Cleveland Bridge is the only operational bridge of its kind in the country, and as such, it is a complex process to understand the implications of any deterioration and any necessary repair works.
The structure continues to be subject to scheduled investigations. These included roped access inspections. The bridge inspections are in accordance with national DFT requirements and are used to ensure the structural integrity of bridges in England.
Our original project plan recognised that more extensive repairs could be identified as the renovation project progressed. Unfortunately, recent investigations identified severe corrosion of hanger bars on one of the bridge supports, which we need to resolve to maintain the structural integrity of Cleveland Bridge.
We anticipate that these additional repairs will be funded by the Department For Transport's headroom uplift for maintenance. You can read more about the funding for the project on our scheme overview page.
Why the hanger bar repairs are essential
The bridge is supported by 4 concrete trusses suspended from hanger bars, which are suspended steel rods that hold up each truss. These supports are needed to maintain the structural integrity of the bridge.
The hanger bars have been subject to visual examinations over a number of years, and a preliminary assessment from the technical team stated that they only required painting and cleaning.
However, while preparing to undertake work on truss 4, tests at the base of the hanger bars identified the need for further investigation. The concrete was then removed, which revealed the hanger bars were severely corroded.
There is currently no identified method of repair for hanger bars, so we now need to assess bespoke solutions to progress with the project.
WSP have investigated options of replacing the affected bars using welded, clamped and coupled connections. These have been discounted due to reliability and constructability concerns. Read the WSP interim update.
Engineers are now assessing an option for installing a bearing under the truss to support the weight of the bridge. This needs detailed assessment because it will alter other load paths on the abutments and bridge.
The change of load path can cause structural elements to act differently, and these are sensitive to change because of the bridge’s age and design.
Careful detailed assessment and computer modelling is being undertaken and we anticipate that a further technical update with recommendations will be available in July.
View the hanger bar corrosion and the location of the defect
The picture below shows the corrosion of the truss 4 hanger bars once the concrete had been removed. The bars are part of the bridge support on the Cleveland Place side of the bridge.
Concrete repairs update
The bridge was built in 1826, and the concrete truss supports were added 93 years ago.
The necessary concrete repairs are deeper and larger than those identified from the rope access inspections, and temporary supports have had to be designed.
Only limited amounts of concrete can be removed and replaced during the repair sequence to ensure there is no risk of failure of the structure.
Our overall project plan identified that until all of the concrete was removed and repaired, the risk of more extensive repairs being found remained.
Traffic management measures
The current traffic management measures will remain in place until the option report for the hangar bars has been completed.
An interim update has been issue by WSP and we anticipate that a further technical update with recommendations will be available in July.