Content of this Article :
Definition of building construction,definition of building,classification of building,definition of foundation,objects of foundation,Causes of failure of foundations and precautions to prevent such failures
Definition of Building construction
Building Construction is an Engineering Science, which deals with the technique of construction of buildings.
Definition of building:
A building is defined as an enclosed space covered by a roof.
Classification of building
Buildings in general can be classified into two categories viz. Public Buildings and Resident al Buildings. Public buildings are those which are primarily meant for the use of the general public, such as an office, a school, a college, a hospital, a cinema house, etc , whereas a residential building is only meant either for a single individual or group of individuals, such as an ordinary dwelling house or a bungalow. As far as techniques of construction are concerned, for an engineer both are the same.
Definition of Foundation
Every structure has two component parts. One is called; foundation and the other super-structure. Foundation is that part of the structure which is generally constructed below the ground level. It is often confused that foundation is constructed to take up the load of the structure or to support it. but actually this is not the case. No doubt the structure rests over the foundation but it is not supported by the foundation. The foundation transmits the load of the structure to the sub-soil below it, never a larger area uniformly. The word foundation as applied to buildings is defined as the extended base of walls and pillars carried below the ground level, to distribute the load of the structure over a larger area of the-sub-soil.
The Foundation is the most important part of a structure. The strength and stability of the structure depends upon its foundation. If the foundation fails, the super-structure however strong it may be, cannot stand. Hence for a stable structure, a good foundation is essential.
Objects of Foundation
As stated above, the foundations are constructed to keep the structure in position. However the following are the objects of the foundation :
- To distribute the load of the structure over a larger area of substratum and prevent overloading.
- To prevent tilting and over-turning of the structure and increasing its stability.
- To prevent the lateral escape of the supporting material.
- To provide a leveled base for the super-structure.
- To prevent unequal settlement of the soil and super-structure by loading the sub-soil evenly.
Causes of failure of foundations and precautions to prevent such failures
Causes of failure of foundations
Unequal settlement of sub-soil.
All soils, except rock and muram, yield under the load of the structure. If this yielding is uniform and within a particular limit, it is harmless, but unequal yielding will cause cracks in the structure and ultimately cause the failure of the structure and the foundation.
Unequal settlement of masonry.
This is caused by shrinkage and compressibility of mortar joints and the poor quality material used in the foundation.
Withdrawal of sub-soil moisture below the foundations.
This occurs when the soil is wet. In dry weather when the moisture of the soil is evaporated, the soil becomes compressed and cracked and thereby causes the failure of the structure.
Lateral pressure on the super-structure.
When the structure is subjected to lateral pressure due to wind or the lateral thrust of arches or a sloping roof or wide cantilever projections, a tendency of tilting or overturning is developed, which causes eccentricity of the loads due to which foundations can fail.
Lateral escape of soft soil from underiie.alh the foundation.
When the building is situated near a deep cutting or a river or a nallah, the soil below the foundation may escape laterally and cause the settlement of the foundation. Similarly, if the depth of the foundation is small or the sub-soil below the foundation is of a sliding nature, it may slip away under the loads and cause the failure of the foundation.
Precautions to prevent such failure of foundation
- To prevent the unequal settlement of sub soil, a right type of foundation, based on the knowledge of soil conditions and all possible loads liable to com; on the structure, should be carefully designed and constructed. The intensity of load should always be kept below the safe bearing capacity of tie soil. The materials to be used for foundation should be strong and durable.
- The unequal settlement of masonry can be prevented by using very stiff mortar, raising the masonry uniformly and the wall should not be constructed more than I’5 m in a day.
- The sub-soil water during hot weather may dry up and cause shrinkage, This can be avoided by driving piles upto a hard stratum or such sites should be avoided.
- The lateral pressure on the super-structure can cause failure of foundation. This can be prevented by providing a sufficient base area below the walls and columns.
- The lateral escape of the supporting material can be prevented by confining to soil by driving Sheet Piles around the foundation.