Jeremy Barnes is our Technical Director here at Whitfield Consulting Services. He is recognised as experienced in the field of temporary works and has recently contributed to Network Rail’s Safety by Design Working Group on the update to their guidance on the early focus on constructability. He has previously authored the Concrete Bridge Development Group’s technical guide, Temporary Works for Concrete Bridges.
We asked him to share his thoughts on why constructability and temporary works are crucial to the success of engineering projects, and on the importance of considering them centrally and early when designing permanent works.
What are temporary works?
Network Rail give a definition: “those parts of the works that allow or enable construction of, protect, support or provide access to, the permanent works and which might or might not remain in place at the completion of the works, including states of the permanent works which are temporary, loading conditions of the permanent works not envisaged by the permanent works design and structures in states of modification or demolition.”
The definition above hints at the different functions temporary works fulfil. Some temporary works will be required to provide support to the permanent works during construction. Their early identification is necessary to determine the final state of stress in the structure and allow the permanent works to be undertaken. The deck propping of multi span bridges is a typical example.
Temporary works also includes arrangements that usually do not influence the final state of stress of a structure. Despite this, early planning on how these arrangements are installed, secured, and removed is key. Externally propped formwork is a typical example.
Where existing assets are affected by construction, other arrangements may be required. In the rail environment alternative temporary arrangements may be necessary to access operational stations. Whilst not necessarily directly connected to the construction works, these arrangements are temporary works and again early focus on their constructability is key.
Temporary works often add to the loading experienced by structures, meaning they must be considered in the design of the permanent elements to ensure they are adequate to support both sources of load. If not, additional support will be required.
The spatial requirements of temporary works and the construction process generally must be considered as additional space will often be required. Whether installing temporary propping until a permanent element of structure is installed, or providing a crane working platform, space for these elements and activities must be allowed for on site.
Challenges and opportunities
Neglecting consideration of temporary works during permanent design can lead to delays, cost over-runs, contractual disputes or, in the worst cases, more serious problems. If the foundations or other elements of a structure cannot support the additional weight present during construction, it can mean lengthy delays as additional measures are hurriedly put in place, with permanent works construction likely pausing while that happens. The most extreme outcome, albeit thankfully rare, is a failure within a structure.
To reduce this risk, collaboration between all parties and the early consideration of constructability and associated temporary works is vital, including the permanent works designer. This approach also drives other benefits, i.e., optimising construction as a process to support the goal of quick, safe building activity that delivers a best-quality outcome on time and on budget.
The importance of considering temporary works carefully and from the earliest phase of each project
Collaboration and communication are vital, ideally with permanent works and temporary works designers interfacing with one another. Ideally a client will appoint their temporary works designers during pre-construction to maximise potential efficiencies. This will allow early communication of key design information between the two, although it is recognised that procurement routes do not always make this possible.
One option is for the permanent works designer to also take temporary works responsibility, and this often happens with early contractor involvement. The advantage with this arrangement is that the degree to which the permanent works team will have clearly thought about temporary works is maximised.
On projects where there is no early contractor involvement, the permanent works designer should still consider the implications of their design on temporary works and vice versa. On some projects the permanent works designer will provide an indicative construction sequence showing how their design can be built efficiently and safely which can feed into and assist the temporary works design process. This approach has obvious benefits in communicating assumed construction methodologies throughout a project team and is now a requirement of the Network Rail assurance process.
Decisions made early during permanent works design can also have a significant impact on the ease of construction and minimising health and safety risks. Careful thought can reduce or in some cases eliminate the need for temporary works completely.
Ideally, a temporary works register will be established in the early project stages by the permanent works designer. As the project progresses this register will be updated. At an appropriate point in project development the register will be passed from permanent works designer to temporary works designer and developed further. If permanent and temporary works designers are informed and engaged early, collaboration is enhanced and opportunities for innovation are maximised. The use of temporary works register is recommended in the latest Network Rail guidance on constructability and temporary works.
Away from the rail environment, in our experience in substation design, we consider the access and temporary works needed to bring heavy plant, such as transformers to site at the earliest stages, including detailed movement and swept path analysis to model and demonstrate how this will come together, to ensure seamless logistics on delivery day. Read more about that here: Solving engineering challenges unique to the power and energy sector.
Modern methods of construction and optimising the programme of works
Another reason that temporary works and construction processes are increasingly understood as very important relates to modern methods of construction. Contractors and those engaging contractors are becoming more aware that new approaches to building works can result in significantly quicker and more cost-effective projects. Design for Manufacture and Assembly (DfMA) and offsite construction is being increasingly used. As an example, the concrete elements for bridge superstructure and sub-structure are now increasingly precast, rather than casting in-situ, achieving benefits with programme and cost savings, as well as reducing safety risks.
In a recent article we discussed how our experience in rail civil structures, particularly bridges, has encouraged a focus on constructability in our design work, read more about that here: Key learnings from rail.
Ensuring that construction is as safe as possible
Both the rail and power & energy sectors are safety critical, and eliminating or reducing health and safety risks is a key reason for the early consideration of buildability and temporary works. DfMA can not only reduce the overall construction programme, but replace the work required in an unpredictable site environment. This is replaced by work being undertaken in a controlled off-site location. In particular, pre-casting off-site can significantly reduce working at height.
The WCS approach to temporary works
WCS is often asked to consult on temporary works, including sometimes formally checking or reviewing the design work of others, as may be required under BS5975. Our team are often nominated as the Temporary Works Co-ordinators on projects. Our approach is to always consider buildability and temporary works centrally, even where our contracted work is permanent only.
WCS are pleased to have contributed to the recent update of the Network Rail Health and Safety by Design, Buildings and Civils Working Group Guidance Note: Early Focus on Constructability and Temporary Works, Issue 4. This important guidance is recommended to all involved in both the rail and wider construction industries.
If you need a temporary works consultant for your next project, please call us on +44 (0)20 8938 375, or email info@wcs-consult.co.uk.
