【正文】 的結(jié)果，This is because of the small slenderness ratio for members of this type, which results in a large buckling stress (from ). 這是因?yàn)檫@種構(gòu)件的長細(xì)比較小，從而產(chǎn)生較高的屈曲應(yīng)力。If the stress at which buckling occurs is greater than the proportional limit of the material, the relation between stress and strain is not linear, and the modulus of elasticity E can no longer be used. 如果屈曲發(fā)生時(shí)的應(yīng)力大于材料的比例極限，應(yīng)力應(yīng)變關(guān)系就不再是線性的，也不能再用彈性模量E。This difficulty was initially resolved by Friedrich Engesser, who proposed in 1889 the use of a variable tangent modulus Et in . 這一困難最初由Friedrich Engesser 所克服，. For a material with a stressstrain curve like the one in , E is not a constant for stress greater than the proportional limit Fpl. The tangent modulus Et is defined as the slope of the tangent to the stressstrain curve for values of f between Fpl and Fy. (的材料)，當(dāng)應(yīng)力超過比例極限時(shí)，E并非常數(shù)，當(dāng)應(yīng)力處于Fpl和Fy之間時(shí)，將切線模量定義為應(yīng)力應(yīng)變曲線的切線的斜率，If the pressive stress at buckling, Pcr/A, is in this region, it can be shown that 如果屈曲時(shí)的壓應(yīng)力在此范圍時(shí)，可以證明 ()This is identical to the Euler equation, except that Et is substituted for E. 除公式中將E代之以Et外，上式與歐拉公式完全相同。Effective Length（計(jì)算長度）Both the Euler and tangent modulus equations are based on the following assumptions: 歐拉和切線模量方程都是基于如下假定：1. The column is perfectly straight, with no initial crookedness. 柱完全豎直，無初始彎曲。2. The load is axial, with no eccentricity. 荷載是軸向加載，無偏心。3. The column is pinned at both ends. 柱在兩端鉸結(jié)。The first two conditions mean that there is no bending moment in the member before buckling. 前兩(假定)條件意味著在屈曲前無彎矩存在。As mentioned previously, some accidental moment will be present, but in most cases it can be neglected. 如前所述，可能偶然會存在一些彎矩，但在大多數(shù)情況下都可被忽略。The requirement for pinned ends, however, is a serious limitation, and provisions must be made for other support conditions. 然而，鉸結(jié)要求是一個(gè)嚴(yán)重的局限，必須對其它支撐條件作出規(guī)定。The pinnedend condition is one that requires that the member be restrained from lateral translation, but not rotation, at the ends. 鉸結(jié)條件要求約束構(gòu)件兩端不發(fā)生側(cè)移，但并不約束轉(zhuǎn)動。Since it is virtually impossible to construct a frictionless pin connection, even this support condition can only be closely approximated at best. 由于實(shí)際上不可能構(gòu)造無摩擦鉸連接，即使這種支撐條件最多也只能是非常近似。Obviously, all columns must be free to deform axially. 顯然，所有柱必須在軸向自由變形。 In order to account for other end conditions, the equations for critical buckling load will be written as 為了考慮其它邊界條件，將臨界荷載寫為如下形式 or ()where KL is the effective length, and K is called the effective length factor. Values of K for different cases can be determined with the aid of the Commentary to the AISC Specification. 式中KL為計(jì)算長度，K稱為計(jì)算長度系數(shù)，各種情況下的K值可借助于AISC（美國鋼結(jié)構(gòu)學(xué)會American Institute of Steel Construction）規(guī)范的條文說明加以確定。Lesson 2 Introduction to structural designNew words1. framework frame+work=frame 構(gòu)架，框架。 frame structure, 框架結(jié)構(gòu)2. constraint vt. constrain 約束，強(qiáng)迫；n. constraint 約束 3. collaborate vt. 合作，通敵；collaboration, collaborative 4. evaluation vt. evaluate, value。 assess, assessment5. fixture vt. fix, fixture 固定設(shè)備，固定物，夾具6. partition vt. n 分割，劃分， make apart。 partition wall7. overlook8. crane n. 超重機(jī)，鶴9. fatigue 疲勞 fatigue strength, fatigue failure10. drift 漂流，漂移，雪堆11. enumerate v. list 列舉12. plumbing n. (衛(wèi)生，自來水)管道，plumber 管道工13. ventilation n. 通風(fēng)， ventilate, ventilate a room, a wellventilated room, vent 通風(fēng)口14. accessibility n. 可達(dá)性， access, n. vt. 通道，接近；accessible 易接近的，可達(dá)到的 15. code n. vt 代碼，編碼，規(guī)范16. administer v. 管理，執(zhí)行；administrate, 管理 17. metropolitan a. 大城市，of metropolis 18. consolidate v. 鞏固，strengthen，reinforce。 consolidation19. prescription n. 規(guī)定，命令，藥方；prescribe 20. municipality n. 市政當(dāng)局，直轄市， municipal government21. specification n. 詳述，規(guī)格, 規(guī)范；specify 22. mandate n. 書面命令，委托，Phrases and expressions 1. functional design 功能設(shè)計(jì)2. bending moment 彎矩3. dead load4. live load5. nonstructural ponents 非結(jié)構(gòu)構(gòu)件6. force due to gravity7. gravity load8. building code9. design specifications 設(shè)計(jì)規(guī)程10. nonprofit organization 非贏利組織，弄nongovernment organization 11. the National Building Code12. the Uniform Building Code13. the Standard Building Code14. Building Officials and Code Administrators International (BOCA) 國際建筑公務(wù)員與法規(guī)管理人員聯(lián)合會15. AISC 美國鋼結(jié)構(gòu)學(xué)會 American Institute of Steel Construction 16. AASHTO 美國公路和運(yùn)輸工作者協(xié)會 American Association of State Highway and Transportation Officials17. AREA 美國鐵道工程協(xié)會 the American Railway Engineering Association 18. AISI 美國鋼鐵學(xué)會 American Iron and Steel InstituteIntroduction to Structural DesignStructural design The structural design of building, whether of structural steel or reinforced concrete, requires the determination of the overall proportions and dimensions of the supporting framework and the selection of the cross sections of individual members. 建筑結(jié)構(gòu)設(shè)計(jì)，不論是鋼結(jié)構(gòu)還是鋼筋混凝土結(jié)構(gòu)，都需要確定其支承結(jié)構(gòu)的整體比例和尺寸以及各構(gòu)件的截面尺寸。In most cases the functional design, including the establishment of the number of stories and the floor plan, will have been done by an architect, and the structural engineer must work within the constraints imposed by this design. 在大多數(shù)情況下，功能設(shè)計(jì)，包括樓層層數(shù)和樓層平面的確定，將要由建筑師來完成，因而結(jié)構(gòu)工程師必須在此約束條件下工作。Ideally, the engineer and architect will collaborate throughout the design process so that the project is pleted in an efficient manner. 在理想狀態(tài)下，工程師和建筑師將在整個(gè)設(shè)計(jì)過程中協(xié)同工作從而高效地完成設(shè)計(jì)工作。In effect, however, the design can be summed up as follows: 然而，事實(shí)上，設(shè)計(jì)過程可概括如下：The architect decides how the building should look。 the engineer must make sure that it doesn’t fall down. 建筑師確定建筑物的外觀，工程師必須確保其不會倒塌。Although this is an oversimplification, it affirms the first priority of the structural engineer: safety. Other important considerations include serviceability (how well the structure performs in terms of appearance and deflection) and economy. 盡管這樣說過分簡單，但它明確了工程師的第一個(gè)主要任務(wù)，即，確保安全。其它要考慮的因素包括適用性（就外觀和撓曲而言其工作性能如何）。An economical structure requires an efficient use of materials and construction labor. Although this can usually be acplished by a design that requires a minimum amount of m