【導(dǎo)讀】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(jìn)行養(yǎng)護(hù)，以加速水泥與水的水化反應(yīng)，最后獲得硬化的混凝土。制成品具有較高的抗壓強(qiáng)度和較低的抗拉強(qiáng)度。其抗拉強(qiáng)度約為抗壓強(qiáng)度的十分之。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(gòu)件中較。由于鋼筋混凝土截面在均質(zhì)性上與標(biāo)準(zhǔn)的木材或鋼的截面存在著差異，因此，需要對結(jié)構(gòu)設(shè)計的基本原理進(jìn)行修改。將鋼筋混凝土這種非均質(zhì)截面的兩種組成部。這一要求是可以達(dá)到的?；A(chǔ)，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。水泥的水化作用發(fā)生在有水分存在，而且氣溫在50°F以上的條件下。證水泥的水化作用得以進(jìn)行，必須具備上述條件。這將有損與混凝土的強(qiáng)度，同時也會影響到水泥水化作用的充分進(jìn)行。的復(fù)核與單純的設(shè)計分別進(jìn)行處理。為了降低土方工程費(fèi)用，填方量應(yīng)該等于。危險的，而對拉鏟挖土機(jī)則是不可能的。

　　

【正文】 ility 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 黃山 學(xué) 院 畢 業(yè) 設(shè) 計 10 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 reduced by given safety factors. (2)Limit states method, in which the structure may be proportioned on the basis of its maximum strength. This strength, as determined 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 ) . Fro m 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。 黃山 學(xué) 院 畢 業(yè) 設(shè) 計 11 (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。 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 )