Description of the study
An independently produced cost comparison study for commercial buildings proves that for most applications structural steel frame solutions are faster to build and more cost effective than reinforced concrete alternatives.
The study includes costings, structural design and programming by a team comprising Davis Langdon, Arup and MACE respectively, and is the latest in a series first carried out in 1993.
The cost comparison considers two typical modern commercial developments, Building A which is a 2,600 square metre office in Manchester, and Building B which represents a prestige office building of 18,000 square metres in London. Both are based on developer specification buildings typical of modern commercial developments.
Building A
Building ‘A’ is typical of a speculative office building of modest specification in a regional UK city. This study assumes it is located in Manchester, which is a major area of growth in steel construction. It is a four storey building, of a width that permits good natural ventilation and lets in plenty of natural light. The building is not air conditioned, but does have perimeter heating. It is serviced from zones at each end of the building, where the stairs and lifts are also located. There are three 10-person lifts.
Inside the building is generally open plan, but may be divided into individual offices. It has a fire resistance of 60 minutes, and is not sprinkler protected. It is clad in traditional brick, with regularly spaced individual windows making up a quarter of the building façade.
The foundations are pad footings on sand, and the ground floor is not suspended. The top floor is designed to take the same loads as all other floors. There is an additional roof structure comprising steel portals, purlins and tiles, which is not suitable for occupancy.
Minor pipework in this building is passed underneath or through the beams or floor. Provision for lighting units, fire protection, ceiling depths and an allowance for deflections are included in the depth of the floor zone.
Building B
Building B is typical of a prestige office building in central London, suitable for a company headquarters or similar high status function. It is a more complex structure than Building A, designed around a central covered atrium. It is eight storeys high and is comfort cooled by a fan coil system.
The structure is serviced from two main zones at opposite ends of the building. The service cores also include fire-fighting lifts and fire-protected lobbies. There are three stairways in the building, and three 16-person lifts adjacent to the entrance lobby, as well as two ten-person lifts in the outer cores.
It has a fire resistance of 90 minutes and is not sprinkler protected.
Inside, the building is open plan, but may be subdivided to create individual offices or meeting rooms around the perimeter. Outside, the façade is glazed, using a proprietary glass curtain walling system. The atrium roof is constructed from tubular steel and glass, and has a mechanical smoke extraction system.
The foundations for this building are single large diameter under-reamed piles, bearing in clay. The pile capacity is achieved by end bearing and side friction. The upper floor has two areas that house the air conditioning equipment, close to the cores that they service. This top floor is designed to take the same loads as other floors, with local strengthening under the heavy equipment. Further plant and major services are located in a basement, which covers a quarter of the building plan area.
