【正文】 ned by rational analysis, shall not be less than that required to support a factored load equal to the sum of the factored live load and dead load ( ultimate state ). The stresses corresponding to working ( service ) conditions with unfactored live and dead loads are pared with prescribed values ( service limit state ) . From the four possible binations of the first two and second two methods, we can obtain some useful putational methods. Generally, two binations prevail: (1)deterministic methods, which make use of allowable stresses. (2)Probabilistic methods, which make use of limit states. The main advantage of probabilistic approaches is that, at least in theory, it is possible to scientifically take into account all random factors of safety, which are then bined to define the safety factor. probabilistic approaches depend upon : (1) Random distribution of strength of materials with respect to the conditions of fabrication and erection ( scatter of the values of mechanical properties through out 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 )。 (3) Uncertainty of the predicted live loads and dead loads acting on the structure。 (4)Uncertainty related to the approximation of the putational method used ( deviation of the actual stresses from puted stresses ). Furthermore, probabilistic theories mean that the allowable risk can be based on several factors, such as : (1) Importance of the construction and gravity of the damage by its failure。 (2)Number of human lives which can be threatened by this failure。 華北水利水電學院畢業(yè)設計 土木工程專業(yè) 7 (3)Possibility and/or likelihood of repairing the structure。 (4) Predicted life of the structure. All these factors are related to economic and social considerations such as： (1) Initial cost of the construction。 (2) Amortization funds for the duration of the construction。 (3) Cost of physical and material damage due to the failure of the construction。 (4) Adverse impact on society。 (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 ) 。 華北水利水電學院畢業(yè)設計 土木工程專業(yè) 8 中文翻譯 素混凝土是由水泥、水、細骨料、粗骨料（碎石或；卵石）、空氣，通常還有其他外加劑等經(jīng)過凝固硬化而成。將可塑的混凝土拌合物注入到模板內(nèi)，并將其搗實，然后進行養(yǎng)護，以加速水泥與水的水化反應，最后獲得硬化的混凝土。其最終制成品具有較高的抗壓強度和較低的抗拉強度。其抗拉強度約為抗壓強度的十分之一。因此，截面的受拉區(qū)必須配置抗拉鋼筋和抗剪鋼筋以增加鋼筋混凝土構件中較弱的受拉區(qū)的強度。 由于鋼筋混凝土截面在均質(zhì)性上與標準的木材或鋼的截面存在著差異，因此，需要對結構設計的基 本原理進行修改。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布置，可以最好的利用這兩種材料。這一要求是可以達到的。因混凝土由配料攪拌成濕拌合物，經(jīng)過振搗并凝固硬化，可以做成任何一種需要的形狀。如果拌制混凝土的各種材料配合比恰當，則混凝土制成品的強度較高，經(jīng)久耐用，配置鋼筋后，可以作為任何結構體系的主要構件。 澆筑混凝土所需要的技術取決于即將澆筑的構件類型，諸如：柱、梁、墻、板、基礎，大體積混凝土水壩或者繼續(xù)延長已澆筑完畢并且已經(jīng)凝固的混凝土等。對于梁、柱、墻等構件，當模板清理干凈后應該在其上涂油， 鋼筋表面的銹及其他有害物質(zhì)也應該被清除干凈。澆筑基礎前，應將坑底土夯實并用水浸濕 6 英寸，以免土壤從新澆的混凝土中吸收水分。一般情況下，除使用混凝土泵澆筑外，混凝土都應在水平方向分層澆筑，并使用插入式或表面式高頻電動振