說一說拱板設(she)備之拱形(xing)承壓的(de)原理
拱(gong)(gong)(gong)(gong)(gong)板設(she)(she)備拱(gong)(gong)(gong)(gong)(gong)形所承受的(de)(de)荷載不(bu)同(tong)，其(qi)壓(ya)力曲線(xian)的(de)(de)線(xian)形也不(bu)相同(tong)，一(yi)般按恒載下壓(ya)力曲線(xian)確定;在活載作用下，拱(gong)(gong)(gong)(gong)(gong)內力可能產生彎矩(ju)，這時鉸(jiao)(jiao)的(de)(de)設(she)(she)置就會影響(xiang)拱(gong)(gong)(gong)(gong)(gong)內彎矩(ju)的(de)(de)分布狀況。與剛架相仿(fang)，只有地(di)基良好(hao)(hao)或兩側拱(gong)(gong)(gong)(gong)(gong)肢處有穩(wen)定邊(bian)跨結構(gou)時才采用無鉸(jiao)(jiao)拱(gong)(gong)(gong)(gong)(gong)，這種拱(gong)(gong)(gong)(gong)(gong)很少用于房屋建筑。雙鉸(jiao)(jiao)拱(gong)(gong)(gong)(gong)(gong)應(ying)用較多，為適應(ying)軟弱(ruo)地(di)基上支(zhi)座沉降差及拱(gong)(gong)(gong)(gong)(gong)拉桿變形，最好(hao)(hao)采用靜(jing)定結構(gou)的(de)(de)三鉸(jiao)(jiao)拱(gong)(gong)(gong)(gong)(gong)。
拱(gong)以曲桿(gan)抗衡并(bing)傳遞外力(li)給支座，故鉸支座不僅承(cheng)受(shou)豎向力(li)，并(bing)有(you)相當大的(de)(de)水平向外的(de)(de)拱(gong)腳推力(li)，其合力(li)就位于拱(gong)軸曲線(xian)在(zai)支座點(dian)的(de)(de)切線(xian)方向上。拱(gong)腳有(you)推力(li)是(shi)其主要力(li)學特征之一(yi)，矢(shi)高f越小，推力(li)越大。一(yi)次超(chao)靜定的(de)(de)雙鉸拱(gong)，支座的(de)(de)垂直(zhi)或水平位移(yi)均(jun)會(hui)引起(qi)內力(li)變化(hua)，對(dui)支座在(zai)推力(li)作用下無變位的(de)(de)要求就更嚴(yan)格。由此可(ke)見(jian)，為了使拱(gong)保(bao)持(chi)正常工作，務必確保(bao)其支座能承(cheng)受(shou)住推力(li)而不位移(yi)，故拱(gong)腳推力(li)的(de)(de)結(jie)構(gou)(gou)處(chu)理，是(shi)拱(gong)結(jie)構(gou)(gou)設計(ji)的(de)(de)中(zhong)心問題。
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