過(guò)程裝備與控制工程專(zhuān)業(yè)英語(yǔ)

1、過(guò)程裝備與控制工程 過(guò)程裝備與控制工程專(zhuān)業(yè)英語(yǔ) 專(zhuān)業(yè)英語(yǔ)學(xué)院：化學(xué)化工學(xué)院 學(xué)院：化學(xué)化工學(xué)院1.Static Analysis of Beams1 A bar that is subjected to forces acting trasverse to its axis is called a beam. In this section we consider only a few of the simplest types of

2、 beams, such as those shown in Flag.1.2. In every instance it is assumed that the beam has a plane of symmetry that is parallel to the plane of the figure itself. Thus， the cross section of the beam has a vertical axis

3、 of symmetry .Also,it is assumed that the applied loads act in the plane of symmetry ,and hence bending of the beam occurs in that plane. Later we will consider a more general kind of bending in which the beam may have a

4、n unsymmetrical cross section.2 The beam in Fig.1.2, with a pin support at one end and a roller support at the other, is called a simply support beam ,or a simple beam. The essential feature of a simple beam is that both

5、 ends of the beam may rotate freely during bending, but the cannot translate in lateral direction. Also ,one end of the beam can move freely in the axial direction (that is, horizontal). The supports of a simple beam may

6、 sustain vertical reactions acting either upward or downward .3 The beam in Flg.1.2(b) which is built-in or fixed at one end and free at the other end, is called a cantilever beam. At the fixed support the beam can neith

7、er rotate nor translate, while at the free end it may do both. The third example in the figure shows a beam with an overhang. This beam is simply supported at A and B and has a free at C.4 Loads on a beam may be concentr

8、ated forces, such as P1 and P2 in Fig.1.2(a) and (c), or distributed loads loads, such as the the load q in Fig.1.2(b), the intesity. Distributed along the axis of the beam. For a uniformly distributed load, illustrated

9、in Fig.1.2(b),the intensity is constant; a varying load, on the other hand, is one in which the intensity varies as a function of distance along the axis of the beam.5 The beams shown in Fig.1.2 are statically determina

10、te because all their reactions can be determined from equations of static equilibrium. For instance ,in the case of the simple beam supporting the load P1 [Fig.1.2(a)], both reactions are vertical, and tehir magnitudes c

11、an be found by summing moments about the ends; thus,we find La L P RA ) ( 1 ? ? LL P RB1 ?The reactions for the beam with an overhang [Fig.1.2 (c)]can be found the same manner.3made as shown.橫梁的靜態(tài)分析 橫梁的靜態(tài)分析1 一條繞其軸水平放置的棒就

12、是所謂的橫梁，本章節(jié)我們將研究最簡(jiǎn)單的橫梁模型形式，如圖 1.2 所示。在每個(gè)例子中，假設(shè)橫梁有平整的外形，并且都與其軸線平衡。并且，交叉的部分都有著外形相垂直的關(guān)系，同時(shí)假設(shè)那些負(fù)載均作用在平整的外形面上，所以彎曲將會(huì)發(fā)生在平整的橫梁上。稍后我們將研究一個(gè)非常普遍常見(jiàn)的并且有垂直于非平整部分的彎曲。2 在圖 1.2（a）的橫梁中，橫梁的一端由鉸鏈支座支撐著，另外一端由滾動(dòng)支座支撐，這就是所謂的簡(jiǎn)單的支撐橫梁，或者簡(jiǎn)單橫梁。此簡(jiǎn)單橫梁的

13、特征為兩端在彎曲過(guò)程可以自由轉(zhuǎn)動(dòng)，但是不能被轉(zhuǎn)動(dòng)到側(cè)面其他方向。同時(shí)，橫梁的一端可以在軸向自由轉(zhuǎn)動(dòng)（水平方向） 。簡(jiǎn)單橫梁的支撐可能會(huì)受到向上或者向下的反作用力。3 在圖 1.2（b）中，橫梁的一端是固定的，另一端是自由懸空的，這就是所謂的懸空梁。橫梁被固定的一端既不能旋轉(zhuǎn)也不能移動(dòng)，但是另一端則是可以旋轉(zhuǎn)和移動(dòng)的。圖中的第三個(gè)例子展示了含有伸出部分的橫梁。這個(gè)橫梁在圖 A 和 B 中被簡(jiǎn)單支撐同時(shí)在 C 中有了自由端。4在橫梁上的負(fù)載

14、可以是垂直的，如圖 1.2（a）和（c）中的力 P1 和 P2，或者是平均分散的負(fù)載，如圖 1.2（b）中的負(fù)載 q. 平均分散的負(fù)載是以他們的密度分布來(lái)區(qū)分，這是以在軸線方向上單位長(zhǎng)度上得力大小。對(duì)于同意的分散負(fù)載，如圖 1.2（b）中所示，其強(qiáng)度為常數(shù)；一個(gè)變化的負(fù)載，在另一方面，是在軸線長(zhǎng)度方向上功能強(qiáng)度發(fā)生變化的。5 在圖 1.2 所示的橫梁均為靜止確定的，因?yàn)樗鼈兯械氖芰笞饔眯Ч蓮撵o態(tài)平衡方程中得到確定。例如，在支撐

15、負(fù)載 P1 的簡(jiǎn)單橫梁所示的情況中，所有的作用效果都是在垂直方向的，并且其大小也可以通過(guò)總結(jié)受力完成瞬間來(lái)確定；而且，我們可知：La L P RA ) ( 1 ? ? LL P RB1 ?同理我們可以找出確定圖 1.2（c）中所示的有外伸端的橫梁作用效果。6 對(duì)于懸梁[圖 1.2(b)]，如圖中所示，應(yīng)用負(fù)載 q 的作用效果可以被固定端的垂直力 RA和力矩 MA 抵消平衡。從垂直方向上力的總結(jié)可得， qb RA ?并且通過(guò)對(duì)質(zhì)點(diǎn) A 的

16、瞬間的總結(jié)可得) 2 ( b a qb MA ? ?MA 的工作效果如圖所示，是延時(shí)鐘方向。7 先前圖示的例子說(shuō)明靜態(tài)確定橫梁的作用效果可以從方程中計(jì)算出來(lái)。靜態(tài)非確定橫梁的作用效果的確定需要考慮橫梁的形變效果，這種研究將在以后的課程學(xué)習(xí)中討論。8 圖 1.2 中所示的理想化支撐條件只是偶爾在實(shí)際中才會(huì)遇到。舉例說(shuō)明如，在橋的大跨度橫梁兩端有時(shí)候也被建成用鉸和滾動(dòng)支撐。當(dāng)然，在短一點(diǎn)的橫梁上，經(jīng)常會(huì)有對(duì)支撐的水平移動(dòng)的制約力。在大部分情