Design Aims - Multi-Storey Buildings.

For the full potential of the advantages of steel-frame construction to be realized, the design of multi-storey buildings requires a considered and disciplined approach by the architects, engineers and contractors involved in the project. They must be aware of the constraints imposed on the design programme by the lead time between placing a contract for the supply of the steel frame and the erection of the first pieces on site. The programme should include such critical dates on information release as are necessary to ensure that material order and fabrication can progress smoothly.

The designer must recognize that the framework is the skeleton around which every other element of the building will be constructed. The design encompasses not only the structure but also the building envelope, services and internal finishes.

All these elements must be co-ordinated by a firm dimensional discipline, which recognizes the modular nature of the components, to ensure maximum repetition and standardization. Consequently it is impossible to consider the design of the framework in isolation. It is vital to see the frame as part of an integrated building design from the outset: the most efficient solution for the structure may not be effective in achieving a satisfactory solution for the total building.

In principle, the design aims can be considered under three headings:

• Technical
• Architectural
• Financial.

Technical aims
The designer must ensure that the framework, its elements and connections are strong enough to withstand the applied loads to which the framework will be subjected throughout its design life.The system chosen on this basis must be sufficiently robust to prevent the progressive collapse of the building or a significant part of it under accidental loading. This is the primary technical aim. However, as issues related to strength have become better understood and techniques for the strength design of frameworks have been formalized, designers have progressively used lighter and stronger materials. This has generated a greater need to consider serviceability, including dynamic floor response, as part of the development of the structural concept.

Other important considerations are to ensure adequate resistance to fire and corrosion. The design should aim to minimize the cost, requirements and intrusion of the protection systems on the efficiency of the overall building.

Architectural aims
For the vast majority of buildings the most effective structural steel frame is the one which is least obtrusive. In this way it imposes least constraint on internal planning, and produces maximum usable floor area, particularly for open-plan offices. It also provides minimal obstruction to the routeing of building services. This is an important consideration, particularly since building services are becoming more extensive
and demanding on space and hence on the building framework.

Occasionally the structure is an essential feature of the architectural expression of the building. Under these circumstances the frame must achieve, among other aims, a balance between internal planning efficiency and an expressed structural form. However, these buildings are special, not appropriate to this manual, and will not be considered in more detail, except to give a number of references.

Financial aims
The design of a steel frame should aim to achieve minimum overall cost. This is a balance between the capital cost of the frame and the improved revenue from early occupation of the building through fast erection of the steel frame: a more expensive framework may be quicker to build and for certain uses would be more economic to a client in overall terms. Commercial office developments are a good example of this balance. Figure 2.1 shows a breakdown of construction costs for a typical development.

Typical cost breakdown
Fig. 2.1 Typical cost breakdown

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