This set of Design of Steel Structures Interview Questions and Answers focuses on “Determination of Wind Loads & Load Combinations”.

1. Which IS Code is used for design loads for buildings and structures for wind load?

a) IS 456

b) IS 875 Part 3

c) IS 500

d) IS 1280

View Answer

Explanation: For design loads for buildings and structures for wind load, IS 875-Part 3 given by Bureau of Indian Standards is used.

2. IS Code gives basic wind speed averaged over a short interval of ______

a) 10 seconds

b) 20 seconds

c) 5 seconds

d) 3 seconds

View Answer

Explanation: Basic wind speed is based on peak wind gust velocity averaged over a short interval of 3s and having return period of 50 years and corresponds to mean above ground level in open terrain.

3. Positive sign of pressure coefficient indicates ______________

a) pressure acting towards the surface

b) pressure acting away the surface

c) pressure acting above the surface

d) pressure acting below the surface

View Answer

Explanation: Positive sign of pressure coefficient indicates pressure acting towards the surface and negative sign of pressure coefficient indicates pressure acting away the surface.

4. Which of the following relation is correct for pressure coefficient?

V_{p} = Actual wind speed at any point on structure at height corresponding to V_{z} (design wind speed)

a) [1+(V_{p}/V_{z})^{2}].

b) [1+(V_{z}/V_{p})^{2}].

c) [1-(V_{z}/V_{p})^{2}].

d) [1-(V_{p}/V_{z})^{2}].

View Answer

Explanation: Pressure Coefficient is the ratio of difference between pressure acting at point on surface and static pressure of incident wind to the design wind pressure.

5. What is return period?

a) number of years, the reciprocal of which gives the probability of extreme wind exceeding given wind speed in any one year

b) number of years, the reciprocal of which gives the probability of extreme wind less than given wind speed in any one year

c) number of years, the reciprocal of which gives the probability of mild wind exceeding given wind speed in any one year

d) number of years, the reciprocal of which gives the probability of mild wind less than given wind speed in any one year

View Answer

Explanation: Wind load acting on structure varies from year to year based on wind speed and maximum that can be expected to occur at a given location only once in so many years. This period is called return period.

6. Wind Pressure at any height of structure does not depend on _______

a) velocity and density of air

b) angle of wind attack

c) topography of ground surface

d) material of structure

View Answer

Explanation: Wind Pressure at any height of structure depend on (i)velocity and density of air, (ii)height above ground level, (iii)shape and aspect ratio of building, (iv) topography of surrounding ground surface, (v)angle of wind attack, (vi)solidity ratio or openings in the structure.

7. Which of the following relation is correct for design wind speed (V_{z}) and basic wind speed (V_{b}) ?

a) V_{z} ∝ V_{b}^{2}

b) V_{z} ∝ 1/V_{b}^{2}

c) V_{z} ∝ V_{b}

d) V_{z} ∝ 1/V_{b}

View Answer

Explanation: V

_{z}= k

_{1}k

_{2}k

_{3}V

_{b}, where k

_{1}=probability factor(risk coefficient), k

_{2}=terrain, height and structure size factor, k

_{3}=topography factor.

8. Calculate design wind speed for a site in a city with basic wind speed of 50 m/s, risk coefficient =1, topography factor = 1, terrain is with closely spaced buildings and height of building (class A) = 15m.

a) 40 m/s

b) 48.5 m/s

c) 50 m/s

d) 52.5 m/s

View Answer

Explanation: V

_{b}= 50m/s, k

_{1}= 1, k

_{3}= 1,

for terrain with closely spaced buildings, height of building=15m, class A : k

_{2}=0.97 (from IS 875 Part 3)

V

_{z}= k

_{1}k

_{2}k

_{3}V

_{b}= 1×0.97x1x50 = 48.5 m/s.

9. Which of the following relation between design pressure, pz and design wind speed, Vz is correct?

a) p_{z} ∝ V_{z}^{2}

b) p_{z} ∝ 1/V_{z}^{2}

c) p_{z} ∝ V_{z}

d) p_{z} ∝ 1/V_{z}

View Answer

Explanation: p

_{z}= 0.6V

_{z}

^{2}, where p

_{z}is in N/m

^{2}and V

_{z}is in m/s. 0.6 factor depends on number of factors and mainly on atmospheric pressure and air temperature.

10. Calculate the design wind pressure if the basic wind speed is 44 m/s, risk coefficient is 1, topography factor is 1, terrain is with closely spaced buildings and height of building(class A) = 20m .

a) 1285 N/m^{2}

b) 1580 N/m^{2}

c) 1085 N/m^{2}

d) 1185 N/m^{2}

View Answer

Explanation: V

_{b}= 44m/s, k

_{1}= 1, k

_{3}= 1,

for terrain with closely spaced buildings, height of building=20m, class A: k

_{2}=1.01 (from IS 875 Part 3)

V

_{z}= k

_{1}k

_{2}k

_{3}V

_{b}= 1×1.01x1x44 = 44.44 m/s

p

_{z}= 0.6Vz2 = 0.6x(44.44)2 = 1184.95 N/m

^{2}.

11. What is the partial safety factor for combination of DL+LL for limit state of strength, where DL=Dead load, LL=imposed load?

a) 1.2

b) 1.0

c) 0.8

d) 1.5

View Answer

Explanation: For limit state of strength, the load combination is 1.5(DL+LL), for limit state of serviceability, the load combination is 1.0(DL+LL), where DL=Dead load, LL=imposed load.

12. Which of the following load combination is not possible?

a) Dead load + imposed load + wind load

b) Dead load + imposed load + earthquake load

c) Dead load + wind load + earthquake load

d) Dead load + imposed load

View Answer

Explanation: According to IS code, it is assumed that maximum wind load and earthquake load will not occur simultaneously on a structure. The following combination of loads with appropriate partial safety factors may be considered : (i)Dead load + imposed load, (ii) Dead load + imposed load + earthquake load or wind load, (iii) Dead load + wind load or earthquake load, (iv) Dead load + erection load.

13. What is the partial safety factor for dead load in combination of DL+LL+WL/EL for limit state of serviceability, where DL=Dead load, LL=imposed load , WL=wind load, EL=earthquake load ?

a) 1.0

b) 0.8

c) 1.5

d) 1.2

View Answer

Explanation: For limit state of strength, the load combination is 1.2(DL+LL+WL/EL), for limit state of serviceability, the load combination is 1.0DL+0.8LL+0.8WL/EL, where DL=Dead load, LL=imposed load, WL=wind load, EL=earthquake load.

14. What is the partial safety factor for dead load in combination of DL+ WL/EL for limit state of serviceability, where DL=Dead load, WL=wind load, EL=earthquake load ?

a) 1.0

b) 1.5

c) 1.2

d) 0.8

View Answer

Explanation: For limit state of serviceability, the load combination is 1.0(DL +WL/EL), for limit state of strength, the load combination is 1.5(DL +WL/EL), where DL=Dead load, WL=wind load, EL=earthquake load.

15. What is the partial safety factor for imposed load in combination of DL+LL+AL , where DL=Dead load, WL=wind load, AL=Accidental load ?

a) 1.0

b) 0.5

c) 0.4

d) 0.35

View Answer

Explanation: The load combination is 1.0DL+ 0.35LL+ 1.0AL, where DL=Dead load, WL=wind load, AL=Accidental load for limit state of strength.

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