【正文】 be stationary or stable, these forces must be kept in balance. The vertical forces, for example, must be equal to each other. If a beam supports a load above, the beam itself must have sufficient strength to counterbalance that weight. The horizontal forces must also equal each other so that there is not too much thrust either to the right or to the left. And forces that might pull the structure around must be countered with forces that pull in the opposite direction. act on ...起作用,作用于 act 產(chǎn)生…..的效果，擔(dān)當(dāng)，見效 vertical 垂直的 horizontal 水平的 sideways rotating轉(zhuǎn)動(dòng)的, 旋轉(zhuǎn)的 turning , 轉(zhuǎn)向 motion , 動(dòng)作 stationary固定的 stable counterbalance vt使平衡 thrust 推力 opposite direction相反方向，反向 總之，這三個(gè)力會(huì)作用在結(jié)構(gòu)上：豎直的那些向上或向下作用的力；水平的—那些向 一側(cè)作用的力；以及那些使旋轉(zhuǎn)或轉(zhuǎn)動(dòng)的作 用力。因?yàn)橛赏聊竟こ處熢O(shè)計(jì)的結(jié)構(gòu)要 固定或者穩(wěn)定，這些力必須保持平衡。如果一片梁要支撐作 用在其上的荷載，梁自身必須要有足夠的強(qiáng) 度來平衡這個(gè)重量。以及那 些可能使結(jié)構(gòu)轉(zhuǎn)動(dòng)的力必須和相反方向轉(zhuǎn)動(dòng) 的力相平衡。 美國(guó)華盛頓州Taa Narrows大橋倒塌的錄 像。 這次事故之所以有名，還在于大橋的倒塌過 程被人錄了下來。大橋在風(fēng)中 扭動(dòng)的場(chǎng)面令人震撼，只使用了三個(gè)月。 現(xiàn)代最為轟動(dòng)一時(shí)的工程事故之一：1940 年的Taa Narrows大橋，就是因?yàn)閷?duì)這些 因素的最后一個(gè)因素：扭轉(zhuǎn)考慮的不夠仔細(xì) 而導(dǎo)致的結(jié)果。幸運(yùn)的是，工程師 從錯(cuò)誤中吸取教訓(xùn)，因此現(xiàn)在通常要在風(fēng)洞 試驗(yàn)室中進(jìn)行橋梁的縮尺模型試驗(yàn)以確定其 空氣動(dòng)力阻力。用砂漿或是 瀝青，一種類似焦油的物質(zhì)或是其他粘合劑 將各層結(jié)合在一起。例如， 希臘帕提農(nóng)神廟的立柱，為了插鐵棒在立柱 中鉆孔，這些鐵棒現(xiàn)在已經(jīng)銹蝕了。 Both steel and cement, the two most important construction materials of modern times, were introduced in the nineteenth century. Steel, basically an alloy of iron and a small amount of carbon, had been made up to that time by a laborious process that restricted it to such special uses as sword blades. After the invention of the Bessemer process in 1856, steel was available in large quantities at low prices. The enormous advantage of steel is its tensile strength。鋼材，主要是 鐵合金和少量的碳，在那時(shí)要通過費(fèi)力的過 程才能提煉出來，這限制它只能用于一些特 殊用途比如劍刃上。鋼材極 大的優(yōu)點(diǎn)是它的抗拉強(qiáng)度，也就是當(dāng)在計(jì)算 等級(jí)的拉力作用下，它不會(huì)喪失其強(qiáng)度，這 個(gè)力，正如我們所見，可以撕開很多材料。 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。它是石灰石和粘土的混合物，它們加熱 后碾(碎)成為粉末。成分的 不同比例可以制造出不同強(qiáng)度和重量的混凝 土。并且鑒于鋼材有很大的 抗拉強(qiáng)度，混凝土有很大的抗壓強(qiáng)度。 They also plement each other in another way: they have almost the same rate of contraction and expansion. They therefore can work together in situations where both pression and tension are factors. Steel rods are embedded in concrete to make reinforced concrete in concrete beams or structures where tension will develop. Concrete and steel also form such a strong bondthe force that unites themthat the steel cannot slip within the concrete. Still another advantage is that steel does not rust in concrete. Acid corrodes steel, whereas concrete has an alkaline chemical reaction, the opposite of acid. Contraction 壓縮 expansion 膨脹 bond 結(jié)合 unite slip 滑動(dòng) rust .(使)生銹 corrode 腐蝕 alkaline reaction n.[化] 堿性反應(yīng) 他們還可以以另一種方式相互補(bǔ)充：他們 有幾乎相同的壓縮和膨脹率。在混 凝土梁或受拉的結(jié)構(gòu)，鋼筋嵌入混凝土中形 成鋼筋混凝土。還有另外一個(gè)好處就是鋼 在混凝土中不會(huì)生銹。 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 pretensioning or posttensioning method. Prestressed concrete has made it possible to develop buildings with unusual shapes, like some of the modern sports arenas, with large spaces unbroken by any obstructing supports. The uses for this relatively new structural method are constantly being developed.reinforcement鋼筋, 增強(qiáng)材料 prestress …預(yù)加 應(yīng)力 pretensioning先張拉 posttensioning 后張拉 arena , 舞臺(tái) obstruct 阻隔 預(yù)應(yīng)力混凝土是鋼筋混凝土的改良形式。然后，通常通過先張法或者 后張法，他們給混凝土施加預(yù)應(yīng)力。這種相對(duì)新的結(jié)構(gòu)方法的使 用在不斷的發(fā)展。鋁 梁已經(jīng)在橋梁結(jié)構(gòu)以及一些框架建筑中使用。一個(gè)幫助在一定程度上減 少混凝土重量系統(tǒng)是使用高分子材料作為混合料的一 部分，這些材料具有用于塑料中的鏈狀化合物。 Structural design involves determining the most suitable proportions of a structure and dimensioning the structural elements and details of which it is posed. This is the most highly technical and mathematical phase of a structural engineering project, but it cannot and certainly should notbe conducted without being fully coordinated with the planning and construction phases of the project. The successful designer is at all times fully conscious of the various considerations that were involved in the preliminary planning for the structure and, likewise, of the various problems that may later be encountered in its construction. Proportion 比, 比率,均衡, 相稱,份, 部份,大小。 容積,比例 Dimensioning 定尺寸，計(jì)算 technical , 技術(shù)上的, 技巧方面的 mathematical , 精確的 conduct 進(jìn)行，實(shí)施,引導(dǎo)，指導(dǎo) coordinate（使）互相配合,（使）協(xié)調(diào)， 調(diào)整 conscious , 有知覺的 consideration , 需要考慮的事項(xiàng), 體諒 be involved in 涉及,有關(guān) preliminary plan初步設(shè)計(jì),初步計(jì)劃 likewise , 照樣地, 又, 也 結(jié)構(gòu)設(shè)計(jì)包括決定結(jié)構(gòu)最合適的比例以及 一個(gè)結(jié)構(gòu)工程項(xiàng)目的最高技術(shù)和計(jì)算階段,但 是,如果沒有工程項(xiàng)目的規(guī)劃和施工階段充分 配合的話, 功的設(shè)計(jì)者總是會(huì)充分意識(shí)到在結(jié)構(gòu)初步設(shè) 計(jì)(規(guī)劃)中的各種考慮,并且,同樣的也會(huì)充分 意識(shí)到在結(jié)構(gòu)后續(xù)施工中所要面臨的各種問 題. Specially, the structural design of any structure first involves the establishment of the loading and other design conditions that must be resisted by the structure and therefore must be considered in its design. Then es the analysis (or putation) of the internal gross forces (thrust, shears, bending moments, and twisting moments), stress intensities, strains, deflections, and reactions produced by the loads, temperature, shrinkage, creep, or other design conditions.(2) Finally es proportioning and selection of materials of the members and connections so as to resist adequately the effects produced by the design conditions. The criteria used to judge whether particular proportions will result in the desired behavior reflect accumulated knowledge (theory, field and model test, and practical experience), intuition, and judgement. establishment , 制定 resist , 反抗, 抗 internal gross forces 總內(nèi)力 bending moment 彎矩 twisting moment 扭矩 stress intensity 應(yīng)力強(qiáng)度 reaction , 反作用 proportioning 確定(幾何)尺寸, 選擇參數(shù) connection 連接,接頭 criteria proportion比例,面積, 部分 model test 模型試驗(yàn) intuition , 直覺的知識(shí) judgement , 意見, 看法 專門的,任何結(jié)構(gòu)物的結(jié)構(gòu)設(shè)計(jì)首先包括荷 載以及其他結(jié)構(gòu)所必須承受的設(shè)計(jì)條件的確 立,并且因此,這些條件必須被考慮到設(shè)計(jì)中. 然后需要進(jìn)行總內(nèi)力(軸力,剪力,彎矩,和扭矩), 應(yīng)力強(qiáng)度,應(yīng)變,撓度,和反作用力的分析(