無梁拱之拱(gong)形所(suo)承受的(de)(de)荷載不同(tong)，其壓力(li)(li)曲線(xian)的(de)(de)線(xian)形也不相(xiang)同(tong)，一般按恒載下壓力(li)(li)曲線(xian)確定(ding)(ding)(ding);在活(huo)載作用(yong)(yong)下，拱(gong)內(nei)力(li)(li)可(ke)能產生彎矩，這(zhe)時鉸(jiao)的(de)(de)設置就(jiu)會影響拱(gong)內(nei)彎矩的(de)(de)分布狀況。與剛架相(xiang)仿，只有地基良好(hao)或兩側拱(gong)肢處有穩定(ding)(ding)(ding)邊跨結構(gou)時才采(cai)用(yong)(yong)無(wu)鉸(jiao)拱(gong)，這(zhe)種拱(gong)很少用(yong)(yong)于房屋建筑。雙鉸(jiao)拱(gong)應(ying)用(yong)(yong)較(jiao)多(duo)，為適應(ying)軟弱地基上支座沉降差及拱(gong)拉桿(gan)變形，最好(hao)采(cai)用(yong)(yong)靜定(ding)(ding)(ding)結構(gou)的(de)(de)三鉸(jiao)拱(gong)。
拱(gong)(gong)以曲桿抗衡并(bing)傳遞外(wai)力(li)(li)(li)給支(zhi)(zhi)座(zuo)，故鉸(jiao)支(zhi)(zhi)座(zuo)不僅(jin)承受豎向(xiang)力(li)(li)(li)，并(bing)有相當大的水平向(xiang)外(wai)的拱(gong)(gong)腳(jiao)推(tui)(tui)力(li)(li)(li)，其合力(li)(li)(li)就位(wei)于拱(gong)(gong)軸曲線(xian)在(zai)(zai)支(zhi)(zhi)座(zuo)點(dian)的切線(xian)方向(xiang)上。拱(gong)(gong)腳(jiao)有推(tui)(tui)力(li)(li)(li)是其主(zhu)要力(li)(li)(li)學(xue)特征之一，矢高f越(yue)小，推(tui)(tui)力(li)(li)(li)越(yue)大。一次超靜定的雙鉸(jiao)拱(gong)(gong)，支(zhi)(zhi)座(zuo)的垂直或水平位(wei)移均會(hui)引起(qi)內(nei)力(li)(li)(li)變化，對支(zhi)(zhi)座(zuo)在(zai)(zai)推(tui)(tui)力(li)(li)(li)作用下無變位(wei)的要求就更嚴格。由此可見(jian)，為了使拱(gong)(gong)保(bao)持正常(chang)工作，務必(bi)確保(bao)其支(zhi)(zhi)座(zuo)能承受住(zhu)推(tui)(tui)力(li)(li)(li)而(er)不位(wei)移，故拱(gong)(gong)腳(jiao)推(tui)(tui)力(li)(li)(li)的結構處(chu)理，是拱(gong)(gong)結構設(she)計的中心問(wen)題。
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