This guidance sets out how structural engineers can use steel specifications to help move the industry towards net zero by 2050. It applies to building projects where the National Structural Steel Specification (7th edition) is used.
When developing a project specification, the engineer should engage with the client and wider design team to ensure that there is full alignment on the project’s sustainability goals.
They should keep in mind that there may be cost, time or logistical implications. This alignment needs to encompass the full supply chain, so should be clearly communicated in the pre-tender qualification process.
Part one: specification additions and modifications
It’s important to ask for Environmental Product Declarations (EPD) to EN 15804 for all steel products. This will help drive adoption of EPD and ultimately help designers make more informed decisions.
Modules A1-A3 have the biggest impact on reaching net zero greenhouse gas (GHG) emissions targets by 2050. Module D impact figures are welcome but will usually be beyond the scope of our project influence. They are likely to have little or no impact on net emissions up to 2050.
Scrap steel is currently turned into new steel products, mainly through EAF mills. This route emits less GHG than steel made from iron ore so it is tempting to specify this on our projects. It may be necessary to specify recycled content limits to comply with Green Rating scheme credits.
This in turn may have cost implications without necessarily resulting in net carbon reduction for the industry. Scrap is a limited resource and to reduce GHG globally we need to achieve reductions in emissions from all steel-making processes.
The recently published SteelZero commitment
gives a more balanced definition of low embodied carbon steel and one which incentivises industry-wide GHG reductions over the next decade. Specification can set targets for the proportion of project steel meeting this definition. Example specification wording is shown below.
‘A minimum of [50%] by mass of the structural steel used on the project shall be from steel products that meet one or more of the following criteria:
- ResponsibleSteelTM Certified Steel, or steel meeting an equivalent international standard
- Steel produced by a steelmaking site where the site’s corporate owner has defined and made public both a long-term emissions reduction pathway and a medium-term, quantitative science-based GHG emissions target for the corporation that has been approved by the SBTi or by SteelZeroo
- Low Embodied Carbon Steel as defined by SteelZero or a steel product supplied with a certified EPD Module A1-A3 Global Warming impact (kgCO2 eq./tonne) not exceeding (1400 - 1200mSM), where mSM is the proportion by mass of secondary material in the feedstock'
Future reuse and design for deconstruction
Making provision for future adaptability or reuse is a positive (for example considering reversibility of beam-to-slab connections). But you should avoid adding significant steel weight in the form of lower utilisations or complicated connections to facilitate this.
You should insist on comprehensive traceability and as-built O&M/Safety File records. Unless required by the Project Specification, the NSSS currently requests partial traceability. With an IFC model, including connection-design information, this will be useful for future flexibility and deconstruction and reuse.
The best means of achieving this should be agreed with your fabricator but the intended output is that the following should be easily accessible for each element (NSSS 4.1.1):
- Section size
- Mill certificates
- Welding certificates
Completed components can be marked with section size, and steel grade as well as an erection mark. This can help with checking and re-design post-construction during refurbishment and at end of life.
Only the erection mark is required under NSSS (4.1.3). These marks will be obscured by intumescent paint and will likely not provide sufficient information for salvage in the absence of the O&M information noted in the suggestion above.
It can also help to set out the process or workflow under which salvaged steel will be accepted. For example, members governed by serviceability requirements could be identified as judicious candidates for salvaged steel. Refer to SCI P427.
Quality Assurance Systems
You can consider adding a requirement for sustainable procurement (BES 6001/ ISO 14001). This will provide evidence that there is a management system in place to responsibly source materials from the supply chain.
Also consider making membership of the BCSA sustainability charter (Gold or Silver) mandatory. This is optional in NSSS (11.1.2). This covers a range of sustainability measures, not merely environmental.
Avoid making temporary steelwork permanent, especially where construction cases dominate permanent design cases. Examples might include angle sections running parallel to metal deck spans along core walls or temporary torsional stiffening for beams supporting precast units.
You will need to discuss this with your client and contractor pre-tender and explicitly set this out in your specification information. This is because it may be quicker and cheaper to increase steel weight and reduce temporary works operations on-site.
Don’t over-rationalise element sizes and connection forces. The fabricator can rationalise at a later stage, with the engineer’s agreement, if necessary.
Don’t specify full-penetration butt welds if fillet welds or partial penetration butt welds are adequate. If possible, design for robustness forces in structural topping rather than specifying as a force for the connection design.
Finally, specify standard connections (Green Book, where feasible) to improve future flexibility.
This will usually be led by the architect, however we can contribute by:
- Minimising paint to internal, non-visual areas
- Using boarded fire protection rather than painted. It will be easier to demount in the future and allows steel to be reused more easily
Part 2: design
The most significant impact designers can make is to reduce the quantity of steel specified. Some initial suggestions are set out below.
: use optimal spans & grids, and proportion steel sections so that strength governs, where possible.
: reduce rationalisation and aim for high utilisation factors. Consider use of fabricated sections, including with varying cross-section properties rather than standard rolled sections, where significant tonnage savings can be achieved. Consider digital optimisation.
Review conservative default assumptions baked into analysis software
: carefully consider element releases to avoid excessive material & fabrication in connections.
Consider using higher grade (S460) steel
: this is explicitly allowed for in NSSS 7th Edition.
Review opportunities to minimise loading
: the self-weight of flooring supported on a steel grid will have a significant impact on the tonnage and thus the carbon impact.