無梁拱,拱(gong)(gong)(gong)(gong)(gong)形屋(wu)(wu)面還具有承壓(ya)(ya)效果(guo)，拱(gong)(gong)(gong)(gong)(gong)所承受的荷載(zai)不同(tong)，其壓(ya)(ya)力(li)(li)曲(qu)線(xian)(xian)的線(xian)(xian)形也不相(xiang)同(tong)，一般按恒載(zai)下(xia)壓(ya)(ya)力(li)(li)曲(qu)線(xian)(xian)確定(ding);在活(huo)載(zai)作(zuo)用(yong)(yong)下(xia)，拱(gong)(gong)(gong)(gong)(gong)內力(li)(li)可能產生(sheng)彎矩(ju)，這(zhe)時鉸的設置就會影響拱(gong)(gong)(gong)(gong)(gong)內彎矩(ju)的分(fen)布狀況(kuang)。與(yu)剛架相(xiang)仿，只有地基良好或(huo)兩側(ce)拱(gong)(gong)(gong)(gong)(gong)肢處有穩定(ding)邊跨結(jie)構時才采用(yong)(yong)無鉸拱(gong)(gong)(gong)(gong)(gong)，這(zhe)種拱(gong)(gong)(gong)(gong)(gong)很少用(yong)(yong)于(yu)房屋(wu)(wu)建(jian)筑。雙(shuang)鉸拱(gong)(gong)(gong)(gong)(gong)應用(yong)(yong)較多(duo)，為適應軟弱(ruo)地基上(shang)支座沉降差(cha)及拱(gong)(gong)(gong)(gong)(gong)拉(la)桿(gan)變形，采用(yong)(yong)靜定(ding)結(jie)構的三鉸拱(gong)(gong)(gong)(gong)(gong)。
拱以曲桿抗衡并傳(chuan)遞外(wai)力(li)(li)(li)給支(zhi)(zhi)座(zuo)，故(gu)鉸支(zhi)(zhi)座(zuo)不(bu)僅(jin)承受豎(shu)向(xiang)(xiang)力(li)(li)(li)，并有相(xiang)當大(da)(da)的(de)(de)水平(ping)向(xiang)(xiang)外(wai)的(de)(de)拱腳(jiao)推(tui)力(li)(li)(li)，其(qi)合(he)力(li)(li)(li)就位于(yu)拱軸(zhou)曲線(xian)在(zai)支(zhi)(zhi)座(zuo)點的(de)(de)切線(xian)方向(xiang)(xiang)上。拱腳(jiao)有推(tui)力(li)(li)(li)是其(qi)主要力(li)(li)(li)學(xue)特征之(zhi)一，矢高f越(yue)小，推(tui)力(li)(li)(li)越(yue)大(da)(da)。一次超靜(jing)定的(de)(de)雙鉸拱，金(jin)屬屋面支(zhi)(zhi)座(zuo)的(de)(de)垂直或水平(ping)位移(yi)均會(hui)引起內(nei)力(li)(li)(li)變化，對支(zhi)(zhi)座(zuo)在(zai)推(tui)力(li)(li)(li)作用(yong)下無變位的(de)(de)要求就更嚴格。由此(ci)可見，為(wei)了使拱保持正(zheng)常工作，務必(bi)確保其(qi)支(zhi)(zhi)座(zuo)能(neng)承受住推(tui)力(li)(li)(li)而不(bu)位移(yi)，故(gu)拱腳(jiao)推(tui)力(li)(li)(li)的(de)(de)結構(gou)處理，是拱結構(gou)設計(ji)的(de)(de)中心問題。
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