A Simplified Analytical/Experimental Method for Evaluating Large Buses and Motor Coaches for Rollover Protection

This paper discusses a simplified analytical/experimental method for evaluating and designing large buses and motor coaches for rollover protection. The proposed method makes use of the work-energy principle in analyzing the energy-absorbing capacity of the roof and sidewall structure of the vehicle. The basic structural unit is treated as a nonlinear, elastoplastic, 4-bar linkage, with the links connected at hinge points. During rollover, the deformation of the structure is focused at these hinge points and energy absorption is achieved through plastic bending and rotation of the hinge material. The proposed method allows the evaluation and design of these plastic hinges to achieve the energy-absorbing requirements for the vehicle. This paper demonstrates the proposed methodology by evaluating an exemplar large bus design against the European ECE-R.66 rollover design standard. This same vehicle was similarly evaluated in a referenced study, using the finite element analysis (FEA) method. The objective of both studies was to determine a minimum weight solution for the vehicle structure. The minimum weight solution must satisfy both the minimum energy absorption requirements and the structural deformation limitations placed on the design by the ECE-R.66 standard. Both a baseline design and an optimized (minimum weight) design were evaluated in this study. The baseline design served as a reference point in determining the weight-saving potential for the vehicle. The FEA results show a weight-saving potential of 78 kg (172 lb) while the simplified, 4-bar linkage model gives a slightly heavier design with a weight-saving potential of 34 kg (77 lb), indicating that the proposed method of analysis is slightly conservative compared to the FEA method.