Correct option is A
For the
overall cost of roof trusses to be minimum, the design should balance the costs of different components such as trusses, purlins, and roof coverings. The minimum cost condition is derived from the principle that the optimal balance minimizes the combined cost.
Key Points:
1.
Trusses: Support the roof and distribute the load to the walls or columns.
2.
Purlins: Secondary supports that carry loads from the roof coverings to the trusses.
3.
Roof Coverings: The materials that protect the building from environmental elements like rain and sun.
Optimal Cost Relationship:
The cost of the trusses should be
approximately twice the cost of the purlins plus the cost of the roof coverings because:
· The trusses form the primary load-carrying structure and account for a significant portion of the overall cost.
· Purlins and roof coverings are secondary and complementary, and their costs must be in proportion for the overall cost to be optimized.
