lower portion of the upper one of the internally confined hollow column units 10 and are opposite the upper anchoring holes 15a, a plurality of bar-like members 40 that are inserted between the upper anchoring holes 15a and the lower anchoring holes 15b, and grout 50 that fixes the bar-like members 40.
These fastening means are constructed to attach the lowermost one of the internally confined hollow column units 10 to the foundation section 20, and between the two adjacent internally confined hollow column units 10, and between the uppermost one of the internally confined hollow column units 10 and the coping section 30 by inserting the bar-like members 40 into the anchoring holes 15a, 15b, 21 and 31, and then curing the grout 50 between the bar-like members 40 and the anchoring holes 15a, 15b, 21 and 31.
In order to provide stronger attachment, as illustrated in
The numbers of the bar-like members 40 and the anchoring holes 15a, 15b, 21 and 31 are preferably adjusted depending on the bending moment generated in the joint sections 80 of the internally confined hollow column units 10.
The grout 50 is used not only for attaching the bar-like members 40 to the anchoring holes 15a, 15b, 21 and 31, but also for preventing the bar-like members 40 from corroding in the case in which each bar-like member 40 is made of a mixture of a steel bar and cement paste or mortar. The grout 50 preferably has fluidity and expansibility suitable to compactly fill the anchoring holes 15a, 15b, 21 and 31.
As illustrated in
According to one embodiment of the present invention, as illustrated in
A lower inner flange 62b is attached to the lower inner circumference of the inner pipe section 13 of the lowermost internally confined hollow column unit 10 and is provided with a plurality of lower inner fastening holes 63b. A plurality of fasteners 101, such as bolts, passes through the lower inner fastening holes 63b, is inserted into a plurality of foundation section inner fastening holes 23b at the upper portion of the foundation section 20, and fastens the lower inner flange 62b to the foundation section 20. Thereby, the means for fastening the foundation section 20 and the lowermost internally confined hollow column unit 10 preferably prevents brittleness of the joint section 80 between the foundation section 20 and the lowermost internally confined hollow column unit 10.
As illustrated in
An upper inner flange 60b is attached to the upper inner circumference of the inner pipe section 13 of the uppermost internally confined hollow column unit 10 and is provided with a plurality of upper inner fastening holes 61b. A plurality of fasteners 101, such as bolts, passes through the upper inner fastening holes 61b, is inserted into a plurality of coping section inner fastening holes 32b at the lower portion of the coping section 30, and fastens the upper inner flange 60b to the coping section 30. Thereby, the means for fastening the coping section 30 and the uppermost internally confined hollow column unit 10 preferably prevents brittleness of the joint section 80 between the coping section 30 and the uppermost internally confined hollow column unit 10.
Further, the means for fastening two adjacent internally confined hollow column units 10 includes an upper outer flange 60a that is attached to the upper outer circumference of the outer pipe section 11 of the lower internally confined hollow column unit 10 and is provided with a plurality of upper outer fastening holes 61a, a lower outer flange 62a that is attached to the lower outer circumference of the outer pipe section 11 of the upper internally confined hollow column unit 10 and is provided with a plurality of lower outer fastening holes 63a opposite the plurality of upper outer fastening holes 61a, and a plurality of fastener tools 100, for example, bolts and nuts, that pass through the upper and lower outer fastening holes 61a and 63a and fasten the upper and lower outer flanges 60a and 62a to each other.
An upper inner flange 60b is attached to the upper inner circumference of the inner pipe section 13 of the lower internally confined hollow column unit 10, and is provided with a plurality of upper inner fastening holes 61b. A lower inner flange 62b is attached to the lower inner circumference of the inner pipe section 13 of the upper internally confined hollow column unit 10, and is provided with a plurality of lower inner fastening holes 63b opposite the plurality of upper inner fastening holes 61b. A plurality of fastener tools 100, for example bolts and nuts, passes through the upper and lower inner fastening holes 61b and 63b and fastens the upper and lower inner flanges 60b and 62b to each other. Thereby, the means for fastening two adjacent internally confined hollow column units 10 preferably prevents brittleness of the joint section 80 between the two adjacent internally confined hollow column units 10.
The flanges 60a, 60b, 62a and 62b, which are attached to the upper and lower circumferences of the internally confined hollow column unit 10, have an annular shape, such as a circular shape or a quadrilateral shape, which can be determined to correspond to the shape of the cross section of the internally confined hollow column unit 10. The hollow inner diameter D4 of each of the upper and lower outer flanges 60a and 62a is equal to the outer diameter D2 of the outer pipe section 11 of the internally confined hollow column unit 10. Thus, the upper and lower outer flanges 60a and 62a can be attached to the outer surfaces of the opposite ends of the outer pipe section 11 by means of welding. Alternatively, in the case in which the outer pipe section 11 is formed of plastic, such as FRP, the upper and lower outer flanges 60a and 62a may be attached to the outer surfaces of the opposite ends of the outer pipe section 11 by means of bonding.
The outer diameter D5 of each of the upper and lower inner flanges 60b and 62b is equal to the inner diameter D3 of the inner pipe section 13 of the internally confined hollow column unit 10. Thus, the upper and lower inner flanges 60b and 62b can be attached to the inner surfaces of the opposite ends of the inner pipe section 13 by means of welding. Alternatively, in the case in which the inner pipe section 13 is formed of plastic, such as FRP, the upper and lower inner flanges 60b and 62b may be attached to the inner surfaces of the opposite ends of the inner pipe section 13 by means of bonding.
According to another embodiment of the present invention, as illustrated in
An inner support 70b is attached in a strip shape to the inner circumference of the joint section 80 between the upper and lower internally confined hollow column units 10. Thereby, the means for fastening two adjacent internally confined hollow column units 10 preferably prevents brittleness of the joint section 80 between the upper and lower hollow column units 10.
The outer and inner supports 70a and 70b are attached to the outer and inner circumferences of the joint section 80 between the upper and lower hollow column units 10 by means of welding in the case in which the outer and inner pipe sections 11 and 13 are formed of steel, or by means of bonding in the case in which the outer and inner pipe sections 11 and 13 are formed of plastic such as FRP. Thereby, the outer and inner supports 70a and 70b prevent brittleness of the joint section 80 between the upper and lower hollow column units 10.
As described above, when the adjacent hollow column units 10 are mutually attached using the flanges 60a, 60b, 62a and 62b or the supports 70a and 70b, they are first attached to each other by means of the bar-like members 40 inserted in the upper and lower anchoring holes 15a and 15b as well as the grout 50, and then by means of either the fastener tools, such as bolts and nuts, fastened to the flanges thereof or the supports 70a and 70b attached to the joint section 80. Thereby, the brittleness of the joint section 80 in the modular column system can be prevented.
Further, in the case in which the internally confined hollow column unit 10 is attached to either the upper portion of the foundation section 20 or the lower portion of the coping section 30, they are first attached to each other by means of the bar-like members 40 inserted between the lower anchoring holes 15b and the foundation section anchoring holes 21 and between the upper anchoring holes 15a and the coping section anchoring holes 31 as well as the grout 50, and then by means of the fasteners 101, such as bolts, that are fastened either to the upper portion of the foundation section 20 through the lower outer and inner flanges 62a and 62b or the lower portion of the coping section 30 through the upper outer and inner flanges 60a and 60b. Thereby, the brittleness of the joint section 80 in the modular column system can be prevented.
Meanwhile, as illustrated in
In step S1 of constructing the foundation section 20, the column unit insertion recess 22, into which the lowermost one of the internally confined hollow column units 10 is inserted, can be formed at the upper portion of the foundation section 20.
The grout 50 is injected into the foundation section anchoring holes 21 (step S2).
Before the grout 50 in the foundation section anchoring holes 21 is cured in step S2, the bar-like members 40, which have been inserted into and attached in the lower anchoring holes 15b of the lowermost internally confined hollow column unit 10 to be placed on the upper portion of the foundation section 20, are inserted into the foundation section anchoring holes 21, into which the grout 50 has been injected, and thus the lowermost internally confined hollow column unit 10 is attached to the foundation section (step S3).
In the case of the bar-like members 40 inserted into the lower anchoring holes 15b of the lowermost internally confined hollow column unit 10, it does not matter that the bar-like members 40 are inserted into the lower anchoring holes 15b at the site before injection of the grout 50 into the lower anchoring holes 15b. However, in this case, the period for construction is delayed due to the time it takes to cure the grout, so that the internally confined hollow column unit 10 is preferably precast in a factory with the bar-like members 40 inserted into and attached in the lower anchoring holes 15b in the interest of reducing the construction period as well as economy.
In step S3 of attaching the lowermost internally confined hollow column unit to the foundation section, the lower outer flange 62a having the plurality of lower outer fastening holes 63a and the lower inner flange 62b having the plurality of lower inner fastening holes 63b are attached to the lower outer and inner circumferences, respectively, of the lowermost internally confined hollow column unit 10, placed on the upper portion of the foundation section. Then, the fasteners 101 are fastened in the foundation section outer and inner fastening holes 23a and 23b of the upper portion of the foundation section 20, thereby attaching the lower outer and inner flanges 62a and 62b to the foundation section 20.
Then, the grout 50 is injected into the upper anchoring holes 15a of the lowermost internally confined hollow column unit 10, which has been placed on the upper portion of the foundation section 20 in step S3 (step S4).
Before the grout 50 in the upper anchoring holes 15a is cured in step S4, the bar-like members 40, which have been inserted into and attached in the lower anchoring holes 15b of the internally confined hollow column unit 10 to be placed on the lowermost internally confined hollow column unit 10 on the foundation section 20, are inserted into the upper anchoring holes 15a of the lowermost internally confined hollow column unit 10, into which the grout 50 has been injected, and thus the adjacent hollow column units 10 are attached to each other (step S5).
According to one embodiment of the present invention, in step S5 of attaching the internally confined hollow column units 10 to each other, the internally confined hollow column units 10 are each provided with the upper and lower outer flanges 60a and 62a and the upper and lower inner flanges 60b and 62b, and then are attached to each other using the fastener tools 100.
Further, according to another embodiment of the present invention, in step S5 of attaching the internally confined hollow column units 10 to each other, the joint section 80 between the internally confined hollow column units 10 is attached to the outer support 70a on the outer circumference thereof and to the inner support 70b on the inner circumference thereof, and thereby the internally confined hollow column units 10 are attached to each other.
The internally confined hollow column units 10 are stacked and attached up to the designed height of the modular column system by means of repetition of steps S4 and S5 (step S6).
Then, the grout 50 is injected into the upper anchoring holes 15a of the uppermost internally confined hollow column unit 10, which has been placed on the upper portion of the foundation section 20 in step S6 (step S7).
Before the grout 50 in the upper anchoring holes 15a is cured in step S7, the bar-like members 40, which have been inserted into and attached in the coping section anchoring holes 31 of the lower portion of the coping section 30, are inserted into the upper anchoring holes 15a, into which the grout 50 has been injected, and thus the uppermost internally confined hollow column unit 10 is attached to the coping section (step S8).
In step S8 of attaching the coping section 30 to the upper portion of the uppermost internally confined hollow column unit 10, the upper outer flange 60a and the upper inner flange 60b are attached to the upper outer and inner circumferences, respectively, of the uppermost internally confined hollow column unit 10, placed under the coping section 30. Then, the fasteners 101 are fastened in the coping section outer and inner fastening holes 32a and 32b of the lower portion of the coping section 30, thereby attaching the upper outer and inner flanges 60a and 60b to the coping section 30.
As apparent from the above description, the modular column system using at least one internally confined hollow column unit and the method of constructing the same in accordance with the present invention provide the following advantages.
First, the resistance to the bending moment is increased using the internally confined hollow column units, in which the concrete section is confined by the inner pipe section, and thus is under triaxial compression load. As a result, the internally confined hollow column units are each reduced in cross section and self-weight, and thus make assembly easy.
Second, the hollow sections of the internally confined hollow column units result in the use of less concrete, a reduction in the cross section of each of the internally confined hollow column units, elimination of the need for forms, elimination of the use of steel bars, and so on. As a result, the economically advantageous effect of reducing labor costs for installation can be obtained.
Third, the internally confined hollow column units are each provided with the inner and outer pipe section formed of plastic, such as FRP, such that they can be used in corrosive environments, such as in an underwater pier, and thus are advantageous for maintenance. In the case of using the FRP, the internally confined hollow column units can be reduced in self-weight.
Fourth, the brittle fracture of the joint sections between the internally confined hollow column units can be prevented by the strong attachment of the joint sections.
Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
