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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Various types of loads acting on building structure

The types of external loads, operating on building and other structures, are categorized as the following :-

1. Static loads belong to the forces which are applied sluggishly and then turns out to be almost constant.

2. One instance is the weight, or dead load associated with a floor or roof system.
3. Dynamic loads fluctuate with time. They comprise of repeated and impact loads.
4. Repeated loads are forces which are used several times. These types of loads can make a difference in the magnitude, and occasionally also in the sense, of the internal forces. A good example is an off-balance motor.

5. Impact loads stand for forces through which energy is occupied in a short timespan by a structure or its components time. An instance is the falling of a heavy weight on a floor slab, or the shock wave emerged out an explosion striking the walls and roof of a building.
6. External forces are also categorized as distributed and concentrated.
7. Uniformly distributed loads belong to a distributed load that contains a constant value like 1kN/m. It’s magnitude stays uniform all through the length. Uniformly distributed load is generally denoted by W and is stated as intensity of udl over the beam, slab etc. The instance of this load is dead weight of a rolled-steel I beam.

8. Concentrated loads belong to forces containing such a small contact area that is omitted corresponding to the whole surface area of the supporting member. As for instance a beam supported on a girder can be taken, for all practical purposes, a concentrated load on the girder.
9. Another common category for external forces which are labeled as axial, eccentric, and torsional.
10. An axial load pertains to a force whose resultant goes over the centroid of a section under consideration and stands upright to the plane of the section.
11. An eccentric load stands for a force that stands upright to the plane of the section under consideration but not going through the centroid of the section, therefore bending the supporting member.

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Published By
Rajib Dey
www.constructioncost.co
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