【正文】 面積。 Lesson 5Philosophy of Structural Design 結(jié)構(gòu)設(shè)計原理 A structural engineering project can be divided into three phase: planning, design, and construction. structural engineering 結(jié)構(gòu)工程, 結(jié)構(gòu)工程學 planning 計劃編制，規(guī)劃 一個結(jié)構(gòu)工程項目可分為三個階段:規(guī)劃、設(shè) 計、施工。 Attempts are also being made to produce concrete with more strength and durability, and with a lighter weight. One system that helps cut concrete weight to some extent uses polymers, which are long chainlike pounds used in plastics, as part of the mixture. durability耐久性 polymers高分子材料 chainlike 鏈狀 pound 化合物 plastics塑料mixture混合料 人們還嘗試制造出強度更高耐久性更好的混凝土同時 重量更輕(高性能混凝土)。 The current tendency is to develop lighter materials. Aluminum, for example, weight much less than steel but has many of the same properties. Aluminum beams have already been uesed for bridge construction and for the framework of a few buildings. aluminum n.[化]鋁 framework ，鋁， 比鋼輕很多但是與鋼有很多同樣的性能。預(yù)應(yīng)力 混凝土使得發(fā)展非常規(guī)形狀的建筑成為可能， 比如一些現(xiàn)代體育場，有很大的不被任何支 柱阻斷的空間。 鋼筋彎成一定形狀（彎成形）給他們必要的 抗拉強度等級。酸腐蝕鋼材，而與酸 相反，混凝土存在堿性化學反應(yīng)?；炷梁弯摻钸€能形成如此 強的粘結(jié)這個粘合他們的力—使得鋼筋在混 凝土中不會滑移。因此，他們可 以在既受壓又受拉的情況下共同工作。因而， 這兩種物質(zhì)可以相互補足。混凝土非常通用，它可以灌注，泵送甚 至噴灑成各種形狀。它可以在施工場地或靠近 施工場地的地方和沙子，骨料（小石子，碎 石或礫石）以及水混合制成混凝土。 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. Portland cement硅酸鹽水泥 limestone clay粘土 grind (碎), 碾(碎) powder粉末 aggregate 骨料 crush , 碾碎 gravel礫石 proportions 比例 ingredient ，組成部分 versatile通用的，多用途的，多方面的 pour , 傾瀉, 涌入 pump 泵送 spray噴射, 噴濺 whereas conj鑒于，然而, 反之，盡管, 但是 plement , 補足 稱為硅酸鹽水泥的現(xiàn)代水泥，在1824年發(fā) 明。 新的合金可以增強鋼材的強度并且消除它的 一些問題，比如疲勞問題，鋼材在應(yīng)力持續(xù) 不斷的變化作用下所導(dǎo)致的強度減弱。1856年在貝色麥法發(fā)明 以后，才能以低價得到大量的鋼材。 that is, it does not lose its strength when it is under a calculated degree of tension, a force which, as we have seen, tends to pull apart many materials. New alloys have further increased the strength of steel and eliminated some of its problems, such as fatigue, which is a tendency for it to weaken as a result of continual changes in stress. alloy合金 laborious費力的，艱苦的 sword blade , 刀片 enormous , 龐大的 tensile strength抗拉強度 calculated , 有計劃的, 適當?shù)? 適合的 eliminate , 消除，除去 fatigue疲勞 鋼材和水泥，這兩種最為重要的現(xiàn)代建筑 材料，是在十九世紀發(fā)明的。羅馬人 也使用稱為火山灰的天然水泥，從火山灰中 制成，當在水中時就會變得和石頭一樣硬。希臘人和羅馬人有時使 用鐵桿或是夾子來加強他們的建筑。 The principal construction materials of earlier times were wood and masonry brick, stone, or tile, and similar materials. The courses or layers 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 buildings. 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 water. principal , 首要的 masonry砌石 brick磚 tile 瓦 course行列, 層 layer mortar砂漿，灰漿 bitumen tar焦油, 柏油，焦油瀝青 binding agent蟲膠粘合劑，接合劑 rod , 棒 clamp , 夾具, 夾鉗 drill 鉆孔 rust 生銹 natural cement天然水泥 pozzolana (可用作水泥原料) volcanic ash 火山灰 早期主要的建筑材料是木材和砌石磚，石頭 或是瓦片以及類似這類的材料。當時在一次暴風雨中，時速 達到65公里每小時的強陣風沖擊著大橋，他 們把大橋沿行車道吹成波浪形加上橫向扭動 導(dǎo)致大橋的行車道落水。主 跨853m。當時有一對新人正在橋頭 舉行婚禮，攝影師本來是去拍喜慶場面的， 不想?yún)s記錄了一座大橋的末日。 這次事故令橋梁的設(shè)計規(guī)范重新修改，風力 和共振分析成為橋梁設(shè)計必不可少的一部分。 One of the most spectacular engineering failures of modern times, the collapse of the Taa Narrows Bridge in 1940, was the result of not considering the last of these factors carefully enough. When strong gusts of wind, up to sixtyfive kilometers an hour, struck the bridge during a storm, they set up waves along the roadway of the bridge and also a lateral motion that caused the roadway to fall. Fortunately, engineers learn from mistakes, so it is now mon practice to test scale models of bridges in wind tunnels for aerodynamic resistance. Spectacular 轟動一時的 Taa 塔科馬[美國華盛頓州西部港市] Narrows 紐約灣海峽(位于美國)，海峽 gust of wind陣風 strike撞擊, 沖擊 lateral motion橫向運動, 側(cè)擺 scale model縮尺模型，幾何相似模型 wind tunnel aerodynamic resistance空氣動力阻力 橋梁史上最有名的事故之一。水平力也必須相互平衡 以使得沒有向左或向右的太大推力。例如， 豎向力必須相互平衡。以一個角度作用的力是水平力和豎向 力的合力。 horizontalthose that act sideways。 剪力可能在垂直面作用，但是也有可能沿著 梁的水平軸，既不受拉也不受壓的中性軸作 用。受壓時，材料受到擠壓或是被推倒一起； 受拉時，材料被撕開或是被拉長，就像一根 橡皮圈。 in tension the material is pulled apart or stretched, like a rubber band. In addition to tension and pression, another force is at work, namely shear, which we defined as the tendency of a material to fracture along the lines of stress. The shear might occur in a vertical plane, but it also might run along the horizontal axis of the beam, the neutral plane, where there is neither tension nor pression. Subject使受到, 使遭到 pression 壓力，壓縮 tension拉力 Press 擠壓，受壓 pull apart stretch , 伸長 rubber band at work , 在運轉(zhuǎn)，在起作用 shear 剪力 fracture v.(使)破碎, (使)破裂，斷裂 vertical plane horizontal axis水平軸 neutral plane中性面 現(xiàn)代工程師還要知道結(jié)構(gòu)中材料承受的不 同的力。他還必須確定安全因素，也即是，額 外的承載能力以確保結(jié)構(gòu)的強度大于這三個 其他因素的組合作用。這就是所說 的恒載，他是結(jié)構(gòu)自身的重量，他還必須考 慮活載，即所有人群、汽車, 家具, 機器, 等等 結(jié)構(gòu)在使用中需要承受的荷載。 Today, however, the engineer has the advantage not only of empirical information, but also of scientific data that permit him to make careful calculations in advance. When a modem engineer plans a structure, he takes into account the total weight of all its ponent materials. This is known as the dead load, which is the weight of the structure itself, He must also consider the live load, the weight of all the people, cars, furniture, machines, and so on that the structure will support when it is in use. In structures such as bridges that will handle fast automobile traffic, he must consider the impact, the force at which the live load will be exerted on the structure, He must also determine the safety factor, that is, an additional capability to make the structure stronger than the bination of the three other factors. empirical , 經(jīng)驗主義的 in advance 提前；預(yù)先 plan , 設(shè)計 take into account , 考慮 ponent , dead load 恒載，永久荷載 live load 活載，活荷載 handle 處理，操作承受 automobile 汽車 impact , 沖擊，撞擊 safety factor exert 作用，施加(壓力等) 然而，今天工程師不僅有經(jīng)驗信息的優(yōu)勢，