JP2022164157A - Load bearing hierarchical rc bridge pier and design method of the same - Google Patents

Abstract

To provide a load bearing hierarchical RC bridge pier having hierarchized load bearing, etc.SOLUTION: A load bearing hierarchical RC bridge pier has a concrete skeleton 2, a load bearing hierarchical reinforcement bar 4, a bearing plate 5, and the like. A hollow sheath 6 having a large hollow part 7 on a bottom side thereof is formed so that a pull-side expansion gap length dx, which is a distance between the upper surface of a bearing pressure plate and the upper surface of the large hollow part in normal times, satisfies the following formula. φls' is the curvature in a plastic hinge section caused by level 2 seismic motion. yls' is the shortest distance from the position of the neutral axis to the position of the opposing load bearing hierarchical reinforcement bar when indicating φls'. Lp is the plastic hinge length. φy is the curvature in a limit state 1. φls3 indicates the curvature in a limit state 3.SELECTED DRAWING: Figure 3

Description

Application for application of Article 30, Paragraph 2 of the Patent Law "September 28, 2020, https://archive.iii.kyushu-u.ac.jp/public/dehEwA8IYw_AumcBob50-iW_fcJgzKzWCeD6fyh4ZPia,"20200924_USB summary collection.zip" (public interest collection.zip) 40th Earthquake Engineering Research Conference, Japan Society of Civil Engineers, Proposal of Road Bridge Collapse Scenario Design Method by Controlling Failure Likelihood), Civil Engineering Research Center, Civil Engineering Materials, Vol.62, No.12 , published on December 1, 2020, pp.8-11, Proposal of road bridge collapse scenario design method for maximum seismic motion-Empowerment of performance-based design method-”

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing-strength-stratified RC bridge pier whose bearing strength is stratified according to the intensity of seismic motion, and a design method thereof.

The design seismic ground motion stipulated in Highway Bridge Specifications V (Japan Road Association: Highway Bridge Specifications and Commentary V Seismic Design Edition, 2017.) is based on past seismic motion characteristics, etc., and the probability of occurrence during the service period of the bridge. Two levels of seismic motion, one with high intensity (level 1 seismic motion) and the other with low probability of occurrence during the service period of the bridge, but with high intensity (level 2 seismic motion), are considered. Type I seismic motion, which assumes a large-scale seismic motion, and Type II seismic motion, which assumes an inland direct earthquake, are considered.
However, it cannot be denied that a maximum seismic motion exceeding the design seismic motion may occur.
For this reason, road bridges are required to maintain their seismic performance against the design seismic motion and not to impair their functions as much as possible against the maximum seismic motion.

Conventionally, as a seismic design method corresponding to two levels of seismic motion intensity, an outer main reinforcing bar and an inner main reinforcing bar are arranged in the concrete frame, and the ends of the inner main reinforcing bars are attached to the concrete frame with an axial gap. A reinforcing bar structure that operates under strong seismic motion is imparted to the bridge pier by fixing it or placing a compressible member at the lower end of the inner main reinforcing bar that operates the inner main reinforcing bar after the compression allowance or tension allowance is eliminated. Techniques have been proposed (see Patent Documents 1 and 2).
However, in these proposals, it is unclear how to set the axial gap and the compression margin and tension margin of the compressible member. Therefore, there is a problem that it is not possible to satisfy the seismic performance against the above-mentioned maximum seismic motion.
That is, when the axial gap and the compression margin of the compressible member are set short, the inner reinforcing bars and the outer reinforcing bars start to operate with an external force less than the design earthquake motion when subjected to the maximum seismic motion. Buckling may occur. Also, if the axial clearance and the tension allowance of the compressible member are set long, the pier may collapse before the inner reinforcing bars are activated.
In addition, there is a possibility that the maximum displacement may exceed the ultimate displacement, and it cannot be denied that the bridge piers will collapse.
Up to the design earthquake motion, seismic performance is ensured by the seismic design of the highway bridge specifications V, so seismic design against the maximum seismic motion is now required.

Japanese Patent Application Laid-Open No. 2001-295220 Japanese Patent Application Laid-Open No. 2002-349011

An object of the present invention is to solve the above-mentioned conventional problems and to achieve the following objects. That is, the present invention provides a strength-strengthened RC bridge pier and a design method thereof, in which the function of the bridge is not likely to be impaired even in the event of the maximum seismic motion while ensuring seismic performance against the design seismic motion. The challenge is to

ただし、前記式（１）、（２）中、φ_ｌｓ’は、レベル２地震動によって生ずる変位がもたらす前記脚部の塑性ヒンジ区間における曲率を示し、ｙ_ｌｓ’は、前記曲率φ_ｌｓ’を示すときの前記塑性ヒンジ区間における中立軸の位置から前記脚部の中心軸を挟んで対向する前記耐力階層化鉄筋の配設位置までの最短距離を示し、Ｌｐは、前記塑性ヒンジ区間の長さである塑性ヒンジ長を示し、φ_yは、道路橋示方書Ｖに示される橋脚の限界状態１とみなす変位における曲率を示し、φ_ｌｓ３は、前記道路橋示方書Ｖに示される前記橋脚の限界状態３とみなす変位における曲率を示す。
＜２＞ 平常時における支圧板底面と大中空部の底面部分との間の距離である圧縮側遊間長ｄｙが下記式（３）を満足するように形成される前記＜１＞に記載の耐力階層化ＲＣ橋脚。

ただし、前記式（３）中、φ_ｌｓ’は、レベル２地震動によって生ずる変位がもたらす脚部の塑性ヒンジ区間における曲率を示し、ｙ_ｌｓ’’は、前記曲率φ_ｌｓ’を示すときの前記塑性ヒンジ区間における中立軸の位置から前記脚部の中心軸を挟まない耐力階層化鉄筋の配設位置までの最短距離を示し、Ｌｐは、前記塑性ヒンジ区間の長さである塑性ヒンジ長を示す。
＜３＞ 支承部は、耐力階層化鉄筋が作動しないときの脚部の水平耐力に相当する水平力では損傷せず、前記耐力階層化鉄筋の作動により最大に増強される前記脚部の前記水平耐力未満の前記水平耐力に相当する水平力で破壊されるように破壊強度が設定される前記＜１＞から＜２＞のいずれかに記載の耐力階層化ＲＣ橋脚。
＜４＞ 前記＜１＞から＜３＞のいずれかに記載の耐力階層化ＲＣ橋脚の設計方法であって、少なくとも、耐力階層化鉄筋が作動しないときにレベル２地震動によって生ずる変位がもたらす脚部の塑性ヒンジ区間における曲率φ_ｌｓ’を算出する曲率算出工程と、前記曲率φ_ｌｓ’を示すときの前記塑性ヒンジ区間における中立軸の位置から前記脚部の中心軸を挟んで対向する前記耐力階層化鉄筋の配設位置までの最短距離ｙ_ｌｓ’を算出する距離算出工程と、前記塑性ヒンジ区間の長さである塑性ヒンジ長Ｌｐを算出する塑性ヒンジ長算出工程と、前記曲率φ_ｌｓ’、前記最短距離ｙ_ｌｓ’及び前記塑性ヒンジ長Ｌｐの算出結果に基づき、下記式（１）及び（２）を満足するように引張側遊間長ｄｘを設定する引張側遊間設定工程と、を含むことを特徴とする耐力階層化ＲＣ橋脚の設計方法。

ただし、前記式（１）、（２）中、φ_ｌｓ’は、レベル２地震動によって生ずる変位がもたらす前記脚部の塑性ヒンジ区間における曲率を示し、ｙ_ｌｓ’は、前記曲率φ_ｌｓ’を示すときの前記塑性ヒンジ区間における中立軸の位置から前記脚部の中心軸を挟んで対向する前記耐力階層化鉄筋の配設位置までの最短距離を示し、Ｌｐは、前記塑性ヒンジ区間の長さである塑性ヒンジ長を示し、φ_yは、道路橋示方書Ｖに示される橋脚の限界状態１とみなす変位における曲率を示し、φ_ｌｓ３は、前記道路橋示方書Ｖに示される前記橋脚の限界状態３とみなす変位における曲率を示す。
＜５＞ 更に、平常時における支圧板底面と大中空部の底面部分との間の距離である圧縮側遊間長ｄｙを下記式（３）を満足するように設定する圧縮側遊間設定工程を含む前記＜４＞に記載の耐力階層化ＲＣ橋脚の設計方法。

ただし、前記式（３）中、φ_ｌｓ’は、レベル２地震動によって生ずる変位がもたらす脚部の塑性ヒンジ区間における曲率を示し、ｙ_ｌｓ’’は、前記曲率φ_ｌｓ’を示すときの前記塑性ヒンジ区間における中立軸の位置から前記脚部の中心軸を挟まない耐力階層化鉄筋の配設位置までの最短距離を示し、Ｌｐは、前記塑性ヒンジ区間の長さである塑性ヒンジ長を示す。
＜６＞ 更に、耐力階層化鉄筋が作動しないときの脚部の水平耐力に相当する水平力では損傷せず、前記耐力階層化鉄筋の作動により最大に増強される前記脚部の前記水平耐力未満の前記水平耐力に相当する水平力で破壊されるように支承部の破壊強度を設定する支承部設定工程を含む前記＜４＞から＜５＞のいずれかに記載の耐力階層化ＲＣ橋脚の設計方法。 Means for solving the above problems are as follows. Namely
<1> A columnar concrete frame, axial reinforcing bars embedded along the height direction inside the concrete frame, and arranged along the height direction inside the concrete frame inside the axial reinforcing bars. a leg provided with a load-bearing stratified reinforcing bar and a band reinforcing bar provided around the outer side of the bundle of axial reinforcing bars in a direction perpendicular to the height direction; And, in the RC pier having, the load-bearing stratified reinforcing bar is fixed to a bearing plate forming a flange projecting in a direction orthogonal to the height direction on the bottom side, and the bottom side portion and the bearing plate It is loosely fitted in a hollow sheath formed inside the concrete frame, and the portion above the bottom side is fixed in the concrete frame, and the bottom side of the hollow sheath accommodates the bearing plate. A large hollow portion having an opening diameter larger than that of the upper portion is formed. and the tension side play length dx, which is the distance between the upper surface of the bearing pressure plate and the tension resistance surface in normal times, satisfies the following formulas (1) and (2): A load-bearing stratified RC pier, characterized in that it is formed to:

However, in the above formulas (1) and (2), φ _ls ' indicates the curvature in the plastic hinge section of the leg caused by the displacement caused by the level 2 seismic motion, and y _ls ' indicates the curvature φ _ls '. Lp represents the shortest distance from the position of the neutral axis in the plastic hinge section to the arrangement position of the load-bearing stratified reinforcing bar facing across the central axis of the leg, and Lp is the length of the plastic hinge section Denotes a certain plastic hinge length, φ _y indicates the curvature at the displacement regarded as the limit state 1 of the pier shown in the road bridge specifications V, φ _ls3 is the limit state of the pier shown in the road bridge specifications V The curvature is shown at displacements taken as 3.
<2> The yield strength according to <1> above, wherein the compression-side clearance dy, which is the distance between the bottom surface of the bearing plate and the bottom surface of the large hollow portion in a normal state, satisfies the following formula (3): Hierarchical RC pier.

However, in the above equation (3), φ _ls ' indicates the curvature in the plastic hinge section of the leg caused by the displacement caused by the level 2 seismic motion, and y _ls '' indicates the plasticity when indicating the curvature φ _ls '. The shortest distance from the position of the neutral axis in the hinge section to the arrangement position of the load-bearing layered reinforcing bar not sandwiching the central axis of the leg, Lp indicates the plastic hinge length, which is the length of the plastic hinge section.
<3> The bearing part is not damaged by a horizontal force equivalent to the horizontal strength of the leg when the bearing strength stratified reinforcing bar does not operate, and the horizontal strength of the leg is maximized by the operation of the bearing strength stratified reinforcing bar. The strength stratified RC pier according to any one of <1> to <2>, wherein the breaking strength is set so as to be broken by a horizontal force corresponding to the horizontal strength less than the bearing strength.
<4> The method for designing a bearing layered RC pier according to any one of <1> to <3>, wherein at least the legs are caused by displacement caused by level 2 seismic motion when the bearing layered reinforcing bars do not operate. and a curvature calculation step of calculating the curvature φ _ls ' in the plastic hinge section of and the bearing layer facing across the central axis of the leg from the position of the neutral axis in the plastic hinge section when the curvature φ _ls ' is indicated a distance calculation step of calculating the shortest distance y _ls ' to the arrangement position of the modified reinforcing bar; a plastic hinge length calculation step of calculating the plastic hinge length Lp that is the length of the plastic hinge section; the curvature φ _ls '; a tension side clearance setting step of setting the tension side clearance dx so as to satisfy the following equations (1) and (2) based on the calculation results of the shortest distance y _ls ' and the plastic hinge length Lp. A method for designing a load-bearing stratified RC pier characterized by:

However, in the above formulas (1) and (2), φ _ls ' indicates the curvature in the plastic hinge section of the leg caused by the displacement caused by the level 2 seismic motion, and y _ls ' indicates the curvature φ _ls '. Lp represents the shortest distance from the position of the neutral axis in the plastic hinge section to the arrangement position of the load-bearing stratified reinforcing bar facing across the central axis of the leg, and Lp is the length of the plastic hinge section Denotes a certain plastic hinge length, φ _y indicates the curvature at the displacement regarded as the limit state 1 of the pier shown in the road bridge specifications V, φ _ls3 is the limit state of the pier shown in the road bridge specifications V The curvature is shown at displacements taken as 3.
<5> Further includes a compression side clearance setting step of setting the compression side clearance length dy, which is the distance between the bottom surface of the bearing plate and the bottom portion of the large hollow portion in normal times, so as to satisfy the following formula (3). The method for designing the load-bearing stratified RC pier according to <4>.

However, in the above equation (3), φ _ls ' indicates the curvature in the plastic hinge section of the leg caused by the displacement caused by the level 2 seismic motion, and y _ls '' indicates the plasticity when indicating the curvature φ _ls '. The shortest distance from the position of the neutral axis in the hinge section to the arrangement position of the load-bearing layered reinforcing bar not sandwiching the central axis of the leg, Lp indicates the plastic hinge length, which is the length of the plastic hinge section.
<6> Furthermore, it is not damaged by a horizontal force equivalent to the horizontal strength of the leg when the bearing strength stratified reinforcing bar does not operate, and is less than the horizontal strength of the leg that is maximized by the operation of the bearing strength stratified reinforcing bar Design of bearing strength stratified RC pier according to any one of <4> to <5> including a bearing part setting step of setting the breaking strength of the bearing part so that it will be destroyed by a horizontal force equivalent to the horizontal strength of Method.

According to the present invention, it is possible to solve the above-mentioned problems in the conventional technology, and while ensuring the seismic performance against the above-mentioned design seismic motion, the functions of the bridge are not likely to be impaired even by the above-mentioned maximum seismic motion, and the bearing strength is stratified. It is possible to provide a bearing layered RC pier and a design method thereof.

1 is a partial cross-sectional view showing an example of an embodiment of a bearing layered RC pier; FIG. FIG. 2 is a cross section taken along the line AA of FIG. 1; It is a partially enlarged cross-sectional view of the pier base. It is a diagram showing the stress-strain relationship of concrete according to the specifications for highway bridges V. FIG. FIG. 4 is a diagram showing the stress-strain relationship of axial reinforcing bars according to the Highway Bridge Specification V. FIG. FIG. 4 is a partially enlarged cross-sectional view of a bridge pier base showing a state when a tensile force is applied due to earthquake motion; FIG. 4 is an explanatory diagram for explaining assumed behavior of a bridge pier in relation to horizontal load-horizontal displacement when subjected to maximum seismic motion exceeding the design seismic motion; FIG. 10 is an explanatory diagram for explaining the state of the load-bearing stratified RC pier in the stage of state 1; FIG. 10 is an explanatory diagram for explaining the state of the load-bearing stratified RC pier at the stage of state 2; FIG. 10 is an explanatory diagram for explaining the state of the load-bearing stratified RC pier in the stage of state 3; FIG. 10 is an explanatory diagram for explaining the state of a bridge pier, such as when there is no load-bearing stratified reinforcing bar; FIG. 10 is an explanatory diagram for explaining the state of the load-bearing stratified RC pier in the stage of state 4; 1 is a flow chart diagram illustrating an example of a preferred embodiment of a load-bearing layered RC pier design method; FIG. It is an explanatory view of a continuous girder type 5-span continuous steel I-girder bridge supported by RC piers and pile foundations assumed in simulation analysis. It is a figure which shows the bar arrangement diagram of the concrete model 2. FIG. FIG. 4 is an explanatory diagram of a multi-mass frame model used for simulation analysis; FIG. 4 is a diagram showing the stress-strain relationship of concrete set in simulation analysis. FIG. 4 is a diagram showing the load-displacement relationship applied to bearing-strength stratified reinforcing bars. FIG. 10 is a diagram showing the results of load gradual analysis for model 1 and model 2;

(strength-strength RC pier)
The load-bearing layered RC pier of the present invention will be described in detail with reference to the drawings.

An example of an embodiment of the bearing layered RC pier is shown in FIG.
As shown in FIG. 1, the strength-strengthened RC bridge pier 1 mainly includes a concrete frame 2, an axial reinforcing bar 3, a leg portion having a strength-strengthened strength-strengthened reinforcing bar 4, a tie bar 8, and a bridge bearing 10. .

The columnar concrete frame 2 is not particularly limited as long as it has a columnar shape, and can be constructed by appropriately selecting from known structures according to the specification V for highway bridges. In the illustrated example, a footing portion 2a that is buried in the ground and forms a bridge pier base, a column portion 2b that is erected on the footing portion 2a, and a beam portion 2c that is arranged on the column portion 2b and is an upper part of the bridge pier. Configured. The columnar portion 2b may have any of a prismatic shape, a columnar shape, and an elliptical columnar shape.

A plurality of axial reinforcing bars 3 are arranged at predetermined intervals inside the concrete frame 2 at positions on the surface side of the circular cross section, and are buried along the height direction (axial direction) of the concrete frame 2. . Also, the bundle of axial reinforcing bars 3 is restrained by a tie bar 8 provided around the bundle in a direction perpendicular to the height direction. These axial reinforcing bars 3 and tie reinforcing bars 8 are not particularly limited, and can be appropriately selected from known structures in accordance with the specification V for highway bridges. Further, the concrete frame 2 may be reinforced by an intermediate band reinforcing bar or the like (not shown).

The bearing layered reinforcing bars 4 are arranged inside the concrete frame 2 inside the axial reinforcing bars 3 along the height direction. As the load-bearing layered reinforcing bars 4, a plurality of bars are arranged inside the concrete frame 2 inside the axial reinforcing bars 3. For example, as shown in FIG. A plurality of strength-stratified reinforcing bars 4 are arranged at regular intervals inside the plurality of axial reinforcing bars 3 arranged at regular intervals over the entire circumference of the inner surface side. However, the strength stratified reinforcing bars 4 need only be able to resist the stress on the tensile side based on the displacement caused by the seismic motion, and need to be arranged over the entire circumference of the inner peripheral position of the reinforcement position of the axial reinforcing bars 3. no.

In addition, as shown in FIG. 3 , this load-bearing layered reinforcing bar 4 is fixed to a bearing plate 5 forming a flange projecting in a direction orthogonal to the height direction on the bottom (base) side. The portion and the bearing plate 5 are loosely fitted in a hollow sheath 6 formed inside the concrete frame 2, and the portion above the bottom side portion is embedded in the concrete frame 2 and fixed. That is, the load-bearing stratified reinforcing bars 4 and the bearing plate 5 are cut off from the concrete frame 2 on the pier base side (for example, the plastic hinge section of the pier). Note that FIG. 3 is a partially enlarged sectional view of the pier base.

The hollow sheath 6 has a large hollow portion 7 whose opening diameter is larger than that of the upper portion and accommodates the bearing plate 5 on the bottom side thereof. A tension-side clearance that is the distance between the upper surface of the bearing plate 5 and the tension resistance surface in a normal state, which is a tension resistance surface that contacts the upper surface of the bearing plate 5 and resists the tensile force when pulled upward. The length dx(m) is formed to satisfy the following equations (1) and (2). In this specification, the term "normal" indicates a state in which the RC pier is not horizontally displaced due to seismic motion.

ただし、前記式（１）、（２）中、φ_ｌｓ’は、レベル２地震動によって生ずる変位がもたらす前記脚部の塑性ヒンジ区間における曲率を示し、ｙ_ｌｓ’は、前記曲率φ_ｌｓ’を示すときの前記塑性ヒンジ区間における中立軸の位置から前記脚部の中心軸を挟んで対向する前記耐力階層化鉄筋の配設位置までの最短距離を示し、Ｌｐは、前記塑性ヒンジ区間の長さである塑性ヒンジ長を示し、φ_yは、道路橋示方書Ｖに示される前記橋脚の限界状態１とみなす変位における曲率を示し、φ_ｌｓ３は、前記道路橋示方書Ｖに示される前記橋脚の限界状態３とみなす変位における曲率を示す。

However, in the above formulas (1) and (2), φ _ls ' indicates the curvature in the plastic hinge section of the leg caused by the displacement caused by the level 2 seismic motion, and y _ls ' indicates the curvature φ _ls '. Lp represents the shortest distance from the position of the neutral axis in the plastic hinge section to the arrangement position of the load-bearing stratified reinforcing bar facing across the central axis of the leg, and Lp is the length of the plastic hinge section Denotes a certain plastic hinge length, φ _y indicates the curvature at the displacement regarded as limit state 1 of the pier shown in the road bridge specification V, φ _ls3 is the limit of the pier shown in the road bridge specification V The curvature is shown at the displacement considered as state 3.

The curvature φ _ls ' in the above equation (1) is set in the range between the curvature φ _y and the curvature φ _ls3 as represented by the above equation (2). The concepts of the curvature φ _y and the curvature φ _ls3 will be specifically described below.
First, the _φy in the formula (2) is the curvature that occurs when the pier reaches the limit state 1 shown in the road bridge specifications V, and the pier is arranged with the bearing strength stratified reinforcing bars. Assuming that the legs are in a non-existent state, the following formula (4) is given based on the highway bridge specification V.

ただし、前記式（４）中、Ｍ_ｌｓ２は、前記道路橋示方書Ｖに示される前記橋脚の限界状態２に相当する、前記橋脚基部断面に作用する曲げモーメント（Ｎ・ｍｍ）を示し、Ｍ_ｙ０は、前記橋脚基部断面の最外縁にある前記軸方向鉄筋が降伏するときの前記橋脚基部断面に作用する曲げモーメント（Ｎ・ｍｍ）を示し、φ_ｙ０は、前記橋脚基部断面の最外縁に位置する前記軸方向鉄筋が降伏するときの曲率（１／ｍｍ）を示す。

However, in the above formula (4), M _ls2 represents the bending moment (N mm) acting on the pier base cross section, which corresponds to the limit state 2 of the pier shown in the road bridge specification V, and M _y0 indicates the bending moment (N mm) acting on the pier base cross section when the axial reinforcing bar at the outermost edge of the pier base cross section yields, and φ _y0 indicates the bending moment at the outermost edge of the pier base cross section. Fig. 1 shows the curvature (1/mm) at which the axial rebar located yields;

The bending moments M _ls2 , M _y0 and φ _y0 in the above equation (4) are the fiber strain proportional to the distance from the neutral axis and the stress degree corresponding to the fiber strain is constant within each minute element, the neutral axis that satisfies the balance condition of the cross section is estimated by the following formulas (5) and (6), and the procedure by the following formulas (7) and (8) Calculated by In addition, n is the number of divisions in the cross section of the pier base, i is the section number representing the n-divided pier base, and j is the element number in the load bearing direction in the pier base cross section. be. Further, the minute elements mean n-divided cross-sectional elements at the pier base.

ただし、前記式（５）中、Ｎ_ｉは、ｉ番目の断面である前記橋脚基部断面に作用する軸力（Ｎ）を示し、σ_ｃｊは、ｊ番目の前記微小要素内の前記コンクリート躯体の応力度（Ｎ／ｍｍ^２）を示し、σ_ｓｊは、ｊ番目の前記微小要素内の前記軸方向鉄筋の応力度（Ｎ／ｍｍ^２）を示し、ΔＡ_ｃｊは、ｊ番目の前記微小要素内の前記コンクリート躯体の断面積（ｍｍ^２）を示し、ΔＡ_ｓｊは、ｊ番目の前記微小要素内の前記軸方向鉄筋の断面積（ｍｍ^２）を示す。
なお、要素分割を行う際の前記コンクリート躯体の要素分割数としては、例えば、５０分割程度であり、例えば、前記軸方向鉄筋１本に相当する幅を１要素として要素分割すればよい。

However, in the formula (5), N _i indicates the axial force (N) acting on the pier base cross section which is the i-th cross section, and σ _cj is the concrete framework in the j-th microelement. is the stress level (N/mm ² ), σ _sj is the stress level (N/mm ² ) of the axial rebar in the j-th micro-element, and ΔA _cj is the stress level in the j-th micro-element and ΔA _sj indicates the cross-sectional area ( ^{mm 2} ) of the axial reinforcing bar in the j-th microelement.
The number of element divisions of the concrete frame when performing element division is, for example, about 50 divisions.

ただし、前記式（６）中、Ｍ_ｉは、前記橋脚基部断面に作用する曲げモーメント（Ｎ・ｍｍ）を示し、ｘ_ｊは、前記微小要素から断面の図心位置までの距離（ｍｍ）を示す。
前記橋脚基部断面において、σ_ｓｊ＝σ_ｓｙ（σ_ｓｙにつき、下記式（８）参照）となるときにσ_ｃｊ＝０とそれ以外との境界線が前記中立軸となる。なお、前記コンクリートの曲げ引張強度（σ_ｂｔ、Ｎ／ｍｍ^２）は、０と仮定する。

However, in the above formula (6), M _i represents the bending moment (N mm) acting on the cross section of the pier base, and x _j represents the distance (mm) from the microelement to the centroid position of the cross section. show.
In the cross section of the pier base, when σ _sj =σ _sy (see formula (8) below for σ _sy ), the boundary line between σ _cj =0 and the rest becomes the neutral axis. The bending tensile strength (σ _bt , N/mm ² ) of the concrete is assumed to be zero.

ただし、前記式（７）及び（８）中、ｘ_ｓは、前記軸方向鉄筋から前記橋脚基部断面の前記中立軸までの距離（ｍｍ）、ε_ｓｙは、前記軸方向鉄筋の降伏ひずみを示し、σ_ｓｙは、前記軸方向鉄筋の降伏応力度（Ｎ／ｍｍ^２）を示し、Ｅ_ｓは、前記軸方向鉄筋のヤング係数（Ｎ／ｍｍ^２）を示す。

However, in the formulas (7) and (8), _{xs is the distance (mm) from the axial reinforcing bar to the neutral axis of the pier base section, and ε sy is} the yield strain of the axial reinforcing bar. , σ _sy denotes the yield stress degree (N/mm ² ) of the axial rebar, and E _s denotes the Young's modulus (N/mm ² ) of the axial rebar.

The bending moment and curvature when the strain generated in the axial reinforcing bars arranged on the outermost side in the pier base section reaches the yield strain ε _sy are obtained, and these are the initial yield bending moment M _y0 and the initial yield Let the curvature be φ _y0 . The bending moment when the tensile strain of the axial reinforcing bar placed on the outermost side reaches the tensile strain _εst2 corresponding to the limit state 2 is defined as _Mls2 .
Here, ε _st2 is given by the following equation (9).

ただし、前記式（９）中、φは、前記軸方向鉄筋の引張ひずみを算出するための前記軸方向鉄筋の直径（ｍｍ）を示し、β_ｓは、前記帯鉄筋の抵抗を表すばね定数（Ｎ／ｍｍ^２）を示し、β_ｃｏは、前記コンクリート躯体のかぶりコンクリートの抵抗を表すばね定数（Ｎ／ｍｍ^２）を示す。
ここで、塑性ヒンジ長Ｌｐ（ｍｍ）は、下記式（１０）及び（１１）により与えられる。

However, in the above formula (9), φ indicates the diameter (mm) of the axial reinforcing bar for calculating the tensile strain of the axial reinforcing bar, and β _s is the spring constant ( N/mm ² ), and β _co represents the spring constant (N/mm ² ) representing the resistance of the cover concrete of the concrete frame.
Here, the plastic hinge length Lp (mm) is given by the following formulas (10) and (11).

ただし、前記式（１０），（１１）中、β_ｎは、前記軸方向鉄筋のはらみ出しに対する抵抗を表すばね定数（Ｎ／ｍｍ^２）を示し、下記式（１２）～（１４）により与えられる。また、φ’は、前記軸方向鉄筋の直径（ｍｍ）（ただし４０ｍｍ以上は４０ｍｍとする）を示し、ｈは、前記橋脚基部から橋脚天端までの距離（ｍｍ）を示す。

However, in the above formulas (10) and (11), βn represents the spring constant ( _N /mm ² ) representing the resistance against protrusion of the axial reinforcing bars and is given by the following formulas (12) to (14). be done. In addition, φ' indicates the diameter (mm) of the axial reinforcing bar (40 mm if it is 40 mm or more), and h indicates the distance (mm) from the base of the pier to the top of the pier.

ただし、前記式（１２）～（１４）中、Ｅ_０は、前記帯鉄筋のヤング係数（Ｎ／ｍｍ^２）を示し、Ｉ_ｈは、前記帯鉄筋の断面二次モーメント（ｍｍ^４）を示し、ｄ’は、前記塑性ヒンジ長Ｌｐを算出するための前記帯鉄筋の有効長（ｍｍ）を示し、ｎ_ｓは、前記塑性ヒンジ長Ｌｐを算出するための前記帯鉄筋の有効長ｄ’が最も大きい前記コンクリート躯体の部分に配置される圧縮側軸方向鉄筋の本数を示し、ｓは、前記帯鉄筋の橋脚高さ方向の配置間隔（ｍｍ）を示し、ｃ_０は、前記塑性ヒンジ長Ｌｐを算出するための前記帯鉄筋の有効長ｄ’が最も大きい前記コンクリート躯体の部分の最外縁側に配置された前記軸方向鉄筋の最外位置から前記コンクリート躯体の最外縁までの最短距離（ｍｍ）を示す。
なお、この算出における前記コンクリート躯体及び前記軸方向鉄筋の各応力－ひずみ関係は、それぞれ、図４，５のように設定される。図４が前記道路橋示方書Ｖに準じた前記コンクリートの応力－ひずみ関係を示す図であり、図５が前記道路橋示方書Ｖに準じた前記軸方向鉄筋の応力－ひずみ関係を示す図である。

However, in the above formulas (12) to (14), E ₀ indicates the Young's modulus (N/mm ² ) of the tie bar, and I _h indicates the geometrical moment of inertia (mm ⁴ ) of the tie bar. , d′ indicates the effective length (mm) of the tie bar for calculating the plastic hinge length _Lp , and ns is the effective length d′ of the tie bar for calculating the plastic hinge length Lp. Indicates the number of compression-side axial rebars arranged in the largest part of the concrete frame, s indicates the arrangement interval (mm) of the pier height direction of the ties, and _c0 is the plastic hinge length Lp. The shortest distance (mm ).
The stress-strain relationships of the concrete frame and the axial reinforcing bars in this calculation are set as shown in FIGS. 4 and 5, respectively. FIG. 4 is a diagram showing the stress-strain relationship of the concrete according to the highway bridge specifications V, and FIG. 5 is a diagram showing the stress-strain relationship of the axial reinforcing bars according to the highway bridge specifications V. be.

Next, the φ _ls3 in the formula (2) is the curvature that occurs when the pier reaches the limit state 3 shown in the road bridge specification V, and the state where the strength stratified reinforcing bars are not arranged. is given by the following formulas (15) to (18) based on the road bridge specification V, assuming the RC pier of
Here, the φ _ls3 is (A) when the tensile strain of the axial reinforcing bars at the outermost edge of the pier base cross section reaches ε _st3 , and (B) the compressive strain of the concrete skeleton at the outermost edge of the pier base cross section. is the curvature that occurs in the pier in the earlier of the two states when ε _ccl is reached.

ただし、前記式（１５）～（１８）中、ε_ｃｃｌは、前記帯鉄筋で拘束された前記コンクリート躯体の限界圧縮ひずみを示し、ε_ｃｃは、前記コンクリート躯体が最大圧縮応力度に達するときのひずみを示し、σ_ｃｃは、前記帯鉄筋で拘束された前記コンクリートの最大圧縮応力度（Ｎ／ｍｍ^２）を示し、Ｅ_ｄｅｓは、下降勾配（Ｎ／ｍｍ^２）を示し、ε_ｓｔ３は、前記限界状態３に相当する前記軸方向鉄筋の引張ひずみを示し、βは、断面補正係数を示し、矩形断面の場合においてβ＝０．４であり、ρ_ｓは、前記帯鉄筋の体積比を示し、σ_ｃｋは、前記コンクリートの設計基準強度（Ｎ／ｍｍ^２）を示す。

However, in the above formulas (15) to (18), ε _ccl indicates the critical compressive strain of the concrete skeleton restrained by the ties, and ε _cc is the maximum compressive stress when the concrete skeleton reaches the maximum compressive stress. indicates the strain, σ _cc indicates the maximum compressive stress intensity (N/mm ² ) of the concrete restrained by the ties, E _des indicates the descending gradient (N/mm ² ), and ε _st3 is indicates the tensile strain of the axial rebar corresponding to the limit state 3, β indicates the section correction factor, β=0.4 in the case of a rectangular section, and ρ _s is the volume ratio of the ties σ _ck indicates the design standard strength (N/mm ² ) of the concrete.

When the pull-side gap length dx satisfies the above formulas (1) and (2), the strength stratified reinforcing bars 4 operate only after receiving an earthquake motion exceeding level 2 seismic motion (said design seismic motion), and the seismic performance against level 2 seismic motion is improved. While ensuring the structure other than the layered reinforcing bars 4, it is possible to obtain the effect of layered strength, in which the function of the bridge is less likely to be impaired by the operation of the layered reinforcing bars 4 even against the maximum seismic motion.
That is, as can be understood from FIG. 6 showing the state when tensile force is applied due to seismic motion, by appropriately setting the tension-side gap length dx based on the above formulas (1) and (2), the strength stratified reinforcing bars 4 does not operate when subjected to an external force of level 2 seismic motion or less, and the tension side clearance is crushed for the first time when it receives a seismic motion exceeding level 2 seismic motion (see arrow A in Fig. 6) (see arrow B in Fig. 6) , act as load-bearing rebars.

The compression side clearance dy, which is the distance between the bottom surface of the bearing plate 5 and the bottom surface of the large hollow portion 7 in the normal state, is preferably formed so as to satisfy the following formula (3). By forming the compression-side clearance dy in this manner, it is possible to prevent the bottom end of the load-bearing stratified reinforcing bar 4 from coming into contact with the bottom surface of the large hollow portion 7 and buckling when a compressive force is applied due to seismic motion.

ただし、前記式（３）中、φ_ｌｓ’は、レベル２地震動によって生ずる変位がもたらす前記脚部の前記塑性ヒンジ区間における曲率を示し、ｙ_ｌｓ’’は、前記曲率φ_ｌｓ’を示すときの前記塑性ヒンジ区間における前記中立軸の位置から前記脚部の中心軸を挟まない前記耐力階層化鉄筋の配設位置までの最短距離を示し、Ｌｐは、前記塑性ヒンジ区間の長さである塑性ヒンジ長を示す。

However, in the formula (3), φ _ls ' indicates the curvature in the plastic hinge section of the leg caused by the displacement caused by the level 2 seismic motion, and y _ls '' indicates the curvature φ _ls '. A plastic hinge that represents the shortest distance from the position of the neutral axis in the plastic hinge section to the arrangement position of the load-bearing layered reinforcing bar that does not sandwich the central axis of the leg, and Lp is the length of the plastic hinge section. length.

Again, referring to FIG. 1, the support 10 is a member whose one end is connected to the beam 2c on the upper part of the concrete frame 2, and whose other end is connected to the upper structure (not shown). It is capable of supporting the superstructure.
The support part 10 is not damaged by a horizontal force corresponding to the horizontal strength of the leg when the bearing strength stratified reinforcing bar 4 does not operate, and is maximized by the operation of the bearing strength stratified reinforcing bar 4. The breaking strength needs to be set so that it breaks with a horizontal force corresponding to the horizontal strength less than the horizontal strength.
For example, in the illustrated example, the bearing portion 10 is constructed by sandwiching a rubber bearing 13 between a base plate 11 and a set plate 12 on the top of the concrete frame 2 , and the base plate 11 is attached to the concrete frame 2 by anchor bolts 14 . Although it is fixed to the end, the breaking strength of the anchor bolt 14 is not damaged by the horizontal force corresponding to the horizontal strength of the leg when the bearing strength stratified reinforcing bar 4 does not operate, and is maximized by the operation of the bearing strength stratified reinforcing bar 4 If it is set to be destroyed by a horizontal force corresponding to the horizontal strength less than the horizontal strength of the legs to be strengthened, the concrete frame 2 and the superstructure are cut off before the yield strength stratified reinforcing bars 4 yield. , it is possible to prevent fatal damage such as bridge collapse due to the collapse of the concrete frame 2 after the yield strength stratified reinforcing bars 4 have yielded.
The member to which the destruction is induced in the support portion 10 to be induced to be destroyed may be a rubber bearing 13 or a set bolt (not shown) that connects the support portion 10 to the bridge via the set plate 12. However, among the constituent members of the support portion 10, the anchor bolts 14 are preferable because they are excellent in serviceability and recovery after destruction.

The operation of the load-bearing layered RC pier 1 configured as described above will be described in more detail with reference to the drawings.
FIG. 7 shows the expected behavior of the bridge piers in the horizontal load-horizontal displacement relationship when subjected to the maximum seismic motion exceeding the design seismic motion.

When subjected to said maximum seismic motion, first of all a state occurs in which the outer axial reinforcing bars 3 yield (state 1).
The load-bearing stratified RC pier 1 in the state 1 stage has no major damage (see FIG. 8(a)).

Next, after reaching State 1, the energy of seismic motion is absorbed as the concrete skeleton 2 plasticizes (State 2).
In the load-bearing stratified RC pier 1 in the stage of state 2, as the concrete frame 2 becomes plasticized, damage occurs to the extent that the horizontal resistance is not lost (see FIG. 8(b)).

Next, after reaching state 2, when the displacement of the concrete frame 2 based on the seismic motion exceeds the displacement corresponding to the level 2 seismic motion, the tension-side clearance disappears, and the load-bearing stratified reinforcing bars 4 begin to operate, and the load-bearing capacity is increased. rises (state 3).
The load-bearing stratified RC pier 1 in state 3 is supported by the load-bearing stratified reinforcing bars 4, and fatal damage such as collapse of the pier is suppressed (see FIG. 8(c)).
At this time, if the load-bearing layered reinforcing bars 4 are not provided or if the load-bearing layered reinforcing bars 4 do not operate, the displacement of the concrete frame 2 increases, leading to fatal damage such as collapse of the bridge piers (Fig. 8 ( d) see).

Next, after reaching state 3, a state occurs in which the support 10 breaks down (state 4).
In the load-bearing stratified RC pier 1 in the stage of state 4, before the load-bearing stratified reinforcing bar 4 yields, the breakage of the bearing part 10 causes a disconnection with the superstructure, and fatal damage such as collapse of the pier is suppressed. (See FIG. 8(e)). At the same time, the severed superstructure does not deviate from the load-bearing stratified RC pier 1, and does not lead to fatal damage such as falling of the bridge (see FIG. 8(e)).
That is, the upper structure separated from the load-bearing stratified RC pier 1 due to the destruction of the bearing part 10 has a gap between the base plate 11 and the top of the concrete frame 2 (beam part 2c) with respect to the load-strength stratified RC pier 1. Only the frictional force is transmitted, and the collapse of the load-bearing stratified RC pier 1 is suppressed. At the same time, the upper structure remains on the load-bearing stratified RC pier 1 that has escaped collapse, etc., and does not lead to fatal damage.
In the resistance-strength-strength RC pier 1, even if the unpredictable maximum earthquake motion occurs, the subsequent collapse scenario is set as described above, and the impact of the maximum earthquake motion is induced to the destruction of the bearing part, thereby preventing the pier from collapsing. It is possible to prevent fatal damage such as falling bridges due to collapse, and by extension, it is possible to promptly perform repairs for subsequent functional recovery.

It should be noted that, in this specification, the terms "states 1-4" are distinguished from the "limit states 1-3" in the highway bridge specification V.
The road bridge specification V defines the limit states 1 to 3 as follows.
Limit State 1: The elastic limit point in a perfect elastoplastic skeletal curve.
Limit state 2: A limit state in which the load-bearing capacity can be secured within an assumed range, although the behavior of members loses reversibility.
Limit state 3: The state of the limit in which the seismic horizontal strength can be maintained.

On the other hand, states 1 to 4 show the behavior of the RC bridge piers on which the strength stratified reinforcing bars are arranged, and can be explained as follows in relation to the limit states 1 to 3.
State 1: A state similar to the limit state 1 described above. However, the bearing portion is not damaged, and the load-bearing stratified reinforcing bars are not in operation.
State 2: A state between the limit states 1-3. However, the bearing is not damaged and the load-bearing stratified reinforcing bars are not working.
State 3: This is the state where the load-bearing stratified rebar begins to work. However, although the limit state 1 is exceeded, the limit state 3 is not exceeded. It is desirable to be about the limit state 2 described above. Also, the bearing is not damaged.
State 4: This is a state in which the load-bearing strength of the pier increases due to the actuation of the load-bearing stratified reinforcing bars, and the bearing portion is destroyed. However, the limit state 3 is not reached.

(Method for designing bearing strength stratified RC piers)
A method for designing a bearing strength stratified RC pier of the present invention is a method of designing the bearing strength stratified RC pier of the present invention, and includes at least a curvature calculation step, a distance calculation step, a plastic hinge length calculation step, and a tension side clearance setting step. , and preferably further includes optional steps such as a compression side clearance setting step and a bearing portion setting step, which are performed as necessary.

The curvature calculation step is a step of calculating the curvature φ _ls ' in the plastic hinge section of the leg caused by displacement caused by a level 2 seismic motion when the load-bearing stratified rebar is not activated.
In the curvature calculation step, the displacement caused by the level 2 seismic motion and the plastic hinge section are calculated in advance for the set pier in which the load-bearing layered reinforcing bars that can be set based on the road bridge specifications V do not exist. Moreover, it can be implemented by calculating the curvature φ _ls ' in the plastic hinge section caused by the displacement.
The method of calculating the displacement and the curvature φ _ls ' is not particularly limited, and for example, a method of applying a fiber element to the plastic hinge section in a known method of gradually increasing load analysis for a multi-mass frame model. be done. In addition, as a method of calculating the plastic hinge section, the method described in Specifications for Highway Bridges V can be used.
The level 2 seismic motion necessary for calculation includes the seismic motion shown in the specifications for highway bridges V, for example, 2-II-II-1, the NS component on the ground in JR West Takatori Station premises, and the like.

In the distance calculation step, the _shortest distance y This is the step of calculating _ls '.
In the distance calculation step, the position of the neutral axis in the plastic hinge section when the curvature φ _ls ' is shown is calculated in advance for the set pier in which the strength stratified reinforcing bar does not exist, and then In the load-bearing stratified RC bridge pier in which the load-bearing stratified reinforcing bars are arranged without changing the position of the vertical axis, the load-bearing stratified reinforcing bars facing each other across the central axis of the leg from the position of the neutral axis. It can be implemented by calculating the shortest distance y _ls ′ to the installation position.
The method of calculating the neutral axis is not particularly limited, and for example, a method of analyzing by applying fiber elements to the plastic hinge section in a known load gradual analysis method for a multi-mass frame model. Further, the setting of the arrangement position of the bearing strength stratified reinforcing bar is set to the inner side when viewed from the axial reinforcing bar.

The plastic hinge length calculation step is a step of calculating a plastic hinge length Lp, which is the length of the plastic hinge section.
The plastic hinge length calculation step can be carried out by calculating the length of the plastic hinge section generated by the level 2 seismic motion with respect to the set bridge pier in which the strength stratified reinforcing bars do not exist.
The method for calculating the length of the plastic hinge section is not particularly limited, and examples thereof include the method described in Specification V for Highway Bridges.

In the tension side clearance setting step, based on the calculation results of the curvature φ _ls ', the shortest distance y _ls ', and the plastic hinge length Lp, the tension side clearance is set so as to satisfy the following expressions (1) and (2). This is the step of setting dx.

ただし、前記式（１）、（２）中、φ_ｌｓ’は、レベル２地震動によって生ずる変位がもたらす前記脚部の前記塑性ヒンジ区間における曲率を示し、ｙ_ｌｓ’は、前記曲率φ_ｌｓ’を示すときの前記塑性ヒンジ区間における前記中立軸の位置から前記脚部の中心軸を挟んで対向する前記耐力階層化鉄筋の配設位置までの最短距離を示し、Ｌｐは、前記塑性ヒンジ区間の長さである塑性ヒンジ長を示し、φ_yは、前記道路橋示方書Ｖに示される前記橋脚の限界状態１とみなす変位における曲率を示し、φ_ｌｓ３は、前記道路橋示方書Ｖに示される前記橋脚の限界状態３とみなす変位における曲率を示す。
なお、前記式（２）における前記曲率φ_ｙ及びφ_ｌｓ３の設定方法としては、前記橋脚を前記耐力階層化鉄筋が配されていない状態の前記脚部と仮定して、前記道路橋示方書Ｖに基づき設定する方法が挙げられ、本発明の前記耐力階層化ＲＣ橋脚について説明した前記曲率φ_ｙ及びφ_ｌｓ３の設定方法を適用して設定することができる。

However, in the formulas (1) and (2), φ _ls ' indicates the curvature in the plastic hinge section of the leg caused by the displacement caused by the level 2 seismic motion, and y _ls ' indicates the curvature φ _ls '. Lp indicates the shortest distance from the position of the neutral axis in the plastic hinge section to the arrangement position of the load-bearing stratified reinforcing bar facing across the central axis of the leg, and Lp is the length of the plastic hinge section is the length of the plastic hinge, φ _y indicates the curvature at the displacement regarded as the limit state 1 of the pier shown in the road bridge specification V, and φ _ls3 is the curvature shown in the road bridge specification V The curvature at the displacement considered as limit state 3 of the pier is shown.
In addition, as a method of setting the curvatures φ _y and φ _ls3 in the formula (2), the road bridge specification V and can be set by applying the method of setting the curvatures φ _y and φ _ls3 described for the bearing layered RC pier of the present invention.

In the compression side clearance setting step, the compression side clearance length dy, which is the distance between the bottom surface of the bearing pressure plate and the bottom portion of the large hollow portion in the normal state, is set so as to satisfy the following formula (3). It is a process.
In the load-bearing stratified RC pier designed by the compression side clearance setting process, the bottom ends of the load-bearing stratified reinforcing bars are prevented from coming into contact with the bottom portion of the large hollow portion and buckling when compressive force due to seismic motion acts. can be done.

ただし、前記式（３）中、φ_ｌｓ’は、レベル２地震動によって生ずる変位がもたらす前記脚部の前記塑性ヒンジ区間における曲率を示し、ｙ_ｌｓ’’は、前記曲率φ_ｌｓ’を示すときの前記塑性ヒンジ区間における前記中立軸の位置から前記脚部の中心軸を挟まない前記耐力階層化鉄筋の配設位置までの最短距離を示し、Ｌｐは、前記塑性ヒンジ区間の長さである塑性ヒンジ長を示す。

However, in the formula (3), φ _ls ' indicates the curvature in the plastic hinge section of the leg caused by the displacement caused by the level 2 seismic motion, and y _ls '' indicates the curvature φ _ls '. A plastic hinge that represents the shortest distance from the position of the neutral axis in the plastic hinge section to the arrangement position of the load-bearing layered reinforcing bar that does not sandwich the central axis of the leg, and Lp is the length of the plastic hinge section. length.

In the step of setting the bearing portion, the horizontal force of the leg exceeds a horizontal force corresponding to the horizontal strength of the leg when the bearing layered reinforcing bar does not operate, and the horizontal force of the leg is maximized by the operation of the bearing layered reinforcing bar. It is a step of setting the breaking strength of the bearing portion so that it is broken by a horizontal force corresponding to the horizontal proof stress less than the proof stress.
In the bearing portion setting step, the horizontal strength of the set pier in which the bearing strength stratified reinforcing bars do not exist is calculated, and the bearing strength stratified RC in the state where the bearing strength stratified reinforcing bars are arranged without changing the setting is calculated. It can be carried out by calculating the maximum horizontal strength of the bridge pier when the strength stratified reinforcing bars are in operation.
A method for calculating the horizontal strength of the set pier is not particularly limited, and examples thereof include a known method such as a load gradual analysis method for a multi-mass frame model using the fiber elements. In addition, the method of calculating the maximum horizontal strength during operation of the strength-stratified reinforcing bars is not particularly limited. There is a method of calculating by replacing with a "spring element" of a trilinear model that is set so as not to resist on the side and is set to resist only after a predetermined displacement occurs on the tension side.
In the load-bearing stratified RC pier designed by the bearing part setting process, the concrete frame and the superstructure are cut off before the yield of the load-bearing stratified reinforcing bars, and the concrete accompanying the yielding of the load-bearing stratified reinforcing bars Fatal damage such as bridge collapse due to the collapse of the frame can be prevented.

Below, an example of a preferred embodiment of the design method of the load-bearing stratified RC pier based on the collapse scenario (see FIGS. 7, 8, etc.) of the load-strength stratified RC pier is shown in FIG. I will explain in detail.

<1 Setting a collapse scenario>
1.1 Determination of Cross Section of Pier The cross section of the pier is designed so as to satisfy the control conditions of the permanent action, the variable action and the accidental action shown in the specification V of the above highway bridge. Here, the pier is assumed to be a pier preceded by a bending failure type shown in the Road Bridge Specification V.

1.2 Design of Bearings According to the Highway Bridge Specification V, the horizontal force acting on the bearings is calculated, and the bearings are designed so as to satisfy the load-bearing performance against the horizontal force.

1.3 Destruction Mode of Bearing Part After determining the number and diameter of the anchor bolts in accordance with the Road Bridge Specification V, the characteristic value of the rupture strength of the anchor bolts is calculated.
When the anchor bolt of the bearing portion is a member that is induced to break, the breaking strength of each member is such that the breakage of the rubber bearing, the set bolt, etc. of the bearing portion does not precede the breakage of the anchor bolt. Set the cross section, etc. based on the variation in

1.4 Setting of pier strength after activation of strength-strengthened reinforcing bars The pier horizontal strength after activation of the strength-strengthened reinforcement is set in consideration of the rupture strength of the members to which the above-mentioned destruction is induced and variations in the horizontal strength of the piers.

1.5 Confirmation of pier failure mode Confirm that other failure modes do not precede the member to which the failure is induced.
Examples include shear failure of the piers. If the characteristic value of the shear strength of the pier is lower than the breaking strength of the member on which the failure is induced, the pier will shear failure before the member on which the failure is induced fails. review muscles.

<2 Design of bearing layered reinforcing bars>
2.1 Gradual Load Analysis Using Fiber Elements In order to set the clearance of the bearing strength stratified reinforcing bars, the analysis using the fiber elements is performed without inserting the bearing strength stratified reinforcing bars. In this analysis, the cross section of the pier determined in "1.1 Determining the cross section of the pier" is modeled.
Gradual load analysis is used to calculate the load-displacement relationship of the bridge pier, the bending moment-curvature relationship of the plastic hinge section, and the like.

2.2 Setting of bearing-strength-stratified reinforcement arrangement Set the bar arrangement position of the bearing-strength-stratified reinforcement.
The reinforcement position of the load-bearing layered reinforcing bars is set inside the axial reinforcing bars set in "1.1 Determining the cross section of the bridge pier" in accordance with the specifications for highway bridges V, while considering the clearance.

2.3 Reference value setting of pull-side gap length of bearing-strength stratified reinforcing bars Set the reference value of the tension-side gap length of the bearing-strength stratified reinforcing bars. The curvature and the neutral axis position of the plastic hinge section at the displacement that actuates the load-bearing stratified reinforcing bar are extracted from the analysis results of "2.1 Carrying out Gradual Load Analysis Using Fiber Elements".
From the extracted curvature and the neutral axis position, and the calculated plastic hinge length, the pull-side clearance is calculated by Equation (1).
If the load-strength-strength-strengthened reinforcing bars increase in strength below the pier displacement caused by level 2 seismic motion, energy absorption by plastic deformation cannot be expected, and the design performed in "1.1 Determining the pier cross section" will not hold. Therefore, the pull-side clearance of the load-bearing stratified reinforcing bars is determined so that the load-bearing stratified reinforcing bars do not operate until the displacement caused by the level 2 seismic motion.

2.4 Specification setting of bearing strength stratified reinforcing bars The number, diameter, Set standards, etc.

<3 Design verification>
Gradual load analysis is performed by modeling the strength stratified reinforcing bars. The analysis model is the model created in "2.1 Gradual Load Analysis Using Fiber Elements" with the above-mentioned strength-stratified reinforcing bars added. The bearing layered reinforcing bar is modeled as a spring element with a gap.
From the results of load gradual analysis of the model reflecting the strength stratified reinforcing bars, the following three points are checked to confirm whether the collapse scenario holds.
First, confirm whether the load-bearing stratified reinforcing bars do not operate below the displacement caused by the level 2 seismic motion. Confirmation can be determined from the load-displacement curve of the load gradual analysis. When the load-bearing stratified reinforcing bars operate below the target displacement, the pull-side clearance of the load-bearing stratified reinforcing bars is reviewed.
Secondly, the horizontal strength of the bridge pier after the strength-stratified reinforcing bars are activated is confirmed. If the horizontal strength set in "1.4 Setting of pier strength" is not obtained, the number, diameter, standard, etc. of the strength stratified reinforcing bars will be reviewed.
Third, make sure that the pier does not exceed limit state 3 before reaching the required rupture capacity of the induced member. If it exceeds, the number and diameter of the bearing layered reinforcing bars, or the pull-side clearance length is reviewed.

According to the method for designing the strength-strength-stratified RC pier of the present invention configured as described above, while ensuring the seismic performance against the design seismic motion, the entire function is unlikely to be impaired against the maximum seismic motion, and the bearing strength is high. A layered bearing layered RC pier can be designed.
In addition, based on the collapse scenario, by inducing the destruction of the bearing part to the member to which the destruction is induced, it is possible to prevent fatal damage such as the collapse of the bridge due to the collapse of the pier, and to recover the function after that. It is possible to design the bearing layered RC pier that can be quickly repaired.

In order to confirm the effectiveness of the bearing strength stratified RC bridge pier and its design method of the present invention, the following simulation analysis was performed.

<Simulation target>
In the simulation analysis, as a typical example, a five-span continuous steel I-girder bridge of continuous girder type supported by RC piers and pile foundations as shown in FIG. 10 was assumed. In addition, FIG. 10 is an explanatory diagram showing the setting of the 5-span continuous steel I-girder bridge.
In the simulation analysis, the middle RC pier of the 5-span continuous steel I-girder bridge is extracted as the design target pier, and the single-leg RC pier is analyzed.
Here, the piers to be designed are model 1 in which the bearing strength stratified reinforcing bars are not set (without the bearing strength stratified reinforcing bars), and model 1 except that the bearing strength stratified reinforcing bars are set. It was set in two ways: Model 2, which is set in the same way as .
FIG. 11 shows a concrete bar arrangement diagram of Model 2. In addition, in model 1, the reinforcing bars are arranged without the "bearing strength stratified reinforcing bars" in FIG.
Each part of the pier to be designed was set as shown in Tables 1 and 2 below based on the method described with reference to FIG. It should be noted that the bearing strength stratified reinforcing bars are set to use high-strength SD490 reinforcing bars in order to improve bearing strength in a limited arrangement space inside the axial reinforcing bars.

<Simulation conditions>
The simulation analysis was performed using TDAPIIII (manufactured by Ark Information Systems Co., Ltd., general-purpose three-dimensional dynamic analysis program for civil engineering and construction).
As the analysis method, the incremental load analysis of displacement control was used. The loading step at that time was set to 0.01 mm/step, and loading was performed up to 200 mm in order to load to a displacement that is regarded as limit state 3 in model 1 or more.
The analysis model adopted a multi-mass frame model. FIG. 12 shows a concrete multi-mass frame model.
As shown in Fig. 12, the multi-mass frame model for the pier to be designed uses a "fiber element" for the plastic hinge section, and a "linear beam element made of rigid members" for the beam at the top of the pier and the footing at the base of the pier. , the column portion between the plastic hinge section and the beam portion was set as a "linear beam element".

The stress-strain relationship of each of the modeled axial reinforcing bars and concrete was set based on the highway bridge specifications V (see FIGS. 4 and 5). However, in the stress-strain relationship of the concrete, in the strain region of the critical compressive strain ε _ccl or more, after the strain ε _cc when the strain ε _c reaches the maximum compressive stress degree σ _cc and descends to the critical compressive strain ε _ccl was also set assuming that the stress would decrease to 0.0 N/mm ² at the same descending slope. FIG. 13 shows the stress-strain relationship of the concrete set in the simulation analysis.

Further, in the model 2 for setting the bearing strength stratified reinforcing bars, the bearing bearing stratified reinforcing bars were further set to be added as "spring elements".
That is, since the bearing-strength-stratified reinforcing bar exhibits an effect of resisting tension only after reaching a predetermined displacement due to the tension-side clearance, it is set as a non-linear "spring element" that resists tension only in the axial direction. was modeled by giving the load-displacement relationship shown in
Here, the load-displacement relationship calculated by the method described with reference to FIG. 9 is set in relation to the tension-side clearance of the strength-stratified reinforcing bars.
Further, the load-bearing stratified reinforcing bars are set so as not to resist compression by having the compression-side clearance larger than the tension-side clearance.
In addition, regarding the setting of the bearing strength stratified reinforcing bars, the tension side clearance length until the bearing strength stratified reinforcing bars are actuated is set to 20 mm, and the load-displacement relationship after the bearing strength stratified reinforcing bars yield is analytically In order to ensure the stability of , it is set by giving a minute gradient of about 10 ⁻⁵ kN/m.

<Simulation result>
FIG. 15 shows the load gradual analysis results for Model 1 and Model 2. FIG.
In FIG. 15, the vertical axis indicates the horizontal strength of the design target pier, and the horizontal axis indicates the displacement at the pier crest of the design target pier.
15 are the characteristic values of the displacement in the model 1 calculated based on the specification V for highway bridges.
From the results shown in FIG. 15, it is confirmed that the following two points can be realized by appropriately setting the pull-side clearance of the load-bearing stratified reinforcing bars arranged in Model 2.
First, since the same response as model 1 is shown up to the displacement corresponding to limit state 2, model 2 is also model Behavior similar to 1 is shown.
Second, when a load larger than level 2 seismic motion occurs, model 2, unlike model 1, exceeds limit state 2 and rises before limit state 3 is reached. Specifically, the horizontal bearing capacity of the pier in model 2 rises from about 5,000 kN, corresponding to limit condition 2, to about 7,000 kN due to the operation of the bearing stratified reinforcing bars.

From the above simulation results, even if a maximum seismic motion exceeding Level 2 seismic motion occurs in the bearing-strength-stratified RC pier of the present invention, the increased horizontal strength suppresses the progress of damage to the design object pier, and the function is impaired. You can get an effect that is hard to get rid of.
In addition, if the rupture strength of the bearing portion is set between 5,000 kN and 7,000 kN, which is the range of increase in the horizontal strength of the pier, even if a maximum seismic motion exceeding level 2 seismic motion occurs, the impact By inducing the collapse of the bearing part, it becomes difficult for the bridge to collapse due to the collapse of the pier, and subsequent repairs can be quickly performed to recover the function.
The above effect can be obtained more reliably by reviewing the breaking strength of the pull-side clearance and the support portion in consideration of variations in performance of the pier constituent members.

1 Strength-strengthened RC bridge pier 2 Concrete frame 2a Footing part 2b Column part 2c Beam part 3 Axial reinforcing bar 4 Strength-strengthened strength reinforcement bar 5 Bearing plate 6 Hollow sheath 7 Large hollow part 8 Tie bar 10 Bearing part 11 Base plate 12 Set plate 13 Rubber Bearing 14 Anchor bolt

Claims (6)

A columnar concrete frame, an axial reinforcing bar embedded along the height direction inside the concrete frame, and a bearing force arranged along the height direction inside the concrete frame inside the axial reinforcing bar. a leg portion comprising a layered reinforcing bar and a band reinforcing bar provided around the outer side of the bundle of axial reinforcing bars in a direction orthogonal to the height direction;
In an RC bridge pier having a bearing part arranged on the upper part of the concrete frame,
The load-bearing stratified reinforcing bars have a bearing plate fixed to the bottom side, forming a flange projecting in a direction orthogonal to the height direction, and the bottom side portion and the bearing plate are formed inside the concrete frame. is loosely fitted in the hollow sheath, and the portion above the bottom side is fixed in the concrete frame,
The hollow sheath has a large hollow portion with an opening diameter larger than that of the upper portion, which accommodates the bearing plate on the bottom side thereof, and the upper surface portion of the large hollow portion faces the upper surface of the bearing plate, and the load-bearing stratified reinforcing bars are arranged above. It is a tension resistance surface that contacts the upper surface of the support plate and resists the tensile force when it is pulled, and the tension side clearance is the distance between the upper surface of the support plate and the tension resistance surface in normal times A load-bearing stratified RC pier characterized by being formed so that dx satisfies the following equations (1) and (2).

However, in the above formulas (1) and (2), φ _ls ' indicates the curvature in the plastic hinge section of the leg caused by the displacement caused by the level 2 seismic motion, and y _ls ' indicates the curvature φ _ls '. Lp represents the shortest distance from the position of the neutral axis in the plastic hinge section to the arrangement position of the load-bearing stratified reinforcing bar facing across the central axis of the leg, and Lp is the length of the plastic hinge section Denotes a certain plastic hinge length, φ _y indicates the curvature at the displacement regarded as the limit state 1 of the pier shown in the road bridge specifications V, φ _ls3 is the limit state of the pier shown in the road bridge specifications V The curvature is shown at displacements taken as 3. The load-bearing stratified RC pier according to claim 1, wherein the compression-side clearance length dy, which is the distance between the bottom surface of the bearing plate and the bottom surface of the large hollow portion in a normal state, is formed so as to satisfy the following formula (3). .

However, in the above equation (3), φ _ls ' indicates the curvature in the plastic hinge section of the leg caused by the displacement caused by the level 2 seismic motion, and y _ls '' indicates the plasticity when indicating the curvature φ _ls '. The shortest distance from the position of the neutral axis in the hinge section to the arrangement position of the load-bearing layered reinforcing bar not sandwiching the central axis of the leg, Lp indicates the plastic hinge length, which is the length of the plastic hinge section. The bearing is not damaged by a horizontal force corresponding to the horizontal strength of the leg when the load-bearing stratified rebar is not actuated, and is less than the horizontal strength of the leg that is maximized by the actuation of the load-stratified rebar. 3. The load-bearing layered RC pier according to any one of claims 1 and 2, wherein the breaking strength is set so that the pier is broken by a horizontal force corresponding to the horizontal strength. A method for designing a load-bearing stratified RC pier according to any one of claims 1 to 3,
a curvature calculation step of calculating at least the curvature φ _ls ' in the plastic hinge section of the leg caused by the displacement caused by the level 2 seismic motion when the load-bearing stratified rebar is not actuated;
A distance for calculating the shortest distance y _ls ' from the position of the neutral axis in the plastic hinge section when the curvature φ _ls ' is indicated to the arrangement position of the load-bearing stratified reinforcing bars facing each other across the central axis of the leg. a calculation step;
a plastic hinge length calculation step of calculating a plastic hinge length Lp, which is the length of the plastic hinge section;
Based on the calculation results of the curvature φ _ls ', the shortest distance y _ls ', and the plastic hinge length Lp, tension-side clearance setting for setting the tension-side clearance dx so as to satisfy the following equations (1) and (2) process and
A method for designing a bearing layered RC pier, comprising:

However, in the above formulas (1) and (2), φ _ls ' indicates the curvature in the plastic hinge section of the leg caused by the displacement caused by the level 2 seismic motion, and y _ls ' indicates the curvature φ _ls '. Lp represents the shortest distance from the position of the neutral axis in the plastic hinge section to the arrangement position of the load-bearing stratified reinforcing bar facing across the central axis of the leg, and Lp is the length of the plastic hinge section Denotes a certain plastic hinge length, φ _y indicates the curvature at the displacement regarded as the limit state 1 of the pier shown in the road bridge specifications V, φ _ls3 is the limit state of the pier shown in the road bridge specifications V The curvature is shown at displacements taken as 3. Further, the compression side clearance setting step of setting the compression side clearance length dy, which is the distance between the bottom surface of the bearing plate and the bottom portion of the large hollow portion in a normal state, so as to satisfy the following formula (3). The design method of the load-bearing stratified RC pier according to .

However, in the above equation (3), φ _ls ' indicates the curvature in the plastic hinge section of the leg caused by the displacement caused by the level 2 seismic motion, and y _ls '' indicates the plasticity when indicating the curvature φ _ls '. The shortest distance from the position of the neutral axis in the hinge section to the arrangement position of the load-bearing layered reinforcing bar not sandwiching the central axis of the leg, Lp indicates the plastic hinge length, which is the length of the plastic hinge section. Furthermore, a horizontal force equivalent to the horizontal strength of the leg when the load-bearing stratified reinforcing bars are not activated does not damage the horizontal strength of the leg less than the horizontal strength of the leg that is maximized by the operation of the load-bearing stratified reinforcing bars. 6. The method for designing a bearing layered RC pier according to any one of claims 4 and 5, further comprising a bearing portion setting step of setting the breaking strength of the bearing portion so that it will be destroyed by a horizontal force corresponding to the bearing portion.

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