Bridges

The previous New Zealand Bridge manual evaluation live loadings for normal traffic were based on multiples of the HN (normal) loading established in 1972, with 0.85HN intended to represent the unfactored effects of general access vehicles. Evaluation loadings for HPMV (high productivity motor vehicles) were set at 0.90HN (L<=25m) or 0.95HN (L> 25m) in the 2013 update.

A study on future design live loadings (NZTA research report 539) recommended that new evaluation loadings be based on multiples of SM1600 loading from AS 5100.2 or alternatively on higher multiples of HN loading. However, we found that neither option could provide consistent fits to effects of conforming vehicles at all span lengths. For HN loadings there are significant shortfalls for negative moment effects in continuous spans and scaled down SM1600 design loadings have a generally poor fit to single vehicle effects.

A goal for the development was to achieve closer harmonisation between the Bridge manual and AS 5100 if possible. Adopting the nominated rating vehicle approach from AS 5100.7 provided the opportunity to realise that goal.

The paper shows that maximum load effects for the full ranges of conforming HPMV and general access vehicles allowed by regulations can be fully represented by small sets of conforming vehicles. The candidate vehicle sets were reduced to three vehicles for full HPMV loading, four vehicles for general access loading, plus two extra vehicles for the 50 tonne (50MAX) loading level, with only minor compromises.

The new loadings provide dependable representation of the effects of conforming vehicles, without substantial overall increases across the full range of span lengths except where the significant shortfall in continuous span effects has been addressed.