Bridges

The Auckland Harbour Bridge (AHB) is a steel truss bridge with welded orthotropic box girder extensions on both sides and provides a critical link over the Waitemata harbour. The logistical layout of the surrounding area does not provide any other economical crossing options which resulted in an annual average compound growth rate of over 4% in traffic volume since the extensions were opened in 1969. Even though growth has slowed recently due to congestion of the motorway network, truck volumes continued to grow at over 4% annually over the last few years [1]. A common phenomenon with low dead weight orthotropic steel decks is high stress cycles that are associated with truck loads. Weld detail on the aging box girder extensions of the AHB are therefore susceptible to fatigue cracking and the details with short remaining fatigue lives have been identified previously [2]. A quantitative cost based risk model was developed to rank the relative importance of the different weld details. A trial test, using acoustic emission monitoring (AEM), to optimize the sensor location with the aim of detecting cracks on the most critical weld detail was conducted. The results of the AEM test, the risk analysis as well as surfacing history on the extensions of the AHB were used to generate a weld inspection strategy for the asset owner (New Zealand Transport Agency) to detect fatigue cracks before they become surface breaking. The aim is to instill confidence in the continued operation and management of the AHB box girder extensions.