JP3797080B2 - H-shaped steel with excellent earthquake resistance and steel structure using the same - Google Patents

Description

【００１５】
【表２】

【００１６】
表３は、長手方向の引張試験におけるウェブ降伏点とフランジ降伏点の比、公称応力を公称歪で除した勾配の最小値、および最大応力時の歪みをフランジの降伏歪みで除して得られる塑性率を示す。
【００１７】
なお、本発明のＨ形鋼（Ａ〜Ｉ）は、塑性率および累積塑性変形倍率が比較Ｈ形鋼（Ｊ〜Ｒ）よりも上回る値を示し、優れた塑性変形能力を示したのに対し、比較Ｈ形鋼は、フランジの降伏後の剛性が低いために座屈に対する抵抗が小さく早期に座屈を誘発するとの、後記する結果となっている。
【００１８】
【表３】

【００１９】
（幅厚比の影響、圧縮試験の結果）
図１は、本発明の一実施の形態に係るＨ形鋼の圧縮荷重に対する耐座屈性を評価する柱圧縮試験の結果であって、材質とウェブの幅厚比（ウエブ幅Ｂの半分をウエブ厚Ｔで除した値Ｂ／２Ｔ）が種々異なるＨ形鋼について、軸方向に圧縮する短柱圧縮試験と称する局部座屈試験により、Ｈ形鋼フランジ部位の材質的な特性と局部座屈発生挙動との相関を調査した結果である。
【００２０】
すなわち、試験体のフランジ部位の幅厚比と座屈発生限界歪の関係は略反比例関係（負の関係）があり、加工硬化指数の値が小さい一般Ｈ形鋼（低ｎ値鋼）では、幅厚比が略８より大きくなると、急激に座屈発生限界歪が小さくなっている。一方、加工硬化指数の値が大きい本発明のＨ形鋼（高ｎ値鋼）は、幅厚比が略８より大きい範囲においても、座屈発生限界歪が急激に低下することがなく、塑性変形能力が改善されている。
【００２１】
なお、建築基準法では、変形能力があるといわれる梁部材のフランジの幅厚比は７．５以下と定められ、この範囲で通常発生する損傷は座屈ではなく，塑性変形に伴う破断であって、変形能力により決定される。一方、幅厚比８以上の範囲では変形能力がそれより劣ると言われ、この範囲で通常発生する損傷は座屈である。しかしながら、本発明は、フランジの幅厚比が８以上でありながら，前記のように塑性変形能力が改善され座屈が発生し難くなっている。
【００２２】
（加工硬化指数の影響、圧縮試験の結果）
図２は、本発明の一実施の形態に係るＨ形鋼の圧縮荷重に対する耐座屈性を評価する圧縮試験の結果であって、加工硬化指数が種々異なるＨ形鋼について、図１と同様の柱圧縮試験をしたものである。すなわち、試験片長手方向をＨ形鋼の軸方向に一致させてフランジから採取した引張試験片を用いて引張試験を行い、降伏後歪み量２％から６％までの範囲における加工硬化指数（応力を歪のベキ乗で整理したときの、ベキ数）を測定した。
【００２３】
図２において、フランジの幅厚比が１０の場合について、加工硬化指数が０．２以上である本発明のH形鋼（図２において黒丸）と、加工硬化指数が０．２未満である従来のH形鋼（図２において白丸）を比較している。
【００２４】
加工硬化指数が０．２未満である従来のＨ形鋼（図２において白丸）は座屈発生限界歪みが０．６％未満であり，降伏歪み（SN490の場合0.16〜0.21％）の４倍未満しか変形能力が得られないのに対し、加工硬化指数が０．２以上の本発明のＨ形鋼（図２において黒丸）は座屈発生限界歪みが０．８％以上であり、降伏歪みの約６倍の変形能力が得られる。
【００２５】
すなわち、通常、塑性座屈により損傷が発生する幅厚比の範囲にありながら、本発明のH形鋼は硬化勾配が大きい（加工硬化指数が大きい）ために、塑性変形の範囲が拡するから、この塑性範囲の拡大に伴って、局所的な塑性座屈が押さえられることになる。
【００２６】
（試験の方法）
図３は、本発明の一実施の形態に係るＨ形鋼を評価する圧縮試験および片持ち繰り返し曲げ試験を示す説明図である。すなわち，（a）はＨ形鋼１０に圧縮力をかけ，その荷重変型関係を測定するもので，Ｈ形鋼１０のフランジおよびウェブには材軸にわたって一様な圧縮応力を作用させるものである。
【００２７】
一方、（b）は一端が固定端である片持ち梁（Ｈ形鋼）１１の他端に正負交番の水平力を作用させ、その荷重変型関係を測定するもので、Ｈ形鋼１１のフランジおよびウェブには材軸にわたって一様でない（三角形分布）圧縮応力を作用させるものである。（片側のフランジは圧縮、他方のフランジは引張）
片持ち繰り返し曲げ試験は、載荷点までの距離を2500ｍｍとし、正負交番の水平力を作用させ、その荷重変形関係を測定する。
【００２８】
圧縮試験の試験体長さは、長辺の３倍および短辺の５倍の小さい方の長さとし、加力は中央圧縮単調載荷とした。載荷板間の変位を試験体長さで除した値を試験体の歪み、載荷荷重を試験体断面積で除した値を試験体の応力とした。
【００２９】
（応力上昇率の影響、繰り返し曲げ試験の結果）
図４は、本発明の一実施の形態に係るＨ形鋼の曲げ荷重に対する耐座屈性および耐破断特性を評価するため、図３に示す片持ち梁の繰り返し裁荷試験をしたものである。
種々異なるＨ形鋼について、図３に示す片持ち梁の繰り返し裁荷試験をしたものである。
【００３０】
すなわち，加工硬化指数が０．２以上で、フランジの幅厚比が7．０である本発明のＨ形鋼において、フランジの応力上昇率（降伏応力ＹＰに対する、一様のびにおける塑性変形応力ＹＢの比である応力上昇率α２（ＹＢ/ＹＰ））が１．２８のもの（以下、1.28Ｈ形鋼と称す）と、フランジの応力上昇率が１．３７のもの（以下、1.37Ｈ形鋼と称す）の塑性変形能力を後記する累積塑性変形倍率により比較した。すなわち、1.28Ｈ形鋼は、累積塑性変形倍率は２０であるのに対し， 1.37Ｈ形鋼の累積塑性変形倍率は４８と大きくなっている。
【００３１】
（累積塑性変形倍率）
図５は累積塑性変形倍率を説明する荷重−変位曲線である。図５において、Ｈ型鋼の全断面が降伏する時（全塑性モーメントＭｐの時）の弾性変形を「降伏変形δｐ」として、例えばｉ回目の載荷が図中Ａ点から開始され、一方向荷重によりＢ点まで変形し、その後、除荷されてＣ点の塑性変形が残ったとき、Ａ点からＣ点まで距離を残存変形量δｉ（塑性変形量の絶対値）として、この残存変形量δｉを降伏変形δpで除した値をｉ回目の塑性変形倍率（δｉ/δｐ）とする。
【００３２】
さらに、ｉ＋１回目の載荷として図中Ｃ点から開始され、ｉ回目とは逆の方句の荷重によりＤ点まで変形し、その後、除荷されてＥ点の塑性変形が残ったとき、Ｃ点からＥ点まで距離距離を残存変形量δｉ+1（塑性変形量の絶対値）とし、この残存変形量δｉ+1を降伏変形δpで除した値を塑性変形倍率（δi+1/δｐ）とする。そして、この塑性変形倍率を１回目から所定の回数ｊまで累積したものをｊ回目の累積塑性変形倍率とする。
【００３３】
（シャルピー吸収エネルギー）
なお，フランジの0度Ｃシャルピー吸収エネルギーは1.28Ｈ形鋼が２５０Ｊで、1.37Ｈ形鋼が１６０Ｊであった。1.28Ｈ形鋼のフランジの0度Ｃシャルピー吸収エネルギーが高いにも関わらず，最終的には梁端の溶接部止端部より延性亀裂が発生してこれが伸展しフランジが破断することにより耐力が決定した。
【００３４】
一方、1.37Ｈ形鋼のフランジの0度Ｃシャルピー吸収エネルギーが低いにも関わらずの累積塑性変形倍率は４８と高く、1.28Ｈ形鋼の約２倍になっている。これは，応力上昇率の高いＨ形鋼の方が同じ載荷側の梁端の変形に対して，溶接部側の梁端溶接部止端部の局部歪みが小さく抑えられるためである。
【００３５】
（フランジの応力上昇率）
さらに、建築構造物の柱梁接合部近辺におけるモーメント勾配を算定する代わり、あるいは、材料の塑性変形応力の上昇勾配を算定する変りに、フランジの応力上昇率すなわち降伏比（ＹＲ）にて材料を規定してもよい。すなわち、フランジの応力上昇率を１．３３以上、すなわち降伏比（ＹＲ）７５％以下とすれば、塑性変形を拡大させることができ、変形能力を確保することができる。
【００３６】
（加工硬化指数を算出するための歪の範囲）
次に、加工硬化指数を算出するための歪の範囲について簡単に説明する。
加工硬化指数を算定するに当たり、その歪範囲を加工硬化を開始した歪から、６％の歪の範囲としたのは、通常および地震時に建築構造の梁端部に生じる平均的な歪範囲に基づく。
【００３７】
図７は、建築構造物の強さ（横軸）に対する建築構造物の平均的な変形（縦軸）を表すものであって、該変形量を柱と梁が成す角度の変化量（回転量、ラジアン）とし、使用材料の最大応力を降伏応力で除した応力上昇率をパラメータとして用いている。図７において、建築構造物の強さが比較的小さく、また、パラメータが小さい場合、建築構造物の平均的な角度の変化量０．０２（２％）である。
【００３８】
図８は、建築構造物の相対回転角（横軸）に対する建築構造物のフランジの歪度（縦軸）を表すものである。建物の中には、損傷が大きくなる梁端と損傷が比較的大きくない梁端があるため、このバラツキを４％程度とすると最も損傷を受ける梁端で６％の最大回転角（横軸）になると考えられる。
【００３９】
図８において、本発明のＨ形鋼である高降伏比材の場合、６％の最大回転角（横軸）に対し、梁フランジの平均歪（縦軸）は６％程度となる。このことは建築鉄骨の梁端部の歪は６％程度までの範囲にあり，それ以上の歪域が発生することは，局部的にはともかく平均的にはまれであることを示している。
【００４０】
また，通常の鋼材は２％程度の降伏棚があるため，この降伏棚が終了して加工硬化が開始する歪と前記６％の歪の範囲とした。すなわち、弾性範囲および降伏棚の範囲を除き、また、実際に建築鉄骨が受ける最大歪以下の範囲において、加工硬化指数を算出するから、建築鉄骨の塑性挙動を適正に表現することが可能になる。なお、前記２％は目安であり，３％〜６％としても本発明の作用効果を発揮するものである。
【００４１】
（化学成分選定の目安）
なお、本発明ではＨ形鋼の製造方法は問わず、圧延、溶接などいずれの方法であっても、上記所定の特性を満足するものであればよい。また、上記特性は、Ｈ形鋼の化学成分や溶接前の例えば鋼板の圧延条件を制御することによって付与しても、また圧延中や圧延後のＨ形鋼に熱処理や加工処理を施すことによって付与してもよく、化学組成や製造条件については特に限定されない。
【００４２】
ただし、化学組成としては、重量％で、Ｃ：0.02％以上0.22％以下、Ｓｉ：0.05％以上0.35％以下、Ｍｎ：0.45％以上1.60％以下、Ｐ：0.020％以下、Ｓ：0.008％以下を含有し、炭素当量0.46％以下、溶接割れ感受性指数0.26％以下となるものが好ましい。このような成分範囲の鋼が好ましいのは以下の理由による。
【００４３】
C：0.02％未満では十分な強度が得られず、また0.22％を超えると溶接性が劣化する。したがって、Ｃ量は0.02％以上0.22％以下が好ましい。
【００４４】
Ｓｉ：0.05％未満では十分な脱酸が行われず、健全な鋼材が得られない。また0.35％を超えた場合には溶接性が劣化する。したがって、Ｓｉ量は0.05％以上0.35％以下が好ましい。
【００４５】
Ｍｎ：0.45％未満では十分な強度が得られず、また1.60％を超えると溶接性が劣化する。したがって、Ｍｎ量は0.45％以上1.60％以下が好ましい。
【００４６】
Ｐ：0.020％を超えると母材の靭性、溶接性が劣化するため、Ｐ量は0.020％以下が好ましい。
【００４７】
Ｓ：0.008％を超えると母材の靭性、溶接性、溶接部の靭性が劣化するため、Ｓ量は0.008％以下が好ましい。
【００４８】
炭素当量：0.46％を超えると溶接性が著しく劣化し、予熱、後熱が必要となる。したがって、炭素当量は0.46％以下が好ましい。なお、炭素当量は、炭素当量＝C＋Mn／6＋Si／24＋Ni／40 +Cr／5＋Mo／4＋V／14 の式で計算した。
【００４９】
溶接割れ感受性：0.26％を超えると、溶接性が著しく劣化し、溶接部に割れが生じるようになる。したがって、溶接割れ感受性は0.26％以下が好ましい。なお、溶接割れ感受性は、溶接割れ感受性＝C＋Si／30＋Mn／20＋Cu／20＋Ni／60 +Cr／20＋Mo／15＋V／10＋5Bの式で計算した。
【００５０】
このような組成の鋼板に対して、圧延条件を制御したり、または圧延中や圧延後のＨ形鋼に熱処理や加工処理を加えることにより、例えば圧延後にウェブには制御冷却、フランジには空冷を施すことにより、ウェブの金属組織を例えばフェライトとベイナイトあるいはフェライトとマルテンサイトの複合組織、フランジをフェライト・パーライト組織とすることにより、上記特性を付与することができる。
【００５１】
［実施の形態２］
図６は、本発明の他の実施の形態に係る耐震性に優れたＨ形鋼を説明するものであって、（ａ）は該H形鋼を梁に用いた鉄骨構造を示す斜視図、（ｂ）は梁に働くモーメント分布と梁フランジに発生する引張り応力の分布を示す力の分布図、（ｃ）は梁に塑性変形が発生した後の、梁フランジに発生する引張り応力の分布を示す力の分布図である。
【００５２】
図６の（ａ）において、柱１に、本発明の実施の形態１に記載したＨ形鋼からなるブラケット２が接合され、ブラケット２にスプライスプレート４を介して梁３が設置されている。
【００５３】
図６の（ｂ）において、ブラケットと柱の接合部分（図中のＣ点）に最大モーメントが作用するため、前記構造物に所定の外力が作用した際、まず、この部分が降伏応力ＹＰに達し塑性変形が発生する。このときのモーメントを塑性モーメントと呼んで以下の説明をする。
【００５４】
（塑性変形の範囲の拡大）
図６の（ｃ）において、塑性変形の範囲が拡大している（図中で点Ｃ〜点Ｘの範囲）。すなわち、点Ｃに作用するモーメント（最大モーメント）が塑性モーメントを越えたとき、点Ｃの材料は加工硬化するため、このモーメントに耐えるだけの応力を負担している。一方、塑性変形と弾性域の境界にある点Ｘには、塑性モーメントが作用し、引張り応力として降伏応力ＹＰが発生している。
【００５５】
換言すると、フランジの点Ｃにおける引張り応力ＳＣ、とフランジの点Ｘにおける引張り応力（降伏応力ＹＰに同じ）との比率ＳＣ／ＹＰ（点Ｘ〜点Ｃの範囲における応力上昇率）は、点ＣにおけるモーメントＭＣ、と点ＸにおけるモーメントＭＸとの比率ＭＣ／ＭＸ（点Ｘ〜点Ｃの範囲におけるモーメント上昇率）に等しい。
【００５６】
すなわち、フランジ部の材料から見ると、モーメントが上昇して点Ｃが一様のびの状態になったとき、一様のびにおける応力ＹＢは、引張り応力ＳＣよりも大きいことを示しているから、フランジの点Ｃにおける応力ＹＢとフランジの点Ｘにおける引張り応力（降伏応力ＹＰに同じ）との比率ＹＢ／ＹＰ（点Ｘ〜点Ｃの範囲における応力上昇率、６％以上の歪範囲のおける応力の上昇勾配に同じ）は、点ＣにおけるモーメントＭＣと、点ＸにおけるモーメントＭＸとの比率ＭＣ／ＭＸ（点Ｘ〜点Ｃの範囲におけるモーメント上昇率、最大モーメントを生じる位置の近傍におけるモーメント勾配に同じ）より大きいことになる。
【００５７】
逆に、前記応力上昇率ＹＢ／ＹＰ（６％以上の歪範囲のおける応力の上昇勾配に同じ）が、モーメント上昇率ＭＣ／ＭＸ（最大モーメントを生じる位置の近傍におけるモーメント勾配に同じ）より小さい場合には、モーメントに耐えるだけの引張り応力が生じないため、フランジが破損することになる。
【００５８】
［実施の形態３］
本発明の他の実施の形態に係る耐震性に優れたＨ形鋼は、前記実施の形態２にいおける、６％以上の歪範囲のおける塑性変形応力の上昇勾配を、降伏応力ＹＰに対する、一様のびにおける応力ＹＢの比である応力上昇率α２（ＹＢ／ＹＰ）に限定し、さらに、最大モーメントを生じる位置の近傍におけるモーメント勾配を、、柱梁接合部より梁せいＨの半分だけ離れた位置におけるモーメントＭＨに対する、柱梁接合部におけるモーメントＭＣの比であるモーメント上昇率α１（ＭＣ/ＭＨ）に限定したものである。
【００５９】
（応力上昇率α２）
６％以上の歪範囲のおける塑性変形応力の上昇がほぼ飽和し、一様のびになった場合、このときの応力ＹＢを、降伏応力ＹＰに対する比で表示し、応力上昇率α２を明確に規定する。
【００６０】
（梁の塑性化領域）
さらに、図６（ｃ）において、点Ｘの位置（梁の塑性化領域）を梁せいＤの半分として、前記応力上昇率ＹＢ／ＹＰを明確に規定している。すなわち、梁の塑性化領域に関しては、従来より梁端が弾性挙動に近い場合、つまり梁端の塑性化による鋼材の応力上昇率の傾きがあまり小さくならない場合には、１．５Ｄといわれている。
【００６１】
しかし、梁端が弾性挙動から離れて、塑性化度合いが進むにつれ、塑性化による鋼材の応力上昇率の傾き（加工硬化の程度）が小さくなった際には、塑性変形が端部に集中して、塑性化領域は１．５Ｄより小さくなる。したがって、数値解析の結果を踏まえ、塑性化領域（点Ｘの位置）を梁端部（点Ｃの位置）から梁せいＤの１／２だけ離れた位置とした。（（社団法人）日本溶接協会，建築鉄骨構造の地震被害と鋼材セミナーテキスト，pp.65-66）
［実施の形態４］
図９は、本発明の他の実施の形態に係る耐震性に優れたＨ形鋼をブラケットに用いた鉄骨構造示す正面図である。図９において、柱１に、本発明の実施の形態１に記載したＨ形鋼からなるブラケット２が接合され、ブラケット２にスプライスプレート４を介して梁３が設置されている。
【００６２】
なお、本発明は該鉄骨構造の全てのブラケットを本発明のＨ形鋼により構成することに限定するものではなく、所定の階層にのみ本発明のＨ形鋼を採用してもよい。さらに、ブラケットを介して柱と梁を接合するものに限定するものではなく、本発明のＨ形鋼からなる梁を、柱に直接接合してもよい。
【００６３】
さらに、梁に対し柱の方を弱く設計する場合には、柱を本発明のＨ形鋼により構成すればよい。さらに、斜材５を本発明のＨ形鋼により構成し、耐震性を向上させてもよい。
【００６４】
【発明の効果】
以上説明したように、本発明によれば、大地震時の終局的大変形に対して、フランジに発生した塑性変形が局所に集中することなく、塑性化領域が拡大することが可能になるから、フランジが薄肉でも局部座屈を起こしにくい塑性変形能力に優れたＨ形鋼を得ることができる。
【００６５】
したがって、本発明のＨ形鋼を用いることにより、Ｈ形鋼の鋼重を増大させることなしに、構造物の耐震性を向上させることが可能となり、大地震が発生した際に、高層建築物の損壊などの災害を防止することができるとの顕著な効果が得られる。
【図面の簡単な説明】
【図１】本発明の一実施の形態に係るＨ形鋼の曲げ荷重に対する耐座屈性を評価する柱圧縮実験の結果である。
【図２】本発明の一実施の形態に係るＨ形鋼の曲げ荷重に対する耐座屈性を評価する柱圧縮実験の結果である。
【図３】本発明の一実施の形態に係るＨ形鋼を評価する短柱圧縮試験および片持ち繰り返し曲げ試験を示す説明図である。
【図４】本発明の一実施の形態に係るＨ形鋼の曲げ荷重に対する耐座屈性を評価する片持ち繰り返し曲げ試験の結果である。
【図５】累積塑性変形倍率を説明する荷重−変位曲線である。
【図６】本発明の一実施の形態に係る耐震性に優れたＨ形鋼を用いた鉄骨構造を示す斜視図である。
【図７】建築構造物の強さに対する建築構造物の平均的な変形を表すものである。
【図８】建築構造物の相対回転角に対する建築構造物のフランジの歪度を表すものである。
【図９】本発明の他の実施の形態に係る耐震性に優れたＨ形鋼をブラケットに用いた鉄骨構造示す正面図である。
【符号の説明】
１ 柱
２ ブラケット
３ 梁
４ スプライスプレート[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an H-section steel used as a structural member for construction and civil engineering, and more particularly to an H-section steel excellent in buckling resistance and plastic deformation ability during an earthquake.
[0002]
[Prior art]
In H-section steel used for conventional structural members for construction, when subjected to large deformation during an earthquake, the column member can withstand a large bending load while supporting an axial load, and the beam member can withstand a bending load. It is required to withstand. In any case, increasing the load bearing capacity and plastic deformation capability by preventing early local buckling and fracture is the key to preventing damage to the structure. For example, the following techniques are disclosed.
[0003]
Japanese Patent Application Laid-Open No. 10-121653 discloses an H-section steel excellent in earthquake resistance in which the web is work-hardened and the stress increase rate of the flange is 1.25 or more. That is, the web having high rigidity even after yielding restrains the local buckling of the flange, while the flange having high plastic deformability absorbs the plastic energy and has good buckling resistance. I was trying.
[0004]
In addition, in steel pipes used for structures, in Japanese Patent Laid-Open No. 9-196243, it is difficult to cause local buckling even with large diameter and thin wall against tensile / compressive stress acting in the axial direction in the event of a large earthquake, Steel pipes excellent in earthquake resistance suitable for gas pipelines, water pipes, building columns, highway piers and the like, which are less likely to cause brittle fracture, have been disclosed. That is, in the nominal stress-nominal strain curve obtained by the tensile test in the axial direction, the gradient of the nominal stress / nominal strain is positive in any strain amount from the yield point to the on-load strain amount of 5%. Is.
[0005]
[Problems to be solved by the invention]
However, the conventional techniques have the following problems.
[0006]
The high-rigidity web H-shaped steel maintains the work hardening of the web, that is, the rigidity after yielding, thereby constraining local buckling due to the decrease in rigidity after the yielding of the flange and improving the plastic deformation capacity. Is defined as 1.25 or more, that is, a yield ratio of 80% or less, and does not define the rigidity of the flange after yielding. Therefore, particularly when receiving a load that generates a moment gradient, there is a problem that the plastic deformation region is concentrated locally when plastic deformation starts on the flange itself. For this reason, a more direct and highly effective technique is desired.
[0007]
Furthermore, for steel pipes, the nominal stress / nominal strain gradient is positive for any strain amount from the yield point to the on-load strain amount of 5%. However, although the limit of the outer diameter / tube thickness ratio that causes local buckling is remarkably large and local buckling is difficult to occur, there is a problem that this knowledge cannot be directly applied to the H-section steel.
[0008]
The present invention has been made in order to solve such a problem, and it is difficult to cause local buckling with respect to a final large deformation at the time of a large earthquake, and various types of plastic deformation are generated over a wide range. An object of the present invention is to provide an inexpensive H-shaped steel excellent in earthquake resistance suitable as a column member and a beam member of a building and a steel structure using the same.
[0009]
[Means for Solving the Problems]
The H-section steel excellent in earthquake resistance according to the present invention has the following characteristics.
[1] The work hardening index n, which is the number of power when the stress in the strain range of up to 6% after the start of work hardening is displayed as the power of the strain, is 0.2 or more,
A flange made of a steel material having a stress increase rate α2 (YB / YP) which is a ratio of the plastic deformation stress YB in the uniform strain to the yield stress YP is 1.33 or more.
[2] H-shaped steel with excellent earthquake resistance that is placed in a building or civil engineering structure and receives a load that generates a moment gradient in the longitudinal direction.
The width-thickness ratio (B / 2T) of the flange width B and the flange thickness T is 10 or less,
The work hardening index n, which is the number of powers when the stress in the strain range up to 6% after starting work hardening is displayed as the power of strain, is 0.2 or more,
Furthermore, when the rising gradient of the plastic deformation stress in the strain range of 6% or more is larger than the moment gradient in the vicinity of the position where the maximum moment is generated, the plastic zone generated at the position where the maximum moment is generated expands to the surroundings. It is a feature.
[3] In a building or civil structure, an H-shaped steel having excellent earthquake resistance, which is a beam member or a beam-joining bracket joined to a column,
The width-thickness ratio (B / 2T) of the flange width B and the flange thickness T is 10 or less,
The work hardening index n, which is the number of powers when the stress in the strain range up to 6% after starting work hardening is displayed as the power of strain, is 0.2 or more,
Further, the ratio of the stress increase rate α2 (YB / YP), which is the ratio of the plastic deformation stress YB in the uniform to the yield stress YP, is a column with respect to the moment MH at a position separated from the column beam joint by half of the beam length H. When the moment increase rate α1 (MC / MH), which is the ratio of the moment MC at the beam joint, is larger (α2> α1), the plastic zone generated at the beam-to-beam joint is the center in the longitudinal direction of the beam or beam joint bracket. It is characterized by expanding toward the side.
[0010]
Furthermore, the steel structure using the H-shaped steel excellent in earthquake resistance according to the present invention has the following characteristics.
[4] The beam member to be joined to the column or the beam joining bracket has a width-thickness ratio (B / 2T) of the flange width B to the flange thickness T of 10 or less, and strain up to 6% after work hardening is started. H-shape with excellent seismic resistance formed by H-shape steel with excellent work resistance index n, whose work hardening index n is 0.2 or more, when the stress in the range is expressed in terms of power of strain A steel structure using steel,
The stress increase rate α2 (YB / YP), which is the ratio of the plastic deformation stress YB of the H-shaped steel flange to the yield stress YP of the H-shaped steel flange, is from the beam-to-column joint to the beam height H in the steel structure. Since the moment increase rate α1 (MC / MH), which is the ratio of the moment MC at the beam-column joint to the moment MH at a position separated by half, (α2> α1), the plastic zone generated at the beam-column joint is The beam or the beam joining bracket expands toward the center in the longitudinal direction.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
(Chemical composition and heat treatment conditions)
Table 1 shows the chemical components (with heat treatment) of the H-section steel according to one embodiment of the present invention.
[0012]
Table 2 shows the dimensions of the H-shaped steel formed by hot rolling the steel having the chemical components shown in Table 1. In Table 2, the symbols A to I, which are H-shaped steels of the present invention, heat the slab at 1250 ° C., reduce the flange by 40% below 950 ° C., and finish hot rolling in the austenite region (finished at 900 ° C.). Thereafter, the flange is kept at 670 ° C., controlled cooling is performed at a rate of 20 ° C./s to 500 ° C. or less, and then left to cool. On the other hand, the symbols J to R, which are comparative materials, are the results obtained when the hot rolling is finished in the same manner as described above, and then the cooling is performed without controlling cooling.
[0013]
Samples were taken from these H-shaped steel webs and flanges and subjected to a tensile test in the longitudinal direction. The yield point, tensile strength, and work hardening index in the range of 2% to 6% strain (in terms of stress and strain) , The number of power when the stress is expressed in terms of the power of strain).
[0014]
[Table 1]

[0015]
[Table 2]

[0016]
Table 3 is obtained by dividing the ratio of the web yield point to the flange yield point in the tensile test in the longitudinal direction, the minimum gradient obtained by dividing the nominal stress by the nominal strain, and the strain at the maximum stress divided by the yield strain of the flange. The plastic modulus is shown.
[0017]
In addition, the H-section steels (A to I) of the present invention showed values that the plasticity ratio and cumulative plastic deformation ratio exceeded that of the comparative H-section steels (J to R), and showed excellent plastic deformation ability. The comparative H-section steel has a result described later that the rigidity after buckling of the flange is low, so that the resistance to buckling is small and buckling is induced early.
[0018]
[Table 3]

[0019]
(Influence of width-thickness ratio, compression test result)
FIG. 1 is a result of a column compression test for evaluating the buckling resistance of a H-section steel according to an embodiment of the present invention against a compressive load. The material characteristics and local buckling of the H-shaped steel flange part were determined by the local buckling test called the short column compression test that compresses in the axial direction for H-section steels with different values (B / 2T divided by the web thickness T). It is the result of investigating the correlation with the generation behavior.
[0020]
That is, the relation between the width-thickness ratio of the flange part of the test specimen and the buckling occurrence limit strain is substantially inversely proportional (negative relation), and in general H-section steel (low n-value steel) having a small work hardening index value, When the width-thickness ratio is greater than about 8, the buckling occurrence limit strain is drastically reduced. On the other hand, the H-section steel (high n-value steel) of the present invention having a large work hardening index does not rapidly decrease the buckling occurrence limit strain even in the range where the width-thickness ratio is greater than about 8, and is plastic. Deformation ability has been improved.
[0021]
In the Building Standards Law, the width-to-thickness ratio of the beam member flange, which is said to be deformable, is determined to be 7.5 or less, and the damage that normally occurs in this range is not buckling but breakage due to plastic deformation. It is determined by the deformation ability. On the other hand, it is said that the deformability is inferior to that in the range where the width-thickness ratio is 8 or more, and the damage that usually occurs in this range is buckling. However, in the present invention, while the flange width-thickness ratio is 8 or more, the plastic deformation ability is improved as described above, and buckling is less likely to occur.
[0022]
(Influence of work hardening index, compression test result)
FIG. 2 is a result of a compression test for evaluating the buckling resistance of a H-section steel according to an embodiment of the present invention against a compressive load, and H-section steels having different work hardening indices are the same as in FIG. This is a column compression test. That is, a tensile test was performed using a tensile test piece taken from the flange with the longitudinal direction of the test piece aligned with the axial direction of the H-section steel, and a work hardening index (stress in the range of 2% to 6% strain after yielding The number of powers when the power is arranged by the power of the distortion was measured.
[0023]
In FIG. 2, when the flange width-thickness ratio is 10, the H-section steel of the present invention having a work hardening index of 0.2 or more (black circle in FIG. 2) and the conventional work hardening index of less than 0.2. H-shaped steels (white circles in FIG. 2) are compared.
[0024]
The conventional H-section steel with a work hardening index of less than 0.2 (white circles in Fig. 2) has a buckling limit strain of less than 0.6%, which is four times the yield strain (0.16 to 0.21% for SN490). While the deformation capacity can be obtained less than the H-shape steel of the present invention having a work hardening index of 0.2 or more (black circle in FIG. 2), the buckling occurrence limit strain is 0.8% or more, and the yield strain About 6 times as large as the deformation capacity.
[0025]
In other words, the H-shape steel of the present invention has a large hardening gradient (high work hardening index), so that the range of plastic deformation is widened, although the width-thickness ratio is usually in the range where damage occurs due to plastic buckling. As the plastic range is expanded, local plastic buckling is suppressed.
[0026]
(Test method)
FIG. 3 is an explanatory diagram showing a compression test and a cantilever repeated bending test for evaluating an H-section steel according to an embodiment of the present invention. That is, (a) applies a compressive force to the H-section steel 10 and measures the load deformation relationship, and applies a uniform compressive stress to the flange and web of the H-section steel 10 over the material axis. .
[0027]
On the other hand, (b) measures the load deformation relationship by applying a positive / negative alternating horizontal force to the other end of the cantilever (H-shaped steel) 11 whose one end is a fixed end. And the web is subjected to compressive stress that is not uniform (triangular distribution) across the material axis. (Flange on one side is compressed, tension on the other is tensile)
In the cantilever repeated bending test, the distance to the loading point is 2500 mm, a horizontal force of alternating positive and negative is applied, and the load deformation relationship is measured.
[0028]
The length of the test body in the compression test was set to the smaller length of 3 times the long side and 5 times the short side, and the applied force was a central compression monotonic load. The value obtained by dividing the displacement between the loading plates by the length of the test body was the strain of the test body, and the value obtained by dividing the loading load by the cross-sectional area of the test body was the stress of the test body.
[0029]
(Effect of stress increase rate, results of repeated bending test)
FIG. 4 is a result of repeated loading tests of the cantilever shown in FIG. 3 in order to evaluate the buckling resistance and the fracture resistance against bending load of the H-section steel according to one embodiment of the present invention. .
FIG. 3 shows the results of repeated loading tests on cantilevers shown in FIG. 3 for various H-shaped steels.
[0030]
That is, in the H-section steel of the present invention having a work hardening index of 0.2 or more and a flange width-thickness ratio of 7.0, the rate of increase in the stress of the flange (the plastic deformation stress YB in a uniform manner with respect to the yield stress YP). The ratio of stress increase rate α2 (YB / YP)) is 1.28 (hereinafter referred to as 1.28H section steel) and that of flange is 1.37H (hereinafter referred to as 1.37H section steel). The plastic deformation ability of the material was compared by the cumulative plastic deformation magnification described later. That is, the 1.28H section steel has a cumulative plastic deformation ratio of 20, whereas the 1.37H section steel has a cumulative plastic deformation ratio of 48.
[0031]
(Cumulative plastic deformation ratio)
FIG. 5 is a load-displacement curve for explaining the cumulative plastic deformation magnification. In FIG. 5, the elastic deformation at the time when the entire cross section of the H-shaped steel yields (when the total plastic moment Mp) is taken as “yield deformation δp”, for example, the i-th loading is started from point A in the figure, When deformation is performed up to point B and then unloading and plastic deformation at point C remains, the distance from point A to point C is defined as the residual deformation amount δi (absolute value of the plastic deformation amount), and this residual deformation amount δi is defined as The value divided by the yield deformation δp is defined as the i-th plastic deformation magnification (δi / δp).
[0032]
Furthermore, when the load is started from point C in the figure as the i + 1th loading, and deformed to the point D by the load of the opposite phrase to the i-th loading, and then unloaded and plastic deformation at the point E remains, the point C The distance from point E to point E is the residual deformation amount δi + 1 (absolute value of the plastic deformation amount), and the value obtained by dividing the residual deformation amount δi + 1 by the yield deformation δp is the plastic deformation magnification (δi + 1 / δp). To do. The jth cumulative plastic deformation magnification is obtained by accumulating the plastic deformation magnification from the first time to a predetermined number j.
[0033]
(Charpy absorbed energy)
The 0 degree C Charpy absorbed energy of the flange was 250 J for the 1.28H section steel and 160 J for the 1.37H section steel. Despite the high 0 ° C Charpy absorbed energy of the 1.28H-shaped steel flange, a ductile crack finally develops from the weld toe at the end of the beam, which extends and breaks the flange, resulting in increased yield strength. Were determined.
[0034]
On the other hand, despite the low 0 degree C Charpy absorbed energy of the 1.37H section steel flange, the cumulative plastic deformation ratio is as high as 48, about twice that of the 1.28H section steel. This is because the H-section steel having a higher rate of stress increase suppresses the local distortion at the toe end of the welded end of the beam end with respect to the deformation of the beam end on the same loading side.
[0035]
(Flange stress increase rate)
Furthermore, instead of calculating the moment gradient in the vicinity of the beam-column joint of the building structure, or instead of calculating the rising gradient of the plastic deformation stress of the material, the material is used with the stress increase rate of the flange, that is, the yield ratio (YR). You may prescribe. That is, if the stress increase rate of the flange is 1.33 or more, that is, the yield ratio (YR) is 75% or less, the plastic deformation can be expanded and the deformation capability can be secured.
[0036]
(Strain range for calculating work hardening index)
Next, a strain range for calculating the work hardening index will be briefly described.
In calculating the work hardening index, the strain range of 6% from the strain that started work hardening is based on the average strain range that occurs at the beam end of the building structure during normal and earthquake. .
[0037]
FIG. 7 shows the average deformation (vertical axis) of the building structure with respect to the strength (horizontal axis) of the building structure, and the amount of change (the amount of rotation) of the angle between the column and the beam. , Radians), and the rate of increase in stress obtained by dividing the maximum stress of the material used by the yield stress is used as a parameter. In FIG. 7, when the strength of the building structure is relatively small and the parameter is small, the average angle change amount of the building structure is 0.02 (2%).
[0038]
FIG. 8 shows the skewness (vertical axis) of the flange of the building structure relative to the relative rotation angle (horizontal axis) of the building structure. In some buildings, there are beam ends that are damaged and beam ends that are not relatively damaged. If this variation is around 4%, the maximum rotation angle (horizontal axis) is 6% at the beam end that is most damaged. It is thought that it becomes.
[0039]
In FIG. 8, in the case of the high yield ratio material which is the H-section steel of the present invention, the average strain (vertical axis) of the beam flange is about 6% with respect to the maximum rotation angle (horizontal axis) of 6%. This indicates that the distortion at the beam end of the building steel frame is in the range of up to about 6%, and the occurrence of a further strain area is rare on the average locally anyway.
[0040]
Further, since a normal steel material has a yield shelf of about 2%, the strain is within the range of 6% strain and strain at which the yield shelf is finished and work hardening starts. In other words, since the work hardening index is calculated in the range below the maximum strain actually received by the building steel, excluding the elastic range and the yield shelf range, it is possible to properly express the plastic behavior of the building steel. . The 2% is a guideline, and the effect of the present invention is exhibited even when 3% to 6%.
[0041]
(Guidelines for selecting chemical components)
In the present invention, the manufacturing method of the H-section steel is not limited, and any method such as rolling or welding may be used as long as it satisfies the predetermined characteristics. In addition, the above characteristics can be imparted by controlling the chemical composition of the H-shaped steel and the rolling conditions of the steel sheet before welding, for example, or by subjecting the H-shaped steel during or after rolling to heat treatment or processing. The chemical composition and production conditions are not particularly limited.
[0042]
However, as chemical composition, C: 0.02% to 0.22%, Si: 0.05% to 0.35%, Mn: 0.45% to 1.60%, P: 0.020% or less, S: 0.008% or less. A carbon equivalent of 0.46% or less and a weld cracking sensitivity index of 0.26% or less is preferable. The reason why the steel having such a component range is preferable is as follows.
[0043]
C: If the content is less than 0.02%, sufficient strength cannot be obtained, and if it exceeds 0.22%, the weldability deteriorates. Therefore, the C content is preferably 0.02% or more and 0.22% or less.
[0044]
When Si is less than 0.05%, sufficient deoxidation is not performed, and a healthy steel material cannot be obtained. If it exceeds 0.35%, the weldability deteriorates. Therefore, the Si content is preferably 0.05% or more and 0.35% or less.
[0045]
If Mn is less than 0.45%, sufficient strength cannot be obtained, and if it exceeds 1.60%, weldability deteriorates. Therefore, the Mn content is preferably 0.45% or more and 1.60% or less.
[0046]
When P exceeds 0.020%, the toughness and weldability of the base metal deteriorate, so the P content is preferably 0.020% or less.
[0047]
S: If it exceeds 0.008%, the toughness of the base metal, the weldability, and the toughness of the welded portion deteriorate, so the amount of S is preferably 0.008% or less.
[0048]
When the carbon equivalent exceeds 0.46%, the weldability is remarkably deteriorated, and preheating and afterheating are required. Therefore, the carbon equivalent is preferably 0.46% or less. The carbon equivalent was calculated by the following formula: carbon equivalent = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14.
[0049]
Weld cracking susceptibility: If it exceeds 0.26%, the weldability is remarkably deteriorated and cracks are generated in the weld. Accordingly, the weld crack sensitivity is preferably 0.26% or less. The weld crack sensitivity was calculated by the formula of weld crack sensitivity = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B.
[0050]
For steel plates having such a composition, by controlling the rolling conditions, or by applying heat treatment or processing to the H-shaped steel during or after rolling, for example, the web is controlled and the flange is air-cooled after rolling. By applying the above, the above characteristics can be imparted by making the metal structure of the web, for example, a composite structure of ferrite and bainite or ferrite and martensite and the flange of a ferrite / pearlite structure.
[0051]
[Embodiment 2]
FIG. 6 illustrates an H-shaped steel excellent in earthquake resistance according to another embodiment of the present invention, and (a) is a perspective view showing a steel structure using the H-shaped steel as a beam, (B) is a force distribution diagram showing the distribution of moment acting on the beam and the tensile stress generated on the beam flange. (C) is the distribution of the tensile stress generated on the beam flange after plastic deformation occurs on the beam. FIG.
[0052]
In FIG. 6A, a bracket 2 made of H-section steel described in Embodiment 1 of the present invention is joined to a column 1, and a beam 3 is installed on the bracket 2 via a splice plate 4.
[0053]
In FIG. 6B, since the maximum moment acts on the joint between the bracket and the column (point C in the figure), when a predetermined external force acts on the structure, this portion is first applied to the yield stress YP. And plastic deformation occurs. The moment at this time is called a plastic moment and will be described below.
[0054]
(Expansion of plastic deformation range)
In FIG. 6C, the range of plastic deformation is enlarged (range from point C to point X in the figure). That is, when the moment (maximum moment) acting on the point C exceeds the plastic moment, the material at the point C is work-hardened, and therefore bears a stress sufficient to withstand this moment. On the other hand, a plastic moment acts on the point X at the boundary between the plastic deformation and the elastic region, and a yield stress YP is generated as a tensile stress.
[0055]
In other words, the ratio SC / YP (stress increase rate in the range from point X to point C) between the tensile stress SC at the flange point C and the tensile stress at the flange point X (same as the yield stress YP) is the point C Is equal to the ratio MC / MX of moment MC at point X and moment MX at point X (moment increase rate in the range from point X to point C).
[0056]
That is, when viewed from the material of the flange portion, when the moment is increased and the point C becomes in a uniform state, the stress YB in the uniform direction is larger than the tensile stress SC. YB / YP ratio of stress YB at point C and tensile stress at point X of the flange (same as yield stress YP) YB / YP (stress increase rate in the range of point X to point C, stress in the strain range of 6% or more) Is the ratio MC / MX between the moment MC at the point C and the moment MX at the point X (the moment increase rate in the range from the point X to the point C and the moment gradient in the vicinity of the position where the maximum moment is generated) ) Will be greater.
[0057]
Conversely, the stress increase rate YB / YP (same as the stress increase gradient in the strain range of 6% or more) is smaller than the moment increase rate MC / MX (same as the moment gradient near the position where the maximum moment is generated). In such a case, since the tensile stress sufficient to withstand the moment is not generated, the flange is damaged.
[0058]
[Embodiment 3]
The H-section steel having excellent seismic resistance according to another embodiment of the present invention has an increase gradient of the plastic deformation stress in the strain range of 6% or more in the second embodiment with respect to the yield stress YP. It is limited to the stress increase rate α2 (YB / YP), which is the ratio of the stress YB in the uniform stretch, and the moment gradient in the vicinity of the position where the maximum moment is generated is separated from the beam-to-column joint by half of the beam length H. The moment increase rate α1 (MC / MH), which is the ratio of the moment MC at the beam-column joint to the moment MH at the selected position, is limited.
[0059]
(Stress increase rate α2)
When the increase in plastic deformation stress in the strain range of 6% or more is almost saturated and becomes uniform, the stress YB at this time is displayed as a ratio to the yield stress YP, and the stress increase rate α2 is clearly specified. To do.
[0060]
(Plastic plasticization region)
Further, in FIG. 6C, the stress increase rate YB / YP is clearly defined with the position of the point X (the plasticized region of the beam) being half of the beam D. In other words, the plasticization region of the beam is said to be 1.5D when the beam end is closer to the elastic behavior than before, that is, when the slope of the stress increase rate of the steel material due to plasticization of the beam end is not so small. .
[0061]
However, as the end of the beam moves away from the elastic behavior and the degree of plasticization progresses, when the slope of the rate of increase in stress of the steel material due to plasticization (the degree of work hardening) decreases, plastic deformation concentrates on the end. Thus, the plasticized region is smaller than 1.5D. Therefore, based on the results of the numerical analysis, the plasticized region (the position of the point X) is set at a position separated from the beam end (the position of the point C) by 1/2 of the beam length D. (The Japan Welding Association, Earthquake damage to steel structures and steel seminar texts, pp.65-66)
[Embodiment 4]
FIG. 9 is a front view showing a steel structure using an H-shaped steel excellent in earthquake resistance according to another embodiment of the present invention for a bracket. In FIG. 9, a bracket 2 made of H-section steel described in Embodiment 1 of the present invention is joined to a pillar 1, and a beam 3 is installed on the bracket 2 via a splice plate 4.
[0062]
In addition, this invention is not limited to comprising all the brackets of this steel structure with the H-section steel of this invention, You may employ | adopt the H-section steel of this invention only for the predetermined | prescribed hierarchy. Furthermore, it is not limited to what joins a pillar and a beam via a bracket, You may join the beam which consists of H-section steel of this invention directly to a pillar.
[0063]
Furthermore, when designing the column to be weaker than the beam, the column may be made of the H-shaped steel of the present invention. Further, the diagonal member 5 may be made of the H-shaped steel of the present invention to improve the earthquake resistance.
[0064]
【The invention's effect】
As described above, according to the present invention, the plasticizing region can be expanded without locally concentrating the plastic deformation generated in the flange with respect to the ultimate large deformation at the time of a large earthquake. In addition, even when the flange is thin, it is possible to obtain an H-shaped steel having excellent plastic deformation ability that hardly causes local buckling.
[0065]
Therefore, by using the H-section steel of the present invention, it becomes possible to improve the earthquake resistance of the structure without increasing the steel weight of the H-section steel, and when a large earthquake occurs, a high-rise building It is possible to obtain a remarkable effect that disasters such as damage can be prevented.
[Brief description of the drawings]
FIG. 1 is a result of a column compression experiment for evaluating the buckling resistance of a H-section steel according to an embodiment of the present invention against a bending load.
FIG. 2 is a result of a column compression experiment for evaluating buckling resistance against bending load of an H-section steel according to an embodiment of the present invention.
FIG. 3 is an explanatory diagram showing a short column compression test and a cantilever repeated bending test for evaluating an H-section steel according to an embodiment of the present invention.
FIG. 4 shows the results of a cantilever repeated bending test for evaluating the buckling resistance of a H-section steel according to an embodiment of the present invention against a bending load.
FIG. 5 is a load-displacement curve illustrating cumulative plastic deformation magnification.
FIG. 6 is a perspective view showing a steel structure using an H-section steel excellent in earthquake resistance according to an embodiment of the present invention.
FIG. 7 represents an average deformation of a building structure with respect to the strength of the building structure.
FIG. 8 shows the degree of distortion of the flange of the building structure relative to the relative rotation angle of the building structure.
FIG. 9 is a front view showing a steel structure using an H-shaped steel excellent in earthquake resistance according to another embodiment of the present invention for a bracket.
[Explanation of symbols]
1 pillar
2 Bracket
3 beams
4 Splice plate

Claims (4)

The work hardening index n, which is the number of powers when the stress in the strain range up to 6% after starting work hardening is displayed as the power of strain, is 0.2 or more,
Excellent in earthquake resistance, characterized by having a flange made of a steel material having a stress increase rate α2 (YB / YP) of 1.33 or more, which is a ratio of plastic deformation stress YB in uniform strain to yield stress YP H-shaped steel. An H-shaped steel with excellent earthquake resistance that is placed in a building or civil structure and receives a load that generates a moment gradient in the longitudinal direction.
The width-thickness ratio (B / 2T) of the flange width B and the flange thickness T is 10 or less,
The work hardening index n, which is the number of powers when the stress in the strain range up to 6% after starting work hardening is displayed as the power of strain, is 0.2 or more,
Furthermore, since the rising gradient of the plastic deformation stress in the strain range of 6% or more is larger than the moment gradient in the vicinity of the position where the maximum moment is generated, the plastic region generated at the position where the maximum moment is generated expands toward the periphery. H-section steel with excellent earthquake resistance. In building or civil engineering structure, it is a H-shaped steel with excellent earthquake resistance, which is a beam member or a beam-joining bracket joined to a column,
The width-thickness ratio (B / 2T) of the flange width B and the flange thickness T is 10 or less,
The work hardening index n, which is the number of powers when the stress in the strain range up to 6% after starting work hardening is displayed as the power of strain, is 0.2 or more,
Further, the rate of increase in stress α2 (YB / YP), which is the ratio of the plastic deformation stress YB in the uniform to the yield stress YP, is a column with respect to the moment MH at a position separated from the column-beam joint by half of the beam length H. When the moment increase rate α1 (MC / MH), which is the ratio of the moment MC at the beam joint, is larger (α2> α1), the plastic zone generated at the beam-to-column joint is the center in the longitudinal direction of the beam or beam joint bracket. H-section steel with excellent earthquake resistance, characterized by expanding toward the side. The beam member to be joined to the column or the bracket for beam joining has a width-thickness ratio (B / 2T) of the flange width B to the flange thickness T of 10 or less, and stress in the strain range up to 6% after work hardening is started. Is a H-shape steel with excellent seismic resistance formed by an H-section steel with excellent seismic resistance, whose work hardening index n is 0.2 or more. Steel structure,
The stress increase rate α2 (YB / YP), which is the ratio of the plastic deformation stress YB of the H-shaped steel flange to the yield stress YP of the H-shaped steel flange, is from the beam-to-column joint to the beam height H in the steel structure. Since the moment increase rate α1 (MC / MH), which is the ratio of the moment MC at the beam-column joint to the moment MH at a position separated by half, (α2> α1), the plastic zone generated at the beam-column joint is Steel structure using H-shaped steel with excellent earthquake resistance, characterized by expanding toward the longitudinal center of the beam or beam joint bracket.

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