Lightweight design of bus body can improve energy consumption and operating cost. Nonetheless, design for strength and crashworthiness of bus superstructure is vital to occupant safety during accidents. This work proposes a methodology to design an effective lightweight frame layout and member sections of bus superstructure under requirements of bending stiffness, torsion stiffness, and rollover safety conforming to ECE-R66 based on optimization techniques. The bus configuration is firstly resolved by iterative topology optimizations with the objective function based on the structural weight and compliance subjected to the maximum displacement constraints for each load case. Topology optimization offers a preliminary design possessing the required stiffness while its structural weight is decreased by 2.5 % from the baseline model. Gauge optimization is then applied to adapt the thicknesses of the frame cross-sections. Due to high computational cost of dynamic rollover test, the correlation between nonlinear rollover test and linear quasi-static test with an adjusted deformation limit is proposed to accelerate the process. The most significant design parameter to rollover safety is shown to be the roof structure. Weight distribution and energy absorption of structural components for different models are examined and discussed as the basis to good practice in design for safety.
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