Structural Optimization, Crashworthiness and Strength Analysis of Midi – Bus Structure in Static and Rollover Condition
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Date
2021-10
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Addis Ababa University
Abstract
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.
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Keywords
Crashworthiness, Deformation, Finite Element Methods, Midi-Bus; Reinforcement, Response Surface Optimization, Rollover, Static Strength, Structural Optimization