Seismic strengthening method for column foot by adding anchor bolts in the concrete foundation of a steel frame factory building

Abstract

To provide an earthquake reinforcement method capable of effectively increasing the degree of fixation of a column leg.SOLUTION: In an earthquake reinforcement method, an unbonded PC steel bar 2 is installed through: a first step of chipping back-filled mortar on a lower surface of a base plate to expose a hoop at the uppermost stage so as to allow its visual observation and to drill a hole with a core drill; a second step of injecting epoxy resin to a hole bottom; a third step of fastening a disk-like anchor plate and a nut together and inserting the unbonded PC steel bar 2 till its tip abuts with the hole bottom to make the epoxy resin overflow to an upper surface of the anchor plate through a gap between a core drill hole and the circular anchor plate; a fourth step of injecting cement milk before the epoxy resin 12 is cured and centering and temporarily fixing an upper part of the unbonded PC steel bar; a fifth step of welding a reinforcement rib after welding a base plate extension part; and a sixth step of placing shrinkage-compensating mortar in a chipped-off portion and putting a nut 18 by setting a square washer after curing to introduce tension force through a rotation angle method.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for seismic reinforcement of column feet by adding anchor bolts in the concrete foundation of a steel frame factory building. More specifically, it relates to a seismic reinforcement method that can effectively increase the fixing degree of column feet during seismic reinforcement.

Background Art

[0002] Anchor bolts in steel frame factories and the like are often designed as pin column feet installed within the column cross-section with a low fixing degree (rotational restraint). Although it would be extremely effective to increase the fixing degree of column feet during seismic reinforcement, major foundation reinforcement such as excavating the foundation is required, which requires a great deal of time, labor, and cost.

[0003] As one of the methods for seismic reinforcement of the concrete foundation at the column feet of a steel frame factory building, there is one described in Patent Document 1. This is by the same inventor as the present application, but it is different from the present invention that attempts to add anchor bolts.

[0004] For example, as in the prior example shown in FIG. 14, the column feet are fixed via a base plate 10 on the concrete foundation directly below the column. Both the concrete foundation and the base plate support a relatively light weight and are only stiff enough to withstand the moment caused by the inertia, which is not very large. The steel frame column 8 is usually an H-shaped steel, and the lower edges of the web and flange of the H-shaped steel are welded to the steel base plate, and reinforcing ribs (not shown) are also welded. And the anchor bolts 7 for fixing the base plate to the concrete foundation are erected in an appropriate number at positions that do not interfere with the main reinforcement bars and stirrups of the concrete foundation in the area surrounded by the web and flange of the H-shaped steel, as shown in the plan view after reinforcement in FIG. 2(a) and the plan view before reinforcement in FIG. 2(b).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, as mentioned above, when an anchor bolt is placed in the surrounding space formed by the web and flange of an existing column, it is regarded as a pinned column base with no bending moment resistance. If the fixity of this type of column base can be increased, it should have a great effect on improving the seismic resistance in a factory building with a lightweight upper floor, unlike an apartment building or an office building. The present invention has been made in view of this situation, and its object is to provide a method for seismic reinforcement of a column base by adding an anchor bolt in a concrete foundation of a steel-frame factory building.

Means for Solving the Problems

[0007] The present invention is applied to a seismic reinforcement method aiming to improve the fixing of anchor bolts in a concrete foundation at the column base of an existing steel-frame factory building. Its feature is, referring to FIG. 5, cutting all or part of the reinforcing ribs of the base plate installed on the upper surface of the concrete foundation 1, suspending the backing mortar 10a on the lower surface of this base plate 10 at the edge part of the base plate, and further suspending the rising part 1 of the concrete foundation so that the uppermost stirrup 4B can be visually observed and exposed. Then, in a first step, a core drill 1A is oriented so as not to hit the stirrup, and a core drill hole 1a is drilled in the rising part of the concrete foundation, In a second step, an epoxy resin 12 is injected into the bottom of the core drill hole, In a third step, an unbonded PC steel bar 2 with a disk-shaped anchor plate 5A as a fixing plate and a tightening nut 5B screwed on the tip side is inserted until the tip hits the bottom of the core drill hole 1a, and the epoxy resin 12 is allowed to overflow onto the upper surface of the anchor plate through the gap 23 (see FIG. 4(a)) between the core drill hole wall 1a and the disk-shaped anchor plate 5A, Before the epoxy resin 12 hardens, inject cement milk 6 into the core drill hole and the hanging part of the rising part of the concrete foundation so that it does not reach the edge part of the base plate. The fourth step is to temporarily fix the upper part of the unbonded PC steel bar 2 by centering (refer to Fig. 8). After welding the plate extension plate 9 to the base plate, the fifth step is to weld the alternative reinforcing rib 15 that replaces the cut reinforcing rib. Place non-shrink mortar 16 at the hanging part of the edge part of the base plate (refer to Fig. 10). After the mortar hardens, set the angle washer 17 on the base end side of the unbonded PC steel bar 2, attach the tightening nut 18, and introduce tension by the rotation angle method. This is the sixth step.

[0008] When the rising width of the concrete foundation is small, refer to Fig. 11. Cut off all or part of the reinforcing ribs of the base plate, lift the floor near the rising part 1 of the concrete foundation, and further lift the part below the floor lifting part to form the footing hanging part 1C. Plane off the top end of the footing, drill a hole with the core drill 1A in this state, inject epoxy resin 12 into the bottom of this core drill hole 1a. Insert the unbonded PC steel bar 2 with the disk-shaped anchor plate 5A as the fixing plate and the tightening nut 5B screwed on the tip side until the tip hits the bottom of the core drill hole 1a, and overflow the epoxy resin 12 onto the upper 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, inject cement milk 6 into the core drill hole (refer to Fig. 8). After temporarily fixing the upper part of the unbonded PC steel bar 2 by centering, A thick-walled seamless steel pipe 21 (see Fig. 11) surrounding the middle body part of the unbonded PC steel bar 2 is set in the footing rib removal part 1C, the backfill mortar 10a on the lower surface of the base plate 10 is suspended at the edge part of the base plate, a backing plate 22 is set, and a plate extension plate 9 is welded to the base plate (see reference numeral 31), and an alternative reinforcing rib 15 replacing the cut-off reinforcing rib is attached. Next, concrete is placed in the rising and widening part and the floor is restored. Finally, a square washer 17 (see Fig. 10) is set on the proximal end side of the unbonded PC steel bar 2, and the tightening nut 18 is fastened, and tension is introduced by the rotation angle method.

[0009] When increasing the root winding height to ensure rigidity, referring to Fig. 12, after removing the floor near the rising part 1 of the concrete foundation, the top end of the footing is flattened and cut off, and in this state, the footing 19 is drilled with a core drill 1A, and epoxy resin 12 is injected into the bottom of this core drill hole 1a (see Fig. 6). An unbonded PC steel bar 2 with a disk-shaped anchor plate 5A as a fixing plate and a tightening nut 5B tightened together at the tip side is inserted until its tip hits the bottom of the core drill hole 1a, and the epoxy resin 12 is overflowed onto the upper 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 Fig. 9) is injected into the core drill hole, a PC steel bar fixing bracket 25 is attached to the steel column 8, and after temporarily fixing the upper part of the unbonded PC steel bar 2 to the PC steel bar fixing bracket 25 with centering, a square washer 17 is set on the proximal end side of the unbonded PC steel bar 2, the tightening nut 18 is fastened, and tension is introduced by the rotation angle method. Finally, stirrups are set and concrete is placed (see Fig. 12).

[0010] In the case of a so-called semi-rigid joint where the anchor bolt is outside the column flange, referring to Fig. 13, core drill holes 1a are drilled with a core drill 1A side by side with the existing anchor bolts 7, and epoxy resin 12 is injected into the bottom of these core drill holes. An unbonded PC steel bar 2, with a disk-shaped anchor plate 5A as a fixing plate and a clamping nut 5B clamped together at the tip side, is inserted until its tip hits the bottom of the core drill hole 1a, and epoxy resin 12 is overflowed onto the upper 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 1, and after temporarily fixing the upper part of the unbonded PC steel bar 2 by centering, a square washer 17 is set on the base end side of this unbonded PC steel bar and a tightening nut 18 is fastened, and tension is introduced by the rotation angle method.

Advantages of the Invention

[0011] According to the fixing method of the present invention, since the PC steel bar is installed outside the column, a greater degree of fixation and greater load-bearing capacity can be obtained compared with existing anchor bolts. Since an appropriate initial tension is introduced into the PC steel bar, the base plate does not deform until the introduced pre-tension is released even if a tensile force is generated by the bending moment acting on the column foot, and a great degree of fixation can be obtained. In addition, the PC steel bar has an elastic range 3 to 4 times that of the anchor bolt, has a large elastic elongation allowance, and is easy to manage the tension.

[0012] When the width of the foundation rise is small, since the cross-sectional area of the thick steel pipe is large and the Young's modulus is about 10 times that of concrete, it is equivalent to having a large cross-section in terms of concrete conversion here. When a bending moment acts, the compressive force acting on the root wrapping widened part can be effectively transmitted to the footing.

[0013] When ensuring rigidity by increasing the root wrapping height, since the root wrapping height increases, the bending rigidity at the column foot can be increased.

[0014] The type column foot in the case of a semi-rigid joint column foot originally has a certain degree of bending rigidity, but the rigidity can be further increased by adding an unbonded PC steel bar. Since the PC steel bar is installed in the same arrangement as the anchor bolt in principle, a width-expanded base plate will be installed by welding.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Mode for Carrying Out the Invention

[0016] As shown in FIG. 1, the present invention inserts an unbonded PC steel bar 2 into a core drill hole 1a drilled in the concrete foundation rising part 1, introduces prestress into it to increase the fixing degree of the column base 3, and is a series of construction procedures shown in FIG. 3 from the column base before construction to the state shown in FIG. 1 from FIG. 14. The outline is as follows. In order not to damage the uppermost hoop bar 4B among the hoop bars that hoop the main reinforcement bar 4A in Fig. 1 from the top end of the foundation starting-up part 1, a guide shallow hole for introducing the core drill 1A (see Fig. 5), which is slightly inclined if necessary, is drilled (not shown), and further drilling is continued to form a core drill hole 1a with the required depth. Then, an unbonded PC steel bar 2 equipped with a disc-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). Thereafter, high-strength cement milk 6 (see Fig. 4) is filled until the core drill hole 1a is full (see Fig. 8). Incidentally, the existing anchor bolt 7 is installed inside the steel column 8 shown in Fig. 2(b), while the unbonded PC steel bar 2 is installed on the plate extension part 9 of the base plate, which will be described later, outside the column 8 as shown in Fig. 2(a). Therefore, a greater degree of fixation and greater bearing capacity can be obtained compared with the existing anchor bolt 7. Since an appropriate prestress is introduced into the unbonded PC steel bar 2, the base plate 10 (see also Fig. 1) does not deform until the introduced prestress is released even if a large tensile force is generated by the bending moment acting on the column foot part. Thus, a greater degree of fixation can be obtained. In addition, the unbonded PC steel bar 2 has an elastic range 3 to 4 times that of the existing anchor bolt 7, so the elastic elongation allowance becomes larger. Therefore, tension management becomes easier. Incidentally, in the drawing of the reinforced part in Fig. 2(a), the angle washer 17 used for the rotation angle method, which will be described later, of the unbonded PC steel bar 2 planned to be located on the right side is drawn, but the angle washer planned to be located on the left side is not drawn.

[0017] Hereinafter, a method for seismic reinforcement of a column foot part by adding an anchor bolt in the concrete foundation of a steel-frame factory building according to the present invention will be described in detail based on the drawings showing its embodiments. This invention aims to modify the fixed structure of the column foot part 3 in Fig. 14 to the fixed structure in Fig. 1. The details are as follows. This is a reinforcement method in which an un-bond prestressed concrete steel bar 2 is inserted into a core drill hole 1a drilled in the rising part 1 of the concrete foundation (see Fig. 1), and prestress is introduced to increase the fixing degree of the column base. The list of all steps is shown in Fig. 3. Incidentally, the PC steel bar is a PC steel bar coated with a special asphalt-based polymer on the surface and further protected by a polyethylene sheath or the like. For example, even when embedded in concrete, it is not restricted by the concrete and can expand and contract when an axial force acts, and prestress can also be applied. From the top end of the rising part 1 of the foundation (see Fig. 1), a core drill 1A (see Fig. 5) is used to drill a hole with a slight inclination or without inclination so as not to damage the strip bar 4B, and after forming a core drill hole 1a with the required depth while maintaining the direction, a high-viscosity epoxy resin 12 shown in Fig. 4 is injected into the bottom of the hole through a pipe 14A (see step 2 of Fig. 3), and an un-bond PC steel bar 2 equipped with a disc-shaped anchor plate 5A and a nut 5B is inserted.

[0018] As shown in Fig. 2(a), which is a plan view of the figure after reinforcement, since the un-bond PC steel bar 2 is installed outside the steel column 8, as mentioned above, a greater fixing degree and greater bearing capacity can be obtained compared to the existing anchor bolts 7. Since an appropriate initial tension is introduced into the un-bond PC steel bar 2, the base plate 10 will not deform until the introduced prestress disappears even when a tensile force is generated by the bending moment acting on the column base, and a large fixing degree can be obtained. In addition, since the un-bond PC steel bar has an elastic range 3 to 4 times that of the deformed bar anchor bolt 7, there is an advantage that the elastic elongation allowance is large and tension management is easy.

[0019] Here, the unbonded PC steel bar 2 will be briefly introduced in advance. Referring to Fig. 4, a disc-shaped anchor plate 5A and a nut 5B are equipped at the tip of the unbonded PC steel bar 2. The anchor plate 5A has an internal thread cut, and its position is fixed by tightening it together with the nut 5B. The diameter of the anchor plate 5A is 2 mm smaller than that of the core drill hole 1a. An epoxy resin 12 is injected in a required amount at the bottom of the core drill hole. When the unbonded PC steel bar is inserted to the bottom of the hole, the resin overflows and stays through the gap 23 between the disc-shaped anchor plate 5A and the hole wall. After the resin 12 hardens, the rotation of the nut 5B is completely restricted. Therefore, even if the torque of the nut 18 (refer to Fig. 10) for final tightening, which will be described later when the tensile force is introduced, acts, it will not rotate together (hereinafter, this staying part is referred to as the unbonded PC steel bar fixing part 26).

[0020] Inject the above-mentioned epoxy resin 12, and before its hardening, inject the high-strength cement milk 6 into the core drill hole 1a through the pipe 14B (refer to Step 4 in Fig. 3). When a tensile force acts on the unbonded PC steel bar 2 after the cement milk hardens, a supporting pressure equal to the tensile force is generated on the upper surface of the anchor plate 5A and is transmitted to the inner surface of the core drill hole 1a through adhesion via the hardened cement milk 6. Since the internal surface area of the hole ensures a sufficient area against the tensile force of the unbonded PC steel bar 2, the tensile force is safely transmitted to the concrete foundation (footing).

[0021] Hereinafter, specifically, the installation procedure of the unbonded PC steel bar will be described. Referring to Fig. 5, first, in the first step, the backing mortar 10a on the lower surface of the existing base plate 10 is troweled (at the location marked with reference numeral 33) until it reaches about 10 mm or more from the edge of the base plate. Next, the base rising part 1 is troweled (at the location marked with reference numeral 34) to expose the topmost strip reinforcement 4B so that it can be visually observed. Above the base plate 10, the axis of the drill is aligned considering the bulkiness of the drill support tool and a certain distance from the flange of the steel column 8. The core drill 1A is appropriately inclined and oriented so as not to hit the topmost strip reinforcement 4B and is set in this state. Drilling is carried out to the required depth in this state. This is because as long as the topmost strip reinforcement 4B is avoided, even if drilling continues, other strip reinforcements below it will not be damaged. In addition, all or part of the reinforcing ribs 11 (see Fig. 1) of the base plate 10 installed on the upper surface of the concrete foundation are cut off in advance. 13 is the floor concrete.

[0022] As shown in Fig. 6, as the second step, an injection pipe 14A is set up at the bottom of the core drill hole 1a to supply a required amount of high-viscosity epoxy resin 12 to the bottom of the hole and is injected.

[0023] As shown in Fig. 7, in the third step, the unbonded PC steel bar 2 with the disk-shaped anchor plate (fixing plate) 5A and the nut 5B tightened together is inserted until it hits the bottom of the core drill hole 1a. A small amount of resin oozes out to cover just above the anchor plate through the gaps around the disk-shaped anchor plate 5A.

[0024] In the fourth step, as shown in Fig. 8, the threaded tip of the unbonded PC steel bar 2 is pushed in until it hits the bottom of the hole. Before the epoxy resin 12 hardens, cement milk 6 (see Fig. 8) is injected to the top of the foundation using an injection pipe 14B (also refer to step 4 in Fig. 3) into the core drill hole 1a and the troweled removal part 34 of the concrete foundation rising part so as not to reach the edge part 33 of the base plate (see Fig. 6). After filling, the upper part of the unbonded PC steel bar is centered and temporarily fixed (not shown).

[0025] As shown in Fig. 9(a), when reaching the fifth step, after welding the enlarged portion 9, which is the plate extension 9A and the widened plate 9B, to the base plate, which is a member necessary for installing the unbonded PC steel bar 2 and the alternative reinforcing rib 15, after the filling of the grout material (cement milk) 6, on the day after the filling, the alternative reinforcing rib 15 that replaces the reinforcing rib cut in the first step is welded (see the welded portion 20). Note that the dashed line in Fig. 9(b) represents the top edge line, and the solid line broken line represents the hatched range.

[0026] As shown in Fig. 10, in the sixth step, a formwork 28 is installed at the hanging portion 33 of the base plate and the edge portion, and the non-shrinking mortar 16 is placed. 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, and the tightening nut 18 is fastened. While taking the reaction force at the enlarged portion 9 of the base plate through the washer 17, the prestress is introduced by the rotation angle method. This rotation angle method, in this case, is a method of controlling the tightening by the rotation angle from the point where the thread of the unbonded PC steel bar 2 starts to mesh with the nut 18, that is, the snag point, and is a method of introducing the tension by the screw feed. In particular, since the unbonded PC steel bar has a small thread pitch, the screwing amount of the nut is also small, and an accurate tension is introduced.

[0027] By the installation procedure of the unbonded PC steel bar 2 through the above first to sixth steps, the fixing degree of the column base can be effectively increased during seismic reinforcement. According to the fixing method through these steps described above, since the unbonded PC steel bar is installed outside the column as shown in the figure, a larger fixing degree and a larger load-bearing capacity can be obtained compared with the existing anchor bolts 7. Since an appropriate prestress is introduced into the unbonded PC steel bar, the base plate does not deform until the introduced prestress disappears even if a tensile force is generated by the bending moment acting on the column base portion, and a large fixing degree can be obtained. In addition, the unbonded PC steel bar has an elastic range 3 to 4 times that of the anchor bolt, has a large elastic elongation allowance, and is easy to manage the tension.

[0028] Incidentally, the case where the rising width of the concrete foundation is small will be described. First, all or part of the reinforcing ribs of the base plate are cut off, and as shown in Fig. 11, the floor near the rising part 1 of the foundation is chiseled off (the chiseled part indicated by reference numeral 1B in the figure). Further, the part below the floor chiseled part is also chiseled to form a footing chiseled part 1C. After that, the top end of the footing is flattened by chiseling. In this state, the footing 19 is drilled with a core drill 1A (see Fig. 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 through Figs. 6, 7, and 8. That is, an injection pipe 14A is set up at the bottom of the hole to supply a necessary amount of high-viscosity epoxy resin 12 to the bottom of the core drill hole 1a (see Fig. 6), and the unbonded PC steel bar 2, which is a co-fastened disc-shaped anchor plate (fixing plate) and nut, 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 to cover directly above the anchor plate through the gap 23 (see Fig. 4) around the disc-shaped anchor plate. The threaded 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 is injected into the core drill hole 1a up to the top end of the foundation using an injection pipe 14B (see step 4 in Fig. 3). After the filling, the upper part of the unbonded PC steel bar is centered and temporarily fixed.

[0029] After that, a thick seamless steel pipe 21 surrounding the middle part of the unbonded PC steel bar is set in the footing rib removal part 1C, and the backing mortar on the lower surface of the base plate is suspended until it enters about 10 mm or more from the edge of the base plate. A backing plate 22 (see the partial extraction view in the upper right part of Fig. 11) is set, and a plate extension plate 9A and a plate widening plate 9B are welded to the base plate, and an alternative reinforcing rib 15 replacing the cut reinforcing rib is attached. Next, the concrete of the rising part 1 is placed and the floor is restored. Finally, a square washer 17 is set on the base end side of the unbonded PC steel bar and a nut 18 is fastened (see Fig. 10), and while taking the reaction force with the plate enlarged part 9 of the base plate through the washer 17, the tension is introduced by the rotation angle method. By introducing the thick seamless steel pipe 21, the elastic range of that part is enlarged and the compressive strength is enhanced, and a remarkable improvement in the footing function is also achieved.

[0030] In this case where the rising width of the foundation is small, since the cross-sectional area of the thick steel pipe is large and the Young's modulus is about 10 times that of concrete, it is equivalent to having a large cross-section in terms of concrete conversion here. When a bending moment acts, the compressive force acting on the collar widening part 30 can be effectively transmitted to the footing.

[0031] Furthermore, when the collar height is increased to ensure rigidity, the construction is carried out as follows shown in Fig. 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 through Figs. 6, 7, and 8 above. After that, the posture of the PC steel bar 2 protruding significantly above the floor concrete 13 is held by the unbonded PC steel bar fixing bracket 25 fixed to the outer surface of the flange of the steel column 8, a square washer 17 is set and a nut 18 is fastened, and the prestress is introduced by the rotation angle method while taking the reaction force with the steel column 8 through the bracket 25. Finally, the collar part stirrup 4C is set, a formwork (not shown) is arranged, and the concrete is placed. Since the collar is intentionally made high, the bending rigidity at the column base is large and a dramatic improvement in seismic reinforcement is achieved.

[0032] In the case of a semi-rigid connection column base, it is shown in Fig. 13. In the case of a so-called semi-rigid connection where the anchor bolts 7 are outside the flange of the steel column 8, the unbonded PC steel bars 2 are installed side by side in the same width direction as the anchor bolts 7. The unbonded PC steel bars 2 are inserted into the core drill holes 1a according to Figs. 6, 7, and 8. This type of column base originally has a certain flexural rigidity, but the rigidity can be increased by adding the unbonded PC steel bars 2. Since the unbonded PC steel bars are generally installed in the same arrangement as the existing anchor bolts 7 (see Fig. 13(b)), a base plate 9C for width expansion is installed by welding.

Description of Symbols

[0033] 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: Reinforcing bar, 4A: Main reinforcement, 4B: Stirrup, 4C: Hooping stirrup, 5A: Disk-shaped anchor plate (fixing plate), 5B: Nut, 6: High-strength cement milk, 7: Existing anchor bolt, 8: Steel column, 9: Plate extension part, 9A: Plate extension plate, 9B: Plate width expansion plate, 9C: Base plate for width expansion, 10: Base plate, 10a: Backfilling mortar, 11: Reinforcing rib, 12: High-viscosity epoxy resin, 13: Floor concrete, 14A, 14B: Injection pipe, 15: Alternative reinforcing rib, 16: Non-shrinking mortar, 17: Angle washer, 18: Tightening nut, 19: Footing, 20: Welded part, 21: Thick-walled steel pipe (thick-walled seamless steel pipe), 22: Backing plate, 23: Gap, 25: Bracket for fixing unbonded PC steel bar, 26: Fixing part of PC steel bar, 28: Formwork, 30: Hooping width expansion part, 31: Welded part. 33: Edge part of base plate, 34: Chipping part of concrete foundation rising part.

Claims

1. In a seismic reinforcement method aiming to improve the anchor bolt fixing in the concrete foundation at the column base of an existing steel factory building, all or part of the reinforcing ribs of the base plate installed on the upper surface of the concrete foundation are cut off, the backfill mortar on the lower surface of the base plate is suspended at the edge part of the base plate, and further the rising part of the concrete foundation is also suspended so that the topmost stirrup bar is exposed and visible. Then, a first step of drilling with a core drill is carried out. A second step of injecting epoxy resin into the bottom of the core drill hole. An unbonded PC steel bar with a disk-shaped anchor plate as a fixing plate and a tightening nut screwed on the tip side is inserted until its tip hits the bottom of the core drill hole, and the epoxy resin is overflowed onto the upper surface of the anchor plate through the gap between the core drill hole wall and the disk-shaped anchor plate. This is the third step. Before the epoxy resin hardens, cement milk is injected into the suspended part of the core drill hole and the rising part of the concrete foundation so as not to reach the edge part of the base plate, and the upper part of the unbonded PC steel bar is temporarily fixed with centering. This is the fourth step. After welding a plate extension plate to the base plate, an alternative reinforcing rib 15 replacing the cut-off reinforcing rib is welded. This is the fifth step. Non-shrink mortar is placed in the suspended part of the edge part of the base plate. After the mortar hardens, a square washer is set on the base end side of the unbonded PC steel bar and the tightening nut is fastened, and tension is introduced by the rotation angle method. This is the sixth step. A method for seismic reinforcement of the column base by adding anchor bolts in the concrete foundation of a steel factory building, characterized by the PC steel bar installation procedure passing through these steps.

2. In a seismic reinforcement method aiming to improve the anchor bolt fixing in the concrete foundation at the column base of an existing steel factory building, When the rising width of the concrete foundation is small, all or part of the reinforcing ribs of the base plate are cut off, the floor near the rising part of the concrete foundation is suspended, and further, the part below this floor suspension part is also suspended to form a footing suspension part. The top end of the footing is planed flat. In this state, the footing is drilled with a core drill, epoxy resin is injected into the bottom of the core drill hole. An unbonded PC steel bar with a disc-shaped anchor plate as a fixing plate and a clamping nut screwed onto the tip side is inserted until its tip hits the bottom of the core drill hole, and epoxy resin is overflowed onto the upper surface of the anchor plate through the gap between the core drill hole wall and the disc-shaped anchor plate. Before the epoxy resin hardens, cement milk is injected into the core drill hole. After temporarily fixing the upper part of the unbonded PC steel bar with centering, a thick-walled steel pipe surrounding the middle part of the unbonded PC steel bar is set in the footing chamfering part. The backing mortar on the lower surface of the base plate is balanced at the edge part of the base plate, a backing plate is set, a plate extension plate is welded to the base plate, and an alternative reinforcing rib replacing the cut reinforcing rib is attached. Next, concrete is placed in the rising and widening part and the floor is restored. Finally, a square washer is set on the base end side of the unbonded PC steel bar, the tightening nut is tightened, and tension is introduced by the rotation angle method. A method for seismic reinforcement of column feet by adding anchor bolts in the concrete foundation of a steel structure factory building is characterized by this.

3. In a seismic reinforcement method aiming to improve the fixing of anchor bolts in the concrete foundation of column feet composed of steel columns of an existing steel structure factory building, When increasing the height of the root wrapping to ensure rigidity, after removing the floor near the rising part of the concrete foundation, the top end of the footing is flattened and cut off, 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 bar with a disc-shaped anchor plate as a fixing plate and a clamping nut screwed onto the tip side is inserted until its tip hits the bottom of the core drill hole, and epoxy resin is overflowed onto the upper surface of the anchor plate through the gap between the core drill hole wall and the disc-shaped anchor plate. Before the epoxy resin hardens, cement milk is injected into the core drill hole. A bracket for fixing the PC steel bar is attached to the steel column. After temporarily fixing the upper part of the unbonded PC steel bar with centering to this bracket for fixing the PC steel bar, a square washer is set on the base end side of the unbonded PC steel bar, the tightening nut is tightened, tension is introduced by the rotation angle method, and finally, stirrups are set and concrete is placed. A method for seismic reinforcement of column feet by adding anchor bolts in the concrete foundation of a steel structure factory building is characterized by this.

4. In a seismic reinforcement method aiming to improve the fixing of anchor bolts in the concrete foundation at the column base of an existing steel-framed factory building, in the case of a so-called semi-rigid connection where the anchor bolts are outside the column flange, all or part of the reinforcing ribs of the base plate installed on the upper surface of the concrete foundation are cut off, core drill holes are drilled in the footing by a core drill horizontally to the existing anchor bolts, and epoxy resin is injected into the bottom of the core drill holes, an unbonded PC steel bar with a disc-shaped anchor plate as a fixing plate and a tightening nut fastened together at the tip side is inserted until its tip hits the bottom of the core drill hole, and the epoxy resin is overflowed onto the upper surface of the anchor plate through the gap between the core drill hole wall and the disc-shaped anchor plate. Before the epoxy resin hardens, cement milk is injected into the core drill hole. After temporarily fixing the upper part of the unbonded PC steel bar in alignment, a base plate extension plate is welded to the base plate and an alternative reinforcing rib replacing the cut-off reinforcing rib is welded, a square washer is set on the threaded part engraved on the proximal end side of the unbonded PC steel bar, the tightening nut is fastened, and tension is introduced by the rotation angle method. A method for seismic reinforcement of the column base by adding anchor bolts in the concrete foundation of a steel-framed factory building, characterized by the above.

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