【正文】 系數(shù)，而不需要采用概率準(zhǔn)則；第二種方法是引入一些而簡化假設(shè)的近似概率方法（半概率方法）。此外，由于強(qiáng)度的分 布規(guī)律和應(yīng)力的分布規(guī)律之間的相互關(guān)系是困難的。 所有這些因素均與經(jīng)濟(jì)和社會(huì)條件有關(guān)，例如： （ 1）建筑物的初始建設(shè)費(fèi)； （ 2）建筑物使用期限內(nèi)的折舊費(fèi)； （ 3）由于建筑物破壞而造成的物質(zhì)和材料損失費(fèi)； （ 4）在社會(huì)上造成的不良影響； （ 5）精神和心理上的考慮。 概率方法，這種方法采用極限狀態(tài)。計(jì)算荷載等于分別乘以荷載系數(shù)的活載與恒載之和。 華北水利水電學(xué)院畢業(yè)設(shè)計(jì) 土木工程專業(yè) 11 （ 2）概率方法，在這種方法中，主要參數(shù)被認(rèn)為是隨機(jī)參數(shù)。其例子包括結(jié)構(gòu)的局部屈曲和整體不穩(wěn)定性；某此界面失效，隨后結(jié)構(gòu)轉(zhuǎn)變?yōu)闄C(jī)構(gòu)；疲勞破壞；引起結(jié)構(gòu)幾何形狀顯著變化的彈性變形或塑性變形或徐變； 結(jié)構(gòu)對(duì)交變荷載、火災(zāi)和爆炸的敏感性。就目前的趨勢(shì)而言，安全系數(shù)與所 使用的材料性質(zhì)及其組織情況無關(guān)，通常把它定義為發(fā)生破壞的條件與結(jié)構(gòu)可預(yù)料的最不利的工作條件之比值。的鉸接式翻斗車。翻斗車的車斗位于大橡膠輪胎車輪前軸的上方，盡管鉸接式翻斗車的卸料方向有很多種，但大多數(shù)車斗是向前翻轉(zhuǎn)的。滿載時(shí)可達(dá) 10 m179。它能在比較平的地面上挖較深的土（但只能挖機(jī)械本身下面的土 ），需要時(shí)可以將土運(yùn)至幾百米遠(yuǎn)，然后卸土并在卸土的過程中把土大致鏟平。正鏟挖土機(jī)能挖取豎直陡峭的工作面，這種方式對(duì)推土機(jī)司機(jī)來說是危險(xiǎn)的，而對(duì)拉鏟挖土機(jī)則是不可能的。推土機(jī)所推運(yùn)的圖的數(shù)量最多，只是運(yùn)輸距離很短。這并不是經(jīng)?？梢宰龅降模?是如果能夠做到則是很理想的，因?yàn)檫@樣做既快捷又省錢。土方設(shè)計(jì)這項(xiàng)工作落到了從事道路設(shè)計(jì)的工程師的身上，因?yàn)橥练焦こ痰脑O(shè)計(jì)比其他任何工作更能決定工程造價(jià)是否低廉。因此，一個(gè)工程師為了使自己在土方挖運(yùn)設(shè)備方面的知識(shí)跟得上時(shí)代的發(fā)展，他應(yīng)當(dāng)花費(fèi)一些時(shí)間去研究現(xiàn)代的機(jī)械。 由于和土木工程中任何其他工種的施工方法與費(fèi)用相比較，土方挖運(yùn)的施工方法與費(fèi)用的變化都要快得多，因此對(duì)于有事業(yè)心的人來說，土方工程是 一個(gè)可以大有作為的領(lǐng)域。由于經(jīng)常需要進(jìn)行多次試算，才能求出所需的截面，因此設(shè)計(jì)時(shí)第一次采用的數(shù)值將導(dǎo)致一系列的試算與調(diào)整工作。 設(shè)計(jì)鋼筋 混凝土構(gòu)件時(shí)顯然需要處理大量的參數(shù)，諸如寬度、高度等幾何尺寸，配筋的面積，鋼筋的應(yīng)變和混凝土的應(yīng)變，鋼筋的應(yīng)力等等。 水泥的水化作用發(fā)生在有水分存在，而且氣溫在 50176。對(duì)于梁、柱、墻等構(gòu)件，當(dāng)模板清理干凈后應(yīng)該在其上涂油， 鋼筋表面的銹及其他有害物質(zhì)也應(yīng)該被清除干凈。這一要求是可以達(dá)到的。其抗拉強(qiáng)度約為抗壓強(qiáng)度的十分之一。 (5) Moral and psychological views. The definition of all these parameters, for a given safety factor, allows construction at the optimum cost. However, the difficulty of carrying out a plete probabilistic analysis has to be taken into account. For such an analysis the laws of the distribution of the live load and its induced stresses, of the scatter of mechanical properties of materials, and of the geometry of the crosssections and the structure have to be known. Furthermore, it is difficult to interpret the interaction between the law of distribution of strength and that of stresses because both depend upon the nature of the material, on the crosssections and upon the load acting on the structure. These practical difficulties can be overe in two ways. The first is to apply different safety factors to the material and to the loads, without necessarily adopting the probabilistic criterion. The second is an approximate probabilistic method which introduces some simplifying assumptions ( semiprobabilistic methods ) 。 (4) Predicted life of the structure. All these factors are related to economic and social considerations such as： (1) Initial cost of the construction。 (3) Uncertainty of the predicted live loads and dead loads acting on the structure。 early or excessive cracks。 failure of some sections and subsequent transformation of the structure into a mechanism。, and the largest standard types are of about m 179。many makers build scrapers 華北水利水電學(xué)院畢業(yè)設(shè)計(jì) 土木工程專業(yè) 5 of 8 cubic meters struck capacity, which carry 10 m 179。F. It is necessary to maintain such a condition in order that the chemical hydration reaction can take place. If drying is too rapid, surface cracking takes place. This would result in reduction of concrete strength due to cracking as well as the failure to attain full chemical hydration. It is clear that a large number of parameters have to be dealt with in proportioning a reinforced concrete element, such as geometrical width, depth, area of reinforcement, steel strain, concrete strain, steel stress, and so on. Consequently, trial and adjustment is necessary in the choice of concrete sections, with assumptions based on conditions at site, availability of the constituent materials, particular demands of the owners, architectural and headroom requirements, the applicable codes, and environmental reinforced concrete is often a siteconstructed posite, in contrast to the standard millfabricated beam and column sections in steel structures. A trial section has to be chosen for each critical location in a structural system. The trial section has to be analyzed to determine if its nomi