Details of Foundation in Construction?

A foundation alias ground sill is the low part or sub-structure of an architectural structure that is artificially constructed on the soil to transmit loads from the structure to the ground securely. Foundation of a structure is built up underneath the ground level with the purpose of making the lateral strength of the structure better. The solid ground on which the foundation is supported is known as the Foundation Bed.

On the basis of the condition and bearing ability of soil and nomenclature of structure, the foundation is categorized as shallow foundation and deep foundation.

If the depth of the foundation is under or similar to its width or if the foundation is built up at proper shallow depth, it is called shallow foundation. A shallow foundation delivers the load to a stratum found in a shallow depth. Shallow foundations are generally found in building up low rise structures.

If the depth of the foundation surpasses its width or if the foundation is developed at considerably large depth, it is call deep foundation. The deep foundation transmits the load to a wider depth under the ground surface. Deep foundation is intended for high rise or multi-storey structures.

1) Shallow Foundations
i. Spread footing or open trench foundations
ii. Grillage foundations
iii. Mat or Raft foundations
iv. Stepped foundations
v. Inverted arch foundations
vi. a) Wall Footing
vii. b) Reinforced cement concrete footing
viii. c) Combined footing
ix. d) Eccentrically loaded footing

Deep Foundations - i. Pile foundations, ii. Well foundations, iii. Caisson foundations

To erect a foundation, trenches are excavated thicker into the soil unless a solid stratum is attained. To make the base foundation, concrete is poured into this trench. These trenches are combined with reinforcement cage to raise the foundation stability.

The estimated steel rods which are provided outwards perform as the bones and should be attached with the substructure above. Once the foundation work is completed successfully, the structure of the building is started.

The construction of the foundation can be done with concrete, steel, stones, bricks etc. The material and the type of foundation selected for the desired structure depends on the design loads and the type of underlying soil.

The design of the foundation must incorporate different effects of construction on the environment. For example, the digging and piling works done for deep foundation may result in adverse disturbance to the nearby soil and structural foundation. These can sometimes cause the settlement issues of the nearby structure. The objective of developing of a foundation is to withstand the attack of injurious substances from outside.

The foundation for each structure is made by adhering to the following guidelines:-

1. The underlying soil beneath the foundation structure does not experience shear failure
2. The settlement should be occurred throughout the first service load or should have been within the limit
3. Acceptable bearing pressure should be described as the pressure the soil can resist devoid of any failure.

Objects of Foundation:

1. To allocate the load of structure on wider area to maintain the intensity of load under the safe bearing capacity of the underlying soil.
2. To allocate the load uniformly on the underlying soil to avoid any unequal settlement of foundation.
3. To arrange leveled and hard surface for the super-structure to be constructed over it.
4. To raise the strength of the structure completely against sliding, overturning or other distressing forces like wind, rain, earthquake etc.

For more information, go through the following article theconstructor.org

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Published By
Rajib Dey
www.constructioncost.co
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Guidelines to follow for acceptance criteria for concrete

As per IS 456 : 2000 (C1 15.1), it is known that 28 days compressive strength shall individually be the standard for approval and disapproval of concrete.

But as per IS 456 : 2000 (C1 16), there exist two criterion for acceptance of concrete that range from compressive strength and flexural strength.

Prior to arrange test results for acceptance criteria, it is necessary to examine validation i.e. whether the sample is proper or improper for acceptance criteria.

The test results should be as follow :-

Test results are average of three specimens.

Individual deviation should be under ± 15% of the average.

Suppose M25 grade of concrete is applied in the construction. Let strength of specimen for first one should be 28.5 MPa (Mega Pascal). For the second one, it should be at 26 mega pascal and for third one, it should be 29 mega pascal.

By summing up, we get the average as 27.83 MPa (mega pascal).

If the individual deviation is computed from the average for first specimen, it shall be 2.4%.

For second, it shall be -6.57%

For third, it shall be 4.20%

From the test result, it can be said that the specimens are legitimate for acceptance criteria as the deviation of individual sample does not surpass 15%.

To get more details, go through the following video tutorial.

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Published By
Rajib Dey
www.constructioncost.co

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Different types of clear cover in reinforcement concrete

This construction video tutorial provides brief instructions on how to arrange clear cover in different areas in proper quantities in reinforcement concrete. It is dependent on the exposure condition and fire resistance.

Clear Cover stands for the minimum distance among the surface of embedded reinforcement and the exterior surface of the concrete (ACI 130). The depth of clear cover is calculated with a cover meter.

Given below the details of clear cover :-

For water retaining structures – The clear cover should vary from 20 mm to 30 mm
For flat slab – The clear cover should be 20 mm
For slab – The clear cover will be 15 mm
For column – The clear cover should have been 40 mm
For strap beam – The clear cover should be 50 mm

For raft foundation at bottom – The clear cover should be 75 mm
For shear wall – The clear cover should be 25 mm
For footing – The clear cover should be 50 mm
For staircase – The clear cover should be 15 mm

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Published By
Rajib Dey
www.constructioncost.co

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Types of footings with diagrams

This is a nice video presentation from Parag Pal, the renowned civil engineer. In this video, Mr. Parag gives brief explanation about types of footings mostly utilized in construction. The types of footings range from isolated footings, mat footings, strap footings, combined footings. All the footings are demonstrated with their diagrams.

Footings are considered as the most vital parts in various foundations like bridges.

Isolated footings - Isolated footings are used in normal home, house constructions. When footing is arranged to provide support to a distinct column, it is known as “isolated footing”. It belongs to circular, square or rectangular slab having identical thickness.

Combined footings - When two or more columns in a straight line are passed on a single spread footing, it is known as a combined footing. It is generally utilized when the two column are very adjacent to each other so that their individual footings would coincide.

Strap footings - A strap footing is a constituent of the foundation of a building. It is one sort of combined footing that contains two or more column footings attached with a concrete beam. This type of beam is known as a strap beam.

Mat/Raft foundation or mat footings - A big, dense, generally reinforced concrete mat that delivers loads from various columns and walls, to the foundational rock or soil. It is called raft foundation.

For online demonstration, watch the following video.

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Published By
Rajib Dey
www.constructioncost.co

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Variation among pad foundation, strip foundation and raft foundation

Shallow foundation is generally described as foundation that contains founding level below 3m from ground surface. Alternatively, when the breadth of the lower most part of the foundation is more than the depth of the lower most part of the foundation from the uppermost of the soil, i.e. Ground Level then it is defined as a Shallow Foundation. It transmits building loads to the earth adjacent to the surface. Shallow foundations comprise of spread footing foundations, mat-slab foundations, slab-on-grade foundations, pad foundations, rubble trench foundations and earthbag foundations.

Pad foundation stands for the foundation that is specifically developed for retaining concentrated loads out of a single point load like structural columns. Pad foundations are specifically designed to provide support to individual or multiple columns, scattering the load to the ground underneath. They are usually square or rectangular in plan, the plan area is defined by the allowable bearing pressure of the soil. The shape in plan will be determined by the arrangement of the columns and the load will be transmitted into the soil.

The thickness of the slab should be adequate to make sure that distribution of the load is perfect. The top of the pad should have been sloping (i.e. the pad is denser in the centre as compared to it is at the edge). It provides a cost-effective solution, though there are construction issues which are associated with casting the slope.

Strip foundation is utilized to provide support to a line of loads like load-bearing walls. As for example, closely-placed columns deliver the imperfect application of pad foundation and strip foundation may be a good choice.

Raft foundation comprises of a concrete slab which expands over the entire loaded area in order that loads from whole structure are expanded over a broader area that results in minimizing of the stress of foundation soils. Besides, raft foundation is useful for resisting differential settlement.

Ref.: www.engineeringcivil.com

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Published By

Rajib Dey

www.constructioncost.co

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Some useful construction tips on concrete mix design

This construction video tutorial focuses on concrete mix design. In this video grades are taken as M 7.5, M10, M15, M20 and mix ratios for cement, sand and aggregate are taken as 1:4:8, 1:3:6, 1:2:4, 1:1.5:3. The amount of water is required for amalgamating concrete in 50 kg cement.

Concrete mix design refers to the method of choosing the appropriate components (cement, sand and coarse aggregates) as well as their relevant proportions with the purpose of developing concrete by maintaining specific minimum strength & durability.

Objective of mix design
To make sure that the optimal ratios of the constituent materials is maintained to satisfy the need of the structure.
To obtain the preferred minimum strength in the hardened stage.

To obtain the needed minimum strength in the hardened stage.
To obtain the preferred strength in the specified environment conditions
To form concrete as inexpensively as possible.

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Published By
Rajib Dey
www.constructioncost.co

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