Foundation Work of A Building
Every building consists of two basic components, the superstructure, and the sub-structure or foundations. The superstructure is usually that part of the building which is above the ground and which serves the purpose of the intended use. The substructure or foundation is the lower portion of the building, usually located below the ground level, which transmits the load of the superstructure to the subsoil. A foundation is therefore that part of the structure which is in direct contact with the ground to which the loads are transmitted.
Foundation have the following purposes. These are:
- To distribute the load of the structure over a large bearing area so as to bring intensity of loading with the safe bearing capacity of the soil lying underneath.
- To load the bearing surface at a uniform rate so as to prevent unequal settlement.
- To prevent the lateral movement of the supporting materials’
- To secure a level and firm bed for building operation.
- To increase the stability of the structure as a whole.
- To ensure safety against undermining and protecting against the soil movements.
- To provide even surface for the structure to rest etc.
A foundation is part of a structure that is in direct contact with the ground to which the loads are transmitted. Since the foundation is constructed below the floor finished level, it is included as one part of the substructure of the building. Foundations are normally placed below the ground level. The soil or rock surface on which a building rests is called the foundation bed
Isolated footing are footings which carry a load from a single column. Reinforcement is provided in the form of steel bars and is placed in both directions. Under normal conditions, square & rectangular footings are economical for supporting columns & wall.
A combined footing is usually used to support the column of unequal loads. In such case, the resultant of the applied loads would not coincide with the centroid of the footings and consequently the soil pressure would not be uniform. Combined foundation is an efficient foundation solution is when there are two interior columns which are so closed to each other that the two isolated footings zones in the soil areas would overlap.
Masonry is the building of structures from individual units, which are often laid in and bound together by mortar the term masonry can also refer to the units themselves. The common materials of masonry construction are brick, building stone such as marble, granite, limestone, cast stone concrete block, and many more. Masonry is generally a highly durable form of construction. However, the materials used, the quality of the mortar and workmanship, and the pattern in which the units are assembled can substantially affect the durability of the overall masonry construction.
These are the works that are executed by laying building units such as stone, brick, and HCB of specified dimensions by providing binding materials such as mortar. A person who constructs masonry is called a mason or bricklayer. Masonry is normally used for the construction of the foundation, walls, columns, and other similar structural components of buildings. Depending upon the type of building units used, the following types of masonry work are done which is listed in the table below.
|Sr.No||Type of Masonry Work|
|3||Hollow Concrete Blocks Masonry|
|4||Reinforced Brick Masonry|
Brick and concrete block are the most common types of masonry in use in industrialized nations and may be either weight-bearing. Concrete blocks, especially those with hollow cores, offer various possibilities in masonry construction. They generally provide great compressive strength, and are best suited to structures with light transverse loading when the cores remain unfilled. Filling some or all of the cores with concrete or concrete with steel reinforcement offers much greater tensile and lateral strength to structures
- The use of material such as bricks and stones can increase the thermal mass of a building.
- Masonry is a non-combustible product and can protect the building from fire.
- Masonry walls are more resistant to projectiles, such as debris from hurricanes or tornadoes.
- Extreme weather, under certain circumstances, can cause degradation of masonry due to expansion and contractions forces associated with freeze-thaw cycles.
- Masonry tends to be heavy and must be built upon a strong foundation, such as reinforced concrete, to avoid settling and cracking.
- Other than concrete, masonry construction does not lend itself well to mechanization, and requires more skilled labor than stick-faming.
- Masonry consists of loose components and has a low tolerance to oscillation as compared to other materials such as reinforced concrete, plastics, wood, or metals.
Masonry has high compressive strength under vertical loads but has low tensile strength (against twisting or stretching) unless reinforced. The tensile strength of masonry walls can be increased by thickening the wall, or by building masonry piers (vertical columns or ribs) at intervals. Where practical, steel reinforcements such as wind-posts can be added.
I got the opportunity to see masonry work above the plinth beam of the building. The masonry below the plinth beam was built of non-modular bricks and above the plinth beam also the non-modular bricks were used. Stone used for masonry work shall be hard and sound, free from vents, cracks, fishers, discoloration or other defects that will adversely affect strength or appearance. After construction masonry wall, the plinth beam was constructed directly over it. It gives an appearance of additional stability to the building and also the clearance from the ground level as shown in figure.
As fresh concrete is in the plastic state when it is placed for construction purposes so, it becomes necessary to provide some temporary structure to confine and support the concrete until it gains sufficient strength for self-supporting. This temporary structure is called formwork. Concrete formwork serves as a mold to produce concrete elements having a desired size and configuration.
It is usually erected for this purpose and then removed after the concrete has cured to a satisfactory strength. In some cases, concrete forms may be left in place to become part of the permanent structure. For satisfactory performance, formwork must be adequately strong and stiff to carry the loads produced by the concrete, the workers placing and finishing the concrete, and any equipment or materials supported by the forms.
In the site the form work material we use was plywood material which has a good surface finish. Plywood is used extensively for concrete forms and provides the following advantages. These are:
- It is economically in large panels.
- It is available in various thickness.
- It creates smooth, finished surfaces on concrete.
- It is easy to handle and convenient to work.
The general step up used to construct a formwork in the site is:
- Prepare the false works in the desired position and level.
- Preparing the form work in a desired shape based on the drawing or the size of the structure that is going to be cast. Painting its inner side with a releasing agent if needed.
- Nailing it with appropriate bracing element and false work.
The type of formwork that was utilized on our site was a combination of ply wood, bamboo and timber where necessary. The purpose of employing ply wood, bamboo and timber is to make sure that quality concrete with perfect alignment would results.
For horizontal structure like reinforced concrete slab the ply wood without being cut was placed. At the same time for the beams they use plywood form work for the soffit and timber or plywood for the sides.
For vertical reinforced concrete structures ply wood formwork with timber false work was used. As most of the elevation columns assume uniform size, the ply wood was cut in size and was produced in a manner it could be easily fixed and dismantled. The bracing was done from timber and nailed perfectly to confine the fresh concrete. Reinforced concrete slabs and beams formwork was supported and fixed on eucalyptus (timber) pops and props. Dismantling of the framework commenced after the allowable dates have elapsed since the day of the concrete casting.
Accordingly column and site frameworks will be dismantled after 16 hours elapsed from the concrete casting and the other soffit formworks should stay in position until the concrete gets cured. The dates of dismantling for the soffit formworks were shortened by the use of fast curing concrete admixtures. The use of these admixtures will allow them to move fast forward with the construction and immediate utilization of the formwork on other successive structures.
|Sr.No||Formwork types||Period of time|
|1||Vertical columns, walls and beams||24 hours|
|2||Soffit work to slab and beam||24-28 Days|
|3||Props to slab and beam||14 Days|
Most of the pads which have larger and smaller in size were made via plywood formworks. Those of pads with a smaller in size were made via together fixed timbers of locally available type. Such formworks was dismantled and directly fitted to their similar type pads.
A foundation column with similar cross-section and height was identified and their respective formworks were made ready, in a manner that they could be able to use them in rotation.
Same as explained in foundation columns. The only expectation here was the height of the columns. Since the height of the columns in some of the blocks is different than the other, the formworks preparations were consider this fact.
Together sawn timbers of locally available type were made ready for all internal and external surfaces of the grade Beam.