外文翻译
           
结构设计
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 i
mplies 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
design翻译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 ,s
ince 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.