JP2004169340A

JP2004169340A - Reinforcement method of beam structure

Info

Publication number: JP2004169340A
Application number: JP2002334468A
Authority: JP
Inventors: Yoshiaki Sato; 嘉昭佐藤; Koji Honma; 宏二本間; Noriyoshi Tominaga; 知徳冨永
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2002-11-19
Filing date: 2002-11-19
Publication date: 2004-06-17
Anticipated expiration: 2022-11-19
Also published as: JP3965106B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reinforcement method of beam structure, improved in fatigue strength of a welded part to attain high durability by performing ultrasonic impact processing for peening to hammer the surface of the welded part using a tool vibrating its tip with an amplitude of 20 μm to 60 μm and with a frequency of 15 kHz to 60 kHz by ultrasonic waves as fatigue improvement measure for the welded part of a beam structure and a reinforcement member. <P>SOLUTION: In this reinforcement method in which CT shape steel is welded along the line of a web of a beam having I-shaped section, when the board thickness of the web of CT shape steel is taken (t), a groove is formed by performing ultrasonic impact processing at a temperature of 100°C or lower within the range of (t) or more from the end part of the CT shape steel. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
桁構造に補強用部材を溶接接合により取り付ける桁構造の補強工法に関する。
【０００２】
【従来の技術】
従来、設計時の運転能力等を上げる必要が生じ、そのため設計時の桁構造の耐久能力を向上する必要が生じる。例えば、クレーンの走行桁等の既存の桁構造の耐久性を向上させるために、既存の桁構造のフランジに補強用部材を取り付けることにより、運転能力アップによる荷重の増加に対応する桁構造の補強工法が実施されている。しかし、既存の桁構造に補強用部材を溶接接合すると、溶接部から疲労亀裂が発生し、かえって桁構造の耐久性を低下させる結果となることが判明している。そのため、既存の桁構造に補強用部材を取り付けるために、既存の桁構造のフランジにボルト孔を削孔し、ボルト等の連結手段により取り付ける桁構造の補強工法が採用されている。
【０００３】
【特許文献１】
特開昭５４−５６９５３号公報
【特許文献２】
特開昭６２−２０７５７９号公報
【特許文献３】
特開平１０−２７９２７３号公報
【非特許文献１】
（ＳｕｒｆａｃｅＮａｎｏｃｒｙｓｔａｌｌｉｚａｔｉｏｎ（ＳＮＣ）ｏｆｍｅｔａｌｌｉｃＭａｔｅｒｉａｌｓ−ＰｒｅｓｅｎｔａｉｏｎｏｆｔｈｅＣｏｎｃｅｐｔｂｅｈｉｎｄａＮｅｗＡｐｐｒｏａｃｈ，Ｊ．Ｍａｓｔｅｒ．Ｓｃｉ．Ｔｅｃｈｎｏｌ．Ｖｏｌ．１５Ｎｏ．３，１９９９）
【０００４】
【発明が解決すべき課題】
しかし、ボルト等の連結手段による補強用部材の桁構造への取り付けは、既存桁構造への削孔作業が必要であり、削孔による断面欠損の問題や、作業性、施工コストの面において、溶接接合より劣るという問題があることから、溶接接合による補強部材の桁構造への取り付けが望まれ、様々な溶接部の疲労向上処理策がとられている。
【０００５】
金属部材の溶接部の疲労向上処理策には大きく分けて２種類あり、まず、疲労が問題となる部分の形状を変えて応力集中を少なくする、グラインディング、ＴＩＧドレッシングなどがある。また、疲労が問題となる部分に圧縮残留応力を与えて、実質的な繰り返し応力範囲を小さくする、ハンマーピーニング、ニードルピーニング、ショットピーニング、低温変態溶材などがある。このうち、ハンマーピーニングに関しては、応力集中を少なくする効果と圧縮応力を導入する効果の両方を持つとされている。
【０００６】
上記の疲労向上処理策のうち、応力集中を少なくする処理策の効果は目に見えて明らかであるが、実際には、疲労が問題となる箇所においてはわずかな傷などが疲労強度をむしろ悪化させる原因となることがあるために、グラインダー処理などに関しては処理に熟練が必要のみならず、作業に時間が必要であり、大きなコスト増加要因となる。
【０００７】
また、ＴＩＧドレッシングに関しても、作業には熟練者が必要なのと、適用部位に熱を加えるために、金属部材の補強に使う場合などについては、応力変動に起因する溶接材料の高温割れを防ぐために作業中は金属部材の使用を止める必要があるなど、やはり大きなコスト増加要因となる。
【０００８】
一方、圧縮残留応力を導入する処理策であるが、圧縮残留応力は目に見えないために、処理後の影響が測定しにくく、検査によって効果を保証することが困難であるということが問題となり、品質管理上の観点から、判断・診断能力あるエンジニアが立ち会えないような状況では、通常は使われない。
【０００９】
また、ハンマーピーニングでは、処理部に大きな塑性変形を与えることができるため、処理の痕跡を大きくし、実施後に処理を特定することはできるが、処理時にできる表面の傷がかえって応力集中をもたらし、疲労強度を低下させることがあるのと、その塑性変形を与えるときの大きな反動のために著しく作業性が悪いために、細かいコントロールが困難であり、品質管理が非常に難しい。
【００１０】
また、上記のような圧縮残留応力を導入する疲労向上処理策を特に金属部材の補修に用いる場合、疲労亀裂の発生初期である寸法１ｍｍ以下の小さな時点では、浸透探傷試験、磁粉探傷試験、渦流探傷試験などの現在の検査法では検出は不可能であるが、このような亀裂を残している状態で、上記の疲労寿命向上処理策を適用しても、亀裂の進展を止めることができないために、圧縮残留応力導入による疲労寿命向上効果はほとんど無いと考えられる。
【００１１】
また、溶接部に低温変態溶材を使用する場合についても、止端部に圧縮残留応力を導入する場合についても、高強度鋼では効果が大きいが、低強度鋼では効果がほとんど無くなってしまうという特性があるのと、やはり、溶接による熱が加えられることから、ＴＩＧドレッシング同様、施工上の問題があって使いにくい部分があり、また、他の処理法と同様に導入した圧縮残留応力の効果が判定しにくい。
【００１２】
上記のように、金属部材の溶接部の応力集中を減らす疲労向上処理策には、主に施工上の効率、施工者の熟練の問題があり、一方、圧縮応力を導入する疲労向上処理策には、その効果を計測して、品質管理を行うことができないことが問題であり、そのために、このような疲労寿命向上処理策を金属部材と補強用部材との溶接部に使うことは困難であった。
【００１３】
本発明は、上記の事情に鑑みてなされたもので、桁構造と補強用部材との溶接部の疲労向上処理策として、超音波で先端を振幅２０μｍ〜６０μｍ、周波数１５ｋＨｚ〜６０ｋＨｚで振動させる工具を用いて、溶接部表面を打撃するピーニングを行う超音波衝撃処理を行い、溶接部の疲労強度を向上させ、耐久性の高い桁構造の補強工法を得ることを目的とする。
【００１４】
【課題を解決するための手段】
本第１発明は、上記課題を解決するために、ＣＴ形鋼をＩ型断面桁のウェブのラインに合わせて溶接した桁構造の補強工法において、ＣＴ形鋼のウェブの板厚をｔとしたとき、ＣＴ形鋼の端部からｔ以上の範囲に温度１００℃以下で超音波衝撃処理を行って溝を形成することにより、止端部の形状を改善することを特徴とする。
【００１５】
本第２発明は、本第１発明の桁構造の補強工法において、ＣＴ形鋼の端部からｔの区間に開先を取り、その回し溶接の脚長を５ｍｍ以上としたことを特徴とする。
【００１６】
本第３発明は、本第１又は第２発明の桁構造の補強工法において、超音波衝撃処理を実施するとき、処理を行う溶接部に引っ張り荷重を載荷した状態で実施することを特徴とする。
【００１７】
本第４発明は、幅がＩ型断面桁または箱断面桁のフランジ幅より狭く端部が直線またカーブした形状のカヴァープレートをＩ型断面桁または箱断面桁のフランジに溶接する補強工法において、カヴァープレートの板厚をｔとしたときに、カヴァープレートの板幅全体および端部からｔ以上の範囲に温度１００℃以下で超音波衝撃処理を行って溝を形成することにより止端部形状を改善することを特徴とする。
【００１８】
本第５発明は、本第４発明の桁構造の補強工法において、カヴァープレートの端部の区間に開先を取り、その重ね溶接の脚長を５ｍｍ以上としたことを特徴とする。
【００１９】
本第６発明は、幅がＩ型断面桁または箱断面桁のフランジ幅より広く端部が直線またカーブした形状のカヴァープレートをＩ型断面桁または箱断面桁のフランジに溶接する補強工法において、カヴァープレートの板厚をｔとしたときに、カヴァープレートの板幅全体および端部からｔ以上の範囲に温度１００℃以下で超音波衝撃処理を行って溝を形成することにより止端部形状を改善することを特徴とする。
【００２０】
本第７発明は、フランジ幅がＩ型断面桁のフランジ幅よりも狭いＨ形鋼をＩ型断面桁のフランジに、そのウェブを前記Ｉ型断面桁のウェブのラインに合わせて溶接した補強工法において、Ｈ形鋼のフランジの板厚をｔとしたとき、Ｈ形鋼の板幅全体および端部からｔ以上の範囲に温度１００℃以下で超音波衝撃処理を行って溝を形成することにより、止端部形状を改善したことを特徴とする。
【００２１】
本第８発明は、Ｉ型断面桁の下フランジにトラス梁を有するガセットプレートを溶接する補強工法において、ガセットプレートの板厚をｔとしたとき、ガセットプレート端部から両側についてｔ以上の範囲に温度１００℃以下で超音波衝撃処理を行って溝を形成することにより止端部形状を改善したことを特徴とする。
【００２２】
【発明の実施の形態】
金属部材の疲労破壊の発生は、応力集中と残留応力に大きく影響される。荷重を受ける金属材においては応力集中部に転移がたまり、それがすべり線の蓄積となって亀裂に発展し、亀裂が発生後はそれが進展して行く。残留応力は、通常、溶接部などで引張残留応力として存在し、実効的な繰り返し応力範囲を拡大させて亀裂を発生しやすくするとともに、生成した亀裂の開口を促進すると考えられている。そのため、金属材の疲労寿命を向上させるには、応力集中を緩和するとともに、残留応力をできるだけ圧縮状態に近づけることが必要となってくる。
【００２３】
金属部材の溶接部には、表面形状の急変部と引っ張り残留応力の両方が存在し、疲労強度的に最も弱点となる。この表面形状の急変部が切り欠きとして作用し、応力集中部となるために、この応力集中部に塑性変形を与え、なだらかな止端半径が大きな曲面によって形成された表面を形成することが、応力集中部を緩和することになる。また、このとき金属材の板厚方向に塑性変形を与えれば、その塑性化した金属材が周囲の金属によって拘束されることによって圧縮力が導入される。
【００２４】
このような、溶接部に対する塑性加工を可能とする手段として、超音波で先端を振幅２０μｍ〜６０μｍ、周波数１５ｋＨｚ〜６０ｋＨｚで振動させる工具を用いて、溶接部表面を打撃するピーニングを行う超音波衝撃処理という処理がある。この手法を用いることによって、溶接部表面に塑性加工を行い、深さ１．５ｍｍほどにまで圧縮残留応力を導入することができる。
【００２５】
この超音波衝撃処理という手法は、基本的にはハンマーピーニングと疲労強度向上に関する基本メカニズムは変わらないが、一回一回の打撃のエネルギーを小さい変わりに、１秒間に１万回以上の打撃を与えることによって、同じような塑性変形を実現している。しかも、一回一回の打撃力は小さいために、機器に生じる反動はほとんどまったく無く、ハンマーピーニングと比較して使用性、施工性の面で非常に有利である。
【００２６】
また、この超音波衝撃処理という処理は、この金属表面に対し非常に多くの回数の打撃を与えているということで、金属材表面に対して従来のハンマーピーニングには無い効果をもたらしている。また、一回一回の打撃エネルギーがショットピーニングより大きいことで、従来のショットピーニングにも無い効果をもたらしている。
【００２７】
まず、回数を多く表面を叩くことで、処理の均一性が得られる。ハンマーピーニングでも数パスを同一線上で実施すればある程度の均一性が得られることは知られているが、超音波衝撃処理の打撃サイクル数は１５〜６０ｋＨｚであり、その得られる均一性はハンマーピーニングと全く異なるレベルにあり、処理スピードが０．５ｍ／分程度であれば、ほとんど溶接部表面を均一に仕上げ、欠陥を全く残すことがない。
【００２８】
また、その処理後の表面は著しい平滑さを持つ。超音波衝撃処理による処理後の平滑さは、グラインダー仕上げ後の溶接部表面よりも著しく平滑である。
【００２９】
また、処理後の溶接部表面の組織は超音波を利用して塑性加工を数多く繰り返すことによって、著しく組織が細かくなることがわかっている。（非特許文献１参照）
【００３０】
実際、超音波衝撃処理を疲労向上の目的で金属材に使った結果、処理前後で金属材組織は大きく変化している。このような、金属材の組織を細かくする効果は、特に金属材の組織が粗大化する溶接近傍のＨＡＺ部で顕著であり、通常は１００μｍまで粗大化するＨＡＺの粒径が、超音波衝撃処理の処理後はほとんど粒径が観察できないほどの寸法に小さくなっており、独特な金属材組織が超音波衝撃処理によって達成されている。
【００３１】
また、超音波衝撃処理によって金属材の表面での金属材の組織が細かくなるのに伴って、硬さが増す。超音波衝撃処理後の母材部、溶金部、ＨＡＺ部の硬さの分布は、特に溶接金属材としてよく用いられる高強度の鋼については、硬さが２０％以上増している。ほか、材質と処理時間によっては、硬さは最大、処理前の約２倍まで増加することがあるが、ただし、これは固くてもろいマルテンサイとなったわけではなく、主に、細粒化による効果と、転移の蓄積による加工硬化であるため、溶接割れをもたらすような種類の硬さの増加ではない。
【００３２】
金属材の疲労破壊は、亀裂の発生と進展から構成される。亀裂発生寿命と亀裂進展寿命の合計が疲労亀裂にいたる全寿命となる。そして、応力集中や、残留応力が厳しい箇所から亀裂が発生する場合が多く、発生した亀裂は、さらに進展を継続して最終的に部材の破断に至る。金属材の疲労破壊の寿命を向上させるためには、疲労亀裂の発生及び疲労亀裂の進展を抑制することが必要である。
【００３３】
しかし、通常はいったん金属材に亀裂が発生すると、その亀裂先端での応力集中は極めて大きく、この進行を止めることは極めて困難であるとされている。例えば、先端にストップホールをあけ、その穴を高力ボルトで締め上げても、亀裂先端を残した場合はボルト内部に亀裂が進展して、切断してしまうことすらある。
【００３４】
初期の疲労亀裂を観察すると、まわし溶接試験体の疲労試験中のひずみ計測により、発生を検知した時点の亀裂の状態である初期の疲労亀裂を観察すると、この時点でまわし溶接継ぎ手での普通の疲労寿命の約１割が経過しており、残りの９割の寿命は、この亀裂の進展寿命であり、この亀裂を取り除かない限りほとんど決まってしまう状態にある。
【００３５】
しかしながら、この状態の亀裂は通常の浸透探傷試験や、磁粉探傷試験では検知することができない。もし、この状態で従来の疲労寿命向上手法であるハンマーピーニングやショットピーニングを行ったとすると、この亀裂を残したまま処理を行ってしまうため、見かけ上は処理面には塑性変形が生じているが、亀裂の進展は止められないために、改善効果は形状改良による応力集中の低減程度しかなく、寿命がほとんど伸びないという状況が考えられる。
【００３６】
ところが、この状態でも超音波衝撃処理を行うと、深さ１．５ｍｍ程度まで塑性変形による圧縮応力を導入するために、亀裂を叩き潰し、亀裂先端を開口しないようにしてしまうことができる。もちろん、圧縮応力を導入できる深さは、ハンマーピーニングでも同程度以上の深さが可能であるが、ハンマーピーニングは処理効果にむらがあり、亀裂を叩けずに残す部分が多いと考えられ、その点、超音波衝撃処理は前述のように打撃回数が著しく多いために、均一に亀裂の開口を抑制することができる。
【００３７】
よって、効果的に疲労寿命向上効果を得るには、溶接金属材については超音波衝撃処理を溶接部の止端部を中心に、溶接金属部、ＨＡＺ部に処理することが基本である。もっとも疲労的な弱点になる溶接金属とＨＡＺの境界面を疲労に対して強化する。また、溶接金属部表面に生じる高温割れの悪影響も著しく緩和できる。ただし、低温の水素割れについてはほとんど効果を持たないと考えられるので注意が必要である。
【００３８】
溶接部の処理にあたっては、１処理線での処理回数は１パスでも充分であるが、より均一性を高めたい場合や、よりコントロール性を向上させたり、過大な塑性変形を防止するために、処理１回あたりの入力パワーを押えたい場合は、２回以上の処理を同一線上に対して行うことにより、より確実な疲労寿命向上効果を得ることができる。
【００３９】
本発明の実施形態を図により説明する。図１（ａ）（ｂ）に示されるように、上下フランジ２、３とウェブ４から構成されるＩ型断面桁１の下フランジ３に、ウェブ６とフランジ７により構成される補強用のＣＴ形鋼５を、そのウェブ６をＩ形断面桁１のウェブ４の位置に合せて溶接接合して補強するものである。図１（ａ）に示されるように、補強用のＣＴ形鋼５は、Ｉ型断面桁１より若干短めで、その端部は斜めに切断された形状とする。Ｉ型断面桁１の下フランジ３と補強用のＣＴ形鋼５の溶接部８の端部からＣＴ形鋼５のウェブ６の板厚ｔ以上の範囲に、圧縮残留応力の導入に効果的である温度が１００℃以下になった状態で、超音波衝撃処理を行って溝を形成し、溶接部８の止端部の形状を応力集中が起こらないように改善する。
【００４０】
また、溶接部８の補強用のＣＴ形鋼５の端部から補強用のＣＴ形鋼５のウェブ６の板厚ｔの区間に開先を取り、その回し溶接の脚長を５ｍｍ以上とし、その範囲に超音波衝撃処理を行い、溶接部８の止端部形状を応力集中が起こらないように改善する。
溶接部８に超音波衝撃処理をする時、処理を行う溶接部７に引っ張り荷重を載荷した状態で行うと、さらに圧縮残留応力の導入に効果的である。
【００４１】
図２（ａ）（ｂ）に示されるように、Ｉ型断面桁１の下フランジ３に補強用のカヴァープレート９溶接接合して補強するものである。図２（ａ）（ｂ）では、補強用のカヴァープレート９の板幅が、Ｉ型断面桁１の下フランジ３の幅より狭いケースを示しているが、図２（ｃ）に示されるように、補強用のカヴァープレート９の板幅をＩ型断面桁１の下フランジ３の幅より広くしてもよい。また、補強用のカヴァープレート９の端部の形状は直線状でもカーブした形状にしてもよい。
Ｉ型断面桁１の下フランジ３とカヴァープレート９の溶接部８のカヴァープレート９の端部の板幅全体と、端部から補強用のカヴァープレート９の板厚ｔ以上の範囲に、圧縮残留応力の導入に効果的である温度が１００℃以下になった時、超音波衝撃処理を行って溝を形成し、溶接部８の止端部の形状を応力集中が起こらないように改善する。
補強用のカヴァープレート９の溶接部８の端部から開先を取り、その重ね溶接の脚長を５ｍｍ以上とし、その範囲に超音波衝撃処理を行い、溶接部８の止端部形状を応力集中が起こらないように改善する。
【００４２】
図３（ａ）（ｂ）に示されるように、Ｉ型断面桁１の下フランジ３に、Ｉ型断面桁１の下フランジ３のフランジ幅より狭いフランジ幅をもつ補強用のＨ形鋼１０のフランジ１１を、そのウェブ１２がＩ型断面桁１のウェブ４と合うように位置させ溶接接合して補強する。補強用のＨ形鋼１０は、Ｉ型断面桁１より短く、その端部は斜めに切断される。
Ｉ型断面桁１と補強用のＨ形鋼１０のフランジ１１の溶接部８の、補強用のＨ形鋼１０のフランジ１１の端部の板幅全体と、端部からＨ形鋼１０のフランジの板厚ｔ以上の範囲に、圧縮残留応力の導入に効果的である温度が１００℃以下になった時、超音波衝撃処理を行って溝を形成し、溶接部８の止端部の形状を応力集中が起こらないように改善する。
【００４３】
図４に示されるように、Ｉ型断面桁１の下フランジ３に、トラス梁１４を備えた補強用のガセットプレート１３を溶接接合して補強する。Ｉ型断面桁１の下フランジ３と補強用のガセットプレート１３の溶接部８の端部から両側のガセットプレート１３の板厚ｔ以上の範囲に、圧縮残留応力の導入に効果的である温度が１００度以下のときに超音波衝撃処理を行って溝を形成し、止端部形状を応力集中が起こらいように改善する。
【００４４】
【発明の効果】
本発明の構成の超音波衝撃処理により、桁構造と補強用部材との溶接部の止端部に１秒間に１万回以上の打撃を与え、一回一回の打撃力が小さいので、他のピーニングに比較し使用性、施工性が優れた衝撃処理が可能となり、溶接部の止端部の形状を改善し、桁構造の耐久性を高める補強工法となる。
【００４５】
超音波衝撃処理は、回数を多く表面を打撃するので、処理の均一性が得られ、処理後の表面の平滑さを得られるので、溶接部の止端部からの疲労亀裂発生が抑制され、桁構造の耐久性を高める補強工法となる。
【００４６】
超音波衝撃処理は、数多くの打撃による塑性加工を繰り返すことにより処理後の金属表面の組織を著しく細かくすることができ、疲労亀裂の発生を抑制でき、桁構造の耐久性を高める補強工法となる。
【００４７】
疲労亀裂の発生しやすい溶接部の止端部、ＨＡＺ部、溶接金属部を超音波衝撃処理するのでもっとも疲労的な弱点となる溶接金属とＨＡＺ部の境界面の疲労に対して強化され、また、溶接金属表面に生じる高温割れの影響も著しく緩和できるので、桁構造の耐久性を高める補強工法となる。
【００４８】
超音波衝撃処理により、溶接部の止端部に圧縮残留応力が導入され、疲労亀裂の発生と進展が抑制される。
【００４９】
桁構造と補強用部材との溶接部の疲労亀裂の発生が抑制され、桁構造と補強用部材が一体となり、桁構造の真の補強がなされ、且つ耐久性の高い桁構造の補強工法となる。
【図面の簡単な説明】
【図１】（ａ）（ｂ）本発明の一実施形態を示す図
【図２】（ａ）（ｂ）（ｃ）本発明の一実施形態を示す図
【図３】（ａ）（ｂ）本発明の一実施形態を示す図
【図４】本発明の一実施形態を示す図
【符号の説明】
１：Ｉ型断面桁
２：Ｉ型断面桁の上フランジ
３：Ｉ型断面桁の下フランジ
４：Ｉ型断面桁のウェブ
５：補強用ＣＴ形鋼
６：ＣＴ形鋼のウェブ
７：ＣＴ形鋼のフランジ
８：溶接部
９：補強用のカヴァープレート
１０：補強用のＨ形鋼
１１：補強用のＨ形鋼のフランジ
１２：補強用のＨ形鋼のウェブ
１３：補強用のガセットプレート
１４：トラス梁[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a reinforcing method for a girder structure in which a reinforcing member is attached to the girder structure by welding.
[0002]
[Prior art]
Conventionally, it has been necessary to increase the operation capacity and the like at the time of design, and therefore it is necessary to improve the durability of the girder structure at the time of design. For example, in order to improve the durability of existing girder structures such as crane traveling girder, by attaching reinforcing members to the flange of the existing girder structure, reinforcement of the girder structure corresponding to the increase in load due to increased operating capacity The construction method has been implemented. However, it has been found that when a reinforcing member is welded to an existing girder structure, a fatigue crack is generated from the welded portion, which results in a reduction in the durability of the girder structure. Therefore, in order to attach the reinforcing member to the existing girder structure, a reinforcing method of the girder structure has been adopted in which a bolt hole is drilled in a flange of the existing girder structure and the bolt is connected by a connecting means such as a bolt.
[0003]
[Patent Document 1]
JP 54-56953 A [Patent Document 2]
JP-A-62-207579 [Patent Document 3]
JP-A-10-279273 [Non-patent document 1]
(Surface Nanocrystallisation (SNC) of metallic Materials-Presentation of the Concept behind a New Approach, J. Master. Sci. Technol. Vol. 15, Vol.
[0004]
[Problems to be solved by the invention]
However, the attachment of the reinforcing member to the girder structure by connecting means such as bolts requires drilling work on the existing girder structure, and in terms of the problem of section loss due to drilling, workability, construction cost, Since there is a problem that it is inferior to welded joint, it is desired to attach a reinforcing member to a girder structure by welded joint, and various measures for improving fatigue of a welded portion have been taken.
[0005]
There are roughly two types of measures for improving the fatigue of a welded portion of a metal member. First, there are grinding, TIG dressing, and the like that reduce the concentration of stress by changing the shape of a portion where fatigue is a problem. In addition, there are hammer peening, needle peening, shot peening, low-temperature transformation molten material, and the like, in which a compressive residual stress is applied to a portion where fatigue becomes a problem to reduce a substantial repetitive stress range. Of these, hammer peening is said to have both the effect of reducing stress concentration and the effect of introducing compressive stress.
[0006]
Of the above-mentioned fatigue improvement treatments, the effect of treatments that reduce stress concentration is clearly evident, but in actuality, in places where fatigue is a problem, slight scratches etc. rather deteriorate fatigue strength. Since grinder processing and the like may be performed, not only skill is required for the processing but also time is required for the operation, which causes a large increase in cost.
[0007]
Also, for TIG dressing, skilled workers are required for the work, and when used to reinforce metal members to apply heat to the application site, in order to prevent hot cracking of the welding material due to stress fluctuation, etc. During the operation, it is necessary to stop using the metal member.
[0008]
On the other hand, although this treatment is to introduce compressive residual stress, the problem is that it is difficult to measure the effect after treatment because the compressive residual stress is not visible, and it is difficult to guarantee the effect by inspection. However, from the viewpoint of quality control, it is not usually used in a situation where an engineer with judgment and diagnosis ability cannot be present.
[0009]
Also, with hammer peening, large plastic deformation can be given to the processing part, so that the trace of the processing can be enlarged and the processing can be specified after the execution, but the surface scratches generated at the time of the processing cause stress concentration, Fine control is difficult, and quality control is very difficult, because the fatigue strength is sometimes reduced and the workability is remarkably poor due to the large reaction when giving plastic deformation.
[0010]
Further, when the above-mentioned fatigue improvement treatment method for introducing compressive residual stress is used particularly for repairing metal members, at the initial stage of the occurrence of fatigue cracks, at a small point of time of 1 mm or less, a penetrant inspection test, a magnetic particle inspection test, an eddy current test Although detection is impossible with current inspection methods such as flaw detection tests, it is not possible to stop the growth of cracks even if the above-mentioned fatigue life improvement measures are applied with such cracks left. In addition, it is considered that there is almost no effect of improving the fatigue life by introducing the compressive residual stress.
[0011]
In addition, when using a low-temperature transformation material for the weld and when introducing compressive residual stress to the toe, the effect is high for high-strength steel, but is almost ineffective for low-strength steel. As with TIG dressing, there is a problem in construction and it is difficult to use because there is heat due to welding. In addition, the effect of the introduced compressive residual stress is similar to other treatment methods. Difficult to judge.
[0012]
As described above, the fatigue improvement measures to reduce the stress concentration at the welded portions of the metal members mainly involve the efficiency of construction and the skill of the installer.On the other hand, the fatigue improvement measures to introduce the compressive stress The problem is that quality control cannot be performed by measuring the effect.Therefore, it is difficult to use such a fatigue life improvement measure for a welded portion between a metal member and a reinforcing member. there were.
[0013]
The present invention has been made in view of the above circumstances, and as a measure for improving fatigue of a welded portion between a girder structure and a reinforcing member, a tool that vibrates the tip with an ultrasonic wave at an amplitude of 20 μm to 60 μm and a frequency of 15 kHz to 60 kHz. An object of the present invention is to perform an ultrasonic impact treatment for performing peening to strike the surface of a welded portion by using the method, improve the fatigue strength of the welded portion, and obtain a highly durable reinforcing method for a girder structure.
[0014]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the first invention of the present invention relates to a reinforcing method for a girder structure in which a CT section steel is welded in accordance with a web line of an I-shaped section girder, and the thickness of the CT section steel web is set to t. At this time, the shape of the toe portion is improved by forming a groove by performing an ultrasonic impact treatment at a temperature of 100 ° C. or less from the end of the CT section steel at a temperature of at least t.
[0015]
The second invention is characterized in that, in the reinforcing method of the girder structure of the first invention, a groove is formed in a section t from the end of the CT section steel, and a leg length of the turn welding is set to 5 mm or more.
[0016]
The third invention is characterized in that in the reinforcing method of the girder structure of the first or second invention, when performing the ultrasonic impact treatment, the ultrasonic impact treatment is carried out in a state where a tensile load is applied to the welded part to be treated. .
[0017]
The fourth invention is a reinforcing method for welding a cover plate having a width narrower than the flange width of an I-shaped cross-section girder or a box cross-section girder and having a straight or curved end to a flange of an I-shaped cross-section girder or a box cross-section girder, When the thickness of the cover plate is defined as t, the shape of the toe portion is formed by performing an ultrasonic impact treatment at a temperature of 100 ° C. or less at a temperature of 100 ° C. or less over the entire width of the cover plate and at least t from the end. It is characterized by improvement.
[0018]
The fifth invention is characterized in that, in the reinforcing method of the girder structure of the fourth invention, a groove is formed in an end section of the cover plate, and a leg length of the lap welding is set to 5 mm or more.
[0019]
The sixth invention is a reinforcing method for welding a cover plate having a width wider than the flange width of the I-shaped cross-section girder or box-shaped girder to the flange of the I-shaped cross-section girder or the box-shaped girder, When the thickness of the cover plate is defined as t, the shape of the toe portion is formed by performing an ultrasonic impact treatment at a temperature of 100 ° C. or less at a temperature of 100 ° C. or less over the entire width of the cover plate and at least t from the end. It is characterized by improvement.
[0020]
The seventh invention provides a reinforcing method in which an H-section steel having a flange width smaller than the flange width of an I-shaped section girder is welded to the flange of the I-shaped section girder, and the web thereof is aligned with the web line of the I-shaped section girder. In the above, when the thickness of the flange of the H-section steel is t, the ultrasonic impact treatment is performed at a temperature of 100 ° C. or less over the entire width of the H-section steel and in a range of t or more from the end to form a groove. , Characterized in that the shape of the toe is improved.
[0021]
The eighth invention provides a reinforcing method for welding a gusset plate having a truss beam to a lower flange of an I-shaped cross-section girder, where t is a thickness of the gusset plate and t is equal to or more than t on both sides from an end of the gusset plate. The shape of the toe is improved by forming a groove by performing an ultrasonic impact treatment at a temperature of 100 ° C. or less.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
The occurrence of fatigue fracture of a metal member is greatly affected by stress concentration and residual stress. In a metal material subjected to a load, a transition is accumulated in a stress concentration portion, which becomes an accumulation of a slip line and develops into a crack, and after a crack occurs, it progresses. Residual stress is usually present as a tensile residual stress in a weld or the like, and is considered to increase the effective repetitive stress range to facilitate crack generation and promote the opening of the generated crack. Therefore, in order to improve the fatigue life of the metal material, it is necessary to alleviate the stress concentration and make the residual stress as close as possible to the compressed state.
[0023]
In the welded portion of the metal member, there are both a sudden change in the surface shape and a tensile residual stress, which are the weakest points in terms of fatigue strength. This sudden change in the surface shape acts as a notch and becomes a stress concentration part, so plastic deformation is applied to this stress concentration part, and it is possible to form a surface formed by a curved surface with a gentle toe radius large, The stress concentration portion is alleviated. At this time, if a plastic deformation is applied in the thickness direction of the metal material, the plasticized metal material is constrained by the surrounding metal, thereby introducing a compressive force.
[0024]
As means for enabling plastic working on such a welded portion, an ultrasonic impact is used to perform peening to strike the surface of the welded portion using a tool that vibrates the tip with an ultrasonic wave at an amplitude of 20 μm to 60 μm and a frequency of 15 kHz to 60 kHz. There is a process called processing. By using this method, plastic working can be performed on the surface of the welded portion, and a compressive residual stress can be introduced to a depth of about 1.5 mm.
[0025]
This method of ultrasonic impact treatment basically does not change the basic mechanism related to hammer peening and improvement of fatigue strength, but instead of reducing the energy of each impact to a small amount, it can perform 10,000 or more impacts per second. By giving, similar plastic deformation is realized. Moreover, since the impact force at each time is small, there is almost no recoil generated in the device, which is very advantageous in terms of usability and workability as compared with hammer peening.
[0026]
In addition, the treatment of the ultrasonic impact treatment gives an effect which is not provided by the conventional hammer peening on the surface of the metal material because the surface of the metal is hit many times. In addition, since the impact energy of each shot is greater than that of shot peening, an effect that cannot be achieved by conventional shot peening is provided.
[0027]
First, by hitting the surface many times, uniformity of the treatment can be obtained. It is known that a certain degree of uniformity can be obtained by performing several passes on the same line in hammer peening, but the number of impact cycles of ultrasonic impact treatment is 15 to 60 kHz, and the obtained uniformity is determined by hammer peening. If the processing speed is about 0.5 m / min, the surface of the welded portion is almost uniformly finished without leaving any defects.
[0028]
Further, the surface after the treatment has remarkable smoothness. The smoothness after the treatment by the ultrasonic impact treatment is significantly smoother than the surface of the weld after finishing the grinder.
[0029]
Further, it has been found that the structure of the welded surface after the treatment is remarkably fined by repeating plastic working many times using ultrasonic waves. (See Non-Patent Document 1)
[0030]
Actually, as a result of using an ultrasonic impact treatment on a metal material for the purpose of improving fatigue, the metal material structure is significantly changed before and after the treatment. Such an effect of refining the structure of the metal material is particularly remarkable in a HAZ portion near the weld where the structure of the metal material is coarsened. Usually, the particle size of the HAZ which is coarsened to 100 μm is reduced by the ultrasonic impact treatment. After the treatment, the particle size becomes so small that the particle size is hardly observable, and a unique metallic material structure is achieved by the ultrasonic impact treatment.
[0031]
Further, as the structure of the metal material on the surface of the metal material becomes finer by the ultrasonic impact treatment, the hardness increases. The hardness distribution of the base metal, the molten metal, and the HAZ after the ultrasonic impact treatment is increased by 20% or more especially in the case of high-strength steel often used as a weld metal material. In addition, depending on the material and the processing time, the hardness may increase up to about twice as much as before, but this does not mean that it became a hard and brittle martensi, mainly due to the effect of fine graining. In addition, because of work hardening due to accumulation of transition, it is not an increase in hardness of a type that causes welding cracks.
[0032]
Fatigue fracture of a metal material consists of crack initiation and propagation. The sum of the crack initiation life and the crack propagation life is the total life up to fatigue cracking. In many cases, cracks are generated from places where stress concentration or residual stress is severe, and the generated cracks continue to further develop and eventually break the member. In order to improve the life of fatigue fracture of a metal material, it is necessary to suppress the occurrence of fatigue cracks and the progress of fatigue cracks.
[0033]
However, once a crack occurs in a metal material, stress concentration at the tip of the crack is extremely large, and it is said that it is extremely difficult to stop the progress. For example, even if a stop hole is made at the tip and the hole is tightened with a high-strength bolt, if the tip of the crack remains, the crack may propagate inside the bolt and even cut.
[0034]
When observing the initial fatigue crack, by observing the initial fatigue crack which is the state of the crack at the time when the occurrence was detected by the strain measurement during the fatigue test of the turning welded specimen, at this point, the ordinary fatigue welding with the turning welding joint Approximately 10% of the fatigue life has elapsed, and the remaining 90% of the life is the extension life of this crack, which is almost determined unless this crack is removed.
[0035]
However, a crack in this state cannot be detected by a normal penetrant inspection test or a magnetic particle inspection test. If hammer peening or shot peening, which is a conventional fatigue life improvement method, is performed in this state, the processing is performed while leaving this crack, so that apparently plastic deformation occurs on the treated surface, Since the growth of the crack cannot be stopped, the improvement effect is only a reduction in stress concentration by the shape improvement, and the situation is considered that the life is hardly extended.
[0036]
However, if the ultrasonic impact treatment is performed even in this state, the crack can be crushed and the crack tip can be prevented from being opened because a compressive stress due to plastic deformation is introduced to a depth of about 1.5 mm. Of course, the depth at which compressive stress can be introduced can be as large as or greater than that of hammer peening, but hammer peening has uneven treatment effects, and it is thought that there are many parts left without hitting cracks. In this regard, since the number of impacts in the ultrasonic impact treatment is extremely large as described above, the opening of a crack can be uniformly suppressed.
[0037]
Therefore, in order to effectively obtain the effect of improving the fatigue life, it is fundamental to apply the ultrasonic impact treatment to the weld metal portion and the HAZ portion of the weld metal material centering on the toe of the welded portion. The interface between the weld metal and the HAZ, which is the most fatigue weak point, is strengthened against fatigue. Further, the adverse effect of the hot crack generated on the surface of the weld metal can be remarkably reduced. However, attention should be paid to the fact that it is considered that there is almost no effect on low-temperature hydrogen cracking.
[0038]
In the processing of the welded part, the number of times of processing in one processing line is enough for one pass, but in order to improve uniformity, to improve controllability, and to prevent excessive plastic deformation, When it is desired to reduce the input power per process, by performing the processes two or more times on the same line, a more reliable fatigue life improvement effect can be obtained.
[0039]
An embodiment of the present invention will be described with reference to the drawings. As shown in FIGS. 1 (a) and 1 (b), a reinforcing CT composed of a web 6 and a flange 7 is provided on a lower flange 3 of an I-shaped cross-section girder 1 composed of upper and lower flanges 2, 3 and a web 4. The section steel 5 is reinforced by welding and joining the web 6 thereof to the position of the web 4 of the I-shaped section girder 1. As shown in FIG. 1 (a), the reinforcing CT section steel 5 is slightly shorter than the I-shaped cross-section girder 1, and its end is obliquely cut. It is effective for introducing compressive residual stress in a range not less than the thickness t of the web 6 of the CT section steel 5 from the lower flange 3 of the I-shaped section girder 1 and the end of the welded portion 8 of the CT section steel 5 for reinforcement. At a certain temperature of 100 ° C. or lower, ultrasonic impact treatment is performed to form a groove, and the shape of the toe of the welded portion 8 is improved so that stress concentration does not occur.
[0040]
Also, a groove is formed in the section of the thickness t of the web 6 of the reinforcing CT section steel 5 from the end of the reinforcing CT section steel 5 of the welded portion 8 and the leg length of the turning welding is set to 5 mm or more. Ultrasonic impact treatment is performed on the area to improve the shape of the toe of the welded portion 8 so that stress concentration does not occur.
When the ultrasonic impact treatment is performed on the welded portion 8, it is more effective to introduce a compressive residual stress if the ultrasonic impact treatment is performed with a tensile load applied to the welded portion 7 to be treated.
[0041]
As shown in FIGS. 2 (a) and 2 (b), the cover plate 9 for reinforcement is welded to the lower flange 3 of the I-shaped section girder 1 for reinforcement. 2A and 2B show a case where the width of the reinforcing cover plate 9 is narrower than the width of the lower flange 3 of the I-shaped section girder 1, as shown in FIG. 2C. Alternatively, the width of the reinforcing cover plate 9 may be wider than the width of the lower flange 3 of the I-shaped section girder 1. The shape of the end of the reinforcing cover plate 9 may be linear or curved.
The compression residual remains within the entire plate width at the end of the cover plate 9 at the welded portion 8 of the lower flange 3 of the I-shaped section girder 1 and the cover plate 9 and within the range of the plate thickness t of the cover plate 9 for reinforcement from the end. When the temperature effective for introducing the stress becomes 100 ° C. or less, ultrasonic impact treatment is performed to form a groove, and the shape of the toe of the welded portion 8 is improved so that stress concentration does not occur.
A groove is formed from the end of the welded portion 8 of the cover plate 9 for reinforcement, the leg length of the lap welding is set to 5 mm or more, an ultrasonic impact treatment is performed in the range, and the toe shape of the welded portion 8 is stress concentrated. Improve so that does not occur.
[0042]
As shown in FIGS. 3 (a) and 3 (b), a reinforcing H-section steel 10 having a flange width smaller than the flange width of the lower flange 3 of the I-shaped girder 1 is provided on the lower flange 3 of the I-shaped girder 1. The flange 11 is positioned so that its web 12 is aligned with the web 4 of the I-shaped cross-section spar 1 and is welded and reinforced. The H-shaped steel 10 for reinforcement is shorter than the I-shaped cross-section girder 1, and its end is cut diagonally.
The entire width of the end of the flange 11 of the H-shaped steel 10 for reinforcement of the welded portion 8 between the I-shaped section girder 1 and the flange 11 of the H-shaped steel 10 for reinforcement, and the flange of the H-shaped steel 10 from the end. When the temperature effective for the introduction of compressive residual stress is reduced to 100 ° C. or less in the range of the thickness t or more, ultrasonic shock treatment is performed to form a groove, and the shape of the toe of the welded portion 8 is formed. Is improved so that stress concentration does not occur.
[0043]
As shown in FIG. 4, a reinforcing gusset plate 13 provided with a truss beam 14 is welded to the lower flange 3 of the I-shaped section girder 1 for reinforcement. The temperature effective for introducing the compressive residual stress is within a range from the end of the welded portion 8 of the lower flange 3 of the I-shaped cross section 1 and the gusset plate 13 for reinforcement to the thickness t of the gusset plates 13 on both sides. When the temperature is less than 100 degrees, ultrasonic impact treatment is performed to form a groove, and the shape of the toe is improved so that stress concentration does not occur.
[0044]
【The invention's effect】
With the ultrasonic impact treatment of the configuration of the present invention, the toe of the welded portion between the girder structure and the reinforcing member is subjected to 10,000 or more impacts per second, and the impact force of each impact is small. Impact treatment with superior usability and workability compared to peening can be achieved, and the reinforcement method improves the shape of the toe of the welded part and increases the durability of the girder structure.
[0045]
Since the ultrasonic impact treatment hits the surface many times, the uniformity of the treatment is obtained and the smoothness of the surface after the treatment is obtained, so the generation of fatigue cracks from the toe of the weld is suppressed, It will be a reinforcement method to increase the durability of the girder structure.
[0046]
Ultrasonic impact treatment is a reinforcement method that can remarkably refine the structure of the metal surface after treatment by repeating plastic processing by numerous impacts, can suppress the occurrence of fatigue cracks, and increase the durability of the girder structure .
[0047]
Ultrasonic impact treatment of the toe, HAZ, and weld metal of the weld, where fatigue cracks are likely to occur, enhances the fatigue at the interface between the weld metal and the HAZ, which is the most fatigue weak point. In addition, since the effect of hot cracks generated on the surface of the weld metal can be remarkably reduced, a reinforcing method for improving the durability of the girder structure is provided.
[0048]
By the ultrasonic impact treatment, compressive residual stress is introduced into the toe of the welded portion, and the occurrence and propagation of fatigue cracks are suppressed.
[0049]
The generation of fatigue cracks in the weld between the girder structure and the reinforcing member is suppressed, the girder structure and the reinforcing member are integrated, and true reinforcement of the girder structure is achieved. .
[Brief description of the drawings]
FIGS. 1 (a) and 1 (b) are diagrams showing an embodiment of the present invention. FIGS. 2 (a), 2 (b) and 2 (c) are diagrams showing an embodiment of the present invention. FIGS. FIG. 4 shows one embodiment of the present invention. FIG. 4 shows one embodiment of the present invention.
1: I-shaped section girder 2: I-shaped section girder upper flange 3: I-shaped section girder lower flange 4: I-shaped section girder web 5: Reinforcing CT section steel 6: CT section steel web 7: CT section Steel flange 8: Weld 9: Reinforcing cover plate 10: Reinforcing H-shaped steel 11: Reinforcing H-shaped steel flange 12: Reinforcing H-shaped steel web 13: Reinforcing gusset plate 14 : Truss beam

Claims

In a reinforcing method in which a CT section steel is welded in accordance with a web line of an I-shaped section girder, assuming that the thickness of the CT section steel web is t, the temperature is 100 ° C. within a range of t or more from the end of the CT section steel. A reinforcing method for a girder structure, characterized in that a shape of a toe portion is improved by forming a groove by performing an ultrasonic impact treatment below.

2. The method of reinforcing a girder structure according to claim 1, wherein a groove is formed in a section t from the end of the CT section steel, and a leg length of the turn welding is 5 mm or more.

The method of reinforcing a girder structure according to claim 1, wherein when the ultrasonic impact treatment is performed, the ultrasonic impact treatment is performed in a state where a tensile load is applied to a welded portion to be treated.

In the reinforcement method of welding a cover plate whose width is narrower than the flange width of an I-shaped section girder or box section girder and whose end is straight or curved to the flange of an I-shaped section girder or box section girder, the thickness of the cover plate is reduced. When t, the shape of the toe is improved by performing an ultrasonic impact treatment at a temperature of 100 ° C. or less to form a groove in the entire width of the cover plate and in a range of t or more from the end to not less than t. Girder structure reinforcement method.

The method for reinforcing a girder structure according to claim 4, wherein a groove is formed in an end section of the cover plate, and a leg length of the lap welding is set to 5 mm or more.

In the reinforcement method of welding a cover plate whose width is wider than the flange width of the I-shaped section girder or box section girder and whose end is straight or curved to the flange of the I-shaped section girder or box section girder, the thickness of the cover plate is reduced. When t, the shape of the toe is improved by performing an ultrasonic impact treatment at a temperature of 100 ° C. or less to form a groove in the entire width of the cover plate and in a range of t or more from the end to not less than t. Girder structure reinforcement method.

In a reinforcing method in which an H-section steel whose flange width is smaller than the flange width of the I-section girder is welded to the flange of the I-section girder and the web thereof is welded along the web line of the I-section girder, Assuming that the thickness of the flange is t, the shape of the toe is changed by performing an ultrasonic impact treatment at a temperature of 100 ° C. or less at a temperature of 100 ° C. or less from the entire width of the H-section steel and from the end to t or more. Reinforcement method characterized by improvement.

In the reinforcing method of welding a gusset plate having a truss beam to the lower flange of an I-shaped section girder, when the thickness of the gusset plate is t, the temperature from the end of the gusset plate to t or more on both sides is 100 ° C or less at a temperature of not less than t. A reinforcing method for a girder structure, characterized in that the shape of a toe portion is improved by forming a groove by performing an acoustic shock treatment.