Question

The economic spacing of roof truss depends on

(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

I had been asked this question in semester exam.

This key question is from Gantry Girders & Design of Industrial Buildings topic in section Gantry Girders, Design of Plate Girders & Industrial Buildings of Design of Steel Structures

Answer 1

Correct option is (b) cost of purlins and cost of roof covering

For 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.