# Design of Steel Structures Questions and Answers – Determination of Earthquake Loads

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This set of Design of Steel Structures Multiple Choice Questions & Answers (MCQs) focuses on “Determination of Earthquake Loads”.

1. Which IS Code is used for designing a structure considering earthquake loads?
a) IS 800
b) IS 875
c) IS 1893
d) IS 456

Explanation: IS 1893(Part 1) is used for designing a structure considering earthquake loads. For all other loads like dead load, wind load, IS 875 is used for design.

a) 1.5
b) 1.3
c) 1.2
d) 1.7

Explanation: In plastic design of steel structures, load factor is 1.7 when combination of dead load and earthquake load is considered i.e. 1.7(DL + EL) or 1.7(DL – EL).

a) 1.5
b) 1.3
c) 1.2
d) 1.7

Explanation: In plastic design of steel structures, load factor is 1.3 when combination of dead load, imposed load and earthquake load is considered i.e. 1.3(DL +/- IL +/- EL ).

a) tension only
b) compression only
c) both tension and compression
d) bending moment

Explanation: Earthquake are cyclic and induce reversal of stresses. Hence as per seismic philosophy, axially loaded members have to resist both tension and compression.

5. For earthquake loads, beams are designed to resist ________________
a) tension only
b) positive and negative bending moments
c) compression only
d) torsion

Explanation: Beams are designed to resist positive and negative bending moments at the same section for earthquake loads.

6. Structures are designed for seismic forces which is ____ than expected seismic force.
a) lesser
b) greater
c) equal to
d) seismic forces are not considered

Explanation: Structures are designed for seismic forces which is less than expected seismic force under strong earthquakes, if the structures were to remain linearly elastic.

7. Which of the following factors does not influence earthquake resistance design?
a) geographical location of structure
b) wind of location
c) site soil
d) strength of structure

Explanation: The factors which influence earthquake resistance design are : (i) geographical location of structure, (ii) site soil and foundation condition, (iii) importance of structure, (iv) dynamic characteristics of structure such as strength, stiffness, ductility and energy dissipation factor.

8. Structures should be designed such that ___________
a) Minor and frequent earthquakes can collapse the structure
b) Moderate earthquakes can cause damage to the structure
c) Major earthquakes should not cause any damage to the structure and the structure should be functional
d) Minor earthquake should not cause any damage to the structure and the structure should be functional

Explanation: As per IS 1893, the following seismic philosophy is adopted
(i) Minor and frequent earthquakes should not cause any damage to the structure
(ii) Moderate earthquake should not cause significant structural damage but could have some non structural damage(the structure should become operational once the damage is repaired)
(iii) Major and infrequent earthquake should not cause collapse( structure will be dysfunctional for further use, but will stand so that people can be evacuated and property can be recovered).

9. Which of the following assumption is correct for earthquake design resistant structure?
a) Earthquake will not occur simultaneously with wind
b) Earthquake will occur simultaneously with maximum flood
c) Earthquake will occur simultaneously with maximum sea waves
d) Earthquake will occur simultaneously with wind

Explanation: As per IS 1893, it is assumed that earthquake is not likely to occur simultaneously with wind or maximum flood or maximum sea waves.

10. Which analysis is used to obtain design seismic force?
a) Elastic Analysis
b) Plastic Analysis
c) Dynamic Analysis
d) Both elastic and plastic analysis

Explanation: Dynamic analysis is used to obtain design seismic force, and its distribution to different level along the height of the building and to various lateral load resisting members.

11. Which of the following relation is correct for design horizontal seismic coefficient?
a) A = ZISa*2Rg
b) A = ZISa/2Rg
c) A = ZISa-2Rg
d) A = ZISa+2Rg

Explanation: Design horizontal seismic coefficient is given by A = ZISa/2Rg, where Z is zone factor, R is response reduction factor, I is importance factor, Sa/g is average response acceleration coefficient.

12. What is structural response factor?
a) factor denoting the acceleration response spectrum of the structure subjected to earthquake ground vibrations
b) factor by which the actual base shear force is reduced
c) factor to obtain the design spectrum
d) factor used to obtain the design seismic force

Explanation: Structural response factor (Sa/g) is the factor denoting the acceleration response spectrum of the structure subjected to earthquake ground vibrations. It depends on natural period of vibration and damping of the structure. Response Reduction Factor(R) is the factor by which the actual base shear force is reduced. Zone Factor(Z) is factor to obtain the design spectrum. Importance Factor (I) is the factor used to obtain the design seismic force.

13. Wind pressure acting normal to individual is element or claddity unit is _________
a) F = [ (Cpe – Cpi)A/pd].
b) F = [ (Cpe + Cpi)A/pd].
c) F = [ (Cpe – Cpi)Apd].
d) F = [ (Cpe – Cpi)/Apd].

Explanation: F = (Cpe – Cpi)A pd , where F=net wind force on element, Cpi= internal pressure coefficient, Cpe=external pressure coefficient, A=surface area of element, pd=design wind pressure.

14. Internal pressure coefficient in a building is positive if acting from ________ and external pressure coefficient in a building is positive if acting from ___________
a) outside to inside, inside to outside
b) inside to outside, outside to inside
c) outside to inside, outside to inside
d) inside to outside, inside to outside

Explanation: Internal pressure coefficient in a building is positive if acting from inside to outside and external pressure coefficient in a building is positive if acting from outside to inside. The pressure depends on degree of permeability of cladding and direction of wind.

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