Criteria for the Selection of Construction Equipment

The selection of type and size of equipment rests on many factors. The cost for unproductive time, especially when the equipment is rented, can be considerable and may impact severely on the ultimate cost of construction. Such costs for idle time are greater for large capacity equipment than for small. The contrary is true for the costs of production. Three approaches to this trade-off give as many expressions for the optimum size of capacity of equipment that gives the least total cost. Seven diverse examples illustrate these optimizing methods. One method gives the quantity of work as a point of indifference in the choice between contending equipment. The other two methods give the optimum size in closed form from simple algebraic expressions. They include factors for the quantity of work, idle and productive times, production rates, and costs of the associated crews. The general relationship between the size or capacity of equipment, S, and the quantity of work, Q, is: S is proportional to the square root of Q.