JP7536396B2 - Methods for reinforcing the foundation footing of existing bridge piers - Google Patents

Description

This invention relates to a method for reinforcing foundation footings in existing bridge piers.

To increase the bearing capacity of the ground, the foundation of the pier is extended horizontally to form a foundation footing, which is integrated with the heads of multiple foundation piles that extend to an appropriate bearing layer.

The method described in Patent Document 1 is known as a method for strengthening the earthquake resistance of existing bridge piers. This involves adding piles around the foundation footing of the existing bridge pier, and connecting the additional concrete poured into the heads of the additional piles to the foundation footing with PC steel, or fastening the heads of the additional piles together with connecting materials that are placed over the top surface of the foundation footing.

Japanese Patent Application Publication No. 03-286028

However, the pile addition method described in Patent Document 1 is large-scale, which increases the construction period and costs, and requires a large construction yard.

In addition, when strengthening the earthquake resistance of existing bridge piers, it is common to improve the pier's strength (by increasing its thickness, etc.) from the perspective of ease of construction. However, if the pier's strength is improved, in the event of an earthquake larger than the set expected load, the seismic force transmitted from the pier to the foundation will also increase, and there is a risk that the foundation will be damaged first.

Therefore, seismic reinforcement of the foundation footing was considered. Specifically, yielding of the footing occurs mainly when a horizontal seismic force acts on the head of the pier, generating a bending moment in the pier, which causes excessive tensile force to act on the lower reinforcing bars in the foundation footing, causing the lower reinforcing bars to yield. Therefore, the following reinforcement plans (1) to (4) were considered. However, each plan has its own problems.

(1) Adding the lower rebar from the side of the footing through post-construction. This requires excavation of the side of the footing, and also requires driving anchors into the ground along the entire length from the side of the footing, making the installation of the anchors difficult.
(2) Increasing the thickness of the top surface of the footing The effective height of the lower reinforcing bars will increase, but the amount of reinforcing bars cannot be increased, so the required thickness will be excessive.
(3) Increasing the thickness of the underside of the footing This will require excavation of the underside of the footing, which will be a major undertaking.
(4) Prestressing using PC steel: Since the piles are restrained, there is a risk that compressive force will not be applied, and the effectiveness of this method is unclear.

The present invention was made in consideration of these circumstances, and aims to provide a foundation footing reinforcement method that can sufficiently reinforce the foundation footing of an existing bridge pier with relatively simple construction work.

The method for reinforcing the foundation footing of an existing bridge pier according to the present invention comprises the steps of:
an excavation process for excavating the ground around the existing pier until the top surface of the foundation footing is exposed;
An anchor installation process in which anchors are installed on the pier side surface and the foundation footing top surface exposed by the excavation;
A reinforcement structure installation process in which a reinforcement structure including a first joint surface that joins to the pier side surface and a second joint surface that joins to the foundation footing upper surface is installed at the corner between the pier side surface and the foundation footing upper surface, and integrated with the anchor reinforcement;
A backfilling process of backfilling the excavated area so as to cover the reinforcement structure;
The present invention is characterized by comprising:

Here, the reinforcing structure may be a steel reinforcing structure.
In this case, the reinforcement structure installation step is a steel reinforcement structure installation step in which a steel reinforcement structure including a vertical plate portion pressed against and joined to the side surface of the pier and a horizontal plate portion pressed against and joined to the upper surface of the foundation footing is used as the reinforcement structure, the steel reinforcement structure is placed at the corner between the side surface of the pier and the upper surface of the foundation footing, and fixed with the anchor bars. The vertical plate portion and the horizontal plate portion each have a mounting hole through which the anchor bars pass, and the mounting hole of the vertical plate portion is a long hole that is long in the direction in which the horizontal plate portion is pressed against the upper surface of the foundation footing, and the mounting hole of the horizontal plate portion is a long hole that is long in the direction in which the vertical plate portion is pressed against the side surface of the pier .

According to the present invention, by installing and integrating a reinforcing structure at the corner between the side of the pier and the top surface of the foundation footing, the rigidity area is expanded, the bending moment is reduced by reducing the cantilever span, and the tensile force acting on the lower reinforcing bars in the foundation footing due to seismic forces is reduced, thereby achieving sufficient earthquake resistance reinforcement.
Furthermore, excavation only needs to be carried out up to the top surface of the foundation footing, which reduces construction costs and time.

A process diagram of a foundation footing reinforcement method shown as the first embodiment of the present invention. Plan view of FIG. A diagram showing the effect of adding corbel concrete A process diagram of a foundation footing reinforcement method shown as a second embodiment of the present invention. Plan view of FIG. Perspective view of steel reinforcement structure

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a process diagram of a foundation footing reinforcing method according to a first embodiment of the present invention.

Referring to Figure 1(a), pier 1 is made of reinforced concrete (RC) and forms part of an existing bridge in service, supporting the bridge girder via a head (bearing part) not shown in the figure.

The foundation of the pier 1 extends horizontally to form a foundation footing 2 of a predetermined thickness in order to increase the bearing capacity of the ground.
The foundation of the pier 1 also comprises a number of foundation piles 3 which are integral with the foundation footing 2 at their heads and extend from the bottom of the foundation footing 2 to a suitable bearing layer.

The method for reinforcing the foundation footing 2 of such a pier (existing pier) 1 is explained using the process diagrams in Figures 1(a) to (c).

FIG. 1(a) shows the drilling process and the surface chipping process.
In the excavation process, the ground G around the pier 1 is excavated until the top surface 2a of the foundation footing 2 is exposed. The excavation depth varies depending on the installation depth of the foundation footing 2, but is generally about 1 to 5 m. Depending on the excavation depth, a retaining wall is constructed to surround the excavated area, and then the inside is excavated. If there is sufficient space around, a gently sloping slope can be provided, making the retaining wall unnecessary.

After the excavation process, the surface moves to the chipping process.
In the surface chipping process, the pier side surface 1a and the foundation footing top surface 2a exposed by excavation (strictly speaking, the area where the haunch concrete will be poured, which will be described later; H in the figure) are chipped (chipped) by impact with a chipping hammer or water jet, etc. This is a surface roughening process (roughening) that creates irregularities of about 1 mm on the surface in order to improve the adhesion of the joint with the haunch concrete, which will be described later.

FIG. 1(b) shows the anchor installation process.
In the anchor bar installation process, a number of anchor bars (joints for fixing) 4 are installed on each of the pier side surface 1a and the foundation footing upper surface 2a (strictly speaking, the area where haunch concrete will be poured, which will be described later) that have been exposed by excavation.

When installing the anchor bars 4, first drill holes at the planned locations for installing the anchor bars on the pier side surface 1a and the top surface 2a of the foundation footing. That is, holes are drilled horizontally (or at a downward incline) on the pier side surface 1a, and vertically on the top surface 2a of the foundation footing.

After drilling the holes, cement milk is poured into the holes, and one end of the anchor bar 4 is inserted into the holes into which the cement milk has been poured, and the two are integrated together. This causes the other end of the anchor bar 4 to protrude from the pier side surface 1a and the top surface 2a of the foundation footing.

FIG. 1(c) shows the process of pouring haunch concrete and backfilling.
In the haunch concrete pouring process, the anchor bars 4 protruding from the pier side surface 1a and the foundation footing upper surface 2a are wrapped around the corner formed by the pier side surface 1a and the foundation footing upper surface 2a, and concrete is poured in place in at least a haunch shape.

"At least haunch-shaped" basically means that the concrete should be poured into the corner in a haunch shape, i.e., in a roughly triangular shape when viewed from the side, but as long as it includes a triangular shape, it can also be a square shape, although this is redundant.

In addition, reinforcement (installation of haunch reinforcement) may be performed in the pouring area prior to pouring the concrete.

In this way, the haunch concrete 5 is constructed as a reinforcing structure at the corner between the pier side surface 1a and the foundation footing upper surface 2a, including a first joint surface that joins to the pier side surface 1a and a second joint surface that joins to the foundation footing upper surface 2a.

Fig. 2 is a plan view of Fig. 1(c). The haunch concrete 5 has a truncated quadrangular pyramid shape so as to surround the four pier side surfaces 1a.

The haunch concrete pouring process includes a formwork installation process that is performed before pouring the concrete, and a formwork removal process that removes the formwork after pouring the concrete.

After the haunch concrete pouring process, the backfilling process begins.
In the backfilling step, the area excavated in the excavation step is backfilled up to the original ground G line so as to cover the haunch concrete 5 as the reinforcing structure.

Figure 3 shows the effect of adding haunch concrete, and shows the analysis results of cracks (shifts) that occur in the foundation footing 2 when a horizontal seismic force acts on the head of the pier 1 in the direction of the arrow F shown.

When an earthquake force acts on the head of pier 1 in the direction of arrow F, a bending moment is generated in pier 1, and a large tensile force is generated at the lower rebar position on the right side of the foundation footing 2 in the diagram. However, compared to the case without haunch in Figure 3(a), the area of cracks (displacement) can be significantly reduced in the case with haunch in Figure 3(b).

In this way, by installing and integrating a reinforcing structure (haunch concrete 5) at the corner between the pier side surface 1a and the foundation footing top surface 2a, the rigidity area is expanded, the bending moment is reduced by reducing the cantilever span, and the tensile force acting on the lower rebar in the foundation footing 2 due to seismic forces is reduced, thereby achieving sufficient seismic reinforcement.

In other words, by setting the rigid zone, the inspection section position is brought closer to the piles, and the bending moment can be reduced by reducing the cantilever span. Also, by increasing the thickness of the member at the inspection section position, the tensile stress on the lower rebar can be reduced. Furthermore, by bringing the shear inspection position closer to the piles, the shear strength can be increased due to the effect of the shear span ratio.

FIG. 4 is a process diagram of a foundation footing reinforcing method according to a second embodiment of the present invention.
FIG. 4(a) shows the drilling process.
In the excavation step, similarly to FIG. 1(a), the ground G around the pier 1 is excavated until the upper surface 2a of the foundation footing 2 is exposed.
After the excavation process, the surface is not subjected to chipping treatment and the process moves to the anchor reinforcement installation process.

Figure 4 (b) shows the anchor bar installation process. In the anchor bar installation process, similar to Figure 1 (b), multiple anchor bars (anchor bolts) 4 are installed on the pier side surface 1a and the foundation footing top surface 2a exposed by excavation (strictly speaking, the installation area of the steel reinforcement structure described later).

FIG. 4(c) shows the steel reinforcement structure installation process and backfilling process.
In the steel reinforcement structure installation process, a steel reinforcement structure 6 is placed at the corner between the pier side surface 1 a and the foundation footing upper surface 2 a and fixed in place with anchor bars 4 .

As shown in Fig. 4(c), as well as Fig. 5 (plan view of Fig. 4(c)) and Fig. 6 (perspective view of steel reinforcement structure 6), the steel reinforcement structure 6 is made of sheet metal and comprises a vertical plate portion 6a joined to the pier side surface 1a, a horizontal plate portion 6b joined to the foundation footing upper surface 2a, and a number of triangular reinforcing plate portions 6c arranged between the vertical plate portion 6a and the horizontal plate portion 6b and connecting them in the form of ribs.

The steel reinforcement structure 6 also has mounting holes 7 on the vertical plate portion 6a and horizontal plate portion 6b through which the anchor bars 4 protruding from the pier side surface 1a and the foundation footing top surface 2a pass.

Therefore, in the steel reinforcement structure installation process, the vertical plate portion (first joint surface) 6a of the steel reinforcement structure 6 is pressed against the pier side surface 1a, the anchor bar 4 protruding from the pier side surface 1a is inserted into the mounting hole 7 of the vertical plate portion 6a, and the lock nut 8 is screwed onto the end of the anchor bar 4 to tighten and fix it in place.

At the same time, the horizontal plate portion (second joint surface) 6b of the steel reinforcement structure 6 is pressed against the upper surface 2a of the foundation footing, the anchor bar 4 protruding from the upper surface 2a of the foundation footing is inserted into the mounting hole 7 of the horizontal plate portion 6b, and the lock nut 8 is screwed onto the end of the anchor bar 4 to tighten and fix it in place.

To facilitate this installation, it is advisable to make at least one of the mounting holes 7 in the vertical plate portion 6a or the horizontal plate portion 6b a long hole. In this case, the mounting hole 7 in the vertical plate portion 6a is a long hole that is long in the up-down direction (the direction in which the horizontal plate portion 6b is pressed against it), and the mounting hole 7 in the horizontal plate portion 6b is a long hole that is long in the left-right direction (the direction in which the vertical plate portion 6a is pressed against it).

In this way, a steel reinforcement structure 6 is installed at the corner between the pier side surface 1a and the foundation footing upper surface 2a as a reinforcement structure including a first joint surface (vertical plate portion 6a) that joins to the pier side surface 1a and a second joint surface (horizontal plate portion 6b) that joins to the foundation footing upper surface 2a.

As can be seen from Figure 5, four steel reinforcement structures 6 are used, one on each of the four sides 1a of the pier 1.

After the steel reinforcement structure installation process, the backfilling process begins.
In the backfilling process, the area excavated in the excavation process is backfilled up to the original ground G line so as to cover the steel reinforcing structure 6 as the reinforcing structure.

Even if such a haunch-shaped steel reinforcement structure 6 is used, the same effect can be obtained as with haunch concrete 5.

In addition, instead of cast-in-place concrete, a precast concrete reinforcement structure can also be used.

It goes without saying that the illustrated embodiments are merely schematic examples of the present invention, and that the present invention encompasses various modifications and variations that may be made by those skilled in the art within the scope of the claims, in addition to those directly shown in the described embodiments.
The claims as originally filed were as follows:
[Claim 1]
A method for reinforcing a foundation footing in an existing bridge pier, comprising:
An excavation process of excavating the ground around the existing pier until the top surface of the foundation footing is exposed;
An anchor installation process in which anchors are installed on the pier side surface and the foundation footing top surface exposed by the excavation;
A reinforcement structure installation process in which a reinforcement structure including a first joint surface that joins to the pier side surface and a second joint surface that joins to the foundation footing upper surface is installed at the corner between the pier side surface and the foundation footing upper surface, and integrated with the anchor reinforcement;
A backfilling process of backfilling the excavated area so as to cover the reinforcement structure;
A method for reinforcing the foundation footing of an existing bridge pier, including:
[Claim 2]
2. The method for reinforcing a foundation footing of an existing pier according to claim 1, wherein the reinforcing structure installation step is a concrete pouring step of wrapping the anchor bars around the side surface of the pier and the top surface of the foundation footing, pouring concrete into at least a haunch shape, and constructing the reinforcing structure by pouring concrete into the place.
[Claim 3 ]
The method for reinforcing a foundation footing of an existing pier according to claim 2, further comprising a surface chipping step of chipping the concrete surfaces of the pier side surface and the top surface of the foundation footing exposed by the excavation after the excavation step and before the concrete pouring step.
[Claim 4]
The reinforcement structure installation step uses a steel reinforcement structure including a vertical plate portion joined to the side surface of the pier and a horizontal plate portion joined to the upper surface of the foundation footing as the reinforcement structure,
2. The method for reinforcing the foundation footing of an existing pier according to claim 1, further comprising a steel reinforcing structure installation step of placing the steel reinforcing structure at the corner between the side surface of the pier and the top surface of the foundation footing and fixing it with the anchor bars.
[Claim 5]
The method for reinforcing the foundation footing of an existing bridge pier according to claim 4, characterized in that the steel reinforcing structure further includes a plurality of reinforcing plate portions arranged between the vertical plate portion and the horizontal plate portion and connecting them in the form of ribs.

1. Pier (existing pier)
1a Pier side surface 2 Foundation footing 2a Foundation footing top surface 3 Foundation pile 4 Anchor bar 5 Haunch concrete (reinforced structure)
6 Steel reinforcement structure 6a Vertical plate portion 6b Horizontal plate portion 6c Reinforcement plate portion 7 Mounting hole 8 Lock nut

Claims (2)

A method for reinforcing a foundation footing in an existing bridge pier, comprising:
An excavation process of excavating the ground around the existing pier until the top surface of the foundation footing is exposed;
An anchor installation process in which anchors are installed on the pier side surface and the foundation footing top surface exposed by the excavation;
A reinforcement structure installation process in which a reinforcement structure including a first joint surface that joins to the pier side surface and a second joint surface that joins to the foundation footing upper surface is installed at the corner between the pier side surface and the foundation footing upper surface, and integrated with the anchor reinforcement;
A backfilling process of backfilling the excavated area so as to cover the reinforcement structure;
Including,
The reinforcement structure installation step uses a steel reinforcement structure including a vertical plate portion pressed against and joined to the side surface of the pier and a horizontal plate portion pressed against and joined to the upper surface of the foundation footing,
A steel reinforcement structure installation process in which the steel reinforcement structure is placed at the corner between the pier side surface and the foundation footing top surface and fixed by the anchor reinforcement;
The vertical plate portion and the horizontal plate portion each have a mounting hole through which the anchor bar passes,
The mounting hole of the vertical plate portion is a long hole that is long in a direction in which the horizontal plate portion is pressed against the upper surface of the foundation footing,
A method for reinforcing the foundation footing of an existing pier, wherein the mounting hole of the horizontal plate portion is a long hole that is long in the direction in which the vertical plate portion is pressed against the side surface of the pier. The method for reinforcing a foundation footing of an existing bridge pier according to claim 1 , wherein the steel reinforcing structure further includes a plurality of reinforcing plate portions arranged between the vertical plate portion and the horizontal plate portion and connecting them in the form of ribs.