拱板(ban)設(she)備之拱形承壓(ya)的原理(li)
拱(gong)(gong)(gong)(gong)形(xing)所承受的(de)荷載不(bu)(bu)同，其壓力曲(qu)線的(de)線形(xing)也不(bu)(bu)相同，一(yi)般按恒載下壓力曲(qu)線確定;在活載作用(yong)(yong)下，拱(gong)(gong)(gong)(gong)內力可(ke)能產生(sheng)彎矩，這時鉸(jiao)的(de)設置(zhi)就會影響拱(gong)(gong)(gong)(gong)內彎矩的(de)分布(bu)狀況(kuang)。與剛(gang)架相仿，只(zhi)有(you)地基良好或(huo)兩側(ce)拱(gong)(gong)(gong)(gong)肢處有(you)穩定邊跨(kua)結構(gou)時才采用(yong)(yong)無鉸(jiao)拱(gong)(gong)(gong)(gong)，這種拱(gong)(gong)(gong)(gong)很少用(yong)(yong)于房屋建筑。雙鉸(jiao)拱(gong)(gong)(gong)(gong)應用(yong)(yong)較多，為適應軟弱地基上(shang)支座沉降差及拱(gong)(gong)(gong)(gong)拉桿變(bian)形(xing)，很好采用(yong)(yong)靜(jing)定結構(gou)的(de)三鉸(jiao)拱(gong)(gong)(gong)(gong)。
拱(gong)(gong)以曲桿(gan)抗衡并傳遞外力(li)(li)(li)給支(zhi)座(zuo)(zuo)(zuo)，故鉸支(zhi)座(zuo)(zuo)(zuo)不(bu)僅(jin)承受(shou)(shou)豎向(xiang)力(li)(li)(li)，并有(you)相當大的水(shui)(shui)平向(xiang)外的拱(gong)(gong)腳推力(li)(li)(li)，其(qi)合力(li)(li)(li)就(jiu)位(wei)于拱(gong)(gong)軸曲線在(zai)支(zhi)座(zuo)(zuo)(zuo)點的切線方(fang)向(xiang)上。拱(gong)(gong)腳有(you)推力(li)(li)(li)是其(qi)主(zhu)要力(li)(li)(li)學特(te)征(zheng)之一，矢高f越小，推力(li)(li)(li)越大。一次超靜定(ding)的雙鉸拱(gong)(gong)，支(zhi)座(zuo)(zuo)(zuo)的垂直或(huo)水(shui)(shui)平位(wei)移均會引起內力(li)(li)(li)變化，對支(zhi)座(zuo)(zuo)(zuo)在(zai)推力(li)(li)(li)作用下(xia)無變位(wei)的要求(qiu)就(jiu)更嚴格(ge)。由此(ci)可見，為了(le)使拱(gong)(gong)保(bao)持正常工(gong)作，務(wu)必確保(bao)其(qi)支(zhi)座(zuo)(zuo)(zuo)能承受(shou)(shou)住推力(li)(li)(li)而不(bu)位(wei)移，故拱(gong)(gong)腳推力(li)(li)(li)的結(jie)(jie)構(gou)處(chu)理，是拱(gong)(gong)結(jie)(jie)構(gou)設計的中心問題。
|
