Evaluation of Influence of the Integrated Welded Handrail System in the Bus Body Frame on Strength and Passive Safety

Achieving the EU 2030 target of a 30% CO2 reduction requires transitioning intercity buses to CNG- or fuel-cell-driven vehicles, and urban buses to electric vehicles. The increasing mass of roof-mounted energy systems, such as battery packs, creates additional loads on the body frame. This study investigates the integration of a welded handrail system into the bus body frame as an additional load-bearing element. A combined approach based on dynamic modeling and finite element analysis was applied to evaluate the structural body response under the UNECE R100 and R110 regulations. The results demonstrate that the structural concept significantly improves the stress–strain state of the body frame. Maximum roof displacements under 5g loading decreased by 34% for the gas-powered model and by 50% for the electric model, enhancing passive safety by reducing window-rack intrusion. Maximum stress decreased by 20%, shifting the stress state below the ultimate strength of S235 steel and preventing rupture. Uniform strength under vertical loading increased significantly (by 58%) due to a more favorable stress distribution within the structure. Overall, the results indicate that integrating a welded handrail truss into the bus body frame can effectively improve structural stiffness and redistribute loads within the frame.