【正文】 e it directly out of the cut and drop it as fill with the same machine. This is not always possible, but when it canbe done it is ideal, being both quick and cheap. Draglines, bulldozers and face shovels an do this. The largest radius is obtained with the dragline,and the largest tonnage of earth is moved by the bulldozer, though only over short disadvantages of the dragline are that it must dig below itself, it cannot dig with force into pacted material, it cannot dig on steep slopws, and its dumping and 4 digging are not accurate. Face shovels are between bulldozers and draglines, having a larger radius of action than bulldozers but less than draglines. They are anle to dig into a vertical cliff face in a way which would be dangerous tor a bulldozer operator and impossible for a dragline. 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 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。. 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. 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 ”, 5 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 capacity. Examples include local buckling or global instability of the structure。 (2) Uncertainty of the geometry of the crosssection sand of the structure ( faults and imperfections due to fabrication and erection of the structure )。 (4) Adverse impact on society。將鋼筋混凝土這種非均質(zhì)截面的兩種組成部分按一定比例適當(dāng)布置，可以最好的利用這兩種材料。必須記住，過分的振搗將導(dǎo)致骨料離析和混凝土泌漿等現(xiàn)象，因而是有害的。 對結(jié)構(gòu)體系的各個(gè)部位均需選定試算截面并進(jìn)行驗(yàn)算，以確定該截面的名義強(qiáng)度是否足以承受所作用的計(jì)算荷載。當(dāng)時(shí)主要的開挖方式是使用正鏟、反鏟、拉鏟或抓斗等挖土機(jī)，盡管這些機(jī)械目前仍然在廣泛應(yīng)用，但是它們只不過是目前所采用的許多方法中的一小部分。 費(fèi)用最低的運(yùn)土方法是用同一臺(tái)機(jī)械直接挖方取土并且卸土作為填方。 正鏟挖土機(jī)介于推土機(jī)和拉鏟挖土機(jī)的之間，其作用半徑大于推土機(jī)，但小于拉鏟挖土機(jī)。 斗式鏟運(yùn)機(jī)通常是 功率非常大的機(jī)械，許多廠家制造的鏟運(yùn)機(jī)鏟斗容量為 8 m179。的自裝式翻斗車，和容量約為 m179。通常有兩種類型的極限狀態(tài)，即： 11 （ 1）強(qiáng)度極限狀態(tài)，它相當(dāng)于結(jié)構(gòu)能夠達(dá)到的最大承載能力。由理論分析確定的這一最大強(qiáng)度應(yīng)不小于結(jié)構(gòu)承受計(jì)算荷載所算得的強(qiáng)度（極限狀態(tài)）。 此外，概率理論意味著可以基于下面幾個(gè)因素來確定允許的危險(xiǎn)率，例如： 建筑物的重要性和建筑物破壞造成的危害性； （ 2）由于建筑物破壞使生活受到威脅的人數(shù)； （ 3）修復(fù)建筑的可能性； （ 4）建筑物的預(yù)期壽命。 參考文獻(xiàn)： 1. 韓靜云 .建筑裝飾材料及其應(yīng)用 .中 國建筑工業(yè)出版社 .2020. 2. 夏燕編著 .土木工程材料 . 武漢大學(xué)出版社 .2020. 3. 王起才 ,霍曼琳 .建筑材料 (第一版 ).蘭州大學(xué)出版社 .1997 4. 張雄主編 .建筑功能材料 .中國建筑工業(yè)出版社 .2020. 5. 嚴(yán)捍東，錢曉倩編著 .新型建筑材料教程 .中國建材工業(yè)出版社 .2020. 6. 張粉芹，趙志曼編著 .建筑裝飾材料 .重慶大學(xué)出版社 .2020. 7. 徐友輝編著 .建筑材料教與學(xué) .西南交通大學(xué)出版社 .2020. 8. 江峰編著 .建筑材料 (土木工程 ).重慶大學(xué)出版社 .2020.