Bridges

At present, a fixed Accompanying Lane Factor (ALF) is stipulated by the Australian Standard 5100.2 (2017) for use in the generation of traffic loadings to account for multiple presence of heavy vehicles.

The ALF is the same for both design of new bridges and the assessment of existing bridges. This one size fits all approach to specifying the ALF can lead to overly conservative assessments of existing bridges located on routes with low traffic volumes. In this research, the effect of heavy vehicle multiple presence was considered using a Monte Carlo simulation technique to estimate the maximum bending moments in bridge girders and determine associated ALFs due to randomly simulated combinations of heavy vehicle loadings. A loading distribution based on a heavy vehicle (HV) traffic volume of 2000 HV/day and an ultimate loading (2000-year return period) equal to a B-double overloaded to two times the legal mass was selected as the basis for the investigation. The research presented in this paper focuses on side-by-side multiple presence events on short to medium span bridges.

ALFs estimated from the Monte Carlo simulations were found to be significantly lower than the Australian Standard ALF for two lanes, and ranged from ~0.4 at 10 HV/day up to 0.7 at 2000 HV/day for simulations based on B-doubles only. A mix of heavy vehicle traffic was also simulated based on observed Hume Highway truck traffic, which resulted in lower maximum moments and ALFs compared with simulations for B-doubles only.

Overall, the results show that there is potential to reduce the ALF in bridge assessment by accounting for site-specific influences including traffic volumes and route heavy vehicle types.