Structural Optimization, Crashworthiness and Strength Analysis of Midi – Bus Structure in Static and Rollover Condition

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Addis Ababa University


Midi-buses are a valuable vehicle to transport services and goods in Ethiopia's rural and urban areas. However, midi-bus are indirectly regulated through inspecting the end product (finished bus) during licensing for the public transport business in Ethiopia. Because of the lack of engineering analysis and testing procedures, the reliability and crashworthiness of a midi-bus are compromised and ultimately costing human lives and the overweight of the bus. Moreover, the weld formation and their types have been done without scientific reasons. Consequently, this method leads to a catastrophic structural failure during accidents. This research aimed to analyze the original midi-bus structure based on the static strength and rollover analysis using United Nations Regulation 66 via numerical investigation (ANSYS & LS-DYNA). Moreover, four design optimizations of the midi-bus structure were conducted: reinforcement design (����������������; numerical optimization (Response Surface Optimization (RSO) in ANSYS DesignXplorer for static case (model – IIstat); Successive Response Surface Method (SRSM) in LS-OPT for rollover case (model – IIroll)); and combined design approach (model - III) by merging of the static and rollover optimized models. Furthermore, the effect of full and spot arc welding on the quasi-static analysis of floor-wall and roof-wall connections was evaluated. The result shows that the maximum deformation in static and tare-weight rollover cases occurs at the baseline structure's roof section and pillar A and bays from one to three, respectively. The bending stiffness of the reinforced design (model – I), model – IIstat, and model – III (combined) was increased by 41.65 % (1911.4 N/m), 55.8 % (2,563.1 N/m), and 58.1 % (2,667 N/m), as compared to the baseline structure. Moreover, compared to the baseline model, the structure's weights of the reinforced model (model – I), model – IIstat, and model – III (combined) were effectively reduced by 5.23 %, 7.73 %, and 2.33 %, respectively. In addition, model – IIroll exhibited the weight of the reinforced model by 5.6 % in the rollover case. During structural connection, full and spot arc welding are formed at the edges and corners of the frames. Accordingly, these types of welds highly affect the energy absorbing capacity of the floor-wall and roof-wall connections. Generally, this research gives vital information on the midi-bus structure weight, stiffness, and crashworthiness capability from slight to severe loading cases for both static and rollover conditions. Moreover, this research suggests the new optimized bus structure and better weld type while welding the structural connections.



Crashworthiness, Deformation, Finite Element Methods, Midi-Bus; Reinforcement, Response Surface Optimization, Rollover, Static Strength, Structural Optimization