JP3684115B2 - Floor slab construction method - Google Patents

Description

【００３３】
つまり、上記の構造によれば、中央部の下向き最大突出量ｆに起因して底鋼板１４の曲げモーメントＭｓが削減され、しかも、この削減度合いは水平力Ｈが大きいほど（すなわち荷重が大きいほど）著しくなる。従って、底鋼板１４に発生する力としては膜引張力が支配的となり、底鋼板１４はその全断面についてほぼ均等に引張られることになる。すなわち、鋼板表面にのみ高い曲げ応力が発生するのを避け、底鋼板１４の全断面を有効に使うことができる。従って、薄肉の底鋼板１４を用いながら、また、補強材の使用を抑えながらも、コンクリート打設時の荷重さらには完成後の輪荷重にも十分対抗できるのである。
【００３４】
さらに、上記図１に示した圧縮材２０等を用いて両主桁１０のフランジ部１２同士が相互接近する方向に変位するのを規制しながらコンクリート２４を打設するようにすれば、支持端の水平力Ｈが主桁１０に有害な変形を与えることを確実に防ぐことができる。
【００３５】
２）床版全体に作用する曲げモーメントとの関係
完成後の床版に対し、支点間に荷重（例えば輪荷重）が作用したとき、これに起因して床版各部に作用する最大曲げモーメント分布は幅方向中央部で最大となる。一方、上記図１に示した床版は、その下面が下に凸の形状をなしているため、幅方向中央部で床版厚が最大となっている。すなわち、この幅方向中央部で断面係数が最大となっており、その分、床版表面に発生する曲げ応力が抑えられる構造となっている。このように、曲げモーメントが最大となる部分と断面係数が最大となる部分とがほぼ合致しているため、床版に生じる応力を幅方向にわたって均一化することができる。
【００３６】
３）従来のアーチ型構造との比較
ａ）弾性座屈について：上記図１７に示したように、支点間部分を上向きに凸の形状としたアーチ型構造の場合、コンクリート打設等による荷重が作用すると、底鋼板には膜圧縮力が働く。従って、この膜圧縮力に起因する底鋼板の弾性座屈を防止するための設計が必要となる。具体的には、底鋼板を厚肉にしたり、リブを増加したりしなければならず、重量及びコストの低減の妨げとなる。特に、構造が長大化して支間が大きくなると、その分底鋼板は座屈しやすくなるため、構造はますます大がかりなものとなってしまう。
【００３７】
これに対して上記図１に示す構造では、アーチ型構造とは逆に底鋼板１４が下向きに凸の形状をなしており、底鋼板１４には膜引張力が作用するため、弾性座屈のおそれがなく、基本的には底鋼板１４の引張強度のみを考慮すれば足りる。従って、底鋼板１４を厚肉にしたりリブを増強したりする必要がなく、構造の軽量化及び低コスト化が果たせる。
【００３８】
ｂ）偏載荷重について：アーチ型構造の場合、図５（ａ）に示すような偏載荷重（支間中央から外れた位置に作用する荷重）を受けると、その荷重作用点から底鋼板の凸部が離れる方向に移りやすく、最悪の場合には下に凸の状態に飛び移るおそれがある。このような変形は極めて大きなものであり、構造の安定性を著しく阻害するものである。これに対し、同図（ｂ）に示すように下に凸の底鋼板１４に偏載荷重が作用した場合、上記とは逆に凸部が当該荷重の作用点に近づく方向に移る傾向があり、大きな変形は生じない。従って、偏載荷重に対しても非常に安定した構造となっている。しかも、その荷重によって両端部（支点部分）との落差が大きくなるほど、底鋼板１４の曲げモーメントＭｓを相殺するモーメント要素（＝Ｈ・ｆ）が大きくなるのであるから、非常に合理的である。
【００３９】
なお、上記凸部分の最大突出量ｆは適宜設定が可能であるが、この突出量ｆが大きくなると、底鋼板１４の曲げモーメント低減度合いが高まる反面、その膨らみ分だけ打設コンクリート量が増えて床版重量が増加するため、そのバランスを考慮して突出量ｆを決めることが望ましい。以下、この点について検討を行う。
【００４０】
いま、支点間距離をＬとし、橋軸直角方向（幅方向）にｙ軸をとるとともに、当該方向の中央位置のｙ座標を０に設定する。そして、底鋼板１４の形状を下に凸な二次曲線であると仮定すると、コンクリート打設による分布荷重ｗ(ｙ)と支持端鉛直反力とに起因して発生する曲げモーメントＭ(ｙ)は、次式で表される。
【００４１】
【数２】

【００４２】
ここで、鉛直下向きにｚ軸座標をとると、上記分布荷重ｗ(ｙ)は次式で表される。
【００４３】
【数３】

【００４４】
この（数３）を上記（数２）に代入して積分演算を行うことにより、次式を得ることができる。
【００４５】
【数４】

【００４６】
この（数４）に基づき、単位荷重法等を用いて水平力Ｈを求めると、次式が得られる。
【００４７】
【数５】

【００４８】
ここで、底鋼板１４の板厚をｔ_sとすると、Ｉ＝ｔ_s３／１２、Ａ＝ｔ_sであるから、μの値は次式で与えられる。
【００４９】
【数６】

【００５０】
ここで板厚ｔ_sが突出量ｆに比べて十分小さい場合、μ≒０と置くことができる。これを（数５）に代入して変形すると、次式を得ることができる。
【００５１】
【数７】

【００５２】
一方、単位長さ当たりの鉄筋コンクリート重量をＷは次式によって表される。
【００５３】
【数８】

【００５４】
この（数８）及び上記（数７）において、通常形態の橋梁用床版ではβ＝0.02〜0.05と想定できる。この範囲内でβに適当な値を代入すると、Ｈ／ρＬ２及びＷ／ρＬ２はαの関数となる。これを同一のグラフに表したものが図４である。
【００５５】
底鋼板の設計は、水平膜引張力Ｈにより生ずる応力と床版完成後に輪荷重により生ずる応力等との和が許容応力度を超えないようになされるため、水平膜引張力Ｈが小さいほど、薄い板を使用することができて経済的となる。
【００５６】
そこで、図４において水平膜引張力Ｈに着目すると、当該引張力Ｈはαが0.02(＝1/50）より小さくなると急激に上昇する。従って、αは1/50以上とする（すなわち突出量ｆを支点間距離Ｌの1/50以上とする）ことが好ましい。さらに、突出量ｆを支点間距離Ｌの1/30以上とすることにより、水平膜引張力Ｈをほぼ最小限に抑えることが可能になる。
【００５７】
一方、コンクリート重量Ｗに着目すると、当該重量Ｗはαの上昇に伴ってほぼ線形的に増加するが、水平膜引張力Ｈの減少する割合が小さくなるα＞1/10以上の領域では、底鋼板の板厚を減少させる効果がほとんど上昇しない。従って、床版軽量化の観点からは、αを1/10(＝0.1）以下とする（すなわち突出量ｆを支点間距離Ｌの1/10以下とする）ことが好ましい。さらに、突出量ｆを支点間距離Ｌの1/20以下とすることが、より好ましい。
【００５８】
第２の実施の形態を図７及び図８に基づいて説明する。
【００５９】
上記第１の実施の形態に示すように、埋め込み用の圧縮材２０として鋼材を用いた場合、この鋼材と打設されるコンクリート２４との異質性が高いため、両者が比較的肌離れしやすく、これに起因してひび割れが発生するおそれがある。
【００６０】
そこで、この実施の形態では、上記圧縮材２０としてプレキャスト（予め成形した）鉄筋コンクリートからなるものを用い、上記肌離れに起因するひび割れを防ぐようにしている。
【００６１】
この場合の主桁１０に対する圧縮材２０の位置決め手段としては、例えば、図８に示すように主桁１０の上側フランジ部１２の上面に突起１３を設け、この突起１３が嵌入可能な孔２８を圧縮材２０側に設けるようにすればよい。
【００６２】
上記肌離れを防ぐには、圧縮材２０の少なくとも表面がコンクリートもしくはこれに類するものであればよく、例えば圧縮材２０全体がコンクリートで一体化されたものであってもよい。ただし、上記のようなプレキャスト鉄筋コンクリートを用いれば、施工時の取扱いが容易で、しかも高い強度を確保できる。
【００６３】
第３の実施の形態を図９に示す。この実施の形態では、上記図１に示したような直線状の圧縮材２０に代え、床版幅方向に延びる圧縮材部分３４の両端から下方に脚部３２を垂設した変位規制部材３０を用いる。そして、その両脚部３２の下端を両フランジ部１２に固定することにより、両フランジ部１２の水平変位を規制する。この状態で圧縮材部分３４よりも下方のレベルまでコンクリートを打設し、これを硬化させた後、両脚部３２を途中部分で切り離して圧縮材部分３４を撤去する。
【００６４】
なお、上記変位規制部材３０以外の各部構造の詳細は、上記図１に示したものと同等である。
【００６５】
この施工方法によれば、圧縮材部分３４の撤去により、それまでの水平変位規制力が解除され、打設されたコンクリートには圧縮力が導入され、完成後の輪荷重等に起因する床版下部の引張応力を低減することができる。また、撤去した圧縮材部分３４は次の施工に繰り返し使用できるので、圧縮材２０を埋め込む方法よりも経済的である。
【００６６】
なお、上記脚部３２の切離し作業を容易にするには、予め切離し部分で脚部３２を分割しておき、この部分をボルト等によって着脱可能に連結しておくようにすればよい。
【００６７】
第４の実施の形態を図１０に示す。ここでは、コンクリートを打設する前に、引張ワイヤ４０の一端を両フランジ部１２に連結し、他端をアンカー４２を介して橋外部の適所に連結しておく。
【００６８】
この方法においても、両フランジ部１２が内側に水平変位するのを引張ワイヤ４０の張力で規制しながら、底鋼板１４上にコンクリートを打設することができる。コンクリートの打設及び硬化後は、フランジ部１２から引張ワイヤ４０を切り離すことにより、上記変位規制力を解除させ、第３の実施の形態と同様にコンクリートにプレストレスを与えることができる。
【００６９】
第５の実施の形態を図１２（ａ）（ｂ）に示す。
【００７０】
上記底鋼板１４とコンクリート２４とのずれ止めを行う手段として、図１２（ａ）（ｂ）に示すように、例えばフラットバーからなる補強リブ４０を底鋼板１４上に立直状態で固定する方法がよく知られている。この方法を本発明のように底鋼板１４が下に凸の曲面状のものに適用するには、当該底鋼板１４の断面が直線となる方向（図１２（ａ）では奥行き方向）に沿って上記補強リブ４０を平行に配すれば、底鋼板１４のもつ膜作用を阻害することなく、これに補強リブ４０を固定することができる。
【００７１】
ところが、この補強リブ４０のみを設けた構造では、その上からコンクリートを打設して補強リブ４０を埋め込むと、当該コンクリートに対して各補強リブ４０が上向きに鋭く食い込んだ状態となるため、その食い込み部分からひび割れが発生し、かつ、このひび割れが上向きに進行しやすい。このようにしてひび割れが最終的にコンクリート上面にまで到達すると、当該コンクリートはリブ配設位置で分断され、いわゆるはり状化された状態となってしまう。
【００７２】
そこで、この実施の形態では、各補強リブ４０に図１２（ｂ）に示すような貫通孔４１を設け、この貫通孔４１に例えば鋼製線材からなる細い鉄筋４２を通し、下に凸の曲面に沿って配するようにしている。
【００７３】
このような構成によれば、底鋼板１４の近傍で打設コンクリートが補強リブ４０と直交する方向に変位することが上記鉄筋４２によって規制されるため、かかる変位に伴う上記ひび割れの進行が最小限に食い止められる。また、鉄筋４２は底鋼板１４とコンクリートとの肌離れを抑制する手段としても期待できる。
【００７４】
しかも、当該鉄筋４２に細いものを用いて底鋼板１４とともに撓み変形できるようにしておけば、底鋼板１４の膜作用を阻害することがなく、本発明の十分な作用効果を得ることが可能である。
【００７５】
また、当該鉄筋４２は、補強リブ４０に設けた貫通孔４１に挿通するだけでよいので、施工も容易である。
【００７６】
第６の実施の形態を図１３（ａ）（ｂ）に示す。
【００７７】
底鋼板１４とコンクリート２４とのずれ止め手段として、上述のスタッドジベルや補強リブも有効であるが、これらは打設されたコンクリートに対して鋭く食い込んだ状態となるため、ひび割れの集中度が高く、耐久性に大きな影響を及ぼすおそれがある。
【００７８】
そこで、この実施の形態では、例えば鉄鋼材料からなる線材を螺旋状にして容易に撓み変形できるようにしたずれ止め線材４６を底鋼板１４上に配し、その底鋼板１４に対して上記ずれ止め線材４６の各下端部４４のみを局所的に固定（例えば点溶接）するようにしている。これら下端部４４は全て固定する必要はなく、特定の下端部４４のみを間欠的に固定するようにしてもよい。
【００７９】
この構成によれば、次のような効果が得られる。
【００８０】
ａ）上記スタッドジベルや補強リブに比べてひび割れの集中度合いが下げられ（すなわちひび割れが分散化され）、その結果、十分な耐久性が維持される。
【００８１】
ｂ）スタッドジベルや補強リブに比べてコンクリートとの接触面積が大きいため、ずれ止め効果や肌離れ抑止効果が高く、また、十分な合成効果を得ることができる。
【００８２】
ｃ）ずれ止め線材４６が容易に撓み変形するので、鋼板１４の膜作用を阻害することがない。
【００８３】
ｄ）スタッドジベルや補強リブに比べて溶接面積が少ないので、施工が容易である。
【００８４】
なお、上記ずれ止め線材４６は必ずしも螺旋状に限られず、撓み変形可能な曲線状をなし、その一部が局所的に底鋼板１４に固定されるものであればよい。例えば、図１４（ａ）に示すような波形あるいはジグザグ形のずれ止め線材４６の谷部分のみを局所的に底鋼板１４上に固定するようにしてもよいし、同図（ｂ）に示すような半円もしくはこれに近似した有端のずれ止め線材４６の両端を底鋼板１４に固定するようにして、このずれ止め線材４６を多数並設するようにしてもよい。
【００８５】
ただし、ずれ止め部材４６を前記図１３に示すような螺旋状とすれば、撓み変形をより容易にできるとともに、コンクリートとの接触面積を効果的に増やしてずれ止め作用をより顕著なものにすることが可能となる。
【００８６】
その他、本発明は例として次のような実施形態をとることも可能である。
【００８７】
(1) 本発明は、橋梁用床版及びその施工に限らず、その他の土木用床版、あるいは建築用床版及びその施工にも適用が可能である。また、橋桁による支持個所も２か所に限らず、３か所以上に設定してもよい。例えば、第７の実施の形態として図１５に示すように、縦横両方向について３か所以上の支点をもつ（すなわち３本以上の橋桁で支持される）床版の場合、各支点間部分１７の少なくとも一つを下に凸の形状とすることにより、その部分において上述の作用・効果を得ることができる。
【００８８】
この場合、どの支点間部分１７を下に凸の形状とするかについては、仕様に応じて適宜設定すればよい。また、このように複数の支点間部分１７が存在する場合、支点間部分１７ごとに別の底鋼板１４を用いる（すなわち支点間部分１７に対応して底鋼板１４を分割する）ようにしてもよいし、全支点間部分１７について共通の底鋼板１４を使用する（すなわち単一の底鋼板１４を橋桁上に載せる）ようにしてもよい。
【００８９】
(2) 上記各実施形態で示した底鋼板１４の具体的な形状は特に問わず、支点間部分が下向きに凸である範囲で適宜設定が可能である。例えば、全体を曲面とする他、図１６（ａ）（ｂ）に示すように複数の平面を組み合わせたものであってもよいし、同図（ｃ）（ｄ）に示すように平面と曲面とを組み合わせたものであってもよい。曲面の具体的な断面形状も種々設定が可能であり、二次あるいはそれよりも高次の曲線、円弧、楕円曲線、双曲線、正弦曲線、懸垂線（双曲線正弦関数曲線）、サイクロイド曲線等、その種類を問わない。
【００９０】
(3) 上記実施形態では、底鋼板１４上に直接コンクリートを打設するようにしているが、床版下部で発生する引張力に対しては、コンクリートはほとんど寄与できないので、予め、当該床版下部に空隙を確保するための箱状部材や管状部材を導入したり、底鋼板１４上に軽量の硬質ウレタン等を敷設したりしておき、その上からコンクリートを打設するようにしてもよい。また、床版の用途によっては、コンクリートに代えてモルタル等を使用できることは前述の通りである。
【００９１】
(4) 上記実施形態では、底鋼板１４と打設コンクリート２４とを一体化して合成床版としたものを示したが、コンクリート打設及び硬化後、底鋼板１４を撤去してコンクリート床版とするようにしてもよい。すなわち、底鋼板１４を型枠としてのみ用いるようにしてもよい。この場合も、底鋼板１４を下に凸の形状とすることにより、簡単な構造で、強度的に不都合なくコンクリートの打設ができることはいうまでもない。また、このように型枠を撤去させるか、型枠を残存させて合成床版とするかにかかわらず、当該型枠の材質は鋼板に限られるものではなく、引張力に対抗する膜部材として使用できるものであれば広く適用が可能である。例えば、ＦＲＰや木板、高強度繊維で織られた布材等も型枠として用いることができる。
【００９２】
【実施例】
上記図１に示した構造において、主桁間隔を8.4ｍ、底鋼板１４の板厚ｔ_sを８mm、最大突出量ｆを390mm、圧縮材２０の高さ寸法及び幅寸法を200mm、圧縮材２０の間隔を１ｍ、支点部分の床版厚ｔ_coを270mmとして施工を行った。この時の主桁フランジ部１２の内向き水平方向変位を数値解析で求めた結果が図１１である。この図に示されるように、上記方向のフランジ部変位は最大でも約1.4mmであり、コンクリートが打設されても主桁１０に有害な影響を与えていないことを確認できた。
【００９３】
なお、この影響の回避を特に厳しく求められる場合には、少なくとも一方の主桁１０が橋軸直角方向に移動するのを許容するように橋梁を構築する等の手段をとればよい。
【００９４】
【発明の効果】
以上のように本発明は、型枠を下から支持し、この型枠の上にコンクリート類を打設することにより床版を形成する施工方法において、上記型枠としてその支点間部分の少なくとも一つが下向きに凸の形状を有するものを用いるものであるので、簡単な構造で、不都合なくコンクリートの打設ができ、また完成後の輪荷重等にも十分に耐えるようにすることができる効果がある。
【図面の簡単な説明】
【図１】 本発明の第１の実施の形態にかかる橋梁の上部構造を示す斜視図である。
【図２】 図１のＡ部の拡大図である。
【図３】 図１に示される底鋼板上にコンクリートが打設される際に発生する各力を示す説明図である。
【図４】 支点間距離に対する最大突出量の比率αと発生膜水平力Ｈ及び必要コンクリート重量Ｗとの関係を示すグラフである。
【図５】 （ａ）は上に凸の底鋼板上に荷重が作用する際に生じ得る変形を示す説明図、（ｂ）は下に取付の底鋼板上に荷重が作用する際に生じ得る変形を示す説明図である。
【図６】 （ａ）は上記底鋼板の一例としての縞鋼板を示す平面図、（ｂ）は（ａ）のＡ−Ａ線断面図である。
【図７】 本発明の第２の実施の形態にかかる施工方法を示す斜視図である。
【図８】 図７に示す圧縮材の位置決め構造例を示す斜視図である。
【図９】 本発明の第３の実施の形態にかかる施工方法を示す斜視図である。
【図１０】 本発明の第４の実施の形態にかかる施工方法を示す説明図である。
【図１１】 本発明の実施例における橋軸直角方向のフランジ部変位の解析結果を示すグラフである。
【図１２】 （ａ）は本発明の第５の実施の形態にかかる施工方法を示す説明図、（ｂ）はその要部を示す斜視図である。
【図１３】 （ａ）は本発明の第６の実施の形態にかかる施工方法を示す説明図、（ｂ）はその施工方法で用いられるずれ止め部材と底鋼板との溶接状態を示す斜視図である。
【図１４】 （ａ）（ｂ）は前記ずれ止め部材の変形例を示す斜視図である。
【図１５】 本発明の第７の実施の形態における床版の支持状態を示す模式図である。
【図１６】 （ａ）（ｂ）（ｃ）（ｄ）は型枠形状の変形例を示す説明図である。
【図１７】 橋梁用床版の従来例を示す断面斜視図である。
【符号の説明】
１０ 主桁（橋桁）
１４ 底鋼板
１４ａ 縞鋼板の突起
１７ 支点間部分
２０ 圧縮材
２４ コンクリート
３０ 変位規制部材
３４ 圧縮材部分
４６ ずれ止め部材[0001]
BACKGROUND OF THE INVENTION
  The present invention is a floor slab used in the field of architecture and civil engineering, and is particularly suitable for a bridge.EditionIt relates to the construction method.
[0002]
[Prior art]
  In general, floor slabs in bridges and the like are roughly classified into steel slabs and broad concrete slabs including synthetic slabs. Of these, steel slabs are lightweight but expensive, and therefore concrete slabs are mainly used when the span is short. In particular, synthetic floor slabs made by placing concrete on the bottom plate made of steel have sufficient strength and durability when completed, and there are few on-site work and a short construction period. It has been.
[0003]
  Conventionally, the following are known as such synthetic slabs.
[0004]
  A) On a flat or substantially flat bottom steel plate, CT steel materials and main reinforcing bars for reinforcement and slip prevention are welded in a lattice shape, and concrete is placed thereon (for example, JP-A-62-21910) No. publication).
[0005]
  B) As shown in FIG. 17, the portion between the fulcrums of the bottom steel plate 3 (the portion between the main girders 2) is formed in an upwardly arched shape, and concrete 4 is placed on the arch, thereby installing And an improvement in strength at the time of completion (see JP-A-59-185209).
[0006]
[Problems to be solved by the invention]
  The above-mentioned floor slab ensures sufficient strength (particularly bending strength) for the bottom steel plate, which is the formwork, during concrete placement and use after completion, and prevents unstable behavior from occurring during construction. There is a need. For this reason, for example, in the floor slab of A), it is necessary to arrange the CT steel material for reinforcement on the bottom steel plate in a fairly dense state. Therefore, there are inconveniences that many processing steps are required and it is difficult to reduce the weight of the entire floor slab.
[0007]
  On the other hand, the floor slab of B) has the following inconvenience because the bottom steel plate has an upwardly convex arch shape.
[0008]
  a)When a load at the time of placing concrete or a ring load after completion is applied on the bottom steel plate, a large film compressive force acts on the bottom steel plate. Therefore, in order to prevent buckling of the bottom steel plate due to this film compressive force, it is necessary to increase the thickness of the bottom steel plate or install ribs, and an increase in weight and cost is inevitable.
[0009]
  b)As is well known, the arch structure is vulnerable to an offset load (a distributed load half of the span and a concentrated load of a quarter of the span), and may be greatly deformed when the offset load is received. Therefore, it is necessary to uniformly cast the concrete on the bottom steel plate, and the construction is difficult.
[0010]
  c)In the entire structure including the concrete part, the floor slab thickness is the smallest at the center part of the span where the maximum bending moment is likely to occur, and the strength design near the fulcrum part may be excessive.
[0011]
  In view of such circumstances, the present invention has a simple structure, a floor on which concrete can be placed without inconvenience, and can sufficiently withstand wheel loads after completion.EditionThe purpose is to provide a construction method.
[0012]
[Means for Solving the Problems]
  As means for solving the above problems, the present invention provides:A construction method for forming a floor slab by supporting a formwork from below and placing concrete on the formwork, wherein at least one of the portions between the fulcrums is downwardly convex as the formwork. It is a method using what has.
[0013]
  The “concrete” referred to here includes concrete and other similar materials. For example, mortar can be used for building floor slabs.
[0014]
  This floor slabAccording to the construction method of theThe part between the fulcrums is belowIn the directionConvex shapeBy using what hasA load is applied from aboveOn the bottom plate of the formworkMembrane tensionCan be generated.Then, the bending moment that is actually generated in the bottom plate by the moment generated by the drop between the fulcrum portion and the fulcrum portion of the bottom plate and the film tension in the horizontal direction.Can be reduced.Therefore, the bottom plate is made thinner and the amount of reinforcing ribs used is reduced, but it can withstand the load caused by concrete placement during construction and the wheel load applied after completion.It is possible to construct an obtainable floor slab.
[0015]
  Further, when focusing on the bending moment acting on the entire slab, the bending moment is maximized at or near the center of the portion between the fulcrums, and the bending stress on the floor slab surface is the most severe at this portion.In construction method,Under the floor slabIn order to use what has a convex shape downward as a mold,The part where the bending moment is maximumInThe thickness of the floor slab itself and the section modulusWill increaseAccordingly, the tensile stress on the bottom of the slab caused by bendingCan be reduced.Therefore, the floor slab according to the present inventionThe construction method isIt can be said that the distribution of the bending moment is very reasonable.
[0016]
  The floor slab to which this construction method is applied isAfter placing concrete, the above-mentioned formwork may be removed to form a concrete floor slab, or the concrete and formwork may be integrated as they are to form a composite floor slab. As the formwork, steel plates with excellent tensile strength are suitable.The
[0017]
  In this method,A large film tensile force acts on the formwork when placing the concrete, and the fulcrum parts of the formwork try to displace in a direction in which they approach each other.To make a placement.
[0018]
  Specifically, a compression material extending in the direction connecting the fulcrums is fixed on the mold, and concrete is placed from above to embed the compression material.Like that.
[0019]
  In this method, for example, a steel material can be used as the compression material. In this case, the compression material and the concrete are highly heterogeneous. Cracks starting from the cracks occur along the compressed material, and the floor slab concrete may be divided into a plurality of beams due to the cracks. Such beaming causes a decrease in durability and may cause a situation where the floor slab cannot resist the wheel load.
[0020]
  Therefore, in this method,Use at least the surface of the compression material made of concrete.The In this way, the compressed materialEven if embedded, the above-mentioned skin separation is unlikely to occur, and cracks due to this are prevented.
[0021]
  In this case, if precast reinforced concrete is used as the compression material, construction is simple and sufficient strength can be ensured.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
  A first embodiment of the present invention will be described with reference to FIGS.
[0023]
  FIG.Floor slab to which the construction method of the floor slab of this embodiment is applied, and thisThe superstructure of the provided bridge is shown. In the figure, left and right main girders (bridge girders) 10 are arranged in parallel to each other. Each main girder 10 has an I-shaped cross section in the illustrated example, and a substantially T-shaped flange portion 12 as shown in FIG.
[0024]
  A thin bottom steel plate 14 that also serves as a mold is supported on both flange portions 12. Specifically, both ends of the bottom steel plate 14 are rigidly connected to the inner ends of both flange portions 12 using bolts 15 or the like shown in FIG.
[0025]
  As a feature of this structure, the bottom steel plate 14 is formed in advance so that the cross-sectional shape of the portion between the fulcrums (intermediate portion in the illustrated example) is a downwardly convex curved shape. Furthermore, both ends of a plurality of compression members (H-shaped steel in the illustrated example) 20 extending in the direction perpendicular to the bridge axis (width direction) are fixed to the inner ends of both flange portions 12 with bolts or the like. This compression material 20 is for restricting horizontal displacement in the direction in which the flange portions 12 approach each other (that is, the inner direction) due to a load or the like at the time of concrete placement described later.The
[0026]
  A flat bottom steel plate 16 is fixed to the outer ends of the flanges 12, and a reinforcing material (T-shaped steel in the illustrated example) 18 is fixed thereon. Each reinforcing material 18 is aligned with the compression material 20, and the upper end portions of the reinforcement material 18 and the compression material 20 are connected to each other through an attachment plate 21.
[0027]
  In order to reinforce the floor slab and prevent cracks in the concrete, reinforcing bars 18 extending in a direction (longitudinal direction) parallel to the bridge axis direction are fixed to the upper surface of the reinforcing member 18 and the compression member 20. A large number of stud dowels 26 are erected on the bottom steel plates 14 and 16 as means for preventing slippage. Then, concrete 24 is cast from above and integrated with both bottom steel plates 14, 16 to form a composite floor slab on both main girders 10, and each reinforcing material 18, compression material 20, The reinforcing bars 22 are embedded in the concrete 24.
[0028]
  If the bottom steel plate 14 is a striped steel plate as shown in FIGS. 6 (a) and 6 (b), that is, a steel plate in which a large number of protrusions 14a are integrally formed on the upper surface, the bottom steel plate 14 can be formed with a simple configuration. The adhesion between the steel plate 14 and the concrete 24 can be increased. As a result, it is possible to effectively prevent the bottom steel plate 14 and the concrete 24 from slipping without providing the above-mentioned stud gibber 26 and reinforcing ribs or the like, or while greatly reducing the number thereof. It is possible to maintain the synthesis effect. Further, it is possible to omit the tensile reinforcing bar to be arranged in the concrete at the lower edge of the floor slab, which leads to simplification of construction. Even if the bottom plate is made of a material other than the steel plate, this effect can be obtained by integrally forming irregularities on the upper surface.
[0029]
  The bottom steel plate 16, the reinforcing material 18, the reinforcing bar 22, the stud gibber 26, and the like are not constituent elements of the present invention and can be omitted as appropriate.
[0030]
  The above structure can be constructed by placing the bottom steel plates 14 and 16 and the compression material 20 on the main girder 10 and then placing concrete 24 thereon, but at the time of placing or completion of construction. In subsequent use, it is very advantageous in terms of strength and economy. Hereinafter, the reason will be described in detail.
[0031]
  1) Reduction of bending moment generated in the bottom steel plate 14
  When the concrete 24 is placed, a distributed load w (y) as shown in FIG. With this load, a vertically upward support reaction force is generated at both ends of the bottom steel plate 14, and a horizontal force H that is balanced with the film tensile force of the bottom steel plate 14 is generated. Similarly, a horizontal force H that balances the film tensile force is also applied to the central portion in the width direction of the bottom steel plate 14. Here, if the amount of protrusion from both end portions (fulcrum portions) to the center portion of the bottom steel plate 14 is f, there is a drop of f in the vertical direction at the point where both horizontal forces H are applied, so these horizontal forces H Moment H · f resulting from is generated. Since the sum of the moment H · f and the bending moment Ms of the bottom steel plate 14 is balanced with the bending moment Mo generated by the distributed load and the vertical reaction force, the following equation can be obtained.
[0032]
[Expression 1]

[0033]
  That is, according to the above-described structure, the bending moment Ms of the bottom steel plate 14 is reduced due to the downward maximum protrusion amount f in the center, and the reduction degree increases as the horizontal force H increases (that is, the load increases). ) Become remarkable. Therefore, the film tensile force is dominant as the force generated in the bottom steel plate 14, and the bottom steel plate 14 is pulled almost uniformly over the entire cross section. That is, it is possible to avoid the occurrence of high bending stress only on the steel plate surface and to effectively use the entire cross section of the bottom steel plate 14. Therefore, while using the thin bottom steel plate 14 and suppressing the use of the reinforcing material, the load at the time of placing the concrete and the wheel load after completion can be sufficiently resisted.
[0034]
  Further, if the concrete 24 is placed while restricting displacement of the flange portions 12 of the two main girders 10 toward each other using the compression material 20 shown in FIG. The horizontal force H can reliably prevent the main girder 10 from being harmfully deformed.
[0035]
  2) Relationship with bending moment acting on the whole slab
  When a load (for example, a wheel load) is applied between fulcrums on the completed floor slab, the maximum bending moment distribution acting on each part of the floor slab due to this is maximized at the center in the width direction. On the other hand, the floor slab shown in FIG. 1 has a maximum floor slab thickness at the center in the width direction because the bottom surface has a downwardly convex shape. That is, the section modulus is maximized at the central portion in the width direction, and the bending stress generated on the floor slab surface is reduced accordingly. As described above, since the portion where the bending moment is maximized and the portion where the section modulus is maximized are substantially matched, the stress generated in the floor slab can be made uniform in the width direction.
[0036]
  3) Comparison with conventional arched structure
  a)Regarding elastic buckling: As shown in FIG. 17 above, in the case of an arch type structure in which the portion between the fulcrums is convex upward, when a load due to concrete placement or the like acts, a film compressive force acts on the bottom steel plate. . Therefore, a design for preventing elastic buckling of the bottom steel plate due to the film compressive force is required. Specifically, the bottom steel plate must be thickened or the ribs increased, which hinders weight and cost reduction. In particular, when the structure becomes longer and the span becomes larger, the bottom steel sheet becomes more likely to buckle, so that the structure becomes increasingly large.
[0037]
  On the other hand, in the structure shown in FIG. 1, the bottom steel plate 14 has a downwardly convex shape contrary to the arched structure, and a film tensile force acts on the bottom steel plate 14, so that the elastic buckling There is no fear and basically only the tensile strength of the bottom steel plate 14 needs to be considered. Therefore, it is not necessary to thicken the bottom steel plate 14 or reinforce the ribs, and the structure can be reduced in weight and cost.
[0038]
  b)About the uneven load: In the case of the arch type structure, when receiving an uneven load (load acting at a position deviating from the center of the span) as shown in FIG. It is easy to move away, and in the worst case, it may jump down. Such deformation is extremely large and significantly impedes structural stability. On the other hand, when an uneven load is applied to the bottom convex steel plate 14 as shown in FIG. 5B, the convex portion tends to move in a direction approaching the point of application of the load, contrary to the above. Large deformation does not occur. Therefore, the structure is very stable against uneven loading. Moreover, since the moment element (= H · f) that cancels the bending moment Ms of the bottom steel plate 14 increases as the drop between the both end portions (fulcrum portions) increases due to the load, it is very reasonable.
[0039]
  The maximum protruding amount f of the convex portion can be set as appropriate. However, when the protruding amount f increases, the bending moment reduction degree of the bottom steel plate 14 increases, but the amount of cast concrete increases by the amount of the swelling. Since the floor slab weight increases, it is desirable to determine the protrusion amount f in consideration of the balance. This point will be discussed below.
[0040]
  Now, the distance between the fulcrums is set to L, the y axis is taken in the direction perpendicular to the bridge axis (width direction), and the y coordinate of the center position in the direction is set to 0. Assuming that the shape of the bottom steel plate 14 is a downwardly convex quadratic curve, the bending moment M (y) generated due to the distributed load w (y) due to concrete placement and the vertical reaction force at the support end. Is expressed by the following equation.
[0041]
[Expression 2]

[0042]
  If the z-axis coordinate is taken vertically downward, the distributed load w (y) is expressed by the following equation.
[0043]
[Equation 3]

[0044]
  By substituting this (Equation 3) into the above (Equation 2) and performing an integral operation, the following equation can be obtained.
[0045]
[Expression 4]

[0046]
  When the horizontal force H is obtained using the unit load method or the like based on (Equation 4), the following equation is obtained.
[0047]
[Equation 5]

[0048]
  Here, the thickness of the bottom steel plate 14 is t_sThen I = t_s3/12, A = t_sTherefore, the value of μ is given by the following equation.
[0049]
[Formula 6]

[0050]
  Where plate thickness t_sIs sufficiently smaller than the protrusion amount f, μ≈0 can be set. Substituting this into (Equation 5) and transforming it gives the following equation.
[0051]
[Expression 7]

[0052]
  On the other hand, the reinforced concrete weight per unit length is expressed by the following equation.
[0053]
[Equation 8]

[0054]
  In this (Equation 8) and the above (Equation 7), it can be assumed that β = 0.02 to 0.05 in the bridge slab of the normal form. By substituting an appropriate value for β within this range, H / ρL2 and W / ρL2 become functions of α. This is shown in the same graph in FIG.
[0055]
  The design of the bottom steel plate is such that the sum of the stress caused by the horizontal membrane tensile force H and the stress caused by the wheel load after completion of the floor slab does not exceed the allowable stress level. A thin plate can be used, which is economical.
[0056]
  Therefore, focusing on the horizontal membrane tensile force H in FIG. 4, the tensile force H increases rapidly when α is smaller than 0.02 (= 1/50). Therefore, α is preferably 1/50 or more (that is, the protrusion amount f is 1/50 or more of the fulcrum distance L). Furthermore, by setting the protrusion amount f to 1/30 or more of the fulcrum distance L, the horizontal membrane tensile force H can be suppressed to a minimum.
[0057]
  On the other hand, when paying attention to the concrete weight W, the weight W increases almost linearly as α increases, but in the region where α> 1/10 or more where the decreasing rate of the horizontal membrane tensile force H decreases, The effect of reducing the thickness of the steel sheet hardly increases. Therefore, from the viewpoint of weight reduction of the floor slab, α is preferably 1/10 (= 0.1) or less (that is, the protrusion amount f is 1/10 or less of the distance L between the fulcrums). Furthermore, it is more preferable that the protruding amount f is 1/20 or less of the fulcrum distance L.
[0058]
  A second embodiment will be described with reference to FIGS.
[0059]
  As shown in the first embodiment, when a steel material is used as the compression material 20 for embedding, since the heterogeneity between the steel material and the concrete 24 to be placed is high, both are relatively easily separated from each other. Due to this, there is a risk of cracking.
[0060]
  Therefore, in this embodiment, a material made of precast (pre-formed) reinforced concrete is used as the compression material 20 to prevent cracks caused by the skin separation.
[0061]
  As a means for positioning the compression material 20 with respect to the main beam 10 in this case, for example, as shown in FIG. 8, a protrusion 13 is provided on the upper surface of the upper flange portion 12 of the main beam 10, and a hole 28 into which the protrusion 13 can be fitted is provided. What is necessary is just to make it provide in the compression material 20 side.
[0062]
  In order to prevent the separation of the skin, it is sufficient that at least the surface of the compression material 20 is concrete or a similar material. For example, the entire compression material 20 may be integrated with concrete. However, if precast reinforced concrete as described above is used, handling during construction is easy and high strength can be ensured.
[0063]
  A third embodiment is shown in FIG. In this embodiment, instead of the linear compression member 20 as shown in FIG. 1, the displacement regulating member 30 having leg portions 32 suspended downward from both ends of the compression member portion 34 extending in the floor slab width direction is provided. Use. And the horizontal displacement of both the flange parts 12 is controlled by fixing the lower end of the both leg parts 32 to the both flange parts 12. In this state, the concrete is cast to a level below the compression material portion 34 and hardened, and then both the leg portions 32 are cut off at the middle portion and the compression material portion 34 is removed.
[0064]
  The details of the structure of each part other than the displacement regulating member 30 are the same as those shown in FIG.
[0065]
  According to this construction method, by removing the compressed material portion 34, the horizontal displacement restriction force until then is released, the compression force is introduced into the placed concrete, and the floor slab caused by the wheel load after completion, etc. Lower tensile stress can be reduced. Moreover, since the removed compressed material part 34 can be repeatedly used for the next construction, it is more economical than the method of embedding the compressed material 20.
[0066]
  In order to facilitate the work of separating the leg portion 32, the leg portion 32 may be divided in advance at a separation portion, and this portion may be detachably connected with a bolt or the like.
[0067]
  A fourth embodiment is shown in FIG. Here, before placing the concrete, one end of the tension wire 40 is connected to both flange portions 12 and the other end is connected to an appropriate position outside the bridge via the anchor 42.
[0068]
  Also in this method, it is possible to place concrete on the bottom steel plate 14 while restricting the horizontal displacement of both flange portions 12 by the tension of the pulling wire 40. After the concrete is placed and hardened, the pulling wire 40 is separated from the flange portion 12 to release the displacement restricting force, and prestress can be applied to the concrete as in the third embodiment.
[0069]
  A fifth embodiment is shown in FIGS. 12 (a) and 12 (b).
[0070]
  As a means for preventing the bottom steel plate 14 and the concrete 24 from slipping, as shown in FIGS. 12 (a) and 12 (b), for example, a method of fixing a reinforcing rib 40 made of a flat bar on the bottom steel plate 14 in an upright state. well known. In order to apply this method to a curved surface with the bottom steel plate 14 projecting downward as in the present invention, the bottom steel plate 14 is along a direction in which the cross section of the bottom steel plate 14 is a straight line (the depth direction in FIG. 12A). If the reinforcing ribs 40 are arranged in parallel, the reinforcing ribs 40 can be fixed to the bottom steel plate 14 without hindering the film action.
[0071]
  However, in the structure where only the reinforcing ribs 40 are provided, when the concrete is cast from above and the reinforcing ribs 40 are embedded, the reinforcing ribs 40 are sharply bited upward into the concrete. A crack is generated from the biting portion, and the crack is likely to progress upward. When the crack finally reaches the top surface of the concrete in this way, the concrete is divided at the rib placement position, and is in a so-called beam-like state.
[0072]
  Therefore, in this embodiment, each reinforcing rib 40 is provided with a through hole 41 as shown in FIG. 12 (b), and a thin reinforcing bar 42 made of, for example, a steel wire is passed through the through hole 41, and a curved surface convex downwards. It is trying to arrange along.
[0073]
  According to such a configuration, displacement of the cast concrete in the direction perpendicular to the reinforcing rib 40 in the vicinity of the bottom steel plate 14 is restricted by the reinforcing bars 42, and therefore, the progress of the crack accompanying the displacement is minimized. Can be stopped. The reinforcing bars 42 can also be expected as a means for suppressing the skin separation between the bottom steel plate 14 and the concrete.
[0074]
  In addition, if the rebar 42 is thin and can be bent and deformed together with the bottom steel plate 14, it is possible to obtain the sufficient effect of the present invention without inhibiting the film action of the bottom steel plate 14. is there.
[0075]
  Further, since the reinforcing bar 42 only needs to be inserted into the through hole 41 provided in the reinforcing rib 40, the construction is easy.
[0076]
  A sixth embodiment is shown in FIGS. 13 (a) and 13 (b).
[0077]
  As the means for preventing the bottom steel plate 14 and the concrete 24 from slipping, the above-mentioned stud gibber and reinforcing rib are also effective, but since these are in a state of being sharply bite into the placed concrete, the concentration of cracks is high. , Durability may be greatly affected.
[0078]
  Therefore, in this embodiment, for example, a non-slip wire 46 that is made of a steel material in a spiral shape so that it can be easily bent and deformed is disposed on the bottom steel plate 14, and the above-described non-slipping to the bottom steel plate 14. Only the lower end portions 44 of the wire 46 are locally fixed (for example, spot welding). It is not necessary to fix all the lower end portions 44, and only a specific lower end portion 44 may be fixed intermittently.
[0079]
  According to this configuration, the following effects can be obtained.
[0080]
  a)Compared with the stud gibber and the reinforcing rib, the concentration of cracks is lowered (that is, cracks are dispersed), and as a result, sufficient durability is maintained.
[0081]
  b)Since the contact area with the concrete is larger than that of the stud gibber and the reinforcing rib, the effect of preventing slippage and the effect of preventing skin separation are high, and a sufficient composite effect can be obtained.
[0082]
  c)Since the slip preventing wire 46 is easily bent and deformed, the film action of the steel plate 14 is not hindered.
[0083]
  d)Construction is easy because the welding area is small compared to stud gibbles and reinforcing ribs.
[0084]
  Note that the above-described slip preventing wire 46 is not necessarily limited to a spiral shape, and may be a curved shape that can be bent and deformed, and a part thereof may be locally fixed to the bottom steel plate 14. For example, only the trough portion of the wavy or zigzag-shaped detent wire 46 as shown in FIG. 14 (a) may be locally fixed on the bottom steel plate 14, or as shown in FIG. 14 (b). It is also possible to fix both ends of the semi-circular semicircle or the end-attached locking wire 46 similar to this to the bottom steel plate 14 and arrange a large number of the locking wires 46 in parallel.
[0085]
  However, if the anti-slip member 46 has a spiral shape as shown in FIG. 13, the deformation can be made easier, and the contact area with the concrete can be effectively increased to make the anti-slipping action more remarkable. It becomes possible.
[0086]
  In addition, this invention can also take the following embodiment as an example.
[0087]
  (1) The present invention is not limited to a bridge slab and its construction, but can also be applied to other civil engineering slabs or a building floor slab and its construction. Also, the number of support points by the bridge girder is not limited to two, and may be set to three or more. For example, as shown in FIG. 15 as the seventh embodiment, in the case of a floor slab having three or more fulcrums in both vertical and horizontal directions (that is, supported by three or more bridge girders), By making at least one convex downward, the above-mentioned actions and effects can be obtained at that portion.
[0088]
  In this case, which fulcrum portion 17 has a downwardly convex shape may be appropriately set according to the specification. Further, when there are a plurality of inter-fulcrum portions 17 as described above, another bottom steel plate 14 is used for each inter-fulcrum portion 17 (that is, the bottom steel plate 14 is divided corresponding to the inter-fulcrum portion 17). Alternatively, a common bottom steel plate 14 may be used for all fulcrum portions 17 (that is, a single bottom steel plate 14 is placed on the bridge girder).
[0089]
  (2) The specific shape of the bottom steel plate 14 shown in the above embodiments is not particularly limited, and can be appropriately set within a range in which the portion between the fulcrums is convex downward. For example, in addition to a curved surface as a whole, a plurality of planes may be combined as shown in FIGS. 16A and 16B, or a plane and a curved surface may be used as shown in FIGS. May be combined. The specific cross-sectional shape of the curved surface can be set in various ways, including quadratic or higher-order curves, arcs, elliptic curves, hyperbolas, sine curves, catenary lines (hyperbolic sine function curves), cycloid curves, etc. Any type.
[0090]
  (3) In the above embodiment, concrete is directly placed on the bottom steel plate 14, but concrete hardly contributes to the tensile force generated at the bottom of the floor slab. A box-like member or a tubular member for securing a gap in the lower part may be introduced, or a lightweight hard urethane or the like may be laid on the bottom steel plate 14, and concrete may be placed thereon. . In addition, as described above, mortar or the like can be used instead of concrete depending on the use of the slab.
[0091]
  (4) In the above embodiment, the bottom steel plate 14 and the cast concrete 24 are integrated to form a composite floor slab. However, after the concrete is placed and hardened, the bottom steel plate 14 is removed to provide a concrete floor slab. You may make it do. That is, you may make it use the bottom steel plate 14 only as a formwork. Also in this case, it is needless to say that the concrete can be placed with a simple structure and no inconvenience in strength by making the bottom steel plate 14 convex downward. Regardless of whether the formwork is removed in this way or the formwork is left as a composite floor slab, the material of the formwork is not limited to a steel plate, but as a membrane member that resists tensile force. If it can be used, it can be widely applied. For example, FRP, a wooden board, a cloth material woven with high-strength fibers, or the like can also be used as a mold.
[0092]
【Example】
  In the structure shown in FIG. 1, the main girder interval is 8.4 m, and the thickness t of the bottom steel plate 14._s8mm, maximum protrusion f is 390mm, the height and width of the compressed material 20 are 200mm, the distance between the compressed materials 20 is 1m, the slab thickness t of the fulcrum part_coThe construction was done with 270mm. FIG. 11 shows the result of numerical analysis of the inward horizontal displacement of the main girder flange 12 at this time. As shown in this figure, the maximum displacement of the flange portion in the above direction is about 1.4 mm, and it has been confirmed that even if concrete is placed, the main girder 10 is not adversely affected.
[0093]
  If it is particularly strictly necessary to avoid this influence, a measure such as building a bridge so as to allow at least one main girder 10 to move in a direction perpendicular to the bridge axis may be taken.
[0094]
【The invention's effect】
  As described above, the present inventionIs the typeIn a construction method for forming a floor slab by supporting a frame from below and placing concrete on the mold, at least one of the fulcrum portions has a downwardly convex shape as the mold Therefore, there is an effect that the concrete can be placed without any inconvenience with a simple structure and that it can sufficiently withstand the wheel load after completion.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an upper structure of a bridge according to a first embodiment of the present invention.
FIG. 2 is an enlarged view of part A in FIG.
FIG. 3 is an explanatory diagram showing each force generated when concrete is placed on the bottom steel plate shown in FIG. 1;
FIG. 4 is a graph showing the relationship between the ratio α of the maximum protrusion amount with respect to the distance between fulcrums, the generated membrane horizontal force H, and the necessary concrete weight W.
5A is an explanatory diagram showing deformation that can occur when a load acts on an upwardly convex bottom steel plate, and FIG. 5B can occur when a load acts on a bottom steel plate that is mounted downward. It is explanatory drawing which shows a deformation | transformation.
6A is a plan view showing a striped steel plate as an example of the bottom steel plate, and FIG. 6B is a cross-sectional view taken along line AA in FIG.
FIG. 7 is a perspective view showing a construction method according to a second embodiment of the present invention.
FIG. 8 is a perspective view showing an example of a positioning structure of the compressed material shown in FIG.
FIG. 9 is a perspective view showing a construction method according to a third embodiment of the present invention.
FIG. 10 is an explanatory diagram showing a construction method according to a fourth embodiment of the present invention.
FIG. 11 is a graph showing an analysis result of flange portion displacement in a direction perpendicular to the bridge axis in the example of the present invention.
12A is an explanatory view showing a construction method according to a fifth embodiment of the present invention, and FIG. 12B is a perspective view showing an essential part thereof.
FIG. 13A is an explanatory view showing a construction method according to a sixth embodiment of the present invention, and FIG. 13B is a perspective view showing a welded state between a detent member used in the construction method and a bottom steel plate. It is.
14 (a) and 14 (b) are perspective views showing a modification of the slip prevention member.
FIG. 15 is a schematic diagram showing a support state of a floor slab in a seventh embodiment of the present invention.
FIGS. 16A, 16B, 16C, and 16D are explanatory views showing a modified form of the formwork.
FIG. 17 is a cross-sectional perspective view showing a conventional example of a bridge slab.
[Explanation of symbols]
  10 Main girder (bridge girder)
  14 Bottom steel plate
  14a Protrusion of striped steel plate
  17 Between fulcrums
  20 Compressed material
  24 concrete
  30 Displacement restricting member
  34 Compressed material
  46 Anti-slip member

Claims (2)

In the construction method of forming a floor slab by supporting the formwork from below and placing concrete on this formwork,
While using at least one of the parts between the fulcrum as the mold has a downwardly convex shape,
A compression material that extends in a direction connecting the fulcrum portions of the mold, and at least the surface of the compression material is formed of concrete, and is fixed on the mold, and concrete is placed on the compression material. A method for constructing a floor slab, wherein concrete is placed while embedding a compression material while restricting displacement of fulcrum portions of the above-mentioned formwork toward each other. In the construction method of the floor slab according to claim 1,
A floor slab construction method characterized by using precast reinforced concrete as the compression material.

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