JPS595734B2 - Connection method between column base of steel frame structure and foundation concrete - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for joining a column base of a steel frame structure used in civil engineering and construction to foundation concrete.

Generally, for column bases of steel frame structures, anchor bolts are buried in the base of a reinforced concrete structure in advance, and column base metal fittings with holes that loosely fit into the anchor bolts are fixed with nuts.On the other hand, column base metal fittings are welded, bolted, etc. Generally, it is fixedly integrated with the column base.

For example, in Fig. 1, an anchor bolt 2 is buried in a foundation 1, a column base hardware 3 is placed, and it is fixed with a nut 4. They are each integrated with the column base metal fittings 3.

As shown in FIG. 3, axial compressive force N, bending moment M, and shear force Q act on the column base as stresses transmitted from the upper structure.

Further, when the upper frame receives a horizontal force, the axial compressive force N may act as a tensile force T.

Conventionally, in the design of column bases, according to the steel structure design standards established by the Architectural Institute of Japan, if the column base metal fittings are sufficiently rigid, the bottom surface of the base where the column base metal parts contact with concrete should be taken as the external dimension, and anchor bolts should be In accordance with the design of columns that are tensile reinforcing bars, the design is such that axial compressive force (N) and bending moment (M) or axial tensile force (T) and bending moment (M) are applied simultaneously.

Regarding shear force, the contact pressure between the column base hardware and concrete is multiplied by the coefficient of friction, and when this value is compared with the acting shear force, it is considered safe if it is large.

However, if the above value is small C, a washer (not shown) is inserted between the nut 4 and the column base metal fitting 3 so that the shear force is transmitted to the anchor bolt 2 shown in FIGS. 1 and 2. Countermeasures such as welding or providing protrusions on the column base hardware 3 are required.

However, there were major problems that could not be solved in the conventional connection between the base of a steel column and the foundation concrete structure.

In other words, how to achieve mechanical continuity, which is a unique problem when joining dissimilar materials such as steel and concrete.

In design calculations, using the external force set as described above, it is possible to make assumptions about the boundary and calculate, for example, a column with the bottom surface of the column base hardware as the external dimension and the anchor bolt on the tension side as the reinforcing bar. However, in reality, the boundaries are not tightly integrated but discontinuous, resulting in unexpected results.

In other words, as shown in Fig. 4, when a bending moment M is applied, it is inevitable that some rotation will occur at the boundary and the column base will tilt as shown by the broken line before it exerts its proof stress. be.

The degree of rotation mentioned above is called the "fixation degree of the column base," and a decrease in the fixity means that when a bending moment is applied to the column base, the column tilts, causing not only horizontal displacement of the upper frame. This causes an unexpectedly large stress to be generated in the upper frame.

Previous research results have disclosed that as a countermeasure against the above, it is necessary to satisfy the following three conditions.

(1) The column base metal fitting 3 is made sufficiently rigid, and the column 5 and the metal fitting 3 are brought into rigid contact.

(2) While sufficiently tightening the column base metal fittings 3 and the foundation concrete 1, a method is adopted in which the tightening effect does not decrease over time or even by the action of external forces.

Of the above, (1) can be solved by design, and (2) can be solved by careful construction.

However, (3) cannot be solved simply by tightening the nut.

In other words, even if tension is applied by engaging a nut to an anchor bolt buried in concrete, an unstable adhesion force due to the bolt surface properties, properties of the concrete, etc. acts between the anchor bolt and the concrete. Because there are
This is because the longitudinal distribution of the tension acting on the anchor bolt is unclear and the mechanical adhesion force is unstable.

5 to 7 are conceptual diagrams showing the distribution of stress generated in the anchor bolt 2 when tension is applied to the anchor bolt 2, respectively.

When the nut 4 is engaged and tightened to the anchor bolt 2 buried in the foundation concrete 1, as shown in Fig. 5, the stress is greater near the nut 4, and the stress decreases as it goes downward. There is a known tendency to

Therefore, the stress distribution range is from 4 to 4.

stay within the range. When tensile force is applied to the anchor bolt 2 over time or during the life of the structure, the adhesive force between the anchor bolt 2 and the foundation concrete 1 gradually disappears from the top to the bottom, and the stress distribution changes to The equal measurement length that changes as shown in the figure and is considered to be considered that an additional tensile force is acting on the anchor bolt 2 is as shown in FIG.

From Fig. 6. It is clear that the length becomes longer as ′.

In other words, Loteri.

' Therefore, if the initial tension is T, the degree of strain with respect to elongation is greater in Fig. 6 than in Fig. 5, so the tension acting on the anchor bolt 2 is smaller than the initial value T. It is theoretically clear that this will be the case.

In other words, even if an initial tension is applied to increase the degree of fixation of the column base, the value will decrease over time and due to the action of external forces, and as a result, the tightening of the anchor bolt 2 and nut 4 will loosen, resulting in the fixation. This results in a decrease in the degree of

The present invention solves the various drawbacks of the conventional methods as described above, prevents anchor bolts from loosening over a long period of time and even under the action of external forces, and secures the fixation of column bases at a high and stable value. The purpose of this invention is to provide a bonding method that is easy to use.

FIGS. 8 to 11 are sectional views of essential parts of an anchor bolt in an embodiment of the method of the present invention.

The anchor bolt 2 shown in FIG. 8 is buried in foundation concrete 1 with a coating layer 7 made of a soft material such as asphalt provided on the outer surface of the anchor bolt 2.
No coating layer is provided on the fixing portion 2a and threaded portion 2b.

By forming it in this way, the anchoring part 2a is firmly joined to the foundation concrete 1, but since the coating layer 7 is interposed between the outer surface of the anchor bolt 2 and the foundation concrete 1, the joint metal fittings are fixed by the nut 4. 3, the anchor bolt 2 fixed to the fixing part 2a or 2a' is not restrained by the foundation concrete 1, and the stress due to the initial tension is evenly distributed over most of the anchor bolt 2.

Therefore, the contact surface between the nut 4 and the column base metal fitting 3, the boundary surface between the bottom surface of the column base metal fitting 3 and the foundation concrete, the anchoring parts 2a, 2a
There is little decrease in the initial tension due to loosening of the nut 4, and there is almost no loosening of the nut 4 even over a long period of time, making it possible to stabilize the fixation of the column base at a high value.

Next, as shown in FIG. 9, an anchor bolt 2 is loosely fitted into a hole 8 provided in a foundation concrete 1.

In this case, the anchoring portion 2a is buried in the foundation concrete 1 in a bonded state as in FIG. 8 above.

By forming it in this way, it is possible to fix the anchor bolt 2 and create a free state, that is, an unrestricted state against elongation in the axial direction, and it exhibits the same effect as the previous embodiment.

In the case shown in FIG. 10, a pipe 9 larger than the outer diameter of the anchor bolt 2 is buried in the foundation concrete 1, so that the anchor bolt 2 is not restrained.

Furthermore, in the one shown in FIG. 11, an unrestrained member 10 made of a flexible material such as gummed tape, vinyl tape, or vinyl film is wrapped around the outer surface of the anchor bolt 2 to form an unrestrained state.

In either case, the operation is the same as that in the previous embodiment.

Next, the restoring force characteristics of the column base obtained by the method of the present invention will be explained.

FIGS. 12 and 13 are diagrams showing the relationship between the rotation angle θ and the bending moment M according to the conventional method and the method of the present invention, respectively.

That is, when an alternating bending moment M is applied to the column base in the state shown in FIG. 4, in the conventional structure shown in FIG. 12, the alternating bending moment M causes residual strain OA.

The reason for this residual strain OA is that the initial stress distribution in the anchor bolt was as shown in Fig. 5, but the alternating bending moment (M) caused tension changes in the anchor bolt, as shown in Fig. 6. Indicates that the situation is as follows.

In other words, this shows that the joint state between the anchor bolt 2 and the foundation concrete 1 is broken, the stress distribution is widened, and the introduced tension is reduced compared to the initial one.

On the other hand, in the method of the present invention shown in Figure 13,
Even after applying the alternating bending moment M, the end point of the hysteresis curve returns to the origin 0, indicating that no residual strain is generated.

In other words, this indicates that the anchor bolts are not loosened, and this is the result of the anchor bolts being buried in the foundation concrete in an unrestrained state.

FIG. 14 is a diagram showing the relationship between the bending moment M acting on the column base and the axial compressive force N.

This figure was drawn in accordance with the provisions of the Kanawa and Steel Structure Design Standards of Japan Architectural Institute, and shows the bending moment M and the axis when a column base metal fitting of a certain size is fixed with an anchor bolt that does not introduce tension. This figure illustrates the allowable proof stress of the column base when a directional compressive force N is applied.

As is clear from the figure, the axial compressive force N acting on the column
Between ONo where is small, tensile force acts on the anchor bolt and the allowable bending moment becomes small.

However, if an axial force is introduced to the anchor bolt as in the present invention, the bottom surface of the column base and the top surface of the foundation are pressed together, so the horizontal coordinate OX has moved in parallel to OX', and the allowable bending moment of the column base increases from OC to OB.

Next, the frictional resistance force of the column base, that is, the allowable shearing force, is calculated by the following formula (%) according to the steel structure design standards of Nippon Kenchiku Kanawa: where Q: Allowable shearing force 2: Tensile force N acting on the anchor bolt : Axial force on column base If axial force is introduced into the anchor bolt, the value of N on the right side of the above equation increases, so the allowable shearing force can inevitably be increased.

FIGS. 15 to 11 and 18 to 20 are diagrams showing the distribution of the pressure bonding force between the column base and the foundation surface in the conventional method and the method of the present invention, respectively.

In the conventional method shown in FIGS. 15 to 17, in rare cases where no bending moment exists, no pressing force is generated as shown in FIG. 15.

When a small bending moment M1 is applied, the crimp force distribution becomes as shown in Fig. 16, tensile force is immediately generated on the anchor bolt as shown by arrow P1, and an even larger bending moment M2 is generated. When this occurs, a very large tensile force P2 is generated in the anchor bolt as shown in FIG. 17.

Therefore, when repeated bending moments are applied to the column base, an additional tensile force is immediately applied to the anchor bolt.

In contrast, the method according to the present invention is shown in FIGS. 18 to 20.
Since the crimp force distribution is as shown in the figure, even if a small bending moment M1 is applied, no additional tensile force is generated on the anchor bolt as shown in Fig. 19, but a large bending moment M2 is applied. Only then does the additional tensile force P occur (Fig. 20).

However, the additional tensile force P is smaller than the conventional one, and even if repeated bending moments are applied to the column base, it is absorbed by changes in the pressure force as shown in Figures 18 to 20. Therefore, the additional stress acting on the anchor bolt is small, and the resistance to fatigue failure is high.

In this embodiment, an anchor bolt whose lower end is bent to form a fixing part is shown, or in addition to such a hook-shaped anchor bolt, an anchor bolt with a bearing protrusion or a bearing pressure plate provided at the lower end of the anchor pole 1 is shown. Of course, the present invention can also be applied to a structure in which adjacent anchor bolts are connected or connected by an anchor frame (FIG. 21).

Further, the means for crimping the column base metal fittings may be fastening means other than bolts and nuts, and in short, the present invention is applicable to anchor members and their fastening members or fixing members in general.

As described above, the gist of the present invention is to bury the anchor member in the foundation concrete in an unrestricted state to ensure the introduction tension of the predetermined length section of the anchor member. It can be effective.

(1) The clamping force of the column base by the anchor member and the fastening member can be maintained at a stable value over a long period of time.

(2) The column base has a high degree of fixation, and a stable value can be maintained even when external forces are applied, so reliability is high.

(3) The allowable bending stress can be increased for columns with small axial compressive force.

(4) It is possible to increase the frictional resistance force of the column base force, that is, the allowable shear force.

(5) Since the anchor member shaft and concrete, which are the main cause of relaxation, are not widely attached, relaxation can be reduced as in the conventional unbonded 7"L/stress construction method.

(6) In construction management of introduced tension, since the anchor member has a large elongation capacity, the introduced tension can be controlled by the elongation when the anchor member is tightened, that is, the rotation angle or movement distance of the tightening member. Construction management is easy.

(Since the shaft of the anchor member is long and has the same elongation capacity, the rotational capacity of the column base is large, which can improve the seismic energy absorption capacity of the entire structure, that is, the seismic performance.

(8) Even if repeated bending stress is applied, it can be absorbed by changes in the compression stress between the column base and the foundation, so the stress added to the anchor member is small and fatigue failure of the anchor member can be prevented.

(9) When the upper surface of the leveling mortar has irregularities, excessive tightening force is applied to the anchor members near the convexities in the conventional type.
In contrast, in the method of the present invention, an excessively small tightening force acts on those near the four parts, and the compressive force becomes uneven throughout the column base.
Since uniform tension is applied to all anchor members without being affected by the unevenness of the upper surface of the leveling mortar, the degree of fixation of the column base is increased and stability is achieved.

[Brief explanation of drawings]

Figures 1 and 2 are both partially cross-sectional front views showing conventional column bases, Figure 3 is an explanatory diagram showing external forces acting on the column base, and Figure 4 shows bending moment applied to the column base. FIGS. 5 to 7 are explanatory diagrams showing the stress distribution generated in the anchor bolt, respectively. FIGS. 8 to 11 are sectional views of main parts in an embodiment of the method of the present invention. Figures 12 and 13 are diagrams showing the relationship between the rotation angle and bending moment 1 for the conventional method and the method of the present invention, respectively, and Figure 14 is the relationship between the bending moment and axial compressive force acting on the column base. 15 to 17 and 18 to 20 are explanatory diagrams, FIG. FIG. 22 is a sectional view of a main part showing other embodiments of the method of the present invention. 1: Foundation concrete, 2: Anchor bolt, 5: Column base, 7: Paint layer, 8: Hole, 9: Pipe, 10: Unrestricted member.

Claims (1)

[Claims] 1. In a method of connecting the tip of a column pedestal of a steel frame structure to foundation concrete via an anchor member fixed to the foundation concrete, a predetermined section of the outer surface of the anchor member is connected to the bottom of the column pedestal. The column base is buried and fixed in the foundation concrete without being constrained in the axial direction, and the column base is placed on the foundation concrete with the upper part of the anchor member protruding while loosely fitting with the joining hardware fixed to the bottom of the column base. Attach the fastening member to the
A method for joining a column base of a steel frame structure and foundation concrete, characterized by applying a predetermined tensile force to an anchor member and applying a compressive force to the boundary between the column base hardware and the foundation concrete. 2. A method for joining a column base of a steel frame structure and foundation concrete according to claim 1, wherein a soft coating layer such as asphalt is provided on the outer surface of the anchor member to form an unrestricted state. 3 Fix the tip of the anchor member in the foundation concrete,
and Claim 1, in which the anchor member is loosely fitted into the hole provided in the foundation concrete to form an unrestrained state.
The method of joining the column base of the steel frame structure and the foundation concrete described in Section 1. 4. Connection of a column base of a steel frame structure according to claim 1, in which an unrestrained member such as a tape made of a flexible material is wrapped around the outer surface of the anchor member to form an unrestrained state, and the foundation concrete. Method. 5. A method for joining a column base of a steel frame structure and foundation concrete according to claim 1, wherein the hole is formed by a pipe into which an anchor member loosely fits. 6. A method for joining a column base of a steel frame structure and foundation concrete according to any one of claims 1 to 5, wherein the anchor member is a bolt and the fastening member is a nut.