Test: Footing & Rafts - 2 - Civil Engineering (CE) MCQ

Plain Concrete pier:

• The height of the pier shall not exceed 6 times the least lateral dimension.
• When the height exceeds 6 times the least lateral dimension, the buckling effect shall be taken into account, but in no case shall the height exceed 12 times the least lateral dimension.
• The minimum horizontal dimension of the pier shall be 2 feet and should not less than 1/12 times its height.

Concept:
The area of footing (Af) is given by

Calculation:
Given:
Load = 330 kN, Self weight = 10% of Given Load = 0.1 × 330 = 33 kN
Total Load = 330 + 33 = 363 kN
Safe bearing capacity = 150 kN/m²

Explanation:
(i) For an isolated foundation on clayey soil, max allowable settlement is 75 mm as per IS 1904.For sands & hard clay it is only 50 mm.
(ii) For rafts founded on sands & hard clay it is limited to 75 mm whereas for soft clays it is allowed upto 100 mm.
Additional Information
For Differential Settlement:
(i) In Sand ⇒ 25 mm
(ii) In Clay ⇒ 40 mm

Strip footing: 
A strip footing is another type of spread footing which is provided for a load-bearing wall. The length of strip footing is considerably greater than its width. A strip footing is also known as continuous footing.
Mat or Raft foundation: 
It is a large slab supporting a number of columns and walls under an entire structure or a large part of the structure. It is used to cover the foundation of the whole building area.
Pile foundation: 
A pile is basically a long cylinder of a strong material such as concrete that is pushed into the ground to act as steady support for structures built on top of it. It is also called a deep foundation. Depth of the pile is very much greater than that of its lateral dimension.
Confusion Point:
For pile foundation ⇒ Depth >>>>> Width
For strip footing ⇒ Length >> Width
∴ Strip Footing is the correct answer.

For weight 'W', stress (load per unit area) (σ) is given by = W/a²
Critical section for punching shear occurs at d/2 from the face of the column.
∴ Punching shear resistance (Force) is given by:

∴ Punching shear stress per unit area is given by: 
From the given data, punching shear resistance is denoted by q