土木工程外文翻译.pdf

Tall Building Structure Tall buildings have fascinated mankind from the beginning of civilization their construction being initially for defense and subsequently for ecclesiastical purposes The growth in modern tall building construction however which began in the 1880s has been largely for commercial and residential purposes Tall commercial buildings are primarily a response to the demand by business activities to be as close to each other and to the city center as possible thereby putting intense pressure on the available land space Also because they form distinctive landmarks tall commercial buildings are frequently developed in city centers as prestige symbols for corporate organizations Further the business and tourist community with its increasing mobility has fuelled a need for more frequently high rise city center hotel accommodations The rapid growth of the urban population and the consequent pressure on limited space have considerably influenced city residential development The high cost of land the desire to avoid a continuous urban sprawl and the need to preserve important agricultural production have all contributed to drive residential buildings upward Ideally in the early stages of planning a building the entire design team including the architect structural engineer and services engineer should collaborate to agree on a form of structure to satisfy their respective requirements of function safety and serviceability and servicing A compromise between conflicting demands will be almost inevitable In all but the very tallest structures however the structural arrangement will be subservient to the architectural requirements of space arrangement and aesthetics The two primary types of vertical load resisting elements of tall buildings are columns and walls the latter acting either independently as shear walls or in assemblies as shear wall cores The building function will lead naturally to the provision of walls to divide and enclose space and of cores to contain and convey services such as elevators Columns will be provided in otherwise unsupported regions to transmit gravity loads and in some types of structure horizontal loads also The inevitable primary function of the structural elements is to resist the gravity loading from the weight of the building and its contents Since the loading on different floors tends to be similar the weight of the floor system per unit floor area is approximately constant regardless of the building height Because the gravity load on the columns increases down the height of a building the weight of columns per unit area increases approximately linearly with the building height The highly probable second function of the vertical structural elements is to resist also the parasitic load caused by wind and possibly earthquakes whose magnitudes will be obtained from National Building Codes or wind tunnel studies The bending moments on the building caused by these lateral forces increase with at least the square of the height and their effects will become progressively more important as the building height increases Once the functional layout of the structure has been decided the design process generally follows a well defined iterative procedure Preliminary calculations for member sizes are usually based on gravity loading augmented by an arbitrary increment to account for wind forces The cross sectional areas of the vertical members will be based on the accumulated loadings from their associated tributary areas with reductions to account for the probability that not all floors will be subjected simultaneously to their maximum live loading The initial sizes of beams and slabs are normally based on moments and shears obtained from some simple method of gravity load analysis or from codified mid and end span values A check is then made on the maximum horizontal deflection and the forces in the major structural members using some rapid approximate analysis technique If the deflection is excessive or some of the members are inadequate adjustments are made to the member sizes or the structural arrangement If certain members attract excessive loads the engineer may reduce their stiffness to redistribute the load to less heavily stressed components The procedure of preliminary analysis checking and adjustment is repeated until a satisfactory solution is obtained Invariably alterations to the initial layout of the building will be required as the client s and architect s ideas of the building evolve This will call for structural modifications or perhaps a radical rearrangement which necessitates a complete review of the structural design The various preliminary stages may therefore have to be repeated a number of times before a final solution is reached Speed of erection is a vital factor in obtaining a return on the investment involved in such large scale projects Most tall buildings are constructed in congested city sites with difficult access therefore careful planning and organization of the construction sequence become essential The story to story uniformity of most multistory buildings encourages construction through repetitive operations and prefabrication techniques Progress in the ability to build tall has gone hand in hand with the development of more efficient equipment and improved methods of construction Earthquake Faults The origin of an earthquake An earthquake originates on a plane of weakness or a fracture in the earth s crust termed a fault The earth on one side of the fault slides or slips horizontally and or vertically with respect to the earth on the opposite side and this generates a vibration that is transmitted outward in all directions This vibration constitutes the earthquake The earthquake generally originates deep within the earth at a point on the fault where the stress that produces the slip is a maximum This point is called the hypocenter or focus and the point on the earth s surface directly above this point is called the epicenter The main or greatest shock is usually followed by numerous smaller aftershocks These aftershocks are produced by slippage at other points on the fault or in the fault zone Types of earthquake faults Faults are classified in accordance with the direction and nature of the relative displacement of the earth at the fault plane Probably the most common type is the strike slip fault in which the relative fault displacement is mainly horizontal across an essentially vertical fault plane The great San Andreas fault in California is of the type Another type is termed a normal fault when the relative movement is in an upward an downward direction on a nearly vertical fault plane The great Alaskan earthquake of 1964 was apparently of this type A less common type is the thrust fault when the earth is under compressive stress across the fault and the slippage is in an upward and downward direction along an inclined fault plane The San Fernando earthquake was generated on what has usually been classified as a thrust fault although there was about as much lateral slippage as up and down slippage due to thrust across the inclined fault plane Some authorities refer to this combined action as lateral thrust faulting The compressive strain in the earth of the San Fernando Valley floor just south of the thrust fault was evidenced in many places by buckled sidewalks and asphalt paving Forces exerted by an earthquake Slippage along the fault occurs suddenly It is a release of stress that has gradually built up in the rocks of the earth s crust Although the vibrational movement of the earth during an earthquake is in all directions the horizontal components are of chief importance to the structural engineer These movements exert forces on a structure because they accelerate This acceleration is simply a change in the velocity of the earth movement Since the ground motion in an earthquake is vibratory the acceleration and force that it exerts on a structure reverses in direction periodically at short intervals of time The structural engineer is interested in the force exerted on a body by the movement of the earth This may be determined from Newton s second law of motion which may be stated in the following form F Ma In which F is a force that produces an acceleration a when acting on a body of mass M This equation is nondimensional For calculations M is set equal to W g then F W g a 1 In which F is in pounds a is in feet per second per second W is the weight of the body also in pounds and g is the acceleration of gravity which is 32 2 feet per second per second Equation 1 is empirical It simply states the experimental fact that for a free falling body the acceleration a is equal to g and the acceleration force F is then equal to the weight W For convenience the acceleration of an earthquake is generally expressed as a ratio to the acceleration of gravity This ratio is called a seismic coefficient The advantage of this system is that the force exerted on a body by acceleration is simply the corresponding seismic coefficient multiplied by the weight of the body This is in accordance with Equation 1 in which a g is the seismic coefficient Activity of faults All faults are not considered to present the same hazard Some are classified as active since it is believed that these faults may undergo movement from time to time in the immediate geologic future Unfortunately in the present state of the art there is a good deal of uncertainty in the identification of potentially active faults For example the fault that generated the San Fernando earthquake did not even appear on any published geological maps of the area This fault was discovered to be active only when it actually slipped and ruptured the ground surface Accordingly the identification of active faults and geologically hazardous areas for land use criteria and for hazard reduction by special engineering may be of questionable value Only in very recent years have geologists begun to try to evaluate the potential activity of faults that have no historical record of activity By close inspection of a fault visible in the side walls of a trench that cuts across the fault it is sometimes possible to determine if it has been active in recent times For example if the trace of the fault extends through a recent alluvial material then there must have been slippage since that material was deposited However fault ruptures may be very difficult or impossible to see in imbedded material such as sand and gravel Also of course the location of the fault must be known and it must reach the surface of the ground in order to inspect it by trenching Evidence of the historical activity of a fault may sometimes be obtained by observing the faulting of geologically young deposits exposed in a trench Such deposits are generally bedded and well consolidated so that fault rupture can easily be seen The approximate time of formation of a fault rupture or scarp has in some cases been determined by radiocarbon analysis of pieces of wood found in the rupture or scarp In addition to evidence of young fault activity obtained by trenching there also may be topographic evidence of young faulting such as is obvious along the San Andreas fault Vertical aerial photographs are one of the most important methods for finding topographic evidence of active faults This evidence which includes scarps offset channels depressions and elongated ridges and valleys is produced by fault activity The age of these topographic features and therefore the time of the fault activity can be estimated by the extent to which they are weathered and eroded 高层建筑结构高层建筑结构 高楼大厦已经着迷 从人类文明的开始 其建设是国防和最初其后教会的目 的 现代高层建筑的增长 然而 这在 19 世纪 80 年代开始 在很大程度上是为 商业和住宅用途 高层商业楼 主要是对商业活动的需求响应作为彼此接近 并到城市中心 如可能 从而使在现有的土地空间的巨大压力 此外 因为它们形成鲜明的标志 性建筑 高层商业楼 经常制定了促进企业组织的威信的象征的城市中心 此外 商业和旅游界与流动性日益增加 已促使更多的 经常的高层需要 市中心酒店住宿 城镇人口的迅速增长和随之而来的压力有限的空间大大影响了城市住宅发 展 土地成本高 为了避免出现连续的城市扩张以及需要维护重要的农业生产都 有助于推动住宅楼宇向上 理想情况下 在规划建设的初期阶段 整个设计团队 包括建筑师 结构工 程师 服务工程师 应互相合作 在商定的结构形式 以满足功能 安全性和可 维护性各自的需求 并提供服务 冲突的要求之间的妥协将是不可避免的 但在所有的结构非常最高 但结构安排将服从安排和空间美学的建筑要求 两个垂直荷载抗高层建筑元素的主要类型列和墙壁 后者代理或者作为剪力 墙或剪力墙作为核心组件独立 该大楼的功能将导致自然提供的墙壁围分裂和空 间 和内核 以遏制和传达 如电梯服务 专栏将提供 在每单不支持的地区 否则 传输重力负荷 并在某些类型的结构 水平荷 载也 不可避免的结构因素的主要功能是抵抗建筑物及其内容的重力负荷重量 由 于不同的楼层负荷往往是相似的 该系统每单位楼面面积重量约不断 不论建筑 物的高度 由于对降低建筑物的高度 重量面积和重力负荷的增加而增加约与建筑的高 度成正比 在极有可能垂直结构构件的第二个功能是抵制也是寄生风荷载和可能的地 震 其震级将由国家建筑守则或风洞研究取得造成的 对这些侧向力的增加造成 的建设的弯矩至少高度广场 和其效果会变得越来越重要 因为建筑物高度的增加 一旦结构功能布局已经确定 设计过程中普遍遵循明确的迭代过程 会员规 模初步测算 通常根据一个任意扩充增量占风力重力负荷 的跨垂直截面面积的成员将根据其相关地区的支流与积累负荷削减 以考虑 到 并非所有的楼层将同时受到其最大的活荷载的概率 最初的梁 板的尺寸通 常为基础 在时刻剪一些简单的我获得 需氧量重力负载分析 或从编纂中和年底跨度值 进行检查 然后做出的最 高水平偏转 并在主要结构构件的力量 使用一些快速近似性能分析技术 如果 变形过大 或部分成员不足 调整 是为成员的大小或结构安排 如果行政长官 成员吸引过度劳累 工程师可减少其刚度重新分配负载量较低强调组件 初步分 析程序 检查和调整 直到满意的解决办法 得到重复 总是以建筑物的初步布局的改动需作为客户端的建设和发展的建筑师的想 法 这将调用结构的修改 或者可能是激进的重新安排 因此必须对结构性的设 计进行全面审查 各种初级阶段 因此可能要重复最终解决之前 多次到达 大多数高层建筑都建在拥挤的城市用地 难以利用 因此仔细的规划和施工 顺序组织是至关重要的 这个故事对大多数高层建筑的故事 鼓励通过反复的统一行动和预制技术建 设 在高大的能力建设已经取得进展的同时更高效的设备和施工方法的改进发展 手 地震断层 地震的起源 据我国地震台起源于软弱的飞机或在地壳断裂 称为 错误 关于一个断 层的一侧地球幻灯片或单就在地球对面横向和 或垂直 这会生成一个向各个方 向传播向外震动 这构成了地震震动 这次地震深度一般起源于对故障点的地球内部的压力下产生的支路是最长 的 这一点被称为震源或重点和地球表面的点上方这一点称为震中 主要的或最 大的震动 随后通常是由众多小的余震 这些余震在其他生产点的过失或在断裂