COBRAS
Concrete Bridge Assessment Program

Since 1994 the COBRAS package has successfully been used by Dr C.R. Middleton on behalf of Cambridge University Technical Services Limited (CUTS) to re-assess the ultimate load carrying capacity of over twenty bridges found to be unsatisfactory when analysed using conventional elastic methods. Of these 'failed' bridges, 70% were found to pass the full 40 tonne requirement when re-assessed using the COBRAS yield-line program. In 1997, Bedfordshire, Cumbria and Northumberland County Councils participated in a trial programme using COBRAS to re-assess some bridges that had been deemed to fail using elastic analysis methods. Of the fourteen bridges re-assessed during this trial, 13 passed at 40 tonnes whilst the 14th was rated at 38 tonnes. All three county councils have remained as trial program users and now assist in the on-going development of the program by testing new program features prior to the general release to other users.

In mid-1998 the COBRAS package was released commercially and is now available from Cambridge University's technology transfer company, Cambridge University Technical Services Limited (CUTS).

Based on the results to date of the assessments undertaken using COBRAS there is a strong case for bridge engineers to at least consider the use of yield-line analysis when assessing the strength of any concrete bridges that have failed an initial elastic analysis due to inadequate flexural capacity.

A paper by Dr Campbell Middleton presented at the Surveyor Bridge Conference in London, March 1998 gives more information on the program and its use for concrete bridge asessment.