土建专业毕业设计外文翻译--建筑的组成部分-建筑结构(编辑修改稿)

土建专业毕业设计外文翻译--建筑的组成部分-建筑结构(编辑修改稿)内容摘要：

n of a foundation depends on many soil factors, such as type of soil, soil stratification, thickness of soil lavers and their paction, and groundwater conditions. Soils rarely have a single position； they generally are mixtures in layers of varying thickness. For evaluation, soils are graded according to particle size, which increases from silt to clay to sand to gravel to rock. In general, the larger particle soils will support heavier loads than the smaller ones. The hardest rock can support loads up to 100 tons per square foot( metric tons/sq meter), but the softest silt can support a load of only ton per square foot( metric tons/sq meter). All soils beneath the surface are in a state of paction； that is, they are under a pressure that is equal to the weight of the soil column above it. Many soils (except for most sands and gavels) exhibit elastic properties— they deform when pressed under load and rebound when the load is removed. The elasticity of soils is often time dependent, that is, deformations of the soil occur over a length of time which may vary from minutes to years after a load is imposed. Over a period of time, a building may settle if it imposes a load on the soil greater than the natural paction weight of the soil. Conversely, a building may heave if it imposes loads on the soil smaller than the natural paction weight. The soil may also flow under the weight of a building； that is, it tends to be squeezed out. Due to both the paction and flow effects, buildings tend settle. Uneven settlements, exemplified by the leaning towers in Pisa and Bologna, can have damaging effects—the building may lean, walls and partitions may crack, windows and doors may bee inoperative, and, in the extreme, a building may collapse. Uniform settlements are not so serious, although extreme conditions, such as those in Mexico City, can have serious consequences. Over the past 100 years, a change in the groundwater level there has caused some buildings to settle more than 10 feet (3 meters). Because such movements can occur during and after construction, careful analysis of the behavior of soils under a building is vital. The great variability of soils has led to a variety of solutions to the foundation problem. Where 4 firm soil exists close to the surface, the simplest solution is to rest columns on a small slab of concrete(spread footing). Where the soil is softer, it is necessary to spread the column load over a greater area； in this case, a continuous slab of concrete(raft or mat) under the whole building is used. In cases where the soil near the surface is unable to support the weight of the building, piles of wood, steel, or concrete are driven down to firm soil. The construction of a building proceeds naturally from the foundation up to the superstructure. The design process, however, proceeds from the roof down to the foundation (in the direction of gravity). In the past, the foundation was not subject to systematic investigation. A scientific approach to the design of foundations has been developed in the 20th century. Karl Terzaghi of the United States pioneered studies that made it possible to make accurate predictions of the behavior of foundations, using the science of soil mechanics coupled with exploration and testing procedures. Foundation failures of the past, such as the classical example of the leaning tower in Pisa, have bee almost nonexistent. F。