拱(gong)(gong)(gong)(gong)板(ban)設(she)備(bei)拱(gong)(gong)(gong)(gong)形所承受的(de)(de)荷(he)載不同(tong)(tong)，其(qi)壓力(li)曲線的(de)(de)線形也不相同(tong)(tong)，一般按(an)恒(heng)載下壓力(li)曲線確定(ding);在(zai)活載作(zuo)用(yong)下，拱(gong)(gong)(gong)(gong)內(nei)力(li)可能產生彎矩(ju)，這時(shi)鉸的(de)(de)設(she)置就會影響(xiang)拱(gong)(gong)(gong)(gong)內(nei)彎矩(ju)的(de)(de)分布狀況。與剛架相仿，只有(you)地基(ji)良(liang)好(hao)或兩側拱(gong)(gong)(gong)(gong)肢處有(you)穩定(ding)邊跨(kua)結(jie)構(gou)時(shi)才(cai)采(cai)用(yong)無(wu)鉸拱(gong)(gong)(gong)(gong)，這種拱(gong)(gong)(gong)(gong)很少用(yong)于房屋建筑。雙鉸拱(gong)(gong)(gong)(gong)應用(yong)較多，為適(shi)應軟弱地基(ji)上支(zhi)座(zuo)沉(chen)降(jiang)差及拱(gong)(gong)(gong)(gong)拉桿變形，最(zui)好(hao)采(cai)用(yong)靜定(ding)結(jie)構(gou)的(de)(de)三(san)鉸拱(gong)(gong)(gong)(gong)。
拱(gong)(gong)(gong)以(yi)曲(qu)桿抗衡并傳遞(di)外力(li)(li)給(gei)支座，故(gu)鉸(jiao)(jiao)支座不僅承受豎向(xiang)力(li)(li)，并有(you)相當大的(de)(de)水(shui)平(ping)向(xiang)外的(de)(de)拱(gong)(gong)(gong)腳推(tui)(tui)力(li)(li)，其(qi)合力(li)(li)就位(wei)于拱(gong)(gong)(gong)軸(zhou)曲(qu)線在(zai)支座點的(de)(de)切線方向(xiang)上。拱(gong)(gong)(gong)腳有(you)推(tui)(tui)力(li)(li)是其(qi)主要力(li)(li)學特征(zheng)之(zhi)一，矢高f越(yue)小，推(tui)(tui)力(li)(li)越(yue)大。一次超(chao)靜定的(de)(de)雙鉸(jiao)(jiao)拱(gong)(gong)(gong)，支座的(de)(de)垂直或水(shui)平(ping)位(wei)移均會引起(qi)內力(li)(li)變(bian)化，對支座在(zai)推(tui)(tui)力(li)(li)作用(yong)下無變(bian)位(wei)的(de)(de)要求就更(geng)嚴格。由此(ci)可見(jian)，為了使(shi)拱(gong)(gong)(gong)保持正常工(gong)作，務必確(que)保其(qi)支座能承受住推(tui)(tui)力(li)(li)而不位(wei)移，故(gu)拱(gong)(gong)(gong)腳推(tui)(tui)力(li)(li)的(de)(de)結(jie)構(gou)處理，是拱(gong)(gong)(gong)結(jie)構(gou)設計(ji)的(de)(de)中心問(wen)題。
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