Strength and safety assessment of concrete bridges

by C.R.Middleton

A new technique for evaluating the ultimate strength of concrete bridges has been developed which enables a wide variety of bridge types and plastic failure mechanisms to be analysed.

Many of the existing difficulties with plastic collapse and yield-line methods, which previously limited their application to simple slab configurations, have been overcome using computer graphics and solid modelling concepts. In contrast to the traditional yield-line approach, the effect of any load combination on complex failure modes can be evaluated rigorously without the need for mathematical expressions relating the failure mode geometry to the bridge structure and the applied loading. In addition, provision for compressive membrane strength enhancement, "realistic" steel arrangements, and the effects of steel corrosion and concrete deterioration can be included.

This generalised collapse analysis method has also been incorporated into a reliability analysis format to evaluate the safety or notional probability of failure of concrete bridges. As a result the effects of variability of the parameters that govern the behaviour of these structures can be studied. This provides a rational method for ranking the safety of bridges which can be used in determining priorities for selecting structures for strengthening or replacement.

A computer program has been written to implement these techniques and evaluate the two measures of structural safety (i.e ultimate strength and reliability for the more common types of concrete bridge under the influence of any loading and/or deterioration of the material components.