Bridges

New Zealand (NZ) has introduced High Productivity Motor Vehicles (HPMV’s) to improve freight efficiency on its road network. The significant increase in vehicle mass limits has required a national bridge load capacity evaluation and strengthening program.NZ has approximately 4,000 State Highway bridges and 14,000 Local Authority bridges. Initial screening of these bridges, based on available structural data, design loading, age, configuration and span length was undertaken. For critical bridges, further inspection and condition assessments, material testing and grillage analyses were undertaken to optimise load capacity. A risk-based approach to load evaluation used a whole-of-life cost approach, reduced load factors, structural monitoring and inspection monitoring to maximise bridge load capacity. Selective strengthening of bridges on specific routes was driven by strong economic outcomes.The HPMV implementation program has resulted in a much improved understanding of bridge load capacity nationally. Risk-based load capacity evaluation has been shown to be very cost effective, maximising capacity and allowing retention of older bridges. Whole-of-life cost analysis strongly supports increasing bridge load capacity, even at the risk of possible increased maintenance cost resulting from higher stress levels. Where necessary, strengthening bridges to increase load capacity rather than replacing bridges, supports sustainable management.