Ultimate capacity of composite columns

During the past decade the rate of high-rise buildingconstruction In major cities has increased rapidly. The columnloads in these building necessitate the use of reinforced concretecolumns having large dimensions, so that the areas of lowerflooring are sometimes totaly covered by the great dimensions ofthe columns. In some medium-rise buildings, to achieve a largespacing between columns, use has been made of steel floor beamsto minimize overall floor depths. However column loads remaingreat and require a large reinforced concrete dimensions withhigh percentage of reinforcement. These columns are subjectednot only to heavy axial loads but also to moments according tothe location of these columns. In some columns such as those Intire buildings where beams and girder frame in two perpendicularplanes they transfer their end moments into the columns. Similarsituations can occur in interior columns particularly in irregularcolumn layouts and variety of other structures. By denoting thedirections of the two principal axes of the column cross-section,if the bending is laid in an inclined plan so that it occurs aboutaxis subtending an angle with the major or minor axis of thecolumn cross-section, it will result in a biaxial bending momentabout the two principal axes. To resist the above combinationof loads and moments, an array of longitudinal bars should beplaced furthest from the column cent er, which will results in alarge column with high percentage of reinforcement.