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1、Structure of BulidingsA building is closely bound up with people, for it provides people with the necessary space to work and live in. As classified by their use, buildings are mainly of two types: industrial buildings and civil buildings. Industrial buildings are used by various factories or indust
2、rial production while civil buildings are those that are used by people for dwelling, employment, education and other social activities.The construction of industrial buildings is the same as that of civil buildings. However, industrial and civil buildings differ in the material used, and in the str
3、ucture forms or systems they are used.Considering only the engineering essentials, the structure of a building can be difined as the assemblage of those parts which exist for the purpose of maintaining shape and stability. Is primy purpose is to resist any loads applied to the building and to transm
4、it those to the ground.In terms of architecture, the structue of a building is and dose much more than that. It is an inseparable part of the building form to varying degrees is a generator of that form. Used skillfully, the building structure can establish or reinforce orders and rhythms among the
5、architecture volumes and planes. It can be visually dominant or recessive. It can develop harmonies or conflicts. It can be both confining and emincipating. And, unfortunately in some cases, it cannot be ingored. It is physical.The structure must also be engineered to maintain the architecture form.
6、 The principles and tools of physics teand mathematics provide the basis for differentiating between rational and inrational forms in terms of construction. Artists can sometimes generate shapes that obviate any consideration of science, but architects cannot.There are at least three items that must
7、 be present in the structure of a building: stabily, strength and stiffness, economy.Taking the first of the three requiements, it is obvious that stability is needed to maintain shape. An unstable building structure implies unbalanced forces or a lack of equilibrium and a consequent acceleration of
8、 the structure or its pieces.The requirement of strength means that the materials selected to resist the stresses generated by the loads and shapes of the structure(s) must be adequate. Indeed, a “factor of safety” is usually provided so that under the anticipated loads, a given material is not stre
9、ssed to a level even close to its rupture point. The material property called stiffness is considered with the requirement of strength. Stiffness is different form strength in that it directly involves how much a structure strains or deflects under load. A material that is very strong but lacking in
10、 stiffness will deform too much to be of value in resisting the forces applied.Economy of a building structure refers to more than just the cost of the material used. Construction economy is a complicated subject invovling raw materials, fabrication, erection, and maintenance. Design and constructio
11、n labor costs and the costs of energy consumption money(interest) are consumption must be consiedered. Speed of construction and the cost of money(interest) are also factors. In most design situations, more than one structural material requires consideration. Completive alternatives almost always ex
12、ist, and the choice is seldom obvious.Apart form these three primary requirements, several other factors are worthy of emphasis. First, the structure or suctructural system must relate to the buildings function. It should not be in conflict in terms of form. For example, a linear function demands a
13、linear structure, and therefore it would be improper to roof a bowling alley with a dome. Similarly, a theater must have large, unobstructed spans but a fine restaurant probably should not. Stated simply, the structure must be appropriate to the function it is to shelter.Second, the structure must b
14、e fire-resistant. It is obvious that the structural system must be able to maintain its integrity at least until the occupuants are safely out. Building codes specify the number of hours for which certain parts of a building must resist the heat without collapse. The structural materials used for th
15、ose elements must be inherently fire-resistant or be adequently protected by fireproofing materials. The degree of fire resistance to be provided will depend upon a number of items, including the use and occupancy load of the space, its dimensions, and the location of the building.Third, the structu
16、re should integrate well with the buildings circulation systems. It should not be in conflict with the piping systems for water and waste, the ducting systems for air, or (most important) the movement of people. It is obvious that the various building systems must be coordinated as the design progre
17、sses. One can design in a sequential step-by-step manner within any one system, but the design of all of them should move in a parallel manner toward completion. Spatially, all the various parts of a building are interdependent.Fourth, the structure must be psychologically safe as well as physically
18、 safe. A highrise frame that sways considerably in the wind might not actually be dangerous but may make the building uninhabitable just the same. Ligheweight floor systems that are too “bouncy” can make the users very uncomfortable. Large glass windows, uninterrupted by dividing motions, can bu qui
19、te safe but will appear very insecure to the occupant standing next to on 40 floors above the street.Sometimes the architect must make deliberate attempts to increase the apparent strength or solidness of the structure. This apparent safety may be more important than honestly expressing the building
20、s structure, because the untrained viewer cannot distinguish between real and perceived safety.The building designer needs to understand the behavior of physical structures under load. An ability to intuit or “feel” structural behavior is possessed by those having much experience involving structura
21、l analysis, both qualitative and quantitative. The consequent knowledge of how forces, stresses, and deformations build up in different materials and shapes is vital to development of this “sense”. Structural analysis is the process of determining the forces and deformations in structures due to spe
22、cified loads so that the structure can be designed rationally, and so that the state of safety of existing structures can be checked.In the design of structures, it is necessary to start with a concept leading to a configuration which can then be analyzed. This is done to members can be sized and th
23、e needed reinforcing determined, in order to: a) carry the design loads without distress or excessive deformations ( serviceability or working condition); and b) to prevent collapse before a specified overload has been placed on the structure (safety or ultimate condition).Since normally elastic con
24、ditions will prevail under working loads, a structural theory based on the assumptions of elastic behavior is appropriate for determining serviceability conditions. Collapse of a structure will usually occur only long after the elastic range of the materials has been exceeded at circal points, so th
25、at an ultimate strength theory based on the inelastic behavior of the material is necessary for a rational determination of the safety of a structure against collapse. Neverthelese, an elastic theory can be used to determine a safe approximation to the strength of ductile structures (the lower bound
26、 approach of plasticity), and this approach is customarily followed in reinforced concrete practice. For this reasion only the elastic theory of gtructure is pursued in this chapter.Looked at critically, all structures are assemblies of three-dimensional elements, the exact analysis of which is a fo
27、rbdding task even under ideal conditions and impossible to contemplate under conditions of professional practice. For this reason, an important part of the analysts work is the simplification of the actual structure and loading conditions to a model which is susceptible to rational analysis.Thus, a
28、structural framing system is decomposed into a slab and floor beams which in turn frame into girders carried by colums which transmit the loads to the foundations. Since traditional structural analysis has been unable to cope with the action of the slab, this has often been idealized into a system o
29、f strips acting as beams. A lso, long-hand methods have been unable to cope with three-dimensional framing systems, so that the entire structure has been modeled by a system of planner subassemblies, to be analyzed one at a time. The modern matrix-computer methods have revolutionized structural anal
30、ysis by making it possible to analyze entrie systems, thus leading to more reliable predictions about the behavior of structures under loads.Actual loading conditions are also both difficult to determine and to express realistically, and must be simplified for purposes of analysis. Thus, traffic loa
31、ds on a bridge structure, which are essentially both of dynamic and random nature, are usually idealized into statically moving standard trucks, or distributed loads, intended to simulate the most severe loading conditions occurring in practice.Similary, continuous beams are sometimes reduced to sim
32、ple beams, rigid joints to pin-joints, fillers-walls are neglected, shear walls considered as beams; in deciding how to model a structure so as to make it reasonably realistic but at the same time reasonably simple, the analyst must remember that each such idealization will make the soulation more s
33、uspect. The more realistic the analysis, the greater will be the confidence which it inspires, and the smaller may be the safety factor ( or factor of ignorance ). Thus, unless code provisions control, the engineer must evaluate the extra expense of a thorough analysis as compared to possible saving
34、s in the structure.The most important use of structure analysis is as a tool in structural design. As such, it will usually be a part of a trial-and-error procedure, in which an assumed configuration with assumed dead loads is analyzed, and the members designed in accordance with the results of the
35、analysis. This phase is called the preliminary design; since this design is still subject to change, usually a crude, fast analysis method is adequate. At this stage, the cost of the structure is estimated, loads and member properties are revised, and the design is checked for possible improvements.
36、 The changes are now incorporated in the structure, a more refined analysis is performed, and the member design is revised. This project is carried to convergence, the rapidity of which will depend on the capability of the designer. It is clear that a variety of analysis methods, ranging from “ quic
37、k and dirty to exact ”, is needed for design purposes.An efficient analyst must thus be in command of the rigorous methods of analysis, must be able to reduce these to shortcut methods by appropriate assumptions, and must be aware of available design and analysis aids, as well as simplification perm
38、itted by applicable building codes. An up-to-date analyst must likewise be versed in the bases of matrix structural analysis and its use in digital computers as well as in the use of available analysis programs or software. 建筑结构建筑物与人类有着密切的关系，它能为人们在其中工作和生活提供必要的空间。根据其功能不同，建筑物主要有两大类：工业建筑和民用建筑。工业建筑有各种工厂
39、或制造厂，而民用建筑指的是那些人们用以居住、工作、教育或其他社会活动的场所。工业建筑的建造与民用建筑相同，但两者在选用的材料、结构形式或体系方面是有差别的。就工程的实质而言，建筑结构可定义为：以保持形状和稳定为目的的各个基本构件的组合体。其基本目的是抵抗作用在建筑物上的各种荷载并把它传到地基上。从建筑学的角度来讲，建筑结构并非仅仅如此。它与建筑风格是不可分割的，在不同程度上是一种建筑风格的体现。如能巧妙地设计建筑结构，则可建立或加强建筑空间与建筑平面之间的格调与节奏。它在直观上可以是显性的或是隐性的。它能产生和谐体或对照体。它可能既局限又开放。不幸的是，在一些情况下，它不能被忽视。它是实际存在
40、的。结构设计还必须与建筑风格相吻合。物理学和数学的原理及工具为区分在结构上的合理和不合理的形式提供了依据。艺术家有时可以不必考虑科学就能画出图形，但建筑师却不行。在建筑结构中至少应包括三项内容：稳定性、强度和刚度，经济性。在上述三种要求中，首先是稳定性。它在保持建筑物形状上是必不可少的。一座不稳定的建筑结构意味着有不平衡的力或失去平衡状态，并由此导致结构整体或构件产生加速度。强度的要求意味着所选择的结构材料足以承受由荷载产生的应力并且结构形状必须适当。实际上，通常都提供一个安全系数以便在预计的荷载作用下，所使用材料的应力不会接近破坏应力。被称为刚度的材料的特性，需与强度要求一起考虑。刚度不同于
41、强度，因为它涉及荷载作用下结构应变的大小和变形的程度。具有很高强度，但刚度较低的材料，在外力作用下会因变形过大而失去其使用价值。建筑结构的经济性指的不仅仅是所用材料的费用。建筑经济是一个复杂的问题，其中包括原材料、制作、安装和维修。必须考虑设计和施工中人工费及能源消耗的费用。施工的速度和资金成本（利息）也是需要考虑的因素。对大多数设计情况，不能仅仅考虑一种建筑材料，经常存在一些有竞争性的其他选择，而具体应该选择哪种并不明显。除了这三种最基本要求之外，其他几种因素也值得重视。首先，结构或结构体系必须和建筑物的功能相吻合而不应该与建筑形式相矛盾。例如，线性功能要求线性结构，所以把保龄球场的顶部盖成
42、圆形是不合适的。同样剧院必须是大跨度、中间没有障碍的结构，而高档饭店也许不是这样。简而言之，结构形式必须与所围护空间的功能相适应。第二，结构必须防火。很显然，至少一直到内部人员安全撤离为止，结构体系必须能保持完整。建筑规范详细规定了建筑物的某些构件抵抗热量而不倒塌的时间。用于那些构件的结构材料自身必须具有防火性或者用耐火材料加以适当保护。所规定的防火等级将取决于一系列因素，它包括建筑空间的占有量和使用情况、建筑物的尺寸及建筑物的位置。第三，结构应与建筑物的循环系统很好的结合。它不应与给排水管道、通风系统或人的活动空间相矛盾（这是最重要的）。很显然，各种建筑系统在设计时必须相互协调。对任何单个系
43、统的设计，可以有顺序的一步一步的进行，而对所有系统的设计则采用并行方式来完成。从空间上来讲，在一座建筑物的所有构件之间都是相互依存的。第四，结构在心理上及外观上必须给人一种安全感。在风荷载作用下晃动剧烈的高层框架虽然没有危害，但仍然不适宜居住。弹性太大的轻质楼盖系统可能给居住者很不舒适的感觉。没有窗棂的巨大玻璃窗户尽管是相当安全的，但对居住在楼房里的人来说，特别是当他站在临街40层高楼的大玻璃窗前时，总会感极很不安全。有事建筑师必须有意采取积极措施来增加建筑结构外表的强度和坚固性。外观的安全性也许比真实表达建筑结构更重要，因为没有受过训练的人是不能分清真实的和感觉中的安全性的。建筑设计师需要理
44、解荷载作用下实际结构的性能。在结构定性和定量分析两方面有丰富经验的设计师拥有直觉或感受结构性能的能力。关于力、应力、变形在不同的材料和形状的结构中是如何建立起来的相关知识，对于发展上述判断力是至关重要的。结构分析是确定在给定荷载下结构中产生的力和变形，以便是结构设计得合理或检查现有结构的安全状况。在结构设计中，必须先从结构的概念开始拟定一种结构形式，然后再进行分析。这样做能确定构件的尺寸以及所需要的钢筋，以便a）承受设计荷载而不出现损坏或过大变形（在正常使用或工作状态）；b）防止结构在荷载未达到规定的超载以前倒塌（安全性或极限状况）。由于通常在使用荷载作用下，结构处于弹性状态，因此以弹性状态假
45、定为基础的结构理论适用于正常使用状态。通常只有当危险截面的材料远远超过弹性范围之后，才可能发生结构倒塌，因而建立在材料非弹性状态基础上的极限强调理论是合理确定结构安全性，防止倒塌所必需的。不过弹性理论可用来确定延性结构强度的安全近似值（塑性下限逼近法），在钢筋混凝土设计中习惯采用这种方法。基于这种原因，在本章中仅采用结构的弹性理论。严格地讲，所有结构都是三维构件的组合体，对其进行精确分析，即使在理想状态下也是棘手的工作，而在实际工程条件下，更是难以想像。基于这种原因，分析人员工作的一个重要部分是将实际结构和荷载状态简化成一个易于合理分析的模型。这样，框架结构体系可分解成平板和楼板梁，楼板梁又通
46、过框架传递给立柱支承的大梁，立柱再讲荷载传递到基础上。由于传统的的结构分析方法不能分析平板的作用，所以经常理想化成类似于梁的条形结构。同样，普通的方法不能分析三维框架体系，因此将整个结构简化为平面框架体系模型，逐一加以分析。现代的矩阵计算机法可以分析整个体系从而革新了结构分析，这样可对荷载作用下结构的性能作出更可靠的预测。实际荷载状态也是很难确定和很难客观表达的，为了进行分析，必须进行简化。例如，桥梁结构上的交通荷载主要是动荷载且是随机的，通常理想化成静态行驶的标准卡车或分布荷载，以用来模拟实际产生的最不利的荷载状态。类似的还有，连续梁有时简化为简支梁，刚性节点简化为铰接点，忽略填充墙，把剪力
47、墙视为梁；在决定如何建立一个结构模型使之比较客观又适度简单时，分析人员必须记住每一个理想化假设都将使产生的解更加不可靠。分析得越客观，产生的信心就越大，而所取的安全系数（或忽略的因素）可能就越小。这样，除非规范条款控制，工程师必须估算出结构精确分析所需追加的费用与由此节省的结构中费用比值，是否合算。结构分析最重要的用途是作为结构设计中的工具。按此定义，它通常是试算过程中的一个环节，在这种方法中，首先，在假定的恒载下对假定的结构体系进行分析，然后根据分析结果设计各构件。这个阶段称为初步设计，由于此时的设计常常会变化，通常采用粗略的快速分析方法就足够了。在此阶段，估计结构的成本，修正荷载及构件特性，并对设计进行检查以便改进。至此，将所作的更改纳入到结构中，再进行更精细的分析，并修改构件设计。这一过程反复进行直至收敛，收敛的速度取决于设计者的能力。很清楚，为了达到设计目的，需要从“迅速而粗略”到“精确”的各种分析方法。因而，有能力的分析人员必须掌握严密的分析方法，必须能够通过适当的假设条件进行简化分析，必须了解可利用的标准设计和分析手段以及建筑规范中允许的简化方法。同时，现代的分析允许的简化方法。同时，现代的分析人员必须精通结构矩阵分析的基本原理及其在数字计算机中的应用并且会应用现有的分析程序及有关软件。