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1、4.4 Reinforced Concrete Column,4.4.1 Types of Column,Columns are defined as members that carry loads chiefly in compression. Columns carry axial compressive loads bending moment compression forces dominate.,4.4.1 Types of Column,Usually columns carry bending moment as well, about one or both axes of
2、 the cross-section.,bending moment about y axis,Bending action may produce tensile force over a part of the cross-section.,Classification of Columns,Based on loading Axially loaded column Eccentrically loaded column Biaxially loaded columns,eccentrically ik5sentrikEli. 偏轴地,Biaxially loaded columns,A
3、xially loaded column,Classification of Columns,Axially loaded column,loads are assumed acting at the centroid of column section.,centroid 5sentrCid 质心,偏心受力,load acts at a distance e from the centroid of column section.,Eccentrically loaded column,Classification of Columns,The distance e could be alo
4、ng the x or y axis, causing moments either about the x axis or y axis.,moments about the y axis,moments about the x axis,Eccentrically loaded column,Classification of Columns,Biaxially loaded columns load is applied at any point on the column section, causing moments about both the x axis and y axis
5、 simultaneously.,Biaxially loaded columns,Classification of Columns,Based on length Short columns Long columns,Short columns columns failure is due to crushing of concrete yielding of steel bars Reach full load capacity upon failure,Long columns (slender columns)长柱 buckling effect 屈曲and slenderness
6、ratio长细比must be taken into consideration reducing the load capacity of the column relative to that of a short column.,在同等条件下，即截面相同，配筋相同，材料相同的条件下，长柱承载力低于短柱承载力,Classification of Columns,Based on lateral reinforcement Columns reinforced with longitudinal bars and lateral ties.普通箍筋柱,纵筋,箍筋：侧向约束纵筋、抗剪,Clas
7、sification of Columns,Based on lateral reinforcement Columns reinforced with longitudinal bars and continuous spirals.螺旋箍筋柱,Classification of Columns,Based on lateral reinforcement Composite compression members组合柱 reinforced longitudinally with structural steel shapes 型钢 structural steel pipe 钢管 str
8、uctural steel tubing 5tju:biN管形材料 with or without additional longitudinal bars with various types of lateral reinforcement,Reinforcement in columns 配筋形式,The main reinforcement in columns is longitudinal, parallel to the direction of the load Lateral reinforcement ： arranged in a square, rectangular,
9、 or circular pattern.,纵筋,箍筋：侧向约束纵筋、抗剪,内折角处！,Reinforcement in columns 配筋形式,Lateral reinforcement Ties individual relatively widely spaced Spirals continuous closely spaced Functions of lateral reinforcement hold the longitudinal bars in positions prevent longitudinal bars from buckling,Lateral reinfo
10、rcement, in the form of individual relatively widely spaced ties or a continuous closely spaced spirals, serves several functions.,max.80mm,Min. 80mm,ties,spiral,For one, such reinforcement is needed to hold the longitudinal bars in positions in the forms while the concrete is being placed. For this
11、 purpose, longitudinal and transverse steel are wired together to form cages, which are then moved into the forms and properly positioned before placing the concrete.,钢筋骨架,For another, transverse reinforcement is needed to prevent the highly stressed, slender longitudinal bars from buckling outward
12、by bursting the thin concrete cover.,4.2.2 Short Columns,Behavior of Axially Loaded Short Column When an axial load is applied to a reinforced concrete short column, the concrete can be considered to behave elastically up to a low stress of about 1/3 fc 当轴向应力小于1/3 fc时，短柱的压缩变形主要为弹性变形。,Two different t
13、ypes of failure occur in columns, depending on whether ties or spirals are used. tied column fails suddenly at the load Na spirally reinforced column continues to deflect,A tied column fails at the load Na concrete fails by crushing or shearing outward along inclined planes混凝土被压碎崩裂 longitudinal stee
14、l bars fail by buckling outward between ties箍筋之间的纵向钢筋压屈而向外凸出,shearing outward along inclined planes,spirally reinforced column when the same load Na is reached, longitudinal steel and the concrete within the core are prevented from moving outward by the spiral. The concrete in the outer shell spalls
15、 off confining action of the spiral starts to take effect if sizable spiral steel is provided, the load will ultimately fail the column by causing the spiral steel to yield.,Spirally reinforced column The axial strain when the column fails can be much larger than that at which the shell spalls off.,
16、The ultimate bearing capacity of a short column reinforced with longitudinal bars and lateral ties,If the load on the column is increased to reach its ultimate strength, concrete will reach the maximum strength steel will reach its yield strength,Detailing Requirements for Reinforcement,Material Strength ： Concrete strength has a pronounced effect on the strength capacity of a column. The high strength concrete C30-C40 or higher grade are generally used. 受压构件的承载力主要取决
