The challenge
Following significant issues with this bridge, a routine of additional monitoring had been put in place. Acoustic sensors were installed and collected evidence of periodic wire breaks within the structure. This led to a programme of measuring the tension of the tendons in the legs, which identified significant changes, raising concern about the structural integrity of this key transport asset.
A Total Station was then used to measure displacements of the bridge deck. The readings showed some downward movement, but it wasn't clear whether this was an anomaly or area of concern, or movement consistent with the bridge's normal behaviour. There simply wasn't enough data. It was imperative to determine whether the bridge needed to be closed immediately for public safety, or whether there was time to investigate further.
Closing the bridge would cause huge disruption and very significant costs. The difficulty is that the observed issues could result from any combination of temperature, long-term creep, transient live loads, construction activities and structural deterioration. Without an understanding of how the bridge had behaved historically, it was hard to tell whether the movements were within the expected range or a genuine cause for alarm. Climate change is now adding further strain to the condition and structural health of assets, making this kind of assessment increasingly important.
The solution
The key thing engineers needed was more data. The team added five years of InSAR history to the on-site measurements to assess millimetre-scale vertical displacement.
BKWAI's advanced data techniques helped engineers analyse the displacement trends and establish normal behaviour across the bridge and separate outliers from that baseline. By bringing in environmental data, the correlation with temperature became clear. This gave the engineers an understanding of how the bridge and the surrounding ground had behaved over the previous five years, and on an ongoing basis as new data continues to be fed in.
The platform brings in-situ and satellite data together, allowing engineers to visualise, interrogate and compare Total Station surveys directly with satellite measurements.
The results
Engineers were able to determine that, at this stage, it was safe for the bridge to remain open and traffic could keep moving. They continue to investigate the causes of the change in tension, but are now comfortable that there is no need to take urgent action.
Ongoing use of the BKWAI platform, with up-to-date sensor and satellite data, lets them keep monitoring the bridge for potential changes in movement while the investigation is completed.
“ We were concerned about material testing results for the bridge and considered the need to close the structure to traffic when traditional monitoring equipment showed vertical displacements of the deck over a short period of time. BKWAI was unique in enabling us to review the historic behaviour of the structure and gave us the confidence that these movements were likely due to seasonal thermal movements. The class-leading platform enabled new insights into the performance of the bridge and continues to provide invaluable information for our ongoing management of the structure.
Ultimately, BKWAI provides crucial information for our CS470 reviews of the structure and gives us the confidence to keep it in use, avoiding huge disruption to the road network. The team are a pleasure to work with, and the platform is continually being improved with powerful new features. ”