Base structure of unbonded precast prestressed concrete columns

Abstract

To provide a structure capable of preventing compression fracture in an un-bonded PCaPC structure.SOLUTION: A structure of a column base part of an un-bonded PCaPC column includes the un-bonded PCaPC column erected on a footing and provided with a notch part in the column base part, and a steel plate provided in the column base part of the un-bonded PCaPC column and in contact with the notch part and the footing, and the un-bonded PCaPC column and the footing are joined by the steel plate. The steel plate may be an L-shaped steel plate, and a rib may be provided on the L-shaped steel plate.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] One embodiment of the present invention relates to a column base structure for an unbonded precast prestressed concrete column. [Background technology]

[0002] An earthquake-resistant building structure has been disclosed in which a steel pipe concrete-filled column can be separated from a pile by providing an axial damper at the column base (see Patent Document 1). The earthquake-resistant building structure disclosed in Patent Document 1 is said to be able to prevent excessive pulling force from acting on the pile, and to be able to effectively absorb earthquake energy by the axial damper.

[0003] On the other hand, unbonded precast prestressed concrete (hereinafter referred to as "unbonded PCaPC") structures are known as structures that can minimize damage during earthquakes and ensure high functionality after an earthquake. Unbonded PCaPC structures are mainly applied to beam members that have been converted to PCa, but it is also expected to be applied to column members to take advantage of the above-mentioned advantages. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-073469 A (Patent No. 4120740) Summary of the Invention [Problem to be solved by the invention]

[0005] Since unbonded PCaPC structures do not have tensile rebars, they are more susceptible to damage caused by compression of the cover concrete at the base of the columns than reinforced concrete structures (hereinafter, such damage will be referred to as "crush" or "compressive failure"). If compressive failure occurs in unbonded PCaPC columns due to earthquakes, etc., it will cause a decrease in seismic resistance, so in order to maintain strength, it will be necessary to repair the compressed failed parts.

[0006] In view of such problems, an object of one embodiment of the present invention is to provide a structure capable of suppressing compressive failure in an unbonded PCaPC structure. [Means for solving the problem]

[0007] The structure of the base of an unbonded PCaPC column in one embodiment of the present invention includes an unbonded PCaPC column that is erected on a footing and has a notch in the base, and a steel plate that is provided at the base of the unbonded PCaPC column and contacts the notch and the footing, and the unbonded PCaPC column and the footing are joined by the steel plate.

[0008] In one embodiment of the present invention, the steel plate may be an L-shaped steel plate, and the L-shaped steel plate may be provided with a rib. The L-shaped steel plate may be connected to the unbonded PCaPC column with a bolt, and may be connected to the footing by a bolt embedded in the footing. Effect of the Invention

[0009] According to one embodiment of the present invention, a notch is provided in the base of an unbonded PCaPC column, and a steel plate is abutted against the notch and the footing to join the unbonded PCaPC column and the footing, thereby improving earthquake resistance and preventing compressive failure of the cover concrete. A building having such a column base structure of an unbonded PCaPC column can improve earthquake resistance, prevent compressive failure of the column body even when a large vibration energy is applied due to an earthquake, etc., and reduce repair work. [Brief description of the drawings]

[0010] [Figure 1] An oblique view showing the structure of the column base of an unbonded PCaPC column in one embodiment of the present invention. [Diagram 2] A front view showing the structure of the column base of an unbonded PCaPC column in one embodiment of the present invention. [Diagram 3]1 is a diagram showing the arrangement of main reinforcement, tendons, a first steel plate, and a second steel plate at the base of an unbonded PCaPC column in one embodiment of the present invention. FIG. [Figure 4] FIG. 4 shows the structure of the column base of an unbonded PCaPC column according to one embodiment of the present invention, and is a diagram showing a schematic planar structure when cut between A1-A2 shown in FIG. 3 and viewed from above. [Diagram 5] This is a diagram explaining the tensile and compressive forces acting on the base of an unbonded PCaPC column when it is rotated and displaced due to an earthquake or other cause. [Figure 6] A front view showing the structure of the column base of an unbonded PCaPC column in one embodiment of the present invention. [Figure 7] 1 is a diagram showing the arrangement of main reinforcement, tendons, a first steel plate, and a second steel plate at the base of an unbonded PCaPC column in one embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the contents of the embodiment of the present invention will be described with reference to the drawings. However, the present invention includes many different aspects, and is not to be interpreted as being limited to the contents of the embodiment exemplified below. In order to make the explanation clearer, the width, thickness, shape, etc. of each part may be shown diagrammatically compared to the actual aspect, but this is merely an example and does not limit the contents of the present invention. Furthermore, in this specification, when an element shown in a certain drawing and an element shown in another drawing are identical or correspond to each other, the same symbol (or a symbol with a, b, etc. added after the number shown as the symbol) may be added, and repeated explanations may be omitted as appropriate. Furthermore, the letters "first" and "second" added to each element are convenient marks used to distinguish each element, and have no further meaning unless otherwise explained.

[0012] Fig. 1 is a perspective view showing the structure of a column base of an unbonded PCaPC column 102 according to one embodiment of the present invention. The unbonded PCaPC column 102 is erected on a footing 104. The footing 104 is made of reinforced concrete, and a foundation beam 106 made of reinforced concrete is joined to the side of the footing 104. Fig. 1 shows an embodiment in which the foundation beam 106 is joined to four sides of the footing 104, but the configuration of the foundation beam 106 is arbitrary and is not limited to the structure shown in the figure.

[0013] The unbonded PCaPC column 102 has a notch 108 at the base of the column. The notch 108 is an area where the surface of the precast reinforced concrete member has been cut out (or removed). In other words, the notch 108 can also be expressed as an area where the surface layer of the cover concrete of the unbonded PCaPC column 102 has been removed. It is preferable that the notch 108 is provided around the entire circumference of the base of the unbonded PCaPC column 102. As described later, providing the notch 108 at the base of the column can prevent damage to the cover concrete.

[0014] The notch 108 is provided at a predetermined length from the column end (lower end) of the unbonded PCaPC column in the material axial direction. For example, the notch 108 is provided at a length of 200 mm to 1000 mm from the column end (lower end) of the unbonded PCaPC column 102 in the material axial direction. For example, the notch 108 is provided at a length of 500 mm from the column end (lower end). The depth of the notch 108 is provided at a predetermined depth. For example, the notch 108 is provided to have a depth of 20 mm to 1000 mm from the surface of the unbonded PCaPC column 102. For example, the notch 108 is provided to have a depth of 50 mm.

[0015] The cutout 108 can be formed when the precast reinforced concrete member is manufactured. That is, by setting the shape of the cutout in the formwork for forming the precast reinforced concrete member, the cutout 108 can be formed by simply pouring concrete. Because the precast reinforced concrete member is manufactured in a factory, the cutout 108 can be formed with high precision, and it is possible to reduce the burden on the work at the construction site.

[0016] The unbonded PCaPC column 102 is joined to the footing 104 by a steel plate 110. The steel plate 110 is provided so as to abut the unbonded PCaPC column 102 and the footing 104, and is attached by a fastener such as a bolt. In detail, the steel plate 110 has a flat surface that abuts the upper surface of the footing 104 and the concrete surface of the notch 108, and is attached to the footing 104 by a first fastener 112 and to the unbonded PCaPC column 102 by a second fastener 114. The first fastener 112 not only joins the steel plate 110 to the footing 104, but also preferably has a strength capable of resisting a tensile force as described later. On the other hand, the second fastener 114 only needs to have a strength capable of joining the steel plate 110 and the unbonded PCaPC column 102. A bolt is used as the first fastener 112. The bolt is embedded in the footing 104 so that the threaded tip is exposed. The second fastener 114 may be a bolt and insert, an anchor bolt, or the like.

[0017] Although not shown, the steel plate 110 may be joined to the footing 104 and the unbonded PCaPC column 102 by an adhesive.

[0018] When the cross-sectional shape of the unbonded PCaPC column 102 is rectangular, the steel plates 110 are preferably provided corresponding to each face. In other words, the unbonded PCaPC column 102 is preferably provided so that the cutout portion 108 is surrounded by the steel plates 110. By providing the steel plates 110 on each face of the cutout portion 108 in this manner, the unbonded PCaPC column 102 can be stably joined to the footing 104. The cutout portion 108 may be provided so as to be continuous with each face of the unbonded PCaPC column 102, that is, over the entire circumference. Although not shown, the steel plates 110 may have a shape that is continuous over two or more faces adjacent to the cutout portion 108.

[0019] The steel plate 110 may have various shapes as long as it has a shape that allows it to come into contact with the footing 104 and the concrete surfaces of the cutout 108 and be fixed with fasteners. FIG. 1 shows an example of the steel plate 110 having an L-shaped cross section. The L-shaped steel plate 110 is installed so that its bottom surface comes into contact with the footing 104 and its upright back surface comes into contact with the concrete surface of the cutout 108. The L-shaped steel plate 110 may be a steel plate bent into an L shape, or may be a steel plate joined into an L shape by welding.

[0020] In the following description, the steel plate 110 will be mainly described as being L-shaped, but the steel plate 110 may be similarly applied even if its cross-sectional shape is U-shaped or rectangular.

[0021] As shown in FIG. 1, the L-shaped steel plate 110 may be provided in such a manner that one wide steel plate 110 covers each side of the cutout portion 108, or multiple L-shaped steel plates 110 may be arranged side by side on each side.

[0022] FIG. 2 shows a front view of the base of an unbonded PCaPC column 102. FIG. 2 shows a structure in which the unbonded PCaPC column 102 is joined to the footing 104 by an L-shaped steel plate 110. The L-shaped steel plate 110 is installed so that its upright back surface contacts the concrete surface of the cutout portion 108 and its bottom surface contacts the upper surface of the footing 104. The L-shaped steel plate 110 is fixed to the footing 104 by a bolt 113 serving as a first fastener 112. The L-shaped steel plate 110 is also fixed to the unbonded PCaPC column 102 by a bolt 115 serving as a second fastener 114. As shown in FIG. 2, the bolts 113 are provided at multiple locations for one L-shaped steel plate 110, and multiple bolts 115 are used.

[0023] The bolt 115 for fixing the L-shaped steel plate 110 to the unbonded PCaPC column 102 is preferably attached so that its head does not protrude from the column surface of the unbonded PCaPC column. In other words, the depth d of the cutout portion 108 is preferably large enough so that the head of the bolt 115 does not protrude from the column surface of the unbonded PCaPC column 102. The depth d is, for example, 30 mm to 50 mm, depending on the column diameter of the unbonded PCaPC column 102 and the shaft diameter of the bolt 115. This configuration can improve the design of the unbonded PCaPC column 102. For example, even if a decorative plate is provided on the surface of the unbonded PCaPC column 102, the head of the bolt 115 does not protrude, so that the appearance of the column is not affected.

[0024] When the L-shaped steel plate 110 is provided in contact with the notch 108, it is preferable that the upper end portion does not contact the step portion of the notch 108. In other words, it is preferable that a gap of a distance h is provided between the upper end portion of the L-shaped steel plate 110 and the step portion formed by the notch 108. The size of the distance h is arbitrary, but is provided to be, for example, 5 mm to 20 mm. By providing a gap of the distance h, even if the unbonded PCaPC column 102 rotates and displaces, and the L-shaped steel plate 110 shifts, it is possible to prevent the upper end portion of the L-shaped steel plate 110 from colliding with the step portion. This makes it possible to prevent cracks and damage to the cover concrete of the unbonded PCaPC column 102.

[0025] The L-shaped steel plate 110 may be provided so as to cover the entire concrete surface of the cutout 108. This makes it possible to compensate for the reduction in strength caused by the cutout 108 being provided in the unbonded PCaPC column 102. It also makes it possible to prevent cracks and breakage of the covering concrete at the cutout 108.

[0026] Fig. 3 shows the internal structure of the unbonded PCaPC column 102 and the mounting structure of the L-shaped steel plate 110. Fig. 4 shows a schematic plan view of the structure when cut between A1 and A2 in Fig. 3 and viewed from above. In the following explanation, Fig. 3 and Fig. 4 will be referred to as appropriate. Note that Fig. 3 shows only the main parts of the internal structure of the footing 104, and the arrangement of reinforcing bars is omitted.

[0027] The unbonded PCaPC column 102 includes a precast reinforced concrete structure including prefabricated rebars 132 (first prefabricated rebars 132a and second prefabricated rebars 132b) and shear reinforcement bars 134. The unbonded PCaPC column 102 has a notch 108 at the base of the column, and so the concrete cover thickness at the notch 108 is reduced if reinforcement is arranged in the normal manner. Therefore, in the unbonded PCaPC column 102, a first prefabricated rebar 132a is arranged in the material axis direction in the region of the notch 108, and a second prefabricated rebar 132b is arranged in the material axis direction in the region above the notch 108.

[0028] The first prefabricated rebar 132a and the second prefabricated rebar 132b are discontinuous, and the second prefabricated rebar 132b is arranged on the outside of the first prefabricated rebar 132a. The first prefabricated rebar 132a and the second prefabricated rebar 132b are arranged so as to overlap at the boundary of the cutout portion 108. The first prefabricated rebar 132a and the second prefabricated rebar 132b are appropriately arranged according to the cross-sectional shape of the unbonded PCaPC column 102, and reinforcing bars are appropriately arranged for the first prefabricated rebar 132a and the second prefabricated rebar 132b.

[0029] The unbonded PCaPC column 102 is provided with an insert 138 in the area where the notch 108 is provided. The insert 138 is embedded in the precast reinforced concrete structure in a position corresponding to the position where the second fastener 114 (bolt 115) is attached. The L-shaped steel plate 110 is installed so as to abut against the concrete surface of the notch 108 and the upper surface of the footing 104.

[0030] The first fastener 112 (bolt 113) is provided so that the portion that fastens the L-shaped steel plate 110 is exposed, and the other portion is embedded in the footing 104. The first fastener 112 (bolt 113) is firmly fixed by an anchoring plate 118 embedded in the footing 104 so that it does not come loose. This structure allows the first fastener 112 (bolt 113) to have the strength to resist the tensile force that occurs when the unbonded PCaPC column 102 is rotated and displaced.

[0031] Furthermore, the L-shaped steel plate 110 is bolted to the unbonded PCaPC column 102 by a bolt 115 used as the second fastener 114 and an insert 138. Although not shown, the insert 138 may be omitted and a bolt (e.g., a core rod driving anchor bolt) implanted in the unbonded PCaPC column 102 may be used as the second fastener 114.

[0032] 7, the L-shaped steel plate 110 and the footing 104 may be joined by using reinforcing bars 115 welded to the L-shaped steel plate 110 as the first fasteners 112 and fixing the reinforcing bars 115 to the footing 104. As in the case of using bolts 113 as the first fasteners 112, the use of reinforcing bars 115 welded to the steel plate 110 can also provide a strength capable of resisting the tensile force generated when the unbonded PCaPC column 102 is rotated and displaced.

[0033] A grout 116 is provided between the unbonded PCaPC column 102 and the footing 104. The unbonded PCaPC column 102 also has an insertion hole 136 through which a PC steel rod 128 is inserted. The insertion hole 136 is provided so as to penetrate the unbonded PCaPC column 102 in the material axial direction. A PC steel rod 128b is inserted into the insertion hole 136 and is connected to a PC steel rod 128a extending from the footing 104 by a joint 130. A compressive stress is applied to the unbonded PCaPC column 102 using the PC steel rod 128.

[0034] The PC steel rod 128a is provided on the footing 104 side. To connect to the PC steel rod 128b on the unbonded PCaPC column 102 side, the PC steel rod 128a crosses the brace bars 120 and is provided so that its upper portion protrudes from the footing 104. An anchoring plate 124 is embedded in the footing 104. The lower end of the PC steel rod 128a is inserted into the anchoring plate 124 and fixed by a nut 126. It is preferable that the upper portion of the anchoring plate 124 is provided with grid bars (anchoring portion reinforcing bars) 122. By providing the grid bars 122, the strength of the footing 104 can be increased and tensile fracture and the like can be prevented when tensile stress acts on the PC steel rod 128a.

[0035] The unbonded PCaPC column 102 erected on the footing 104 has compressive stress applied by the PC steel rods 128 installed in an unbonded state, so it is stronger than normal reinforced concrete and is less likely to crack. Since the PC steel rods 128 have a restoring force, even if an excessive load is temporarily applied to the unbonded PCaPC column 102, it will return to its original state when the load is removed.

[0036] As shown in Fig. 5(A), when an unbonded PCaPC column 999 is rotated and displaced due to lateral shaking caused by an earthquake, a tensile force acts on one side of the column base and a compressive force acts on the other side. As shown diagrammatically in Fig. 5(A), a conventional unbonded PCaPC column 999 has a problem in that the cover concrete on the side where the compressive force acts due to the rotational displacement is easily subjected to compressive failure.

[0037] In contrast, the unbonded PCaPC column 102 according to the present embodiment has a cutout 108, which effectively reduces the diameter of the base and reduces the cross-sectional area of ​​the base. This structure reduces the rotational rigidity of the unbonded PCaPC column 102, but reduces the column base moment caused by horizontal forces such as earthquakes, i.e., the compressive force generated in the outer periphery concrete of the unbonded PCaPC column 102 is reduced compared to the structure shown in Fig. 5(A), thereby suppressing compressive failure of the cover concrete. Although the reduction in the cross-sectional area of ​​the base reduces the rotational rigidity of the unbonded PCaPC column 102, the L-shaped steel plate 110 and the bolt 113 plastically deform to absorb the energy that causes rotational displacement, thereby reducing damage to the unbonded PCaPC column 102.

[0038] Also, by providing the cutout 108 around the entire circumference of the unbonded PCaPC column 102, it is possible to prevent compressive failure of the column end against forces that cause rotational displacement acting from any direction. Furthermore, by providing an L-shaped steel plate 110 to cover the cutout 108, the covering concrete is protected and compressive failure can be suppressed.

[0039] The unbonded PCaPC column 102 according to this embodiment can improve long-term reliability by having an L-shaped steel plate 110 at the column base joined with a bolt 113. Even if the PC steel bar 128 rusts and breaks, the L-shaped steel plate 110 joined with the bolt 113 as the first fastener 112 can bear the tensile force for the long-term load and ensure safety.

[0040] The L-shaped steel plate 110 is not limited to the structure shown in Fig. 2. For example, as shown in Fig. 6, the L-shaped steel plate 110 may be provided with a rib 140. By having such a structure, the rigidity of the L-shaped steel plate 110 can be increased. As a result, even if a force that causes rotational displacement acts on the unbonded PCaPC column 102, the resistance to rotational displacement can be increased.

[0041] In this way, the column base structure of the unbonded PCaPC column 102 according to this embodiment can attenuate the energy that causes rotational displacement to the unbonded PCaPC column 102, and can prevent compressive failure of the covering concrete. A building having the column base structure of the unbonded PCaPC column 102 according to this embodiment can increase earthquake resistance, and can prevent compressive failure of the column body and reduce repair work even when a large vibration energy is applied due to an earthquake or the like. [Explanation of symbols]

[0042] 102 ···Unbonded PCaPC column, 104 ···Footing, 106 ···Foundation beam, 108 ···Notch, 110 ···Steel plate, 112 ···First fastener, 114 ···Second fastener, 115 ···Reinforcing bar, 116 ···Grout, 118 ···Anchoring plate, 120 ···Strip bar, 122 ···Grid bar, 124 ···Anchoring plate, 126 ···Nut, 128 ···PC steel bar, 130 ···Joint, 132 ···Assembled reinforcing bar, 134 ···Shear reinforcement bar, 136 ···Through hole, 138 ···Insert, 140 ···Rib

Claims

1. an unbonded precast prestressed concrete column erected on a footing and having a notch at the column base; A steel plate is provided at the base of the unbonded precast prestressed concrete column and contacts the notch and the footing; Including, The precast prestressed concrete column is provided in an unbonded state with a PC steel rod having a lower end fixed to the footing inserted in the material axial direction, and a compressive stress is applied by the PC steel rod, Column base structure of an unbonded precast prestressed concrete column, characterized in that the steel plate is connected to the unbonded precast prestressed concrete column and the footing by a fastener.

2. The column base structure of an unbonded precast prestressed concrete column according to claim 1, wherein the steel plate is an L-shaped steel plate.

3. The column base structure of an unbonded precast prestressed concrete column according to claim 2, wherein the L-shaped steel plate is provided with a rib.

4. 4. The column base structure of an unbonded precast prestressed concrete column according to claim 2 or 3, wherein the L-shaped steel plate is connected to the footing by a first fastener and to the unbonded precast prestressed concrete column by a second fastener.

5. 5. The column base structure of an unbonded precast prestressed concrete column according to claim 4, wherein the notch has a depth such that the second fastener does not protrude from the column surface of the unbonded precast prestressed concrete column.

6. 5. The unbonded precast prestressed concrete column base structure according to claim 4, wherein the first fastener and the second fastener are bolts.

7. 7. The column base structure of an unbonded precast prestressed concrete column according to claim 1, wherein the unbonded precast prestressed concrete column includes a first assembly reinforcing bar arranged in a column base portion and a second assembly reinforcing bar arranged in a portion other than the column base portion, and the first assembly reinforcing bar is arranged on the inside of the second assembly reinforcing bar.

8. 8. The column base structure of an unbonded precast prestressed concrete column according to claim 7, wherein the first assembly rebar and the second assembly rebar are discontinuously arranged and include an area where the first assembly rebar and the second assembly rebar overlap above the column base.

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