土木工程类外文文献翻译-建筑结构(编辑修改稿)

土木工程类外文文献翻译-建筑结构(编辑修改稿)内容摘要：

. Each piece of equipment should be level of their tracks and for deep digs in pact material a backacter is most useful, but its dumping radius is considerably less than that of 4 the same escavator fitted with a face shovel. Rubbertyred bowl scrapers are indispensable for fairly level digging where the distance of transport is too much tor a dragline or face shovel. They can dig the material deeply ( but only below themselves ) to a fairly flat surface, carry it hundreds of meters if need be, then drop it and level it roughly during the dumping. For hard digging it is often found economical to keep a pusher tractor ( wheeled or tracked ) on the digging site, to push each scraper as it returns to dig. As soon as the scraper is full,the pusher tractor returns to the beginning of the dig to heop to help the nest scraper. Bowl scrapers are often extremely powerful machines。 many makers build scrapers of 8 cubic meters struck capacity, which carry 10 m 179。 heaped. The largest selfpropelled scrapers are of 19 m 179。 struck capacity ( 25 m 179。 heaped )and they are driven by a tractor engine of 430 horsepowers. Dumpers are probably the monest rubbertyred transport since they can also conveniently be used for carrying concrete or other building materials. Dumpers have the earth container over the front axle on large rubbertyred wheels, and the container tips forwards on most types, though in articulated dumpers the direction of tip can be widely varied. The smallest dumpers have a capacity of about m 179。 , and the largest standard types are of about m 179。 . Special types include the selfloading dumper of up to 4 m 179。 and the articulated type of about m 179。 . The distinction between dumpers and dump trucks must be remembered .dumpers tip forwards and the driver sits behind the load. Dump trucks are heavy, strengthened tipping lorries, the driver travels in front lf the load and the load is dumped behind him, so they are sometimes called reardump trucks. 3. Safety of Structures The principal scope of specifications is to provide general principles and putational methods in order to verify safety of structures. The “ safety factor ”, which according to modern trends is independent of the nature and bination of the materials used, can usually be defined as the ratio between the conditions. This ratio is also proportional to the inverse of the probability ( risk ) of failure of the structure. Failure has to be considered not only as overall collapse of the structure but also as unserviceability or, according to a more precise. Common definition. As the reaching of a “ limit state ” which causes the construction not to acplish the task it was designed for. There are two categories of limit state : (1)Ultimate limit sate, which corresponds to the highest value of the loadbearing 5 capacity. Examples include local buckling or global instability of the structure。 failure of some sections and subsequent transformation of the structure into a mechanism。 failure by fatigue。 elastic or plastic deformation or creep that cause a substantial change of the geometry of the structure。 and sensitivity of the structure to alternating loads, to fire and to explosions. (2)Service limit states, which are functions of the use and durability of the structure. Examples include excessive deformations and displacements without instability。 early or excessive cracks。 large vibrations。 and corrosion. Computational methods used to verify structures with respect to the different safety conditions can be separated into: (1)Deterministic methods, in which the main parameters are considered as nonrandom parameters. (2)Probabilistic methods, in which the main parameters are considered as random parameters. Alternatively, with respect to the different use of factors of safety, putational methods can be separated into: (1)Allowable stress method, in which the stresses puted under maximum loads are pared with the strength of the material。