Why Rectangular Column Shape preferred over Circular Column?
The most regularly used shapes for columns in building projects are rectangular shape, circular shape and square shape. In most of the projects, rectangular column shape is preferred over circular columns. Sometimes square columns are also preferred over circular columns. Seismic resistance point of view, circular column may be better than rectangular columns.
It is important for the young engineers to understand the practical reasons. This helps to have the right co-ordination at the right time and helps in avoiding abortive works during the scheme development stage. Deciding the shape of the column has as importance as deciding the size and orientation and position of columns and beams.
Reasons that decide the shape of a column
The shape of a column like any building, is decided based on many factors like architectural shape of the building, functional use of the building, structural requirement of the building and so on.?
Architectural Reason
Aesthetics is one of the main reasons that decides the shape of a column. For that matter, circular shape for a column is aesthetically pleasing and hence it is used many times. However, the usage is limited in colleges, verandas and institutional buildings. Indian Parliament building is an example where the shape of the building itself suits the column to be circular.
Difficulty and cost of Formworks
It is easy to do the formwork of a rectangular or square section than circle. Achieving circular shape that do not have corners and edges need more workmanship as well as better formwork materials. Many times, you may need to use new plywood or aluminium formwork. It is more difficult to achieve concrete finishing. Even plastering a curved surface to desirable quality is challenging than that of a plane surface. This will result in additional time and costs. Most medium scale projects are on tight budgets and clients will be more concerned about the cost increase aspects.
It is also more difficult to control the pressure of the concrete in circular formwork. Especially if the column heights are more, it will be challenging to ensure stability of the formwork against the concrete pressure. More quality control and formwork supporting arrangements will have to be adopted at site. The workmanship needed is more for ensuring all of these aspects and hence the cost will be much higher than that of a rectangular column construction.
Functional Requirement In many buildings like offices, columns are used as display wallsfor pictures and images and notice boards and signages. Rectangular surfaces provide plane surface where you can post notices and directives.
In basements used as parking areas too, the rectangular or square columns provides a plane surface for notices, warning boards and signages for the movement of traffic. You can see these in basements of shopping malls and other commercial establishments.
Structural Reasons
Though, for seismic point of view, circular columns are needed, sometimes we will have the need of more stiffness in one direction. Think of a slender building with less base width and a larger length. We may prefer to have more stiffness in the slender direction. If we adopt a circular column, say you need 450 dia. But then providing an equivalent area as a rectangle will be 200x800 which may give more stiffness if 800 is oriented towards the slender direction. This helps in reducing deflection and drift better than a circular column.
This helps in reducing deflection and drift better than a circular column. Another structural reason that decides the shape is the aspect ratios needed and the minimum member sizes needed for columns as per IS 456 and IS1893. This reason decides between square and rectangular shapes than circular though.