现代建筑与建筑材料

2．Modern Buildings and Structural Materials 现代建筑与建筑材料

Many great buildings built in earlier ages are still in existence and in use. Among them are the Pantheon and the Colosseum in Rome, Hagia Sophia in Istanbul; the gothic churche s of France and England, and the renaissance cathedrals, with their great domes, like the Duomo in Florence and ST.Peter’s in Rome.许多古代修建的大型建筑物现仍存在着，而且仍在使用。其中有罗马的万神庙和大圆形竞技场，伊斯坦布尔的圣索非亚教堂，法国和英国的哥特式教堂，和带有巨大的穹窿顶的文艺复兴式教堂，象佛罗伦萨的大教堂和罗马的圣彼得大教堂。They are massive structures with thick stone walls that counteract the thrust of their great weight. Thrust is the pressure exerted by each part of a structure on its other parts.它们都是些厚石墙的庞大建筑。这种厚石墙能抵抗建筑物本身巨大重量所形成的推力。推力是建筑物各部分作用于其它部分的压力。

These great buildings were not the product of knowledge of mathematics and physics. They were constructed instead on the basis of experience and observation, often as the result of trial and error.这些大型建筑物并非数学和物理知识的结晶。它们都是依据经验和观察而建造起来的，往往是反复试验出来的结果。One of the reasons they have survived is because of the great strength that was built into them-strength greater than necessary in most cases.它们能留存下来的原因之一是因为它们建造得强度很大——多数情况下超出所需要的强度。But the engineers of earlier times also had their failure. In Rome, for example, most of the people lived in insula, great tenement blocks that were often ten stories high. Many of them were poorly constructed and sometimes collapsed with considerable loss of life.可是古代的工程师也失败过。例如在罗马，大部分人民都住在公寓中，这种公寓通常是一排排的有十层高的公寓大楼。其中有许多建造得很差，并且有时会倒塌，使许多人丧生。

Today, however, the engineer has the advantage not only of empirical information, but also of scientific data that permit him to make careful calculations in advance. 但是，现在的工程师具备许多有利条件，不仅有经验资料，而且有科学数据供他预先做详细计算。When a modern engineer plans a structure, he takes into account the total weight of all its component materials. This is known as the dead load, which is the weight of the structure itself.一个现代工程师当他设计一座建筑物时，他要考虑这座建筑物所有组成材料的总重量，这就是所谓的静荷载，即建筑物自身的重量。He must also consider the live load, the weight of all the people, cars, furniture, machines, and so on that the structure will support when it is in use. 他还必须考虑动荷载，即在建筑物投入使用时它要承受的人，车辆，设备、机器等等的重量。In structures such as bridges that will handle fast automobile traffic, he must consider the impact, the force at which the live load will be exerted on the structure.对于象桥梁这种需要承担高速汽车交通的构筑物，他必须考虑到冲力，即动荷载将借以作用于结构物的那种力。He must also determine the safety factor, that is, an additional capability to make the structure stronger than the combination of the three other factors.他还必须确定出安全系数，即附加的承载能力，以使建筑物的承载能力比上述三个因素结合起来还要强些。

The modern engineer must also understand the different stresses to which the materials in a structure are subject.现代工程师还必须了解建筑物所用材料经常承受的各种应力。These include the opposite forces of compression and tension. In compression the material is pressed or pushed together; in tension the material is pulled apart or stretched, like a rubber band.其中包括压力和拉力这两种相反的力。在压力下，材料被压紧或推拢到一起，在拉力下，材料象一个橡皮筋那样被拉开或拉长。In addition to tension and compression, another force is at work, namely shear, which we defined as the tendency of a material to fracture along the lines of stress.除了拉力和压力之外，还有一种称为剪力的力在起作用，我们给它下定义为，使材料沿应力线断裂的趋势。The shear might occur in a vertical plane, but it also might run along the horizontal axis of the beam, the neutral plane, where there is neither tension nor compression。剪力可能发生在垂直面上，但它也可能沿着梁的水平轴线——中性面——作用，中性面上既没有拉力也没有压力。

Altogether, three forces can act on a structure: vertical-those that act up or down; horizontal-those that act sideways; and those that act upon it with a rotating or turning motion.总的说来，有三种力作用于建筑物，垂直