【正文】 irders otherwise required for vertical loads. 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 added 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 upper 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 highrise buildings without too much sacrifire in economy . Increase the effective width of the momentresisting 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 does require that vertical ponents of the widened subsystem be suitably connected to actually gain this subsystems such that the pone nts are made to interact in the most efficient manner . Remember that all highrise buildings are essentially 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 these applications will now be described in subsequent sections in the following . ShearWall Systems When shear walls are patible with other functional requirements , they can be economically utilized to resist lateral forces in highrise buildings . For example , apartment buildings naturally require 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 mon . If given sufficient length ,such walls can economically resist lateral forces up to 30 to 40 stories or more . However , shear walls can resist lateral load only the plane of the walls ( 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 orientation 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 Lshaped or channelshaped subsystems . Indeed , internal shear walls can be connected 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 ShearWall Seystems resisting lateral loads 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 tension or pression under the action of view , and they offer some opportunity and deflectionlimitation point of view , and they offer some opportunity for peration between members . Of course , the inclined members of trusses must be suitable placed so as not to interfere with requirements for wiondows and for circulation service peratio ns though these walls . In many highrise buildings , a bination of walls and shafts can offer excellent resistance to lateral forces when they are suitably located ant connected to one another . It is also desirable that the stiffness offered these subsystems be moreorless symmertrical in all directions . RigidFrame Systems In the design of architectural buildings , rigidframe systems for resisting vertical and lateral loads have long been accepted as an important and standard means for designing building . They are employed for lowand medium means for designing buildings . They are employed for low and medium up to highrise building perhaps 70 or 100 stories high . When pared to shearwall systems , these rigid frames both within 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 will not be as stiff as shearwall construction , and therefore may produce excessive deflections for the more slender highrise buildings designs . But because of this flexibility , they are often considered as being more ductile and thus less susceptible to catastrophic earthquake failure when pared with ( some ) shearwall designs . For example , if over stressing occurs at certain portions of a steel rigid frame ( .,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 on the structure . For this reason , rigidframe construction is considered by some to be a “best”seismicresisting type for highrise steel buildings . On the other hand ,it is also unlikely that a welldesigned sharewall system would collapse. In the case of concrete rigid frames ,there is a divergence of opinion . It true