JPH0130982B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved exposed type column base fixing structure for steel pipe columns in steel frame buildings, and more specifically, it is capable of withstanding large external forces such as earthquake motion. Pertains to steel pipe column base fixed structure.

In the field of architectural structures, it is customary to fix anchor bolts made of round steel with smooth surfaces, so-called plain anchor bolts, in foundation concrete, install a base plate at the lower end of a steel pipe column on top of the foundation concrete, and tighten the bolts. It is. In this case, if the anchor bolt is subjected to a pulling force, the adhesion between the concrete and the surface of the anchor bolt will be lost early, and only the anchoring effect will be due to the bent part at the lower end of the anchor bolt. The degree of fixation of is extremely reduced. Therefore, it is said that plain anchor bolts cannot be expected to secure column bases, and for this reason, when fixing column bases, a method of reinforcing the column base by surrounding it with concrete is adopted. The problem is that this involves complicated construction.

The purpose of the present invention is to provide a simple exposed fixed column base that solves the above-mentioned problems. A structure in which a base plate at the end of a column is tightened to the deformed steel bar anchor bolt and installed on a foundation concrete in which a deformed steel bar anchor bolt and a spiral reinforcement arranged around the deformed steel bar anchor bolt are buried. This invention relates to an exposed fixed column base for a steel pipe column characterized by: Note that in the present invention, the steel pipe column includes both a square steel pipe column and a circular steel pipe column.

Next, the principle of the present invention will be explained. It is thought that an axial force N in the axial direction, a bending moment M, and a shearing force Q act on the column base 1 of a steel structure building as shown in Fig. 1, and these stresses act constantly. It is well known that it becomes extremely large during earthquakes and storms.

A column base type that can safely transmit the bending moment M that occurs in the column base to the foundation when stress analysis is performed on the frame with the column base as rigid is called a fixed column base. It is also possible to take the allowable bending moment calculated from the proof stress. A type of column base designed to be able to rotate with respect to a bending moment is called a pin column base, and the present invention does not include such a pin column base.

By the way, in the case of a fixed column base as shown in Figure 1,
The axial force N is transmitted to the foundation concrete 2 by the bearing stress R of the concrete, and the shear force Q is ultimately transmitted to the foundation by the friction force between the base plate 3 and the foundation concrete 2 and the shear strength of the anchor bolts 4. is transmitted to.

Among the forces applied to the anchor bolt 4, the tensile force P generated by the bending moment M is the most important. The bending moment M of the column base 1 is transmitted to the base plate 3, and is balanced with the moment of the concrete bearing stress R and the anchor ball tensile force P generated at the bottom of the base plate.

In other words, the tensile force P generated in the anchor bolt is a pulling force acting on the anchor bolt, and is transmitted to the inside of the foundation concrete 2 by the adhesive force between the surface of the anchor bolt and the concrete.

In this case, the forces that oppose the pull-out force of the anchor bolt are the adhesion force between the surface of the anchor bolt and the concrete and the anchoring force of the bent portion of the tip of the anchor bolt. However, so-called plain anchor bolts with smooth surfaces do not have a very large adhesion force, and as described above, the adhesion force is quickly lost due to the pulling force.

In order to achieve a mechanical fit between the concrete and the anchor bolt in order to expect a large adhesion effect (adhesion force), it is conceivable to use a deformed steel bar with a tab as the anchor bolt.
There are examples of column base fixing structures using deformed steel bar anchor bolts being used as column bases in structures that support mechanical equipment. ,
At the same time, they are designed to simplify construction by being shorter than plain anchor bolts, and are not designed and constructed with consideration to large external forces such as earthquake forces. In the present invention, a deformed steel bar anchor bolt is used as an anchor bolt for fixing a column base of a building structure in consideration of tensile force (pulling force) based on a bending moment M caused by a large external force such as an earthquake force.

When used as an anchor bolt, in order to safely transmit the allowable stress Pa to the foundation concrete 2, for example, the thickness of the steel bar at the threaded portion is made thicker than the steel bar at the capping portion, or by changing its surface shape or the bar 5.
When a deformed steel bar 5 having a predetermined shape is used as an anchor bolt 41, as shown in FIG. The x-direction component of the reaction force s _x generates a force that pushes and spreads the surrounding concrete, and this force destroys the concrete around the deformed steel bar anchor bolt 41 (see Figure 3). . In the present invention, in order to prevent this, the anchor bolt 41
A spiral muscle 6 is arranged around.

In this case, as a result of the destruction of the concrete 7 inside the spiral reinforcement 6 being restrained by the spiral reinforcement 6, the breakable area of the concrete is considered to shift to the outer edge 71 of the spiral reinforcement 6,
In reality, the fracture surface of the concrete column surrounded by the spiral reinforcements 6 is a conical surface 73 that forms a 45° angle from the spiral reinforcements on the bottom surface 72, as shown in Figure 4, but multiple anchor bolts are lined up. However, since each cone overlaps and the fracture surface becomes complicated, it is better to simplify the calculation by considering it as column 7 as shown in Figure 5, and the anchor bolt, spiral reinforcement, and concrete inside it can be calculated. As something that becomes one,
For example, the diameter D of the spiral muscle can be determined by considering the pull-out strength of the entire system, and the result will be on the safer side. Practically speaking, the spiral diameter D is 10~
It will be about 20cm.

It is normal for steel structure buildings to have an appropriate amount of reinforcement in the foundation concrete of the column bases.
This reinforcement arrangement enhances the integrity of the anchor bolts, spiral reinforcements, the concrete inside them, and the surrounding foundation concrete, and has the effect of preventing overall destruction.

Next, embodiments shown in the accompanying drawings will be described.
A deformed steel bar anchor bolt 41 is placed at a predetermined position, and a spiral reinforcement 6 is placed concentrically with the anchor bolt 41. Reinforcing bars are arranged around the spiral reinforcement 6 using a conventional method. Concrete is poured and hardened as usual, and the base plate 31 at the end of the steel pipe column is placed on the foundation concrete surface 21 and fixed by tightening with anchor bolts 41.

As explained above, in the exposed type column base fixing structure of the present invention, a deformed steel bar is used for the anchor bolt, and the pulling force based on the bending moment acting on the column base is supported by the pressure on the concrete side against the flange surface of the deformed steel bar. When a large pulling force is applied to the anchor bolt, the spiral reinforcement placed around the anchor bolt unites the anchor bolt with the surrounding concrete, preventing the concrete from breaking or anchoring. This is designed to prevent anchor bolts from falling out due to cracks in the foundation concrete that occur around the bolts, and the combination of deformed steel bar anchor bolts and spiral reinforcement effectively strengthens the exposed fixed structure of column bases. Therefore, despite its simple structure, it has extremely great technical and economical effects as a reinforced structure against seismic forces and the like.

[Brief explanation of drawings]

Figure 1 is a partially fragmented elevation view to explain the various forces acting on the exposed fixed column base, and Figure 2 is a partially exploded elevation view to explain the relationship between the pull-out force and lateral pressure acting on the deformed steel bar anchor bolt. Schematic diagram showing stress transmission,
Fig. 3 is a cross-sectional view of a deformed steel bar anchor bolt showing the horizontal component of lateral pressure, and Fig. 4 shows the foundation concrete failure area assumed to be caused by the pull-out force acting on the anchor bolt according to the present invention. FIG. 5 is a perspective view showing a hypothetical column body having an outer edge formed of spiral reinforcement according to the present invention, and FIG. 6 is a partially fragmented longitudinal cross-sectional view showing an embodiment according to the present invention. N... Axial force, M... Rotating moment, Q... Shearing force, 1, 11... Column base, 2... Foundation concrete, 3, 31... Base plate, 4, 41
...Anchor bolt, 5...Deformed steel bar, 51...
6...Spiral reinforcement, 7...Concrete column, 72...Spiral reinforcement bottom surface, 73...Pyramidal surface (destruction surface).

Claims (1)

[Claims] 1. In the exposed fixed column base of a steel pipe column fixed to an anchor bolt, a deformed steel bar anchor bolt fixed in the foundation concrete and a spiral reinforcement placed concentrically around the deformed steel bar anchor bolt are buried. An exposed type fixed column base for a steel pipe column characterized by a structure in which a base plate at the end of the column base is fastened to the deformed steel bar anchor bolt and installed on a concrete foundation.