JP2009097257A - Designing method for bridge pier joint structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide wide practical application of a bridge pier structure in which the lower end of a steel bridge pier is joined to an RC footing. <P>SOLUTION: According to a design method for a bridge pier joint structure, a pressure Pi that concrete receives from a reinforcing basket is calculated from the equation: Pi=T*tanθ/(ψ*π*Le), where a design tensile force acting on a circular steel pipe is T, the outer diameter of the reinforcing basket is ψi, the outer diameter of the circular steel pipe is ψo, an effective joint length between the reinforcing basket and the circular steel pipe is Le, and the angle of a compression strut formed between the reinforcing basket and the circular steel pipe is θ. Then, the reinforcing basket outer diameter ψi, the effective joint length Le, or the blending of concrete is determined so that the calculated Pi is equal to or less than the yield strength or rupture strength of the concrete. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a design method for a pier joint structure in which a lower end of a steel pier is joined to an RC footing.

  When joining the lower end of a steel pier to the foundation, a steel frame called an anchor frame is manufactured in advance, and then embedded in a footing, which is a reinforced concrete foundation, and then anchor bolts extending from the anchor frame are used. A method of bolting the lower end of a steel pier to an anchor frame has been widely used.

  Recently, in addition to such a method, a steel pipe with a large diameter called a socket steel pipe is installed on the foundation constructed in the ground, and then the lower end of the steel pier is inserted into the socket steel pipe, and then the steel pier A method of integrating the lower end of the steel pier, the socket steel pipe and the foundation by filling concrete between the outer surface and the inner surface of the socket steel pipe is also known, and according to such a method, rapid construction is possible. Therefore, it is possible to proceed with construction in a short construction period in a place with a lot of traffic.

  On the other hand, the joining method using an anchor frame is inherently expensive to produce an anchor frame. Therefore, when the size of a bridge is increased, the production cost is increased due to the increase in the size of the anchor frame and the strengthening of steel. In addition, the so-called double pipe construction method using the socket steel pipe inevitably increases the construction cost because the steel pipe is used twice.

JP-A-9-13320 JP-A-9-209308

  Under such circumstances, a joint construction method capable of reducing costs has been researched and developed. For example, a rib is provided on the inner surface of a steel pipe constituting a pier and a reinforcing bar is arranged at a position facing the rib, and in this state, A construction method (Patent Documents 1 and 2) in which concrete is placed on the surface has been developed.

  According to such a conventional construction method, the concrete filled in the steel pipe and the reinforcing bars embedded in the concrete form a reinforced concrete body in the steel pipe, and the forced rotation due to the pulling load received from the steel pipe and the horizontal displacement of the pier head Resist deformation.

  Therefore, not only the anchor frame but also the steel pier can be firmly joined to the footing, and a concrete restraining effect by the steel pipe can be expected. In addition, the construction method is more advantageous than RC piers that require formwork and demolding work when placing concrete.

  However, in actual construction of such a pier joint structure, there is no design guideline yet, and there is a limit to its wide application to actual pier construction.

  The present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to provide a method for designing a pier joint structure in which a pier joint structure in which the lower end of a steel pier is joined to an RC footing can be widely applied in practice. And

  In order to achieve the above object, according to the design method for a pier joint structure according to the present invention, a predetermined gap is formed between a footing formed of reinforced concrete and an upper surface of the footing. As described above, in a vertical position, a circular steel pipe that is disposed above the footing and has a rib formed on the inner surface thereof, a steel pipe joining longitudinal bar that is embedded in one end of the footing, and a steel pipe joining longitudinal pipe that is filled in the steel pipe. In the method of designing a pier joint structure composed of a reinforced concrete body formed of concrete in which the other end of the reinforcement is buried,

  A plurality of the steel pipe joining longitudinal bars are arranged along the inner surface of the circular steel pipe so that the overall outer diameter φi is smaller than the inner diameter φo of the circular steel pipe and substantially concentric with the circular steel pipe. It is configured to form a steel bar joint with the steel pipe joining transverse bars arranged in a plurality of stages in a circumferential shape so as to be orthogonal to the joining longitudinal bars,

The design tensile force acting on the circular steel pipe is T, the outer diameter of the reinforcing bar is φi, the inner diameter of the circular steel pipe is φo, the effective joint length between the reinforcing bar and the circular steel pipe is Le, the reinforcing bar and the When the angle of the compression strut formed on the concrete between the circular steel pipe is θ and the thickness of the circular steel pipe is to, the pressure Pi that the concrete receives from the rebar rod,
Pi = T · tanθ / (φi · π · Le)
The circumferential stress σ _HO generated in the circular steel pipe is calculated from
σ _HO = T · tanθ / (2π · Le · to)
Calculated from

  While determining the outer diameter φi of the reinforcing bar or the joint effective length Le so that the Pi is less than the yield strength or the fracture strength of the concrete, or selecting the blend of concrete,

The thickness to or the joint effective length Le of the circular steel pipe is determined so that the σ _HO is equal to or less than the yield strength of the circular steel pipe.

  In the design method of the pier joint structure according to the present invention, when the design tensile force acting on the circular steel pipe is T, the cylindrical concrete extending between the reinforcing bar rod and the circular steel pipe has a circular steel pipe on its outer peripheral surface. The tensile force T acts on the upper side, and the reaction force T having the same magnitude as the tensile force T acts on the inner peripheral surface downward.

Therefore, when the outer diameter of the reinforcing bar is φi and the effective joint length between the reinforcing bar and the circular steel pipe is Le, the average bond stress τi between the concrete and the reinforcing bar is as follows. , The following formula:
τi = T / (π · φi · Le) (1)
It can be calculated by

Similarly, when the inner diameter of the circular steel pipe is φo, the average adhesion stress τo between the concrete and the circular steel pipe is expressed as
τo = T / (π · φo · Le) (2)
It can be calculated by

  Here, the effective joint length Le between the reinforcing bar rod and the circular steel pipe means a length that effectively acts as a joint with the circular steel pipe among the length L of the reinforcing bar rod. It is determined by the angle θ of the compression strut formed between the reinforcing bar and the tensile force.

Next, the pressure Pi that the concrete receives from the reinforcing bar is
Pi = τi · tanθ (3)
Therefore, this is substituted into (1) and Pi = T · tan θ / (π · φi · Le) (4)
Is obtained.

And the pressure Po which concrete receives from a circular steel pipe is
Po = τo · tanθ (5)
Therefore, by substituting this into (2), Po = T · tanθ / (π · φo · Le) (6)
Is obtained.

Next, the pressure Po is expressed by the shell thin wall theory, where σ _{HO is the} circumferential stress generated in the circular steel pipe, and to is the thickness of the circular steel pipe,
Po = σ _HO · to / (φo / 2) (7)
So,
σ _HO = T · tanθ / (2π · Le · to) (8)
Is obtained.

That is, the outer diameter φi of the reinforcing bar and the joint effective length Le are determined so that Pi obtained by the equation (4) is less than the yield strength or the fracture strength of the concrete, or the blending of the concrete is selected. It is possible to design a rational pier joint structure by determining the thickness to and the joint effective length Le of the circular steel pipe so that σ _HO obtained by the equation (8) is equal to or less than the yield strength of the circular steel pipe. It becomes possible.

  In addition, although the steel pipe which comprises a pier is often called a steel shell, in this invention, it shall call a steel pipe as a concept also including a steel shell for convenience.

  The footing is made of reinforced concrete and generally accompanied by a pile, but in the present invention, the foundation structure is constituted only by the footing or it is joined to the pile and its head. It does not matter whether the foundation structure is composed of footing.

  The vertical reinforcing bar for joining steel pipes is one in which one end is embedded in the footing and the other end is embedded in concrete filled in the steel pipe, and can be constituted by a deformed reinforcing bar, for example.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of a design method for a pier joint structure according to the present invention will be described with reference to the accompanying drawings. Note that components that are substantially the same as those of the prior art are assigned the same reference numerals, and descriptions thereof are omitted.

  FIG. 1 is a view showing a pier joint structure to be designed by the design method according to the present embodiment. As can be seen from the figure, the pier joint structure 1 used in the present embodiment is formed by joining a pier 3 composed of a circular steel pipe 2 having ribs 5 formed on the inner surface thereof to a footing 4 formed of reinforced concrete.

  Between the lower end of the circular steel pipe 2 and the upper surface of the footing 4, the circular steel pipe 2 is arranged above the footing 4 in a vertical posture so that a gap h is formed.

  One end of the steel pipe joining vertical bar 6 a is embedded in the footing 4, and the other end of the vertical bar is embedded in the concrete 7 filled in the circular steel pipe 2.

  As shown in FIG. 2, the steel pipe joining longitudinal bars 6a are formed along the inner surface of the circular steel pipe so that the entire outer diameter φi is smaller than the inner diameter φo of the circular steel pipe 2 and is substantially concentric with the circular steel pipe 2. A plurality of transverse bars 6b for annular steel pipe joining are arranged so as to surround the longitudinal bars in the circular steel pipe 2 so as to be orthogonal to the longitudinal bars 6a for joining steel pipes.

  These steel pipe joining vertical bars 6a and steel pipe joining horizontal bars 6b form a reinforcing bar 6 having an outer diameter φi and a height L in the circular steel pipe 2. Here, the reinforcing bar 6 is preferably provided with auxiliary reinforcing bars in the vertical direction that are not embedded in the footing 4 as necessary.

  On the other hand, the reinforcing bar 6 forms a reinforced concrete body 8 together with the concrete 7 filled in the circular steel pipe 2, and when the pulling force acts from the pier 3, the reinforced concrete body resists the pulling force and acts on the footing 4. In addition to transmitting, when a horizontal force acts on the head of the pier 3, it acts to bend and resist the rotational deformation of the steel pipe 2 due to the horizontal force and transmit the horizontal force to the footing 4.

  In designing the pier joint structure 1 according to the present embodiment, first, a design tensile force T acting on the circular steel pipe 2 is appropriately determined. The design tensile force T corresponds to the pulling force from the superstructure at the time of an earthquake, for example.

Next, the outer diameter of the reinforcing bar 6 is φi, the effective joint length of the reinforcing bar 6 and the circular steel pipe 2 is Le, and the angle of the compression strut formed on the concrete between the reinforcing bar 6 and the circular steel pipe 2 is θ The pressure Pi that the concrete receives from the reinforcing bar 6 is
Pi = T · tanθ / (φi · π · Le)
(See FIGS. 2B and 2C).

Similarly, when the inner diameter of the circular steel pipe 2 is φo, the pressure Po received by the concrete from the circular steel pipe 2 is
Po = T · tanθ / (φo · π · Le)
(See FIGS. 2B and 2C).

Further, the circumferential stress σ _HO generated in the circular steel pipe 2 is expressed as follows when the thickness of the circular steel pipe is to:
σ _HO = T · tanθ / (2π · Le · to)
(See FIG. 2 (d)).

The above calculation formula can be derived by the following procedure. That is, the average adhesion stress τi (FIGS. 2 (b) and 2 (c)) between the cylindrical concrete extending between the reinforcing bar 6 and the circular steel pipe 2 and the reinforcing bar 6 is determined by the area of the reinforcing bar 6 peripheral surface. If you pay attention, the following formula,
τi = T / (π · φi · Le) (1)
It can be calculated by

Similarly, the average adhesion stress τo between the above-mentioned concrete and the circular steel pipe 2 can be expressed by the following equation when focusing on the area of the inner surface of the circular steel pipe 2:
τo = T / (π · φo · Le) (2)
It can be calculated by

  Here, the effective joint length Le between the reinforcing bar 6 and the circular steel pipe 2 means a length that effectively acts as a joint with the circular steel pipe 2 among the length L of the reinforcing bar 6. It is determined by the angle θ (FIG. 2 (c)) of the compression strut formed between the circular steel pipe 2 and the reinforcing bar 6 when the tensile force T acts on it.

 The angle θ of the compression strut can be set to 45 ° to 50 °, for example, but may be about 55 ° on the safe side.

Next, the pressure Pi that the above-mentioned concrete receives from the reinforcing bar 6 is
Pi = τi · tanθ (3)
Therefore, this is substituted into (1) and Pi = T · tan θ / (π · φi · Le) (4)
Is obtained.

Similarly, the pressure Po that concrete receives from a circular steel pipe is:
Po = τo · tanθ (5)
Therefore, by substituting this into (2), Po = T · tanθ / (π · φo · Le) (6) F
Is obtained.

Next, the pressure Po is expressed by the shell thin wall theory, where σ _{HO is the} circumferential stress generated in the circular steel pipe 2 and to is the thickness of the circular steel pipe,
Po = σ _HO · to / (φo / 2) (7)
So,
σ _HO = T · tanθ / (2π · Le · to) (8)
Is obtained.

Next, it is determined whether Pi obtained by the equation (4) is less than or equal to the yield strength or fracture strength of the concrete, and if it exceeds these values, the outer diameter φi of the reinforcing bar 6 Or by increasing the height L, or by increasing the compressive strength by changing the concrete mix,
Pi <Yield strength of concrete or fracture strength of concrete (9)
The above calculation is repeated until

On the other hand, it is determined whether or not σ _HO obtained by equation (8) is less than or equal to the yield strength of the circular steel pipe 2, and if it exceeds these values, the thickness to of the circular steel pipe 2 is increased. Or by increasing the height L of the reinforcing bar 6
P _HO <Yield strength of round steel pipe (10)
The above calculation is repeated until

  In order to construct the joint structure 1 between the pier and the footing according to the present embodiment, first, as shown in FIG. 3, after the pile 11 is driven into the ground (not shown), the footing 4 is attached to the head of the pile. In the foundation work, the footing is formed so that one end of the steel pipe joining longitudinal bar 6 a is embedded in the footing 4.

  Next, as shown in FIG. 4, the mold material 12 is placed on the upper surface of the footing 4. The mold member 12 is composed of an annular frame having an L-shaped cross section, and the lower end of the circular steel pipe 2 and the upper surface of the footing 4 are mounted on the shoulder 13 formed on the inner peripheral side. In addition to closing the gap h, the load of the circular steel pipe 2 can be temporarily received.

  Next, the circular steel pipe 2 is suspended above the footing 4 in a vertical posture so that the lower end of the circular steel pipe 2 is placed on the shoulder 13 of the mold material 12, and temporarily received by the mold material 12.

  Next, concrete 7 is cast and filled in the circular steel pipe 2 to a height at which the reinforcing bar 6 is embedded.

  When the cast concrete 7 is hardened, the formwork 12 is finally removed.

As described above, according to the design method of the pier joint structure according to the present embodiment, it is determined whether Pi obtained by the equation (4) is less than the yield strength or the fracture strength of the concrete. If it exceeds the value of the above, by increasing the outer diameter φi or height L of the reinforcing bar 6, or by changing the blending of concrete to increase the compressive strength,
Pi <Yield strength of concrete or fracture strength of concrete (9)
Until the above calculation is repeated, it is determined whether σ _HO obtained by the equation (8) is equal to or less than the yield strength of the circular steel pipe 2, and if these values are exceeded, By increasing the thickness to of the circular steel pipe 2 or increasing the height L of the reinforcing bar 6,
P _HO <Yield strength of round steel pipe (10)
Since the above calculation is repeated until it becomes, it becomes possible to design a rational pier joint structure.

It is the figure which showed the pier joining structure 1 used by this embodiment, (a) is a longitudinal cross-sectional view, (b) is a cross-sectional view which follows an AA line. The schematic diagram which showed the calculation basis in the design method of the pier junction structure which concerns on this embodiment. The figure which showed the construction procedure of the pier joining structure 1 used by this embodiment. The figure which showed the construction procedure of the pier joining structure 1 used by this embodiment continuously.

Claims (1)

A round steel pipe which is arranged above the footing in a vertical posture so that a predetermined gap is formed between the footing formed of reinforced concrete and the upper surface of the footing, and a rib is formed on the inner surface. Designed a pier joint structure composed of a steel pipe joint longitudinal bar with one end buried and a reinforced concrete body filled with concrete filled in the steel pipe and the other end of the steel pipe joint buried In the way to
A plurality of the steel pipe joining longitudinal bars are arranged along the inner surface of the circular steel pipe so that the overall outer diameter φi is smaller than the inner diameter φo of the circular steel pipe and substantially concentric with the circular steel pipe. It is configured to form a steel bar joint with the steel pipe joining transverse bars arranged in a plurality of stages in a circumferential shape so as to be orthogonal to the joining longitudinal bars,
The design tensile force acting on the circular steel pipe is T, the outer diameter of the reinforcing bar is φi, the inner diameter of the circular steel pipe is φo, the effective joint length between the reinforcing bar and the circular steel pipe is Le, the reinforcing bar and the When the angle of the compression strut formed on the concrete between the circular steel pipe is θ and the thickness of the circular steel pipe is to, the pressure Pi that the concrete receives from the rebar rod,
Pi = T · tanθ / (φi · π · Le)
The circumferential stress σ _HO generated in the circular steel pipe is calculated from
σ _HO = T · tanθ / (2π · Le · to)
Calculated from
While determining the outer diameter φi of the reinforcing bar or the joint effective length Le so that the Pi is less than the yield strength or the fracture strength of the concrete, or selecting the blend of concrete,
A design method for a pier joint structure, wherein a thickness to or a joint effective length Le of the circular steel pipe is determined so that the σ _HO is equal to or less than a yield strength of the circular steel pipe.

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