【正文】 ct. When the structure for a lowor mediumrise 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 frames 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 highrise buildings because the problem is primarily resistance to moment and 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 highrise buildings sufficiently resistant to much higher lateral deformations . As previously mentioned , the quantity of structural material required per square foot of floor of a highrise buildings is in excess of that required for lowrise buildings . The vertical ponents carrying the gravity load , such as walls , columns , and shafts , will need to be strengthened over the 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 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 . 1. 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 benefit. 2. Design subsystems such that the ponents are made to interact in the most efficient manner . For example , use truss systems with chords and diagonals efficiently stressed , place reinforcing for walls at critical locations , and optimize stiffness ratios for rigid frames . 3. Increase the material in the most effective resisting ponents . For example , materials added in the lower floors to the flanges of columns and connecting girders will directly decrease the overall deflection and increase the moment resistance without contributing mass in the upper floors where the earthquake problem is aggravated . 4. Arrange to have the greater part of vertical loads be carried directly on the primary momentresisting ponents . This will help stabilize the buildings against tensile overturning forces by prepressing the major overturnresisting ponents . 5. 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 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 . 6. Sufficient horizontal diaphragm action should be provided floor . This will help to bring the various resisting elements to work together instead of separately . 7. Create megaframes by joining large vertical and horizontal ponents 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 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 . The vertical subsystems in a highrise building transmit accumulated gravity load from story to story , thus 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 rapidly 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 structure for a lowor mediumrise 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 frames in“short”buildings can easily be provided by filling certain panels ( or even all panels ) without increasing the sizes of the columns and g