# Design of Steel Structures Mcqs

Q:

A) 0.4kN/m² | B) 0.2kN/m² |

C) 0.75kN/m² | D) 0.8kN/m² |

Answer & Explanation
Answer: A) 0.4kN/m²

Explanation: The live load for roof truss should not be less than 0.4kN/m². For roof slopes ≤ 10⁰ and access provided, the live load to be taken is 1.5kN/m² of plan area. For roof slopes > 10⁰ and access is not provided , the live load to be taken is 0.75kN/m² of plan area.

Explanation: The live load for roof truss should not be less than 0.4kN/m². For roof slopes ≤ 10⁰ and access provided, the live load to be taken is 1.5kN/m² of plan area. For roof slopes > 10⁰ and access is not provided , the live load to be taken is 0.75kN/m² of plan area.

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Q:

A) Dead load + crane load | B) Dead load + wind load |

C) Dead load + earthquake load | D) Dead load + live load + wind load |

Answer & Explanation
Answer: C) Dead load + earthquake load

Explanation: Earthquake loads are not significant for roof trusses because of the small self weights. The following load combinations can be considered : (i) Dead load + snow load, (ii) Dead load + partial/full live load, (iii) dead load + live load + internal positive air pressure, (iv) dead load + live load + internal suction air pressure, (v) dead load + live load + wind load.

Explanation: Earthquake loads are not significant for roof trusses because of the small self weights. The following load combinations can be considered : (i) Dead load + snow load, (ii) Dead load + partial/full live load, (iii) dead load + live load + internal positive air pressure, (iv) dead load + live load + internal suction air pressure, (v) dead load + live load + wind load.

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Q:

A) cost of trusses should be equal to twice the cost of purlins | B) cost of trusses should be equal to twice the cost of purlins minus cost of roof coverings |

C) cost of trusses should be equal to the cost of purlins plus cost of roof coverings | D) cost of trusses should be equal to twice the cost of purlins plus cost of roof coverings |

Answer & Explanation
Answer: D) cost of trusses should be equal to twice the cost of purlins plus cost of roof coverings

Explanation: For economic spacing of roof trusses, the cost of trusses should be equal to twice the cost of purlins plus cost of roof coverings. This equation is used for checking the spacing of trusses and not for design of trusses.

Explanation: For economic spacing of roof trusses, the cost of trusses should be equal to twice the cost of purlins plus cost of roof coverings. This equation is used for checking the spacing of trusses and not for design of trusses.

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Q:

A) cost of purlins only | B) cost of purlins and cost of roof covering |

C) dead loads | D) cost of roof covering and dead loads |

Answer & Explanation
Answer: B) cost of purlins and cost of roof covering

Explanation: The economic spacing of the truss is the spacing that makes the overall cost of trusses, purlins, roof coverings, columns, etc. the minimum. It depends upon the relative cost of trusses, purlins, roof coverings, spacing of columns, etc. If the spacing is large, the cost of these trusses per unit area decreases but the cost of purlin increases. But if the spacing of trusses is small, the cost of trusses per unit area increases. Roof coverings cost more if the spacing of trusses is large.

Explanation: The economic spacing of the truss is the spacing that makes the overall cost of trusses, purlins, roof coverings, columns, etc. the minimum. It depends upon the relative cost of trusses, purlins, roof coverings, spacing of columns, etc. If the spacing is large, the cost of these trusses per unit area decreases but the cost of purlin increases. But if the spacing of trusses is small, the cost of trusses per unit area increases. Roof coverings cost more if the spacing of trusses is large.

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Q:

A) 1 in 12 | B) 1 in 6 |

C) 1 in 10 | D) 1 in 18 |

Answer & Explanation
Answer: B) 1 in 6

Explanation: The pitch of truss depends upon the roofing material. The minimum recommended rise of trusses with galvanised iron sheets is 1 in 6 and with asbestos cement sheets is 1 in 12.

Explanation: The pitch of truss depends upon the roofing material. The minimum recommended rise of trusses with galvanised iron sheets is 1 in 6 and with asbestos cement sheets is 1 in 12.

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Q:

A) L/500 | B) L/700 |

C) L/600 | D) L/800 |

Answer & Explanation
Answer: A) L/500

Explanation: The vertical deflection of gantry girder where the cranes are manually operated should not exceed L/500, where L is the span of gantry girder. The maximum vertical deflection allowed for a gantry girder where the cranes are travelling overhead and operated electrically upto 500kN is L/750 and operated electrically over 500kN is L/1000. When gantry girders carry moving loads such as charging cars, the deflection should not exceed L/600.

Explanation: The vertical deflection of gantry girder where the cranes are manually operated should not exceed L/500, where L is the span of gantry girder. The maximum vertical deflection allowed for a gantry girder where the cranes are travelling overhead and operated electrically upto 500kN is L/750 and operated electrically over 500kN is L/1000. When gantry girders carry moving loads such as charging cars, the deflection should not exceed L/600.

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Q:

A) one-third distance at span | B) two-third distance at span |

C) end of span | D) centre of span |

Answer & Explanation
Answer: D) centre of span

Explanation: The bending moment considered in the design of gantry girder are the bending moment due to maximum wheel loads (with impact) and the bending moment due to dead load of the girder and rails. The bending moment due to dead loads is maximum at the centre of span.

Explanation: The bending moment considered in the design of gantry girder are the bending moment due to maximum wheel loads (with impact) and the bending moment due to dead load of the girder and rails. The bending moment due to dead loads is maximum at the centre of span.

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Q:

A) crane crab is farthest to gantry girder | B) crane crab is closest to gantry girder |

C) crane crab is not attached | D) crane crab is at mid span |

Answer & Explanation
Answer: B) crane crab is closest to gantry girder

Explanation: The maximum wheel load is obtained when crane crab is closest to gantry girder. The crab in such position on the crane girder gives maximum reaction on the gantry girder. The vertical reaction of crane girder is transferred through its two wheels on to the gantry girder. Therefore, the maximum wheel load is half of this reaction. This maximum wheel load is then increased for impact and used for design of gantry girder.

Explanation: The maximum wheel load is obtained when crane crab is closest to gantry girder. The crab in such position on the crane girder gives maximum reaction on the gantry girder. The vertical reaction of crane girder is transferred through its two wheels on to the gantry girder. Therefore, the maximum wheel load is half of this reaction. This maximum wheel load is then increased for impact and used for design of gantry girder.

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