JP4088041B2

JP4088041B2 - Steel sheet pile with improved buckling strength

Info

Publication number: JP4088041B2
Application number: JP2001005844A
Authority: JP
Inventors: 裕章中山; 健二西海; 昌毅龍田; 和彦江田
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2001-01-15
Filing date: 2001-01-15
Publication date: 2008-05-21
Anticipated expiration: 2021-01-15
Also published as: JP2002206234A

Description

【０００１】
【発明の属する技術分野】
本発明は、鋼矢板に関するもので、例えば、土木建築分野における地下土留め、基礎構造及び港湾、河川における岸壁、更には地中における止水壁に用いる構造部材としての鋼矢板に係り、特に、座屈耐力を向上させた鋼矢板に関する。
【０００２】
【従来の技術】
従来、土木建築分野において地中に打設する壁体として、一般的に図５に示すようなＵ形鋼矢板（従来例１）または、図６、図７に示すような特許第２６８９７９４号に示されているハット形鋼矢板（従来例２）が用いられている。
【０００３】
図５に示すＵ形鋼矢板１は、幅寸法（Ｌ）を有するウェブ部（Ｕ形状の底の部分）２の両端に隅角部３を介してフランジ（Ｕ形状の両側部）４を接続し、フランジ４の端部を同じ向きに折り曲げて継手部５が構成されている。前記Ｕ形鋼矢板１は、左右対称形であり、１枚毎に、継手部５を介して左右逆向に接続して打設される。
【０００４】
また、図５のＵ形鋼矢板１においては、フランジ４の途中を折曲げ部６を介して湾曲させることで、Ｕ形鋼矢板１の積み重ね時に上下の継手部５が互いに接触しない構成として、当該継手部５の損傷を防ぐことができる。また、前記の構成とすることで、上下に積み重ねたＵ形鋼矢板１のウェブ２間に隙間が形成されるため、個々のＵ形鋼矢板１を掴（つか）み易く、運搬時に積み重ねた鋼矢板を取り外すことが容易な構造となっている。
【０００５】
図６に示すハット形鋼矢板７にあっては、幅寸法（Ｌ）を有するウェブ部２の両端に隅角部３を介してフランジ部４を接続し、フランジ部４の両端に継手支持部８を設け、その先端に左右側で逆向きの継手部５が構成されている。前記ハット形鋼矢板７は、左右非対称形であり、継手部５を介して左右同一方向に接続して打設される。
【０００６】
図６に示すハット形鋼矢板７においては、継手部５が大きな荷重が作用する中立軸から最も遠い位置に存在するため、中立軸の断面剛性を確保でき、かつ継手部効率が低下することがない構造となっている。
【０００７】
【発明が解決しようとする課題】
しかし、前記のＵ形鋼矢板やハット形鋼矢板は、前記の利点がある反面、ウェブ部２の幅寸法（Ｌ）については何らの配慮がなされておらず、一般に幅寸法（Ｌ）が広いため、ウェブ部２の板厚（ｔ）が小さい場合は、（１）打設時にウェブ部２が座屈しやすく、（２）図７に示す共用時においては、壁面土圧による曲げ荷重等を受けた際にウェブ部２が局部座屈を起こしやすい。ウェブ部２の座屈の発生を防ぐためには、板厚（ｔ）を増さなければならず、鋼材重量が増え不経済である。
【０００８】
他方、硬めの地盤に鋼矢板を打設する場合、オーガー等を併用して、打設周辺地盤を緩めてから地中に鋼矢板を打ち込む方法が採用されているが、前記のハット形鋼矢板７では、ハット形状の凹部、つまりウェブ部２とフランジ部４で囲まれた領域１０が狭く、この領域１０に配設されるオーガーの地盤攪拌径が小さい。したがって、オーガーによる地盤軟化の影響範囲が小さいために、矢板断面全体に渡って周辺地盤を軟化させることが困難であり、特に、継手支持部８を介してオーガーから離れて位置する継手部５の周辺地盤では、元の硬質地盤のままの状態で鋼矢板を打ち込むことに陥りやすい。
【０００９】
しかし、鋼矢板７の継手部５においては、先行して打設された鋼矢板７の継手部５と嵌合する側と反対の片側側面が長手方向に渡ってフリーとなっており、打設時の地盤抵抗に対して最も抵抗力が小さいため、打設時に継手部５が変形し、施工性が低下する危険性が非常に高い。
【００１０】
従来技術では、前述のような問題点については着目されておらず、したがって、その解決方法についての示唆がなされていない。
【００１１】
本発明者は、硬質地盤に打設する鋼矢板について種々研究した結果、Ｕ形鋼矢板やハット形鋼矢板の改良すべき問題点のうち、特に前述の問題点、つまり、鋼矢板の地盤への打設時の座屈耐力向上の問題、およびオーガーによるより効率的な地盤軟化の問題に着目した。そして、これらの諸問題を、構造的な変更を可及的に少なく抑え、各部材の配置関係、寸法関係を所定の関係に設定し、構成することで、解決できる方法を見出した。
【００１２】
本発明は、前記の知見にもとづいて、前記の問題点を解決すべく提案したもので、鋼矢板の打設時および共用時に座屈しづらく、かつ施工性に優れた鋼矢板を提供することを目的とする。
【００１３】
【問題を解決するための手段】
前記の目的を達成するために、本発明は、次のように構成する。
【００１４】
第１の発明は、隣り合う鋼矢板の継手部を嵌合し壁体として各鋼矢板が一体となったとき、前記継手部が壁体の中立軸から離れた位置になるように構成された断面略Ｕ字形の鋼矢板であって、当該鋼矢板は、座屈耐力向上用ウェブ部を構成するため、前記ウェブ部とフランジ部との隅角部を多角形状に折り曲げた断面形状に変化させることにより、直線状断面の前記ウェブ部の幅寸法（Ｌ₁）を短縮させ、ウェブ部の板厚が下記（１）式を満たすことを特徴とする座屈耐力向上の鋼矢板。
Ｌ _１／４８≦ｔ＜Ｌ／４８・・・（１）
ここで、Ｌ：両側のフランジ面を延長し、ウェブ部の延長面と交わる両交線間の距離で定義されるウェブ部の幅寸法
Ｌ _１：座屈耐力向上用ウェブ部の幅寸法
ｔ：ウェブ部の板厚
【００１５】
第１発明のように、ウェブ部の幅寸法（Ｌ₁）、つまり、両側フランジ部の屈曲部間の直線距離を短くすることで、幅寸法（Ｌ₁）に対する鋼板の板厚の比（これを幅厚比という）を小さくし、同じウェブ部の板厚でも、従来のＵ形鋼矢板またはハット形鋼矢板よりも座屈しづらくする。特に、共用時に、最も大きな応力が発生する中立軸からの最外位置にあるウェブ部で、その屈曲部間の幅寸法（Ｌ₁）を短くすれば、本発明の目的・作用である座屈耐力を得る上で好適である。
【００１７】
また、第１発明によると、ウェブ部とフランジ部との隅角部を多角形状に折り曲げるという比較的成形容易な構成で、幅寸法（Ｌ₁）の短縮した直線状断面のウェブ部を構成できる。さらに、第１発明によると、幅寸法（Ｌ ₁ ）を短縮することで、幅厚比を４８以下の値を保って、なおかつ、板厚（ｔ）を薄肉化しても、壁面土圧による曲げ荷重等を受けた際に局部座屈を起こさず、板厚（ｔ）の増大や、鋼材重量の増大を招くという不具合を解決できる。
【００１８】
第２発明は、第１発明において前記ウェブ部とフランジ部との隅角部を中立軸よりもウェブ部側に設けたことを特徴とする。
【００１９】
第２発明によると、ウェブ部とフランジ部との隅角部を鋼矢板の中立軸よりもウェブ部寄りの位置に設けるので、打設重機がウェブを掴んで打設した場合に矢板断面に生じる偏心荷重が小さく座屈しずらい形状となる。
【００２０】
第３発明は、前記鋼矢板断面中心から継手部が設けられているフランジ端縁までの距離（Ｌ₄）よりも、継手部のフランジ部からの突出長（Ｌ₂）の方が短くなるように当該継手部をフランジ部近傍に設けることで、鋼矢板断面積に占めるウェブ部とフランジ部で囲まれた領域を大きくすることを特徴とする。
【００２１】
第３発明の構成としたことで、同じ断面積を保有する従来のハット形鋼矢板と本発明による鋼矢板とを比較した場合、凹部形状の部分の面積が本発明による鋼矢板の方がより大きくなることから、オーガーを併用して打設する場合、地盤攪拌径を大きくとることができ、より大きな範囲の地盤を軟化することができるので、硬質な地盤への打設が容易になる。また、フランジ部からの継手の突出長を小さくすることで、打設時に継手部のねじれや反り等の変形が生じづらくなり、施工性が向上する。
【００２２】
第４発明は、第３発明において、継手支持部１８の幅寸法（Ｌ2）を継手の嵌合に必要な長さ以上５０ｍｍ以下とすることを特徴とする。第４発明によると、鋼矢板２０の拡大された凹部形状の領域２１ａに配置されるオーガーによる地盤軟化の効果が、継手部１５も含めて矢板断面全体に確実にかつ十分に行き渡るようにすることができる。
【００２３】
【発明の実施の形態】
本発明の実施形態を図を参照して説明する。
【００２４】
図１、図２は、本発明の実施形態１に係る座屈耐力を向上させた鋼矢板を示し、図１は、鋼矢板の単体の平面図、図２は前記鋼矢板の継手部の嵌合連結状態での平面図である。図３、図４は、本発明の実施形態２に係る座屈耐力を向上させた鋼矢板を示し、図３は、鋼矢板の単体の平面図、図４は、前記鋼矢板の継手部の嵌合連結状態での平面図である。
【００２５】
図１、図２の実施形態１を説明すると、本発明の鋼矢板１７は、概略Ｕ字形（Ｕ字形及びハット形を含む広い意味で使用する）であって、幅寸法（Ｌ₁）と板厚（ｔ）を有するウェブ部１２の両端に隅角部１３を介してフランジ部１４を接続し、フランジ部１４の両端に継手支持部１８を設け、その先端に左右側で逆向きの継手部１５を設けて構成されている。また、前記の鋼矢板１７は、左右非対称形であり、左右同一方向に接続して打設される。
【００２６】
本発明の鋼矢板１７におけるウェブ部１２は、概略Ｕ字形の鋼矢板１７の底部を構成し、かつ両側のフランジ部１４を屈曲部（つまり、隅角部１３）を介して連結すべく直線状に構成される。特に、このウェブ部１２の幅寸法（Ｌ₁）は、本発明が解決しようとする課題である鋼矢板１７の座屈耐力向上、つまり、ウェブ部１２に荷重が作用した場合における、当該ウェブ部１２の曲がり、ねじれなどに対する座屈耐力向上の手段として、必要かつ最小の幅寸法に構成している。このように、ウェブ部１２の幅寸法（Ｌ₁）を意図的に短縮化することにより、短縮した分、当該ウェブ部１２に作用する、曲がり、ねじれなどに対する座屈耐力を向上できる。さらに後述のように、ウェブ部１２の板厚（ｔ）の薄肉化が可能となる。
【００２７】
実施形態１では、ウェブ部１２の幅寸法（Ｌ₁）を、必要最小の直線状の幅寸法に設ける手段として、フランジ部１４とウェブ部１２とが接続する隅角部（屈曲部）１３を、フランジ部１４の途中に形成される第１角部１３ａと、フランジ部１４とウェブ部１２が交わる位置に形成される第２角部１３ｂと、第１、第２角部１３ａ、１３ｂの間を接続する傾斜部１３ｃとから構成している。第１、第２角部１３ａ、１３ｂを形成する位置は、図示のように、打設重機がウェブ１２を掴んで打設した場合に矢板断面に生じる偏心荷重が小さく座屈しずらい形状となるように、中立軸１６からウェブ部１２までの距離を短くするために、少なくとも鋼矢板１７の中立軸１６よりもウェブ部１２寄りの位置に設けるのがよい。
【００２８】
前記の隅角部１３は、多角形状に折り曲げたことにより屈曲部を多く有する断面構造とすることで、ウェブ部１２の幅寸法（Ｌ₁）は、図１に鎖線で示す従来の鋼矢板のように、ウェブ部２とフランジ部４の隅角部３が多角形状を有しない、ウェブ部の幅寸法（Ｌ）に比較して、（Ｌ₁）＜（Ｌ）に構成できる。
【００２９】
さらに、鋼矢板１７において、中立軸１６から最外縁部に位置するウェブ部１２の幅寸法（Ｌ₁）と板厚（ｔ）の比（これを幅厚比という）を小さくすると、当該鋼矢板１７の打設時の座屈強度を高める上で好適である。具体的には、左右の屈曲部（隅角部１３）間においては、社団法人日本道路協会発行の「道路橋示方書・同解説ＩＩ鋼橋編」に規定されている、圧縮応力を受ける両縁支持板の最小板厚にしたがって、幅厚比を４８以下の値とすることが望ましい。ウェブ部１２の幅厚比をこのように４８以下の値とし、かつ、板厚（ｔ）を可及的に薄く構成した場合でも、本実施形態１の構成とすることで、鋼矢板１７の打設時の必要な座屈強度を十分確保できる。
【００３０】
つまり、鋼矢板１７のウェブ部１２の板厚（ｔ）が小さい場合は、図１の鎖線で示す従来の幅寸法（Ｌ）のウェブ部２の構成であると、▲１▼打設時に座屈しやすく、▲２▼共用時においては、壁面土圧による曲げ荷重等を受けた際に局部座屈を起こしやすい。座屈の発生を防ぐためには、板厚（ｔ）を増さなければならず、鋼材重量が増え不経済である。しかし、前記ウェブ部１２の幅厚比を４８以下の値の下で、板厚（ｔ）を薄くしようにも、従来の構成では、ウェブ部２の幅寸法（Ｌ）に制限されて、自ずから限界がある。この点、本実施形態１の構成によると、幅寸法（Ｌ₁）を短縮することで、幅厚比を４８以下の値を保って、なおかつ、板厚（ｔ）を薄肉化しても、壁面土圧による曲げ荷重等を受けた際に局部座屈を起こさず、板厚（ｔ）の増大や、鋼材重量の増大を招くという不具合を解決できる。
【００３１】
さらに、実施形態１では、図２のように継手部１５同士を嵌合して壁体１９として各鋼矢板１７が一体となったとき、継手部１５は中立軸１６から遠く離れて位置し、中立軸１６をまたいでその左右側が一体構成であるので、この点でも、鋼矢板１７の曲げ耐力が向上すると共に、継手部１５は中立軸１６から外れて位置することで、継手部効率を有効に発揮させることができる。
【００３２】
次に、図３、図４に示す実施形態２を説明する。実施形態２に係る鋼矢板２０は、実施形態１と近似の形状、つまり、概略Ｕ字形であって、幅寸法（Ｌ₁）と板厚（ｔ）を有するウェブ部１２の両端に隅角部１３を介してフランジ部１４を接続し、フランジ部１４の両端に継手支持部１８を設け、その先端に左右側で逆向きの継手部１５を設けて構成されている。また、鋼矢板２０が、左右非対称形であり、左右同一方向に接続して打設される点は実施形態１と同様である。
【００３３】
実施形態２の鋼矢板２０が、実施形態１および従来技術のいずれの鋼矢板とも相違する点は、次の構成である。すなわち、実施形態２の鋼矢板２０は、概略Ｕ字形の鋼矢板において、フランジ部１４とウェブ部１２で囲まれた凹部の領域２１ａを大きくし、この凹部形状の領域２１ａに配置するオーガーの地盤攪拌径を可及的に大きくすると共に、オーガーによる地盤攪拌の範囲を継手部１５に出来るだけ近ずけ、これにより鋼矢板１７の打設効率を高めることにある。この点、従来発明の解決課題には、本実施形態２の解決課題、つまり、オーガーの地盤攪拌径を可及的に大きくすると共に、地盤攪拌を継手部１５に出来るだけ近い範囲まで行うことで、鋼矢板の効率的な打設を行うという着眼点ないし課題意識は存在しない。
【００３４】
本発明者は次に述べる知見に基づいて、前述の課題に着目した。すなわち、硬めの地盤に鋼矢板を打設する場合、オーガー等を併用して、打設周辺地盤を緩めてから地中に矢板を打ち込む方法が採用されているが、例えば、従来の図６に示すハット形鋼矢板７では、継手部５の突出長、つまり、継手支持部５の幅寸法（Ｌ₃）が比較的長い反面、ハット形状の凹部、つまり、ウェブ部２とフランジ部４で囲まれた領域１０は、幅寸法（Ｌ）の長さによって相対的に制限される（つまり、フランジ部４が中心部寄りに近づく）ため狭くなり、この領域１０に配設されるオーガーの攪拌径が小さい。したがって、オーガーによる地盤軟化の影響範囲が小さいために、矢板断面全体に渡って周辺地盤を軟化させることが困難であり、特に、オーガーから離れて位置する継手部５の周辺地盤では、元の硬質地盤のままの状態で鋼矢板７を打ち込むことに陥りやすい。
【００３５】
しかし、鋼矢板の継手部においては、既述のとおり、先行して打設された鋼矢板の継手部と嵌合する側と反対の片側側面が長手方向に渡ってフリーとなっており、打設時の地盤抵抗に対して最も抵抗力が小さいため、打設時に継手部が変形し、施工性が低下する危険性が非常に高い。
【００３６】
本発明者は、前記の知見を得た上で、図３に示すとおり、ウェブ部１２とフランジ部１４で囲まれる凹部の領域２１ａを拡大し、この領域２１ａに配設されるオーガーの地盤攪拌径を大きくすることで、前述の課題を解決できることを見出した。そして、凹部の領域２１ａを拡大する手段として、本実施形態２では、継手支持部１８の幅寸法（Ｌ₂）を、図に鎖線で示す、従来の継手支持部の幅寸法（Ｌ₃）に比して、（Ｌ₂）＜（Ｌ₃）となるように小さく設ける。具体的には、（Ｌ₂）を従来の継手支持部の長さの略１／２の長さに設けることで、図に鎖線で示す、従来の両フランジ部４の位置を、同図実線で示す、両フランジ１４の位置まで外側に広げることができ、それに伴って、領域２１を領域２１ａに拡大したものである。
【００３７】
前記の構成を別の観点から説明すると、継手部１５同士を嵌合し壁体１９として各鋼矢板２０が一体に結合されたとき、矢板断面中心２２から継手部１５が設けられているフランジ縁端までの距離（Ｌ₄）よりも、継手部１５のフランジ部１４からの突出長、つまり継手支持部１８の幅寸法（Ｌ₂）の方が短くなるように（Ｌ₂）＜（Ｌ₄）に構成する。これにより、領域２１ａが拡大し、鋼矢板単位の断面積当りの凹部形状で囲まれた旧領域２１（図７のハット形鋼矢板７の領域１０）よりも広がる構造にでき、しかも、継手部１５をフランジ端縁の近傍に寄せて設けることができ、その分、継手部１５をオーガーによる地盤軟化領域に近づけて設けることができる。
【００３８】
具体的には、鋼矢板２０の拡大された凹部形状の領域２１ａに配置されるオーガーによる地盤軟化の効果が、継手部１５も含めて矢板断面全体に確実にかつ十分に行き渡るようにするためには、通常オーガーは、羽根の５０ｍｍ程度外側まで地盤を軟化させることができるため、継手部１５の突出長、つまり継手支持部１８の幅寸法（Ｌ₂）を５０ｍｍ以下とすることが望ましい。
【００３９】
実施形態２に係る鋼矢板２０の構成は、図３の外側位置に鎖線で示す従来形の鋼矢板に実施できると共に、図３に実線で示す実施形態１と同じ構成の鋼矢板にも適用できる。つまり、同図の実線で示す構成では、フランジ部１４とウェブ部１２とが接続する隅角部１３を、中立軸１６よりもウェブ部１２寄りの位置に設けて、フランジ部１４の途中に形成される第１角部１３ａと、フランジ部１４と、ウェブ部１２が交わる位置に形成される第２角部１３ｂと、第１、第２の両角部１３ａ、１３ｂの間を接続する傾斜部１３ｃから構成することで、ウェブ部１２の幅寸法（Ｌ₁）を短縮している。
【００４０】
したがって、図３に実線で示す鋼矢板２０の場合、オーガーを配置する領域２１ａを拡大したことによる作用に加えて、実施形態１と同様に、ウェブ部１２の幅寸法（Ｌ₁）の短縮による鋼矢板２０の座屈耐力向上と、板厚（ｔ）の薄肉化の作用が奏せられる。
【００４１】
【発明の効果】
本発明の鋼矢板は、両フランジ部とウェブ部の接続する各屈曲部の間（つまり、ウェブ部の幅寸法Ｌ₁）、の幅を小さくすると共に、幅厚比を小さくできるので鋼矢板を座屈しにくい構造にできる。また、ウェブ部の板厚が薄くても剛性を高めることができるため、板厚の薄い鋼板による矢板の製作が可能となり、製作費、材料費、運搬等の面で経済的であり、施工時の取り扱いも容易となる。
【００４２】
また、オーガーを併用して鋼矢板を打設する場合に、矢板断面積当りのオーガーによる掘削面積を大きく取れ、これにより地盤の軟化領域を大きくでき、かつ継手部の突出長が短く、変形しずらい構造で、しかも地盤の軟化領域に打設できるため、鋼矢板の地盤への圧入が容易になり、工期の短縮につながる効果がある。
【図面の簡単な説明】
【図１】本発明の実施形態１に係る隅角部を屈曲させた鋼矢板単体の平面図である。
【図２】図１の鋼矢板の嵌合連結状態で示す平面図である。
【図３】本発明の実施形態２に係る隅角部を屈曲させた鋼矢板単体の平面図である。
【図４】図３の鋼矢板の嵌合連結状態で示す平面図である。
【図５】第１従来例として示すＵ形鋼矢板の平面図である。
【図６】第２従来例として示すハット形鋼矢板の平面図である。
【図７】図６のハット形鋼矢板の嵌合連結状態で示す平面図である。
【符号の説明】
１Ｕ形鋼矢板
２ウェブ
３隅角部
４フランジ
５継手部
６折曲げ部
７ハット形鋼矢板
８継手支持部
１０領域
１２ウェブ部
１３隅角部
１４フランジ部
１５継手部
１６中立軸
１７鋼矢板
１８継手支持部
１９壁体
２０鋼矢板
２１領域
２２矢板断面中心[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel sheet pile, for example, a steel sheet pile as a structural member used for underground earth retaining, foundation structures and harbors, quay walls in rivers, and still water walls in the earth, The present invention relates to a steel sheet pile with improved buckling strength.
[0002]
[Prior art]
Conventionally, as a wall body to be placed in the ground in the field of civil engineering and construction, a U-shaped steel sheet pile (conventional example 1) as shown in FIG. 5 or Japanese Patent No. 2687794 as shown in FIGS. The hat-shaped steel sheet pile shown (conventional example 2) is used.
[0003]
A U-shaped steel sheet pile 1 shown in FIG. 5 has flanges (U-shaped side portions) 4 connected to both ends of a web portion (U-shaped bottom portion) 2 having a width dimension (L) via corner portions 3. And the joint part 5 is comprised by bending the edge part of the flange 4 in the same direction. The said U-shaped steel sheet pile 1 is a left-right symmetric shape, and it connects and drives in the left-right reverse direction via the joint part 5 for every sheet.
[0004]
Further, in the U-shaped steel sheet pile 1 of FIG. 5, by bending the middle of the flange 4 via the bent portion 6, the upper and lower joint portions 5 are not in contact with each other when the U-shaped steel sheet pile 1 is stacked. Damage to the joint portion 5 can be prevented. Moreover, since a gap is formed between the webs 2 of the U-shaped steel sheet piles 1 stacked up and down with the above configuration, the individual U-shaped steel sheet piles 1 can be easily grasped and stacked at the time of transportation. The steel sheet pile is easy to remove.
[0005]
In the hat-shaped steel sheet pile 7 shown in FIG. 6, flange portions 4 are connected to both ends of the web portion 2 having a width dimension (L) via corner portions 3, and joint support portions are connected to both ends of the flange portion 4. 8 is provided, and a joint portion 5 that is opposite in the left and right sides is formed at the tip thereof. The hat-shaped steel sheet pile 7 is asymmetrical in the left-right direction, and is placed by being connected in the same direction on the left and right via the joint portion 5.
[0006]
In the hat-shaped steel sheet pile 7 shown in FIG. 6 , since the joint portion 5 exists at the farthest position from the neutral shaft on which a large load acts, the cross-sectional rigidity of the neutral shaft can be secured and the joint portion efficiency can be reduced. It has no structure.
[0007]
[Problems to be solved by the invention]
However, while the U-shaped steel sheet pile and the hat-shaped steel sheet pile have the above-mentioned advantages, no consideration has been given to the width dimension (L) of the web portion 2, and the width dimension (L) is generally wide. Therefore, when the plate thickness (t) of the web portion 2 is small, (1) the web portion 2 is likely to buckle during placement, and (2) during the common use shown in FIG. When receiving, the web part 2 tends to be locally buckled. In order to prevent the occurrence of buckling of the web part 2, the thickness (t) must be increased, which increases the weight of the steel material and is uneconomical.
[0008]
On the other hand, when a steel sheet pile is placed on a hard ground, a method of driving the steel sheet pile into the ground after loosening the ground surrounding the placement using an auger or the like is adopted. 7, the hat-shaped recess, that is, the region 10 surrounded by the web portion 2 and the flange portion 4 is narrow, and the ground stirring diameter of the auger disposed in this region 10 is small. Therefore, since the influence range of the ground softening by the auger is small, it is difficult to soften the surrounding ground over the entire cross section of the sheet pile, and in particular, the joint portion 5 located away from the auger via the joint support portion 8. In the surrounding ground, it is easy to fall into driving steel sheet piles with the original hard ground.
[0009]
However, in the joint part 5 of the steel sheet pile 7, one side surface opposite to the side fitted with the joint part 5 of the steel sheet pile 7 previously placed is free in the longitudinal direction, Since the resistance force is the smallest with respect to the ground resistance at the time, the joint portion 5 is deformed at the time of placing, and the risk that the workability is lowered is very high.
[0010]
The prior art does not pay attention to the above-mentioned problems, and therefore does not suggest a solution method.
[0011]
As a result of various researches on steel sheet piles to be placed on hard ground, the present inventor, among the problems to be improved of U-shaped steel sheet piles and hat-shaped steel sheet piles, particularly to the above-mentioned problems, that is, to the ground of steel sheet piles. We focused on the problem of improving buckling strength at the time of casting and the more effective problem of softening the ground by auger. The present inventors have found a method that can solve these problems by minimizing structural changes as much as possible, and setting and configuring the arrangement relationship and dimensional relationship of each member to a predetermined relationship.
[0012]
The present invention is based on the above knowledge and has been proposed to solve the above problems, and provides a steel sheet pile that is difficult to buckle when placing and sharing a steel sheet pile and that has excellent workability. Objective.
[0013]
[Means for solving problems]
In order to achieve the above object, the present invention is configured as follows.
[0014]
1st invention was comprised so that the joint part might be in the position away from the neutral axis | shaft of the wall body, when the joint part of adjacent steel sheet piles was fitted and each steel sheet pile was united as a wall body. It is a steel sheet pile having a substantially U-shaped cross section, and the steel sheet pile changes to a cross-sectional shape obtained by bending a corner portion of the web portion and the flange portion into a polygonal shape in order to constitute a web portion for improving buckling strength. Thus, the steel sheet pile for improving buckling strength, wherein the width dimension (L ₁ ) of the web portion having a linear cross section is shortened and the thickness of the web portion satisfies the following expression (1) .
_{L 1/48 ≦ t <L} / 48 ··· (1)
Here, L: The width dimension of the web part defined by the distance between the two intersecting lines extending the flange surfaces on both sides and intersecting the extended surface of the web part
L ₁ : Width dimension of the web portion for improving buckling strength
t: Thickness of the web part
As in the first aspect of the invention, by reducing the width dimension (L ₁ ) of the web part, that is, the linear distance between the bent parts of both side flange parts, the ratio of the plate thickness of the steel sheet to the width dimension (L ₁ ) (this The width-thickness ratio) is reduced, and even with the same web thickness, it is more difficult to buckle than a conventional U-shaped steel sheet pile or hat-shaped steel sheet pile. In particular, when the web portion located at the outermost position from the neutral axis where the greatest stress is generated when sharing is used, if the width dimension (L ₁ ) between the bent portions is shortened, the buckling that is the object and action of the present invention is achieved. It is suitable for obtaining proof stress.
[0017]
In addition, according to the first invention , a web portion having a linear cross section with a reduced width dimension (L ₁ ) can be configured with a relatively easy configuration in which corner portions between the web portion and the flange portion are bent into a polygonal shape. . Further, according to the first invention, the width dimension (L ₁ ) is shortened so that the width-thickness ratio can be maintained at a value of 48 or less, and even if the plate thickness (t) is reduced, the bending due to the wall pressure is performed. When receiving a load or the like, local buckling does not occur, and the problem of increasing the plate thickness (t) and the steel material weight can be solved.
[0018]
According to a second invention, in the first invention, a corner portion between the web portion and the flange portion is provided closer to the web portion than the neutral shaft.
[0019]
According to the second invention, since the corner portion of the web portion and the flange portion is provided at a position closer to the web portion than the neutral shaft of the steel sheet pile, it occurs in the cross section of the sheet pile when the driving heavy machine grabs the web and drives it. The eccentric load is small and it is difficult to buckle.
[0020]
The third invention, than the distance from the previous SL steel sheet pile sectional center to the flange end edge joint portion is provided (L _4), towards the protruding length from the flange portion of the joint portion (L ₂₎ is shortened Thus, by providing the said joint part in the flange part vicinity, the area | region enclosed by the web part and flange part which occupies the steel sheet pile cross-sectional area is enlarged, It is characterized by the above-mentioned.
[0021]
When the conventional hat-shaped steel sheet pile having the same cross-sectional area and the steel sheet pile according to the present invention are compared with each other, the area of the recessed portion is more in the steel sheet pile according to the present invention. Therefore, when placing with an auger, the ground agitation diameter can be increased and the ground in a larger range can be softened, so that it is easy to place on a hard ground. Moreover, by reducing the protrusion length of the joint from the flange portion, deformation such as torsion and warpage of the joint portion is less likely to occur at the time of placing, and workability is improved.
[0022]
The fourth invention is characterized in that, in the third invention, the width dimension (L2) of the joint support 18 is not less than the length necessary for fitting of the joint and not more than 50 mm. According to the fourth invention, the effect of the ground softening by the auger arranged in the enlarged concave-shaped region 21a of the steel sheet pile 20 is surely and sufficiently distributed over the entire sheet pile cross section including the joint portion 15. Can do.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to the drawings.
[0024]
1 and 2 show a steel sheet pile having improved buckling strength according to Embodiment 1 of the present invention, FIG. 1 is a plan view of a single sheet pile, and FIG. 2 is a fitting of a joint portion of the steel sheet pile. It is a top view in the combined state. 3 and 4 show a steel sheet pile with improved buckling strength according to Embodiment 2 of the present invention, FIG. 3 is a plan view of a single steel sheet pile, and FIG. 4 is a joint portion of the steel sheet pile. It is a top view in a fitting connection state.
[0025]
1 and 2, the steel sheet pile 17 of the present invention is substantially U-shaped (used in a broad sense including U-shape and hat shape), and has a width dimension (L ₁ ) and a plate. A flange portion 14 is connected to both ends of the web portion 12 having a thickness (t) via a corner portion 13, joint support portions 18 are provided at both ends of the flange portion 14, and joint portions that are opposite to each other on the left and right sides are provided at the tips. 15 is provided. Moreover, the said steel sheet pile 17 is a right-and-left asymmetrical form, and is connected and driven in the left-right same direction.
[0026]
The web portion 12 of the steel sheet pile 17 of the present invention constitutes a bottom portion of the substantially U-shaped steel sheet pile 17 and is linear so as to connect the flange portions 14 on both sides via bent portions (that is, corner portions 13). Configured. In particular, the width dimension (L ₁ ) of the web portion 12 is an improvement in buckling strength of the steel sheet pile 17 which is a problem to be solved by the present invention, that is, the web portion when a load is applied to the web portion 12. As a means for improving the buckling strength against twelve bends, torsion, etc., the necessary and minimum width dimension is adopted. As described above, by intentionally shortening the width dimension (L ₁ ) of the web portion 12, it is possible to improve the buckling resistance against bending, twisting, etc. acting on the web portion 12 by the shortened amount. Further, as will be described later, the thickness (t) of the web portion 12 can be reduced.
[0027]
In the first embodiment, as a means for providing the width dimension (L ₁ ) of the web portion 12 to the minimum linear width dimension, the corner portion (bent portion) 13 where the flange portion 14 and the web portion 12 are connected is formed. Between the first corner portion 13a formed in the middle of the flange portion 14, the second corner portion 13b formed at the position where the flange portion 14 and the web portion 12 intersect, and the first and second corner portions 13a, 13b. It is comprised from the inclination part 13c which connects. As shown in the figure, the positions where the first and second corner portions 13a and 13b are formed have a shape in which the eccentric load generated in the cross section of the sheet pile is small and the buckling is difficult to buckle when the driving heavy machine holds the web 12 and drives it. Thus, in order to shorten the distance from the neutral shaft 16 to the web portion 12, it is preferable to provide at least a position closer to the web portion 12 than the neutral shaft 16 of the steel sheet pile 17.
[0028]
The corner portion 13 is formed into a cross-sectional structure having many bent portions by being bent into a polygonal shape, and the width dimension (L ₁ ) of the web portion 12 is that of a conventional steel sheet pile shown by a chain line in FIG. Thus, the corner part 3 of the web part 2 and the flange part 4 can be configured as (L ₁ ) <(L) as compared with the width dimension (L) of the web part, which does not have a polygonal shape.
[0029]
Further, in the steel sheet pile 17, when the ratio of the width dimension (L ₁ ) and the thickness (t) of the web portion 12 located at the outermost edge from the neutral shaft 16 is reduced (this is referred to as the width-thickness ratio), the steel sheet pile This is suitable for increasing the buckling strength at the time of placing 17. Specifically, between the left and right bent parts (corner part 13), both of the parts subjected to compressive stress as defined in the “Road Bridge Specification / Explanation II Steel Bridge Edition” published by the Japan Road Association. It is desirable that the width-thickness ratio be 48 or less according to the minimum thickness of the edge support plate. Even when the width-thickness ratio of the web portion 12 is set to a value of 48 or less and the plate thickness (t) is made as thin as possible, the configuration of the first embodiment allows the steel sheet pile 17 to Sufficient buckling strength at the time of placing can be secured.
[0030]
That is, when the thickness (t) of the web portion 12 of the steel sheet pile 17 is small, the structure of the web portion 2 having the conventional width dimension (L) shown by the chain line in FIG. It is easy to bend, and when it is shared, it tends to cause local buckling when it receives a bending load due to earth wall pressure. In order to prevent the occurrence of buckling, the plate thickness (t) must be increased, which increases the weight of the steel material and is uneconomical. However, in order to reduce the plate thickness (t) under the width-thickness ratio of the web portion 12 of 48 or less, the conventional configuration is limited to the width dimension (L) of the web portion 2 and naturally. There is a limit. In this regard, according to the configuration of the first embodiment, by reducing the width dimension (L ₁ ), even if the width-thickness ratio is maintained at a value of 48 or less and the plate thickness (t) is reduced, the wall surface When receiving a bending load or the like due to earth pressure, local buckling does not occur, and the problem of increasing the plate thickness (t) and the steel material weight can be solved.
[0031]
Furthermore, in Embodiment 1, when the joint parts 15 are fitted to each other as shown in FIG. 2 and the steel sheet piles 17 are integrated as the wall body 19, the joint parts 15 are located far from the neutral shaft 16, Since the left and right sides of the neutral shaft 16 are integrated with each other, the bending strength of the steel sheet pile 17 is also improved in this respect, and the joint portion 15 is positioned away from the neutral shaft 16 to effectively improve the joint portion efficiency. Can be demonstrated.
[0032]
Next, Embodiment 2 shown in FIGS. 3 and 4 will be described. The steel sheet pile 20 according to the second embodiment has a shape approximate to that of the first embodiment, that is, a substantially U shape, and has corner portions at both ends of the web portion 12 having a width dimension (L ₁ ) and a plate thickness (t). The flange part 14 is connected via 13, the joint support part 18 is provided at both ends of the flange part 14, and the joint part 15 opposite in the left and right sides is provided at the tip. Moreover, the steel sheet pile 20 is a left-right asymmetric shape, and is the same as that of the first embodiment in that it is connected and driven in the same direction on the left and right.
[0033]
The steel sheet pile 20 of the second embodiment is different from the steel sheet piles of the first embodiment and the prior art in the following configuration. That is, the steel sheet pile 20 according to the second embodiment is a substantially U-shaped steel sheet pile, in which the concave region 21a surrounded by the flange portion 14 and the web portion 12 is enlarged, and the ground of the auger disposed in the concave shape region 21a. The purpose of this is to increase the stirring diameter as much as possible and bring the ground stirring range by the auger as close as possible to the joint portion 15, thereby increasing the placement efficiency of the steel sheet pile 17. In this respect, the problem to be solved by the conventional invention is to solve the problem of the second embodiment, that is, by increasing the ground stirring diameter of the auger as much as possible and performing ground stirring as close as possible to the joint portion 15. However, there is no focus or problem awareness on the efficient placement of steel sheet piles.
[0034]
The inventor paid attention to the above-mentioned problems based on the following knowledge. That is, when placing a steel sheet pile on a hard ground, a method of driving a sheet pile into the ground after loosening the ground surrounding the placement using an auger or the like is used. For example, in FIG. In the illustrated hat-shaped steel sheet pile 7, the protrusion length of the joint portion 5, that is, the width dimension (L ₃ ) of the joint support portion 5 is relatively long, but the hat-shaped recess portion, that is, the web portion 2 and the flange portion 4 are surrounded. The region 10 is narrowed because it is relatively limited by the length of the width dimension (L) (that is, the flange portion 4 approaches the center portion), and the stirring diameter of the auger disposed in this region 10 is reduced. Is small. Accordingly, since the influence range of the ground softening by the auger is small, it is difficult to soften the surrounding ground over the entire cross section of the sheet pile. In particular, in the surrounding ground of the joint portion 5 located away from the auger, the original hard It is easy to fall into driving the steel sheet pile 7 in the state of the ground.
[0035]
However, in the joint portion of the steel sheet pile, as described above, the one side surface opposite to the side mating with the joint portion of the steel sheet pile previously placed is free in the longitudinal direction, and Since the resistance is the smallest to the ground resistance at the time of installation, the joint part is deformed at the time of installation, and there is a very high risk that the workability will deteriorate.
[0036]
After obtaining the above knowledge, the present inventor enlarges the concave region 21a surrounded by the web portion 12 and the flange portion 14 as shown in FIG. 3, and agitates the ground of the auger disposed in this region 21a. It has been found that the above-mentioned problems can be solved by increasing the diameter. Then, as a means to expand the region 21a of the recess, in the second embodiment, the width of the joint support portion 18 (L _2), indicated by a chain line in the figure, the width of the conventional joint supporting part (L ₃₎ In comparison, (L ₂ ) <(L ₃ ). Specifically, by providing (L ₂ ) approximately half the length of the conventional joint support portion, the positions of the conventional flange portions 4 indicated by chain lines in the figure are shown as solid lines in the figure. The area 21 can be expanded outward to the position of both flanges 14, and the area 21 is expanded to the area 21a accordingly.
[0037]
If the said structure is demonstrated from another viewpoint, when the joint parts 15 will be fitted and each steel sheet pile 20 is united integrally as the wall body 19, the flange edge from which the joint part 15 is provided from the sheet pile cross-section center 22 will be described. (L ₂ ) <(L ₄ ) so that the protrusion length from the flange portion 14 of the joint portion 15, that is, the width dimension (L ₂ ) of the joint support portion 18 is shorter than the distance (L ₄ ) to the end. ). As a result, the region 21a is enlarged, and can be structured to be wider than the old region 21 (region 10 of the hat-shaped steel sheet pile 7 in FIG. 7) surrounded by the concave shape per cross-sectional area of the steel sheet pile unit. 15 can be provided close to the flange end edge, and accordingly, the joint portion 15 can be provided close to the ground softening region by the auger.
[0038]
Specifically, in order to ensure that the effect of the ground softening by the auger arranged in the enlarged concave-shaped region 21a of the steel sheet pile 20 spreads over the entire sheet pile cross section including the joint portion 15. In general, since the auger can soften the ground to the outside of the blade about 50 mm, it is desirable that the protruding length of the joint portion 15, that is, the width dimension (L ₂ ) of the joint support portion 18 is 50 mm or less.
[0039]
The configuration of the steel sheet pile 20 according to the second embodiment can be applied to a conventional steel sheet pile indicated by a chain line at the outer position in FIG. 3 and can also be applied to a steel sheet pile having the same configuration as that of the first embodiment indicated by a solid line in FIG. . In other words, in the configuration shown by the solid line in the figure, the corner portion 13 where the flange portion 14 and the web portion 12 are connected is provided at a position closer to the web portion 12 than the neutral shaft 16 and is formed in the middle of the flange portion 14. First corner portion 13a, flange portion 14, second corner portion 13b formed at the position where web portion 12 intersects, and inclined portion 13c connecting between first and second corner portions 13a, 13b. by configuring from, and shorten the width of the web portion 12 (L _1).
[0040]
Therefore, in the case of the steel sheet pile 20 shown by the solid line in FIG. 3, in addition to the effect of expanding the region 21a in which the auger is arranged, the width dimension (L ₁ ) of the web portion 12 is shortened as in the first embodiment. The effect of improving the buckling strength of the steel sheet pile 20 and reducing the thickness (t) can be achieved.
[0041]
【The invention's effect】
The steel sheet pile of the present invention can reduce the width between each bent portion where the flange portion and the web portion are connected (that is, the width dimension L ₁ of the web portion) and the width-thickness ratio. It can be structured to resist buckling. In addition, because the rigidity can be increased even if the web part is thin, it is possible to produce sheet piles with thin steel sheets, which is economical in terms of production costs, material costs, transportation, etc. Is easy to handle.
[0042]
In addition, when a steel sheet pile is driven together with an auger, the excavation area by the auger per sheet pile cross-sectional area can be increased, which can increase the softening area of the ground, and the joint protrusion length is shortened and deformed. Since it has a staggered structure and can be placed in the softened area of the ground, it is easy to press-fit the steel sheet pile into the ground, leading to the effect of shortening the construction period.
[Brief description of the drawings]
FIG. 1 is a plan view of a single steel sheet pile with bent corner portions according to Embodiment 1 of the present invention.
FIG. 2 is a plan view showing the steel sheet pile of FIG. 1 in a fitted and connected state.
FIG. 3 is a plan view of a steel sheet pile with a corner portion bent according to Embodiment 2 of the present invention.
4 is a plan view showing the steel sheet pile of FIG. 3 in a fitted and connected state. FIG.
FIG. 5 is a plan view of a U-shaped steel sheet pile shown as a first conventional example.
FIG. 6 is a plan view of a hat-shaped steel sheet pile shown as a second conventional example.
7 is a plan view showing a fitted connection state of the hat-shaped steel sheet pile of FIG. 6. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 U-shaped steel sheet pile 2 Web 3 Corner part 4 Flange 5 Joint part 6 Bending part 7 Hat-shaped steel sheet pile 8 Joint support part 10 Area | region 12 Web part 13 Corner part 14 Flange part 15 Joint part 16 Neutral shaft 17 Steel sheet pile 18 Joint support part 19 Wall body 20 Steel sheet pile 21 Area 22 Sheet pile cross-sectional center

Claims

A steel with a substantially U-shaped cross section configured such that when the steel sheet piles are integrated as a wall body by fitting the joint parts of adjacent steel sheet piles, the joint part is positioned away from the neutral axis of the wall body. It is a sheet pile, and the steel sheet pile comprises a linear cross section by changing the corner portion of the web portion and the flange portion into a polygonal shape in order to constitute a web portion for improving buckling strength. A steel sheet pile with improved buckling strength characterized in that the width dimension (L1) of the web part is shortened and the thickness of the web part satisfies the following formula (1).
L1 / 48 ≦ t <L / 48 (1)
Here, L: The distance between the two intersecting lines extending the flange surfaces on both sides and intersecting the extended surface of the web part
Defined web section width dimension
L1: Width dimension of the web part for improving buckling strength
t: Thickness of the web part

The steel sheet pile according to claim 1, wherein a corner portion between the web portion and the flange portion is provided closer to the web portion than the neutral shaft.

The flange portion is connected to the flange portion so that the projection length (L2) from the flange portion of the joint portion is shorter than the distance (L4) from the center of the steel sheet pile cross section to the flange edge where the joint portion is provided. 3. The steel sheet pile according to claim 1, wherein a region surrounded by the web portion and the flange portion occupying the cross-sectional area of the steel sheet pile is enlarged by being provided in the vicinity.

The steel sheet pile according to claim 3, wherein a width dimension (L2) of the joint support portion 18 is not less than a length required for fitting of the joint and not more than 50 mm.