Using wind tunnel analysis to avoid unnecessary costs on a major public infrastructure project
Old Oak Common Station has been designed to serve as a hub on Britain’s new high-speed rail line, HS2. Situated in west London, the £1-billion facility will be the largest station in the UK built in a single stage, spanning 850m and extending 200m below ground. The project also aims to serve as a catalyst for local economic regeneration – turning a brownfield into a residential and commercial area that will include tens of thousands of homes and jobs.
In addition to its large scale and long-span roof – both inherently challenging engineering features – the station will have an unusual shape, resembling a row of interlocking wedges. To ensure that the structure would efficiently meet all relevant wind loading requirements, the project’s engineering consultants, structural designers, and architects – WSP, Expedition Engineering and Wilkinson Eyre (WE) respectively – sought specialized analysis from RWDI’s world-leading team of wind engineers. Seeking to maximize value for taxpayers in this publicly funded project, the design team also hoped that RWDI’s analysis could help to identify opportunities to enhance structural efficiency. The goal was to meet rigorous safety and performance standards while reducing the station’s requirements for structural steel.
Our team designed a series of physical tests to be carried out in our wind tunnel facility in Milton Keynes. To understand wind loading on the structure both at its completion and over the longer term, we tested two different configurations. One focused on the station in isolation, and the other had the station surrounded by the many new structures expected to result from the area’s rejuvenation. A large number of sensors carefully laid out along the surface of the building and the surrounding area enabled us to gather detailed information about how wind flowed around the building, and how wind effects on the structure would change under diverse weather conditions, both typical and extreme.
After our engineers had analyzed the test data – taking into account both wind and snow loading – they delivered detailed reports to the design team. Collaborating closely, RWDI, WSP, WE and Expedition were able to establish that the building’s non-standard structure met all relevant safety and performance requirements. What’s more, our wind tunnel analysis helped the project team to identify areas in which the structural thicknesses and profiles in the station roof could be modified. The designers had made conservative assumptions in light of the ambiguities presented by the building’s unusual shape; now, armed with plenty of data from rigorous physical testing, they were confident they could use 27% less steel without making any compromise in the safety of their design.
As a result of these collaborative efforts, the Old Oak Common project saved 1,000 tonnes of structural steel, equivalent to a 2,700 tonne reduction in embodied carbon. Although numerous factors contributed to the refinement of the station’s design, the project team attributed about a third of the total cost savings of £7 million to RWDI’s analysis. Our work gave rise to additional opportunities for efficiency in the design process: once we had developed the sensor-equipped scale models for the primary tests – wind and snow loading – we were able to reuse the models for additional analysis. At little extra cost, we were able to conduct tests to ensure that the station would meet its objectives with respect to pedestrian comfort in areas surrounding the station, and that its fire ventilation strategy was sound. Phase one of the Old Oak Common Station is scheduled for completion between 2028 and 2031.