ROPS Design Evolution with Respect to the Requirements of the Strength Test Procedures

A standardised strength test for Rolling Over Protective Structures (ROPSs) fitted on agricultural tractors was first introduced in 1967 and was based on a dynamic procedure (OECD Code 3). A static test procedure for protective structures, currently adopted worldwide, was added in 1983 (OECD Code 4) in order to resolve some limitations of the dynamic procedure. The advent of narrow track tractors required the adoption of ad hoc ROPS standardised static testing procedures for these special tractors (OECD Codes 6 and 7, 1991). Static ROPS tests provide a sequence of loadings, determined on the basis of the tractor reference mass while ensuring a survival volume for driver protection in the event of a tractor rollover. Over the years, the procedure requirements in terms of force and energy applied and clearance zone to be respected have remained substantially unchanged. In the meantime, agricultural tractors have undergone a deep technological evolution in design and normal operation in the field. In this context, it was considered appropriate to assess if, over the years, the ROPSs tested according to the static procedure have undergone a similar evolution in design and in the mountings on the tractor chassis to evaluate if the modifications affect the performance and the requirements of the testing procedure. The ROPSs fitted on standard and narrow track tractors tested at the University of Bologna in the last twenty-five years according to OECD Codes 4 and 7 were analysed. The ROPSs considered were the four-pillar frame and the cab types. The evolution of the ROPS design over time was evident. Cabs in both standard and narrow track tractors normally replaced the four pillar frames. In standard tractors, the ROPS cabs were progressively integrated to the tractor platform and the rear mudguards, and the latest application seems to be represented by cabs which were suspended on the rear of the tractor chassis. In narrow track tractors, a similar trend in terms of progressive integration of the cab to the tractor platform and the rear mudguards was observed but low profile highly rounded cabs exemplify the most modern approach. Different behaviour of the ROPSs was observed during the official strength tests. The cabs integrated to the tractor platform showed a shift in the vertical reference plane during lateral loading, affecting survival volume evaluation. Difficulties in identifying the loading points, in the case of low profile highly rounded cabs, were evident with respect to specific Code provisions.