In this article, we will be talking about structural components for the correct structure of DNA components that can be presented of a Reinforced concrete building
A Reinforced Concrete building is made up of elements that transfer the loads applied on it to the ground and maintain the structural integrity of the building.
For this article, we assume a 4 storied luxury building having a podium and a basement.
A structure can be majorly divided into 2 components which are Substructure and Superstructure
The structure which is below ground is generally called substructures of Building and the structure above ground is called superstructure of a Reinforced Concrete Building
Sub Structure of a Reinforced Concrete Building
Starting from the substructure first, we have is the Plain Cement Concrete, also termed as PCC
Plain Cement Concrete (PCC)
- It is a low strength mixture of cement, fine aggregates (usually sand) and coarse aggregates.
- The main purpose of PCC is to provide a firm, rigid, non-porous, impervious and levelled base for RCC footings, ground beams and Slab on grade.
After PCC, the foundation is laid which takes loads from above and transfers them to the ground below it.
- Various kinds of footings are used in accordance with loading, site conditions, soil properties and design.
- First, we have Isolated Footings, then comes Combined Footings which hold 2 or more than 2 columns, then comes to the Raft foundation or Mat footings and finally Strip Footing which in this case is provided to the basement wall.
Isolated or combined footings can be connected by Tie Beams if required by design.
- These tie beams run from column to column having reinforcement similar to floor beams.
- Structures also use Pile foundations with different numbers and arrangements of piles having a pile cap over them.
- Raft footings can also be combined by piles below it or thickening below columns if required by design.
Next, we will see the retaining wall or basement wall.
Retaining Wall or Basement Wall
- Retaining wall or Basement walls are provided to retain soil from one side and they may or may not have columns resting above them or embedded in them.
- The retaining wall or basement wall may have strip footing which may or may not be eccentric as per the property limits.
- Such walls are also used for water tanks below the ground.
Next, we are looking at columns below the ground also called a column neck as their length is shorter.
- Their columns are embedded in soil and require appropriate waterproofing over them.
- After that, we take a look at ground beams which run from column to column and may have secondary beams also. These beams also are protected by PCC and waterproofing.
- Check BBS for column
After ground beams come to Slab on Grade or SOG.
- As the name suggests SOG (Slab on Grade) is laid on the grade or ground after PCC or waterproofing.
- Generally, sab on grade is not connected to column beam framing and directly rests on the well-compacted ground below it.
Next, we are looking at the podium with a little decal of our channel.
- Podium is generally required for landscaping, internal vehicular movements like cars and bikes and even fire trucks in case of a fire. It may house ducts for ventilation to the basement.
Next, we will talk about pits, manholes and trenches for drainage purposes.
- These components may be cast in concrete, brickwork or may come as precast units, as per requirement. These elements also require PCC at the bottom and proper waterproofing.
- These elements support heavy machinery or types of equipment such as generators, water pumps, transformers and provide a firm base to them.
- Concrete pads can be reinforced or unreinforced as per design requirements and can be cast on-site or come in a precast unit with the equipment.
This ends our substructure and now we will see superstructure members.
Super Structure of a Reinforced Concrete Building
- First, we see columns that are vertical load-bearing members on which beams and slabs rest. Columns transfer the gravity loads and lateral loads from wind and earthquake.
- Columns can exist in various shapes and sizes according to architectural and design requirements.
- They can be T shaped, L shaped, Circular, Rectangular or Square shape.
Next, we discuss various types of walls present in the superstructure.
Types of Walls
First comes the Shear wall
- These walls are part of the lateral load resisting system which counter the wind and earthquake forces.
- Shear walls are placed at appropriate locations of the building by design and they start right from the foundation of the building.
- A combination of shear walls connected rigidly with each other is called a Core Wall.
- The core walls generally enclose elevators, staircase or utility services.
- Core walls are also part of the lateral load resisting system of a building.
- Lastly under the walls category comes Upstand walls which are reinforced concrete walls usually of lesser height and thickness and having one end free.
- Parapet Walls are generally present as parapet walls or around openings or on the ground where some amount of retention is required.
Next in Superstructure comes Floor beams
- Floor beams take the load from slabs and transfer it to columns, shear walls or core walls.
Beams are basically of 2 types.
- The first is Primary Beams which are directly connected to columns or shear walls
- The second type is Secondary Beams in a building Structure which are connected to primary beams and transfer loads from slab to primary beams.
- The beams which have one free end are called cantilever beams.
- The beams which run on the perimeter of the building are called spandrel beams.
- Slabs are the horizontal surface that takes the load on them and transfers it to the beams and columns.
- Slabs in the superstructure are also called suspended slabs as they are suspended in the air and not rested on the ground as in the case of Slab on grade which we discussed earlier.
There are various types of slabs based on the structural load transfer mechanism. Based on the design, the slab can be broadly categorized into 2 types first is a Framed Slab System and the second is a Flat Slab System.
Framed Slab System
- In framed type arrangement the slab rests on beams. These beams may be further divided into primary, secondary and tertiary beams.
- In this building, we also have a ramp that connects the Basement to the podium and can take vehicular traffic.
- The ramp is also a part of the slab system and is supported on beams and columns.
- The second category is the flat slab system in which the slab directly transfers loads to the column having dropped or without it.
- The drops above the columns prevent the punching of columns in the slab and provide stiffness above that area. If the thickness of slab alone is enough to resist the shear, the drops can be removed.
- The flat slab also can be accompanied by beams at required locations such as on the perimeter of the building and around the openings.
Last but not least comes stairs which can be cast at the site or can come in precast panels.
- Stairs Case can be of various types such as L shaped, U shapes, spiral, Curved as per requirement.
- The stairs can be enclosed in a core wall like in this case or rest on columns and beams as per design.
|Components of the Staircase
Domiriat, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
- I would also like to mention openings as a part of structural components as openings break the load path and extra care has to be taken while providing the size of openings and reinforcement around them.
- Openings are mainly governed by architectural or MEP requirements.