Correct Answer - Option 2 : 5%
Explanation
The weight of trusses cannot be determined or calculated until the stresses in members are determined and the truss design.
Exact calculations of stresses are not possible until the weights are known. Hence the weight of the truss has to be estimated. The weight of the truss varies with the span, and the rise of the truss, the spacing of trusses, and the type of roof covering material. It is not possible to have an exact formula that includes all these factors. The self-weight of the truss may be assumed as 0.090 to 0.150 kN per square meter of the plan area.
- As the weight of trusses cannot be determined or calculated until the stresses in members are determined and the truss design.
- When calculating the weight of a steel structure, there is a general method to calculate the weight of all of the various members and plates first and then add an additional percentage to account for the weight of nuts and bolts. This percentage is usually taken as 5 % of the total weight.
The self-weight of truss is found by empirical formula as self-weight of truss in kN/sqm of the plan are
A) Dead loads:
The simple formula for estimation of the approximate deadweight of roof truss in N/m2 is
\({\rm{Dead\;weight}} = \left( {\frac{{\rm{L}}}{3} + 5} \right) \times 10\)
where L = Span of the truss