Concrete frame construction is a construction method which comprises a network of columns and beams to transfer the loads coming onto the structure to the foundation successfully. Wholistically, it forms a structural skeleton for the building which is used to support other members such as Floors, Roof, Walls, and Claddings.
In this article, we study the types, major components, advantages and disadvantages of concrete framed construction.
Type of Framed Structure
1. Rigid Frame Structure
These frames are built at the site and may or may not be poured monolithically. They provide more stability and resist rotations effectively. The advantage of a rigid frame is that they feature positive and negative bending moments throughout the structure due to the interaction of walls, beams, and slabs.
2. Braced Frame Structure
This frame structure resists lateral forces by the bracing action of diagonal members used to resist the sideways forces. The structure is braced by inserting diagonal structural members into the rectangular areas of a structural frame. Braced structural frames are more efficient than the rigid structural frame.
Major Parts of Concrete Frame Construction
1. Columns in Framed Structure
Columns are an important structural member of a frame building. They are the vertical members which carry the loads from the beam and upper columns and transfer it to the footings.
The loads carried may be axial or eccentric. Design of columns is more important than the design of beams and slabs. This is because, if one beam fails, it'll be a local failure of one floor, but if one column fails, it can lead to the collapse of the whole structure.
2. Beams in Framed Structure
Beams are the horizontal load-bearing members of the framed structure. They carry the loads from slabs and also the direct loads of masonry walls and their self-weights.
The beams may be supported on the other beams or may be supported by columns forming an integral part of the frame. These are primarily the flexural members. They are classified into 2 types :
- Main Beams - Transmitting floor and secondary beam loads to the columns.
- Secondary Beams - Transmitting floor loads to the main beams.
3. Slab in Framed Structure
A slab is a flat horizontal place that is used for covering the building from the above and provide shelter for the inhabitants. These are the plate element and carry the loads primarily by flexure. They usually carry vertical loads.
Under the action of horizontal loads, due to a large moment of inertia, they can carry large wind and earthquake forces, and then transfer them to the beam.
4. Foundation in Framed Structure
The sole function of the foundation is to transmit the load coming from the above columns and beams to the solid ground.
5. Shear Walls in Framed Structure
These are important structural elements in high-rise buildings. Shear walls are actually very large columns because of which they appear like walls rather than columns. They take care of the horizontal loads like wind and earthquake loads.
Shear walls also carry vertical loads. It’s important to understand that they only work for horizontal loads in one direction, which is the axis of the long dimension of the wall.
6. Elevator Shaft in Framed Structure
The elevator shaft is a vertical concrete box in which the elevator is provided to move up and down. These shafts help in resisting horizontal loads and also carry the vertical loads.
Advantages of Framed Concrete Structure
- It is good in compression when compared to the other materials used for construction. Besides, the structure is good in tension as well.
- Its resistance to fire is better than steel so it is capable of resisting fire for a longer time.
- It has a long service life with low maintenance cost.
- In some structures like piers, dams, and footings, it is the most economical structural material.
- It can be cast to any shape required, making it the most economical structural material.
- It yields rigid members with minimum deflection.
- The yield strength of steel is about 15 times the compressive strength of structural concrete and well over 100 times its tensile strength.
- By using steel in concrete the cross-sectional dimension would get reduced.
- Less skilled labors are required for erection as compared to other structural systems.
Disadvantages of Framed Concrete Structure
- It needs meticulous mixing, casting and curing, all of which affect the final strength of the member.
- The cost of formwork used to cast concrete is relatively high.
- It has low compressive strength when compared to steel which leads to large sections of columns/beams in multistory buildings, cracks development in concrete due to shrinkage and the application of live loads is high.
- If concreting is not done properly, the steel starts corroding thereby losing strength and ultimately the life gets reduced. Also, the repairs are then very expensive and difficult.
Codes for Designing Framed Structure
- IS (Indian Standard) 456-2000
- ACI (American Concrete Institute) 318-89
- ICC (International Building Code) 2009
- NZS (New Zealand Standard) 3101
- Euro 2