Engineering and Construction

The time taken to realize a steel building from concept to completion is generally less than that for a reinforced concrete alternative.This reduces time-related building costs, enables the building to be used earlier, and produces an earlier return on the capital invested.

To gain full benefit from the ‘factory’ process and particularly the advantages of speed of construction, prefabrication, accuracy and lightness, the cladding and finishes of the building must have similar attributes. The use of heavy, slow and in situ finishing materials is not compatible with the lightweight, prefabricated and fast construction of a steel framework.

The cost of steel frameworks is governed to a great extent by the degree of simplicity and repetition embodied in the frame components and connections.This also applies to the other elements which complete the building.

The criterion for the choice of an economic structural system will not necessarily be to use the minimum weight of structural steel. Material costs represent only 30–40% of the total cost of structural steelwork.The remaining 60–70% is accounted for in the design, detailing, fabrication, erection and protection. Hence a choice which needs a larger steel section to avoid, say, plate stiffeners around holes or allows greater standardization will reduce fabrication costs and may result in the most economic overall system.

Because a steel framework is made up of prefabricated components produced in a factory, repetition of dimensions, shapes and details will streamline the manufacturing process and is a major factor in economic design (Fig. 2.10).

Fig. 2.10 Structural costs: (a) economic and (b) uneconomic layouts