Industrial Roof Trusses MCQ with answer and solution

Concept

Gantry girders support crane loads including vertical wheel loads, lateral loads (transverse surge), and longitudinal loads (longitudinal surge). Wind load is treated as a primary load on the overall building frame rather than a specific component load for gantry girder design.

Step-by-step solution

1. Identify the loads acting on a gantry girder from crane operation: Vertical loads (self-weight of crane + maximum wheel load with impact factor), Lateral loads (transverse surge due to trolley movement, usually taken as 5-10% of the weight of the trolley and lifting load), and Longitudinal loads (longitudinal surge due to starting/stopping of the crane, usually taken as 5% of the static wheel loads excluding crane self-weight). 2. Note that wind loads act on the building enclosure, roof trusses, and columns, but are not factored into the local crane-induced design loads of the gantry girder. 3. Conclude that wind load is NOT considered directly in gantry girder design among the choices provided.

Explanation

Gantry girders are designed to support overhead traveling cranes. The loads considered in their design include vertical loads (crane weight and maximum wheel loads), lateral loads (surge due to trolley movement), and longitudinal loads (surge due to crane acceleration/braking). Wind load acts on the building structure and industrial roof trusses, but it is not directly considered as part of the crane loads acting on the gantry girder itself per standard design practices.

Why the other options are wrong

A: Lateral loads (transverse surge) are considered in gantry girder design. B: Vertical loads (crane wheel loads with impact) are the primary loads considered. D: Gravity loads (dead weight of girder, rails, and crane vertical loads) are definitely considered.

Shortcut

Remember gantry girders handle crane-specific loads: vertical (wheel loads + impact), lateral (crane surge), and longitudinal. Wind acts on the whole building, not the gantry girder design directly.

Common mistake

Students often confuse loads on roof trusses (where wind load is crucial) with loads on gantry girders (which are designed for crane live loads and surges).