The column is a vertical structural member. It transmits the load from the ceiling/roof slab and beam, including its self-weight to the foundation. Columns may be subjected to a pure compressive load or a combination of compressive load and bending moment. Different types of Columns may be constructed of stone or brick masonry, Timber, Reinforcement Cement Concrete (R.C.C.) or Structural steel sections. R.C.C. columns are the most widely used nowadays.
definitions
effective length
The effective length of a column is not necessarily its actual or proper length. It depends upon the conditions of the end supports of the column.
column failure
It depends on the Effective length of the column compared to its cross-section.
types of columns
Types of columns based on the Effective Length, columns are classified as follows
- Long column or Slender
- Short column
- Intermediate column
long column or slender
If the ratio of the effective length to the least dimension of the column (or diameter of the column of circular cross-section) is ≥ 12, the column is known as a Long column or slender. Slender means narrow in width.
In a long column, the ultimate load is governed by the compressing and bending strengths of the materials of the column and the dimensions of the cross-section. In addition, the ultimate load is also influenced by slenderness. Thus, for long columns, failure loads are characterized by buckling or instability.
short column
If the ratio of the effective length to the least lateral dimension is ≤ 12, the column is known as the Short column. in a short column.
The ultimate load is governed only by the compressive strength of the material of the column and the dimensions of the cross-section. For the short column, the failure load is characterized by yielding.
intermediate column
A column with a length that is between the short and long columns is called an intermediate column. Intermediate columns fail by both yielding and buckling.
types of columns
Types of columns based on shape, materials used
r.C.C. Columns
If the effective length of a compression member is equal to or less than thrice the least lateral dimension, the member is made of plain cement concrete. If the effective length is more than thrice the lateral dimension, the member should be of R.C.C.
R.C.C. columns are reinforced with vertical longitudinal steel bars ( vertical main reinforcement steel bars ) tied by lateral steel bars, which act as lateral ties. Lateral ties are also known as Stirrups.
stirrups
Stirrups are tying the main bars so that the main bars should not buckle outward under load. Thus, lateral ties provide lateral to the column. Also, these ties keep the main bar in position without getting dislocated during concreting and compaction.
In the R.C.C. columns, longitudinal bars take the main load. Stirrups prevent the buckling of longitudinal bars and keep them in position with respect to each other.
the load carrying capacity of r.C.C. column
If the percentage of steel used is large in a column, the concrete fails first.
If the percentage of steel used is less, the steel will reach its yield strength prior to concrete. The column will not fail because it can take more loads at this stage. Thus, the strength of the column is fully utilized.
spirally reinforced column
Sometimes, for the circular column, the lateral ties are made in the form of a continuous spiral, It is called a spirally reinforced column.
pitch
Pitch should not be more than 1/6 diameter of the column.
precautions to be observed in the column construction
process of construction
Construction of concrete columns ( i.e., concreting, compacting and curing ) is similar to the construction of any R.C.C. works such as beams, etc.
the vertical height of the concrete
The vertical height of concrete placed in one layer should not exceed one metre in height.
columns for more than one storey
Concreting of columns for more than one storey is to be carried out very accurately. Central lines of columns must be accurately kept one above the other for columns placed on different floors. Otherwise, eccentricity in loading will result.
load of the column of the top storey
The loads on the top storey are relatively lesser. Hence, the cross-section of the column designed for the top storey should be relatively less.
uses of R.C.C. columns
R.C.C. columns are used in multi-storey buildings and heavily loaded structures.
steel columns or stanchions
Steel columns are also known as stanchions. These are used in industrial structures to support beams and trusses.
The steel column is a vertical compression member. It supports the floors or girders in a building. Girder is the main load-carrying member to which floor beams or joints are connected. Joists are beam members, which are used to carry floors and roofs of buildings flight loads supported on long columns.
standards structural steel sections
Structural steel is a factory made in several forms called rolled steel sections, standard steel sections, namely, I-Section, channel section, equal angle section, tee section, z section, round section and tubular section are used for light loads.
The shape of the cross-section of the steel section and the section area should be designed carefully to avoid buckling.
The important property required for a compression member is a high value of the moment of inertia. The moment of inertia of a body about any axis refers to the internal resistance of the body to rotation about that axis.
built-up column sections
When the loads on the column are heavy built-up column sections are used.
When two or three steel sections of rolled sheets and cover plates are connected to form a column, it is known as a built-up column or box column. Cover plates (or Additional plates) are properly welded with the main sections.
Shows different types of columns in built-up section steel columns. The type of built-up section to be used depends on the types of structure and the end connections of the column.
uses
Built-up sections are used in steel skeleton constructions, roof trusses, etc.
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