Flooring | Features

Cost comparison: Steel vs concrete
	Steel frame, lightweight reinforced-concrete composite deck (£/m² typical floor area)	RC columns, post-tension RC flat slab (£/m² typical floor area)
Structure costs
Beams	128.00	n/a
Columns	39.00	27.00
Slab	60..00	182.00
Frame subtotal	227.00	209.00
Foundations	38.00	50.00
Structure total	265.00	259.00
The table illustrates that for a typical West End or City of London office development, the costs of composite steel deck frame and a post-tensioned concrete flat slab on a concrete frame are broadly comparable. Recent increases in steel material prices have resulted in corresponding increases in installed costs of up to 30% over the past year for components including fabricated steel, decking and bar reinforcement. This has affected both concrete and steel options. However, with its highly efficient use of steel, the post-tensioned option has become increasingly competitive. In practice, however, the selection of frame and upper-floor solutions is driven by many factors, including programme, cladding system and constraints of storey heights. Precast, post-tensioned units have, for example, become widely used where an exposed soffit with an architectural finish is required. The shape and size of the building will also have an effect on the selection of the structural solution. Small floor plates, or floor plates with an irregular profile, will result in post-tensioned slabs being a less economic solution because of the higher costs of anchors. Furthermore, the reduction in steelwork weights that can be achieved on simple frame structures, without setbacks and other transfer structures, can also result in cost advantages for a steel-based solution. It is essential, therefore, that the decision to adopt a particular structural solution is based upon an appraisal of the characteristics of the project together with a full range of cost and performance criteria. Costs in the table are based on central London prices for large commercial office developments obtained in general competition, and are current to the fourth quarter 2004.