JP2008082073A

JP2008082073A - Joint structure of pile and post

Info

Publication number: JP2008082073A
Application number: JP2006264915A
Authority: JP
Inventors: Toshiharu Nakamura; 敏晴中村; Takashi Misawa; 孝史三澤
Original assignee: Okumura Corp
Current assignee: Okumura Corp
Priority date: 2006-09-28
Filing date: 2006-09-28
Publication date: 2008-04-10
Anticipated expiration: 2026-09-28
Also published as: JP4708295B2

Abstract

<P>PROBLEM TO BE SOLVED: To increase the bending strength and toughness of the joint portion between a pile and a post without overlapping the upper end of a reinforcement 11 of the pile with the lower end of a reinforcement 31 of a post to bending strength and toughness equal to or higher than those in the case that the upper end of the reinforcement of the pile is overlapped with the lower end of the reinforcement of the post in a joint structure between the pile and the post for connecting the pile 1 and the post 3 to each other through a steel tube 5 which is so buried as to ride over the pile and the post. <P>SOLUTION: When a predetermined horizontal force acting on the joint portion between the pile and the post is Q, a bearing force against the steel tube of the pile 1 necessary for resisting the horizontal force is P, the depth of the steel tube buried into the pile is L, the tensile yield strength of a lateral tie disposed around the steel tube is fsy, the cross sectional area of the lateral tie per unit length of the steel tube is As, and a correction factor is α, As is so determined so that an expression P=α×fsy×As×cos45°×P×L/(2P-Q) is established with α set to 1.5 to 3.0. The lateral tie in an amount matching the As is disposed at a pile portion around the steel tube. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、主として１杭１柱式の鉄道ＲＣラーメン高架橋で採用される鉄筋コンクリート造の杭と鉄筋コンクリート造の柱との接合構造に関する。 The present invention mainly relates to a joint structure between a reinforced concrete pile and a reinforced concrete column employed in a 1-pile 1-column type railway RC rigid frame viaduct.

従来、この種の杭と柱の接合構造は図１３に示すようになっている。図中ＧＬは地面、ＧＬ´は盛土、１は鉄筋コンクリート造の杭を示している。杭１は、ケーシング工法により地表から掘削した孔内に鉄筋１１を建て込んだ後、孔内にコンクリートを打設することにより造成される。杭１の上端には、橋台２を支える鉄筋コンクリート造の柱３が接続されている。尚、柱３の下端部は鉄筋コンクリート造の地中梁４に一体に連続するフーチング３ａになっている。杭１の鉄筋１１と柱３の鉄筋３１は、夫々、周方向の間隔を存して配設した軸方向に長手の主筋１２，３２と、これら主筋１２，３２を取り囲む、軸方向の間隔を存して配設したリング状の帯鉄筋１３，３３とで構成される。 Conventionally, this type of pile-column connection structure is as shown in FIG. In the figure, GL is the ground, GL ′ is embankment, and 1 is a reinforced concrete pile. The pile 1 is constructed by placing a reinforcing bar 11 in a hole excavated from the ground surface by a casing method and then placing concrete in the hole. A reinforced concrete column 3 that supports the abutment 2 is connected to the upper end of the pile 1. In addition, the lower end part of the column 3 is a footing 3a that is integrally continuous with the underground beam 4 made of reinforced concrete. The reinforcing bar 11 of the pile 1 and the reinforcing bar 31 of the column 3 are respectively provided with axially long main bars 12 and 32 arranged in the circumferential direction and the axial distance surrounding these main bars 12 and 32. It is composed of ring-shaped reinforcing bars 13 and 33 that are arranged and exist.

杭１の鉄筋１１の上端部は、杭１の上端面より上方にのびて、柱３の鉄筋３１の下端部にオーバーラップしている。これにより杭１と柱３の接続強度が向上する。然し、柱３の鉄筋３１の下端部における配筋作業がこれにオーバーラップする杭１の鉄筋１１に邪魔されて非常に面倒になり、また、鉄筋１１，３１のオーバーラップ部分へのコンクリートの打設も面倒になり、施工性が悪くなる不具合がある。 The upper end portion of the reinforcing bar 11 of the pile 1 extends upward from the upper end surface of the pile 1 and overlaps the lower end portion of the reinforcing bar 31 of the column 3. Thereby, the connection strength of the pile 1 and the pillar 3 improves. However, the bar arrangement work at the lower end of the reinforcing bar 31 of the column 3 is very troublesome because it is obstructed by the reinforcing bar 11 of the pile 1 that overlaps it, and the concrete is applied to the overlapping part of the reinforcing bars 11 and 31. There is a problem that the installation becomes troublesome and the workability becomes worse.

かかる不具合を解消するため、鉄筋コンクリート造の杭と鉄筋コンクリート造の柱とを、杭の鉄筋の上端部を柱の鉄筋の下端部にオーバーラップさせることなく接続する杭と柱の接合構造も従来知られている（例えば、特許文献１参照）。このものでは、所定長さの鋼管の下半部が杭の上端部の鉄筋で囲われる断面中央部に埋め込まれると共に、鋼管の上半部が柱の下端部の鉄筋で囲われる断面中央部に埋め込まれ、杭と柱が鋼管を介して接続される。
特開２００５−７６３３０号公報 In order to solve this problem, a pile-column connection structure that connects a reinforced concrete pile and a reinforced concrete column without overlapping the upper end of the reinforcing bar of the pile with the lower end of the reinforcing bar of the column is also known. (For example, refer to Patent Document 1). In this, the lower half of the steel pipe of a predetermined length is embedded in the center of the cross section surrounded by the reinforcing bar at the upper end of the pile, and the upper half of the steel pipe is embedded in the central part of the cross section surrounded by the reinforcing bar at the lower end of the column. Embedded, piles and columns are connected via steel pipes.
JP-A-2005-76330

上記の如く杭と柱とを鋼管を介して接続するものでは、杭の鉄筋の上端部が柱の鉄筋の下端部にオーバーラップしないため、施工性が著しく向上する。然し、このものでは、本願発明者が行った後述する試験の結果、杭に埋め込まれた鋼管の周囲の帯鉄筋の量が不足すると、鋼管周囲のコンクリートが割裂破壊し、杭と柱の接続部分の曲げ耐力が低下すると共にじん性能も低下して、所要の耐震性能を確保できなくなることが判明した。 In the case where the pile and the column are connected via the steel pipe as described above, the workability is remarkably improved because the upper end of the reinforcing bar of the pile does not overlap the lower end of the reinforcing bar of the column. However, in this case, if the amount of steel bars around the steel pipe embedded in the pile is insufficient as a result of the test described later by the present inventor, the concrete around the steel pipe breaks and breaks, and the connection part between the pile and the column It has been found that the required seismic performance cannot be ensured due to the decrease in the bending strength and the dust performance.

本発明は、以上の点に鑑み、鋼管の周囲の帯鉄筋の量を適切に設定して、杭と柱の接続部分の曲げ耐力とじん性能とを杭の鉄筋の上端部が柱の鉄筋の下端部にオーバーラップするものと同等以上に向上できるようにした杭と柱の接合構造を提供することをその課題としている。 In view of the above points, the present invention appropriately sets the amount of steel bar reinforcement around the steel pipe, and determines the bending strength and dust performance of the connection part between the pile and the column. An object of the present invention is to provide a pile-column joint structure that can be improved to be equal to or higher than that overlapping the lower end portion.

上記課題を解決するために、本発明は、鉄筋コンクリート造の杭と鉄筋コンクリート造の柱とを、杭の鉄筋の上端部を柱の鉄筋の下端部にオーバーラップさせることなく接続する杭と柱の接合構造であって、所定長さの鋼管の下半部が杭の上端部の鉄筋で囲われる断面中央部に埋め込まれ、鋼管の上半部が柱の下端部の鉄筋で囲われる断面中央部に埋め込まれるものにおいて、鋼管の太さ及び肉厚は、鋼管の断面の曲げ耐力が杭の鉄筋の主筋全体の断面の曲げ耐力と同等になるように設定され、杭と柱の接続部分に作用する所定の水平力に抗するのに必要な杭の鋼管に対する支圧力と、杭への鋼管の埋め込み深さとから杭の主筋を取り囲むリング状の帯鉄筋の量を決定し、この量の帯鉄筋を鋼管の周囲の杭部分に配設することを特徴とする。 In order to solve the above-described problems, the present invention provides a connection between a pile and a column that connects a reinforced concrete pile and a reinforced concrete column without overlapping the upper end of the reinforcing bar of the pile with the lower end of the reinforcing bar of the column. In the structure, the lower half of the steel pipe of a predetermined length is embedded in the center of the cross section surrounded by the reinforcing bar at the upper end of the pile, and the upper half of the steel pipe is embedded in the central part of the cross section surrounded by the reinforcing bar at the lower end of the column. In the embedded structure, the thickness and wall thickness of the steel pipe are set so that the bending strength of the cross section of the steel pipe is equal to the bending strength of the cross section of the main reinforcing bar of the pile, and acts on the connection part of the pile and column. The amount of ring-shaped rebar that surrounds the main bar of the pile is determined from the support pressure on the steel pipe of the pile necessary to withstand a predetermined horizontal force and the depth of embedding of the steel pipe in the pile. It arrange | positions in the pile part around a steel pipe, It is characterized by the above-mentioned.

杭と柱の接続部分に作用する水平力に抗する抵抗力は、主として鋼管に対するその前背面のコンクリートによる支圧力で得られる。この支圧力は、鋼管の周囲のコンクリートが健全なときに期待できるものであり、このコンクリートが割裂破壊する場合には、支圧力は期待できず、曲げ耐力及びじん性能が低下する。従って、曲げ耐力及びじん性能を向上させるには、鋼管の周囲のコンクリートをしっかりと拘束してその割裂破壊を抑制できるように、鋼管の周囲の杭部分に配設する帯鉄筋の量を適切に設定することが必要になる。そして、本願発明によれば、杭と柱の接続部分に作用する所定の水平力に抗するのに必要な杭の鋼管に対する支圧力が得られるように帯鉄筋の量を決定し、この量の帯鉄筋を鋼管の周囲の杭部分に配設するため、杭と柱の接続部分に所定の水平力が作用しても鋼管の周囲のコンクリートは割裂破壊しない。その結果、杭と柱の接続部分の曲げ耐力及びじん性能が向上する。 The resistance force against the horizontal force acting on the connection part between the pile and the column is obtained mainly by the support pressure by the concrete on the front and back surfaces of the steel pipe. This bearing pressure can be expected when the concrete surrounding the steel pipe is healthy. If this concrete breaks and breaks, the bearing pressure cannot be expected, and the bending strength and the dust performance deteriorate. Therefore, in order to improve the bending strength and the toughness performance, the amount of the steel bars to be arranged in the pile part around the steel pipe is appropriately adjusted so that the concrete around the steel pipe can be firmly restrained and the split fracture can be suppressed. It becomes necessary to set. And according to the present invention, the amount of the rebar is determined so that the supporting pressure against the steel pipe of the pile necessary to resist the predetermined horizontal force acting on the connecting portion of the pile and the column is obtained, and this amount Since the steel bars are arranged in the pile portion around the steel pipe, the concrete around the steel pipe does not split and break even if a predetermined horizontal force acts on the connection portion between the pile and the column. As a result, the bending strength and the dust performance of the connection part of a pile and a column improve.

より具体的には、鋼管の断面形状が正方形である場合、杭と柱の接続部分に作用する所定の水平力をＱ、この水平力に抗するのに必要な杭の鋼管に対する支圧力をＰ、杭への鋼管の埋め込み深さをＬ、鋼管の周囲に配設する帯鉄筋の引張降伏耐力をｆｓｙ、鋼管の単位長さ当りの帯鉄筋の断面積をＡｓ、補正係数をαとして、次式、
Ｐ＝α・ｆｓｙ・Ａｓ・ｃｏｓ４５°・Ｐ・Ｌ／（２Ｐ−Ｑ）
が、αを１．５〜３．０の値にして成立するように、Ａｓを決定し、このＡｓに見合う量の帯鉄筋を鋼管の周囲の杭部分に配設する。これによれば、後述する試験結果から明らかなように、杭と柱の接続部分の曲げ耐力とじん性能を杭の鉄筋の上端部が柱の鉄筋の下端部にオーバーラップするものと同等以上に向上できる。 More specifically, when the cross-sectional shape of the steel pipe is a square, the predetermined horizontal force acting on the connecting portion of the pile and the column is Q, and the support pressure to the steel pipe of the pile necessary to resist this horizontal force is P , L is the depth of steel pipe embedded in the pile, fsy is the tensile yield strength of the steel bars disposed around the steel pipe, As is the cross-sectional area of the steel bars per unit length of the steel pipe, and α is the correction factor. formula,
P = α, fsy, As, cos 45 °, P, L / (2P-Q)
However, As is determined so that α is set to a value of 1.5 to 3.0, an amount of the reinforcing bar corresponding to the As is disposed in the pile portion around the steel pipe. According to this, as is clear from the test results described later, the bending strength and the dust performance of the connection part of the pile and the column are equal to or higher than those in which the upper end of the reinforcing bar of the pile overlaps the lower end of the reinforcing bar of the column. Can be improved.

尚、Ａｓを大きくすればする程αは小さくなるが、Ａｓの増大に伴い施工性が悪くなるため、αの下限は１．５としている。また、αが３．０を上回る場合は、Ａｓが小さくなり過ぎて、鋼管周囲のコンクリートが帯鉄筋による拘束力不足で割裂破壊しやすくなる。そして、杭の鉄筋の上端部が柱の鉄筋の下端部にオーバーラップするものと同等以上の曲げ耐力とじん性能とを得ることができなくなる。そこで、αの上限は３．０としている。 In addition, although α becomes small, so that As is enlarged, since workability worsens with the increase in As, the lower limit of α is set to 1.5. Moreover, when (alpha) exceeds 3.0, As will become small too much, and the concrete around a steel pipe will be easy to split and break by the restraint force with a strip reinforcement insufficient. And it becomes impossible to obtain the bending strength and the dust performance equivalent to or higher than those in which the upper end of the reinforcing bar of the pile overlaps the lower end of the reinforcing bar of the column. Therefore, the upper limit of α is set to 3.0.

図１は本発明の実施形態の杭と柱の接合構造を示している。尚、図１３に示した上記従来例と同様の部材、部位には上記と同一の符号を付している。本実施形態では、図２に示されているように、杭１が断面円形であり、柱２が断面正方形である。 FIG. 1 shows a joint structure between a pile and a column according to an embodiment of the present invention. Note that the same members and parts as those in the conventional example shown in FIG. In this embodiment, as FIG. 2 shows, the pile 1 is circular in cross section and the pillar 2 is cross-sectional square.

また、本実施形態では、杭１の鉄筋１１の上端部が柱３の鉄筋３１の下端部にオーバーラップしていない。その代り、図２に示す如く断面正方形の鋼管５を用い、この鋼管５の下半部を杭１の上端部の鉄筋１１で囲われる断面中央部に埋め込むと共に、鋼管５の上半部を柱３の下端部の鉄筋３１で囲われる断面中央部に埋め込んでいる。これにより、杭１と柱３とが鋼管５を介して接続される。尚、杭１と柱３の接続部分の曲げ耐力が杭１の鉄筋１１の上端部を柱３の鉄筋３１の下端部にオーバーラップさせる図１３に示すものと同等になるように、鋼管５の太さと肉厚は、鋼管５の断面の曲げ耐力が杭１の鉄筋１１の主筋１２全体の断面の曲げ耐力と同等になるように設定されている。 Moreover, in this embodiment, the upper end part of the reinforcing bar 11 of the pile 1 does not overlap the lower end part of the reinforcing bar 31 of the column 3. Instead, as shown in FIG. 2, a steel pipe 5 having a square cross section is used, and the lower half of the steel pipe 5 is embedded in the center of the cross section surrounded by the reinforcing bar 11 at the upper end of the pile 1, and the upper half of the steel pipe 5 is a column. 3 is embedded in the central portion of the cross section surrounded by the reinforcing bar 31 at the lower end. Thereby, the pile 1 and the column 3 are connected via the steel pipe 5. The bending strength of the connection portion between the pile 1 and the column 3 is equal to that shown in FIG. 13 where the upper end of the reinforcing bar 11 of the pile 1 overlaps the lower end of the reinforcing bar 31 of the column 3. The thickness and thickness are set so that the bending strength of the cross section of the steel pipe 5 is equivalent to the bending strength of the cross section of the entire main bar 12 of the reinforcing bar 11 of the pile 1.

ここで、鋼管５及びコンクリートの材料強度を十分利用して、杭１と柱３の接続部分の曲げ耐力及びじん性能を効率良く向上させるには、杭１の鋼管５の周囲のコンクリートを杭１の帯鉄筋３３でしっかりと拘束して、鋼管５の周囲のコンクリートが割裂破壊しないようにすることが必要になる。そこで、鋼管５の周囲の杭１の部分に配設する帯鉄筋３３の量をどのように決定すれば良いかを調べるため、下記の試験を行った。 Here, in order to efficiently improve the bending strength and the dust performance of the connection part of the pile 1 and the column 3 by making full use of the material strength of the steel pipe 5 and concrete, the concrete around the steel pipe 5 of the pile 1 is piled up. Therefore, it is necessary to prevent the concrete surrounding the steel pipe 5 from being split and broken. Therefore, in order to investigate how to determine the amount of the rebar 33 disposed in the portion of the pile 1 around the steel pipe 5, the following test was performed.

試験に用いた試験体はＮｏ１からＮｏ６までの６種類であり、何れの試験体も外形寸法は図３に示す通りである。即ち、試験体は、鉄道ＲＣラーメン高架橋の１柱１杭式の基礎に一般的に用いられるφ１０００ｍｍの杭の１／２モデルのφ５００（長さ２０００ｍｍ）の鉄筋コンクリート造の杭１であり、その一端にフーチング３ａに対応する平面形状２５００ｍｍ×１５００ｍｍ高さ８００ｍｍの直方体形状の接合部３ａ´が一体に形成されている。そして、接合部３ａ´を下にした上下反転姿勢で試験体を試験機のベースに接合部において固定し、杭１の上端に自重による圧縮応力度に相当する１Ｎ／ｍｍ^２の鉛直荷重を載荷する。また、接合部３ａ´から１５００ｍｍ離れた杭１の上部を油圧ジャッキで水平方向に押し引きし、この部分に正負交番の水平荷重を載荷するようにした。 There are six types of test bodies used in the tests from No1 to No6, and the outer dimensions of all the test bodies are as shown in FIG. In other words, the specimen is a reinforced concrete pile 1 of φ500 (length 2000 mm) which is a half model of φ1000 mm pile generally used for the foundation of a 1-column 1-pile type of RC RC ramen viaduct. In addition, a rectangular parallelepiped joining portion 3a ′ having a planar shape of 2500 mm × 1500 mm and a height of 800 mm corresponding to the footing 3a is integrally formed. Then, the test body is fixed to the base of the testing machine in the upside down posture with the joint 3a ′ down, and a vertical load of 1 N / mm ² corresponding to the degree of compressive stress due to its own weight is loaded on the upper end of the pile 1 To do. Further, the upper part of the pile 1 that is 1500 mm away from the joint 3a ′ is pushed and pulled in the horizontal direction with a hydraulic jack, and a positive and negative alternating horizontal load is loaded on this part.

Ｎｏ１の試験体は、図１３に示した従来例を模したものであり、図４（ａ）に示すように、主筋１２が接合部３ａ´に亘って配設されている。主筋１２は、杭１の断面中心と同心の直径３６０ｍｍの円周上に周方向に等間隔で１６本配設されている。また、帯鉄筋１３は、図４（ａ）にＡ，Ｃで示す杭１の上部と接合部３ａ´内の領域では軸方向に１２０ｍｍ間隔で配設され、Ｂで示す領域では軸方向に６０ｍｍ間隔で配設されている。 The test specimen No. 1 simulates the conventional example shown in FIG. 13, and as shown in FIG. 4A, the main muscle 12 is disposed across the joint 3 a ′. Sixteen main bars 12 are arranged at equal intervals in the circumferential direction on a circumference having a diameter of 360 mm concentric with the cross-sectional center of the pile 1. In addition, the belt reinforcing bars 13 are arranged at intervals of 120 mm in the axial direction in the upper portion of the pile 1 indicated by A and C in FIG. 4A and the region in the joint portion 3a ′, and 60 mm in the axial direction in the region indicated by B. They are arranged at intervals.

Ｎｏ２〜Ｎｏ６の試験体も、主筋１２が杭１の断面中心と同心の直径３６０ｍｍの円周上に周方向に等間隔で１６本配設されているが、主筋１２は、図４（ｂ）に示すように、接合部３ａ´の６０ｍｍ手前で終端している。そして、杭１の鉄筋１１で囲われる断面中央部に接合部３ａ´の下端に達する鋼管５が埋め込まれている。また、帯鉄筋１３は、図４（ｂ）にＡで示す杭１の上部領域では軸方向に１２０ｍｍ間隔で配設され、Ｂに示す鋼管５の周囲の杭部分を含む領域では６０ｍｍ間隔で配設されている。 In the specimens No. 2 to No. 6, 16 main bars 12 are arranged at equal intervals in the circumferential direction on the circumference of 360 mm in diameter concentric with the cross-sectional center of the pile 1, but the main bars 12 are shown in FIG. As shown in FIG. 4, it terminates 60 mm before the joint 3a ′. And the steel pipe 5 which reaches the lower end of joining part 3a 'is embedded in the cross-sectional center part enclosed by the reinforcing bar 11 of the pile 1. FIG. In addition, the strip reinforcing bars 13 are arranged at intervals of 120 mm in the axial direction in the upper region of the pile 1 shown by A in FIG. 4B, and are arranged at intervals of 60 mm in the region including the pile portion around the steel pipe 5 shown in B. It is installed.

ここで、主筋１２は、Ｎｏ１〜Ｎｏ６の何れの試験体においても、ＳＤ３４５製の直径１６ｍｍのものである。また、鋼管５は、Ｎｏ２〜Ｎｏ６の何れの試験体においても、ＳＭ４９０製で、断面形状が一辺２００ｍｍの正方形である。また、鋼管５の肉厚は、鋼管５の断面の曲げ耐力が１６本の主筋１２全体の断面の曲げ耐力と同等になるように、８ｍｍに設定されている。 Here, the main muscle 12 is made of SD345 and has a diameter of 16 mm in any of the test bodies No1 to No6. Further, the steel pipe 5 is made of SM490 and has a square shape with a cross-sectional side of 200 mm in any of the test bodies No2 to No6. Further, the thickness of the steel pipe 5 is set to 8 mm so that the bending strength of the cross section of the steel pipe 5 is equivalent to the bending strength of the cross section of the entire 16 main bars 12.

Ｎｏ１の試験体の図４（ａ）のＡ，Ｂ，Ｃ各領域と、Ｎｏ２〜Ｎｏ６の試験体の図４（ｂ）のＡ領域に配設する帯鉄筋１３は何れもＳＤ３４５製の直径１０ｍｍのものである。また、Ｎｏ２〜Ｎｏ４の試験体の図４（ｂ）のＢ領域に配設する帯鉄筋１３は、上記と同様にＳＤ３４５製の直径１０ｍｍのものであるが、杭１への鋼管５の埋め込み深さＬがＮｏ２の試験体では８００ｍｍ、Ｎｏ３の試験体では６００ｍｍ、Ｎｏ４の試験体では４００ｍｍになっている。また、Ｎｏ５とＮｏ６の試験体は、杭１への鋼管５の埋め込み深さＬが共に６００ｍｍになっているが、図４（ｂ）のＢ領域に配設する帯鉄筋１３を、Ｎｏ５の試験体ではＳＤ３４５製の直径１３ｍｍのものとし、Ｎｏ６の試験体ではＳＤ３４５製の直径１６ｍｍのものとしている。 4A of the No. 1 test body, each of the reinforcing bars 13 disposed in the A area of FIG. 4B of the No. 2 to No. 6 test specimens is 10 mm in diameter made of SD345. belongs to. Moreover, although the band reinforcement 13 arrange | positioned in the B area | region of FIG.4 (b) of the test body of No2-No4 is the thing of diameter 10mm made from SD345 like the above, the embedding depth of the steel pipe 5 to the pile 1 is carried out. The length L is 800 mm for the No. 2 specimen, 600 mm for the No. 3 specimen, and 400 mm for the No. 4 specimen. Moreover, although the embedded depth L of the steel pipe 5 to the pile 1 is both 600 mm, the test specimens of No5 and No6 have the band reinforcing bars 13 arranged in the region B of FIG. The body is made of SD345 with a diameter of 13 mm, and the specimen No. 6 is made of SD345 with a diameter of 16 mm.

各試験体に用いた主筋１２、帯鉄筋１３、鋼管５及びコンクリートの材料強度の試験値を下記表１に示す。 Table 1 below shows the test values of the material strength of the main reinforcement 12, the band reinforcement 13, the steel pipe 5, and the concrete used for each test specimen.

試験は、各試験体の杭１の上部に上記の如く油圧ジャッキの押し引きで正負交番の水平荷重を載荷することで行った。荷重・変位の制御は、Ｎｏ１の試験体において以下の手順で行った。即ち、降伏するまでは荷重制御で水平荷重を正負１サイクル毎に１０ｋＮ宛増加させて載荷した。降伏の判定は、油圧ジャッキを押し出す方向の載荷において、引張側４５°方向（水平荷重の作用線に対し水平方向に４５°回転した方向）の主筋１１のひずみが降伏ひずみに達した時点とし、このときの変位を降伏変位とした。降伏後は、変位が降伏変位の偶数倍で３サイクル毎に段階的に増加するように変位制御で水平荷重を載荷した。載荷の終了は荷重―変位曲線の包絡線における水平荷重が最大水平荷重の５０％を下回ることを目標にした。Ｎｏ２〜Ｎｏ６の試験体の載荷試験は、Ｎｏ１の試験体の降伏変位を用いてＮｏ１の試験体の場合と同様の方法で行った。 The test was carried out by loading a horizontal load of alternating positive and negative by pushing and pulling the hydraulic jack as described above on the top of the pile 1 of each specimen. The load / displacement control was performed in the following procedure in the No. 1 specimen. That is, until yielding, the horizontal load was increased by 10 kN for each positive and negative cycle by load control and loaded. The determination of yield is made when the strain of the main bar 11 in the direction of 45 ° in the tension side (the direction rotated 45 ° in the horizontal direction with respect to the action line of the horizontal load) reaches the yield strain in the loading in the direction of pushing out the hydraulic jack. The displacement at this time was defined as the yield displacement. After yielding, a horizontal load was loaded with displacement control so that the displacement increased evenly every three cycles and increased stepwise every three cycles. The end of loading was aimed at the horizontal load in the envelope of the load-displacement curve being below 50% of the maximum horizontal load. The loading test of No2-No6 specimens was performed in the same manner as the No1 specimen using the yield displacement of No1 specimen.

以下の説明では、Ｎｏ１の試験体の降伏変位８．７ｍｍをΔと記し、油圧ジャッキを押し出す方向の水平荷重・水平変位を＋、油圧ジャッキを引き戻す方向の水平荷重・水平変位を−とする。また、荷重、変位は水平荷重の作用点の水平荷重、水平変位を意味する。 In the following description, the yield displacement 8.7 mm of the No. 1 specimen is denoted by Δ, the horizontal load / horizontal displacement in the direction of pushing out the hydraulic jack is +, and the horizontal load / horizontal displacement in the direction of pulling back the hydraulic jack is −. Moreover, a load and a displacement mean the horizontal load and horizontal displacement of the action point of a horizontal load.

図５は各試験体の荷重と変位の履歴曲線を示している。尚、荷重は、鉛直方向荷重による偏心曲げモーメントの影響を加味した値になっている。 FIG. 5 shows a load and displacement history curve of each specimen. The load is a value that takes into account the effect of the eccentric bending moment due to the vertical load.

Ｎｏ１の試験体では、変位８．７ｍｍ、荷重１４８ｋＮで引張側４５°方向の主筋１２のひずみが降伏ひずみに達し、杭基部及び杭側面に３本の水平な曲げひび割れが発生した。その後、６Δまでは１７５ｋＮ前後の一定の荷重のまま変形が増大した。この間に曲げひび割れの先端から斜め下方へ向かうせん断ひび割れが発生した。せん断ひび割れは杭基部から３０ｃｍ程度の区間で密に発生した。また、杭基部には、コンクリートの圧壊に伴う縦方向のひび割れも生じた。 In the No. 1 test body, the strain of the main bar 12 in the direction of 45 ° in the tension side reached the yield strain at a displacement of 8.7 mm and a load of 148 kN, and three horizontal bending cracks occurred on the pile base and the pile side. Thereafter, deformation increased with a constant load of around 175 kN up to 6Δ. During this time, shear cracks occurred obliquely downward from the tip of the bending crack. Shear cracks occurred densely in the section about 30 cm from the pile base. In addition, vertical cracks caused by concrete crushing occurred in the pile base.

そして、６Δで杭基部コンクリートの圧壊に伴う被りコンクリートの剥落が始まり、変形が進むのに伴い剥落範囲が大きくなって、荷重が低下した。その後、１２Δの２，３サイクル目の繰り返し載荷において荷重は１サイクル目に比べ低下が顕著になり、１２Δの３サイクル〜１４Δにかけて主筋１２が破断して荷重は大きく低下した。履歴曲線の形状は、図５（ａ）に示すように、紡錘型の吸収エネルギーが大きい形状になった。また、破壊形式は、杭基部に塑性ヒンジが形成され、主筋１２が座屈して被りコンクリートがはらみ出す曲げ破壊であった。 Then, at 6Δ, the covering concrete started to peel off due to the collapse of the pile base concrete, and as the deformation progressed, the peeling range increased and the load decreased. Thereafter, in the repeated loading of the second and third cycles of 12Δ, the load became significantly lower than that in the first cycle, and the main bar 12 broke and the load was greatly reduced from the third cycle to 14Δ of 12Δ. As shown in FIG. 5 (a), the hysteresis curve has a spindle-shaped absorption energy. Moreover, the failure type was a bending failure in which a plastic hinge was formed at the pile base, the main reinforcement 12 buckled and the concrete covered.

Ｎｏ２の試験体では、変位１７．３ｍｍ、荷重１７１ｋＮで鋼管５の引張側ひずみが降伏ひずみに達した。また、２Δまでに水平のひび割れが鋼管埋め込み部（鋼管５の上端より下方の杭部分）の上部に３〜４本発生すると共に、鋼管埋め込み端部（鋼管５の上端と同レベルの部分）から下方にのびる鉛直の割裂ひび割れ及び杭基部から上方にのびる鉛直の割裂ひび割れが発生した。その後、２〜４Δの間で水平の曲げひび割れの進展とともに鉛直の割裂ひび割れも進展した。この鉛直の割裂ひび割れは荷重作用線に対し水平方向に±４５°回転した位置に集中して発生した。 In the No. 2 specimen, the tensile strain on the steel pipe 5 reached the yield strain at a displacement of 17.3 mm and a load of 171 kN. In addition, 3 to 4 horizontal cracks are generated in the upper portion of the steel pipe embedded portion (pile portion below the upper end of the steel pipe 5) by 2Δ, and from the steel pipe embedded end portion (the same level as the upper end of the steel pipe 5). Vertical split cracks extending downward and vertical split cracks extending upward from the pile base occurred. After that, vertical split cracks progressed with horizontal bending cracks between 2 and 4Δ. The vertical split cracks were concentrated at a position rotated ± 45 ° in the horizontal direction with respect to the load action line.

そして、４Δで杭基部コンクリートの圧壊に伴う被りコンクリートの剥落が始まり、剥落範囲は徐々に大きくなったが、１２Δまでは２１５ｋＮ前後でほぼ一定の荷重のまま変形が増大した。１２Δでコンクリートの圧壊に伴う被りコンクリートの剥落が大きくなり、その後１６Δまで１２Δのときに比べ荷重の低下は見られるが、繰り返し載荷において荷重の低下は顕著ではなかった。履歴曲線は、図５（ｂ）に示すように、紡錘型の吸収エネルギーが大きい形状になった。載荷は試験機の限界から＋１６Δ、−１８Δで終了した。そのため、終局状態は確認できなかったが、破壊形式は杭基部での鋼管５の座屈による曲げ破壊と考えられる。 Then, at 4Δ, the covering concrete started to fall off due to the collapse of the pile base concrete, and the peeling range gradually increased, but until 12Δ, the deformation increased with a substantially constant load around 215 kN. At 12Δ, peeling of the covered concrete accompanying the crushing of the concrete increased, and thereafter, a load decrease was seen up to 16Δ compared to 12Δ, but the load decrease was not significant in repeated loading. As shown in FIG. 5B, the hysteresis curve has a shape with a large spindle-type absorbed energy. Loading was completed at + 16Δ and −18Δ due to the limit of the testing machine. Therefore, although the final state could not be confirmed, the failure type is considered to be bending failure due to buckling of the steel pipe 5 at the pile base.

Ｎｏ３の試験体では、変位２２．４ｍｍ、荷重１７２ｋＮで鋼管５の引張側ひずみが降伏ひずみに達した。また、２Δまでに水平のひび割れが鋼管埋め込み部の上部に４本発生すると共に、鋼管埋め込み端部から下方にのびる鉛直の割裂ひび割れ及び杭基部から上方にのびる鉛直の割裂ひび割れが発生した。その後、２〜４Δの間で水平の曲げひび割れの進展とともに鉛直の割裂ひび割れも進展した。この鉛直の割裂ひび割れは荷重作用線に対し水平方向に±４５°回転した位置に集中して発生した。 In the No. 3 specimen, the tensile strain on the steel pipe 5 reached the yield strain at a displacement of 22.4 mm and a load of 172 kN. In addition, four horizontal cracks occurred in the upper part of the steel pipe embedded part by 2Δ, and a vertical split crack extending downward from the steel pipe embedded end part and a vertical split crack extending upward from the pile base part were generated. After that, vertical split cracks progressed with horizontal bending cracks between 2 and 4Δ. The vertical split cracks were concentrated at a position rotated ± 45 ° in the horizontal direction with respect to the load action line.

そして、４Δで２０２ｋＮの最大荷重を示すが、この時点で鋼管埋め込み端部の水平の曲げひび割れ及び鉛直の割裂ひび割れが大きくなり、鋼管埋め込み端部下方の被りコンクリートの剥落が始まった。その後、４〜６Δまでは荷重をかろうじて維持したが、６Δで鋼管埋め込み端部下方の被りコンクリートの剥落が大きくなり、鋼管埋め込み端部下方２０ｃｍで折れ曲がったような変形状態になった。そして、８Δの繰り返し載荷において鋼管埋め込み端部を中心とした被りコンクリートの剥落を生じて荷重の低下が顕著になり、１０Δ、１２Δで荷重は大きく低下した。履歴曲線の形状は、図５（ｃ）に示すように、スリップ型に近似した吸収エネルギーが小さい形状になった。破壊形式は、鋼管５の周囲のコンクリートの割裂破壊であった。 The maximum load of 202 kN is shown by 4Δ. At this time, the horizontal bending crack and the vertical split crack at the embedded end of the steel pipe became large, and the covering concrete under the embedded end of the steel pipe began to peel off. Thereafter, the load was barely maintained from 4 to 6Δ, but at 6Δ, the concrete stripped under the steel pipe embedded end was greatly peeled off, and it was in a deformed state that was bent 20 cm below the steel pipe embedded end. Then, in the repeated loading of 8Δ, the covered concrete peeled off centering on the steel pipe embedded end portion, and the load was significantly reduced, and the load was greatly reduced at 10Δ and 12Δ. As shown in FIG. 5C, the hysteresis curve has a shape with small absorbed energy that approximates a slip type. The fracture type was split fracture of concrete around the steel pipe 5.

Ｎｏ４の試験体では、鋼管５の引張側ひずみが降伏ひずみを越えなかった。また、２Δまでに水平のひび割れが鋼管埋め込み部の上部に２本発生すると共に、鋼管埋め込み端部から下方にのびる鉛直の割裂ひび割れ及び杭基部から上方にのびる鉛直の割裂ひび割れが発生した。その後、２〜４Δの間で水平の曲げひび割れの進展とともに鉛直の割裂ひび割れも進展した。この鉛直の割裂ひび割れは荷重作用線に対し水平方向に±４５°回転した位置に集中して発生した。 In the No. 4 specimen, the tensile strain on the steel pipe 5 did not exceed the yield strain. In addition, two horizontal cracks occurred in the upper part of the steel pipe embedded part by 2Δ, and a vertical split crack extending downward from the steel pipe embedded end part and a vertical split crack extending upward from the pile base part were generated. After that, vertical split cracks progressed with horizontal bending cracks between 2 and 4Δ. The vertical split cracks were concentrated at a position rotated ± 45 ° in the horizontal direction with respect to the load action line.

そして、４Δで１４０ｋＮの最大荷重を示すが、この時点で鋼管埋め込み端部の水平の曲げひび割れ及び鉛直の割裂ひび割れが大きくなり、鋼管埋め込み端部付近の被りコンクリートの剥落が始まった。その後、荷重は４Δでの値を維持することなく６Δ、８Δ、１０Δで順に低下していった。また、６Δで鋼管埋め込み端部付近の被りコンクリートの剥落が大きくなり、鋼管埋め込み端部下方２０ｃｍで折れ曲がったような変形状態になった。そして、８Δの繰り返し載荷において荷重の低下が顕著になった。履歴曲線の形状は、図５（ｄ）に示すように、スリップ型に近似しており、Ｎｏ３の試験体に比べ吸収エネルギーは更に小さい。破壊形式は、Ｎｏ３の試験体と同様に鋼管５の周囲のコンクリートの割裂破壊であった。 The maximum load of 140 kN is indicated by 4Δ. At this time, horizontal bending cracks and vertical split cracks at the steel pipe embedded end portion became large, and peeling of the covered concrete near the steel pipe embedded end portion began. Thereafter, the load gradually decreased at 6Δ, 8Δ, and 10Δ without maintaining the value at 4Δ. Moreover, peeling of covering concrete in the vicinity of the steel pipe embedded end portion became large at 6Δ, and it was in a deformed state that was bent 20 cm below the steel pipe embedded end portion. And the load reduction became remarkable in the repeated loading of 8Δ. As shown in FIG. 5D, the shape of the hysteresis curve approximates a slip type, and the absorbed energy is smaller than that of the No. 3 specimen. The fracture type was split fracture of concrete around the steel pipe 5 as in the case of No. 3 specimen.

Ｎｏ５の試験体では、変位２０．６ｍｍ、荷重１７５ｋＮで鋼管５の引張側ひずみが降伏ひずみに達した。また、２Δまでに水平のひび割れが鋼管埋め込み部の上部に２〜３本発生すると共に、鋼管埋め込み端部から下方にのびる鉛直の割裂ひび割れ及び杭基部から上方にのびる鉛直の割裂ひび割れが発生した。その後、２〜４Δの間で水平の曲げひび割れの進展とともに鉛直の割裂ひび割れも進展した。この鉛直の割裂ひび割れは荷重作用線に対し水平方向に±４５°回転した位置に集中して発生した。 In the specimen No. 5, the tensile strain on the steel pipe 5 reached the yield strain at a displacement of 20.6 mm and a load of 175 kN. In addition, 2 to 3 horizontal cracks occurred in the upper part of the steel pipe embedded part by 2Δ, and vertical split cracks extending downward from the steel pipe embedded end part and vertical split cracks extending upward from the pile base part occurred. After that, vertical split cracks progressed with horizontal bending cracks between 2 and 4Δ. The vertical split cracks were concentrated at a position rotated ± 45 ° in the horizontal direction with respect to the load action line.

そして、８Δで杭基部コンクリートの圧壊に伴う被りコンクリートの剥落が始まり、剥落範囲は徐々に大きくなったが、１６Δまで２００ｋＮ前後でほぼ一定の荷重のまま変形が増大した。１６Δで杭基部コンクリートの圧壊に伴う被りコンクリートの剥落が大きくなったが、荷重は殆ど低下しなかった。１８Δの繰り返し載荷において荷重の低下が顕著になり、３サイクル目を＋２０Δまで載荷した。履歴曲線の形状は、図５（ｅ）に示すように、紡錘型の吸収エネルギーの大きい形状になった。尚、試験機の限界はＮｏ２の試験体で載荷を終了した１６Δ程度であるが、Ｎｏ５，６の試験体では安全を確認しながら限界を超えて載荷を続行した。破壊形式は杭基部での鋼管５の座屈による曲げ破壊であった。 Then, at 8Δ, the covering concrete started to fall off due to the collapse of the pile base concrete, and the peeling range gradually increased, but the deformation increased with a nearly constant load at around 200 kN up to 16Δ. At 16Δ, the peeling of the covered concrete accompanying the crushing of the pile base concrete increased, but the load hardly decreased. The load drop became remarkable in repeated loading of 18Δ, and the third cycle was loaded up to + 20Δ. As shown in FIG. 5 (e), the hysteresis curve has a spindle shape with large absorbed energy. The limit of the testing machine was about 16Δ when loading was completed with the No. 2 specimen, but with the No. 5 and 6 specimens, loading was continued beyond the limit while confirming safety. The failure mode was bending failure due to buckling of the steel pipe 5 at the pile base.

Ｎｏ６の試験体では、変位１７．８ｍｍ、荷重１７６ｋＮで鋼管５の引張側ひずみが降伏ひずみに達した。また、２Δまでに水平のひび割れが鋼管埋め込み部の上部に２〜３本発生すると共に、鋼管埋め込み端部から下方にのびる鉛直の割裂ひび割れ及び杭基部から上方にのびる鉛直の割裂ひび割れが発生した。その後、２〜４Δの間で水平の曲げひび割れの進展とともに鉛直の割裂ひび割れも進展した。この鉛直の割裂ひび割れは荷重作用線に対し水平方向に±４５°回転した位置に集中して発生した。 In the specimen No. 6, the tensile strain on the steel pipe 5 reached the yield strain at a displacement of 17.8 mm and a load of 176 kN. In addition, 2 to 3 horizontal cracks occurred in the upper part of the steel pipe embedded part by 2Δ, and vertical split cracks extending downward from the steel pipe embedded end part and vertical split cracks extending upward from the pile base part occurred. After that, vertical split cracks progressed with horizontal bending cracks between 2 and 4Δ. The vertical split cracks were concentrated at a position rotated ± 45 ° in the horizontal direction with respect to the load action line.

そして、８Δで杭基部コンクリートの圧壊に伴う被りコンクリートの剥落が始まり、剥落範囲は徐々に大きくなったが、１６Δまで２１０ｋＮ前後でほぼ一定の荷重のまま変形が増大した。１６Δで杭基部コンクリートの圧壊に伴う被りコンクリートの剥落が大きくなったが、荷重は殆ど低下しなかった。１８Δの繰り返し載荷において荷重の低下が顕著になり、２０Δの繰り返し載荷において荷重の低下が更に顕著になり、３サイクル目を＋２２Δまで載荷した。履歴曲線の形状は、図５（ｆ）に示すように、紡錘型の吸収エネルギーの大きい形状になった。破壊形式は杭基部での鋼管５の座屈による曲げ破壊であった。 Then, at 8Δ, the covering concrete started to fall off due to the collapse of the pile base concrete, and the peeling range gradually increased, but the deformation increased with a substantially constant load around 210 kN up to 16Δ. At 16Δ, the peeling of the covered concrete accompanying the crushing of the pile base concrete increased, but the load hardly decreased. The decrease in load became remarkable in repeated loading of 18Δ, and the decrease in load became more remarkable in repeated loading of 20Δ, and the third cycle was loaded up to + 22Δ. As shown in FIG. 5F, the shape of the hysteresis curve is a spindle-type shape having a large absorbed energy. The failure mode was bending failure due to buckling of the steel pipe 5 at the pile base.

各試験体の試験結果を下記表２に示す。尚、表２中の損傷レベル２は繰り返し載荷で耐力低下が顕著にならない最大変位時点を意味する。 The test results for each specimen are shown in Table 2 below. In addition, the damage level 2 in Table 2 means the maximum displacement point at which the yield strength does not become noticeable with repeated loading.

図６（ａ）は、Ｎｏ１の試験体と、鋼管５の埋め込み深さが互いに異なるＮｏ２，３，４の試験体の荷重―変位曲線の包絡線を示している。同図より、Ｎｏ２の試験体はＮｏ１の試験体よりじん性能が優れていることが分かる。尚、鋼管５の断面の曲げ耐力を主筋１２全体の断面の曲げ耐力と同程度に設定しているにも拘らず、Ｎｏ２，３，５，６の試験体はＮｏ１の試験体より最大荷重、即ち、曲げ耐力が大きくなっている。これは、鋼材の材料の規格値と実強度とが表１に示されているように異なること、即ち、主筋１２（ＳＤ３４５）では降伏点規格値が３４５ｋＮであるのに対し実降伏点が３８１〜３９１と異なり、鋼管５（ＳＭ４９０）では降伏点規格値が３２５ｋＮであるのに対し実降伏点が４０２〜４３１ｋＮと異なることに起因すると考えられる。 FIG. 6A shows the envelopes of the load-displacement curves of the No. 1 test body and the No. 2, 3 and 4 test bodies having different embedding depths of the steel pipe 5. From the figure, it can be seen that the No. 2 specimen has better dust performance than the No. 1 specimen. Although the bending strength of the cross section of the steel pipe 5 is set to the same level as the bending strength of the cross section of the entire main reinforcement 12, the test pieces of Nos. 2, 3, 5, and 6 have the maximum load than the No. 1 test piece. That is, the bending strength is increased. This is because the standard values and actual strengths of the steel materials are different as shown in Table 1, that is, the yield point standard value is 345 kN for the main reinforcement 12 (SD345), whereas the actual yield point is 381. Unlike 391, it is considered that the steel pipe 5 (SM490) has a yield point standard value of 325 kN, whereas the actual yield point is different from 402 to 431 kN.

Ｎｏ３の試験体は、Ｎｏ２の試験体とほぼ同等の曲げ耐力を有するが、じん性能はＮｏ１の試験体よりも劣り、Ｎｏ４の試験体は曲げ耐力及びじん性能がＮｏ１の試験体よりも劣ることが分かる。これは、杭１への鋼管５の埋め込み深さＬがＮｏ２の試験体の８００ｍｍに対しＮｏ３の試験体では６００ｍｍ、Ｎｏ４の試験体では４００ｍｍと小さくなっていることによる影響である。 The No. 3 test body has almost the same bending strength as the No. 2 test body, but the dust performance is inferior to the No. 1 test body, and the No. 4 test body is inferior to the No. 1 test body in bending strength and dust performance. I understand. This is due to the fact that the embedding depth L of the steel pipe 5 in the pile 1 is as small as 600 mm for the No3 specimen and 400 mm for the No4 specimen compared to 800 mm for the No2 specimen.

図６（ｂ）は、Ｎｏ１の試験体と、鋼管５の埋め込み深さＬが６００ｍｍと同一で帯鉄筋１３の太さが互いに異なるＮｏ３，５，６の試験体の荷重―変位曲線の包絡線を示している。Ｎｏ３の試験体では終局変位が１０７．０ｍｍでじん性率（終局変位を降伏変位で除した値）が３．３であるのに対し、Ｎｏ５の試験体では終局変位１５０．５ｍｍじん性率７．３、Ｎｏ６の試験体では終局変位１６３．１ｍｍじん性率９．２とじん性能が大きく向上している。これは、鋼管５の周囲の杭部分に配設する帯鉄筋１３の径をＮｏ３の試験体の１０ｍｍからＮｏ５の試験体では１３ｍｍ、Ｎｏ６の試験体では１６ｍｍとして、帯鉄筋１３の量を大きくしたことによる影響である。 FIG. 6B shows the envelope of the load-displacement curve of the No. 1 specimen and No. 3, 5 and 6 specimens in which the embedding depth L of the steel pipe 5 is the same as 600 mm and the thicknesses of the strip reinforcing bars 13 are different from each other. Is shown. In the No. 3 specimen, the ultimate displacement is 107.0 mm and the toughness ratio (the value obtained by dividing the ultimate displacement by the yield displacement) is 3.3, whereas in the No. 5 specimen, the ultimate displacement is 150.5 mm. .3, No. 6 specimen has a final displacement of 163.1 mm toughness of 9.2 and a great improvement in toughness. This is because the diameter of the band rebar 13 arranged in the pile portion around the steel pipe 5 is 10 mm to 13 mm for the No3 test body and 16 mm for the No6 test body, and the amount of the band rebar 13 is increased. It is an influence by that.

図７に、２Δの載荷時におけるＮｏ１，２の試験体の引張側の主筋１２のひずみ及びＮｏ２の試験体の鋼管５の引張側の面のひずみの高さ方向の分布を示す。縦軸は杭基部（接合部３ａ´の上端）からの高さを示している。Ｎｏ１の試験体では、主筋１２のひずみが杭基部の近傍で最大になる。一方、Ｎｏ２の試験体では、主筋１２のひずみが鋼管埋め込み端部の近傍で最大になり、杭基部に向けて減少する。また、鋼管５のひずみは杭基部の近傍で最大になる。このことから、Ｎｏ２の試験体においては、鋼管埋め込み端部から杭基部に向けて主筋１２が断面の引張応力を徐々に分担しなくなり、代わりに鋼管５が断面の引張応力を分担することが分かる。これは鋼管５を埋め込んだＮｏ３〜Ｎｏ６の試験体でも同様である。 FIG. 7 shows the distribution in the height direction of the strain of the main muscle 12 on the tensile side of the No. 1 and No. 2 specimens and the strain on the surface of the steel pipe 5 of the No. 2 specimen when 2Δ is loaded. The vertical axis indicates the height from the pile base (the upper end of the joint 3a ′). In the No. 1 test body, the strain of the main bar 12 is maximized in the vicinity of the pile base. On the other hand, in the No. 2 specimen, the strain of the main reinforcement 12 becomes maximum in the vicinity of the steel pipe embedded end and decreases toward the pile base. Further, the strain of the steel pipe 5 is maximized in the vicinity of the pile base. From this, it can be seen that in the No. 2 test body, the main bar 12 does not gradually share the tensile stress of the cross section from the steel pipe embedded end toward the pile base, and instead the steel pipe 5 shares the tensile stress of the cross section. . The same applies to the test bodies No. 3 to No. 6 in which the steel pipe 5 is embedded.

帯鉄筋１３のひずみの水平断面における分布は、荷重の作用線に対し水平方向に±４５°回転した位置で最大になる。これは、鉛直の割裂ひび割れが荷重作用線に対し水平方向に±４５°回転した位置で集中的に発生することと一致する。図８に、８Δの載荷時におけるＮｏ１，２の試験体の荷重作用線に対し４５°回転した位置での帯鉄筋１３のひずみの高さ方向の分布を示す。Ｎｏ１の試験体では、杭基部より上方へ３６０ｍｍまでの区間でひずみが他区間より大きくなる。一方、Ｎｏ２の試験体では、鋼管埋め込み端部と杭基部とでひずみが大きくなり、鋼管埋め込み部の中間部分ではひずみが小さくなる。これは鋼管５を埋め込んだＮｏ３〜Ｎｏ６の試験体でも同様である。 The distribution of the strain of the rebar 13 in the horizontal section is maximized at a position rotated ± 45 ° in the horizontal direction with respect to the line of action of the load. This is consistent with the fact that vertical split cracks occur intensively at positions rotated ± 45 ° in the horizontal direction with respect to the load action line. FIG. 8 shows the distribution in the height direction of the strain of the band rebar 13 at a position rotated by 45 ° with respect to the load action line of the No. 1 and No. 2 specimens when 8Δ is loaded. In the test body of No1, distortion becomes larger than other sections in the section up to 360 mm from the pile base. On the other hand, in the specimen No. 2, the strain increases at the steel pipe embedded end portion and the pile base portion, and the strain decreases at the intermediate portion of the steel pipe embedded portion. The same applies to the test bodies No. 3 to No. 6 in which the steel pipe 5 is embedded.

次に、杭１に鋼管５を埋め込んだ場合における曲げモーメント・水平力に対する耐荷メカニズムについて考察する。帯鉄筋１３のひずみ分布が上記の如く鋼管埋め込み端部と杭基部とで大きく中間部分で小さいことから、耐荷メカニズムは図９のようにモデル化できる。このモデルでは、曲げモーメントＭと水平力Ｑに対する抵抗力は、鋼管５に対するその前背面のコンクリートによる支圧力Ｐ及び鋼管５とコンクリートの摩擦力Ｔから成るものとしている。この支圧力Ｐ及び摩擦力Ｔは、鋼管５の周囲のコンクリートが健全なときに期待できるものである。Ｎｏ３，４の試験体のように鋼管５の周囲のコンクリートが割裂破壊する場合には、曲げ耐力及びじん性能が低下することから分かるように、支圧力Ｐ及び摩擦力Ｔは期待できない。従って、曲げ耐力及びじん性能を向上させるには、鋼管５の周囲のコンクリートをしっかりと拘束してその割裂破壊を抑制できるように、鋼管５の周囲の杭部分に配設する帯鉄筋１３の量を適切に設定することが必要になる。 Next, the load bearing mechanism against bending moment and horizontal force when the steel pipe 5 is embedded in the pile 1 will be considered. Since the strain distribution of the band reinforcement 13 is large at the steel pipe embedded end and the pile base as described above and small at the middle portion, the load bearing mechanism can be modeled as shown in FIG. In this model, the resistance force against the bending moment M and the horizontal force Q is composed of the support pressure P by the concrete on the front and back surfaces of the steel pipe 5 and the friction force T between the steel pipe 5 and the concrete. The supporting pressure P and the frictional force T can be expected when the concrete around the steel pipe 5 is healthy. When the concrete around the steel pipe 5 breaks and breaks like the No. 3 and 4 specimens, the bearing pressure P and the frictional force T cannot be expected as can be seen from the decrease in bending strength and dust performance. Therefore, in order to improve the bending strength and the dust performance, the amount of the strip reinforcing bars 13 disposed in the pile portion around the steel pipe 5 so that the concrete around the steel pipe 5 can be firmly restrained and the split fracture can be suppressed. Must be set appropriately.

このような帯鉄筋１３の量の算定方法について以下説明する。図９に示した杭１に作用する力のモーメントの釣り合いにより、鋼管５の断面の一辺の長さをｄとして、次式が得られる。
Ｍ＝Ｔ・ｄ＋{Ｌ・Ｐ^２／３（２Ｐ−Ｑ）}＋（Ｌ−Ｑ）・Ｌ・（５Ｐ−２Ｑ）／３（２Ｐ−Ｑ）…（１）
鋼管５に作用する摩擦力の合力Ｔは、粘着力をｃ（＝０．７Ｎ／ｍｍ^２）、摩擦角をφ（＝２０°）として、次式のようになる。
Ｔ＝ｃ・ｄ・Ｌ・{（Ｐ−Ｑ）／（２Ｐ−Ｑ）}＋（Ｐ−Ｑ）ｔａｎφ…（２）
支圧力の合力Ｐは、帯鉄筋１３の拘束力で発揮されるものとし、帯鉄筋１３の引張降伏応力をｆｓｙ、鋼管５の単位長さ当りの帯鉄筋１３の断面積をＡｓ、補正係数をαとして、次式で算定する。 A method for calculating the amount of the rebar 13 will be described below. By the balance of moments of force acting on the pile 1 shown in FIG. 9, the following equation is obtained, where d is the length of one side of the cross section of the steel pipe 5.
^{M = T · d + {L} · P 2/3 (2P-Q)} + (L-Q) · L · (5P-2Q) / 3 (2P-Q) ... (1)
The resultant force T of the frictional force acting on the steel pipe 5 is expressed by the following equation, where the adhesive force is c (= 0.7 N / mm ² ) and the friction angle is φ (= 20 °).
T = c · d · L · {(PQ) / (2PQ)} + (PQ) tan φ (2)
The resultant force P of the support pressure is assumed to be exerted by the restraining force of the band reinforcing bar 13, the tensile yield stress of the band reinforcing bar 13 is fsy, the cross-sectional area of the band reinforcing bar 13 per unit length of the steel pipe 5 is As, and the correction coefficient is α is calculated by the following formula.

Ｐ＝α・ｆｓｙ・Ａｓ・ｃｏｓ４５°・Ｐ・Ｌ／（２Ｐ−Ｑ）…（３）
式（３）は、図１０に示すように、水平断面内で帯鉄筋１３のひずみが最大になる位置、即ち、水平力作用線に対し水平方向に±４５°回転した位置での帯鉄筋１３の引張力で支圧力Ｐが規定されるとしたものである。補正係数αは、支圧力Ｐを求める際の簡略化等に対する補正としての係数である。 P = α · fsy · As · cos 45 ° · P · L / (2P-Q) (3)
As shown in FIG. 10, the expression (3) indicates that the band rebar 13 is located at a position where the distortion of the band rebar 13 is maximum in the horizontal section, that is, at a position rotated ± 45 ° in the horizontal direction with respect to the horizontal force action line. The supporting pressure P is defined by the tensile force of The correction coefficient α is a coefficient as a correction for simplification or the like when obtaining the support pressure P.

図１１は、縦軸に式（１）と式（２）とを用いて試験から得られる支圧力、横軸に式（３）右辺のαを除いた項の値を取り、Ｎｏ２〜Ｎｏ６の試験体の試験値をプロットしたものである。試験から得られる支圧力を計算するための水平力は、帯鉄筋１３の拘束力を十分期待できる範囲にとどめることを考慮して、帯鉄筋１３が降伏する時点のものとした。図１１より、じん性能の劣るＮｏ３，４の試験体では補正係数αが４．５以上になることが分かる。一方、じん性能に優れるＮｏ２の試験体ではα≒３．０、Ｎｏ５の試験体ではα≒２．５、Ｎｏ６の試験体ではα≒２．０になることが分かる。 FIG. 11 shows the bearing pressure obtained from the test using the formula (1) and formula (2) on the vertical axis and the value of the term excluding α on the right side of the formula (3) on the horizontal axis. The test value of the test body is plotted. The horizontal force for calculating the bearing pressure obtained from the test was set at the time when the band reinforcing bar 13 yielded in consideration of keeping the binding force of the band reinforcing bar 13 within a sufficiently expectable range. From FIG. 11, it can be seen that the correction coefficient α is 4.5 or more in the No. 3 and 4 specimens with inferior dust performance. On the other hand, it can be seen that α 2 is approximately 3.0 for the No. 2 specimen, which is excellent in dust performance, α is approximately 2.5 for the No 5 specimen, and α is approximately 2.0 for the No 6 specimen.

図１２はＮｏ２，３，５，６の試験体の補正係数αとじん性率との関係をプロットしたものである。図１２より、補正係数αが３．０以下であればじん性率が７程度以上の大きな値になることが分かる。従って、式（３）がα≦３．０の範囲で成立するように、鋼管５の単位長さ当りの帯鉄筋１３の断面積Ａｓを決定し、この断面積Ａｓに見合う量の帯鉄筋１３を鋼管５の周囲の杭部分に配設すれば、図１３に示す従来例のものと同等以上の曲げ耐力及びじん性能を得ることができる。但し、式（３）がα＜１．５の範囲で成立するように断面積Ａｓを決定した場合には、鋼管５の周囲の杭部分に配設する帯鉄筋１３が密になり過ぎて施工性が悪くなる。そのため、式（３）が１．５≦α≦３．０の範囲で成立するように断面積Ａｓを決定すべきである。 FIG. 12 is a plot of the relationship between the correction coefficient α and the toughness rate of No. 2, 3, 5, and 6 specimens. From FIG. 12, it can be seen that if the correction coefficient α is 3.0 or less, the toughness rate becomes a large value of about 7 or more. Therefore, the cross-sectional area As of the band rebar 13 per unit length of the steel pipe 5 is determined so that the formula (3) is satisfied in the range of α ≦ 3.0, and the amount of the band rebar 13 corresponding to the cross-sectional area As is determined. If it is arrange | positioned in the pile part around the steel pipe 5, the bending proof stress and dust performance equivalent to or more than the thing of the prior art example shown in FIG. 13 can be obtained. However, when the cross-sectional area As is determined so that the formula (3) is established in the range of α <1.5, the rebar 13 disposed in the pile portion around the steel pipe 5 becomes too dense and is constructed. Sexuality gets worse. Therefore, the cross-sectional area As should be determined so that the formula (3) is established in the range of 1.5 ≦ α ≦ 3.0.

尚、鋼管５の単位長さ当りの帯鉄筋１３の断面積Ａｓを大きくするため、Ｎｏ５，６の試験体では帯鉄筋１３を太くしているが、帯鉄筋１３の軸方向間隔を狭くして断面積Ａｓを大きくするようにしても良い。また、Ｎｏ２〜Ｎｏ６の試験体では、鋼管５の周囲の杭部分より広範囲の図４（ｂ）のＢ領域で帯鉄筋１３の軸方向間隔を狭めているが、上記の如く決定される断面積Ａｓに見合う量の帯鉄筋１３を配設する領域は鋼管５の周囲の杭部分に限定しても良い。また、杭１への鋼管５の埋め込み深さＬが鋼管５の断面の一辺の長さｄの３倍より小さくなるＮｏ４の試験体では曲げ耐力が大幅に低下するため、埋め込み深さＬは３ｄ以上にすることが望ましい。 In addition, in order to increase the cross-sectional area As of the band rebar 13 per unit length of the steel pipe 5, the band rebar 13 is thickened in the No. 5 and 6 specimens, but the axial interval of the band rebar 13 is reduced. The cross-sectional area As may be increased. Moreover, in the test body of No2-No6, although the axial direction space | interval of the band reinforcement 13 is narrowed in the B area | region of FIG.4 (b) wider than the pile part around the steel pipe 5, the cross-sectional area determined as mentioned above The region where the rebar 13 corresponding to the amount of As is disposed may be limited to the pile portion around the steel pipe 5. In addition, since the bending strength of the No. 4 test body in which the embedding depth L of the steel pipe 5 in the pile 1 is smaller than three times the length d of one side of the cross section of the steel pipe 5 is greatly reduced, the embedding depth L is 3d. It is desirable to make it above.

本発明の実施形態の接合構造を示す杭と柱の縦断面図。The longitudinal cross-sectional view of the pile and pillar which show the joining structure of embodiment of this invention. 図１のＩＩ−ＩＩ線切断面図。The II-II line | wire sectional view of FIG. （ａ）試験体の正面図、（ｂ）試験体の平面図。(A) The front view of a test body, (b) The top view of a test body. （ａ）Ｎｏ１の試験体の配筋を示す図、（ｂ）Ｎｏ２〜Ｎｏ６の試験体の配筋を示す図。(A) The figure which shows the bar arrangement of the test body of No1, (b) The figure which shows the bar arrangement of the test body of No2-No6. 各試験体の荷重と変位の履歴曲線を示すグラフ。The graph which shows the history curve of the load and displacement of each test body. 各試験体の荷重―変位曲線の包絡線を示すグラフ。The graph which shows the envelope of the load-displacement curve of each test body. 主筋と鋼管のひずみ分布を示すグラフ。The graph which shows the strain distribution of a main reinforcement and a steel pipe. 帯鉄筋のひずみ分布を示すグラフ。The graph which shows strain distribution of a belt reinforcement. 耐荷モデルを示す図。The figure which shows a load-bearing model. 支圧力の算定原理を説明する図。The figure explaining the calculation principle of a bearing pressure. 各試験体の補正係数αを示すグラフ。The graph which shows the correction coefficient (alpha) of each test body. 補正係数αとじん性率との関係を示すグラフ。The graph which shows the relationship between the correction coefficient (alpha) and a toughness rate. 従来例の接合構造を示す杭と柱の縦断面図。The longitudinal cross-sectional view of the pile and pillar which show the joining structure of a prior art example.

符号の説明Explanation of symbols

１…杭、１１…杭の鉄筋、１２…主筋、１３…帯鉄筋、３…柱、３１…柱の鉄筋、５…鋼管。 DESCRIPTION OF SYMBOLS 1 ... Pile, 11 ... Pile reinforcement, 12 ... Main reinforcement, 13 ... Strip reinforcement, 3 ... Column, 31 ... Column reinforcement, 5 ... Steel pipe.

Claims

鉄筋コンクリート造の杭と鉄筋コンクリート造の柱とを、杭の鉄筋の上端部を柱の鉄筋の下端部にオーバーラップさせることなく接続する杭と柱の接合構造であって、所定長さの鋼管の下半部が杭の上端部の鉄筋で囲われる断面中央部に埋め込まれ、鋼管の上半部が柱の下端部の鉄筋で囲われる断面中央部に埋め込まれるものにおいて、
鋼管の太さ及び肉厚は、鋼管の断面の曲げ耐力が杭の鉄筋の主筋全体の断面の曲げ耐力と同等になるように設定され、
杭と柱の接続部分に作用する所定の水平力に抗するのに必要な杭の鋼管に対する支圧力と、杭への鋼管の埋め込み深さとから杭の主筋を取り囲むリング状の帯鉄筋の量を決定し、この量の帯鉄筋を鋼管の周囲の杭部分に配設することを特徴とする杭と柱の接合構造。 A pile-column connection structure that connects a reinforced concrete pile and a reinforced concrete column without overlapping the upper end of the reinforcing bar of the pile with the lower end of the reinforcing bar of the column. The half is embedded in the center of the cross section surrounded by the reinforcing bar at the upper end of the pile, and the upper half of the steel pipe is embedded in the center of the cross section surrounded by the reinforcing bar at the lower end of the column.
The thickness and wall thickness of the steel pipe are set so that the bending strength of the cross section of the steel pipe is equivalent to the bending strength of the cross section of the entire main reinforcing bar of the pile,
The amount of ring-shaped rebar that surrounds the main bar of the pile is determined from the support pressure to the steel pipe of the pile necessary to resist the predetermined horizontal force acting on the connection part of the pile and the column, and the embedding depth of the steel pipe in the pile. A pile-column connection structure characterized by deciding and arranging this amount of steel bars in a pile portion around a steel pipe.

請求項１記載の杭と柱の接合構造であって、前記鋼管の断面形状が正方形であるものにおいて、
前記水平力をＱ、前記支圧力をＰ、前記埋め込み深さをＬ、鋼管の周囲に配設する帯鉄筋の引張降伏耐力をｆｓｙ、鋼管の単位長さ当りの帯鉄筋の断面積をＡｓ、補正係数をαとして、次式、
Ｐ＝α・ｆｓｙ・Ａｓ・ｃｏｓ４５°・Ｐ・Ｌ／（２Ｐ−Ｑ）
が、αを１．５〜３．０の値にして成立するように、Ａｓを決定し、このＡｓに見合う量の帯鉄筋を鋼管の周囲の杭部分に配設することを特徴とする杭と柱の接合構造。 In the joint structure of a pile and a column according to claim 1, wherein the cross-sectional shape of the steel pipe is square,
The horizontal force is Q, the supporting pressure is P, the embedding depth is L, the tensile yield strength of the steel bars disposed around the steel pipe is fsy, and the cross-sectional area of the steel bars per unit length of the steel pipe is As, Assuming that the correction coefficient is α,
P = α, fsy, As, cos 45 °, P, L / (2P-Q)
Is determined such that α is established with a value of 1.5 to 3.0, and a reinforcing bar having an amount corresponding to the As is disposed in a pile portion around the steel pipe. And column connection structure.