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rs were bound together with mortar or bitumen, a tarlike substance, or some other binding agent. The Greeks and Romans sometimes used iron rods or clamps to strengthen their building. The columns of the Parthenon in Athens, for example, have holes drilled in them for iron bars that have now rusted away. The Romans also used a natural cement called pozzolana, made from volcanic ash, that became as hard as stone under 、石塊、瓦片等類似材料的石材。磚層或夾層用砂漿、像焦油狀的瀝青或其他粘合劑年節(jié)在一起,有時(shí)希臘和羅馬人用鐵桿或夾鉗加固建筑物。例如,帕臺(tái)農(nóng)神廟的柱子上就有一些鉆孔,現(xiàn)在鉆孔中的鐵已經(jīng)銹蝕盡了。羅馬人常用一種稱做白榴火山灰的水泥,他的成份是火山灰,在水中它會(huì)變得像石頭一樣堅(jiān)硬。Modern cement, called Portland cement, was invented in 1824. It is a mixture of limestone and clay, which is heated and then ground into a powder. It is mixed at or near the construction site with sand, aggregate (small stones, crushed rock, or gravel), and water to make concrete. Different proportions of the ingredients produce concrete with different strength and weight. Concrete is very versatile。 it can be poured, pumped, or even sprayed into all kinds of shapes. And whereas steel has great tensile strength, concrete has great strength under pression. Thus, the two substances plement each other.被稱為波特蘭的現(xiàn)代水泥于1824年制成的,它是粘土和石灰石的混合物,他們?cè)诩訜釙r(shí)會(huì)裂化成粉末在施工現(xiàn)場(chǎng)或附近,與砂,骨料,水,攪拌制成水泥,水泥因組成成分比例的不同會(huì)有強(qiáng)度和重量的差異,水泥的用途非常多,它們以澆筑、泵送,甚至噴射成各種形狀,由于鋼筋有很好的抗拉強(qiáng)度,水泥有較高的抗壓強(qiáng)度。所以這兩種材料相互補(bǔ)充。Prestressed concrete is an improved form of reinforcement. Steel rods are bent into the shapes to give them the necessary degree of tensile strength. They are then used to prestress concrete, usually by one of two different methods. The first is to leave channels in a concrete beam that correspond to the shapes of the steel rods. When the rods are run through the channels, they are then bonded to the concrete by filling the channels with grout, a thin mortar or binding agent. In the other (and more mon) method, the prestressed steel rods are placed in the lower part of a form that corresponds to the shape of the finished structure, and the concrete is poured around them. Prestressed concrete uses less steel and less concrete. Because it is so economical, it is a highly desirable material.預(yù)應(yīng)力混凝土是混凝土一種強(qiáng)度增大的形式,鋼筋屈服所需要抗拉強(qiáng)度的形狀。然后用于使混凝土受預(yù)應(yīng)力,通常運(yùn)用兩種方法之一。第一種實(shí)在混凝土梁中留出預(yù)應(yīng)力鋼筋通道,當(dāng)預(yù)應(yīng)力鋼筋穿過通道時(shí),通過往其中填充灰漿,一種薄砂漿或粘合劑。把其粘固在其中。另一種更常用的方法是,將預(yù)應(yīng)力鋼筋固定在已設(shè)計(jì)好的結(jié)構(gòu)模型向相應(yīng)的部分,然后圍繞它澆筑混凝土,預(yù)應(yīng)力混凝土用較少的鋼筋和混凝土所以它很經(jīng)濟(jì),是一種非常理想的材料。第四單元Mechanics of Materials deals with the response of various bodies, usually called members, to applied forces. In Mechanics of engineering Materials the members have shapes that either exist in actual structures or are being considered for their suitability as parts of proposed engineering structures. The materials in the members have properties that are characteristic of monly used engineering materials such as steel, aluminum, concrete, and wood.材料力學(xué)處理各種實(shí)體的力學(xué)反應(yīng),這些實(shí)體通常被稱作構(gòu)件。在工程材料的力學(xué)中,構(gòu)件所擁有的形狀,在實(shí)際結(jié)構(gòu)中已經(jīng)存在,或者正在考慮其是否適合作為擬議的工程結(jié)構(gòu)的部分。在構(gòu)件中的材料有常用工程材料具有的普遍特性,如鋼、鋁、混凝土和木材具有的特性。As you can see already from the variety of materials, forces, and shapes mentioned, Mechanics of Engineering Materials is of in