關于拱板設備之拱形承壓的原理
拱(gong)(gong)形所承受的荷載不同(tong)，其(qi)壓力曲線的線形也不相(xiang)同(tong)，一(yi)般按恒載下壓力曲線確定(ding);在(zai)活載作用(yong)下，拱(gong)(gong)內力可能產生彎矩，這(zhe)時鉸(jiao)(jiao)的設置(zhi)就會影(ying)響(xiang)拱(gong)(gong)內彎矩的分布狀(zhuang)況。與剛架(jia)相(xiang)仿，只(zhi)有(you)地基良好或兩(liang)側拱(gong)(gong)肢處有(you)穩定(ding)邊跨結(jie)構時才采用(yong)無(wu)鉸(jiao)(jiao)拱(gong)(gong)，這(zhe)種拱(gong)(gong)很少用(yong)于房(fang)屋建筑。雙鉸(jiao)(jiao)拱(gong)(gong)應用(yong)較多，為適應軟弱(ruo)地基上支座沉降差及拱(gong)(gong)拉桿(gan)變形，最好采用(yong)靜定(ding)結(jie)構的三鉸(jiao)(jiao)拱(gong)(gong)。
拱(gong)以曲桿抗衡并傳遞外力(li)(li)(li)(li)給支(zhi)(zhi)座(zuo)，故鉸(jiao)支(zhi)(zhi)座(zuo)不(bu)僅承受豎向力(li)(li)(li)(li)，并有(you)相當大的(de)水(shui)平(ping)向外的(de)拱(gong)腳推(tui)力(li)(li)(li)(li)，其(qi)合(he)力(li)(li)(li)(li)就位于拱(gong)軸曲線在支(zhi)(zhi)座(zuo)點的(de)切線方向上。拱(gong)腳有(you)推(tui)力(li)(li)(li)(li)是(shi)其(qi)主要力(li)(li)(li)(li)學特(te)征之一(yi)，矢高(gao)f越小，推(tui)力(li)(li)(li)(li)越大。一(yi)次(ci)超(chao)靜(jing)定(ding)的(de)雙(shuang)鉸(jiao)拱(gong)，支(zhi)(zhi)座(zuo)的(de)垂直或水(shui)平(ping)位移均會(hui)引(yin)起(qi)內力(li)(li)(li)(li)變化(hua)，對支(zhi)(zhi)座(zuo)在推(tui)力(li)(li)(li)(li)作用下無(wu)變位的(de)要求就更(geng)嚴格。由此(ci)可見(jian)，為了使拱(gong)保持(chi)正常工(gong)作，務必確(que)保其(qi)支(zhi)(zhi)座(zuo)能承受住(zhu)推(tui)力(li)(li)(li)(li)而不(bu)位移，故拱(gong)腳推(tui)力(li)(li)(li)(li)的(de)結(jie)構(gou)處理，是(shi)拱(gong)結(jie)構(gou)設計的(de)中(zhong)心(xin)問題。
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