The correct answer is $\frac{{\text{L}}}{3}$ to $\frac{{\text{L}}}{2}$.
The economical spacing of trusses is the distance between the centers of adjacent trusses. It is determined by a number of factors, including the span of the truss, the type of loading, and the material used.
In general, the economical spacing of trusses is between $\frac{{\text{L}}}{3}$ and $\frac{{\text{L}}}{2}$, where L is the span of the truss. This is because a spacing that is too small will result in an increase in the cost of the truss, while a spacing that is too large will result in an increase in the deflection of the truss.
The following are some of the factors that affect the economical spacing of trusses:
- The span of the truss: The longer the span, the greater the economical spacing. This is because a longer span requires a stronger truss, which can be achieved by using a wider spacing.
- The type of loading: The type of loading also affects the economical spacing. For example, a truss that is subjected to a live load (such as a bridge) will require a wider spacing than a truss that is subjected to a dead load (such as a roof).
- The material used: The material used to construct the truss also affects the economical spacing. For example, a truss that is made of steel will require a wider spacing than a truss that is made of wood.
The economical spacing of trusses is a complex issue that is affected by a number of factors. The best way to determine the economical spacing for a particular truss is to consult with a structural engineer.