JP4049682B2

JP4049682B2 - Threaded joint for steel pipe pile and fastening method

Info

Publication number: JP4049682B2
Application number: JP2003029871A
Authority: JP
Inventors: 英司津留; 哲己近藤; 憲二郎岡; 徹羽馬; 治之永吉; 秀樹冨田
Original assignee: Nippon Steel Corp; Toyo Construction Co Ltd
Current assignee: Nippon Steel Corp; Toray Engineering Co Ltd
Priority date: 2003-02-06
Filing date: 2003-02-06
Publication date: 2008-02-20
Anticipated expiration: 2023-02-06
Also published as: JP2004238942A

Description

【０００１】
【発明の属する技術分野】
本発明は橋梁柱、建築物等の基礎補強及び地盤改良等に用いる鋼管杭並びに地すべり抑止杭等を安価で迅速に接合し得る鋼管杭用ねじ継手に関する。
【０００２】
【従来の技術】
軟弱地盤の改良、基礎補強のために、橋梁柱、鉄塔の基礎杭として、外径８０ｍｍ〜３００ｍｍ程度の鋼管杭が用いられてきた。これらの杭長は十数メートルに及ぶ場合もあるが、輸送、施工性の観点から３〜９ｍの短尺杭を施工現場で接合しながら孔中に降下させ、その後、ミルクセメントなどを充填し、補強する方法が採られてきた。
【０００３】
鋼管杭の接合には、溶接、ねじ継手等が用いられるが、効率性からねじ継手が主流になりつつある。鋼管杭のねじ継手には、管体と同等の引張及び圧縮強度に加え、重要な性能として曲げ強度も要求される。鋼管杭用ねじ継手は、少数の継手を締結後、場所を移動しながら複数個所で順次、あるいは同時に締結するものである。この鋼管杭用ねじ継ぎ手は、通常、人力によって締結される。従って、良好な施工性と人力による締結でも引張、圧縮、曲げ性能が発揮でき、尚かつ、安価な継手が要求されてきた。
【０００４】
このような鋼管杭を締結するねじ継手として、特許文献１及び特許文献２に地すべり抑止杭が開示されている。これらは、施工性の観点からテーパーねじを採用し、継手外径を管体と同等に抑えている。しかし、管体以上の曲げ強度の要求に対して、管体よりも高強度のねじ継手を溶接しなければならないため、ねじ継手の杭本体への溶接費用が大きく、安価な供給ができない。
【０００５】
これに対して、ねじ継手の杭本体への溶接を伴わず、カプラーにより杭同士を締結する方法が、特許文献３及び特許文献４に開示されている。しかし、これらの方法は、カプラー中央部に鋼管杭の先端と接触するショルダー部と呼ばれる突起を設けて、ねじ継ぎ手の曲げ強度を確保するものである。カプラー内面又は外面にショルダー部を設けることで曲げ強度を向上させることをできるが、ショルダー部の作製により製造コストが上昇し、更にカプラー素管全体が厚肉化するため、素管コスト及びねじ切削費用の著しい上昇を招く。
【０００６】
また、特許文献５、特許文献６及び特許文献７には、カプラー中央部でピン先端同士が衝接するねじ継手が開示されている。しかし、これらは油井管用ねじ継手であり、同一の孔中に数百個もの継手を使用し、かつ継手の気密性が要求される。そのため、油井管用ねじ継手は、カプラーと鋼管のねじが確実に嵌合していることが要求されるものであり、締結時の摩擦力による抵抗が大きく、鋼管杭とは異なり、機械による締結が行われている。
【０００７】
油井管用ねじ継手においても、締結時の摩擦力を低下させるために、特許文献８には、引張荷重面のみが接触する不完全ねじ部を設ける方法が、特許文献９には、締結時に螺合部の引張荷重面のみが接触し、ねじ山とねじ谷間及び圧縮荷重面に間隙を設ける方法が開示されている。しかし、特許文献８の油井管用ねじ継手は、ねじ山とねじ谷間が接触する完全ねじ部が必要であり、特許文献９による方法は、締結終了時には引張荷重面間と圧縮荷重面間の両方が接触することが必要であるため、何れも人力による締結は不可能である。
【０００８】
【特許文献１】
特開平０７−８２７３８号公報
【特許文献２】
特開平０７−１０２５５５号公報
【特許文献３】
特開平０６−１９３０５５号公報
【特許文献４】
特開２００２−６１１７５号公報
【特許文献５】
特開平０６−１２３３８６号公報
【特許文献６】
特開平０８−３０３６５７号公報
【特許文献７】
特開平１１−１０８２６４号公報
【特許文献８】
特開２００２−２９５７４７号公報
【特許文献９】
特開２００２−６１７７９号公報
【０００９】
【発明が解決しようとする課題】
本発明は、ねじ継手を鋼管杭本体に溶接することなく、鋼管杭に必要な引張、圧縮、曲げ強度を確保し得る、人力による締結が可能な、鋼管杭用ねじ継手を安価に提供するものである。
【００１０】
【課題を解決するための手段】
本発明者は、カプラー製造コスト削減のために、カプラーにショルダーを設けずに、鋼管杭の継手の曲げ強度を向上させ、人力による締結を可能とする方法について詳細に検討した。その結果、曲げ強度の向上には、鋼管杭のねじ部とカプラーのねじの螺合部において、鋼管杭のねじ部の先端同士を衝接させることが有効であり、更に、鋼管杭のねじ部の台形ねじとカプラーの台形ねじの接触部位を少なくすることにより、締結時の摩擦力の低減が可能であるという知見を得た。そのためには、鋼管杭のねじ部の台形ねじ及びカプラーの台形ねじのピッチ径を最適化し、台形ねじ同士の接触長であるねじ山勘合高さを確保することが重要であることを見出した。
【００１１】
本発明は、このような知見に基づき、鋼管杭用ねじ継手の要求性能、施工特性、加工特性を総合的に分析することによって、初めて完成できたものであり、ショルダーのないカプラーを用いて、カプラーのほぼ中央部で２つの鋼管杭のねじ部の先端同士を衝接させた、人力による締結が可能な鋼管杭用ねじ継手であり、その要旨は以下のとおりである。
【００１２】
（１）少なくとも一端に台形ねじをテーパー状に配列した２本の鋼管杭と、両側に台形ねじをテーパー状に配列し、該鋼管杭を螺合したカプラーからなるねじ継手において、２本の鋼管杭ねじ部の先端同士が衝接し、第１の鋼管杭とカプラーの片側の螺合部の該鋼管杭のねじ部のねじ山と該カプラーのねじ底及び／又は該鋼管杭のねじ部のねじ底と該カプラーのねじ山が接触し、第２の鋼管杭とカプラーの他の片側の螺合部のねじ山及びねじ谷間、及び圧縮荷重面に間隙を有し、かつ引張荷重面が接触していることを特徴とする鋼管杭用ねじ継手。
【００１４】
（２）第２の鋼管杭の台形ねじのピッチ径とカプラーの他の片側の台形ねじのピッチ径の差の絶対値が、該鋼管杭の台形ねじのピッチ径公差と該カプラーの台形ねじのピッチ径公差の和以上であり、該鋼管杭のねじ部の台形ねじと該カプラーの台形ねじの接触長であるねじ山有効嵌合高さが鋼管杭の直径の０．３％以上であることを特徴とする（１）記載の鋼管杭用ねじ継手。
【００１５】
（３）第１の鋼管杭のねじ部のねじ山とカプラーの片側のねじ底及び／又は該鋼管杭のねじ部のねじ底と該カプラーのねじ山を接触させるように螺合した後、第２の鋼管杭とカプラーの他の片側のねじ山及びねじ谷間並びに圧縮荷重面に間隙を有し、かつ引張荷重面を接触させるように螺合することを特徴とする（１）又は（２）に記載の鋼管杭用ねじ継手の締結方法。
【００１６】
【発明の実施の形態】
図１は、本発明の一例であり、カプラーの両側に１本ずつ鋼管杭を締結した鋼管杭用ねじ継手の螺合部を示したものである。カプラーの両側の内面にテーパーねじ１（雌ねじ１という）を刻設し、ねじ形状は台形ねじ５を呈する。カプラーの片側の雌ねじは、第１の鋼管杭の端部の外面にテーパーねじを刻設した部位である鋼管杭のねじ部（雄ねじ２という）と螺合している。更にカプラーの他の片側は、第２の鋼管杭の端部の外面にテーパーねじを刻設した部位である鋼管杭のねじ部（雄ねじ３という）と螺合している。
【００１７】
更に、この鋼管杭用ねじ継手の螺合部は、先行して締結した鋼管杭の雄ねじ２の先端と後行して締結した雄ねじ３の先端が、雄ねじ先端６で衝接している。この構造により、カプラーにショルダー部を設けなくても先行して締結した第１の鋼管杭の雄ねじ２の先端が、その後締結した、第２の鋼管杭の雄ねじ３を締結する際にショルダーの役割を果たし、衝接した雄ねじ先端６により、曲げ強度が著しく向上する。
【００１８】
本発明により曲げ強度が改善できるメカニズムを図２によって説明する。鋼管杭に曲げ荷重が負荷され、図２のねじ継手の両端に上向きの曲げモーメントが加わると、雄ねじ２と雄ねじ３が衝接していない従来技術の場合、雄ねじ２から雌ねじ１へ、雌ねじ１から雄ねじ３へ圧縮応力が伝達される。継手設計において鋼管杭本体とカプラー材に強度が同等である材料を使用する場合は、例えば雄ねじ３と雌ねじ１の螺合部において、雄ねじ３の先端のカプラー危険断面での断面係数を少なくとも管体の断面係数以上に設計することでカプラーからの破断を防止できる。
【００１９】
これに対し、雄ねじ２と雄ねじ３が衝接している本発明では、曲げ荷重により発生する圧縮応力は、従来技術と同様のねじ部からの伝達に加え、雄ねじ先端６において雄ねじ２から雄ねじ３に直接伝達される。その結果、従来技術と同様の、雄ねじ２，３と雌ねじ１を介して伝達する力が軽減する。更に、従来技術に比較して、雄ねじ２，３を雌ねじ１に、より深く螺合しているため、同じ形状のテーパーねじを有するカプラーを用いた場合、カプラー危険断面でのカプラーの肉厚が大きくなり、断面係数を増大させることができる。従って、ショルダーを有しないテーパーねじを形成したカプラーを用いたねじ継手においても、鋼管杭のねじ部の先端同士を衝接させることによって、曲げ強度を確保することが可能になる。
【００２０】
なお、鋼管杭の雄ねじの長さは、完全ねじ山長さで鋼管杭の直径の２０〜４０％であることが好ましく、カプラーの長さは、雄ねじの長さの２倍程度であることが好ましい。更に、鋼管杭の強度は４００〜８００ＭＰａ、カプラー強度の強度は５００〜１０００ＭＰａであることが好ましく、鋼管杭の強度とカプラー強度を継手性能の観点から適宜、組み合わせることが好ましい。
【００２１】
次に本発明をテーパーねじに特定した理由について説明する。平行ねじの場合、ねじの締結を開始する際に、軸合わせを精度良く行うことが必要であり、更に迅速に締結するには、ねじリードを大きくすることが唯一の方法である。これに対してテーパーねじでは、テーパーによって軸合わせが容易になり、締結性はねじリードに加え、ねじ列テーパーとねじ山高さにも依存し、平行ねじよりも速く締結できることが、多くの研究から実証されている。
【００２２】
通常、テーパーねじにおいて、ねじの形状が角ねじや台形ねじである場合は締め付けによるねじ山とねじ底の半径方向の干渉により、ねじ継手を自立させることができる。一方、ねじの形状が三角ねじや丸山ねじである場合は圧縮荷重や引張荷重を受け持つフランク面の干渉により、ねじ継手を自立させることができる。しかし、人力による締結を行う場合、ねじ部の先端同士を衝接させ、尚かつ、ねじを自立させるにはねじ山とねじ底の半径方向の干渉と、圧縮荷重面及び引張荷重面の干渉が同時に生じると達成できないことがわかった。
【００２３】
また、鋼管杭のねじ部の先端同士を衝接させることは、機械を用いた締結の場合は容易であるが、人力によって締結する場合には、カプラー及び鋼管杭のねじの形状を最適化することが好ましい。即ち、ねじの形状の最適化により、先行の鋼管杭の雄ねじの先端がカプラーの中央部に達する前に、摩擦力が大きくなり過ぎて、後行の鋼管杭の雄ねじの先端が先行の鋼管杭の雄ねじの先端まで届かないという問題や、鋼管杭の雄ねじの先端同士は接触しても、継手のねじ山の嵌合が不十分で、継手が抜け落ちるという問題を回避することができる。そこで工業生産上、十分な加工公差を有し、人力による締結でも雄ねじ先端同士を確実に衝接し得る方法について検討を行った。
【００２４】
図３は、雄ねじ先端６が接触した図１と同様の構成であり、更に好ましい鋼管杭の雄ねじとカプラーの雌ねじの螺合部の特徴を示したものである。第１の鋼管杭のねじ部とカプラーの片側の螺合部の例として、第１の鋼管杭のねじ部のねじ山とカプラーの片側のねじ底の間隙７（雄ねじ山−雌ねじ底間隙７という）及び第１の鋼管杭のねじ部のねじ底とカプラーの片側のねじ山の接触８（雄ねじ底−雌ねじ山接触８という）を示している。また、第２の鋼管杭のねじ部とカプラーの他の片側の螺合部は、第２の鋼管杭のねじ部のねじ底とカプラーの他の片側のねじ山との間隙９（雄ねじ底−雌ねじ山間隙９という）、第２の鋼管杭のねじ部のねじ山とカプラーの他の片側のねじ底との間隙１０（雄ねじ山−雌ねじ底間隙１０という）、圧縮荷重面間隙１１を有し、引張荷重面１２が接触している。
【００２５】
本発明により、人力により確実な締結が可能になるメカニズムについて、カプラーの雌ねじ１の片側と第１の鋼管杭の雄ねじ２を先に締結し、後からカプラーの雌ねじ１の他の片側と第２の鋼管杭の雄ねじ３を締結する場合を例として説明する。まず、カプラーの雌ねじ１の片側に鋼管杭の雄ねじ２を螺合する際、テーパーねじの場合は螺合が進むと、雌ねじ１の特定の部位においては雄ねじ２の外径が次第に広がる。鋼管杭ねじ部の先端がカプラーの中央付近に到達するまで雌ねじと雄ねじの螺合進み、雄ねじのねじ底と雌ねじのねじ山が接触し、雄ねじ底−雌ねじ山接触８を形成すると、締結のトルクが増加し、人力による締結は限界に至る。
【００２６】
このとき、雄ねじと雌ねじは、台形ねじの引張荷重面の嵌合により、十分に固定されており、雄ねじ先端が実質上のショルダー部を形成している。続いてカプラー１の他の片側に雄ねじ３を螺合し、鋼管杭ねじ部の先端同士を接触させると、雄ねじは互いに反力を受けて、ねじの引張荷重面が接触し、カプラーと雄ねじが固定される。この際、カプラー１の他の片側と雄ねじ３の螺合部において、雄ねじの先端同士が接触するまで、雄ねじ底−雌ねじ山間隙９、雄ねじ山−雌ねじ底間隙１０が形成されていれば、雄ねじ先端同士の衝接以前にトルクの急激な増加は起こらない。更に、圧縮荷重面にも圧縮荷重面間隙１１が形成されていれば、圧縮荷重面と引張荷重面が同時に接触しないため、雄ねじ先端が接触する以前の締め付けトルクの急激な増加を抑制することができる。
【００２７】
なお、図３では、雄ねじ山−雌ねじ底間隙７、雄ねじ底−雌ねじ山接触８を有する例を説明したが、雄ねじ山−雌ねじ底が接触して、雄ねじ底−雌ねじ山に間隙を有しても良く、雄ねじ山−雌ねじ底と雄ねじ底−雌ねじ山が共に接触しても良い。
【００２８】
本発明による継手は図４に示すように通常、工場出荷時に搬送、あるいは不測の衝撃などによりカプラーが緩まない程度に手締め、又は機械により締結されるが、施工現場では人力による締結が標準となる。従って、工場出荷時に第１の鋼管杭のねじ部を、例えば雄ねじ山−雌ねじ底間隙７、雄ねじ底−雌ねじ山接触を形成するようにカプラーの片側と締結し、その後、施工現場では人力で、第２の鋼管杭のねじ部を、雄ねじ底−雌ねじ山間隙９、雄ねじ山−雌ねじ底間隙１０及び圧縮荷重面間隙１１を形成し、引張荷重面１２が接触する状態でカプラーの他の片側に螺合する。
【００２９】
次に、人力でカプラーと鋼管杭を締結する際、安定してカプラー中央部で鋼管杭ねじ部の先端同士を衝接させる方法について検討を行った。カプラー中央部にショルダーを有する継手では、鋼管杭ねじ部の先端がショルダーに接触すると締結が完了するため、鋼管杭ねじ部の先端同士は接触せず、相互に影響を及ぼすことはない。しかし、本発明はカプラー中央部のショルダーを省略するため、締結が終了した際に、鋼管杭ねじ部の先端の位置がカプラー中央部付近の適切な範囲に入ることが極めて重要である。これには、雌ねじと雄ねじのピッチ径の差を適切な範囲にすることが重要である。
【００３０】
本発明者らは、第１の鋼管杭の雄ねじのピッチ径公差とカプラーの片側の雌ねじのピッチ径公差によって生じる、締結後の鋼管杭の雄ねじの先端の位置の変動を、図５に示すようにカプラーの他の片側の台形ねじのピッチ径１４（雌ねじピッチ径１４という）と第２の鋼管杭のねじ部のピッチ径１５（雄ねじピッチ径１５という）との差の絶対値を、カプラーの他の片側の台形ねじのピッチ径の公差（雌ねじピッチ径公差という）と第２の鋼管杭のねじ部の台形ねじのピッチ径の公差（雄ねじピッチ径公差という）との和よりも小さくすることによって吸収する方法を指向した。
【００３１】
図５において下側の雄ねじ３と雌ねじ１が螺合している。雌ねじピッチ径１４は、雌ねじ１の台形ねじのねじ高さの中央部を結ぶ直線であり、雄ねじピッチ径１５は雄ねじ３の台形ねじのねじ高さの中央部を結ぶ直線である。この雌ねじピッチ径と雄ねじピッチ径の差の絶対値を、雌ねじピッチ径公差と雄ねじピッチ径公差の和以上にすれば、安定的に雄ねじ先端がカプラーのほぼ中央で衝接する。
【００３２】
雌ねじ及び雄ねじのピッチ径はスタンドオフゲージと呼ばれる円錐状の計測器を用いて測定することができる。また、雌ねじ及び雄ねじのピッチ径公差は、スタンドオフゲージの入り具合、即ち、軸方向の移動長さとして測定することができる。
【００３３】
雄ねじ先端同士の衝接を優先すると、ねじ山の嵌合が甘くなる場合があり、特に引張軸力に対して十分な強度を得られず、継手がジャンプアウト（抜け落ち）することがある。これを防止するには、引張荷重面における雄ねじと雌ねじのねじ山の接触長である、ねじ山有効嵌合高さ１６を直径比の０．３％以上とすることが必要である。これにより、引張強度、圧縮強度に代表される継手性能も確保できる。ねじ山有効嵌合高さの上限は、鋼管杭の外径、台形ねじのねじ山高さ、雄ねじ底−雌ねじ山間隙９及び雄ねじ山−雌ねじ底間隙１０によって決まるものであり、特に規定しない。ねじ山有効嵌合高さを高くすればピッチ径公差を大きく取れる反面、カプラーの危険断面を補うために、カプラー外径を大きくすることが必要になる。
【００３４】
ねじ山有効嵌合高さは、鋼管杭ねじ部とカプラーを締結した際の断面形状から計測することができる。テーパーとピッチ径から図６に示したような図面を作成して測定することも可能である。
【００３５】
また、台形ねじのねじ山高さは、鋼管杭外径にも左右されるが、外径２００ｍｍ以下の鋼管杭では、ねじ山高さ１〜２ｍｍ、２００ｍｍ以上では１．３〜３ｍｍ程度とすることにより、継手の要求性能を満足し、製造コストを抑えることができる。台形ねじの形状については、具体的にはＡＰＩスタンダード５Ｂのバットレスねじ、ＥＬケーシングねじなどが好ましい。また、鋼管杭のねじ部及びカプラーのねじテーパーは特に規定しないが、加工効率及びコスト面から１／８〜１／１６の範囲とすることが好ましい。
【００３６】
なお、本発明は、カプラー中央部にショルダー部を有さず、先行して螺合し、締結した雄ねじ先端を実質的にショルダーとして作用させるために、図３のように、雄ねじ２を、雄ねじ山−雌ねじ底間隙７、雄ねじ底−雌ねじ山接触８を形成するように、カプラーの片側の雌ねじ１に締結し、その後、雄ねじ３を、雄ねじ底−雌ねじ山間隙９、雄ねじ山−雌ねじ底間隙１０及び圧縮荷重面間隙１１を有し、引張荷重面１２が接触するように、カプラーの他の片側の雌ねじと締結し、雄ねじ２と雄ねじ３の先端同士を衝接させることが好ましい。
【００３７】
以上の説明は、カプラーを雌ねじ、鋼管杭のねじ部を雄ねじとした例であるが、鋼管杭の端部の内面に雌ねじを刻設し、カプラーの外面に雄ねじを刻設しても良い。この場合は、図１及び図３において、図の下側が外面、図の上側が内面になる。
【００３８】
【実施例】
（実施例１）
外径１１４ｍｍの鋼管杭の雄ねじのピッチ径及びピッチ径公差並びに内径が鋼管杭と同程度のカプラーの雌ねじのピッチ径及びピッチ径公差をＡＰＩスタンダード５Ｂに示されるスタンドオフゲージによって測定した。鋼管杭及びカプラーのピッチ径公差は、ともに０．０７５ｍｍであった。即ち、鋼管杭のピッチ公差とカプラーのピッチ径公差の和は０．１２５ｍｍである。
【００３９】
第１の鋼管杭をカプラーの片側に締結し、第２の鋼管杭をカプラーの他の片側に締結した。螺合した継手の雄ねじ先端同士の衝接の有無を目視により確認した。また、継手の螺合部のねじ山有効嵌合高さをスタンドオフ値より求めた。
鋼管杭の雄ねじとカプラーの雌ねじのピッチ径差、ねじ山有効嵌合高さ及び雄ねじ先端同士の衝接の有無を表１に示す。ここで雄ねじと雌ねじのピッチ径差が大きくなるほど、雄ねじ先端同士の衝接サンプル数は増加し、雄ねじと雌ねじのピッチ公差の和を超えると未衝接サンプルは皆無となった。
【００４０】
【表１】

【００４１】
（実施例２）
外径２４４ｍｍの鋼管杭の雄ねじのピッチ径及びピッチ径公差並びに内径が鋼管杭と同程度のカプラーの雌ねじのピッチ径及びピッチ径公差を実施例１と同様にして測定した。鋼管杭及びカプラーのピッチ径公差は、ともに０．１２５ｍｍであった。即ち、鋼管杭のピッチ公差とカプラーのピッチ径公差の和は０．２５０ｍｍである。第１の鋼管杭をカプラーの片側に締結し、第２の鋼管杭をカプラーの他の片側に締結した。螺合した継手の雄ねじ先端同士の衝接の有無を目視により確認し、継手の螺合部のねじ山有効嵌合高さを、実施例１と同様にして測定した。
【００４２】
鋼管杭の雄ねじとカプラーの雌ねじのピッチ径差、ねじ山有効嵌合高さ及び雄ねじ先端同士の衝接の有無を表２に示す。ここで雄ねじと雌ねじのピッチ径差が大きくなるほど、雄ねじ先端同士の衝接サンプル数は増加し、雄ねじと雌ねじのピッチ公差の和を超えると未衝接サンプルは皆無となった。
【００４３】
【表２】

【００４４】
（実施例３）
外径８０ｍｍ〜２７３ｍｍの鋼管杭の雄ねじを内径が鋼管杭と同程度のカプラーの雌ねじの両側に螺合した。この際、第１の鋼管杭をカプラーの片側に人力により締結した後、第２の鋼管杭をカプラーの他の片側に人力により締結した。螺合した継手の雄ねじ先端同士の衝接の有無を目視により確認し、更に、第２の鋼管杭とカプラーの他の片側のねじ継手の螺合部において、雄ねじ山−雌ねじ谷間隙、雄ねじ底−雌ねじ山間隙、圧縮荷重面間隙及び引張荷重面間隙を求めた。
【００４５】
雄ねじ山−雌ねじ谷間隙、雄ねじ底−雌ねじ山間隙、圧縮荷重面間隙及び引張荷重面間隙は、スタンドオフゲージによるピッチ径及びピッチ径公差の値から予測した値とした。なお、この予測値が実測値と同等であることを以下のようにして確認している。まず雄ねじ及び雌ねじのスタンドオフ値を測定して間隙の値を予測した。次にこの雄ねじと雌ねじを螺合し、螺合部を軸方向に切断し、螺合後の断面写真からねじ間隙を測定した。更にこの実測した間隙の値と予測した間隙の値が同等であることを確認した。
【００４６】
表３に、ねじ山とねじ底の間隙の最小値を山谷最小間隙として示し、更に圧縮荷重面間隙及び雄ねじ先端同士の衝接の有無も示した。表３において、山谷最小間隙は、締め込み完了時点の雄ねじ山−雌ねじ谷間隙と雄ねじ底−雌ねじ山間隙の何れか小さい方の間隙である。また、ＡサイドとＢサイドとはカプラー両側のねじを区別したものであり、先行して締結した第１の鋼管杭のねじ部とカプラーの片側とのねじ継手をＡサイド、後行して締結した第２の鋼管杭のねじ部とカプラーの他の片側とのねじ継手をＢサイドとした。引張荷重面間はいずれも接触していた。
【００４７】
比較例１３，１５，１８、２０，２１，２２はＡ，Ｂ両サイドとも山谷間が接触しているため、雄ねじ先端の衝接が得られなかった。比較例１４、１６、１９は何れか片側のねじに山谷間隙を有しているが、山谷間隙を有している側の圧縮荷重面が接触しているため、雄ねじ先端の衝接が得られなかった。比較例１７，１８、２３は両側のねじに山谷間隙を有しているが、いずれのねじも圧縮荷重面が接触しているため、雄ねじ先端の衝接が得られなかった。
【００４８】
実施例１２，１８，１９はＡサイドに山谷間と圧縮荷重面に同時に間隙を有し、締め込み完了時点で雄ねじ先端の衝接が得られた。実施例１０，１１，１３、１４、１５，１６、１７はＢサイドに山谷間と圧縮荷重面に同時に間隙を有し、締め込み完了時点で雄ねじ先端の衝接が得られた。
【００４９】
【表３】

【００５０】
（実施例４）
表４に示した外径、肉厚及び鋼種の鋼管杭の雄ねじを、同じ鋼種で内径及び肉厚が鋼管杭と同じ程度であるカプラーの雌ねじの両側に、実施例３と同様に螺合した。２本の鋼管杭の雄ねじ及びカプラーの雌ねじのピッチ径並びにピッチ径公差を実施例１と同様にして求めた。
【００５１】
螺合した継手の雄ねじ先端同士の衝接の有無を目視により確認し、更に、ねじ継手の螺合部において、雄ねじ山−雌ねじ谷間隙、雄ねじ底−雌ねじ山間隙、圧縮荷重面間隙及び引張荷重面間隙間を実施例３と同様に測定した。また、継手の螺合部のねじ山有効嵌合高さを、実施例１と同様にして測定した。
【００５２】
曲げ試験は継手部を中央に配置した４点曲げ試験とし、曲げ強度は最大負荷荷重時の荷重を曲げモーメントに換算した。また、引張、圧縮試験では試験期間中の最大荷重を示す。
【００５３】
表４に、先行して締結したねじ継手をＡサイド、後行のねじ継手をＢサイドとして、山谷最小間隙、圧縮荷重面間隙、雄ねじ先端同士の衝接の有無、ねじ山有効嵌合高さ、継手性能を示した。表４において、山谷最小間隙として、締め込み完了時点の雄ねじ山−雌ねじ谷間隙と雄ねじ底−雌ねじ山間隙の何れか小さい方の間隙を示した。また、引張荷重面間はいずれも接触していた。
【００５４】
比較例２４，２５、２７，２８、３０，３１はいずれも締め込み終了時点で雄ねじ先端が衝接していないため、ねじ山有効嵌合高さは十分にあるものの、継手曲げ強度が雄ねじ先端が衝接している継手に比較して明らかに劣った。比較例２６、２９、３２は締め込み終了時点で雄ねじ先端は衝接しているものの、ねじ山有効嵌合高さが管径比で０．３％に満たないため、特に継手引張試験でジャンプアウトが多発し、継手強度自身もねじ山有効嵌合高さが管径比で０．３％以上あるものに比較して劣った。
【００５５】
一方、いずれの実施例も雄ねじ先端が衝接し、ねじ山有効嵌合高さが管径比で０．３％以上あるため、曲げ強度、引張強度とも高位に安定した。圧縮強度は雄ねじ先端の衝接の有無、ねじ山有効嵌合高さの大小に関わらず、ほぼ一定の値を示した。これは短柱圧縮試験では圧縮荷重が管体降伏強度を超えた付近から管体部で座屈現象が起きるためである。
【００５６】
【表４】

【００５７】
【発明の効果】
本発明により、人力による締結が可能であり、曲げ強度、引張強度が改善された鋼管杭用ねじ継手を提供することができ、産業上の貢献が極めて高い。
【図面の簡単な説明】
【図１】本発明による鋼管杭用ねじ継手の構成図。
【図２】曲げ負荷時の本発明による効果を説明する図。
【図３】本発明による継手のねじ間隙を示す図。
【図４】本発明によるねじ締結例を示す図。
【図５】本発明におけるねじ間隙とピッチ径を示す図。
【符号の説明】
１…カプラーの両側の内面のテーパーねじ１
２…第１の鋼管杭のねじ部
３…第２の鋼管杭のねじ部
４…第１の鋼管杭とカプラーの片側の螺合
５…台形ねじ
６…鋼管杭のねじ部の先端の衝接
７…第１の鋼管杭のねじ部のねじ山とカプラーの片側のねじ底の間隙
８…第１の鋼管杭のねじ部のねじ底とカプラーの片側のねじ山との接触
９…第２の鋼管杭のねじ部のねじ底とカプラーの他の片側のねじ山との間隙
１０…第２の鋼管杭のねじ部のねじ山とカプラーの他の片側のねじ底との間隙
１１…圧縮荷重面間隙
１２…引張荷重面
１３…圧縮荷重面
１４…カプラーの他の片側の台形ねじのピッチ径
１５…第２の鋼管杭のねじ部の台形のピッチ径
１６…ねじ山有効嵌合高さ[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a steel pipe pile threaded joint that can quickly and inexpensively join steel pipe piles, landslide suppression piles, and the like used for foundation reinforcement and ground improvement of bridge columns and buildings.
[0002]
[Prior art]
In order to improve the soft ground and strengthen the foundation, steel pipe piles with an outer diameter of about 80 mm to 300 mm have been used as bridge pillars and foundation piles for steel towers. These pile lengths may extend to more than a dozen meters, but from the viewpoint of transportation and workability, 3-9m short piles are lowered into the holes while being joined at the construction site, and then filled with milk cement, Reinforcement methods have been taken.
[0003]
For joining steel pipe piles, welding, threaded joints, and the like are used, but threaded joints are becoming mainstream for efficiency. In addition to the tensile and compressive strength equivalent to that of pipes, the threaded joints of steel pipe piles are required to have bending strength as an important performance. The threaded joint for steel pipe piles is to be fastened sequentially or simultaneously at a plurality of places while moving a place after fastening a small number of joints. The steel pipe pile screw joint is usually fastened by human power. Accordingly, there has been a demand for an inexpensive joint that can exhibit tensile, compression, and bending performance even with good workability and fastening by human power.
[0004]
As a threaded joint for fastening such a steel pipe pile, landslide prevention piles are disclosed in Patent Document 1 and Patent Document 2. These employ a taper screw from the viewpoint of workability, and keep the joint outer diameter the same as that of the pipe body. However, since it is necessary to weld a threaded joint having a strength higher than that of the tubular body in response to a demand for bending strength higher than that of the tubular body, the welding cost of the threaded joint to the pile main body is high, and it is not possible to supply at a low cost.
[0005]
On the other hand, Patent Literature 3 and Patent Literature 4 disclose a method of fastening piles with a coupler without welding a threaded joint to a pile body. However, in these methods, a protrusion called a shoulder portion that comes into contact with the tip of the steel pipe pile is provided at the center of the coupler to ensure the bending strength of the screw joint. Bending strength can be improved by providing a shoulder portion on the inner or outer surface of the coupler, but the manufacturing cost increases due to the production of the shoulder portion, and the entire coupler base tube becomes thicker. Incurs a significant increase in costs.
[0006]
Patent Document 5, Patent Document 6, and Patent Document 7 disclose a threaded joint in which pin tips come into contact with each other at a coupler central portion. However, these are threaded joints for oil well pipes, and hundreds of joints are used in the same hole, and the tightness of the joint is required. For this reason, threaded joints for oil well pipes are required to ensure that the coupler and steel pipe screws are securely fitted, and the resistance due to frictional force during fastening is large. Has been done.
[0007]
Also in oil well pipe threaded joints, in order to reduce the frictional force at the time of fastening, Patent Document 8 discloses a method of providing an incomplete threaded portion that contacts only the tensile load surface, and Patent Document 9 discloses a method of screwing at the time of fastening. A method is disclosed in which only the tensile load surfaces of the portions are in contact with each other, and a gap is provided between the screw threads and the thread valleys and in the compression load surface. However, the threaded joint for oil country tubular goods in Patent Document 8 requires a complete thread portion where the thread and the thread valley contact, and the method according to Patent Document 9 requires that both the tension load surface and the compression load surface be separated at the end of fastening. Since it is necessary to contact, the fastening by human power is impossible.
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 07-823838
[Patent Document 2]
Japanese Unexamined Patent Publication No. 07-102555
[Patent Document 3]
Japanese Patent Laid-Open No. 06-193055
[Patent Document 4]
JP 2002-61175 A
[Patent Document 5]
Japanese Patent Laid-Open No. 06-123386
[Patent Document 6]
Japanese Patent Laid-Open No. 08-303657
[Patent Document 7]
JP-A-11-108264
[Patent Document 8]
JP 2002-295747 A
[Patent Document 9]
JP 2002-61779 A
[0009]
[Problems to be solved by the invention]
The present invention provides inexpensively a threaded joint for steel pipe piles that can secure the tensile, compression, and bending strength necessary for the steel pipe pile without welding the threaded joint to the steel pipe pile body and that can be fastened by human power. It is.
[0010]
[Means for Solving the Problems]
The present inventor has studied in detail a method for improving the bending strength of the joint of the steel pipe pile and enabling fastening by human power without providing a shoulder to the coupler in order to reduce the coupler manufacturing cost. As a result, in order to improve the bending strength, it is effective to bring the ends of the threaded portion of the steel pipe pile into contact with each other at the threaded portion of the steel pipe pile and the coupler screw. It was found that the frictional force at the time of fastening can be reduced by reducing the contact area between the trapezoidal screw and the trapezoidal screw of the coupler. For this purpose, it was found that it is important to optimize the pitch diameter of the trapezoidal screw of the threaded portion of the steel pipe pile and the trapezoidal screw of the coupler, and to secure the thread fitting height which is the contact length between the trapezoidal screws.
[0011]
Based on such knowledge, the present invention was completed for the first time by comprehensively analyzing the required performance, construction characteristics, processing characteristics of the threaded joint for steel pipe piles, using a coupler without a shoulder, This is a threaded joint for steel pipe piles that can be fastened by human power, in which the threaded ends of two steel pipe piles are brought into contact with each other at substantially the center of the coupler, and the gist thereof is as follows.
[0012]
(1) In a threaded joint comprising two steel pipe piles with trapezoidal screws arranged in a tapered shape at least at one end and a coupler in which trapezoidal screws are arranged in a tapered shape on both sides and the steel pipe piles are screwed together, two steel pipes The tip of the pile threaded part hits each other The thread of the threaded portion of the steel pipe pile and the threaded bottom of the coupler and / or the threaded bottom of the threaded portion of the steel pipe pile and the thread of the coupler are in contact with each other. The second steel pipe pile and the coupler have a gap between the thread and thread valley of the threaded portion on the other side, and the compression load surface, and the tensile load surface is in contact A threaded joint for steel pipe piles.
[0014]
( 2 ) The absolute value of the difference between the pitch diameter of the trapezoidal screw of the second steel pipe pile and the pitch diameter of the trapezoidal screw on the other side of the coupler is the pitch diameter tolerance of the trapezoidal screw of the steel pipe pile and the pitch diameter of the trapezoidal screw of the coupler It is equal to or greater than the sum of the tolerances, and the thread effective fitting height, which is the contact length between the trapezoidal screw of the threaded portion of the steel pipe pile and the trapezoidal screw of the coupler, is 0.3% or more of the diameter of the steel pipe pile. And ( 1 ) Threaded joint for steel pipe piles.
[0015]
( 3 ) After screwing so that the thread of the threaded portion of the first steel pipe pile and the thread bottom of one side of the coupler and / or the thread bottom of the threaded part of the steel pipe pile and the thread of the coupler are brought into contact, The steel pipe pile and the coupler are threaded together so that there is a gap in the thread and thread valleys on the other side of the coupler and the compression load surface, and the tensile load surface is brought into contact (1). Or (2) The fastening method of the threaded joint for steel pipe piles described in 2.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an example of the present invention and shows a threaded portion of a threaded joint for steel pipe piles in which one steel pipe pile is fastened to each side of a coupler. Tapered screws 1 (referred to as female screws 1) are engraved on the inner surfaces of both sides of the coupler, and the screw shape is a trapezoidal screw 5. The female thread on one side of the coupler is screwed with a threaded portion (referred to as a male thread 2) of a steel pipe pile, which is a part where a taper screw is engraved on the outer surface of the end of the first steel pipe pile. Furthermore, the other side of the coupler is screwed with a threaded portion (referred to as a male thread 3) of the steel pipe pile, which is a part where a taper screw is engraved on the outer surface of the end portion of the second steel pipe pile.
[0017]
Further, in the threaded portion of the steel pipe pile threaded joint, the front end of the male screw 2 of the steel pipe pile fastened in advance is in contact with the front end of the male screw 3 fastened behind. With this structure, the front end of the male screw 2 of the first steel pipe pile fastened in advance without providing a shoulder portion on the coupler is used as the shoulder when the male screw 3 of the second steel pipe pile fastened after that is fastened. The bending strength is remarkably improved by the male screw tip 6 which meets the above.
[0018]
A mechanism by which the bending strength can be improved by the present invention will be described with reference to FIG. When a bending load is applied to the steel pipe pile and an upward bending moment is applied to both ends of the threaded joint shown in FIG. A compressive stress is transmitted to the male screw 3. In the joint design, when the steel pipe pile main body and the coupler material using the same strength are used, for example, at the threaded portion of the male screw 3 and the female screw 1, the section coefficient at the coupler dangerous section at the tip of the male screw 3 is at least the tubular body. It is possible to prevent breakage from the coupler by designing the section modulus to be greater than.
[0019]
On the other hand, in the present invention in which the male screw 2 and the male screw 3 are in contact with each other, the compressive stress generated by the bending load is transmitted from the screw portion to the male screw 3 at the male screw tip 6 in addition to the transmission from the screw portion as in the prior art. Directly transmitted. As a result, the force transmitted through the

male screws

2 and 3 and the female screw 1 is reduced as in the prior art. Furthermore, compared with the prior art, since the

male screws

2 and 3 are screwed deeper into the female screw 1, when a coupler having a taper screw of the same shape is used, the thickness of the coupler in the coupler critical section is reduced. The section modulus can be increased and the section modulus can be increased. Therefore, even in a threaded joint using a coupler in which a taper screw having no shoulder is formed, bending strength can be secured by bringing the ends of the threaded portions of the steel pipe piles into contact with each other.
[0020]
In addition, it is preferable that the length of the external thread of the steel pipe pile is a complete screw thread length and is 20 to 40% of the diameter of the steel pipe pile, and the length of the coupler is about twice the length of the external thread. preferable. Furthermore, the strength of the steel pipe pile is preferably 400 to 800 MPa, and the strength of the coupler strength is preferably 500 to 1000 MPa, and the strength of the steel pipe pile and the coupler strength are preferably combined appropriately from the viewpoint of joint performance.
[0021]
Next, the reason why the present invention is specified as a taper screw will be described. In the case of a parallel screw, it is necessary to accurately align the shaft when starting screw fastening, and the only way to fasten the screw is to increase the screw lead. On the other hand, with taper screws, the taper makes it easy to align the axis, and the fastening performance depends on the thread row taper and the thread height in addition to the thread lead, and it can be fastened faster than parallel threads. Proven.
[0022]
Usually, in a taper screw, when the shape of the screw is a square screw or a trapezoidal screw, the threaded joint can be made independent by interference in the radial direction between the screw thread and the screw bottom by tightening. On the other hand, when the shape of the screw is a triangular thread or a round thread, the threaded joint can be made self-supporting due to the interference of the flank surface responsible for compressive load or tensile load. However, in the case of fastening by human power, the front ends of the screw parts are brought into contact with each other, and in order to make the screw self-supporting, interference between the radial direction of the screw thread and the screw bottom, and interference between the compression load surface and the tensile load surface occur. It turns out that it cannot be achieved if it occurs simultaneously.
[0023]
In addition, it is easy to bring the ends of the threaded parts of steel pipe piles into contact with each other when fastening using a machine, but when fastening with human power, the shape of the coupler and steel pipe pile threads are optimized. It is preferable. That is, by optimizing the shape of the screw, before the tip of the male screw of the preceding steel pipe pile reaches the center of the coupler, the frictional force becomes too large, and the tip of the male screw of the succeeding steel pipe pile becomes the leading steel pipe pile. The problem that the tip of the male screw does not reach the end, and even if the tips of the male pipe piles are in contact with each other, the fitting thread is insufficiently fitted and the joint is prevented from falling off. In view of this, an investigation was made of a method that has sufficient processing tolerances in industrial production and that can reliably bring the male screw tips into contact with each other even when tightened manually.
[0024]
FIG. 3 shows a configuration similar to that shown in FIG. 1 in which the male screw tip 6 is in contact, and further shows the characteristics of the threaded portion of the male screw of the steel pipe pile and the female screw of the coupler. As an example of the threaded portion of the first steel pipe pile and one side of the coupler, the thread 7 of the threaded portion of the first steel pipe pile and the gap 7 between the screw bottom of the one side of the coupler (male screw thread-female screw bottom gap 7). ) And the contact 8 between the thread bottom of the threaded portion of the first steel pipe pile and the thread on one side of the coupler (referred to as male thread bottom-female thread contact 8). Further, the threaded portion of the second steel pipe pile and the other one side of the coupler are connected to a gap 9 (male thread bottom − between the screw bottom of the second steel pipe pile and the other one side of the coupler. A female thread gap 9), a gap 10 between the thread of the threaded portion of the second steel pipe pile and the screw bottom on the other side of the coupler (referred to as male screw thread-female screw bottom gap 10), and a compression load surface gap 11. The tensile load surface 12 is in contact.
[0025]
According to the present invention, with respect to a mechanism that enables reliable fastening by human power, one side of the female screw 1 of the coupler and the male screw 2 of the first steel pipe pile are fastened first, and then the other side of the female screw 1 of the coupler and the second side The case where the male thread 3 of the steel pipe pile is fastened will be described as an example. First, when the male screw 2 of the steel pipe pile is screwed onto one side of the female screw 1 of the coupler, the outer diameter of the male screw 2 gradually increases at a specific portion of the female screw 1 when the screwing proceeds in the case of a taper screw. When the threaded part of the steel pipe pile thread reaches the center of the coupler, the threading of the female thread and the male thread proceeds, the thread bottom of the male thread and the thread of the female thread come into contact, and the male thread bottom-female thread contact 8 is formed. Increase, and the conclusion by human power will reach the limit.
[0026]
At this time, the male screw and the female screw are sufficiently fixed by fitting the tensile load surface of the trapezoidal screw, and the tip of the male screw forms a substantial shoulder portion. Subsequently, when the male screw 3 is screwed onto the other side of the coupler 1 and the tips of the steel pipe pile screw portions are brought into contact with each other, the male screws receive a reaction force with each other, the tensile load surface of the screw comes into contact, and the coupler and the male screw Fixed. At this time, if the male screw bottom-female screw thread gap 9 and the male screw thread-female screw bottom gap 10 are formed until the male screw tips come into contact with each other at the threaded portion of the other side of the coupler 1 and the male screw 3, the male screw There is no sudden increase in torque before the tips meet. Further, if the compression load surface gap 11 is also formed on the compression load surface, the compression load surface and the tensile load surface do not contact at the same time, so that a rapid increase in tightening torque before the male screw tip contacts can be suppressed. it can.
[0027]
In addition, although the example which has the external thread thread-internal thread bottom gap 7 and the external thread bottom-internal thread contact 8 has been described in FIG. 3, the external thread thread-internal thread bottom is in contact, and the external thread bottom-internal thread thread has a gap. The male screw thread-female screw bottom and the male screw thread-female screw thread may be in contact with each other.
[0028]
As shown in FIG. 4, the joint according to the present invention is usually fastened by hand or by a machine to the extent that the coupler does not loosen due to transportation at the factory shipment or unexpected impact, etc. Become. Therefore, at the time of factory shipment, the threaded portion of the first steel pipe pile is fastened to one side of the coupler so as to form, for example, a male screw thread-female screw bottom gap 7 and a male screw bottom-female screw contact, The threaded portion of the second steel pipe pile is formed with a male thread bottom-female thread gap 9, a male thread-female thread bottom gap 10 and a compression load surface gap 11, and on the other side of the coupler with the tensile load surface 12 in contact. Screw together.
[0029]
Next, when fastening the coupler and the steel pipe pile by human power, a method for stably bringing the ends of the steel pipe pile threaded parts into contact with each other at the center of the coupler was examined. In the joint having a shoulder in the coupler central portion, the fastening is completed when the tip of the steel pipe pile threaded portion comes into contact with the shoulder, so the tips of the steel pipe pile threaded portion do not contact each other and do not affect each other. However, since the present invention omits the shoulder at the center of the coupler, it is extremely important that the position of the tip of the steel pipe pile screw portion falls within an appropriate range near the center of the coupler when the fastening is completed. For this purpose, it is important to set the difference in pitch diameter between the female screw and the male screw within an appropriate range.
[0030]
The present inventors show the fluctuation of the position of the front end of the male screw of the steel pipe pile after fastening caused by the pitch diameter tolerance of the male screw of the first steel pipe pile and the pitch diameter tolerance of the female screw on one side of the coupler as shown in FIG. The absolute value of the difference between the pitch diameter 14 of the trapezoidal screw on the other side of the coupler (referred to as the female thread pitch diameter 14) and the pitch diameter 15 of the threaded portion of the second steel pipe pile (referred to as the male thread pitch diameter 15) is To be smaller than the sum of the tolerance of the pitch diameter of the trapezoidal screw on one side (referred to as female thread pitch diameter tolerance) and the tolerance of the pitch diameter of the trapezoidal screw on the threaded part of the second steel pipe pile (referred to as male thread pitch diameter tolerance) Oriented how to absorb by.
[0031]
In FIG. 5, the lower male screw 3 and female screw 1 are screwed together. The female thread pitch diameter 14 is a straight line that connects the central part of the screw height of the trapezoidal screw of the female thread 1, and the male thread pitch diameter 15 is a straight line that connects the central part of the thread height of the trapezoidal screw of the male screw 3. If the absolute value of the difference between the female screw pitch diameter and the male screw pitch diameter is set to be equal to or larger than the sum of the female screw pitch diameter tolerance and the male screw pitch diameter tolerance, the male screw tip is stably brought into contact with approximately the center of the coupler.
[0032]
The pitch diameter of the female screw and the male screw can be measured using a conical measuring instrument called a stand-off gauge. Further, the pitch diameter tolerance of the female screw and the male screw can be measured as the depth of the standoff gauge, that is, the moving length in the axial direction.
[0033]
If priority is given to the contact between the male screw tips, the screw threads may be loosely fitted. In particular, sufficient strength against the tensile axial force may not be obtained, and the joint may jump out. In order to prevent this, it is necessary that the effective thread height 16 which is the contact length between the male thread and female thread on the tensile load surface is 0.3% or more of the diameter ratio. Thereby, joint performance represented by tensile strength and compressive strength can be secured. The upper limit of the thread effective fitting height is determined by the outer diameter of the steel pipe pile, the thread height of the trapezoidal screw, the male thread bottom-female thread gap 9 and the male thread-female thread bottom gap 10, and is not particularly defined. If the effective thread height is increased, the pitch diameter tolerance can be increased, but the coupler outer diameter needs to be increased in order to compensate for the dangerous section of the coupler.
[0034]
The thread effective fitting height can be measured from the cross-sectional shape when the steel pipe pile thread portion and the coupler are fastened. It is also possible to create and measure a drawing as shown in FIG. 6 from the taper and pitch diameter.
[0035]
In addition, the thread height of the trapezoidal screw depends on the outer diameter of the steel pipe pile, but for steel pipe piles with an outer diameter of 200 mm or less, the thread height is 1-2 mm, and when it is 200 mm or more, it is about 1.3 to 3 mm. The required performance of the joint can be satisfied, and the manufacturing cost can be suppressed. Specifically, the trapezoidal screw is preferably an API standard 5B buttress screw, EL casing screw, or the like. Moreover, although the thread part of a steel pipe pile and the screw taper of a coupler are not prescribed | regulated in particular, it is preferable to set it as the range of 1/8-1/16 from processing efficiency and a cost surface.
[0036]
The present invention does not have a shoulder portion at the central portion of the coupler, but in order to make the front end of the male screw that has been screwed and fastened substantially act as a shoulder, as shown in FIG. Fastened to the female screw 1 on one side of the coupler so as to form a thread-female screw bottom gap 7, a male screw bottom-female thread contact 8, and then the male screw 3 is connected to a male screw bottom-female screw gap 9, male screw thread-female screw bottom gap. 10 and the compression load surface gap 11 are preferably fastened to the female screw on the other side of the coupler so that the tensile load surface 12 is in contact, and the tips of the male screw 2 and the male screw 3 are brought into contact with each other.
[0037]
The above description is an example in which the coupler is a female screw and the threaded portion of the steel pipe pile is a male screw. However, a female screw may be engraved on the inner surface of the end of the steel pipe pile and a male screw may be engraved on the outer surface of the coupler. In this case, in FIG.1 and FIG.3, the lower side of a figure becomes an outer surface, and the upper side of a figure becomes an inner surface.
[0038]
【Example】
Example 1
The pitch diameter and pitch diameter tolerance of the male thread of the steel pipe pile having an outer diameter of 114 mm, and the pitch diameter and pitch diameter tolerance of the female thread of the coupler having the same inner diameter as the steel pipe pile were measured by a stand-off gauge shown in API Standard 5B. The pitch diameter tolerance of the steel pipe pile and coupler was both 0.075 mm. That is, the sum of the pitch tolerance of the steel pipe pile and the pitch diameter tolerance of the coupler is 0.125 mm.
[0039]
The first steel pipe pile was fastened to one side of the coupler, and the second steel pipe pile was fastened to the other side of the coupler. The presence or absence of contact between the male screw tips of the screwed joint was visually confirmed. Moreover, the effective thread height of the threaded portion of the joint was determined from the standoff value.
Table 1 shows the pitch diameter difference between the male thread of the steel pipe pile and the female thread of the coupler, the effective thread height, and the presence or absence of contact between the male thread tips. Here, as the pitch diameter difference between the male screw and the female screw increased, the number of contact samples between the ends of the male screw increased, and when the sum of the pitch tolerances of the male screw and the female screw was exceeded, there was no non-contact sample.
[0040]
[Table 1]

[0041]
(Example 2)
The pitch diameter and pitch diameter tolerance of the male thread of the steel pipe pile having an outer diameter of 244 mm and the pitch diameter and pitch diameter tolerance of the female thread of the coupler having the same inner diameter as the steel pipe pile were measured in the same manner as in Example 1. Both the steel pipe pile and the coupler had a pitch diameter tolerance of 0.125 mm. That is, the sum of the pitch tolerance of the steel pipe pile and the pitch diameter tolerance of the coupler is 0.250 mm. The first steel pipe pile was fastened to one side of the coupler, and the second steel pipe pile was fastened to the other side of the coupler. The presence or absence of contact between the male screw tips of the screwed joint was visually confirmed, and the thread effective fitting height of the screwed portion of the joint was measured in the same manner as in Example 1.
[0042]
Table 2 shows the pitch diameter difference between the male thread of the steel pipe pile and the female thread of the coupler, the effective thread height, and the presence or absence of contact between the male thread tips. Here, as the pitch diameter difference between the male screw and the female screw increased, the number of contact samples between the ends of the male screw increased, and when the sum of the pitch tolerances of the male screw and the female screw was exceeded, there was no non-contact sample.
[0043]
[Table 2]

[0044]
(Example 3)
The external thread of a steel pipe pile having an outer diameter of 80 mm to 273 mm was screwed onto both sides of a female thread of a coupler having an inner diameter similar to that of the steel pipe pile. At this time, after the first steel pipe pile was fastened to one side of the coupler by human power, the second steel pipe pile was fastened to the other side of the coupler by human power. The presence or absence of contact between male screw tips of the screwed joint is visually confirmed, and at the screwed portion of the screw joint on the other side of the second steel pipe pile and coupler, the male screw thread-female thread valley gap, male screw bottom -Female thread gap, compression load face gap and tensile load face gap were determined.
[0045]
The male screw thread-female screw valley gap, the male screw bottom-female screw thread gap, the compression load surface gap, and the tensile load surface gap were values predicted from the values of the pitch diameter and pitch diameter tolerance by the stand-off gauge. It is confirmed that the predicted value is equivalent to the actually measured value as follows. First, the standoff value of the male screw and the female screw was measured to predict the gap value. Next, the male screw and the female screw were screwed together, the screwed portion was cut in the axial direction, and the screw gap was measured from a cross-sectional photograph after screwing. Furthermore, it was confirmed that the actually measured gap value was equivalent to the predicted gap value.
[0046]
Table 3 shows the minimum value of the gap between the screw thread and the screw bottom as the peak-valley minimum gap, and further shows the presence / absence of contact between the compression load surface gap and the male screw tip. In Table 3, the peak-valley minimum gap is the smaller one of the male screw thread-female screw valley gap and the male screw bottom-female screw gap at the time of completion of tightening. Also, the A side and B side distinguish the screws on both sides of the coupler, and the threaded joint between the threaded part of the first steel pipe pile and the one side of the coupler, which were fastened in advance, is tightened by moving back to the A side. The threaded joint between the threaded portion of the second steel pipe pile and the other side of the coupler was designated as the B side. The tensile load surfaces were all in contact.
[0047]
In Comparative Examples 13, 15, 18, 20, 21, and 22, both the A and B sides were in contact with the valleys, so that the contact of the male screw tip could not be obtained. Comparative Examples 14, 16, and 19 have a crevice gap on one side of the screw, but because the compression load surface on the side having the crevice gap is in contact, the contact of the male screw tip is obtained. There wasn't. In Comparative Examples 17, 18, and 23, the screw on both sides had a crevice and valley gap, but since any of the screws was in contact with the compression load surface, the front end of the male screw could not be obtained.
[0048]
In Examples 12, 18, and 19, there were gaps between the valleys on the A side and the compression load surface at the same time, and the contact of the male screw tip was obtained when the tightening was completed. Examples 10, 11, 13, 14, 15, 16, and 17 had gaps between the valleys on the B side and the compression load surface at the same time, and the contact of the male screw tip was obtained when tightening was completed.
[0049]
[Table 3]

[0050]
Example 4
The male thread of the steel pipe pile of the outer diameter, wall thickness, and steel type shown in Table 4 was screwed in the same manner as in Example 3 on both sides of the female thread of the coupler having the same steel type and the same inner diameter and wall thickness as the steel pipe pile. . The pitch diameter and pitch diameter tolerance of the male thread of the two steel pipe piles and the female thread of the coupler were determined in the same manner as in Example 1.
[0051]
The presence or absence of contact between the male screw tips of the threaded joint is visually confirmed. The inter-surface gap was measured in the same manner as in Example 3. Further, the thread effective fitting height of the threaded portion of the joint was measured in the same manner as in Example 1.
[0052]
The bending test was a four-point bending test in which the joint portion was arranged in the center, and the bending strength was converted from the load at the maximum load load to the bending moment. In the tensile and compression tests, the maximum load during the test period is shown.
[0053]
Table 4 shows the thread joint that was fastened in advance as the A side and the subsequent threaded joint as the B side. The minimum gap between the valleys and valleys, the compression load surface clearance, the presence or absence of contact between the male screw tips, and the effective thread height The joint performance was shown. In Table 4, the smallest gap between the male screw thread-female screw valley gap and the male screw bottom-female screw thread gap at the time of completion of tightening is shown as the minimum groove / valley gap. Further, the tensile load surfaces were all in contact.
[0054]
In all of Comparative Examples 24, 25, 27, 28, 30, and 31, since the male screw tip does not abut at the end of tightening, the effective thread height is sufficient, but the joint bending strength is the male screw tip. It was clearly inferior to the joints that were in contact. In Comparative Examples 26, 29, and 32, the end of the male screw was in contact at the end of tightening, but the effective thread height was less than 0.3% in terms of the pipe diameter ratio. The joint strength itself was inferior to that having an effective thread height of 0.3% or more in terms of the pipe diameter ratio.
[0055]
On the other hand, in each of the examples, the end of the male screw was abutted and the effective thread height was 0.3% or more in terms of the pipe diameter ratio, so both the bending strength and the tensile strength were stable at a high level. The compressive strength was almost constant regardless of whether or not the front end of the male screw was in contact and the height of the effective thread height. This is because, in the short column compression test, a buckling phenomenon occurs in the tube from the vicinity where the compressive load exceeds the tube yield strength.
[0056]
[Table 4]

[0057]
【The invention's effect】
According to the present invention, it is possible to provide a threaded joint for steel pipe piles that can be fastened by human power and has improved bending strength and tensile strength, and the industrial contribution is extremely high.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a threaded joint for steel pipe piles according to the present invention.
FIG. 2 is a diagram for explaining the effect of the present invention at the time of bending load.
FIG. 3 is a view showing a thread gap of a joint according to the present invention.
FIG. 4 is a view showing an example of screw fastening according to the present invention.
FIG. 5 is a diagram showing a screw gap and a pitch diameter in the present invention.
[Explanation of symbols]
1 ... Tapered screw 1 on both sides of coupler
2 ... Screw part of the first steel pipe pile
3 ... Screw part of the second steel pipe pile
4 ... Screwing of one side of the first steel pipe pile and coupler
5 ... Trapezoidal screw
6 ... Abutting of the tip of the threaded part of the steel pipe pile
7: The gap between the screw thread of the first steel pipe pile and the screw bottom on one side of the coupler
8: Contact between the thread bottom of the threaded portion of the first steel pipe pile and the thread on one side of the coupler
9: Gap between the thread bottom of the threaded portion of the second steel pipe pile and the thread on the other side of the coupler
10 ... Gap between the thread of the threaded portion of the second steel pipe pile and the thread bottom of the other side of the coupler
11: Compression load surface clearance
12 ... Tensile load surface
13: Compression load surface
14 ... Pitch diameter of trapezoidal screw on the other side of the coupler
15 ... trapezoidal pitch diameter of the threaded part of the second steel pipe pile
16: Effective thread height

Claims

Two steel pipe pile thread portions in a threaded joint comprising two steel pipe piles with trapezoidal screws arranged in a taper shape at at least one end and a coupler in which trapezoidal screws are arranged in a taper shape on both sides and screwed to the steel pipe piles. The first steel pipe pile and the coupler, and the threaded portion of the threaded portion of the steel pipe pile and the threaded bottom of the coupler and / or the threaded bottom of the threaded portion of the steel pipe pile, The thread of the coupler is in contact, there is a gap in the thread and thread valley of the second steel pipe pile and the threaded part on the other side of the coupler, and the compression load surface, and the tensile load surface is in contact A threaded joint for steel pipe piles.

The absolute value of the difference between the pitch diameter of the trapezoidal screw of the second steel pipe pile and the pitch diameter of the trapezoidal screw on the other side of the coupler is the pitch diameter tolerance of the trapezoidal screw of the steel pipe pile and the pitch diameter tolerance of the trapezoidal screw of the coupler The effective height of the thread, which is the contact length between the trapezoidal screw of the threaded portion of the steel pipe pile and the trapezoidal screw of the coupler, is 0.3% or more of the diameter of the steel pipe pile, The threaded joint for steel pipe piles according to claim 1 .

After screwing so that the thread of the threaded portion of the first steel pipe pile and the thread bottom of one side of the coupler and / or the thread bottom of the threaded portion of the steel pipe pile and the thread of the coupler are brought into contact, the second steel pipe The steel pipe pile according to claim 1 or 2 , wherein the pile and the coupler are screwed together so that there is a gap in the thread and valley of one side of the coupler and the compression load surface, and the tensile load surface is brought into contact. For fastening screw joints.