What Is Column?
• Mainly columns, struts, and pedestals are used as compression members in buildings, bridges, supporting systems of tanks, factories, and many more such structures.
• A column is defined as a vertical compression member who is mainly subjected to the effective length and axial loads of which exceeds three times its least lateral dimension.
• The compression member whose effective length is less than three times its least lateral dimension is called Pedestal
• The compression member who is inclined or horizontal and is subjected to axial loads is called Strut. Struts are used in trusses.
• The function of columns is to transfer the load of the structure vertically downwards to transfer it to a foundation. Apart from the wall performs the following functions also:
(a) It encloses building areas into different compartments and provides privacy.
(b) It provides safety from burglary and insects.
(c) It keeps the building warm in cools in summer and winter.
Also, read: What is CBR Test in Civil
Classification of Columns
A columns are classified based on different criteria such as:
• Shapes of Cross-Section
• Material of Construction
• Type of Loading
• Slenderness Ratio
• Type of Lateral Reinforcement
Shapes of Cross-Section
• T-Shape or L-Shape etc.
Material of Construction
• Timber Column
• Masonry Column
• R.C.C Column
• Steel Column
• Composite Column
Type of Loading
• Axially Loaded Column
• Eccentrically Loaded Column
• Long Column
• Short Column
• Intermediate Column
What Is Short Column? | Short Column
• When this ratio of effective length to the least lateral dimensions of this column is less than 12, then it is knowns a short column.
• When this ratio of effective length to the least radius of gyration is less than 45, then it is called a short column
• When the length of the column is less as compared to its c/s dimension, it is called the Short column.
• Short Column
• Le/r main < 50
• Le/d < 15
• Crushing Load: The load at which a short column fails by crushing is called a crushing load.
What Is Intermediate Column? | Intermediate Column
• Column is Intermediate
• 30d > L > 4d
• 100 > Le / r min > 30or Critical slenderness ratio.
What Is Long Column? | Long Column
• When this ratio of effective length to the least radius of gyration is greater than 45, then it is called a long column.
• A long column is subjected to a bending moment in addition to direct compressive stress.
• The load-carrying capacity of a long column is less than a short column.
• The load-carrying capacity of a long column depends upon slenderness ratio (slenderness ratio increases then the capacity of the column decreases)
• When the length of a column is more as compared to its c/s dimension, it is called a long column.
• Le/r min > 50
• Le. = Effective Length of Column
• r min = Minimum radius of gyration
Difference Between Short Column and Long Column
|Sr.No.||Long Column||Short Column|
|1||This column is considered to be long if the ratio of effective length of column to its least lateral dimension is greater than 12.||This column is considered to be short if the ratio of effective length to its least lateral dimension is less than or equal to 12.|
|2||The column, whose lateral dimension is very small when compared to its length (or height), is called as long column.||The column, whose lateral dimension is very large when compared to its length (or height), is called a short column.|
|It is generally fails by buckling.||It generally fails by crushing.|
|4||The slenderness ratio is greater than 45.||The slenderness ratio is less than 45.|
|5||As the height of column increases the load carrying capacity is less.||As the height of the column decreases the load-carrying capacity is more.|
|6||The Radius of gyration is less.||The radius of gyration is more.|
|7||Load carrying capacity is less.||Load-carrying capacity is more.|
|8||Long column is subjected to buckling stress||The short column is subjected to compressive stress.|
|9||Long and slender columns buckle easily.||The buckling tendency is very low.|
|10||The ratio of effective length of a long column to its least radius of gyration is greater than 40.||The ratio of the effective length of a short column to its least radius of gyration is less than or equal to 40.|
|11||The failure of the short column is by crushing. ||The column generally fails in buckling. |
Type of Lateral Reinforcement
• A column with Lateral Ties
• A column with Helical Ties
Failure Mode of Column
• A column can fail in one of three condition
• Compression failure of concrete or steel reinforcement
• Combination of compression and buckling failure
• Compression failure is likely to occur with columns that are short and stocky.
• Buckling is probable with a column which is long and slender
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