JP2004036290A - Thin plate lightweight shape steel excellent in fire resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin plate lightweight shape steel excellent in fire resistance without causing a sharp decline in its proof stress even in the case of high temperature. <P>SOLUTION: The thin plate lightweight shape steel excellent in fire resistance constituted by molding the thin plate of a fire resisting steel not more than 215.6 GPa of Young's modulus in normal temperature and at least 147 GPa of Young's modulus at 700°C to make cold working is provided. Design proof stress P of the thin plate lightweight shape steel is regulated in the formula. Where: F<SB>o</SB>= yield stress in normal temperature, F<SB>1</SB>= yield stress at 700°C, E<SB>0</SB>= Young's modulus in normal temperature, E<SB>1</SB>= Young's modulus at 700°C, b<SB>e</SB>= effective flange width of a plate element of the shape steel and t = design plate thickness. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、スチールハウス（板厚１ｍｍ前後の薄板軽量形鋼による枠材と構造用面材による鉄鋼系パネル構造）の柱や梁などに用いられる薄板軽量形鋼であって、特に７００℃の高温時においても大幅な耐力低下を起こさない耐火性に優れた薄板軽量形鋼に関する。
【０００２】
【従来の技術】
近年ではフリープラン対応型住宅の一例として、薄板軽量形鋼による枠材と構造用面材による壁枠組工法のスチールハウスが注目を集めている（図４参照）。このスチールハウスは枠材に鋼材を用いているため、従来の木造の壁枠組工法と比べて地震や強風に強く、高い安全性を確保できる。またスチールハウスでは高強度の壁枠組パネルが家全体を周囲から支持するため、建物内部の柱に依存しない大空間を確保できるなど、設計の自由度が非常に高い点でも優れている。
【０００３】
【発明が解決しようとする課題】
しかし、通常の鋼材の耐力は３５０℃程度で常温時の６０％〜７０％まで低下するため、建築物に鋼材を用いる場合にはその耐火性に十分考慮する必要がある。特にスチールハウスの枠材に用いられる薄板軽量形鋼は、板厚１ｍｍ前後の冷延鋼板に冷間加工を施して形成されており、火災発生時に高温によって薄板軽量形鋼のヤング係数が低下した場合、薄板軽量形鋼に局部座屈が生じて耐力低下を起こすおそれがある点で改善の余地がある。
【０００４】
本発明は上記従来技術の課題を解消するためにされたものであり、高温時においても大幅な耐力低下を起こさない耐火性に優れた薄板軽量形鋼を提供することを目的とする。
【０００５】
【課題を解決するための手段】
本発明の耐火性に優れた薄板軽量形鋼は、常温におけるヤング係数が２１５．６ＧＰａ（約２２０００ｋｇｆ／ｍｍ^２）以下で、かつ７００℃におけるヤング係数が１４７ＧＰａ（約１５０００ｋｇｆ／ｍｍ^２）以上となる板厚２．３ｍｍ未満の耐火鋼の薄板を冷間加工して成形される。ここで、本明細書において常温とは、２０℃から３０℃の範囲を意味する。
【０００６】
また、本発明の耐火性に優れた薄板軽量形鋼は、設計耐力Ｐが以下の式で規定される。

Ｆ_０＝常温時の降伏応力度
Ｆ_１＝７００℃における降伏応力度
Ｅ_０＝常温時のヤング係数
Ｅ_１＝７００℃におけるヤング係数
ｂ_ｅ＝形鋼の板要素の有効幅
ｔ＝設計板厚
【０００７】
さらに上記式における形鋼の板要素の有効幅ｂ_ｅは以下の式で規定される。

Ｆ_０＝常温時の降伏応力度
Ｅ_０＝常温時のヤング係数
ｔ＝設計板厚
ｋ＝座屈係数
【０００８】
【発明の実施の形態】
以下、本発明の実施形態を図面を参照しつつ詳細に説明する。
本発明の薄板軽量形鋼には、常温（２０℃から３０℃）におけるヤング係数が２１５．６ＧＰａ（約２２０００ｋｇｆ／ｍｍ^２）以下で、かつ７００℃におけるヤング係数が１４７ＧＰａ（約１５０００ｋｇｆ／ｍｍ^２）以上となる耐火鋼が用いられる。本発明において７００℃におけるヤング係数を規定するのは、火災時において建築物が崩壊しない実用的な基準となるからである。すなわち、火災時において柱や梁の温度が部分的にでも７００℃に達するには数十分程度の時間がかかり、この時間内に消火活動が完了することも多い。したがって、７００℃の条件下でも薄板軽量形鋼が大幅に耐力低下しなければ、耐火性能が十分実用的な水準に達しているといえるからである。
【０００９】
前記耐火鋼は、低Ｃ−低Ｍｎ鋼に微量のＮｂと適当量のＭｏとを複合添加することで高温領域での耐力を増加させたものである。前記耐火鋼は、図１に示すように７００℃を超えてから急激にヤング係数が低下し、７００℃の条件下でも比較的高いヤング係数［１４７ＧＰａ（約１５０００ｋｇｆ／ｍｍ^２）］を確保できるという特徴を有する。一方、通常の普通鋼は、図１に示すように５００〜６００℃の領域でヤング係数は急激に低下する。
【００１０】
具体的には、前記耐火鋼は、重量比で、Ｃ０．０４〜０．１５％、Ｓｉ０．６％以上、Ｍｎ０．５〜１．６％、Ｎｂ０．００５〜０．０４％、Ｍｏ０．４〜０．７％、Ａｌ０．１％以下、Ｎ０．００１〜０．００６％を含有し、残部がＦｅおよび不可避不純物（ＰおよびＳ）からなる鋼片を、１１００℃〜１３００℃の温度域で加熱した後、熱間圧延を８００℃〜１０００℃の温度範囲で終了して得ることができる。
【００１１】
ここで、前記耐火鋼に複合添加されたＮｂ、Ｍｏは微細な炭窒化物を形成し、さらにＭｏは固溶体強化によって高温強度を増加させる役目を果たす。しかも、前記耐火鋼ではミクロ組織がフェライト主体組織となっているため、常温耐力に対して７００℃の条件下での耐力の割合が大きい。
【００１２】
また前記耐火鋼については、重量比で、Ｃ０．０４〜０．１５％、Ｓｉ０．６％以上、Ｍｎ０．５〜１．６％、Ｎｂ０．００５〜０．０４％、Ｍｏ０．４〜０．７％、Ａｌ０．１％以下、Ｎ０．００１〜０．００６％に加えて、Ｔｉ０．００５〜０．１０％、Ｚｒ０．００５〜０．０３％、Ｖ０．００５〜０．１０％、Ｎｉ０．０５〜０．５％、Ｃｕ０．０５〜１．０％、Ｃｒ０．０５〜１．０％、Ｂ０．０００３〜０．００２％、Ｃａ０．０００５〜０．００５％、ＲＥＭ０．００１〜０．０２％のうち１種または２種以上を含有し、残部がＦｅおよび不可避不純物（ＰおよびＳ）からなる鋼片を、１１００℃〜１３００℃の温度域で加熱した後、熱間圧延を８００℃〜１０００℃の温度範囲で終了して得るようにしてもよい。Ｔｉ、Ｚｒ、Ｖ、Ｎｉ、Ｃｕ、Ｃｒ、Ｂ、Ｃａ、ＲＥＭを選択的に添加することで、強度、靭性の向上についてさらに好ましい結果を得ることができる。
【００１３】
さらに、常温時における前記耐火鋼のヤング係数は、図１に示すように軟鋼とほぼ同じであるため、前記耐火鋼は軟鋼と同等の良好な加工性を有している。したがって、本発明の薄板軽量形鋼は、１ｍｍ前後の耐火鋼の薄板にロールフォーミングなどの冷間加工を施して成形することができる。本発明の薄板軽量形鋼としては、断面Ｃ形の溝形鋼あるいはリップ付溝形鋼の他、角形鋼（ＢＯＸ形鋼）、Ｚ形鋼、リップ付Ｚ形鋼などが含まれる。
【００１４】
なお、重量比で、Ｃ０．０３％以下、Ｓｉ１％以上、Ｍｎ０．１〜０．２％、Ａｌ０．０１％〜０．１％、Ｎｂ０．１〜１％を含む上記成分に加えて、Ｔｉ０．２５％以下、Ｂ０．０００１〜０．０１％のうち１種または２種を含む場合がある成分を有する鋼片を、１１００℃〜１３００℃の温度域で加熱した後、熱間圧延を８００℃〜１０００℃の温度範囲で終了して得た鋼を、前記の耐火鋼に替えて用いることもできる。かかる組成の場合にもＮｂの比率が高く、かつ再結晶温度も高いことから、常温耐力に対して７００℃の条件下での耐力の割合が大きいことが推察できる。
【００１５】
＜薄板軽量形鋼の設計耐力の決定＞
ここで、本発明の薄板軽量形鋼の設計耐力Ｐを決定する場合には、まず部材断面の板要素の有効幅ｂ_ｅから部材断面の有効断面Σｂ_ｅ×ｔを算出する必要がある。
【００１６】
設計耐力Ｐの決定において、部材断面の板要素の有効幅ｂ_ｅを考慮するのは以下の理由による。すなわち、本発明の薄板軽量形鋼は部材断面を形成する板要素の板厚が１ｍｍ前後となり、ウエブの幅厚比やフランジの幅厚比が一般に使用される形鋼よりも大きい点に特徴がある。そのため、薄板軽量形鋼に圧縮応力度が作用する場合には、この圧縮応力度が一定以上になると部材が局部座屈を起こすため、座屈挙動を考慮する必要が生じるからである。
【００１７】
図２に示すように、両縁を支持された板が支持縁に平行な圧縮力を受ける場合、変形が拘束されている支持縁付近では応力が再分配され、座屈後にも耐力上昇が計測できる。この場合、応力度分布は板縁辺部の応力度が高く、中央部が低い凹状の応力度分布となる。そこで本発明では、板要素の支持縁に発生する最大応力度σ_ｍａｘを基準強度（常温時の降伏応力度Ｆ_０）として、形鋼の板要素の有効幅ｂ_ｅを以下の式（１）で求める。
【００１８】

Ｆ_０＝常温時の降伏応力度
Ｅ_０＝常温時のヤング係数
ｔ＝設計板厚
ｋ＝座屈係数
▲１▼二縁支持とする圧縮板要素　　　　　　ｋ＝４
▲２▼一縁支持、他縁自由の圧縮板要素　　　ｋ＝０．４２５
▲３▼両縁を単純支持とするせん断板要素　　ｋ＝８．９８
など
【００１９】
そして板要素の有効断面は、形鋼の板要素の有効幅ｂ_ｅに設計板厚ｔを乗じた式（２）で求めることができる。

【００２０】
図３（ａ）に示すように、例えば薄板軽量形鋼がリップ付溝形鋼の場合、ウエブおよびフランジは二縁支持とする圧縮板要素（ｋ＝４）として有効幅ｄ_ｅ、ｂ_１ｅが決定され、リップは一縁支持、他縁自由の圧縮板要素（ｋ＝０．４２５）として有効幅ｃ_ｅが決定される。そして形鋼の有効断面は、ウエブの有効幅ｄ_ｅと、２つのフランジの有効幅２ｂ_１ｅと、２つのリップの有効幅ｃ_ｅとを合計したものに設計板厚ｔを乗じて求められる。
【００２１】
また図３（ｂ）に示すように、例えば薄板軽量形鋼が断面Ｃ形の溝形鋼の場合、ウエブは二縁支持とする圧縮板要素（ｋ＝４）として有効幅ｄ_ｅが決定され、フランジは一縁支持、他縁自由の圧縮板要素（ｋ＝０．４２５）として有効幅ｂ_２ｅが決定される。そして形鋼の有効断面は、ウエブの有効幅ｄ_ｅと、２つのフランジの有効幅２ｂ_２ｅとを合計したものに設計板厚ｔを乗じて求められる。
【００２２】
薄板軽量形鋼の基本設計耐力Ｐ_０は、以下の式（３）で求めることができる。なお、式（３）からも分かるように、形鋼の耐力はヤング係数Ｅと降伏応力度Ｆの平方根に比例する。
【００２３】

α＝安全率
【００２４】
ところで火災等によって鋼材の温度が上昇した場合、降伏応力度およびヤング係数がともに低下することが知られている。したがって、火災時における安全性を向上させるためには、高温時（７００℃）での終局耐力Ｐ_１が基本設計耐力Ｐ_０と比較して大きく低下しないことが条件となる。
【００２５】
そこで本発明では、基本設計耐力Ｐ_０から終局耐力Ｐ_１での降伏応力度およびヤング係数の低下を見込んで最終的な設計耐力Ｐを決定することで、７００℃での安全性を大幅に向上させている。具体的には、７００℃での終局耐力Ｐ_１と基本設計耐力Ｐ_０との比率（Ｐ_１／Ｐ_０）を基本設計耐力Ｐ_０に乗じることで、７００℃での設計耐力Ｐを決定すればよい。
【００２６】
ここで前記の式（３）で示したように、基本設計耐力Ｐ_０および終局耐力Ｐ_１はヤング係数Ｅと降伏応力度Ｆの平方根に比例するので、終局耐力Ｐ_１と基本設計耐力Ｐ_０との比率（Ｐ_１／Ｐ_０）は以下の式（４）で求めることができる。なお、式（４）では、終局耐力Ｐ_１の安全率を最低値の１．０に設定している。
【００２７】

Ｆ_１＝７００℃における降伏応力度
Ｅ_１＝７００℃におけるヤング係数
【００２８】
そして以下の式（５）に示すように、薄板軽量形鋼の最終的な設計耐力Ｐは、前記式（３）の基本設計耐力Ｐ_０に、前記式（４）の終局耐力Ｐ_１と基本設計耐力Ｐ_０との比率（Ｐ_１／Ｐ_０）を乗じて決定される。

【００２９】
＜実施例＞
一例として、耐火鋼での終局耐力Ｐ_１と基本設計耐力Ｐ_０との比率（Ｐ_１／Ｐ_０）は以下の式（６）に示すように０．８０９８となる。したがって、薄板軽量形鋼が７００℃でも安全にするためには、設計耐力Ｐを常温時の基本設計耐力Ｐ_０の約８１％に設定すればよい。
【００３０】

（実施例における耐火鋼のデータ）
常温時のヤング係数Ｅ_０＝２１，０００ｋｇｆ／ｍｍ^２
常温時の降伏応力度Ｆ_０＝３０ｋｇｆ／ｍｍ^２
安全率α＝１．５
７００℃におけるヤング係数Ｅ_１＝１５，３００ｋｇｆ／ｍｍ^２
７００℃における降伏応力度Ｆ_１＝１２ｋｇｆ／ｍｍ^２
【００３１】
＜比較例＞
また前記実施例の比較例として、普通鋼での終局耐力Ｐ_１と基本設計耐力Ｐ_０との比率（Ｐ_１／Ｐ_０）を以下の式（７）に示す。この場合、終局耐力Ｐ_１と基本設計耐力Ｐ_０との比率（Ｐ_１／Ｐ_０）は０．３６６０となる。すなわち、普通鋼の場合には、常温時の基本設計耐力Ｐ_０の約３７％まで設計耐力Ｐを低下させなければ高温時での安全性を確保することが困難である。
【００３２】

（比較例における普通鋼のデータ）
常温時のヤング係数Ｅ_０＝２１，０００ｋｇｆ／ｍｍ^２
常温時の降伏応力度Ｆ_０＝２８ｋｇｆ／ｍｍ^２
安全率α＝１．５
７００℃におけるヤング係数Ｅ_１＝７，０００ｋｇｆ／ｍｍ^２
７００℃における降伏応力度Ｆ_１＝５ｋｇｆ／ｍｍ^２
【００３３】
【発明の効果】
本発明の薄板軽量形鋼は、７００℃におけるヤング係数が１４７ＧＰａ（約１５０００ｋｇｆ／ｍｍ^２）以上であって、高温時（７００℃）において通常の軟鋼よりも高いヤング係数を維持できる耐火鋼で形成される。したがって、７００℃の条件下でも薄板軽量形鋼が座屈する可能性は低く、耐火性能が非常に優れている。特に本発明の薄板軽量形鋼をスチールハウスに用いた場合、火災時において柱や梁の温度が部分的にでも７００℃に達するには数十分程度の時間がかかるので、十分な耐火性能が確保できる。さらに、薄板軽量形鋼の耐火性能が高いため、石膏ボード等の板厚を減少させた設計も可能となる。
【００３４】
また本発明の薄板軽量形鋼を形成する耐火鋼は、常温（２０℃〜３０℃）におけるヤング係数が２１５．６ＧＰａ（約２２０００ｋｇｆ／ｍｍ^２）以下であり、軟鋼と同等の良好な加工性を有している。
【００３５】
さらに本発明の薄板軽量形鋼では、常温時における基本設計耐力Ｐ_０から終局耐力Ｐ_１での降伏応力度およびヤング係数の低下を見込んで最終的な設計耐力Ｐを決定している。このとき、高温時（７００℃）での終局耐力Ｐ_１が基本設計耐力Ｐ_０と比較して大きく低下せず、火災時における安全性が大幅に向上している。
【００３６】
また本発明の薄板軽量形鋼は、部材断面を形成する板要素の板厚が１ｍｍ前後となり、一般に使用される形鋼よりも幅厚比が大きい点に特徴がある。そのため応力度分布は板縁辺部の応力度が高く、中央部が低い凹状の応力度分布となる。そこで本発明では、薄板軽量形鋼の設計耐力Ｐにおいて、部材の座屈挙動を反映させるべく部材断面の有効幅ｂ_ｅから板要素の有効断面を算出している。
【図面の簡単な説明】
【図１】耐火鋼および普通鋼のヤング係数と温度との関係をあらわしたグラフである。
【図２】（ａ）は両縁が支持された板要素が圧縮力を受けた場合の応力度分布を示した図であり、（ｂ）は（ａ）のＡ−Ａ´断面図である。
【図３】（ａ）は薄板軽量形鋼がリップ付溝形鋼の場合の有効断面を示した図であり、（ｂ）は薄板軽量形鋼が溝形鋼の場合の有効断面を示した図である。
【図４】（ａ）は薄板軽量形鋼を用いたスチールハウスの部分斜視図であり、（ｂ）は薄板軽量形鋼と面材との壁枠組を示す斜視図である。
【符号の説明】
１　　スチールハウス
２　　薄板軽量形鋼
３　　面材[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a thin, lightweight section steel used for columns, beams, etc. of a steel house (a steel-based panel structure formed of a thin, lightweight section steel sheet having a thickness of about 1 mm and a structural panel). The present invention relates to a thin, lightweight section steel having excellent fire resistance which does not cause a significant reduction in proof stress even at high temperatures.
[0002]
[Prior art]
In recent years, as an example of a free plan-compatible house, a steel house of a wall frame construction method using a frame material made of thin and lightweight shaped steel and a structural surface material has attracted attention (see FIG. 4). Since this steel house uses steel as the frame material, it is more resistant to earthquakes and strong winds than conventional wooden wall frame construction methods, and can secure high safety. In steel houses, high-strength wall framing panels support the entire house from the surroundings, so it has a very high degree of freedom in design, such as a large space that does not depend on pillars inside the building.
[0003]
[Problems to be solved by the invention]
However, since the proof stress of ordinary steel materials is reduced to about 350 ° C. to 60% to 70% at room temperature, when steel materials are used for buildings, it is necessary to sufficiently consider the fire resistance. In particular, the light-weight thin section steel used for the frame material of the steel house is formed by cold-working a cold-rolled steel sheet having a thickness of about 1 mm. In this case, there is room for improvement in that there is a possibility that local buckling may occur in the thin lightweight shaped steel and the proof stress may be reduced.
[0004]
An object of the present invention is to solve the above-mentioned problems of the prior art, and it is an object of the present invention to provide a thin and lightweight section steel having excellent fire resistance which does not cause a significant decrease in proof stress even at high temperatures.
[0005]
[Means for Solving the Problems]
The thin lightweight lightweight steel having excellent fire resistance of the present invention has a Young's modulus at room temperature of 215.6 GPa (about 22,000 kgf / mm ² ) or less and a Young's modulus at 700 ° C. of 147 GPa (about 15000 kgf / mm ² ) or more. It is formed by cold working a thin plate of refractory steel having a plate thickness of less than 2.3 mm. Here, the ordinary temperature in the present specification means a range of 20 ° C. to 30 ° C.
[0006]
Further, in the thin and lightweight section steel having excellent fire resistance of the present invention, the design strength P is defined by the following equation.

F ₀ = effective width t = design thickness of the yield stress of _F 1 = 700 Yield Stress _E at ° C. ₀ = plate element of Young's modulus _{b e} = section steel in Young's modulus _E 1 = 700 ° C. at the normal temperature at normal temperature [0007]
Further effective width b _e of the plate elements in the form steel in the above formula is defined by the following equation.

F ₀ = Yield stress at normal temperature E ₀ = Young's modulus at normal temperature t = Design plate thickness k = buckling coefficient
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Laminated lightweight shape steel of the present invention, room temperature Young's modulus in (20 30 ° C. from ° C.) is 215.6GPa (about 22000kgf / mm ²⁾ or less, and the Young's modulus at 700 ℃ 147GPa (about 15000kgf / ^mm 2) The refractory steel described above is used. The reason for defining the Young's modulus at 700 ° C. in the present invention is that it is a practical standard that does not cause the building to collapse in the event of a fire. That is, in the event of a fire, it takes several tens of minutes for the temperature of the pillars or beams to reach 700 ° C. even partially, and fire extinguishing activities are often completed within this time. Therefore, it can be said that the fire resistance has reached a sufficiently practical level unless the proof strength of the thin lightweight steel section is significantly reduced even under the condition of 700 ° C.
[0009]
The refractory steel has an increased yield strength in a high-temperature region by adding a small amount of Nb and an appropriate amount of Mo to a low C-low Mn steel. As shown in FIG. 1, the refractory steel rapidly decreases its Young's modulus after exceeding 700 ° C., and can secure a relatively high Young's modulus [147 GPa (about 15000 kgf / mm ² )] even under the condition of 700 ° C. Has features. On the other hand, in ordinary ordinary steel, the Young's modulus sharply decreases in the range of 500 to 600 ° C. as shown in FIG.
[0010]
Specifically, the refractory steel has a weight ratio of C 0.04 to 0.15%, Si 0.6% or more, Mn 0.5 to 1.6%, Nb 0.005 to 0.04%, Mo 0.4 A steel slab containing ０．７0.7%, Al 0.1% or less, N 0.001 to 0.006%, and the balance being Fe and unavoidable impurities (P and S) in a temperature range of 1100 ° C. to 1300 ° C. After heating, hot rolling can be completed in a temperature range of 800 ° C to 1000 ° C.
[0011]
Here, Nb and Mo combined with the refractory steel form fine carbonitrides, and Mo serves to increase high-temperature strength by solid solution strengthening. Moreover, since the microstructure of the refractory steel is mainly composed of ferrite, the ratio of the proof stress at 700 ° C. to the normal temperature proof stress is large.
[0012]
In addition, as for the refractory steel, in terms of weight ratio, C 0.04 to 0.15%, Si 0.6% or more, Mn 0.5 to 1.6%, Nb 0.005 to 0.04%, Mo 0.4 to 0. 7%, Al 0.1% or less, N 0.001 to 0.006%, Ti 0.005 to 0.10%, Zr 0.005 to 0.03%, V 0.005 to 0.10%, Ni0. 0.05 to 0.5%, Cu 0.05 to 1.0%, Cr 0.05 to 1.0%, B 0.0003 to 0.002%, Ca 0.0005 to 0.005%, REM 0.001 to 0.02 %, And the remainder is heated in a temperature range of 1100 ° C. to 1300 ° C. after the steel slab comprising Fe and unavoidable impurities (P and S) is heated to 800 ° C. The temperature may be obtained in a temperature range of 1000 ° C. By selectively adding Ti, Zr, V, Ni, Cu, Cr, B, Ca, and REM, it is possible to obtain more favorable results with respect to improvement in strength and toughness.
[0013]
Further, since the Young's modulus of the refractory steel at room temperature is almost the same as that of mild steel as shown in FIG. 1, the refractory steel has the same good workability as mild steel. Therefore, the thin lightweight steel sheet of the present invention can be formed by performing cold working such as roll forming on a thin sheet of refractory steel of about 1 mm. Examples of the thin, lightweight section steel of the present invention include a square section steel (BOX section steel), a Z section steel, a lip section Z-section steel, and the like, in addition to a C-section channel steel or a lip-section channel steel.
[0014]
In addition, in addition to the above components containing 0.03% or less of C, 1% or more of Si, 0.1% to 0.2% of Mn, 0.01% to 0.1% of Al, and 0.1% to 1% of Nb by weight, Ti0 After heating a steel slab having a component that may contain one or two of B 0.0001 to 0.01% in a temperature range of 1100 ° C. to 1300 ° C., hot rolling is performed by 800% or less. Steel obtained by ending in a temperature range of ℃ to 1000 ℃ can be used in place of the refractory steel. Even in the case of such a composition, since the ratio of Nb is high and the recrystallization temperature is high, it can be inferred that the ratio of proof stress under the condition of 700 ° C. to the proof stress at normal temperature is large.
[0015]
<Determining the design strength of thin lightweight steel>
Here, when determining the design strength P of thin lightweight shaped steel of the present invention, it is necessary to calculate the effective cross-sectional .SIGMA.b _e × t of the member cross-section from the effective width b _e of the plate element of the first member section.
[0016]
In determining the design strength P, according to the following reasons to consider effective width b _e of the plate element of the member cross-section. That is, the thin and lightweight section steel of the present invention is characterized in that the thickness of the plate element forming the member cross section is about 1 mm, and the width ratio of the web and the width ratio of the flange are larger than those of the commonly used section steel. is there. For this reason, when the degree of compressive stress acts on a thin lightweight steel plate, if the degree of compressive stress exceeds a certain value, the member locally buckles, and it is necessary to consider the buckling behavior.
[0017]
As shown in Fig. 2, when a plate supported on both edges receives a compressive force parallel to the supporting edge, the stress is redistributed near the supporting edge where the deformation is constrained, and the proof stress rise is measured even after buckling. it can. In this case, the stress level distribution is a concave stress level distribution where the stress level at the edge of the plate is high and the center level is low. In the present invention therefore, the maximum stress intensity sigma _max reference intensity generated to the support edges of the plate elements as (yield stress of F ₀ of the normal _{temperature),} the following equation effective width b _e of the plate elements of section steel (1) Ask for.
[0018]

F ₀ = Yield stress at normal temperature E ₀ = Young's modulus at normal temperature t = Designed plate thickness k = buckling factor {circle around (1)} Compression plate element to be supported on two edges k = 4
{Circle around (2)} One edge support, other edge free compression plate element k = 0.425
{Circle around (3)} Shear plate element with simple support at both edges k = 8.98
[0019]
The effective cross section of the plate elements can be found by equation (2) multiplied by the design thickness t to the effective width b _e of the plate element of shape steel.

[0020]
As shown in FIG. 3 (a), for example, when thin lightweight shaped steel is channel steel with a lip, the web and flange effective width d _e as a compression plate elements (k = 4) to the two-hem _support, b _1e is The effective width c _e is determined as the compression plate element (k = 0.425) with one edge supported and the other edge free. The effective cross-sectional shape steel, the effective width d _e of the web, and two effective width 2b _1e of the flange, obtained by multiplying the design thickness t of the effective width c _e of the two lips to the sum.
[0021]
Also as shown in FIG. 3 (b), for example, when thin lightweight shape steel of cross section C-shaped channel steel, the web effective width d _e is determined as the compression plate elements (k = 4) to the two-hem support The effective width _b2e is determined as a compression plate element (k = 0.425) with one edge supported and the other edge free. The effective cross-sectional shape steel, the effective width d _e of the web is determined by multiplying the design thickness t and two effective width 2b _2e of the flange to that sum.
[0022]
Basic design strength P of thin lightweight shape steel ₀ can be obtained by the following equation (3). As can be seen from equation (3), the yield strength of the section steel is proportional to the square root of the Young's modulus E and the yield stress F.
[0023]

α = safety factor
It is known that when the temperature of a steel material rises due to a fire or the like, both the yield stress and the Young's modulus decrease. Therefore, in order to improve the safety in case of fire, ultimate strength P ₁ at high temperatures (700 ° C.) is a condition that does not decrease significantly as compared to the basic design strength P _0.
[0025]
Therefore, in the present invention, the safety at 700 ° C. is greatly improved by determining the final design strength P in consideration of the decrease in the yield stress and the Young's modulus at the basic design strength P ₀ to the ultimate strength P _1. Let me. Specifically, the design strength P at 700 ° C. is determined by multiplying the basic design strength P ₀ by the ratio (P ₁ / P ₀ ) of the ultimate strength P ₁ at 700 ° C. to the basic design strength P _0. Just fine.
[0026]
Here, as shown in the above equation (3), the basic design strength P ₀ and the ultimate strength P ₁ are proportional to the Young's modulus E and the square root of the yield stress F, so that the ultimate strength P ₁ and the basic design strength P _0. (P ₁ / P ₀ ) can be obtained by the following equation (4). In the formula (4) are set the safety factor of the ultimate strength P ₁ to 1.0 minimum.
[0027]

The yield stress at F ₁ = 700 ° C. Young's modulus at E ₁ = 700 ° C.
Then, as shown in the following equation (5), the final design strength P of thin lightweight shaped steel is the basic design strength P ₀ of the formula (3), ultimate strength P ₁ and the base of the formula (4) It is determined by multiplying a ratio (P ₁ / P ₀ ) to the design proof stress P ₀ .

[0029]
<Example>
As an example, the ratio (P ₁ / P ₀ ) between the ultimate strength P ₁ and the basic design strength P _{0 of} fire-resistant steel is 0.8098 as shown in the following equation (6). Therefore, in order to thin lightweight shaped steel is safe even 700 ° C. may be set to the design strength P about 81% of the basic design strength P ₀ at the normal temperature.
[0030]

(Data of refractory steel in Examples)
Young's modulus at normal temperature E ₀ = 21,000 kgf / mm ²
Yield stress at normal temperature F ₀ = 30 kgf / mm ²
Safety factor α = 1.5
Young's modulus at 700 ° C. E ₁ = 15,300 kgf / mm ²
The yield stress at 700 ° C. F ₁ = 12 kgf / mm ²
[0031]
<Comparative example>
Further, as a comparative example of the above example, the ratio (P ₁ / P ₀ ) between the ultimate strength P ₁ and the basic design strength P _{0 of} ordinary steel is shown in the following equation (7). In this case, the ratio (P ₁ / P ₀ ) between the ultimate proof stress P ₁ and the basic design proof stress P ₀ is 0.3660. That is, in the case of ordinary steel, it is difficult to ensure safety at high temperatures unless reduce the design strength P to about 37% of the basic design strength P ₀ at the normal temperature.
[0032]

(Data of ordinary steel in comparative example)
Young's modulus at normal temperature E ₀ = 21,000 kgf / mm ²
Yield stress at normal temperature F ₀ = 28 kgf / mm ²
Safety factor α = 1.5
Young's modulus at 700 ° C. E ₁ = 7,000 kgf / mm ²
Yield stress at 700 ° C. F ₁ = 5 kgf / mm ²
[0033]
【The invention's effect】
The thin and light section steel of the present invention has a Young's modulus at 700 ° C. of 147 GPa (about 15000 kgf / mm ² ) or more, and is formed of fire-resistant steel capable of maintaining a higher Young's modulus at a high temperature (700 ° C.) than ordinary mild steel. Is done. Therefore, even under the condition of 700 ° C., the possibility of buckling of the thin lightweight steel plate is low, and the fire resistance is extremely excellent. In particular, when the thin and light section steel of the present invention is used for a steel house, it takes several tens of minutes for the temperature of columns and beams to reach 700 ° C. even in a partial fire, so that sufficient fire resistance performance is obtained. Can be secured. Furthermore, since the fire resistance of the thin lightweight steel plate is high, it is possible to design a gypsum board or the like with a reduced thickness.
[0034]
Further, the refractory steel forming the thin and light section steel of the present invention has a Young's modulus of 215.6 GPa (about 22000 kgf / mm ² ) or less at room temperature (20 ° C. to 30 ° C.), and has good workability equivalent to mild steel. Have.
[0035]
Furthermore a thin lightweight shaped steel of the present invention is to determine the final design strength P anticipates a decrease in the yield stress level and Young's modulus of at Ultimate Strength P ₁ from the basic design strength P ₀ at the time of normal temperature. At this time, ultimate strength P ₁ at high temperatures (700 ° C.) is not significantly reduced compared to the basic design strength P _0, safety in case of fire is greatly improved.
[0036]
Further, the thin and light section steel of the present invention is characterized in that the plate element forming the member cross section has a thickness of about 1 mm, and has a larger width-to-thickness ratio than a commonly used section steel. Therefore, the stress distribution has a concave stress distribution with a high stress at the edge of the plate and a low stress at the center. In this invention, the design strength P of thin lightweight shape steel, and calculates the effective cross section of the plate element from the effective width b _e member section to reflect the buckling behavior of the member.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the Young's modulus of refractory steel and ordinary steel and temperature.
2A is a diagram illustrating a stress distribution when a plate element having both edges supported is subjected to a compressive force, and FIG. 2B is a cross-sectional view taken along line AA ′ of FIG. .
FIG. 3 (a) is a diagram showing an effective cross section when the thin plate lightweight section steel is a grooved steel section with a lip, and FIG. 3 (b) is a view showing an effective cross section when the thin sheet lightweight section steel is a channel section steel. FIG.
FIG. 4A is a partial perspective view of a steel house using a thin lightweight steel plate, and FIG. 4B is a perspective view showing a wall framework of the thin lightweight steel plate and a face material.
[Explanation of symbols]
1 Steel House 2 Thin and Light Section Steel 3 Face Material

Claims (3)

常温におけるヤング係数が２１５．６ＧＰａ以下で、かつ７００℃におけるヤング係数が１４７ＧＰａ以上となる板厚２．３ｍｍ未満の耐火鋼の薄板を冷間加工して成形してなる耐火性に優れた薄板軽量形鋼。A thin, lightweight fire-resistant sheet formed by cold-working a thin steel sheet having a Young's modulus of 215.6 GPa or less at room temperature and a Young's modulus at 700 ° C. of 147 GPa or more and a sheet thickness of less than 2.3 mm and having a thickness of less than 2.3 mm. Shaped steel. 設計耐力Ｐが以下の式で規定されてなる請求項１に記載の耐火性に優れた薄板軽量形鋼。

Ｆ_０＝常温時の降伏応力度
Ｆ_１＝７００℃における降伏応力度
Ｅ_０＝常温時のヤング係数
Ｅ_１＝７００℃におけるヤング係数
ｂ_ｅ＝形鋼の板要素の有効幅
ｔ＝設計板厚The thin and lightweight section steel having excellent fire resistance according to claim 1, wherein the design strength P is defined by the following equation.

F ₀ = effective width t = design thickness of the yield stress of _F 1 = 700 Yield Stress _E at ° C. ₀ = plate element of Young's modulus _{b e} = section steel in Young's modulus _E 1 = 700 ° C. at the normal temperature at normal temperature 形鋼の板要素の有効幅ｂ_ｅが以下の式で規定されてなる請求項２に記載の耐火性に優れた薄板軽量形鋼。

Ｆ_０＝常温時の降伏応力度
Ｅ_０＝常温時のヤング係数
ｔ＝設計板厚
ｋ＝座屈係数Refractory excellent in thin lightweight shaped steel according to claim 2, the effective width b _e of the plate element of the shaped steel is defined by the following equation.

F ₀ = Yield stress at normal temperature E ₀ = Young's modulus at normal temperature t = Design plate thickness k = Buckling coefficient

Images