JP7705626B2 - A method for seismic reinforcement of column bases by adding anchor bolts to concrete foundations of steel-framed factory buildings - Google Patents

Description

The present invention relates to a method for seismic reinforcement of column bases by adding anchor bolts to the concrete foundations of steel-frame factory buildings, and more specifically, to a seismic reinforcement method that can effectively increase the degree of fixation of column bases during seismic reinforcement.

Anchor bolts in steel frame factories and the like are often designed as pin column bases that are installed within the column cross section and have a low degree of fixation (rotational restraint). If the degree of fixation of the column base could be increased during earthquake reinforcement, it would be extremely effective, but this would require extensive foundation reinforcement such as excavating the foundation, which requires a lot of time, effort, and cost.

One method of seismic reinforcement for concrete foundations at the bases of columns in steel-frame factory buildings is described in Patent Document 1. This method was created by the same inventor as the present application, but is different from the present invention, which seeks to add anchor bolts.

For example, as shown in the conventional example in Figure 14, the base of the column is fixed via a base plate 10 on the concrete foundation directly below the column. Both the concrete foundation and the base plate support a light weight and are only strong enough to withstand moments caused by a not-so-large inertia. The steel column 8 is usually an H-shaped steel, and the lower edge of the web and flange of the H-shaped steel are welded to the steel base plate, and a reinforcing rib (not shown) is also welded. Then, as shown in the plan view after reinforcement in Figure 2 (a) and the plan view before reinforcement in Figure 2 (b), an appropriate number of anchor bolts 7 that fix the base plate to the concrete foundation are erected in the area surrounded by the web and flange of the H-shaped steel, in positions that do not interfere with the main reinforcement or tie bars of the concrete foundation.

Patent Publication 2022-18701

As mentioned above, when an anchor bolt is placed within the space enclosed by the web and flange of an existing column, it is considered to be a pin-jointed column base that has no bending moment resistance. If it were possible to increase the degree of fixation of this type of column base, it would be extremely effective in improving the earthquake resistance of factory buildings, which, unlike apartment buildings and office buildings, have light upper floors. The present invention was made in light of this situation, and its purpose is to provide a method for seismically reinforcing column bases by adding anchor bolts to the concrete foundations of steel-frame factory buildings.

The present invention is applied to a seismic reinforcement method for improving anchor bolt fixing in concrete foundations at the bases of columns of existing steel-frame factory buildings. Its features are as follows: (1) cutting off all or part of the reinforcing ribs of the base plate installed on the upper surface of the concrete foundation 1, (2) chipping off the backfill mortar 10a on the lower surface of the base plate 10 at the edge of the base plate, and (3) chipping off the rising concrete foundation portion 1 to expose the uppermost hoop 4B so that it can be seen. (4) Then, (5) orienting the core drill 1A so as not to hit the hoops and drilling a core drill hole 1a in the rising concrete foundation portion.
A second step of injecting epoxy resin 12 into the bottom of the core drill hole;
a third step of inserting an unbonded PC steel rod 2 having a disk-shaped anchor plate 5A as a fixing plate and a co-fastening nut 5B screwed to its tip end into the core drill hole 1a until its tip hits the bottom of the core drill hole 1a, and allowing the epoxy resin 12 to overflow onto the top surface of the anchor plate through a gap 23 (see FIG. 4(a)) between the core drill hole wall 1a and the disk-shaped anchor plate 5A;
A fourth step (see FIG. 8 ) is to inject cement milk 6 into the core drill holes and the chipped portion of the concrete foundation rise portion so as not to reach the edge portion of the base plate before the epoxy resin 12 hardens, and to center and temporarily fix the upper portion of the unbonded PC steel bar 2. A fifth step is to weld a plate enlargement plate 9 to the base plate, and then weld a replacement reinforcing rib 15 to replace the cut reinforcing rib.
A non-shrink mortar 16 is poured into the chipped portion of the edge of the base plate (see FIG. 10 ). After the mortar hardens, a square washer 17 is set on the base end of the unbonded PC steel bar 2, a tightening nut 18 is attached, and tension is introduced by the rotation angle method in the sixth step.

When the width of the concrete foundation rise is small, referring to FIG. 11, all or part of the reinforcing ribs of the base plate are cut off, the floor near the concrete foundation rise 1 is chipped off, and the floor below the chipped part is also chipped off to form the footing chipped part 1C, the top end of the footing is scraped off flat, and in this state a hole is drilled with a core drill 1A, and epoxy resin 12 is injected into the bottom of this core drill hole 1a,
An unbonded PC steel rod 2 having a disk-shaped anchor plate 5A as a fixing plate and a co-fastening nut 5B screwed to its tip end is inserted into the core drill hole 1a until its tip touches the bottom, and epoxy resin 12 is allowed to overflow onto the top surface of the anchor plate through the gap between the core drill hole wall 1a and the disk-shaped anchor plate 5A,
Before the epoxy resin 12 hardens, cement milk 6 is injected into the core drill hole (see FIG. 8), and the upper part of the unbonded PC steel bar 2 is centered and temporarily fixed.
A thick-walled seamless steel pipe 21 (see Figure 11) surrounding the center body portion of this unbonded PC steel bar 2 is set in the footing chipping portion 1C, the backfill mortar 10a on the underside of the base plate 10 is chipped off at the edge portion of the base plate, a backing metal 22 is set, a plate expansion plate 9 is welded to the base plate (see symbol 31), and an alternative reinforcing rib 15 is attached to replace the reinforcing rib that was cut out. Next, concrete is poured in the rising widening portion and the floor is restored. Finally, a square washer 17 (see Figure 10) is set on the base end side of the unbonded PC steel bar 2, a final tightening nut 18 is attached, and tension is introduced by the rotation angle method.

When the height of the foundation is increased to ensure rigidity, as shown in FIG. 12, the floor near the rising part 1 of the concrete foundation is chipped off, the top end of the footing is then scraped off flat, and in this state, the footing 19 is drilled with a core drill 1A, and epoxy resin 12 is injected into the bottom of the core drill hole 1a (see FIG. 6).
An unbonded PC steel rod 2, with a disk-shaped anchor plate 5A as a fixing plate and a fastening nut 5B fastened to its tip end, is inserted into the core drill hole 1a until its tip touches the bottom, and epoxy resin 12 is allowed to overflow onto the top surface of the anchor plate through the gap between the core drill hole wall 1a and the disk-shaped anchor plate 5A,
Before the epoxy resin 12 hardens, cement milk 6 (see Figure 9) is injected into the core drill hole, a bracket 25 for fixing the PC steel bar is attached to the steel column 8, the upper part of the unbonded PC steel bar 2 is centered and temporarily fixed to the bracket 25 for fixing the PC steel bar, a square washer 17 is set on the base end of the unbonded PC steel bar 2 and a final tightening nut 18 is attached, tension is introduced by the rotation angle method, and finally the tie bars are set and concrete is poured (see Figure 12).

In the case of a so-called semi-rigid connection in which the anchor bolt is located on the outside of the column flange, referring to FIG. 13, a core drill hole 1a is drilled next to the existing anchor bolt 7 by a core drill 1A, and epoxy resin 12 is injected into the bottom of this core drill hole.
An unbonded PC steel rod 2, with a disk-shaped anchor plate 5A as an anchor plate and a co-tightening nut 5B co-tightened at its tip, is inserted into a core drill hole 1a until its tip hits the bottom, epoxy resin 12 is allowed to overflow onto the top surface of the anchor plate through the gap between the core drill hole wall 1a and the disk-shaped anchor plate 5A, and cement milk 6 is injected into the core drill hole 1 before the epoxy resin 12 hardens. After the upper part of the unbonded PC steel rod 2 is centered and temporarily fixed, a square washer 17 is set on the base end side of the unbonded PC steel rod and a final tightening nut 18 is attached, and tension is introduced by the rotation angle method.

According to the fixing method of the present invention, the PC steel rod is installed on the outside of the column, so a greater degree of fixation and greater strength can be obtained compared to existing anchor bolts. Since an appropriate initial tension is applied to the PC steel rod, even if a tensile force is generated by the bending moment acting on the base of the column, the base plate will not deform until the applied pretension is released, and a greater degree of fixation can be obtained. In addition, the PC steel rod has an elastic range three to four times larger than that of an anchor bolt, and the elastic elongation is large, making tension management easy.

When the foundation rise width is small, the cross-sectional area of the thick steel pipe is large and the Young's modulus is about 10 times that of concrete, so this is equivalent to having a large cross-section in concrete terms. When a bending moment is applied, the compressive force acting on the root-wrapped widening section can be effectively transmitted to the footing.

When the root wrapping height is increased to ensure rigidity, the bending rigidity at the column base can be increased because the root wrapping height is increased.

In the case of semi-rigid joint column bases, the column base originally has a certain degree of bending rigidity, but the rigidity can be further increased by adding unbonded PC steel bars. In principle, the PC steel bars are installed in the same arrangement as the anchor bolts, so a width-expanding base plate is installed by welding.

FIG. 2 is a post-reinforcement elevation view of a method for seismic reinforcement of a column base by adding anchor bolts to the concrete foundation of a steel-framed factory building according to the present invention. (a) is a plan view after reinforcement, and (b) is a plan view before reinforcement. A diagram showing all processes. Processing and application state diagram of PC steel bar. This is a process diagram of procedure 1 of installing PC steel bars, showing the first step of the construction procedure. FIG. 6 is a process diagram of step 2 following FIG. 5 . A process diagram of step 3 following Figure 6. FIG. 8 is a process diagram of step 4 following FIG. 7 . FIG. 9 is a process diagram of step 5 following FIG. 8 . A process diagram of step 6 following Figure 9. Reinforcement structure when the foundation rise width is small. Reinforcement structure when increasing the root wrapping height to ensure rigidity. Reinforcement structure for semi-rigid column base. Elevation before reinforcement.

As shown in Figure 1, the present invention is a series of construction procedures shown in Figure 3, in which an unbonded PC steel bar 2 is inserted into a core drill hole 1a drilled in a rising part 1 of a concrete foundation, prestress is introduced to increase the fixation degree of the column base 3, and the column base before construction is changed from Figure 14 to the state shown in Figure 1.
The outline of the method is as follows: A shallow guide hole (not shown) for the introduction of a core drill 1A (see FIG. 5), slightly inclined if necessary, is drilled so as not to damage the top tie bar 4B of the tie bars that hoop the main reinforcement 4A in FIG. 1 from the top end of the foundation rise part 1, and further drilling is continued to form a core drill hole 1a of the required depth, after which an unbonded PC steel bar 2 equipped with a disk-shaped anchor plate 5A and a nut 5B shown in FIG. 4 is inserted (see FIG. 6). Prior to this, high-viscosity epoxy resin 12 is injected into the bottom 1b of the core drill hole 1a (the injected state is shown in FIG. 4). After that, high-strength cement milk 6 (see Fig. 4) is filled into the core drill hole 1a until it is full (see Fig. 8). (Note that the existing anchor bolts 7 are installed on the inside of the steel column 8 shown in Fig. 2(b), whereas the unbonded PC steel bars 2 are installed on the plate expansion portion 9 of the base plate (described later) on the outside of the column 8 as shown in Fig. 2(a). This provides a higher degree of fixation and a higher strength than the existing anchor bolts 7. Since an appropriate pretension is introduced into the unbonded PC steel bars 2, the unbonded PC steel bars 2 are resistant to the bending moment acting on the column base. Even if a larger tensile force is generated, the base plate 10 (see also Figure 1) will not deform until the introduced pretension is released, so a large degree of fixation can be obtained. Also, the unbonded PC steel bar 2 has an elastic range that is 3 to 4 times larger than that of the existing anchor bolt 7, so the elastic elongation margin is large. This makes tension management easy. Note that the diagram after reinforcement in Figure 2(a) shows a square washer 17 that will be used for the rotation angle method described later for the unbonded PC steel bar 2 that is to be located on the right side, but does not show the square washer that is to be located on the left side.

The method for seismic reinforcement of the column base by adding anchor bolts to the concrete foundation of a steel-framed factory building according to the present invention will be described in detail below with reference to the drawings showing the embodiment. This invention aims to improve the fixing structure of the column base 3 shown in Figure 14 to the fixing structure shown in Figure 1.
The details are as follows. It is a reinforcement method that aims to increase the fixation of the column base by inserting an unbonded prestressed concrete steel bar 2 into a core drill hole 1a drilled in the rising part 1 of the concrete foundation (see Figure 1) and introducing prestress into it, and a list of all steps is shown in Figure 3. Incidentally, the PC steel bar is a PC steel bar whose surface is covered with a special asphalt-based polymer and whose outer periphery is further protected by a polyethylene sheath or the like, and it is not restrained by the concrete even when buried in it, for example, and it can expand and contract when an axial force is applied, and it can also be pretensioned. A core drill 1A (see Figure 5) is used to drill a hole from the top of the foundation rise part 1 (see Figure 1), with or without a slight inclination so as not to damage the tie bars 4B, and a core drill hole 1a of the required depth is formed while maintaining that orientation.After that, high-viscosity epoxy resin 12 shown in Figure 4 is injected into the bottom of the hole through a pipe 14A (see step 2 in Figure 3), and an unbonded PC steel rod 2 equipped with a disk-shaped anchor plate 5A and a nut 5B is inserted.

As shown in Figure 2(a), which is a plan view of the post-reinforcement view, the unbonded PC steel bars 2 are installed on the outside of the steel column 8, and as mentioned above, a greater degree of fixation and greater strength can be obtained compared to the existing anchor bolts 7. Since an appropriate initial tension is applied to the unbonded PC steel bars 2, even if a tensile force is generated due to the bending moment acting on the base of the column, the base plate 10 will not deform until the applied pretension disappears, and a greater degree of fixation can be obtained. In addition, unbonded PC steel bars have an elastic range three to four times larger than that of the deformed rebar anchor bolts 7, so they have the advantage of greater elastic elongation and easier tension management.

Here, we will briefly discuss the unbonded PC steel rod 2. Referring to FIG. 4, the tip of the unbonded PC steel rod 2 is equipped with a disk-shaped anchor plate 5A and a nut 5B. The anchor plate 5A is female-threaded, and is fixed in position by tightening it together with the nut 5B. The diameter of the anchor plate 5A is 2 mm smaller than the diameter of the core drill hole 1a. A required amount of epoxy resin 12 is injected into the bottom of the core drill hole, and when the unbonded PC steel rod is inserted to the bottom of the hole, the resin overflows and accumulates through the gap 23 between the disk-shaped anchor plate 5A and the hole wall. After the resin 12 hardens, the rotation of the nut 5B is completely restricted, and therefore it does not rotate together even if the torque of the nut 18 (see FIG. 10) for final tightening, which will be described later, is applied when tension is introduced (hereinafter, this accommodating portion is referred to as the unbonded PC steel rod fixing portion 26).

After the epoxy resin 12 is injected, high-strength cement milk 6 is injected into the core drill hole 1a via pipe 14B (see step 4 in Figure 3) before it hardens. When a tensile force acts on the unbonded PC steel bar 2 after the cement milk has hardened, a bearing pressure equal to the tensile force is generated on the top surface of the anchor plate 5A, and this is transmitted to the inner surface of the core drill hole 1a by adhesion via the hardened cement milk 6. The internal surface area of the hole is sufficient to withstand the tensile force of the unbonded PC steel bar 2, so the tensile force is safely transmitted to the concrete foundation (footing).

The specific procedure for installing unbonded PC steel bars will be described below.
Referring to FIG. 5, in the first step, the backfill mortar 10a on the underside of the existing base plate 10 is chipped off to a point about 10 mm or more from the edge of the base plate (at the point marked with reference numeral 33), and then the foundation rising portion 1 is chipped off (at the point marked with reference numeral 34) to expose the top tie bars 4B so that they can be seen. The core of the drill is aligned above the base plate 10 at a certain distance from the flange of the steel column 8, taking into consideration the bulkiness of the drill support tool. The core drill 1A is set so as to be oriented by appropriately tilting it so as not to hit the top tie bars 4B. In this state, the drill is drilled to the required depth. As long as the top tie bars 4B are avoided, the other tie bars below will not be damaged even if drilling is continued. In addition, all or part of the reinforcing ribs 11 (see FIG. 1) of the base plate 10 installed on the top surface of the concrete foundation are cut off in advance. 13 is floor concrete.

As shown in FIG. 6, in the second step, an injection pipe 14A is erected at the bottom of the core drill hole 1a to inject the required amount of high-viscosity epoxy resin 12 into the bottom of the hole.

As shown in Figure 7, in the third step, the unbonded PC steel rod 2, which is fastened together with the disk-shaped anchor plate (fixing plate) 5A and nut 5B, is inserted into the core drill hole 1a until it hits the bottom. A small amount of resin is allowed to seep out through the gap around the disk-shaped anchor plate 5A to the extent that it covers the area directly above the anchor plate.

In the fourth step, as shown in Figure 8, the screw tip of the unbonded PC steel bar 2 is pushed in until it hits the bottom of the hole, and before the epoxy resin 12 hardens, cement milk 6 (see Figure 8) is injected up to the top of the foundation using an injection pipe 14B (see also step 4 in Figure 3) into the core drill hole 1a and the chipped part 34 of the rising part of the concrete foundation so that it does not reach the base plate edge part 33 (see Figure 6). After filling, the upper part of the unbonded PC steel bar is centered and temporarily fixed (not shown).

As shown in Figure 9(a), when the fifth step is reached, the day after filling the grout material (cement milk) 6, the plate extension plate 9A and the widening plate 9B, which are the expansion part 9, are welded (see welded part 20) to the base plate, which is a necessary part for installing the unbonded PC steel bar 2 and the alternative reinforcing rib 15, and then the alternative reinforcing rib 15 is welded to replace the reinforcing rib cut off in the first step. Note that the dashed line in Figure 9(b) indicates the top edge line, and the solid broken line indicates the chipping area.

As shown in Figure 10, in the sixth step, a formwork 28 is installed on the chipped portion 33 of the base plate and edge portion, and non-shrink mortar 16 is poured. After the mortar hardens, a square washer 17 is set on the threaded portion engraved on the upper end of the unbonded PC steel bar 2, a tightening nut 18 is attached, and pretension is introduced by the rotation angle method while the reaction force is taken by the base plate expansion portion 9 via the washer 17. In this case, this rotation angle method is a method of tightening management based on the rotation angle from the point where the thread of the unbonded PC steel bar 2 begins to mesh with the nut 18, i.e., the snug point, and is a method of introducing tension by screw feed. In particular, since the thread pitch of unbonded PC steel bar is small, the amount of screwing of the nut is small, and accurate tension is introduced.

By installing the unbonded PC steel bar 2 through steps 1 to 6 above, the degree of fixation of the column base can be effectively increased during seismic reinforcement. According to the fixing method through these steps described above, the unbonded PC steel bar is installed on the outside of the column as shown in the figure, so a greater degree of fixation and greater strength can be obtained compared to the existing anchor bolt 7. Since an appropriate pretension is introduced into the unbonded PC steel bar, even if a tensile force is generated by the bending moment acting on the column base, the base plate will not deform until the introduced pretension disappears, and a greater degree of fixation can be obtained. In addition, the unbonded PC steel bar has an elastic range three to four times larger than that of an anchor bolt, and the elastic elongation is large, making tension management easy.

Now, let us consider the case where the width of the concrete foundation rise is small. First, all or part of the reinforcing ribs of the base plate are cut off, and the floor near the foundation rise 1 is chipped off (the chipped off part indicated by the symbol 1B in the figure) as shown in Figure 11. Furthermore, the part of the floor below the chipped off part is also chipped off to form the footing chipped part 1C, and then the top of the footing is scraped off flat. In this state, the footing 19 is drilled with a core drill 1A (see Figure 5) to form the unbonded PC steel bar fixing part 26, and the unbonded PC steel bar 2 is inserted into the core drill hole 1a via Figures 6, 7, and 8. That is, in order to supply the necessary amount of high-viscosity epoxy resin 12 to the bottom of the core drill hole 1a, an injection pipe 14A is erected at the bottom of the hole and injected (see Figure 6), and an unbonded PC steel rod 2 with a disk-shaped anchor plate (fixing plate) and a nut fastened together is inserted into the core drill hole 1a until it hits the bottom of the core drill hole 1a. The resin 12 is pushed up through the gap 23 (see Figure 4) around the disk-shaped anchor plate to the extent that it covers just above the anchor plate. The screw tip of the unbonded PC steel rod 2 is pushed in until it hits the bottom of the hole, and before the epoxy resin 12 hardens, cement milk 6 is injected into the core drill hole 1a up to the top of the foundation using an injection pipe 14B (see step 4 in Figure 3), and after filling, the upper part of the unbonded PC steel rod is centered and temporarily fixed.

Then, the thick seamless steel pipe 21 surrounding the central part of the unbonded PC steel bar is set in the footing chipping section 1C, the backfill mortar on the underside of the base plate is chipped off to a point about 10 mm or more from the edge of the base plate, the backing metal 22 (see the partial removal diagram in the upper right part of Figure 11) is set, the plate extension plate 9A and the plate widening plate 9B are welded to the base plate, and the replacement reinforcement rib 15 is attached to replace the reinforcement rib that was cut off. Next, concrete is poured in the rising part 1 and the floor is restored. Finally, the square washer 17 is set on the base end side of the unbonded PC steel bar and the nut 18 is attached (see Figure 10), and tension is introduced by the rotation angle method while the plate expansion part 9 of the base plate takes the reaction force through the washer 17. The introduction of the thick seamless steel pipe 21 expands the elastic range and strengthens the compressive pressure resistance of that part, and a significant improvement in the footing function is also achieved.

In this case, where the foundation rise width is small, the cross-sectional area of the thick steel pipe is large and the Young's modulus is about 10 times that of concrete, so it is equivalent to having a large cross-section in concrete terms. When a bending moment is applied, the compressive force acting on the root-wrapping expansion section 30 can be effectively transmitted to the footing.

When the height of the root wrapping is increased to ensure rigidity, construction is performed as shown in Figure 12. The unbonded PC steel bar fixing part 26 is formed as described above, and the unbonded PC steel bar 2 is inserted into the core drill hole 1a via the above-mentioned Figures 6, 7, and 8. After that, the unbonded PC steel bar fixing bracket 25 fixed to the outer surface of the flange of the steel column 8 holds the posture of the PC steel bar 2 protruding significantly above the floor concrete 13, and the square washer 17 is set and the nut 18 is hung. The pretension is introduced by the rotation angle method while the steel column 8 via the bracket 25 takes the reaction force. Finally, the root wrapping part tie bars 4C are set, and concrete is poured after placing a formwork (not shown). Since the root wrapping is intentionally made high, the bending rigidity at the base of the column is large, and seismic reinforcement is dramatically improved.

The case of a semi-rigid joint column base is shown in Figure 13. In the case of a so-called semi-rigid joint where the anchor bolt 7 is on the outside of the steel column 8 flange, unbonded PC steel bars 2 are installed in the same width direction as the anchor bolts 7. The unbonded PC steel bars 2 are inserted into the core drill holes 1a in accordance with Figures 6, 7, and 8. This type of column base originally has a certain degree of bending rigidity, but the rigidity can be increased by adding unbonded PC steel bars 2. In principle, the unbonded PC steel bars will be installed in the same row as the existing anchor bolts 7 (see Figure 13 (b)), so a width-enlarging base plate 9C is installed by welding.

1: Concrete foundation rising part, 1A: Core drill, 1a: Core drill hole, 1B: Floor chipping part, 1C: Footing chipping part, 2: Unbonded PC steel bar, 3: Column base part, 4: Reinforcement bar, 4A: Main bar, 4B: Hoop bar, 4C: Root wrapping part hoop bar, 5A: Disk-shaped anchor plate (fixing plate), 5B: Nut, 6: High-strength cement milk, 7: Existing anchor bolt, 8: Steel column, 9: Plate expansion part, 9A: Plate extension plate, 9B: Plate widening plate, 9C: Width expansion base plate, 1 0: Base plate, 10a: Backfill mortar, 11: Reinforcement rib, 12: High viscosity epoxy resin, 13: Floor concrete, 14A, 14B: Injection pipe, 15: Alternative reinforcement rib, 16: Non-shrinkage mortar, 17: Square washer, 18: Final tightening nut, 19: Footing, 20: Welded part, 21: Thick steel pipe (thick seamless steel pipe), 22: Backing metal, 23: Gap, 25: Bracket for fixing unbonded PC steel bar, 26: PC steel bar fixing part, 28: Formwork, 30: Root wrapping widening part, 31: Welded part, 33: Base plate edge part, 34: Chiseling part of concrete foundation rising part.

Claims (4)

In an earthquake-resistance reinforcement method aimed at improving anchor bolt fixing in concrete foundations at the bases of columns of existing steel-frame factory buildings,
a first step of cutting off all or a part of the reinforcing ribs of the base plate installed on the upper surface of the concrete foundation, chipping off the backfill mortar on the lower surface of the base plate at the edge portion of the base plate, and further chipping off the rising portion of the concrete foundation to expose the uppermost tie bars so that they can be seen, and then drilling holes with a core drill;
a second step of injecting epoxy resin into the bottom of the core drill hole;
a third step of inserting an unbonded PC steel rod having a disk-shaped anchor plate as a fixing plate and a co-fastening nut screwed to its tip end until its tip touches the bottom of the core drill hole, and overflowing the epoxy resin onto the top surface of the anchor plate through a gap between the wall of the core drill hole and the disk-shaped anchor plate;
A fourth step of injecting cement milk into the core drill hole and the chipped part of the concrete foundation before the epoxy resin hardens, so as not to reach the edge part of the base plate, and centering and temporarily fixing the upper part of the unbonded PC steel bar;
a fifth step of welding a plate enlargement plate to the base plate and then welding a replacement reinforcing rib 15 to replace the cut reinforcing rib;
A method for seismic reinforcement of column bases by adding anchor bolts to the concrete foundations of steel-framed factory buildings, comprising the steps of: pouring non-shrink mortar into the chipped portion of the edge portion of the base plate; and after the mortar hardens, setting a square washer on the base end side of the unbonded PC steel bar, attaching a tightening nut to it, and introducing tension by the rotation angle method. In an earthquake-resistance reinforcement method aimed at improving anchor bolt fixing in concrete foundations at the bases of columns of existing steel-frame factory buildings,
If the width of the concrete foundation rise is small, all or part of the reinforcing ribs of the base plate are cut off, the floor near the concrete foundation rise is chipped off, and the floor below the chipped part is also chipped off to form a footing chipped part, the top edge of the footing is scraped off flat, and in this state the footing is drilled with a core drill and epoxy resin is injected into the bottom of the core drill hole,
An unbonded PC steel rod having a disk-shaped anchor plate as a fixing plate and a co-fastening nut screwed to the tip end is inserted into the core drill hole until its tip touches the bottom, and epoxy resin is allowed to overflow onto the top surface of the anchor plate through the gap between the wall of the core drill hole and the disk-shaped anchor plate,
Before the epoxy resin hardens, cement milk is injected into the core drill hole, the upper part of the unbonded PC steel bar is centered and temporarily fixed, and then a thick-walled steel pipe surrounding the middle part of the unbonded PC steel bar is set in the footing chipping section, the backfill mortar on the underside of the base plate is chipped off at the edge part of the base plate, a backing metal is set, a plate expansion plate is welded to the base plate, and a replacement reinforcing rib is attached to replace the removed reinforcing rib, concrete is poured in the rising widening part and the floor is restored, and finally, a square washer is set on the base end side of the unbonded PC steel bar, a final tightening nut is attached, and tension is introduced by the rotation angle method. This is a method for seismic reinforcement of a column base by adding anchor bolts to the concrete foundation of a steel frame factory building, characterized in that In an earthquake-resistance reinforcement method aimed at improving anchor bolt fixing to concrete foundations at the bases of steel columns of existing steel frame factory buildings,
When increasing the height of the root wrapping to ensure rigidity, the floor near the rising part of the concrete foundation is chipped off, the top of the footing is scraped off flat, and in this state the footing is drilled with a core drill, epoxy resin is injected into the bottom of the core drill hole, and an unbonded PC steel rod with a co-tightening nut at the tip end and a disk-shaped anchor plate as a fixing plate is inserted until its tip touches the bottom of the core drill hole, and the epoxy resin is allowed to overflow onto the top of the anchor plate through the gap between the wall of the core drill hole and the disk-shaped anchor plate,
This method for seismic reinforcement of column bases by adding anchor bolts to the concrete foundations of steel-frame factory buildings is characterized by the following features: before the epoxy resin hardens, cement milk is injected into the core drill holes, a bracket for fixing PC steel bars is attached to the steel column, the upper part of the unbonded PC steel bars is centered and temporarily fixed to the bracket for fixing PC steel bars, a square washer is set on the base end side of the unbonded PC steel bars and a nut for final tightening is attached, tension is introduced by the rotation angle method, and finally, tie bars are set and concrete is poured.
In an earthquake-resistance reinforcement method aimed at improving anchor bolt fixing in concrete foundations at the bases of columns of existing steel-frame factory buildings,
In the case of so-called semi-rigid connections where the anchor bolt is located on the outside of the column flange,
Removing all or a part of the reinforcing ribs of the base plate installed on the upper surface of the concrete foundation;
A core drill hole is drilled in the footing next to the existing anchor bolt using a core drill, and epoxy resin is injected into the bottom of the core drill hole.
An unbonded PC steel rod with a disk-shaped anchor plate as a fixing plate and a fastening nut fastened to the tip end is inserted until its tip touches the bottom of the core drill hole, epoxy resin is allowed to overflow onto the top surface of the anchor plate through the gap between the wall of the core drill hole and the disk-shaped anchor plate, cement milk is injected into the core drill hole before the epoxy resin hardens, and the top of the unbonded PC steel rod is centered and temporarily fixed,
A base plate enlargement plate is welded to the base plate, and a replacement reinforcing rib is welded to replace the removed reinforcing rib;
This method of earthquake-resistance reinforcement of column bases by adding anchor bolts to the concrete foundations of steel-framed factory buildings is characterized in that a square washer is set on the threaded portion engraved on the base end side of the unbonded PC steel bar, a tightening nut is attached, and tension is introduced by the rotation angle method.