A major study of the risk of failure of bridges is currently underway. Reliability theory provides a method for allowing for variability in the major parameters governing the behavior of a bridge. For example, a bridge may be designed for a concrete strength of 40 MPa whereas in practice the actual strength of concrete within a bridge is likely to have a range of values between say 35 and 50 MPa. Similarly most other parameters of strength, dimension and load can be more realistically modelled by a statistical distribution of specified mean, standard deviation and type.
By considering the probability that a combination of values exist that will result in failure, i.e. low strength parameters and high load values, the likelihood or probability of collapse can be determined. This provides a rational means for ranking the safety of bridges that can be used in determining priorities for selecting structures for strengthening or replacement.
By incorporating the COBRAS collapse analysis technique within a reliability analysis framework, a powerful new analysis tool has been developed for investigating the strength and safety of concrete bridges.
Dr Campbell Middleton
Dr Victoria Hogg