ABSTRACT
Many nations around the world have a significant proportion of their road bridges approaching end of life. As an example, over 25% of New Zealand’s existing State Highway bridges were constructed over a 15 year period between 1926 and 1941, many of which are expected to require significant repairs or replacement within the next 10-15 years. In addition to an aging asset, vehicle load requirements are also continuing to increase with a strong demand for heavier vehicles on roads. In New Zealand, the introduction of high productivity motor vehicles (HPMV’s) has significantly increased the demands on existing road infrastructure, causing loads in excess of the capacity of most road bridges constructed prior to the early 1940’s. Therefore, it is becoming essential for asset owners to utilise modern optimisation techniques to extend the life of these structures to avoid having to replace or strengthen a large number of bridges over a short period of time.
This paper outlines a case study of how modern optimisation techniques have allowed the longest bridge in New Zealand, the Rakaia River Bridge, to support increased loading without the need for costly strengthening or replacement. Optimisation has involved a wide range of conventional and state-of-the-art techniques, including materials testing, verification of boundary conditions, advanced modelling calibrated with field testing, and calculation of a statistically appropriate load factor and bridge specific impact factor. By refining both the capacity of the structure and the load demand, a significant increase in the bridges theoretical capacity was achieved, saving the asset owner over $10 M in strengthening costs.
