JP5196638B2 - Column base semi-rigid joint building - Google Patents

Description

  The present invention relates to a building having a frame that concentrates plastic deformation during a large earthquake on a beam, and in particular, by semi-rigidly joining the lower end of a column on a specific floor in the building, The present invention relates to a building that can reduce bending moment and at the same time reduce damage.

  In multi-story buildings with seismic frames composed of column beams, in the event of a large earthquake, the structure in which the beam yields before the column is generally in a collapse mode compared to the structure in which the column yields before the beam. It is considered that it is preferable for earthquake resistance because of the large energy absorption until it reaches. For this purpose, there is a type of frame that concentrates plastic deformation on the beam during a large earthquake. For example, it is a frame with a precast concrete beam bonded to a column and a frame made of steel with a partially low yield point (Fig. 1). Such a building concentrates plastic deformation on a specific part of a beam (for example, a crimped joint at the end of a beam or a steel part with a low yield point) during a large earthquake, and that part becomes a plastic hinge to perform nonlinear behavior. It is known to do.

  According to the conventional column beam structure shown in FIG. 2A, the beam 210 is a precast concrete structure to which a compressive force is applied by a PC steel material (or high strength steel material) 212, and the end portion 204 of the PC steel material 212 is formed of the column 100. And is anchored on the opposite side of the beam 210. On the other hand, the reinforcing bars other than the PC steel material of the beam 210 are not anchored to the column 100, and the beam 210 is crimped to the column 100 at the end by the tension of the PC steel material. In the example shown in the figure, the pillar 100 is also made of a precast prestressed concrete structure, and the PC steel material 202 is anchored at both ends of the pillar.

  The conventional column beam structure shown in FIG. 2B is different from the column beam structure shown in FIG. 2A in that the lower end portion 222 of the column is integrated with the foundation beam, but the precast beam has a column at its end 220. It is the same in that it is crimped to the same. In the conventional column beam structure shown in FIG. 2C, a beam 232 made of a steel material having a low yield point is partially bonded to a steel bracket 231 with one end embedded in the column 230 and the other end protruding by a bolt or the like. It is a thing. In the case of this structure, the column beam may be rigidly joined, but may be one in which the rigidity of the beam at the column beam joint portion is reduced by bolt joining.

  The column beam structure shown in FIGS. 2A to 2C causes the beam to yield before the column yields in a large earthquake due to the tensile yield of PC steel or the yield of steel with a low yield point used for a part of the beam. It is a structure that is plastically deformed.

  On the other hand, the joint between the pile head and the foundation is made semi-rigid and the bending moment generated at the joint is reduced, damage to the pile head and the foundation joined to the pile head is reduced, and the design of these members is rationalized. (Patent Document 1).

In the case of the above-mentioned frame that concentrates plastic deformation on the beam in the event of a large earthquake, the rigidity of the beam inevitably decreases, so that stress tends to concentrate on the column base of the first layer as shown in FIG. 3B. Produce. This is because in a building where the ratio of the rigidity of the beam 310 to the rigidity of the column 300 (beam rigidity / column rigidity) at the column-beam joint is low, the rigidity of the column mainly resists horizontal force. In the deformation mode of the building, the deformation of the column base 302 of the first layer column is dominant simultaneously with the deformation of the beam 310. After the beam is plastically deformed, the concentration of the bending moment on the first layer column base becomes more prominent. Therefore, in the case of a frame that concentrates plastic deformation on a beam during a large earthquake, a structure that reduces stress concentration on the column base is desired.
Japanese Patent No. 3661997

  In order to solve the above-described problems, the present invention proposes a building having a frame that concentrates plastic deformation on a beam and having a reinforced concrete column whose lower end is semi-rigidly joined to a specific layer.

  In this specification, the specific layer generally refers to a so-called first floor portion, but is not limited thereto. The specific layer may be an underground floor or a floor above the first floor. Moreover, only one layer may be sufficient and a several layer may be sufficient. In this specification, the lower end portion of the column means a range of about a quarter of the floor height from the column base portion or the lower end portion of the column, preferably a range less than 10 cm from the lower end portion of the column.

  The semi-rigid joint refers to a joint in which the rigidity of the joint portion is remarkably lower than that of a so-called rigid joint in which the reinforcement of column beams having a constant cross-sectional area is penetrated and embedded in concrete. Specifically, the method of reducing the cross-sectional area of the joint part of the column compared to other parts (or notching part of the column), the method of joining only with concrete without penetrating the column reinforcement, It can be realized by a method of penetrating a steel material only in the vicinity of the center of the cross section, a method using a specific mechanical joint, or the like. The cross section of the column may be gradually reduced linearly or curvedly, but may be reduced stepwise. In order to make the transmission of the shearing force more reliable, the column preferably has an axial steel material at the semi-rigid joint. The axial steel is located in the reduced column cross section and connects the column and its underlying structure.

  The present invention further proposes a building having the above-described structure, wherein the lower end portion of the pillar of the specific layer has a horizontal sectional area that gradually decreases downward.

  In the case of this structure, the cross-sectional area of the column decreases linearly, curvilinearly, or stepwise from the top to the bottom at the bottom end of the column. Such a reduction in the column cross-sectional area may extend from the lower end of the column to, for example, about 1/4 of the floor height.

  As described above, the column whose lower end is semi-rigidly joined may be a first layer column of the building, but is not limited thereto. Moreover, it may be semi-rigidly joined over a plurality of floors. Further, it is not always necessary that the lower end portions of the columns are semi-rigidly joined for all the columns of the specific layer, and only certain columns may be semi-rigidly joined.

  The beam that supports the upper floor of the specific layer may be joined to the column by a precast crimping method, or may be a steel beam, for example, a hysteretic yield type damping structure beam using ultra-soft steel. Good. Further, it is desirable that the structure is such that the plastic deformation at the time of a large earthquake is concentrated on the beam side of the column beam joint portion, particularly in the vicinity of the column face position, like a structure in which precast beams are crimped to concrete columns throughout the building.

  Moreover, the bottom direction vicinity of the pillar of a specific layer may connect the bottom direction part of a pillar, and its lower structure as needed.

  According to the present invention, since the pillar of the specific layer is semi-rigidly joined to the lower structure at the lower end portion, the rigidity is remarkably low as compared with other portions. Therefore, not only can the bending moment generated particularly in the column base portion during an earthquake be significantly reduced, but also the column can flexibly absorb the horizontal deformation of the building. Furthermore, the rotational deformation of the lower end of the semi-rigidly joined column can compensate for bending deformation and shear deformation of the column itself, and damage to the semi-rigid joint can be reduced.

  In addition, because the axial steel is parallel to the outer surface of the column, the column maintains high yield strength and toughness despite the gradual reduction of the cross-section, making it safe even against very large earthquake motions. Shear force can be transmitted.

  When the cross-sectional area of a column in a specific layer gradually decreases downward, the deformation capacity of the column in that layer can be used to the maximum, reducing the bending moment generated during an earthquake and reducing damage to the column base. More advantageous. In general, since the maximum bending moment is generated in the column base of the first layer during an earthquake, it is advantageous to apply the present invention to the first layer, but the application of the present invention is limited to the first layer. Even if it is a basement floor or more than the second layer, the above-mentioned effects can be obtained.

  The tendency for a large bending moment to occur at the column base of the first layer during an earthquake is that when the column beam of the first layer is bonded by pressure bonding, and when the rigidity of the beam bonded by pressure bonding is low, that is, during an earthquake. This is more conspicuous in the case of a structure in which it is difficult to effectively transmit the bending moment generated in the column due to the horizontal force to the beam. Therefore, when the beam supporting the upper floor of the specific layer is joined to the beam by the precast crimping method, or when the beam supporting the upper floor of the specific layer is a steel beam, The effect is particularly remarkable.

  Depending on the structure, a tensile force may be applied to the column during an earthquake, such as when the height of the building is relatively high compared to the width. In such a case, in the vicinity of the lower end portion of the column of the specific layer, the structure in which the vertical steel material connects the lower end portion of the column and its lower structure can effectively transmit the tensile force. In this case, by concentrating the vertical steel material in the vicinity of the central portion of the horizontal cross section of the column, it is possible to effectively resist the axial force and realize a joint having low rigidity with respect to the moment.

Hereinafter, the present invention will be described in detail with reference to examples. However, it is needless to say that the examples are illustrations for helping understanding of the invention, and the present invention is not limited to these examples.
FIG. 1 is a diagram showing a framework of a building having a four-span, seven-layer column beam structure to which the present invention is applied. The column is reinforced concrete, and the column base of the first layer is semi-rigidly joined, but the column base of the upper layer has normal rigidity. The column base portion of the first layer reduces the cross-sectional area of the joint portion with the lower structure. That is, in this example, the first layer corresponds to the specific layer described above. The beam is a precast concrete structure, and the end of the beam is pressure-bonded to the column by introducing tension into the PC steel material of the beam and anchoring it to the column.

  FIG. 4A shows the first layer portion of the embodiment of the present invention shown in FIG. The prestressed concrete beam 410 applied with prestressing force by the PC steel material 412 is pressure-bonded to the column at the beam end portion 414 by anchoring the end portion 404 of the PC steel material 412 to the column. The cross-sectional area of the lower end portion of the column gradually decreases downward, and the cross-sectional area of the lowermost end portion of the column is smaller than the upper cross-sectional area. Moreover, the lower end part of the main reinforcement of the pillar remains inside the pillar and does not penetrate into the underlying structure. On the other hand, a vertical reinforcing bar 409 penetrates the column and the lower structure in the vicinity of the center of the column cross section to connect the two.

  The beam-column joint shown in FIG. 4A has high rigidity in the direction in which the beam is pressed against the column, but in the direction in which the beam is away from the column, it resists only by the rigidity of the PC steel material 412, so the rigidity is low, As a result, the bending rigidity of the beam attached to the beam-column joint is relatively small. Further, in the event of a large earthquake, the plastic deformation of the beam precedes the plastic deformation of the column due to the withdrawal or yielding of the PC steel material 412.

  FIG. 5 shows a structure in which all column beams including the first layer column base are rigidly joined (conventional frame, FIG. 5A) and the first layer column base is semi-rigidly joined by applying the present invention. It is the figure which showed typically distribution of the bending moment which generate | occur | produces at the time of an earthquake with a frame (FIG. 5B). In the conventional frame, a large bending moment is generated in the column base, whereas in the frame to which the present invention is applied, the bending moment in the column base is reduced. According to the present invention, a remarkable bending moment (stress) reduction effect can be obtained only by semi-rigidly joining the column base to the foundation beam as shown in the figure. Furthermore, in the present invention, the deformation of the column itself is reduced by the amount of deformation of the semi-rigid bonded joint, and it can be seen that the damage to the lower part of the column is further reduced according to the present invention. If the toughness and deformation capacity of the first-layer pillars are improved, the seismic likelihood during a large earthquake will be further improved.

  FIG. 4B is a conceptual diagram showing a state in which a hysteretic yielding type damping structure beam using extremely mild steel is joined to a column. In the case of the structure shown in FIG. 4B, the bending of the column base of the first layer is caused in the case of the structure shown in FIG. The moment tends to increase. Therefore, in the case of such a structure, the bending moment reduction and the damage reduction effect of the joint according to the present invention are more remarkable.

A framework diagram of a building to which the present invention is applied The column beam part of a conventional frame that concentrates plastic deformation on the beam during a large earthquake is shown. The part of the frame that concentrates plastic deformation on the beam in the event of a large earthquake shows the concentration of deformation in the event of a large earthquake. The column beam part of the frame based on this invention is shown. It is the figure which showed typically distribution of the moment which generate | occur | produces at the time of an earthquake in the frame by a prior art, and the frame by this invention.

Explanation of symbols

100 Reinforced concrete seismic frame for building 106 Lower end 110 of the first layer column 110 Columns constituting the frame (columns other than the first layer)
120, 210, 410 Beams 214, 220, 414 constituting the frame Beam end portion 408 joined to the column by pressure bonding Column lower end portion (semi-rigid contact portion)
409 Axial rebar

Claims (4)

It has a frame that concentrates plastic deformation on the beam, and has a reinforced concrete column with a semi-rigid joint at the lower end in a specific layer. sectional area of the parts is smaller than the cross-sectional area of the upper and lower ends of the main reinforcement of the pillar is stayed inside the pillar, not been intruded in the structure below the vicinity of the central portion of the cross section in the vicinity of the lower end of the column A building with a vertical rebar that penetrates into the lower structure and connects the two.   The building according to claim 1, wherein the specific layer is a first layer of a building. The building according to claim 1 or 2 , wherein the beam is made of precast concrete and is pressure-bonded to the column. The building according to claim 1 or 2, wherein the beam is made of steel, and at least part of the beam is made of a steel material having a low yield point.

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