JP2822845B2 - Structure of box-type embedded column base - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a steel structure such as a building, in which axial force, bending moment and shear force generated in a steel column can be transmitted to a foundation beam.
The present invention relates to a box-type embedded column base structure for improving the load-carrying capacity of a steel column base.

[0002]

2. Description of the Related Art In a steel structure such as a building, a column base of a steel column plays a role of smoothly transmitting an axial force, a bending moment, a shearing force, and the like acting on the steel column to a foundation beam. It is desired that the steel column has a load-bearing capacity enough to transmit the bending moment when the plastic column is completely plastically deformed, that is, the total plastic moment to the foundation beam. One of the structures of steel column bases is a type in which a steel column is directly embedded in a foundation beam, and is called an embedded column base.
Recessed column bases are constructed by constructing a steel column and arranging the surrounding foundation beams before placing concrete, and placing concrete with a box-shaped hole for building a steel column left in the foundation beam. After the steel column is built in the hole, the space around the steel column is filled with concrete, and the latter is called a boxless embedded column base. The box-type embedded column base has the advantage that the construction period is relatively short.However, since the box-shaped hole is filled later, a concrete joint is formed in the foundation beam, and a hoop-shaped part is used to prevent a drop in the load-bearing capacity of that part. However, there is a disadvantage in that a large-scale reinforcement such as stretching a reinforcing bar is required.

In order to improve this disadvantage, a steel box is used in place of a paper or the like which has been generally used until now for a box punching form for forming a box-shaped hole.
3-165626. That is, as shown in FIG. 2, a box-forming form 3 made of steel pipe (hereinafter referred to as a steel pipe form) is provided, and a main reinforcement 4 of a foundation beam is connected to the steel pipe form by welding or the like. Steel pipe is a strength member,
Since it can contribute to the transmission of the bending moment acting on the steel column, the reinforcement of this portion can be simple, and the construction period and cost can be further reduced.

[0004] The construction is performed as follows. First, the main reinforcement 4 and the stirrup 5 are arranged in a formwork for forming the foundation beam 8, and the steel pipe formwork 3 is disposed at a position where the steel column 2 is embedded. 8 is welded or arranged in a U-shape so as to surround the outer periphery of the steel pipe form, and then concrete is poured into the steel pipe form while leaving the inside thereof, and the foundation beam 8 is constructed. Next, the steel column 2 is erected inside the steel pipe form, and post-cast concrete or grout mortar 6 is cast in the gap between the steel column and the steel pipe form to complete.

[0005]

A boxless embedded column base using a steel pipe for a boxless mold (hereinafter, referred to as a boxless embedded columnar base of a steel tube form) has advantages in terms of construction period and cost. However, there are the following problems in the conventional box-pierced embedded column base of the steel pipe form type as disclosed in JP-A-63-165626.

[0006] From the idea that the moment of the steel column is directly transmitted to the foundation beam through the steel tube form, the main reinforcement of the foundation beam is connected to the steel tube form by welding or the like, so that the arrangement of the main reinforcement of the foundation beam is restricted. Yes, hindering the rational design of foundation beams.
That is, since the allowable bending moment of a reinforced concrete beam is proportional to the distance between the stress centers of bending, it is advantageous to arrange a large number of reinforcing bars at the upper and lower ends of the foundation beam because the allowable bending moment of the beam is higher. In order to connect to the frame by welding, etc., two
Only one book can be assigned to the main line. Therefore, when the allowable bending moment of the foundation beam is insufficient with two main reinforcements at the upper and lower ends, an additional main reinforcement is arranged in two or three layers in the height direction of the foundation beam and the steel pipe formwork is arranged. Will be linked to As a result, compared to the case where all the additional main reinforcements are arranged at the upper end or lower end of the foundation beam, the distance between the stress centers of the bending of the cross section becomes shorter and the allowable bending moment decreases,
It is necessary to increase the number of main bars and increase the diameter. This is inefficient and uneconomical for the design of foundation beams.

In order to increase the number of main bars at the upper and lower ends of the foundation beam, reinforcing joint plates 31 are attached to the upper and lower ends of the steel pipe formwork 3 as shown in FIG. Japanese Patent Laid-Open No. 4-49328 discloses a column base structure in which the required number of main reinforcements 4 of the foundation beam are joined. However, even if this structure can increase the number of main reinforcements arranged at the upper and lower ends, out-of-plane deformation of the steel pipe form is likely to be large, and the fixing degree of the pillar is reduced. In order to prevent a decrease in the degree of fixation, reinforcement with a diaphragm, a side stiffener, or the like is necessary, and there is a disadvantage that the cost is high.

SUMMARY OF THE INVENTION The present invention has been made in order to improve the problem of the conventional steel tube form-type boxless embedded column base, and without reinforcing the steel tube form. The purpose of the present invention is to eliminate the restriction on the arrangement of reinforcing bars and to make the design of foundation beams rational.

[0009]

SUMMARY OF THE INVENTION The object of the present invention is to provide a so-called steel pipe form-type boxless embedded column base, in which the main reinforcement of the foundation beam is arranged to the side of the steel pipe form and the anchor reinforcement is connected to the steel pipe form. In addition, this problem can be solved by wrapping the main reinforcement of the foundation beam from both sides with the anchor reinforcement, and further forming the anchor reinforcement with a structure surrounded by a shear reinforcing material such as stirrups. At this time, it is important that the main reinforcement of the foundation beam is not connected to the steel pipe form by winding or welding. Further, the anchor bar and the main bar of the foundation beam are wrapped by a length necessary for smoothly transmitting the stress from the anchor bar connected to the steel pipe form to the main bar of the foundation beam.

[0010] wrap length of the main reinforcement of the Anchors and foundation beams for concrete design strength ^{180kgf / cm 2 ~300kgf / cm 2} , the hook is provided on each of the front end of the main reinforcement of the anchor muscle and foundation beams In this case, the diameter is preferably 20 to 40 times the diameter of the anchor bar. Considering the design standard of the lap joint of the reinforcing steel in the reinforced concrete construction, if it is less than 20 times, it is difficult to smoothly transmit a bending moment, a shearing force, and the like acting on the steel column to the foundation beam. On the other hand, if it exceeds 40 times, it becomes excessively reinforced and is uneconomical. When no hook is provided, the diameter is preferably 30 to 60 times the diameter of the anchor bar. The diameter of the anchor bars may be designed by considering the portion where the anchor bars are arranged as a reinforced concrete beam whose virtual beam is the depth of embedding of the steel pipe form into the foundation beam. Further, the stirrups arranged around the anchor bars may be designed based on the design standard of the reinforced concrete beam so that the portion where the anchor bars are arranged does not yield due to the bending moment and the shearing force acting on the steel column.

The anchor bar may be a U-shaped anchor bar which is connected to the steel tube form so as to surround the outer periphery of the steel tube frame, or a U-shaped metal member and a linear anchor bar are joined by a coupler or the like. You may use what was done. Further, the linear anchor bar may be directly joined to the steel pipe form by welding or the like. Further, a circular steel pipe can be used as the steel pipe formwork.

[0012]

[Action] In the column base of the steel column configured as described above,
The bending moment and shearing force acting on the steel column are transmitted from the steel pipe form to the anchor bar, and transmitted from the anchor bar to the main bar of the foundation beam via the adhesive force of concrete. That is, the main reinforcement of the foundation beam has an indirect connection with the anchor reinforcement, and the steel pipe form has a connection through the anchor reinforcement. Therefore, there is no restriction on the arrangement of the main reinforcement of the foundation beam,
Three or more main reinforcing bars can be arranged at the upper and lower ends of the foundation beam, respectively. As a result, the foundation beam can be designed rationally.

[0013]

FIG. 1 is a diagram showing a first embodiment of the present invention. (A) is a plan view, (b) is an AA cross-sectional view. The main reinforcement 4 of the foundation beam is arranged in one step at each of the upper and lower ends of the foundation beam 8 and stopped at the frame of the steel pipe formwork 3. The U-shaped anchor bar 1 is arranged so as to surround the outer periphery of the steel pipe form 3 and wrap the main bar 4 of the foundation beam. The stirrup 5 surrounds the anchor 1.

In order to evaluate the load carrying capacity of the above embodiment,
It was compared with a conventional box-less embedded column base without steel tube formwork. The main dimensions and the like of the embodiment are as follows. The steel column 2 is a square steel pipe of □ 450 × 16, and the steel pipe formwork 3 is a square steel pipe of □ 500 × 9. The embedding depth of the steel column is 900 mm, and the embedding depth of the steel pipe formwork is 1.1.
50 mm. Concrete 7 is filled in the embedded depth of the steel column. The main reinforcement 4 of the foundation beam is a D32 rebar, and three reinforcement bars are provided at each of the upper and lower ends of the foundation beam. The anchor bar 1 is a D29 bar. The wrap length is set to 1,280 mm because neither the anchor bar nor the main bar of the foundation beam is provided with a hook.
If both the anchor bar and the main bar of the foundation beam are provided with hooks, the wrap length may be 960 mm. The stirrup 5 is a D16 reinforcing bar. On the other hand, a comparative example is as shown in FIG. 4, in which the steel column 2 is a square steel pipe of □ 450 × 16, and the embedding depth of the steel column is 1,250 mm. Concrete 7 is filled in the embedded depth of the steel column. The main reinforcement 4 of the foundation beam is a D29 rebar, and is arranged in two steps at each of the upper and lower ends of the foundation beam. Large and strong reinforcement is provided by the hoop streaks 21, the vertical streaks 22, and the studs 23. Note that stirrup 5 has D
16 rebars are used.

FIG. 5 is a diagram showing the relationship between the lateral load and the horizontal displacement at the point where the load is applied when a lateral load is actually applied to the steel column to give a moment. (A) is for an example, and (b) is for a comparative example. The yield strength of the embodiment is
Similar to the comparative example, the short-term design load of the steel column was greatly exceeded. In the restoring force characteristic, the comparative example slightly changes to a slip type near the end, whereas the embodiment draws a stable loop. Taking the ratio of the measured bending stiffness under a short-term design load to the theoretical bending stiffness in which the embedded part is considered to be completely fixed at the center of the foundation beam, the degree of fixing of the example is 0.99, and the degree of fixing is 0.99. Is a better value than the fixed degree of 0.92.

From these results, it has been clarified that the column base according to the present invention has a load carrying capacity equal to or higher than that of the ordinary boxless embedded column base. In addition, the problem of the conventional steel tube form-type boxless embedded column base, which is a limitation of being able to arrange only two bars at each of the upper and lower ends of the foundation beam, has been solved, and the design is efficient.

FIG. 6 shows a second embodiment of the present invention. In place of the U-shaped anchor bar 1 in the first embodiment, a U-shaped metal member 9 and a linear anchor bar 11 are connected to a coupler 10. This is the case where they are used by bonding. The metal mold 9 is attached to the steel pipe form 3 in advance, and after the steel pipe form is installed and the reinforcement of the foundation beam is provided, the straight anchor bar 1 is attached to the metal mold 9.
1 are joined by a coupler 10. This function is the same as that of the U-shaped anchor rebar, but when the steel pipe form is installed close to the root cutting, the load of the rebar arrangement work is reduced as compared with the U-shaped anchor rebar. .

FIG. 7 shows a third embodiment of the present invention, in which a linear anchor bar 11 is directly joined to a steel pipe form 3 by welding. Welding work is increased, but the work of arranging anchor bars becomes easier.

FIG. 8 shows a fourth embodiment of the present invention, in which a circular steel pipe 13 is used as a steel pipe formwork.
When the steel pipe form is a circular steel pipe, the U-shaped anchor bar 1 is well adapted to the U-shaped anchor bar 1, which is advantageous in transmitting the moment. When a steel pipe with ribs is used for the steel pipe form, the circular steel pipe is less likely to deform out of plane than the square steel pipe, so the circular steel pipe form has a larger gap between the rib and concrete or between the rib and grout mortar. However, there is also an advantage that the adhesive strength is good because the film cannot be formed. In this embodiment, the steel column 2 is also a circular steel tube, but the steel column may be an H-shaped steel tube or a square steel tube. Further, if a square steel pipe having a large corner R is used for the steel pipe form, there is an effect similar to using a circular steel pipe form.

[0020]

According to the present invention, in a steel tube form-type boxless embedded column base, an anchor bar is connected to the steel tube frame, and the anchor bar is connected to the main bar of the foundation beam through the adhesive force of concrete. Therefore, the number of main reinforcements arranged at the upper and lower ends of the foundation beam can be increased, and the rational design of the foundation beam can be performed. In addition, since the column base and the foundation beam can be individually designed and connected, the design period can be shortened. In addition, since what is connected to the steel pipe form is not a long main bar but a relatively short anchor bar, handling is easy, and there is an advantage also from the viewpoint of bar arrangement work.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention, in which (a)
Is a plan view, and FIG.

FIGS. 2A and 2B are diagrams showing the structure of a conventional steel tube form-type box-piercing embedded column base, wherein FIG. 2A is a plan view and FIG.

FIG. 3 is a view showing the structure of a steel tube form-type boxless embedded column base of Japanese Patent Application Laid-Open No. 4-49328 in which a steel reinforcing plate is attached to the upper and lower ends of a steel tube form.

FIGS. 4A and 4B are diagrams of a comparative example showing a structure of a boxless embedded column base that does not use a steel pipe form, where FIG. 4A is a plan view and FIG.

5A and 5B are diagrams showing a relationship between a lateral load and a horizontal displacement. FIG. 5A is a diagram showing a relationship in the first embodiment of the present invention, and FIG. 5B is a diagram showing a relationship in a comparative example.

FIG. 6 is a diagram showing a second embodiment of the present invention.

FIG. 7 is a diagram showing a third embodiment of the present invention.

FIG. 8 is a diagram showing a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... U-shaped anchor bar 2 ... Steel column 3 ... Box-framed formwork made of steel pipe (steel tube formwork) 4 ... Main bar of foundation beam 5 ... Stirrup 6 ... Grout mortar 7 ... Concrete 8 ... Foundation beam 9 ... Ko Mold 10: Coupler 11: Straight anchor bar 13: Circular steel pipe 21: Hoop bar 22: Vertical bar 23: Stud 31: Reinforcement joint plate 32: Connecting plate

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Chihiro Yasuzaki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (56) References JP-A-6-33469 (JP, A) JP-A Heihei 6-33468 (JP, A) Jiko 61-41789 (JP, Y2) (58) Fields investigated (Int. Cl. ⁶ , DB name) E02D 27/00 E04B 1/24

Claims (5)

(57) [Claims] 1. A boxless die-mounting column base part in which a steel column is embedded in a hole provided in a foundation beam, and a box-removing formwork made of steel pipe and a main reinforcement of the foundation beam arranged near the frame of the formwork. And an anchor bar connected to the formwork and arranged so as to wrap the main bar of the foundation beam from both sides, and a stirrup surrounding the anchor bar. Structure. 2. The box-pierced embedded column base structure according to claim 1, wherein the anchor bar has a U-shape surrounding the outer periphery of the box-piercing die made of steel pipe. 3. The box-pierced embedded column base structure according to claim 1, wherein the anchor bar is formed by joining a U-shaped metal member and a linear anchor bar. 4. The box-pierced embedded column base structure according to claim 1, wherein the anchor bar is formed by directly joining a linear anchor bar to a box-piercing mold made of steel pipe. 5. The box-pierced embedded column base structure according to claim 1, wherein the box-pierceed formwork made of steel pipe is a circular steel pipe.