自动弯管机装置及其电器设计含开题及18张CAD图
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自动弯管机装置及其电器设计含开题及18张CAD图,自动,弯管,装置,及其,电器,设计,开题,18,CAD
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结构设计Augustine J.Fredrich摘要：结构设计是选择材料和构件类型，大小和形状以安全有用的样式承担荷载。一般说来，结构设计暗指结构物如建筑物和桥或是可移动但有刚性外壳如船体和飞机框架的工厂稳定性。设计的移动时彼此相连的设备（连接件），一般被安排在机械设计领域。 关键词：结构设计 ； 结构分析 ； 结构方案 ； 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.结构设计结构设计包含至少5个不同方面的工作：工程要求，材料，结构方案，分析和设计。对于不一般的结构或材料，又包含一个方面：试验。这些方面不是严格按步骤进行，因为不同材料在不同方案大多数是有效的，试验会导致设计变更，最终设计由初步估计设计开始，然后经过分析和再设计几个循环后完成。通常，可替代的设计证明在费用，强度和使用性上十分接近。结构工程师，业主或最后住户基于其它的考虑选择一种。工程要求。在开始设计前，结构工程师必须决定容易接受的执行标准。必须提供承担的荷载或力。对于一些专门结构，当支持一台已知载重的机器或起重机时，这可能直接给出，对于普通建筑物，采用市政，县，州的建筑规范，提供了设计所需活载（人群荷载和设备，屋顶雪荷载，等等）的最小值。工程师将计算出设计期间的恒载（结构和已知永久性设备）。对要正常使用的结构，也必须控制其挠度，因为安全的结构可能会存在令人不安的振动。机器的支座有严格的变形限制，因为梁下沉会导致驱动轴弯曲，烧毁，部件错位和上面的吊车熄火。挠度限制在跨度/1000 (梁长的1/1000）以下是很普通的。在传统建筑里，支持板的梁挠度限制在跨度1/360以避免粉刷开裂或跨度1/240以避免人的担忧（保持在可感知的变动范围内）。梁的刚度也影响板“振动”，如果不能控制会令人很头疼。另外，高层建筑的侧面变形，位移或摇摆通常限定在高度/500（建筑物高度的1/500）里，把在有风的日子里上面楼层的人移动的不舒服降到最小。构件尺寸在结构设计里起主要作用。例如，由于下面留作水上交通的净空不够或过高威胁到飞机的特定类型的桥是不可接受的。在建筑设计里，天花板高度和楼板之间高度影响楼板框架的选择。墙厚和柱子尺寸和跨度也影响不同框架方案的适用性。选择材料。技术的进步创造了许多新材料，如碳纤维加强复合材料和硼纤维加强复合材料，它们都具有极好的强度，刚度和强度重量比特性。然而，由于费用高和非通常的制造要求，它们仅用在有限特殊领域。强化玻璃合成物如玻璃纤维是很普遍，但被限制应用在小荷载情况下。用在结构设计上的主要材料更多是普通的，包括钢材，铝，钢筋混凝土，木材，砌体。结构方案。在一个实际方案里，结构构件承担很多力，包括拉，压，弯，剪和扭。然而所选择的方案将会影响这些力产生的概率，也会影响材料选择过程。 抗拉是有效的承担荷载的方法，整个构件的横截面性能得到发挥，并且不涉及到弯曲变形。任何抗拉方案必须也对抗拉构件的锚固。例如，在悬索桥里，锚固体通常是位于主要绳索尾段的强大自重。为了避免在荷载移动或变形时有不期望的几何变形，抗拉方案通常要求是刚性梁和桁架。抗压是另一个很有效的承担荷载方法。全部杆件截面发挥了作用，但是设计时必须避免弯曲，或者是做成粗短构件或者是增加附加支撑。圆顶和拱形建筑，拱桥和柱是很普遍的建筑方案。拱产生了必须抵挡住的水平外推力。这靠设计合适的基础或建在车道或楼板的上面的拱
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