Transport for London (TfL) and Costain, and Ramboll-Parsons Brinckerhoff Joint Venture
Strengthening the ties that bind
The Hammersmith Flyover carries the four-lane A4 arterial road over the Hammersmith gyratory and links the west to central London. Constructed more than 50 years ago, the Hammersmith Flyover is a 622-meter-long pre-cast, post-tensioned bridge supported by 15 central piers.
Transport for London (TfL), the organization responsible for London’s roadways, realized that the post-tensioning system was deteriorating, and it executed an emergency repair in 2012. But again, the bridge was in need of significant strengthening and repair, so TfL also engaged the firms of Costain, Ramboll, and Parsons Brinkerhoff to develop a new post-tensioning system for the structure, while identifying a key requirement – keep the bridge open during construction.
With little space for the installation of a new post-tensioning system, the design team sought a way to accurately account for the details of the existing structure, and to precisely design a solution. They decided to turn to a model-based design process, and to use Autodesk Inventor as a core design tool. Traditionally associated with product design ,Inventor provided a model-based environment that helped the team simulate and analyze the design as they worked.
Starting from an initial as-built model, the team explored a number of conceptual post-tensioning options. The team determined that positioning cables to achieve maximum eccentricity provided an efficient solution. During the conceptual design process, the team found that Inventor excelled at setting out complex cable deviator curves.
To enhance the accuracy of the as-built model of the existing bridge, the team carried out laser surveys and processed the data using Autodesk ReCap. They created 3D models of existing elements not captured by the record drawings.
As the project progressed, the team refined the design and began collaborating with the general contractor, Costain, and a specialty post-tensioning subcontractor, Freyssinet. They used the 3D models as a basis for discussions, and this collaboration enhanced the models with input from the construction team. By continuously checking for interferences throughout the design process, they were able to address clashes between cable runs and against existing concrete to find a best-fit solution before construction.
On completion of Concept design the Principal Contractor, Costain were appointed by TfL. Costain continued to use the 3d model, and in close collaboration, the design was refined to incorporate Costain’s system preferences and construction methodology. Costain later appointed a specialist post tensioning sub-contractor, Freyssinet, which brought about further model based design refinement.
With construction currently underway, a model-based approach has helped to improve project delivery at the worksite. The team modeled the temporary works needed to carry out the project in order to minimize disruption to traffic flow during construction. The model also helped the team to select tools and equipment for use in construction.
For more information on the competition, visit infrastructure-excellence.com.