Structural Design Guide for RCC Building

RCC stands for reinforced cement concrete. RCC building is the main structural member of the building like slabs, viz, beams, columns, and foundations which are made of reinforced cement concrete.

Design of the Foundation

Foundation design is a structural component of RCC.

1) Design of Foundation

Column footing is the most common type of foundation which is used. The strength of the foundation directly determines the structural stability of the building.

Foundation transfers loads of the building to the ground. The design of the foundation depends on the soil, structure, and load. Foundation has two types. One is the shallow foundation and another one is the deep foundation.

2) Calculation of loads in Foundation Design

It is very important for the structural design.

Types of loads

1. Self-weight of the column x Number of floors
2. Self-weight of beams per running meter
3. A load of walls per running meter
4. Total Load of the slab (Dead load + Live load + Self-weight)

For columns

The self-weight of Concrete is around 2400 kg per cubic meter. The self-weight of Steel is around 8000 kg per cubic meter. Let’s assume that a large column size of 230 mm x 600 mm with 1% steel and 3 meters standard height, the self weight of the column is around 1000 kg per floor, which is equivalent to 10 kN. So, the self-weight of the column to be between 10 to 15 kN per floor.

For beams

The same calculation is applicable also for this.

3) Types of Foundations

a) Deep foundation

b) Shallow foundation

1. Footings
2. Mats
3. Combined footings
4. Strap footings
5. Strip footings

Design of beams

Beams have two types.

1) Doubly reinforced beam

It is the most used product in RCC construction.

Process of design

Step 1: Users have to determine the limiting moment of resistance for the given c/s(Mulim) using the equation for singly reinforced beam
Mulim = 0.87.fy.Ast1.d [1 – 0.42Xumax]

Step 2: If factored moment Mu > Mulim, then a doubly reinforced beam is required to be designed for an additional moment.
Mu – Mulim = fsc.Asc (d – d’)

Step 3: An additional area of tension steel Ast2
Ast2 =Asc.fsc/0.87fy

Step 4: Total tension-steel Ast,
Ast = Ast1 + Ast2

2) Singly reinforced beam

This type of beam is reinforced only in the tension zone. So it is known as a singly reinforced beam. The bending moment and the tension are carried by the reinforcement. Concrete carries the compression.

steel reinforcement is used on the tensile side of the concrete. singly reinforced beams reinforced on the tensile face. It is good in compression and also in tension.

Design of columns

1) Design of RCC column

It is an important element in a structure. The column is designed to resist the axial and lateral forces. It also transfers the load to the footings in the ground. The axial load carrying capacity of a column is deduced from the formula
Pu =0.4 fck Ac + 0.67 fy Asc

Based on shape

1. Rectangle
2. Square
3. Circular
4. Polygon

Based on the slenderness ratio

1. Short RCC column, =< 10
2. Long RCC column, > 10
3. Short Steel column, =<50
4. Intermediate Steel column >50 & <200
5. Long Steel column >200

Based on the pattern of lateral reinforcement

1. Tied RCC columns
2. Spiral RCC columns

2) Rules for column layout

There are three types of rules.

Size of the Columns: The minimum size of an RCC column should be 9” x 12” (225mm x 300mm) with 4 bars of 12 MM Fe415 Steel.

Distance between Columns: In a beam of 5 meters in length, the secondary spans are 4 meters, wall loads of up to 8 kN per running meter,
Top Steel – 2 bars of 12 MM
Crank bars – 2 bars of 12 MM, cranked at an angle of 45° at a distance of L/4 at both ends of a simply supported beam.
Bottom Steel – 3 bars of 12 MM.

Alignment of columns: To place columns depend on the plan. The column is placed to reduce the point loads and complications. It also reduces the cost of the construction process and time. It does not require much steel and concrete depth to ensure safety.

Wrap up

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Structural Design Guide for RCC Building