JP4007726B2

JP4007726B2 - Ramen structure

Info

Publication number: JP4007726B2
Application number: JP22235899A
Authority: JP
Inventors: 雅史秦
Original assignee: Okumura Corp
Current assignee: Okumura Corp
Priority date: 1999-08-05
Filing date: 1999-08-05
Publication date: 2007-11-14
Anticipated expiration: 2019-08-05
Also published as: JP2001049740A

Description

【０００１】
【発明の属する技術分野】
本発明は、柱・梁接合部での脆性破壊を防止し、エネルギ吸収能を高めることができるラーメン構造に関する。
【０００２】
【従来の技術】
従来のラーメン構造として、例えば図７に示すようなものが知られている。このラーメン構造は、図７(Ａ)に示すように、立設したＨ形鋼からなる複数の柱２１を、Ｈ形鋼の梁２２により複数層に溶接で連結した多層矩形ラーメンであり、各梁２２の両端の柱２１との溶接接合部は、図７(Ｂ)に示すように、梁２２のＨ形鋼端のウェブにスカラップ２３を切欠いて、梁,柱Ｈ形鋼の両フランジの当接部を開先をもつ突合せ溶接２４で接合し、スカラップ２３によって露出した梁Ｈ形鋼端のフランジの裏面に、補強板２５を当ててすみ肉溶接２６で接合している。
上記柱・梁の溶接接合部は、このラーメン構造に地震等による過大外力が加わったとき、梁２２側の両端が最初に塑性変形して全塑性モーメント(図８のＭp1,Ｍp2参照)を伝えつつ回転する塑性ヒンジになるように、両Ｈ形鋼の寸法および溶接継手の形状,材質などが決められていて、いわゆる梁降伏先行型の設計が行なわれている。
【０００３】
ところが、神戸大震災やノースリッジ地震における鉄骨構造物の被害調査の結果、塑性ヒンジによる大きな変形能が期待される溶接接合部の突合せ溶接２４に、図７(Ｂ)に示すような割れに起因する脆性破壊２７が多発していることが明かになった。なお、図８は、両端が塑性ヒンジになった上下の梁２２に加わる曲げモーメントの分布を示すモーメント図であり、左右端の塑性ヒンジにおけるモーメントは、夫々Ｍp1,Ｍp2であり、剪断力Ｑは、梁長さをＬとするときＱ＝(Ｍp1＋Ｍp2)／Ｌとなる。
【０００４】
そこで、このような梁両端の柱との溶接接合部における脆性破壊を防止するため、米国ではDog-bone仕口と呼ばれる図９に示すような対策が採られている。この対策は、柱(２１')・梁(２２)接合部から離れた梁２２の中央側において、Ｈ形鋼２８の上下のフランジ２８a,２８bに、図９(Ａ)の平面図に示すような切欠き２９を設けて断面積減少部とし、梁両端の溶接接合部３０で脆性破壊が生じる前に、切欠き２９をもつＨ形鋼を塑性変形させて塑性ヒンジにするものである。
【０００５】
【発明が解決しようとする課題】
しかしながら、図９に示した従来のDog-bone仕口をもつ梁２２は、地震等の過大外力で生じる曲げモーメントにより圧縮応力が加わる側のフランジが、断面積が減少する切欠き２９の箇所で座屈を起こして面外に膨出し易いため、切欠き２９をもつＨ形鋼２８に補剛材が必要となり、あるいは床スラブを補剛材として機能させるには、切欠き２９をもつＨ形鋼２８に接合材を設ける必要がある。しかるに、Ｈ形鋼２８のフランジ２８a,２８bに切欠き２９があるため、面積的に余裕がなく、補剛材や接合材を設けることが難しいという問題がある。
【０００６】
そこで、本発明の目的は、梁の断面積を減少することなく材質を変化させることによって梁端から離れた箇所に塑性ヒンジを形成することによって、柱・梁接合部での脆性破壊を防止しつつ、梁のエネルギ吸収能を高めることができるラーメン構造を提供することにある。
【０００７】
【課題を解決するための手段】
上記目的を達成するため、本発明のラーメン構造は、Ｈ形鋼で形成される梁の大部分を、所定の鋼材で形成するとともに、上記梁の両端部から所定距離隔たったＨ形鋼の上下のフランジに、外縁に向かって広がる１対の台形の切欠きを夫々設け、これらの切欠きに上記所定の鋼材よりも低い降伏点をもつ鋼板を嵌め込んで溶接接合したことを特徴とする。
【０００８】
上記ラーメン構造では、梁の大部分を所定の鋼材のＨ形鋼で形成し、梁の両端部から所定距離隔たったＨ形鋼の上下のフランジに、外縁に向かって広がる１対の台形の切欠きを夫々設け、これらの切欠きに上記所定の鋼材よりも低い降伏点をもつ鋼板を嵌め込んで溶接接合している。
上下のフランジに切欠きを設け、この切欠きに低降伏点の鋼板を嵌め込んで溶接接合したＨ形鋼の部分は、所定の鋼材のＨ形鋼からなる梁の両端部よりも降伏点が低い分だけ小さいモーメントで、その全断面が塑性変形して最初に塑性ヒンジになり、全塑性モーメントを伝えつつ回転するが、塑性ヒンジの回転能は降伏点が低い分だけ逆に大きい。従って、塑性ヒンジは、柱の傾きに対応する変形角と両塑性ヒンジ間の梁の部材角との和に対応して十分回転できて、地震等のエネルギを効果的に吸収し、従来のラーメン構造に比して地震時の水平変位を略３０％抑えることができる。
また、上記梁に生じる最大剪断力は、梁のスパンが短くなるため、低降伏点鋼材を用いた塑性ヒンジにおける全塑性モーメントが小さくても、従来のように梁のスパン全体に上記所定の鋼材を用い,梁端部に塑性ヒンジが生じるラーメン構造の場合と同程度の剪断力を維持することができる。
なお、低降伏部は、従来のように梁のフランジを切り欠いたままのものではないので、座屈の虞もなく、フランジ切欠部に別途補剛材や接合材を設ける必要もないうえ、低降伏点鋼材からなる形鋼を継手板付きの高力ボルト接合で所定の鋼材に連結するものでもないので、嵩ばらず、施工が容易になる。
【０００９】
【００１０】
【００１１】
【００１２】
【００１３】
【発明の実施の形態】
以下、本発明を図示の実施の形態により詳細に説明する。図１は、本発明のラーメン構造の一例を示す全体立面図であり、このラーメン構造は、図７と同じＨ形鋼の柱２１を水平方向に複数層で連結する梁１を、梁の大部分を占める比較的高い降伏点(以下、便宜上、高降伏点と称す)をもつＨ形鋼２と、梁両端部から所定距離Ｌ₁隔たった箇所に上記高降伏点よりも低い降伏点をもつ鋼板を含むＨ形鋼からなり,塑性ヒンジとなりうる低降伏部３とで構成している。なお、低降伏部３の長さＬ₂は、Ｈ形鋼の高さ程度にしている。
上記低降伏部３,３は、図６を参照して後述するように、高降伏点をもつＨ形鋼２,２の梁１の両端部からＬ ₁ 隔たったＨ形鋼の上下のフランジに長さＬ ₂ の１対の切欠きを設け、この切欠に上記高降伏点よりも低い降伏点をもつ鋼板を嵌め込んで溶接接合して作られる。一方、梁１の両端部と柱２１,２１は、図７(Ｂ)で述べたと同じ溶接接合で剛接されている。
【００１４】
図２は、ラーメン構造に地震等の過大外力が加わって、柱(２１)・梁(１)接合部に先立って低降伏部３が塑性ヒンジになったときの梁の曲げモーメント分布図である。塑性ヒンジとなった左右の低降伏部３,３が伝達する全塑性モーメントを夫々Ｍp1',Ｍp2'とすると、剪断力Ｑ'は、塑性ヒンジ間長さをＬ'とするときＱ'＝(Ｍp1'＋Ｍp2')／Ｌ'となる。
上記ラーメン構造は、図７で述べた従来例と同等の耐力をもつ必要があるから、曲げモーメントを表わす直線を図２の一点鎖線で示すように両側へ延ばしたときの梁端部での曲げモーメントが、従来の図８で述べた梁両端の全塑性モーメントＭp1,Ｍp2に等しくなければならず、そうすれば、曲げモーメント図の微係数である剪断力も自ずと等しくなるので、最大剪断力Ｑ'も従来例の最大剪断力Ｑと等しくできる。
【００１５】
図３は、ラーメン構造の耐力を上述のように従来と同程度に維持しつつ、従来の柱・梁接合部での脆性破壊を防止し、梁のエネルギ吸収能を高めるために、低降伏部３を設ける所定位置Ｌ₁と低,高降伏点鋼材の降伏点比σy'／σｙの関係式を求める手法を示している。但し、以下の計算は、長さＬ ₂ の低降伏部３のＨ形鋼が、上下のフランジのみならず全体が低降伏点鋼材からなると仮定している。
いま、梁断面が一定で、図３(Ａ)の如く梁両端から所定距離Ｌ₁だけ隔たった箇所に低降伏部(塑性ヒンジ)３を設けるとし、図８で述べた梁両端の塑性ヒンジの全塑性モーメント,剪断耐力(最大剪断力)を夫々Ｍp(＝Ｍp1,Ｍp2),Ｑu、図３に示す低降伏部３の塑性ヒンジの全塑性モーメント,剪断耐力(最大剪断力)を夫々Ｍp'(＝Ｍp1,Ｍp2),Ｑu'とすれば、
Ｑu＝２Ｍp／Ｌ＝２σyＺp／Ｌ…(1)
Ｑu'＝２Ｍp'／Ｌ'＝２σy'Ｚp／Ｌ'…(2)
但し、Ｚpは梁の塑性断面係数
上記低降伏部３が梁両端に先立って塑性ヒンジになるためには、図３の梁の剪断耐力Ｑu'が図８の梁の剪断耐力Ｑuよりも小さくなければならないから、
Ｑu'≦Ｑuが成立し、図３(Ａ)の梁長さの関係からＬ'＝Ｌ−２Ｌ₁…(3)が成立する。そこで、上記不等式に式(1),(2),(3)を代入してこの不等式をＬ₁について解くと、
Ｌ₁≦Ｌ(１−σy'／σy)／２…(4) が求まる。
【００１６】
一般に、低降伏部３の低降伏点鋼材の降伏点σy'は、１０〜２５kgf/mm²で、高降伏点鋼材２の降伏点σy＝３０〜５０kgf/mm²である。従って、選択した鋼材の降伏点比σy'／σｙは、１／３程度であり、この降伏点比に応じて式(4)の等号が成り立つような所定距離Ｌ₁に設定すれば、剪断耐力Ｑu'が図８の梁の剪断耐力Ｑuと略等しくなり、図２で既述の如く、剪断力の積分値である曲げモーメントＭも、図３(Ａ)に示すように、塑性ヒンジ３における値Ｍp'を梁端まで延長したときの値が、図８の従来例の梁両端の全塑性モーメントＭp(＝Ｍp1,Ｍp2)に略等しくなり、このラーメン構造の耐力を従来例の耐力と略同等に維持できるのである。
【００１７】
図３(Ｃ)は、左右の低降伏部３が塑性ヒンジになった場合の梁１の変形状態を示している。左右の低降伏部３が塑性ヒンジになる直前には、梁１は、図３(Ｂ)に示すように両端に作用する材端モーメントによって変形角θで変形するが、低降伏部３が塑性ヒンジになると、図３(Ｃ)に示すように左右の塑性ヒンジが全塑性モーメントＭp'を伝えつつ節点回転角θ'で回転する。この節点回転角θ'は、図３(Ｂ)に示す変形角θと塑性ヒンジ間の梁の部材角Ｒとの和であり、部材角Ｒは、幾何学的関係よりＲ＝２θＬ₁／Ｌ'となるから、
θ'＝θ＋Ｒ＝θ＋２θＬ₁／(Ｌ−２Ｌ₁)＝θＬ／(Ｌ−２Ｌ₁)…(5) となる。
【００１８】
塑性ヒンジの節点回転角θ'は、純幾何学的には上式(5)で表わされるが、実際には低降伏鋼材が破断までにどれだけ塑性変形するか,つまり低降伏鋼材の伸び能力によって決まり、鋼材の塑性ヒンジの回転角は、一般に鋼材の降伏点の逆数に比例する。従って、低降伏点,高降伏点鋼材の回転角を夫々θ',θとすれば、θ'／θ＝σy／σy'となる。ここで、段落[0015]で述べたようにσy'／σy≧１／３であるので、所定距離Ｌ₁を求める式(4)中の−σy'／σyは、−σy'／σy≦−１／３となって、式(4)の右辺は最大でもＬ(１−１／３)／２＝Ｌ／３に限られる。
よって、低降伏部３を設ける所定位置Ｌ₁は、
Ｌ₁≦min{Ｌ(１−σy'／σy)／２,Ｌ／３}…(6) で与えられる。
図４は、高降伏点鋼材に対する低降伏点鋼材の降伏点比α＝σy'／σyを横軸に、高降伏点鋼材に対する低降伏点鋼材の塑性ヒンジの回転角倍率を縦軸にとって、両者の関係を表わしている。図４の破線で示すように、降伏点比が0.33〜0.5の低降伏点鋼材を用いれば、２〜３倍の塑性ヒンジ回転能が得られることが判る。
【００１９】
図５は、本発明の実施例ではなく、参考例としてのラーメン構造を示す詳細立面図である。このラーメン構造の低降伏部は、柱２１に溶接接合３０で剛接された梁１の高降伏点σyをもつＨ形鋼２の端部から上記式(6)を満たす所定距離Ｌ₁に設けられた同一断面形状の低降伏点σy'をもつＨ形鋼３からなる。Ｈ形鋼３の柱側端は、Ｈ形鋼２の上下フランジとウェブに跨るように当てた継手板５,５,５を介して高力ボルト６でＨ形鋼２に接合される一方、反対側端は、突合せ溶接４でＨ形鋼２に接合されている。
【００２０】
図５のラーメン構造は、地震等の過大外力に対して次のように挙動する。
低降伏部のＨ形鋼３は、過大外力が加わると降伏点σy'が低い分だけ小さいモーメントＭp'で梁端の溶接接合部３０よりも先に塑性変形して塑性ヒンジとなり、この全塑性モーメントＭp'を伝えつつ回転するが、回転能は降伏点の逆数に比例して大きくなる。従って、上記塑性ヒンジは、図３(Ｃ)に示すように、柱の傾きに対応する変形角θと両塑性ヒンジ間の梁の部材角Ｒとの和であるθ'まで十分回転できて、過大外力のエネルギを効果的に吸収し、図７,８で述べた従来のラーメン構造に比して水平変位を略３０％も抑えることができる。
また、低降伏部のＨ形鋼３は、剪断耐力Ｑ'が、図８に示す従来のラーメン構造の剪断耐力Ｑと略等しくなるような材質および所定距離Ｌ₁で高降伏点σyをもつＨ形鋼２の間に設けられているので、段落[0015]で述べたように従来のラーメン構造と略同等の耐力を発揮することができる。
なお、低降伏部のＨ形鋼３は、図９で述べた従来の梁２２と異なりフランジ２８a,２８bに切欠き２９を作ったものではないので、座屈の虞もなく、座屈対策として切欠き部に補剛材や接合材を設ける必要もないのは勿論である。
さらに、上記式(6)を満たすので、梁両端の溶接接合部３０に必ず先立ってＨ形鋼３が塑性ヒンジになるから、上述の作用効果が確実に奏される。
【００２１】
なお、上記参考例では、低降伏部のＨ形鋼３の片端のみを溶接接合とし、もう片側を高力ボルト接合としているので、溶接割れに起因するＨ形鋼３の脆性破壊の発生を抑え、塑性ヒンジの作用を助成できるという利点がある。
【００２２】
図６は、本発明のラーメン構造の一例を示す詳細平面図および断面図である。このラーメン構造の低降伏部は、柱２１'に溶接接合３０で剛接された高降伏点σyをもつＨ形鋼２からなる梁１の端部から上記式(6)を満たす所定距離Ｌ₁の箇所で、上下のフランジ２a,２bに図６(Ａ)の平面図に示すような外縁に向かって広がる１対の台形の切欠き７を設け、この切欠きに低降伏点σy'をもつ同じ板厚の鋼板８を嵌め込んで溶接接合してなる。
図６の実施の形態では、低降伏部８が、梁１に曲げモーメントが加わったときに最大の圧縮または引張応力が生じるＨ形鋼の外縁部であるフランジに設けられている。従って、この低降伏部８が確実に最初に塑性変形して塑性ヒンジになるうえ、図５の参考例に示した継手板５を介して低降伏点をもつＨ形鋼３を高力ボルト接合する場合に比して、外方突出部がなくて嵩ばらず、現場施工も容易になるという利点がある。
【００２３】
【００２４】
【発明の効果】
以上の説明で明らかなように、本発明のラーメン構造は、梁の大部分を所定の鋼材のＨ形鋼で形成し、梁の両端部から所定距離隔たったＨ形鋼の上下のフランジに、外縁に向かって広がる１対の台形の切欠きを夫々設け、これらの切欠きに上記所定の鋼材よりも低い降伏点をもつ鋼板を嵌め込んで溶接接合しているので、低い降伏点をもつ鋼板を溶接接合したＨ形鋼が、低降伏点ゆえ回転能の大きい塑性ヒンジになって、地震等のエネルギを効果的に吸収して水平変位を抑えることができるとともに、両端が塑性ヒンジになる従来の梁と同等の剪断力および曲げモーメントに耐えることができ、梁の耐力を上記従来の梁と同程度に維持することができる。また、上記Ｈ形鋼は、従来のように梁のフランジを切り欠いたままのものではないので、座屈の虞もなく、フランジ切欠部に別途補剛材や接合材を設ける必要もないうえ、低降伏点鋼材からなる形鋼を継手板付きの高力ボルト接合で所定の鋼材に連結するものでもないので、嵩ばらず、施工が容易になる。
【００２５】
【００２６】
【図面の簡単な説明】
【図１】本発明のラーメン構造の一例を示す全体立面図である。
【図２】図１の梁の低降伏部が塑性ヒンジになったときの曲げモーメント分布図である。
【図３】低降伏部を設ける位置と低,高降伏点鋼材の降伏点比σy'／σyの関係式を導く手法を示す図である。
【図４】降伏点比σy'／σyと塑性ヒンジの回転角倍率の関係を示すグラフである。
【図５】ラーメン構造の参考例を示す詳細立面図である。
【図６】本発明のラーメン構造の一例を示す詳細平面図および断面図である。
【図７】従来のラーメン構造を示す全体立面図および部分詳細図である。
【図８】図７の梁の両端が塑性ヒンジになったときの曲げモーメント分布図である。
【図９】柱・梁接合部からの脆性破壊を防止する従来のラーメン構造を示す平面図および立面図である。
【符号の説明】
１梁
２高降伏点のＨ形鋼
３低降伏点のＨ形鋼
４突合せ溶接
５継手板
６高力ボルト
７切欠き
８低降伏点の鋼板
２１柱
２２梁[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rigid frame structure capable of preventing brittle fracture at a column / beam joint and enhancing energy absorption capacity.
[0002]
[Prior art]
For example, a conventional ramen structure as shown in FIG. 7 is known. As shown in FIG. 7 (A), this ramen structure is a multi-layered rectangular ramen in which a plurality of columns 21 made of standing H-section steel are connected to a plurality of layers by means of H-shaped steel beams 22. As shown in FIG. 7 (B), the welded joint between the beam 21 at both ends of the beam 22 is formed by notching a scallop 23 to the web at the end of the H-shaped steel of the beam 22 and The contact portion is joined by butt welding 24 having a groove, and a reinforcing plate 25 is applied to the back surface of the flange at the end of the beam H-shaped steel exposed by the scallop 23 and joined by fillet welding 26.
When an excessive external force due to an earthquake or the like is applied to this rigid frame structure, the welded joints of the above columns and beams are first plastically deformed at both ends on the beam 22 side and transmit the total plastic moment (see Mp1 and Mp2 in Fig. 8). On the other hand, the dimensions of both H-section steels and the shape and material of the welded joint are determined so as to be a plastic hinge that rotates while the so-called beam yielding advance design is performed.
[0003]
However, as a result of the damage investigation of the steel structure in the Kobe earthquake and the Northridge earthquake, the butt weld 24 of the welded joint, which is expected to have a large deformability due to the plastic hinge, is caused by a crack as shown in FIG. It was revealed that brittle fracture 27 occurred frequently. FIG. 8 is a moment diagram showing the distribution of bending moments applied to the upper and lower beams 22 with both ends being plastic hinges. The moments at the left and right plastic hinges are Mp1 and Mp2, respectively, and the shearing force Q is When the beam length is L, Q = (Mp1 + Mp2) / L.
[0004]
Therefore, in order to prevent brittle fracture at the welded joints between the pillars at both ends of the beam, a countermeasure as shown in FIG. 9 called a dog-bone joint is adopted in the United States. As shown in the plan view of FIG. 9 (A), this measure is applied to the upper and lower flanges 28a and 28b of the H-shaped steel 28 on the center side of the beam 22 away from the column (21 ′) / beam (22) joint. A notch 29 is provided to reduce the cross-sectional area, and the H-shaped steel having the notch 29 is plastically deformed into a plastic hinge before brittle fracture occurs at the welded joints 30 at both ends of the beam.
[0005]
[Problems to be solved by the invention]
However, in the conventional beam 22 having the dog-bone joint shown in FIG. 9, the flange on the side to which the compressive stress is applied by the bending moment generated by an excessive external force such as an earthquake is located at the notch 29 where the cross-sectional area decreases. Since it tends to bulge out of the plane due to buckling, a stiffener is required for the H-shaped steel 28 having the notch 29, or to make the floor slab function as a stiffener, the H-shaped with the notch 29 is used. It is necessary to provide the steel 28 with a bonding material. However, since there are notches 29 in the flanges 28a and 28b of the H-section steel 28, there is a problem in that there is no room for the area and it is difficult to provide a stiffener or a bonding material.
[0006]
Therefore, an object of the present invention is to prevent brittle fracture at the column-beam joint by forming a plastic hinge at a location away from the beam end by changing the material without reducing the cross-sectional area of the beam. However, it is providing the frame structure which can improve the energy absorption capacity of a beam.
[0007]
[Means for Solving the Problems]
To achieve the above object, La Men structure of the present invention, most of the beams are formed by H-beams, thereby forming a predetermined steel, the H-section steel spaced a predetermined distance from both ends of the beam A pair of trapezoidal notches extending toward the outer edge are provided on the upper and lower flanges , respectively , and steel plates having a lower yield point than the predetermined steel material are fitted into these notches and welded. .
[0008]
In the above-mentioned rigid frame structure, most of the beam is formed of a predetermined steel H-shaped steel, and a pair of trapezoidal cuts extending toward the outer edge on the upper and lower flanges of the H-shaped steel separated by a predetermined distance from both ends of the beam. Notches are provided, and steel plates having a yield point lower than that of the predetermined steel material are fitted into these notches and welded .
Notches on the upper and lower flanges, and a steel plate with a low yield point fitted into these notches and welded together, the portion of the H-section steel has a yield point higher than both ends of the beam made of the H-shaped steel of the specified steel material. With a small moment, the entire cross section is plastically deformed to become a plastic hinge first, and rotates while transmitting the total plastic moment. However, the rotational ability of the plastic hinge is large because the yield point is low. Therefore, the plastic hinge can sufficiently rotate corresponding to the sum of the deformation angle corresponding to the inclination of the column and the member angle of the beam between the two plastic hinges, and effectively absorbs energy such as earthquakes. Compared to the structure, the horizontal displacement during an earthquake can be suppressed by approximately 30%.
In addition, the maximum shearing force generated in the beam shortens the span of the beam. Therefore, even if the total plastic moment in the plastic hinge using the low yield point steel material is small, the predetermined steel material is applied to the entire span of the beam as in the past. Can be used to maintain the same level of shear force as in the case of a rigid frame structure in which a plastic hinge is formed at the beam end.
In addition, the low yield portion is not the one with the notched flange of the beam as in the prior art, so there is no risk of buckling, and there is no need to separately provide a stiffener or bonding material at the flange notched portion, Since the shape steel made of the low yield point steel material is not connected to a predetermined steel material by high-strength bolt joint with a joint plate, it is not bulky and the construction is easy .
[0009]
[0010]
[0011]
[0012]
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 is an overall elevation view showing an example of a ramen structure of the present invention. This ramen structure is composed of a beam 1 that connects the same H-shaped steel columns 21 in FIG. H-section steel 2 with a relatively high yield point (hereinafter referred to as a high yield point for the sake of convenience) occupying the majority, and a yield point lower than the above high yield point at a predetermined distance L ₁ from both ends of the beam It consists of H-shaped steel including steel plate with low yield part 3 that can be a plastic hinge. Note that the length L ₂ of the low yield portion 3 is about the height of the H-section steel.
As will be described later with reference to FIG. 6 , the low yield portions 3 and 3 are formed on upper and lower flanges of the H- section steel, which are separated by L ₁ from both ends of the beam 1 of the H- section steel 2 and 2 having a high yield point. A pair of notches having a length L ₂ is provided, and a steel plate having a yield point lower than the high yield point is fitted into the notches and welded. On the other hand, both end portions of the beam 1 and the columns 21 and 21 are rigidly connected by the same welding joint as described in FIG.
[0014]
FIG. 2 is a distribution diagram of bending moment of a beam when an excessive external force such as an earthquake is applied to the ramen structure and the low yielding portion 3 becomes a plastic hinge prior to the joint of the column (21) and the beam (1). . Assuming that the total plastic moments transmitted by the left and right low yielding portions 3 and 3 that are plastic hinges are Mp1 ′ and Mp2 ′, respectively, the shearing force Q ′ is Q ′ = (when the length between the plastic hinges is L ′. Mp1 ′ + Mp2 ′) / L ′.
Since the above-mentioned rigid frame structure needs to have the same proof strength as the conventional example described in FIG. 7, the bending at the beam end when the straight line representing the bending moment is extended to both sides as shown by the one-dot chain line in FIG. The moment must be equal to the total plastic moments Mp1, Mp2 at both ends of the beam described in FIG. 8, and the shearing force, which is the derivative of the bending moment diagram, is naturally equal, so the maximum shearing force Q ′ Can be made equal to the maximum shearing force Q of the conventional example.
[0015]
FIG. 3 shows a low yielding portion in order to prevent brittle fracture at the conventional column / beam joint and increase the energy absorption capacity of the beam while maintaining the proof strength of the rigid frame structure at the same level as before. 3 and the predetermined position L ₁ providing a low shows a method for obtaining a relational expression of the yield point ratio .sigma.y '/ .sigma.y high yield point steel. However, the following calculation assumes that the H-section steel of the low yield portion 3 having the length L ₂ is made of a low yield point steel material as well as the upper and lower flanges.
Now, assuming that the cross section of the beam is constant and a low yielding portion (plastic hinge) 3 is provided at a position separated by a predetermined distance L ₁ from both ends of the beam as shown in FIG. 3A, the plastic hinges at both ends of the beam described in FIG. The total plastic moment and shear strength (maximum shear force) are Mp (= Mp1, Mp2) and Qu, respectively, and the total plastic moment and shear strength (maximum shear force) of the plastic hinge of the low yield part 3 shown in FIG. (= Mp1, Mp2), Qu '
Qu = 2Mp / L = 2σyZp / L (1)
Qu ′ = 2Mp ′ / L ′ = 2σy′Zp / L ′ (2)
However, Zp is the plastic section modulus of the beam. In order for the low yield portion 3 to become a plastic hinge prior to both ends of the beam, the shear strength Qu ′ of the beam in FIG. 3 must be smaller than the shear strength Qu of the beam in FIG. Because you have to
Qu ′ ≦ Qu is established, and L ′ = L−2L ₁ (3) is established from the relationship between the beam lengths in FIG. Therefore, substituting the equations (1), (2), (3) into the above inequality and solving this inequality for L ₁ ,
L ₁ ≦ L (1−σy ′ / σy) / 2 (4) is obtained.
[0016]
Generally, the yield point σy ′ of the low yield point steel material of the low yield part 3 is 10 to 25 kgf / mm ² , and the yield point σy of the high yield point steel material 2 is 30 to 50 kgf / mm ² . Therefore, the yield point ratio σy ′ / σy of the selected steel material is about 1/3, and if it is set to a predetermined distance L ₁ such that the equality of the equation (4) is established according to the yield point ratio, the shear point As shown in FIG. 2, the bending moment M, which is the integrated value of the shearing force, is also equal to the plastic hinge 3 as shown in FIG. The value when the value Mp 'in the beam is extended to the beam end is substantially equal to the total plastic moment Mp (= Mp1, Mp2) at both ends of the beam in the conventional example in FIG. It can be maintained approximately the same.
[0017]
FIG. 3C shows a deformed state of the beam 1 when the left and right low yield portions 3 are plastic hinges. Immediately before the left and right low yield portions 3 become plastic hinges, the beam 1 is deformed at a deformation angle θ by the material end moment acting on both ends as shown in FIG. 3B, but the low yield portions 3 are plastic. When it becomes a hinge, as shown in FIG. 3C, the left and right plastic hinges rotate at the nodal rotation angle θ ′ while transmitting the total plastic moment Mp ′. This node rotation angle θ ′ is the sum of the deformation angle θ shown in FIG. 3B and the member angle R of the beam between the plastic hinges, and the member angle R is R = 2θL ₁ / L from the geometrical relationship. 'Because it becomes
θ ′ = θ + R = θ + 2θL ₁ / (L−2L ₁ ) = θL / (L−2L ₁ ) (5)
[0018]
The nodal rotation angle θ 'of the plastic hinge is purely expressed by the above equation (5), but in reality, how much the low yield steel is plastically deformed before fracture, that is, the elongation capability of the low yield steel The rotation angle of the plastic hinge of the steel material is generally proportional to the reciprocal of the yield point of the steel material. Accordingly, θ ′ / θ = σy / σy ′, where θ ′ and θ are the rotation angles of the low yield point and high yield point steel materials, respectively. Here, since σy ′ / σy ≧ 1/3 as described in paragraph [0015], −σy ′ / σy in the equation (4) for obtaining the predetermined distance L ₁ is −σy ′ / σy ≦ −. 1/3, and the right side of Equation (4) is limited to L (1-1 / 3) / 2 = L / 3 at the maximum.
Therefore, the predetermined position L _{1 where} the low yield portion 3 is provided is
L ₁ ≦ min {L (1−σy ′ / σy) / 2, L / 3} (6)
FIG. 4 shows the ratio of the yield point of the low yield point steel to the high yield point steel α = σy '/ σy on the horizontal axis and the rotation angle magnification of the plastic hinge of the low yield point steel on the high yield point steel on the vertical axis. Represents the relationship. As shown by the broken line in FIG. 4, it can be seen that if a low yield point steel material having a yield point ratio of 0.33 to 0.5 is used, a plastic hinge rotational capability of 2 to 3 times can be obtained.
[0019]
Figure 5 is not in the embodiment of the present invention, a detailed elevational view illustrating a noodle structure as reference example. The low yield portion of this rigid frame structure is provided at a predetermined distance L ₁ satisfying the above equation (6) from the end of the H-section steel 2 having the high yield point σy of the beam 1 rigidly connected to the column 21 by the weld joint 30. It is made of the H-section steel 3 having a low yield point σy ′ having the same cross-sectional shape. The column-side end of the H-section steel 3 is joined to the H-section steel 2 with high-strength bolts 6 through joint plates 5, 5, and 5 that straddle the upper and lower flanges of the H-section steel 2 and the web. The opposite end is joined to the H-section steel 2 by butt welding 4.
[0020]
The ramen structure shown in FIG. 5 behaves as follows with respect to an excessive external force such as an earthquake.
When an excessive external force is applied, the low yield portion H-shaped steel 3 is plastically deformed before the welded joint 30 at the beam end with a small moment Mp ′ corresponding to the low yield point σy ′, and becomes a plastic hinge. While rotating while transmitting the moment Mp ′, the rotational power increases in proportion to the reciprocal of the yield point. Therefore, as shown in FIG. 3C, the plastic hinge can sufficiently rotate to θ ′, which is the sum of the deformation angle θ corresponding to the inclination of the column and the member angle R of the beam between the plastic hinges. The energy of the excessive external force is effectively absorbed, and the horizontal displacement can be suppressed by about 30% as compared with the conventional ramen structure described in FIGS.
Further, the H-section steel 3 of the low yield portion is a material having a high yield point σy at a predetermined distance L ₁ and a material whose shear strength Q ′ is substantially equal to the shear strength Q of the conventional rigid frame structure shown in FIG. Since it is provided between the section steels 2, as described in paragraph [0015], it is possible to exhibit a proof stress substantially equivalent to that of the conventional rigid frame structure.
Unlike the conventional beam 22 described in FIG. 9, the low yield portion H-section steel 3 does not have a notch 29 formed in the flanges 28a and 28b. Of course, it is not necessary to provide a stiffener or a bonding material at the notch.
Furthermore, since the above formula (6) is satisfied, the H-shaped steel 3 becomes a plastic hinge before the welded joints 30 at both ends of the beam, so that the above-described effects can be reliably achieved.
[0021]
In the above reference example , only one end of the H-section steel 3 in the low yield portion is welded and the other side is a high-strength bolt joint, so that the occurrence of brittle fracture of the H-section 3 due to weld cracking is suppressed. There is an advantage that the action of the plastic hinge can be subsidized.
[0022]
FIG. 6 is a detailed plan view and a cross-sectional view showing an example of the ramen structure of the present invention . The low yield portion of this rigid frame structure is a predetermined distance L ₁ satisfying the above formula (6) from the end of the beam 1 made of the H-section steel 2 having the high yield point σy rigidly connected to the column 21 ′ by the weld joint 30. In FIG. 6A, a pair of trapezoidal notches 7 extending toward the outer edge as shown in the plan view of FIG. 6A are provided in the upper and lower flanges 2a and 2b, and the notches have a low yield point σy ′. The steel plates 8 having the same thickness are fitted and welded.
In the embodiment of FIG. 6, the low yield portion 8 is provided on a flange which is an outer edge portion of an H-shaped steel in which a maximum compressive or tensile stress is generated when a bending moment is applied to the beam 1. Therefore, the low yield portion 8 is surely first plastically deformed to become a plastic hinge, and the H-section steel 3 having a low yield point is joined to the high strength bolt via the joint plate 5 shown in the reference example of FIG. Compared with the case where it does, there exists an advantage that there is no outward protrusion part, it is not bulky, and field construction becomes easy.
[0023]
[0024]
【The invention's effect】
As can be seen from the above description, the ramen structure of the present invention is formed by forming a large part of the beam with an H-shaped steel of a predetermined steel material, and on the upper and lower flanges of the H-shaped steel separated by a predetermined distance from both ends of the beam. A pair of trapezoidal notches that extend toward the outer edge are provided, and steel plates having a lower yield point than the above-mentioned steel material are fitted into these notches and welded together, so that the steel plate having a low yield point H-shaped steel with a welded joining, taken large plastic hinge because low yield point rotational capacity, it is possible to suppress the horizontal displacement and effectively absorbs the energy of an earthquake or the like, conventionally both ends becomes plastic hinge The beam can withstand the shearing force and bending moment equivalent to those of the conventional beam, and the proof strength of the beam can be maintained at the same level as the conventional beam. In addition, since the H-shaped steel is not the one in which the flange of the beam is cut out as in the prior art, there is no risk of buckling, and it is not necessary to separately provide a stiffener or a bonding material in the flange notch. Further, since the shape steel made of a low yield point steel material is not connected to a predetermined steel material by high-strength bolt joint with a joint plate, it is not bulky and the construction becomes easy .
[0025]
[0026]
[Brief description of the drawings]
FIG. 1 is an overall elevation view showing an example of a ramen structure according to the present invention.
FIG. 2 is a bending moment distribution diagram when the low yield portion of the beam in FIG. 1 is a plastic hinge.
FIG. 3 is a diagram showing a method for deriving a relational expression between a position where a low yield portion is provided and a yield point ratio σy ′ / σy of a steel material having low and high yield points.
FIG. 4 is a graph showing the relationship between the yield point ratio σy ′ / σy and the rotation angle magnification of the plastic hinge.
5 is a detail elevational view showing a reference example of La Men structures.
FIG. 6 is a detailed plan view and a cross-sectional view showing an example of a ramen structure according to the present invention .
FIG. 7 is an overall elevation view and a partial detail view showing a conventional ramen structure.
FIG. 8 is a distribution diagram of bending moment when both ends of the beam in FIG. 7 are plastic hinges.
FIGS. 9A and 9B are a plan view and an elevation view showing a conventional rigid frame structure for preventing brittle fracture from a column / beam joint. FIGS.
[Explanation of symbols]
1 Beam 2 H-shaped steel with high yield point 3 H-shaped steel with low yield point 4 Butt weld 5 Joint plate 6 High strength bolt 7 Notch 8 Steel plate 21 with low yield point Column 22 Beam

Claims

In the ramen structure where the beam is made of H-section steel ,
A large part of the beam is formed of a predetermined steel material, and a pair of trapezoidal cutouts extending toward the outer edge are provided on the upper and lower flanges of the H-shaped steel spaced a predetermined distance from both ends of the beam , respectively. A ramen structure characterized in that a steel plate having a yield point lower than that of the predetermined steel material is fitted into these notches and welded .