单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,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 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,Axially 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,M,N,c,N,t,e,0,=,M,/,N,c,N,c,e,0,=,M,/,N,t,N,t,转化为,N,c,e,0,load acts at a distance,e,from the centroid of column section.,Eccentrically,loaded column,Classification of Columns,The distance,e,could be along 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 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 f,ull load capacity upon failure,Long columns(slender columns),长柱,buckling effect,屈曲,and,slenderness 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，即截面一样，配筋一样，材料一样的条件下，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.一般箍筋柱,纵筋,箍筋：侧向约束纵筋、抗剪,b,h,Classification 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,structural 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,or circular pattern.,纵筋,箍筋：侧向约束纵筋、抗剪,内折角处！,b,h,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 reinforcement,in the form of,individual,relatively widely spaced,ties or,a,continuous,closely spaced,spirals,serves several functions.,max.8,0mm,Min.8,0mm,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 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 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 types 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 steel 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 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,.,Sp,irally reinforced column,The axial strain when the column fails can be much larger than that at which the shell spalls off.,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 str