自動彎管機及其電氣設計,自動彎管機及其電氣設計,自動,彎管,及其,電氣設計 外文翻譯 結構設計 結構設計 Augustine J.Fredrich 摘要：結構設計是選擇材料和構件類型，大小和形狀以安全有用的樣式承擔荷載。一般說來，結構設計暗指結構物如建筑物和橋或是可移動但有剛性外殼如船體和飛機框架的工廠穩(wěn)定性。設計的移動時彼此相連的設備（連接件），一般被安排在機械設計領域。 關鍵詞：結構設計 ； 結構分析 ； 結構方案 ； 工程要求 Abstract: Structure design is the selection of materials and member type ,size, and configuration to carry loads in a safe and serviceable fashion .In general ,structural design implies the engineering of stationary objects such as buildings and bridges ,or objects that maybe mobile but have a rigid shape such as ship hulls and aircraft frames. Devices with parts planned to move with relation to each other(linkages) are generally assigned to the area of mechanical . Key words: Structure Design ； Structural analysis ；structural scheme ； Project requirements Structure Design Structural design involved at least five distinct phases of work: project requirements, materials, structural scheme, analysis, and design. For unusual structures or materials a six phase, testing, should be included. These phases do not proceed in a rigid progression , since different materials can be most effective in different schemes , testing can result in change to a design , and a final design is often reached by starting with a rough estimated design , then looping through several cycles of analysis and redesign . Often, several alternative designs will prove quite close in cost, strength, and serviceability. The structural engineer, owner, or end user would then make a selection based on other considerations. Project requirements. Before starting design, the structural engineer must determine the criteria for acceptable performance. The loads or forces to be resisted must be provided. For specialized structures, this may be given directly, as when supporting a known piece of machinery, or a crane of known capacity. For conventional buildings, buildings codes adopted on a municipal, county , or , state level provide minimum design requirements for live loads (occupants and furnishings , snow on roofs , and so on ). The engineer will calculate dead loads (structural and known, permanent installations ) during the design process. For the structural to be serviceable or useful , deflections must also be kept within limits ,since it is possible for safe structural to be uncomfortable “bounce” Very tight deflection limits are set on supports for machinery , since beam sag can cause drive shafts to bend , bearing to burn out , parts to misalign , and overhead cranes to stall . Limitations of sag less than span /1000 ( 1/1000 of the beam length ) are not uncommon . In conventional buildings, beams supporting ceilings often have sag limits of span /360 to avoid plaster cracking, or span /240 to avoid occupant concern (keep visual perception limited ). Beam stiffness also affects floor “bounciness,” which can be annoying if not controlled. In addition , lateral deflection , sway , or drift of tall buildings is often held within approximately height /500 (1/500 of the building height ) to minimize the likelihood of motion discomfort in occupants of upper floors on windy days . Member size limitations often have a major effect on the structural design. For example, a certain type of bridge may be unacceptable because of insufficient under clearance for river traffic, or excessive height endangering aircraft. In building design, ceiling heights and floor-to-floor heights affect the choice of floor framing. Wall thicknesses and column sizes and spacing may also affect the serviceability of various framing schemes. Materials selection. Technological advances have created many novel materials such as carbon fiber and boron fiber-reinforced composites, which have excellent strength, stiffness, and strength-to-weight properties. However, because of the high cost and difficult or unusual fabrication techniques required , they are used only in very limited and specialized applications . Glass-reinforced composites such as fiberglass are more common, but are limited to lightly loaded applications. The main materials used in structural design are more prosaic and include steel, aluminum, reinforced concrete, wood , and masonry . Structural schemes. In an actual structural, various forces are experienced by structural members , including tension , compression , flexure (bending ), shear ,and torsion (twist) . However, the structural scheme selected will influence which of these forces occurs most frequently, and this will influence the process of materials selection. Tension is the most efficient way to resist applied loads ,since the entire member cross section is acting to full capacity and bucking is not a concern . Any tension scheme must also included anchorages for the tension members . In a suspension bridge , for example ,the anchorages are usually massive dead weights at the ends of the main cables . To avoid undesirable changes in geometry under moving or varying loads , tension schemes also generally require stiffening beams or trusses. Compression is the next most efficient method for carrying loads . The full member cross section is used ,but must be designed to avoid bucking ,either by making the member stocky or by adding supplementary bracing . Domed and arched buildings ,arch bridges and columns in buildings frames are common schemes . Arches create lateral outward thrusts which must be resisted . This can be done by designing appropriate foundations or , where the arch occurs above the roadway or floor line , by using tension members along the roadway to tie the arch ends together ,keeping them from spreading . Compression members weaken drastically when loads are not applied along the member axis , so moving , variable , and unbalanced loads must be carefully considered. Schemes based on flexure are less efficient than tension and compression ,since the flexure or bending is resisted by one side of the member acting in tension while the other side acts in compression . Flexural schemes such as beams , girders , rigid frames , and moment (bending ) connected frames have advantages in requiring no external anchorages or thrust restrains other than normal foundations ,and inherent stiffness and resistance to moving ,variable , and unbalanced loads . Trusses are an interesting hybrid of the above schemes . They are designed to resist loads by spanning in the manner of a flexural member, but act to break up the load into a series of tension and compression forces which are resisted by individually designed tension and have excellent stiffness and resistance to moving and variable loads . Numerous member-to-member connections, supplementary compression braces ,and a somewhat cluttered appearance are truss disadvantages . Plates and shells include domes ,arched vaults ,saw tooth roofs , hyperbolic paraboloids , and saddle shapes .Such schemes attempt to direct all force along the plane of the surface ,and act largely in shear . While potentially very efficient ,such schemes have very strict limitations on geometry and are poor in resisting point ,moving , and unbalanced loads perpendicular to the surface. Stressed-skin and monologue construction uses the skin between stiffening ribs ,spars ,or columns to resist shear or axial forces . Such design is common in airframes for planes and rockets, and in ship hulls . it has also been used to advantage in buildings. Such a design is practical only when the skin is a logical part of the design and is never to be altered or removed . For bridges , short spans are commonly girders in flexure . As spans increase and girder depth becomes unwieldy , trusses are often used ,as well as cablestayed schemes .Longer spans may use arches where foundation conditions ,under clearance ,or headroom requirements are favorable .The longest spans are handled exclusively by suspension schemes ,since these minimize the crucial dead weight and can be erected wire by wire . For buildings, short spans are handled by slabs in flexure .As spans increase, beams and girders in flexure are used . Longer spans require trusses ,especially in industrial buildings with possible hung loads . Domes ,arches , and cable-suspended and air –supported roofs can be used over convention halls and arenas to achieve clear areas . Structural analysis . Analysis of structures is required to ensure stability (static equilibrium ) ,find the member forces to be resisted ,and determine deflections . It requires that member configuration , approximate member sizes ,and elastic modulus ; linearity ; and curvature and plane sections . Various methods are used to complete the analysis . Final design . once a structural has been analyzed (by using geometry alone if the analysis is determinate , or geometry plus assumed member sizes and materials if indeterminate ), final design can proceed . Deflections and allowable stresses or ultimate strength must be checked against criteria provided either by the owner or by the governing building codes . Safety at working loads must be calculated . Several methods are available ,and the choice depends on the types of materials that will be used . Pure tension members are checked by dividing load by cross-section area .Local stresses at connections ,such as bolt holes or welds ,require special attention . Where axial tension is combined with bending moment ,the sum of stresses is compared to allowance levels . Allowable : stresses in compression members are dependent on the strength of material, elastic modulus ,member slenderness ,and length between bracing points . Stocky members are limited by materials strength ,while slender members are limited by elastic bucking . Design of beams can be checked by comparing a maximum bending stress to an allowable stress , which is generally controlled by the strength of the material, but may be limited if the compression side of the beam is not well braced against bucking . Design of beam-columns ,or compression members with bending moment ,must consider two items . First ,when a member is bowed due to an applied moment ,adding axial compression will cause the bow to increase .In effect ,the axial load has magnified the original moment .Second ,allowable stresses for columns and those for beams are often quite different . Members that are loaded perpendicular to their long axis, such as beams and beam-columns, also must carry shear. Shear stresses will occur in a direction to oppose the applied load and also at right angles to it to tie the various elements of the beam together. They are compared to an allowable shear stress. These procedures can also be used to design trusses, which are assemblies of tension and compression members. Lastly, deflections are checked against the project criteria using final member sizes. Once a satisfactory scheme has been analyzed and designed to be within project criteria, the information must be presented for fabrication and construction. This is commonly done through drawings, which indicate all basic dimensions, materials, member sizes, the anticipated loads used in design, and anticipated forces to be carried through connections. 結構設計 結構設計包含至少5個不同方面的工作：工程要求，材料，結構方案，分析和設計。對于不一般的結構或材料，又包含一個方面：試驗。這些方面不是嚴格按步驟進行，因為不同材料在不同方案大多數是有效的，試驗會導致設計變更，最終設計由初步估計設計開始，然后經過分析和再設計幾個循環(huán)后完成。通常，可替代的設計證明在費用，強度和使用性上十分接近。結構工程師，業(yè)主或最后住戶基于其它的考慮選擇一種。 工程要求。在開始設計前，結構工程師必須決定容易接受的執(zhí)行標準。必須提供承擔的荷載或力。對于一些專門結構，當支持一臺已知載重的機器或起重機時，這可能直接給出，對于普通建筑物，采用市政，縣，州的建筑規(guī)范，提供了設計所需活載（人群荷載和設備，屋頂雪荷載，等等）的最小值。工程師將計算出設計期間的恒載（結構和已知永久性設備）。 對要正常使用的結構，也必須控制其撓度，因為安全的結構可能會存在令人不安的振動。機器的支座有嚴格的變形限制，因為梁下沉會導致驅動軸彎曲，燒毀，部件錯位和上面的吊車熄火。撓度限制在跨度/1000 (梁長的1/1000）以下是很普通的。在傳統(tǒng)建筑里，支持板的梁撓度限制在跨度1/360以避免粉刷開裂或跨度1/240以避免人的擔憂（保持在可感知的變動范圍內）。梁的剛度也影響板“振動”，如果不能控制會令人很頭疼。另外，高層建筑的側面變形，位移或搖擺通常限定在高度/500（建筑物高度的1/500）里，把在有風的日子里上面樓層的人移動的不舒服降到最小。構件尺寸在結構設計里起主要作用。例如，由于下面留作水上交通的凈空不夠或過高威脅到飛機的特定類型的橋是不可接受的。在建筑設計里，天花板高度和樓板之間高度影響樓板框架的選擇。墻厚和柱子尺寸和跨度也影響不同框架方案的適用性。 選擇材料。技術的進步創(chuàng)造了許多新材料，如碳纖維加強復合材料和硼纖維加強復合材料，它們都具有極好的強度，剛度和強度重量比特性。然而，由于費用高和非通常的制造要求，它們僅用在有限特殊領域。強化玻璃合成物如玻璃纖維是很普遍，但被限制應用在小荷載情況下。用在結構設計上的主要材料更多是普通的，包括鋼材，鋁，鋼筋混凝土，木材，砌體。 結構方案。在一個實際方案里，結構構件承擔很多力，包括拉，壓，彎，剪和扭。然而所選擇的方案將會影響這些力產生的概率，也會影響材料選擇過程。 抗拉是有效的承擔荷載的方法，整個構件的橫截面性能得到發(fā)揮，并且不涉及到彎曲變形。任何抗拉方案必須也對抗拉構件的錨固。例如，在懸索橋里，錨固體通常是位于主要繩索尾段的強大自重。為了避免在荷載移動或變形時有不期望的幾何變形，抗拉方案通常要求是剛性梁和桁架。 抗壓是另一個很有效的承擔荷載方法。全部桿件截面發(fā)揮了作用，但是設計時必須避免彎曲，或者是做成粗短構件或者是增加附加支撐。圓頂和拱形建筑，拱橋和柱是很普遍的建筑方案。拱產生了必須抵擋住的水平外推力。這靠設計合適的基礎或建在車道或樓板的上面的拱解決，靠沿著車道用抗拉構件把兩端的拱連接起來，阻止他們拉開。當荷載不是作用在構件軸線上時，抗壓構件顯著地被削弱。所以，必須認真考慮移動，變化和不平衡的荷載。 基于受彎的方案的效率比受拉和壓低，因為彎曲是靠構件一邊受拉另一邊受壓來抵抗。受彎方案如主梁，次梁，剛架和受彎框架在外部錨固或推力限制，與一般基礎不同，靠內部剛度阻擋可移動，變化和不平衡的荷載的情況下有利。 桁架是上面方案的混合體。它們設計成荷載橫跨在受彎構件上，但是分解成一系列拉力和壓力，由抗拉和抗壓構件承擔。桁架方案設計時不需要特殊錨固或推力的限制，并且有很好的剛度抵抗移動或變化的荷載。大量的構件之間連結和抗壓構件的附加支撐，看起來有點雜亂，這就是桁架的不利處。 板和殼包括圓頂，拱頂，有齒屋頂，雙曲拋物面和馬鞍形。這樣的方案把所有的力直接作用在平板表面并且作用有巨大的剪力。盡管可能效率很高，但是這樣的方案對幾何有嚴格的限制，并且在移動，和不平衡垂直作用在表面的荷載的能力很弱。 薄殼結構和硬殼結構利用加勁肋，梁之間的殼板抵抗剪力和軸向力。這樣的設計在飛機機體和火箭，船體方面很普遍。它在建筑方面也是有利的。這樣的設計僅僅在殼是設計的邏輯部分并且永遠不會被替代和移除時才實際些。 對于橋梁，短跨是很普遍受彎的梁。當跨度增加和梁高變得很大時，通常用桁架和斜拉結構。更長跨時也許用拱，要考慮基礎條件和凈空要求。最長的跨靠懸索方案處理，因為這可把關鍵性的自重降到最小并且能索連索地建造起來。 對于橋，短跨靠板承擔彎矩。當跨度增加時，主梁和次梁被用來承擔彎曲。更長的跨要求用桁架，尤其是在工業(yè)建筑有吊車荷載時，圓頂，拱和懸索和充氣屋頂被用在傳統(tǒng)的大廳和競技場里以獲得凈面積。 結構分析。結構分析要求確定穩(wěn)定性（靜力平衡），構件承擔的力和變形。它需要構件形狀，大概尺寸，已知或假設的材料特性。分析包括：平衡，應力，應變和彈性模量，線形，塑性和彎曲和板截面。很多方法可以完成分析過程。 最終設計。一旦結構分析完成（如果分析是正確的，只用幾何方法；反之附加構件尺寸和材料假設）。最終設計可以進行，必須對照業(yè)主或政府建筑規(guī)范標準來檢查變形和允許應力或極限強度。必須計算工作荷載下的安全性。一般方法是可行的，依據所使用的材料類型做出選擇。 純抗拉構件檢查橫截面應力。特別注意螺栓孔或焊接處的應力。拉彎構件中，用應力之和與分析應力作比。受壓構件中的允許應力取決于構件強度，彈性模量，長細比和支點間距離。粗短構件由材料強度決定，然而長細構件由彈性彎曲決定。 梁的設計由對于最大彎曲應力和允許應力來檢驗，通常由材料強度控制，但是如果受壓一邊沒有側向支撐就會被限制。 梁，柱或有彎矩的受壓構件的設計必須考慮兩項。首先，當構件由于承受彎矩而彎曲時，軸力會增加彎曲量，實際上，軸壓放大了原始彎矩。其次，對于柱和梁的允許應力是不同的。 承受垂直于長軸的荷載的構件。如梁和梁——柱，也必須承擔剪力。剪應力和荷載的方向相反并且在其右邊，把梁的不同部分連接起來。它們與允許剪應力作對比。這些步驟也能用來設計由受拉和受壓構件組成的桁架。最后，用工程標準檢驗變形，使用最后的構件。 一旦被分析和在工程標準內的設計方案是令人滿意的，必須提出制造和建立信息。通過作圖，指明所以基本尺寸，材料和構件大小。設計中預期荷載和節(jié)點承擔的預期力。