文档介绍：本课程介绍
在学****普通英语（包括常用词汇和语法结构）的基础上，接合前几个学期已经掌握的关于土木工程的专业知识，本课程节选了《土木工程专业英语》上册中的内容，涉及建筑材料、材料力学、结构力学、钢筋混凝土结构、钢结构、测量、土力学、招投标、建筑施工等九个方面的专业英语知识，从而使大家对土木工程领域内的专业词汇以及科技类文献中的常用句型有个初步的、基本的学****和了解，为以后查阅专业文献和参与国际交流打好基础。
第三单元
The principal construction materials of earlier times were wood and masonry-brick, stone, or tile, and similar materials. The courses or layers（砖层）were bound together with mortar or bitumen, a tarlike substance, or some other binding agent. The Greeks and Romans sometimes used iron rods or clamps to strengthen their building. The columns of the Parthenon in Athens（雅典的帕台农神庙）, for example, have holes drilled（钻孔） in them for iron bars that have now rusted away（锈蚀殆尽）. The Romans also used a natural cement called pozzolana, made from volcanic ash, that became as hard as stone under water.
早期主要的建筑材料是木材和砌体，如砖、石、瓦以及类似的材料。砖层之间通过砂浆、沥青（一种焦油状的物质）或其他一些粘合剂粘合在一起。希腊人和罗马人有时用铁条或夹子来加固他们的房屋。例如，雅典的帕台农神庙柱子中曾钻孔以便加入铁条，如今都已锈蚀殆尽。罗马人也用称作白榴火山灰的天然水泥，它用火山灰制作，在水中会变得与石头一样坚硬。
Both steel and cement, the two most important construction materials of modern times, were introduced（推广） in the nineteenth century. Steel, basically an alloy of iron （铁合金）and a small amount of carbon, had been made up to that time（到那个时候） by a laborious（繁复的） process that restricted it to such special uses as sword blades（刀刃）. After the invention of the Bessemer process （贝塞麦炼钢法）in 1856, steel was available in large quantities at low prices. The enormous advantage of steel is its tensile strength; that is, it does not lose its strength when it is under a calculated degree (适当的) of tension, a force which, as we have seen, tends to （往往）pull apart many materials. New alloys have further increased the strength of steel and eliminated some of its problems, such as fatigue, which is a tendency for it to weaken as a result of continual changes in stress（连续的应力变化）.
作为现代两种最重要的建筑材料，钢材与水泥在十九世纪得到了推广。直到那个时候，钢材才通过繁复的过程制造出来，基本上是铁合金，并含有少量的碳，因而被限制在一些特殊的用途如刀刃。在1856年发明了贝塞麦炼钢法后，钢材才得以大量低价获得。钢材巨大的优势即是它的抗拉强度，也就是当它在适当的拉力下不会失去强