Introduction

Steel framed construction is a very popular structural form for multi-storey buildings as it provides great flexibility.

Modern steel framed buildings are designed on the principle of the structure as an independent loadbearing frame carrying both vertical and lateral loads down to the building foundations. This form of construction makes possible the creation of large column-free internal spaces which can be divided by interchangeable partitions and, by eliminating the external wall as a loadbearing element, allows the development of large window areas, curtain walling and cladding systems.

Multi-storey steel-framed buildings can accommodate a wide range of functions and can adapt to a wide range of architectural styles. The term 'multi-storey' means structures with more than one storey, and covers buildings used for many different purposes including:

Although the basic anatomy of each building is similar, they may have different requirements for column grid, services, and internal/external finishes. For example, a car park may be designed with floors of moderate spans and will have minimal requirements for cladding, finishes and services, whereas a prestige office development may need large column-free areas with air conditioning and under-floor cabling for computers.

Multi-storey steel framed construction has its origins in Chicago in the late 19th century 

The versatility of new materials in building such as wrought and cast iron and ultimately steel was increasingly exploited in the 19th Century, although the first example of a fully framed structure in which the external wall was non-loadbearing being Green's Boathouse at Sheerness, built in 1859.

However, it was in Chicago in the 1880s and 90s that the entirely loadbearing frame revolutionised building construction and made possible the modern concept of a light, disciplined facade with large window areas and open internal layouts based on clearly defined planning grids. An early example of the transition from external loadbearing walls to steel frame was achieved by Holabird and Roche with the 14 storey Tacoma Building built in 1884 but sadly subsequently demolished. The earliest surviving example of a structure on this principle is the Manhattan Building by William Le Baron Jenney in 1890, which was followed by a flowering of the Chicago School in architecture into the 1920s. Of course, the development of multi-storey buildings as a practical proposition depended as much on the development of mechanical services and, in particular, the passenger lift. This illustrates the symbiotic relationship of structure and building services which has become a fundamental theme in modern buildings.

New methods of construction have reduced costs.

In recent years, largely as a result of overcoming difficulties with fire protection and developing fast and efficient methods of construction, the development of steel framed buildings with composite metal deck floors has transformed the construction of office buildings in the UK.

It is important to take a global approach when considering optimum design solutions.

With the growth of increasingly sophisticated building services and expensive cladding systems, there has been a steady decline in the cost of the structure as a proportion of the overall cost of the building. However the choice of structural system remains the key factor in the design of a coherent and successful building.

The individual contributions of major components to the overall building cost can vary significantly with building function, size and architectural treatment. However they are generally within the following ranges:

• Foundations 5% to 10%
• Steel Skeleton 10% to 20%
• Floor Structure 5% to 10%
• Cladding/Finishes 15% to 40%
• Services 15% to 40%

It is clear that the cost of the structure is a relatively small proportion. Consequently it is often beneficial to use a somewhat more expensive structural solution if other costs can be reduced as a result. For example, longer span beams will provide greater flexibility, and shallow floors will facilitate service installation and reduce cladding costs. These considerations should be made over the projected life of the building, recognising that this will often involve major refurbishment including replacement of services, fittings, and possibly envelope.

When considering the cost of the structure it is important to recognise that weight of material is less important than processing costs associated with construction.

Even when the cost of the structure is considered in isolation, 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 percent of the total cost of structural steelwork. The remaining 60-70 percent 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 standardisation, will reduce fabrication costs and may result in the most economic overall system.