Cow Bridge

Built in the 1950s, during the reclamation of Hackney Marshes after World War II, the bridge was in use right up until 2002 when it was eventually closed to traffic due to defects and inadequate design capacity.

The bridge was earmarked by the Council as central to the improvement plans for Hackney Marshes, providing access for works traffic to the site of a new community facility on the South Marsh. Initial studies priced the demolition and rebuild at £3m — twice the intended budget — and so the project lay dormant for two years.

While working on the Hackney Marshes Centre project, we were asked to appraise the existing bridge structure to see if it was feasible to reopen it with a pedestrian walkway. We carried out an inspection and recommended that the ramp and parapet walls were reconditioned, and the defective central span be replaced with a lighter construction so no verifications would need to be made on the substructure. This solution met the budget and, by retaining the original structure, the scheme also minimised the need for temporary works, making an additional cost savings.

The existing span of the bridge was replaced with a new steel deck which sits on the existing abutments to accommodate two-lane traffic, and a steel walkway is cradled alongside this to allow safe pedestrian crossing. The geometries of the new spans are informed by the steepness of the abutments — with the existing abutments too steep for disabled access, the walkway hangs below the level of the roadway to achieve compliance with DDA regulations.

The diagrid steel structure is lightweight in comparison to the pre-existing concrete deck, eliminating the need to verify foundation piles, and reduces bearing requirements. A composite steel and polymer sandwich plate deck system provides a lightweight surface for vehicular and pedestrian traffic.

The result is an eye-catching, economic, and sustainable solution for Hackney, reinstating much-needed access to the marshes.