拱(gong)形(xing)(xing)所承受的(de)荷載(zai)不同，其壓(ya)力(li)曲(qu)線的(de)線形(xing)(xing)也(ye)不相(xiang)同，一般按恒載(zai)下壓(ya)力(li)曲(qu)線確定(ding);在(zai)活載(zai)作用(yong)下，拱(gong)內力(li)可能產生彎矩(ju)，這(zhe)時鉸(jiao)的(de)設置(zhi)就(jiu)會影響拱(gong)內彎矩(ju)的(de)分布狀況。與剛架(jia)相(xiang)仿，只有地基良好或兩側拱(gong)肢處有穩定(ding)邊跨結構時才采用(yong)無鉸(jiao)拱(gong)，這(zhe)種拱(gong)很(hen)少(shao)用(yong)于房屋(wu)建筑。雙鉸(jiao)拱(gong)應用(yong)較多，為(wei)適應軟弱(ruo)地基上(shang)支座沉降差及拱(gong)拉桿變(bian)形(xing)(xing)，最好采用(yong)靜定(ding)結構的(de)三(san)鉸(jiao)拱(gong)。
拱以曲桿(gan)抗衡并(bing)傳遞(di)外力給支座(zuo)(zuo)，故鉸(jiao)支座(zuo)(zuo)不僅(jin)承受豎(shu)向(xiang)(xiang)力，并(bing)有相(xiang)當大(da)的水平向(xiang)(xiang)外的拱腳推力，其合力就位于拱軸曲線在支座(zuo)(zuo)點的切線方向(xiang)(xiang)上
拱(gong)(gong)(gong)板(ban)設(she)備(bei)拱(gong)(gong)(gong)腳(jiao)有(you)推(tui)力(li)是(shi)其(qi)主要力(li)學特征之一，矢高f越(yue)小，推(tui)力(li)越(yue)大。一次超靜定(ding)的(de)(de)(de)雙鉸拱(gong)(gong)(gong)，支(zhi)座的(de)(de)(de)垂直或水平位(wei)(wei)移均會引起(qi)內力(li)變化，對支(zhi)座在(zai)推(tui)力(li)作用下無變位(wei)(wei)的(de)(de)(de)要求就更嚴格。由(you)此可見(jian)，為了使拱(gong)(gong)(gong)保持正常工作，務(wu)必確保其(qi)支(zhi)座能(neng)承受住推(tui)力(li)而不位(wei)(wei)移，故拱(gong)(gong)(gong)腳(jiao)推(tui)力(li)的(de)(de)(de)結構處理，是(shi)拱(gong)(gong)(gong)結構設(she)計的(de)(de)(de)中心問題(ti)。
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