Introduction

A wide range of structural forms may be used to enclose a single storey volume including loadbearing, framed, shell and membrane structures, utilising a range of materials including steel, concrete, timber, fabrics and composites. The building typology is very common, with a range of precedents, and with many opportunities offered by new materials and techniques.

Planar load bearing structures can be used for smaller buildings, with adaptations such as fins and diaphragm walls being used for large buildings. Roofs can be formed from timber joists for spans up to 5-6m, and larger spans may be achieved with glulam sections and trusses. Concrete can be used to form walls and slabs or beams can also be used to form roofs. Membranes or shells may enclose large volumes and can take curvilinear forms.

However, the most widely used system for single storey buildings is a structural frame, allowing the concentration of primary structure into a series of linear elements, joined together to form a strong, rigid structural system. Whilst concrete and timber can be used, the use of steel provides a lightweight and efficient frame assembled from prefabricated elements and easily joined together.

A key factor in the single storey building is that it does not require a system to support intermediate floors and this gives considerable freedom of form. The two main structural elements that therefore determine the structural form are the walls and roof.

There are several advantages to the use of steel in a frame system. These include its high strength, prefabrication and ease of connection and assembly, and flexibility.

The advantages of steel framing can be summarised as:

• Large clear spans can be provided (flat roofs up to say 40m, possibly more).
• They can be easily fabricated from standard elements with shop welding and site bolting. (On some jobs it may be reasonable to use some site welding.)
• They are rapidly erected on prepared bases, with 3-dimensional stability ensured by early incorporation of diagonal bracing elements.
•  Main frames are often "portals" designed using the plastic behaviour of steel, thereby reducing element sizes or allowing larger spans.
• Roof decking can be fixed rapidly to keep rain off the floor laying operations below.
• Side walls, which can be fixed at any stage after the frame has been erected, can all be of lightweight cladding/glazing, all masonry (possibly for fire protection close to boundaries), or a combination.
•  Large openings can be created easily between the columns.
• Later adaptations within the building, extensions to it and disassembly are relatively simple.
• Rapid dry construction allows quicker occupation and hence provides a faster return on capital.

A range of structural sections can be used to achieve the enclosures required, from simple beams and columns, through trusses and portals, to more complex tension and multibay structures.

Members most commonly used are Universal Beam (UB) or Universal Column (UC) sections. Castellated or cellular sections can be used for greater depth and to allow service penetration. Members are fabricated in straight lengths but can be curved to required shapes, or plates can be cut and welded to form more complex shapes. Tubular sections (Square, Circular or Rectangular Hollow Sections) may be used for truss members and columns (at some additional cost).

Typical wind bracing elements are either small diameter rods or flat sections (tension only cross-bracing); angles or circular hollow sections, which are both more efficient and elegant, could be used as single element diagonal bracing resisting compression or tension

Cold rolled Z and M sections may be used for secondary structural elements eg. purlins.

The structural system that is used will depend on functional, technical and aesthetic requirements and these criteria should be assessed during the design stages.

Functional requirements must be satisfied in the building and will normally be part of the brief. They will include:

• size of volume to be enclosed
• clear height required
• span required
• lateral stability
• column spacing
• opening size required
• environmental control and servicing
• natural lighting

Technical solutions to the functional criteria, set with certain parameters, may be, for example, the size of beam able to achieve a given span, or ability of a structure to integrate with services. The parameters will include factors such as:

• cost
• availability
• buildability
• limitations on size
• integration
• movement
• fire protection
• fabrication and assembly
• transportation
• sustainability

Both the functional and technical requirements form part of the aesthetic and architectural requirements of the building, which may or may not directly include the structural system. They will include the importance and visual impact of the general building shape and form, the nature of the building skin and enclosure, expression and visual appearance of structural elements.

Whilst these may not have exact definitions, ideas about the architectural intent will be of critical importance at design stages and may redefine some technical parameters.

For example, a more expensive, but visually impressive structure may used to define the architectural aesthetic. On the other hand, an alternative aesthetic requirement may lead to a different approach to the structure, for example, a very cheap and efficient hidden structure that allows the use of a more sophisticated building skin.

These requirements will be considered during design stages, with the ultimate aim of producing a building that satisfies all these considerations.