Concrete Foundation Work in Building Construction

Building construction is an engineering science which deals with technique of construction of buildings.

This is part one article of "Concrete foundation work in building construction", after read this part properly you can check out more about concrete foundation work in building construction from second part of above article,
Read part 02;- Concrete Foundation Work in Building Construction (part 02)

A building is define as an enclosure and covered by a roof.
buildings can be categorized in two.

1. public buildings

e.g. :- schools, hospitals, bus/ railway station‍ etc.

2. resisencial buildings

Every Structure (Buildings) has two Components.

1. Sub Structure (Foundation)
which is generally constructed below the ground level or below the D.P.C level.(damp proof course)

2. Super Structure
which is generally constructed above the D.P.C LEVEL.

Definition of Foundation

The foundation is the most important part of the structure. Foundation can bears the load of the structure and transmit the loads of the structure to the sub soil. The strength and stability of the structure depends on it’s foundation. If the foundation fails the super structure however strong it, may cannot stand like a stable structure.

The ground, which receives the building is known as a natural foundation. The expanded base which are constructed of concrete or masonry are called artificial foundation.

An artificial foundation may consist of...

1. A concrete bed only

2. One or more courses of stone work.(rubble/brick)

3. Footings (with reinforcements)

4. A concrete bed together with footing

Object of Foundation

1. To distribute the load of the structure over a sufficient area of bearing surface so as to prevent the subsoil from spreading and to avoid unequal settlement of the structure.

2. To prevent tilting and over turning of the structure and increasing it’s stability.

3. To provide a leveled base for the structure.

The requirement of the building regulations, the foundation shall be...

1. Constructed to sustain the dead an imposed loads to transmit these to the ground in such a way that the pressure on it will not cause settlement which would impair the stability of the building or adjoining structures.

2. Taken sufficiently deep to guard the building against damage by swelling or shrinking of the subsoil.

The loads applying on foundation are divided in four...

Live Load (Imposed Load)

It’s a moving load or a temporary load, which mentions the weight of the inhabitants of the building, the weight of the furniture and any stored materials that are called live load or imposed load.
In design stage of foundation, the live load on the structure is also very important to Design more economical and durable Structure for foundation.

Dead load

It is a permanent load of the structure. Means the weight of the structure it self.

For example:- the weight of the walls, floors, slabs, roofs, weight of fixed machinery and any other immovable loads are called dead loads.

Wind Load

The pressure of wind is called wind load.

The wind pressure has severe affect on tall buildings but has very little in the low height buildings. The height of the building is less than the twice the width of the building, where the wind pressure should be neglected.

The wind pressure may coming on buildings walls, roofs etc.

Snow load

In places which have a heavy snow falls, the roof have to bear the load of the snow in addition to the dead load, the live load and the wind load. For this purpose in design stage snow load may be counted.

Types of Foundation

Different type of foundations apply on the different situations. the followings are the different types of foundations used depending on the structure.

Foundation can be divided mainly as a Shallow Foundation and Deep Foundation (seems like a following figure.)

Foundation design approach

↘ Determined the foundation load to be supported.

↘ Evaluate the sub soil condition according to the testing program.(borehole report)

↘ Prepare the final soil profile, determined the layer suitability for shallow or deep foundation. if ground condition is unsuitable, then the soil treatment procedure to be adopted which means after removing the unsuitable soil up to the required level and then to be back filled and compacted using selected material such as suitable soil, sand or quarry dust.

* The depth of foundation can be calculated by using a Ranking’s formula

D = P/W (1 - sin theta/1+ sin ϴ)2

where,
D = depth of foundation

p = safe bearing capacity of soil

w = weight of soil (cubic meter)

ϴ = Angle of repose of soil

↘ Consider and prepare alternative design for shallow or deep foundation

↘ Prepare estimate for feasible, alternative foundations design including all associated sub structure.

↘ Select a optimum foundation alternative.

Shallow foundation

Shallow foundation is commonly accepted as foundation with founding level less than 3m from ground surface. In case surface loads or surface conditions could still affect the bearing capacity, the foundation which sits on it is called shallow foundation.

The different types of shallow foundation are,

↪ Strip footing
↪ Spread or isolated footing
↪ Combined footing Strap or cantilever footing
↪ Mat or raft Foundation.

Strip Foundation

Strip foundation is used to support a line of loads such as load-bearing walls.

These foundations are made by rubble, bricks and reinforcement concrete also.

Reinforcement concrete strip foundations used to support and transmit the loads from heavy walls. the effect of the walls on the relatively thin foundation is act as a point load and the result ground pressure will induce tension on the underside across the width of the strip. Tensile Reinforcement is required in the low face of the strip with distribution bars in the second layer running longitudernaly.

The continues strip serves as a level based on which the wall is built and is such width as its necessary to spread the load on the foundation to an area of sub soil capable of supporting the load with out induce settlement. typical steps footing and R.c.c. footing under a walls are shown in figures.

Pad Foundation

This is used to transmit the load and support the loads from piers and columns, where the sub soil is poor bearing capacity for some depth below the surface has as the case of filled up ground. It's often economically to use a foundation of a column or pad foundation.

Combined pad foundation

The foundation of adjustment columns are combined with common pad. When column is so closed it is combine with the base of and adjacent column to form a combined or balanced base foundation.

Raft Foundation

Raft foundation consist of a slab (mat) of R.C.C. under the whole building design to transits the load of the building to the sub soil below the raft. raft foundations are used for buildings on compressible soil with poor bearing capacity such as soft clays, filled materials etc.

The raft foundation consist of reinforce cement concrete slab or R.C.C. beams place over a entire area. The “T” beams are more suitable for column structure.