Modal Analysis of Bus Roll Cage Structure for Optimum Rollover Design

Improvement of vehicle stability and crashworthiness to reduce rollover and to provide increased occupant protection in the event of rollover requires that the effects of design parameters on vehicle rollover propensity are thoroughly understood. Improvement of rollover characteristics of buses currently requires extensive experimentation and considerable resources associated with rollover destruction of experimental bus structures. There is an unmet need for a more efficient developmental process which would incorporate computer modelling and simulation. This paper presents an alternative research approach based on experimental and analytical modal analysis of the bus roll cage structure. Modal analysis is used to identify the dynamic characteristics of the structure and to tailor those characteristics in order to increase the overall rollover stability of the bus and its rollover strength while minimising the deformation of the internal residual space. Full scale tests have been carried out on a standard roll cage structure which has been designed and manufactured to suit typical two axle single deck bus constructions used for route, school or charter bus services.