1、高 层 建 筑关于高层建筑是很难给出明确的定义的，我们可以定义 1-2 层的建筑物为低层建筑，3 到 4 层为中层建筑或者可以说 10 到 20 层甚至更高层。虽然原则上，高层建筑和低层建筑在水平构件和垂直构件的设计方面并没有太的差别，但使竖向构件的设计成为高层设计有两个控制性的因素。高层建筑承受荷载大，对柱子截面尺寸要求很大，需要更多的墙体，若是筒体结构，还需要更多的筒体，一旦受到侧向力，就会产生很大的倾覆力矩，剪力和弯矩，因此在设计时，就必须仔细认真对结构进行设计。墙体和柱子主要负责由高层建筑竖向构件传来的荷载，竖向荷载主要是自重，因此柱子的尺寸必须很大，除了竖向荷载，柱子等承重构件还要承
2、受水平荷载，如风荷载，地震荷载，柱子将这些水平荷载和地震荷载通过基础最终传递给地基。但是，侧向荷载的分布不同于竖向荷载，它们是非线性的，并且沿着建筑物高度的增加而迅速地增加。在其他条件都相同时，建筑所承受的风荷载在建筑物底部引起的倾覆力矩随建筑物高度近似地成平方规律变化，而在顶部的侧向位移与其高度的四次方成正比。特别是地震作用，地震本身产生的侧向力就很大，再经由 4 次方放大，地震的破坏性将会更大。对于低层和多层建筑物设计只需考虑恒荷载和部分活荷载时，建筑物的柱、墙、楼梯或电梯等就自然能承受大部分水平力。所考虑的问题主要是抗剪问题。对于现代的钢架系统支撑设计，如无特殊承载需要，无需加大柱和梁的
3、尺寸，而通过增加板的厚度就可以实现。然而，对于高层建筑要解决很多问题，首先要解决的不仅仅是抗剪问题，还有抵抗力矩和抵抗变形问题。高层建筑中的柱、梁、墙及板等经常需要采用特殊的结构布置和特殊的材料，以抵抗相当高的侧向荷载以及过大的变形正如前面所说的，高层建筑上部承受更大的侧向力，而底部则承受更大的竖向荷载，因此高层建筑中每平方英尺建筑面积结构材料的用量要高于低层建筑。支撑重力荷载的竖向构件，如墙、柱及井筒，在沿建筑物整个高度方向上都应予以加强。用于抵抗竖向构件随着高度累计而产生的自重，同时侧向荷载的材料要求也更多。钢结构建筑和混凝土结构的建筑的一个最大的区别就是自重，对于钢筋混凝土建筑，随着建筑
4、物层数的增加，对材料的要求也随着增加。混凝土材料的质量增加而带来的建筑物自重增加，要比钢结构增加得多，而为抵抗风荷载的能力而增加的材料用量却不是那么多，因为混凝土自身的重量可以抵抗倾覆力矩。不过不利的一面是混凝土建筑自重的增加，将会加大抗震设计的难度。在地震荷载作用下，顶部质量的增加将会使侧向荷载剧增。混凝土自重除了在地震时不利外，还会加大地基上的压力，造成地基过大沉降。高层建筑设计的主要内容是抗侧向力方面的设计。无论对于混凝土结构设计，还是对于钢结构设计，下面这些基本的原则都有助于在不需要增加太多成本的前提下增强建筑物抵抗侧向荷载的能力。增加抗弯构件的有效宽度。由于当其他条件不变时能够直接减
5、小扭矩，并以宽度增量的三次幂形式减小变形，因此这一措施非常有效。但是必须保证加宽后的竖向承重构件非常有效地连接。在设计构件时，尽可能有效地使其加强相互作用力。例如，可以采用具有有效应力状态的弦杆和桁架体系；也可在墙的关键位置加置钢筋；以及最优化钢架的刚度比等措施。增加最有效的抗弯构件的截面。例如，增加较低层柱以及连接大梁的翼缘截面，将可直接减少侧向位移和增加抗弯能力，而不会加大上层楼面的质量，否则，地震问题将更加严重。通过设计使大部分竖向荷载，直接作用于主要的抗弯构件。这样通过预压主要的抗倾覆构件，可以使建筑物在倾覆拉力的作用下保持稳定。通过合理地放置实心墙体及在竖向构件中使用斜撑构件，可以有
6、效地抵抗每层的局部剪力。但仅仅通过竖向构件进行抗剪是不经济的，因为使柱及梁有足够的抗弯能力，比用墙或斜撑需要更多材料和施工工作量。每层应加设充足的水平隔板。这样就会使各种抗力构件更好地在一起工作，而不是单独工作。在中间转换层通过大型竖向和水平构件及重楼板形成大框架，或者采用深梁体系。应当注意的是，所有高层建筑的本质都是地面支撑的悬臂结构。如何合理地运用上面所提到的原则，就可以利用合理地布置墙体、核心筒、框架、筒式结构和其他竖向结构分体系，使建筑物取得足够的水平承载力和刚度。本文后面将对这些原理的应用做介绍。剪力墙结构在能够满足其他功能需求时，高层建筑中采用剪力墙可以经济地进行高层建筑的抗侧向荷
7、载设计。例如，住宅楼需要很多隔墙，如果这些隔墙都设计为实例的，那么他们可以起到剪力墙的作用，既能抵抗侧向荷载，又能承受竖向荷载。对于 20 层以上的建筑物，剪力墙极为常见。如果给与足够的宽度，剪力墙能够有效地抵抗 30-40 层甚至更多的侧向荷载。但是，剪力墙只能抵抗平行于墙平面的荷载（也就是说不能抵抗垂直于墙的荷载） 。因此有必要经常在两个相互垂直的方向设置剪力墙，或者在尽可能多的方向布置，以用来抵抗各个方向的侧向荷载。并且，墙体设计还应考虑扭转的问题。在设计过程中，两面或者更多的剪力墙会布置成 L 型或者槽形。实际上，四面内剪力墙可以被联结成矩形，以更有效地抵抗侧向荷载。如果所有外部剪力墙
8、都连接起来，整个建筑物就像是一个筒体，将会具有很强的抵抗水平荷载和抵抗扭矩的能力。通常混凝土就剪力墙都是实体的，并在有要求时开洞，而钢筋剪力墙常常是做成桁架式。这些桁架上可能布置成蛋单斜撑、X 斜撑及 K 斜撑。在侧向力作用下这些桁架的组合构件受到或拉或压力。从强度和变形控制角度来说，桁架有着很好的功效，并且管道可以在构件之间穿过。当然，钢桁架墙的斜向构件在墙体上要正确放置，以免妨碍开窗、循环以及管道穿墙。如上所述，电梯强、楼梯间及设备竖井都可以形成筒状体，常常用它们既抵抗竖向荷载又抵抗水平荷载。这些筒的横断面一般驶矩形或圆形，由于筒结构作用，筒状结构能够有效地进行各个方向上的抗弯和抗剪。不过
9、在这样的结构设计中存在的问题是，如何保证在门洞口和其他孔洞的强度。对于钢筋混凝土结构，通过使用特殊的钢筋配置在这些孔洞的周围。对于钢剪力墙，则要求在开洞处加强节点连接，以抵抗洞口变形。对于很多高层建筑，如果墙体和筒架进行合理地安排与连接，会起到很好的抵抗侧向荷载的作用。还要求由这些结构分体系提供的刚度在各个方向上应大体对称。框架结构在建筑物结构设计中，用于抵抗竖向和水平荷载的框架结构，常作为一个重要且标准的型式而被采用。它适用于低层、多层建筑物，亦可用于 70-100 层高的高层建筑物。同剪力墙结构相比，这种结构更适合在建筑物的内部或者外围的墙体上开设矩形孔洞。同时它还能充分利用建筑物内在任何
10、情况下都要采用的梁和柱的刚度，但当柱子与梁刚性连接时，通过框架受弯来抵抗水平和竖向荷载会使这些柱子的承载能力变得更大。通常情况下，框架结构的刚度不如剪力墙结构，因此对于高宽比较大的高层建筑可能会产生过多的挠度。但正由于这种柔性，使得混凝土框架结构通常被人们认为更具延展性，因此相比使用剪力墙结构设计的建筑，框架结构在地震时更不易发生毁灭性的灾难。例如，如果框架局部出现超应力时，延性将使结构作为一个整体，整体平动，但它绝不会塌陷，即使出现了一个比预期更大的外力作用在结构上。由于整体性的原因，框架结构也被认为是“最好的”高层抗震建筑。在另一方面，经过特殊设计的剪力墙结构在强地震时也可能不会坍塌。在使
11、用混凝土框架结构的情况下，还存在的一些分歧。的确，如果一个框架结构建筑的设计是按照常规的方式进行，如果不特别留意，结构就会产生很大的延展性，从而造成建筑不能够承受比荷载设计标准值大好几倍的地震作用效应。因此，有些人认为它可能没有拥有和钢刚架一样大的承受额外超载的能力。但现代研究和经验已经表明，当有足够的箍筋和窗框加固被设计到框架时，混凝土框架结构建筑可被设计为具有延展能力的形式。新建筑规范对所谓延性混凝土框架有专门的规定。然而，这些规范往往要求在框架的某处增设过多的钢筋，从而造成施工困难。尽管如此，混凝土框架还是可以设计出既实用又经济的特性。当然，也有可以将刚性框架结构与剪力墙系统结合在一建筑
12、物中，例如，可以用混合结构形式设计这样一幢建筑，可在一个方向上使用框架结构，而在另一个方向上使用剪力墙结构等。结论以上所述的各种高层建筑常用的结构形式。在设计过程中，应根据经济实用的原则尽可能地选择合理的结构形式。High-Rise BuildingsIt is difficult to define a high-rise building . One may say that a low-rise building ranges from 1 to 2 stories . A medium-rise building probably ranges between 3 or 4 stori
13、es up to 10 or 20 stories or more . Although the basic principles of vertical and horizontal subsystem design remain the same for low, medium , or high-rise buildings , when a building gets high the vertical subsystems become a controlling problem for two reasons . Higher vertical loads will require
14、 larger columns , walls , and shafts . But , more significantly , the overturning moment and the shear deflections produced by lateral forces are much larger and must be carefully provided for .The vertical subsystems in a high-rise building transmit accumulated gravity load from story to story , th
15、us requiring larger column or wall sections to support such loading . In addition these same vertical subsystems must transmit lateral loads , such as wind or seismic loads , to the foundations. However , in contrast to vertical load , lateral load effects on buildings are not linear and increase ra
16、pidly with increase in height . For example under wind load , the overturning moment at the base of buildings varies approximately as the square of a buildings may vary as the fourth power of buildings height , other things being equal. Earthquake produces an even more pronounced effect.When the str
17、ucture for a low-or medium-rise building is designed for dead and live load , it is almost an inherent property that the columns , walls , and stair or elevator shafts can carry most of the horizontal forces . The problem is primarily one of shear resistance . Moderate addition bracing for rigid fra
18、mes in“short”buildings can easily be provided by filling certain panels ( or even all panels ) without increasing the sizes of the columns and girders otherwise required for vertical loads.Unfortunately , this is not is for high-rise buildings because the problem is primarily resistance to moment an
19、d deflection rather than shear alone . Special structural arrangements will often have to be made and additional structural material is always required for the columns , girders , walls , and slabs in order to made a high-rise buildings sufficiently resistant to much higher lateral deformations . As
20、 previously mentioned , the quantity of structural material required per square foot of floor of a high-rise buildings is in excess of that required for low-rise buildings . The vertical components carrying the gravity load , such as walls , columns , and shafts , will need to be strengthened over t
21、he full height of the buildings . But quantity of material required for resisting lateral forces is even more significant .With reinforced concrete , the quantity of material also increases as the number of stories increases . But here it should be noted that the increase in the weight of material a
22、dded for gravity load is much more sizable than steel , whereas for wind load the increase for lateral force resistance is not that much more since the weight of a concrete buildings helps to resist overturn . On the other hand , the problem of design for earthquake forces . Additional mass in the u
23、pper floors will give rise to a greater overall lateral force under the of seismic effects . In the case of either concrete or steel design , there are certain basic principles for providing additional resistance to lateral to lateral forces and deflections in high-rise buildings without too much sa
24、crifire in economy . Increase the effective width of the moment-resisting subsystems . This is very useful because increasing the width will cut down the overturn force directly and will reduce deflection by the third power of the width increase , other things remaining cinstant . However , this doe
25、s require that vertical components of the widened subsystem be suitably connected to actually gain this benefit.Design subsystems such that the components are made to interact in the most efficient manner . For example , use truss systems with chords and diagonals efficiently stressed , place reinfo
26、rcing for walls at critical locations , and optimize stiffness ratios for rigid frames . Increase the material in the most effective resisting components . For example , materials added in the lower floors to the flanges of columns and connecting girders will directly decrease the overall deflection
27、 and increase the moment resistance without contributing mass in the upper floors where the earthquake problem is aggravated . Arrange to have the greater part of vertical loads be carried directly on the primary moment-resisting components . This will help stabilize the buildings against tensile ov
28、erturning forces by precompressing the major overturn-resisting components . The local shear in each story can be best resisted by strategic placement if solid walls or the use of diagonal members in a vertical subsystem . Resisting these shears solely by vertical members in bending is usually less
29、economical , since achieving sufficient bending resistance in the columns and connecting girders will require more material and construction energy than using walls or diagonal members . Sufficient horizontal diaphragm action should be provided floor . This will help to bring the various resisting e
30、lements to work together instead of separately . Create mega-frames by joining large vertical and horizontal components such as two or more elevator shafts at multistory intervals with a heavy floor subsystems , or by use of very deep girder trusses .Remember that all high-rise buildings are essenti
31、ally vertical cantilevers which are supported at the ground . When the above principles are judiciously applied , structurally desirable schemes can be obtained by walls , cores , rigid frames, tubular construction , and other vertical subsystems to achieve horizontal strength and rigidity . Some of
32、 these applications will now be described in subsequent sections in the following . Shear-Wall SystemsWhen shear walls are compatible with other functional requirements , they can be economically utilized to resist lateral forces in high-rise buildings . For example , apartment buildings naturally r
33、equire many separation walls . When some of these are designed to be solid , they can act as shear walls to resist lateral forces and to carry the vertical load as well . For buildings up to some 20storise , the use of shear walls is common . If given sufficient length ,such walls can economically r
34、esist lateral forces up to 30 to 40 stories or more .However , shear walls can resist lateral load only the plane of the walls ( i.e.not in a diretion perpendicular to them ) . There fore ,it is always necessary to provide shear walls in two perpendicular directions can be at least in sufficient ori
35、entation so that lateral force in any direction can be resisted . In addition , that wall layout should reflect consideration of any torsional effect . In design progress , two or more shear walls can be connected to from L-shaped or channel-shaped subsystems . Indeed , internal shear walls can be c
36、onnected to from a rectangular shaft that will resist lateral forces very efficiently . If all external shear walls are continuously connected , then the whole buildings acts as tube , and connected , then the whole buildings acts as a tube , and is excellent Shear-Wall Seystems resisting lateral lo
37、ads and torsion . Whereas concrete shear walls are generally of solid type with openings when necessary , steel shear walls are usually made of trusses . These trusses can have single diagonals , “X”diagonals , or“K”arrangements . A trussed wall will have its members act essentially in direct tensio
38、n or compression under the action of view , and they offer some opportunity and deflection-limitation point of view , and they offer some opportunity for penetration between members . Of course , the inclined members of trusses must be suitable placed so as not to interfere with requirements for wio
39、ndows and for circulation service penetrations though these walls . As stated above , the walls of elevator , staircase ,and utility shafts form natural tubes and are commonly employed to resist both vertical and lateral forces . Since these shafts are normally rectangular or circular in cross-secti
40、on , they can offer an efficient means for resisting moments and shear in all directions due to tube structural action . But a problem in the design of these shafts is provided sufficient strength around door openings and other penetrations through these elements . For reinforced concrete constructi
41、on , special steel reinforcements are placed around such opening .In steel construction , heavier and more rigid connections are required to resist racking at the openings . In many high-rise buildings , a combination of walls and shafts can offer excellent resistance to lateral forces when they are
42、 suitably located ant connected to one another . It is also desirable that the stiffness offered these subsystems be more-or-less symmertrical in all directions .Rigid-Frame SystemsIn the design of architectural buildings , rigid-frame systems for resisting vertical and lateral loads have long been
43、accepted as an important and standard means for designing building . They are employed for low-and medium means for designing buildings . They are employed for low- and medium up to high-rise building perhaps 70 or 100 stories high . When compared to shear-wall systems , these rigid frames both with
44、in and at the outside of a buildings . They also make use of the stiffness in beams and columns that are required for the buildings in any case , but the columns are made stronger when rigidly connected to resist the lateral as well as vertical forces though frame bending . Frequently , rigid frames
45、 will not be as stiff as shear-wall construction , and therefore may produce excessive deflections for the more slender high-rise buildings designs . But because of this flexibility , they are often considered as being more ductile and thus less susceptible to catastrophic earthquake failure when co
46、mpared with ( some ) shear-wall designs . For example , if over stressing occurs at certain portions of a steel rigid frame ( i.e.,near the joint ) , ductility will allow the structure as a whole to deflect a little more , but it will by no means collapse even under a much larger force than expected
47、 on the structure . For this reason , rigid-frame construction is considered by some to be a “best”seismic-resisting type for high-rise steel buildings . On the other hand ,it is also unlikely that a well-designed share-wall system would collapse.In the case of concrete rigid frames ,there is a dive
48、rgence of opinion . It true that if a concrete rigid frame is designed in the conventional manner , without special care to produce higher ductility , it will not be able to withstand a catastrophic earthquake that can produce forces several times lerger than the code design earthquake forces . ther
49、efore , some believe that it may not have additional capacity possessed by steel rigid frames . But modern research and experience has indicated that concrete frames can be designed to be ductile , when sufficient stirrups and joinery reinforcement are designed in to the frame . Modern buildings codes have specifications for the so-called ductile concrete frames . However , at present , these codes often require excessive reinforcement at certain points in the frame so as to cause congestion and result in construction difficulties 。Even so , concrete frame design can be both effe
