Conceptual Electric Bus Body Structure with Battery-Integrated Pillars: Beam-Based Finite Element Modelling and UNECE R66 Rollover Assessment

The electrification of urban buses under forthcoming Euro 7 regulations requires new structural solutions ensuring both safety and efficient mass distribution. This study proposes a novel conceptual electric bus body structure with battery-integrated inter-window pillars, in which energy storage systems are embedded. The concept was evaluated using finite element analysis in ANSYS under UNECE R66 rollover conditions by comparing an original diesel configuration (O-model) with a battery-integrated electric (B-model) one. Despite a substantial increase in body mass (from 1947 to 5464 kg), the B-model demonstrated improved structural performance. The maximum deformation decreased from 1489.5 to 1319.7 mm, while the difference between the control point displacements decreased from 32.21 to 12.68 mm. The average relative deformation of pillars decreased from 8.48% to 3.59%, and the intrusion amplitude was reduced from approximately 566 to 167 mm. Analysis showed comparable peak von Mises stresses (414.62 MPa vs. 439.19 MPa), but the B-model exhibited a 6.7% reduction in critical regions and a 16.9% decrease in average stress levels. The B-model remained within the elastic regime at the end of the simulation, whereas the O-model showed residual plastic deformation. The results indicate that integrating battery systems into load-bearing pillars leads to improved structural stiffness and deformation behaviour under rollover conditions, while full certification-level verification of UNECE R66 compliance is beyond the scope of the present study.