The latest edition of AS 2809 allows the Performance Based Standards (PBS) Static Rollover Threshold (SRT) calculations as an alternative to prescriptive stability angle requirements.
Whilst this provides some additional flexibility for road tank design it does not necessarily mean higher tank centroid heights are possible using the PBS SRT assessment.
However, PBS does provide more flexibility in relation to controlling fill levels and slosh effects which can reduce payload CG height and improve stability. This may prove to be the most advantageous aspect of the AS 2809 changes for road tank designers and operators.
PBS SRT assessment is easily done with the PBS assessment software like Hevi Spec which takes suspension stiffness and geometry, tare weights, axle mass limits, axle spacing, weight distribution, centre of gravity, fill levels and tyre characteristics into consideration.
Australian Standard AS 2809.1-2020 road tank vehicles for dangerous goods general requirements for all road tank vehicles was released in September 2020. The new standard allows the NHVR PBS 0.4 g Static Rollover Threshold (SRT) standard as an alternative method of stability compliance.
Historically, AS 2809 has controlled road tank stability by prescribing the maximum tank centroid height base on a 64° (Rigid road tankers) or 62° (All other road tanks) maximum stability angle. The stability angle is the base angle of an isosceles triangle formed from the vehicle’s ground contact width and tank centroid height (see diagram).