Introduction

Steel is synonymous with modern architecture. Throughout the twentieth century the material has inspired architects and engineers, for it combines strength and efficiency with unparalleled opportunities for sculptural expression. Today, in an era of architectural pluralism, and of engineering innovation, steel plays a central role in many of the most sophisticated and accomplished examples of modern building design. Partly this is due to the strides that have been made in metallurgy, structural analysis, fabrication and construction; but perhaps more fundamentally is testament to the continuing commitment and fascination of architects and engineers with a material that offers outstanding design opportunities.

Key attributes of steel include high strength and relatively low weight, which gives remarkable spanning and load carrying ability. Steel lends itself to prefabrication. Whole structures can be created in a factory environment and then constructed quickly on site. Steel building are highly adaptable in that frames can be modified and altered. Costs are low, recycling simple and  aesthetic opportunities rich and varied. As designers, fabricators and constructors continually advance the boundaries of steel design, both technically and expressively, the role as core part of modern architecture seems assured.

Steel is basically iron and carbon however its properties can be enhanced and modified by the addition of other alloying elements and by the manufacturing process. The material is then made into sections, plate or sheet, and these simple products used to produce structures and many other building components.

Standard approaches have evolved for many types of structure, the most common of which are described in the following sections. They are not constraining however. Departures from norms are commonplace, for steel lends itself to creative solutions. Modern architecture is rich with solutions that defy simple categorisation.

The most widely used structural frames rely on hot rolled steel sections made from material that has been heated and passed as a billet through heavy rollers that gradually reduce the cross-section whilst at the same time increasing length. Gradually the material flows to the required shape. Simple wide span column and beam frames where the structural members are arranged in a three dimensional matrix , and portal frames are mainly based on these sections.

For larger spans hot rolled sections and plate can be fabricated to form particularly deep beams or other structural members, and the same technique can be used for geometrically complex members such as the roof beams on the Renault Centre or the steel arch of Lehrter Bahnhof. Standard sections can also be curved after manufacture using heavy bending equipment, or be converted to perforated web profiles using a variety of approaches some of which split the beam into two and then reweld it so that its depth and spanning ability is much increased.

Lighter steel sections can be formed by bending sheet steel to C, Z or ‘ sections. Normally this is done using either a press or folding machine for special sections, or a cold rolling line for standard sections. Cold formed sections generally have greater structural capacity than equivalent timber sections with common structural profiles ranging from around 75 to 500 mm. These are particularly suitable for close centre frames such as wall and floor panels, roof purlins that support cladding, light portal frames, beams and columns (where spans and loads permit), and for lightly loaded and nonstructural applications such as support to internal walls and partitions. Increasingly these sections are being used for whole buildings such as houses, apartments, hotels and offices and for modular buildings. Profiled cladding, floor decks and similar products are also produced by cold rolling.

Steel members can be joined using a wide variety of techniques including welding and bolting and connection design is an important part of any structural system. Like the structures of which they are a part, connection arrangements can be highly standardised or individual such as the mast connection for the Commonwealth Games Stadium. Often in expressed steelwork, connections become important architectural elements in their own right.

This publication provides a simple overview of some of the basic constructional and structural concepts on which most buildings are founded, and also includes selected aspects of associated technologies such as cladding and fire protection.