拱板設備之拱(gong)形承壓的原理(li)
拱(gong)(gong)所承受的荷載不(bu)同，其(qi)壓力曲線的線形也不(bu)相同，一(yi)般(ban)按恒(heng)載下(xia)壓力曲線確(que)定(ding)(ding);在活載作(zuo)用(yong)(yong)(yong)下(xia)，拱(gong)(gong)內力可能(neng)產生彎矩，這時鉸的設(she)置就會影(ying)響拱(gong)(gong)內彎矩的分(fen)布狀況。與(yu)剛架相仿，只有地基良好(hao)或兩側拱(gong)(gong)肢處有穩定(ding)(ding)邊跨結構時才采用(yong)(yong)(yong)無鉸拱(gong)(gong)，這種(zhong)拱(gong)(gong)很少用(yong)(yong)(yong)于房屋建(jian)筑。雙鉸拱(gong)(gong)應用(yong)(yong)(yong)較多，為(wei)適應軟弱地基上支(zhi)座沉降(jiang)差及拱(gong)(gong)拉桿變形，最好(hao)采用(yong)(yong)(yong)靜定(ding)(ding)結構的三(san)鉸拱(gong)(gong)。
拱以曲桿抗衡(heng)并傳遞外(wai)力(li)(li)(li)給支(zhi)座，故鉸支(zhi)座不僅承(cheng)受豎向力(li)(li)(li)，并有(you)相當大的(de)(de)(de)水平向外(wai)的(de)(de)(de)拱腳(jiao)(jiao)推(tui)力(li)(li)(li)，其(qi)(qi)合力(li)(li)(li)就位(wei)(wei)于(yu)拱軸曲線在支(zhi)座點的(de)(de)(de)切線方向上。拱腳(jiao)(jiao)有(you)推(tui)力(li)(li)(li)是其(qi)(qi)主要力(li)(li)(li)學特征之一(yi)，矢高(gao)f越(yue)小，推(tui)力(li)(li)(li)越(yue)大。一(yi)次超靜定的(de)(de)(de)雙鉸拱，支(zhi)座的(de)(de)(de)垂直或(huo)水平位(wei)(wei)移均會(hui)引起內力(li)(li)(li)變化，對支(zhi)座在推(tui)力(li)(li)(li)作用下(xia)無變位(wei)(wei)的(de)(de)(de)要求(qiu)就更嚴格。由此可(ke)見，為(wei)了使拱保持正常工作，務必確保其(qi)(qi)支(zhi)座能承(cheng)受住(zhu)推(tui)力(li)(li)(li)而不位(wei)(wei)移，故拱腳(jiao)(jiao)推(tui)力(li)(li)(li)的(de)(de)(de)結構處(chu)理(li)，是拱結構設計的(de)(de)(de)中心(xin)問題。
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