Dr David Moore, CEO of the British Constructional Steelwork Association (BCSA) answers readers’ questions on constructional steelwork.

What are the main advantages of steel structures over timber and concrete ones?

Steel’s strength and versatility gives architects the freedom to achieve ambitious designs. Its durability coupled to its ability to be recycled repeatedly, without quality loss, makes it compatible with long-term sustainable development. Steel facilitates long spans providing flexible, light, open and airy spaces that can be reconfigured, extended or adapted with minimal disruption. Precision offsite manufacturing minimises waste and construction programmes, cellular beams facilitate service integration and its lightweight nature minimises foundation loads. Steel is often the first choice on the basis of cost alone.

Is steel suitable for all types of building structure?

In 2022 the Construction Markets annual survey demonstrated that steel commanded a 98.4 per cent share by floor area of all industrial shed construction in the UK and 65.9 per cent of non-residential multi-storey construction.

What type/grades of steel are commonly used in building structures and what are their main advantages and disadvantages?

Structural steel (or hot-rolled steel), in the form of open sections (I and H-shaped) or hollow/closed sections, are available in the UK in three main steel grades: S275, S355 and S460, where the figures indicate the yield strength. Steel grade S355 is commonly specified for buildings, although grade S460 is increasingly used.

How do steel structures perform with regards to fire?

All structural steel sections have some inherent fire resistance, and this is a function of the size of the section, the degree of exposure to the fire and the applied loading. For small steel sections that are fully loaded and exposed to fire on all sides, the fire resistance period can be as little as 12 minutes. For very large sections that are lightly loaded with some partial fire protection from the supported concrete floor, the fire resistance period can be as much as 50 minutes. Full-scale fire tests have shown that steel sections supporting concrete composite floors can survive a complete burn-out, even with a number of the supporting steel beams unprotected.

How long will steel structures typically last?

Steel buildings generally have a 50-year design life but they can last much longer provided the necessary inspection, assessment and/or repair work is undertaken. The Iron Bridge in Coalbrookdale has survived more than 200 years, while the Forth Bridge is more than 100 years old.

What are the best ways of maintaining steel structures?

All paint systems have a limited life and ultimately break down due to the corrosivity of the environment. However, the use of a well-designed, planned, paint maintenance programme will extend the life of the coating system by catching any damage or breakdown in its early stages.

How sustainable is steel compared to other structural materials?

Steel’s superior strength-to-weight ratio means a little goes a long way. It is versatile and infinitely recyclable. Steel buildings are safe, robust, durable and adaptable, meaning they have longevity. When required, steel buildings can be easily disassembled and either reused or recycled into new products.

How easy is it to recycle steel structures at the end of their lives?

Since steel was first mass-produced in the 1880s it has always been highly recycled and this continues today with >95 per cent of structural steel recovered for recycling or reuse. Steel is easy to recycle through all modern steel production routes, and all new steel contains a proportion of scrap ranging from 20-100 per cent. Scrap steel’s economic value ensures its recovery at end of life, and its magnetic properties mean that it can be efficiently segregated from mixed waste streams. Steel is a true circular economy material that can be recycled into new steel products in contrast to other common structural materials which are generally downcycled into lower grade materials, for example by crushing or chipping. There is also a growing market for reusing reclaimed structural steelwork. Reuse is generally preferable to recycling since it avoids the environmental impacts associated with remelting scrap steel.

How do steel structures compare in terms of cost to concrete and timber alternatives?

In 2016, the BCSA and Steel for Life commissioned AECOM to provide impartial cost guidance applicable to a broad range of construction professionals. Published quarterly in Building magazine, ‘Costing Steelwork’ provides guidance on the key elements of costing structural steelwork, up-to-date cost ranges for various frame types based on actual buildings, and cost comparison studies between steel and other framing materials. It comprises studies of office, education, residential/mixed-use, retail and industrial buildings. The latest data for 2022 (Q1) shows the steel-framed options as the most cost-effective solution on a whole building basis for all five building types.

What kinds of warranties if any are provided for steel structures?

A structural steelwork contractor carrying out design work can provide the usual construction security package such as collateral warranties or third party rights backed by professional indemnity insurance, performance bonds, and, if appropriate a parent company guarantee.

For further information visit www.bcsa.org.uk