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# Shallow Foundations – Combined Footing and Strap Footing

The design of rigid rectangular combined footing consist in determining the ____________

a) Pressure distribution

b) Location of center of gravity of column

c) Shear force

d) Safe bearing pressure

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Answer: b

Explanation: The design of rigid rectangular footing consists in determining the location of center of gravity of the column loads and using length and width dimension such that centroid of footing and the center of gravity of columns loads coincide.

If the independent spread footing of two columns are connected by a beam, it is called ___________

a) Combined footing

b) Trapezoidal combined footing

c) Strap footing

d) Raft footing

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Answer: c

Explanation: In strap footing, two independent columns are supported by as trap or beam at the bottom.

Which of the following condition is true regarding the transfer of load from strap to soil, used in strap footing?

a) Transfer load to soil

b) Does not transfer load to soil

c) Partially transfer to load

d) None of the mentioned

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Answer: b

Explanation: The strap used does not remain in contact with soil, and thus does not transfer any pressure to the soil.

When the allowable soil is low or the building loads are heavy, the footing used is ___________

a) Raft footing

b) Strap footing

c) Trapezoidal combined footing

d) Rectangular combined footing

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Answer: a

Explanation: When the allowable soil pressure is low, or the building loads are heavy, the use of spread footings would cover more than one-half of the area and it may prove more economical to use mat or raft foundation.

If the resultant of the soil pressure coincides with the resultant of the loads, the soil is pressure is assumed to be ____________

a) Non-uniformly

b) Uniformly distributed

c) Zero

d) None of the mentioned

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Answer: b

Explanation: If the resultant of the soil pressure coincides with the resultant of the loads and the center of gravity of the footing, the soil pressure is assumed to be uniformly distributed.

In designing rectangular combined footing _________ should be adopted as the design value.

a) Stress distribution

b) Compression index

c) Maximum bending moment

d) Safe bearing pressure

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Answer: c

Explanation: The maximum bending moment should be adopted as the design value for the reinforced concrete rectangular footing, which should also be checked for maximum shear and bond etc.

For a rectangular combined footing, x̅ is given as ___________

a) x̅ = L/2

b) L/3 < x̅ < L/2

c) x̅ = L/3

d) None of the mentioned

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Answer: a

Explanation: For a rectangular combined footing, x̅ = L/2 and for a trapezoidal combined footing solutions lies between the limits L/3 < x̅ < L/2.

Generally combined footing is assumed to rest on ___________

a) Cohesive soil

b) Homogeneous soil

c) Cohesion-less soil

d) Non homogeneous soil

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Answer: b

Explanation: It is assumed that the combined footings are rigid and rests on a homogeneous soil, so as to give rise to a linear stress distribution on the bottom of the footing.

The design procedure of strap footing is essentially that of _____________

a) Direct method

b) Trial and error method

c) Graphical method

d) None of the mentioned

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Answer: b

Explanation: The designing of strap or cantilever footing is based on trial and error method, it begins with a trial value of e so that the length L1 is known. The calculations are repeated with another value of e till values of the reactions R1 and R2 calculated by both the procedure, coincide.

What will be the shape of footing if a=0, is substituted in the pressure intensity equation “q2 = a. qs”?

a) Rectangular

b) Triangular

c) Trapezoidal

d) Circular

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Answer: b

Explanation: In the pressure intensity equation q2 = a. qs, if a= 0 we have a triangle with x̅ = L/3.