Improving the Design and Analysis of Commercial Bus Structures Using Vehicle Performance Envelopes

A challenge in structural design is the inability to quickly assess how a change in use can affect the structural performance of the system. This is particularly important in the bus industry where there is often multiple variations of one base product type for many customers. Thus for a single design there can be frequent changes to mission profiles or customer constraints, which must be considered within short time periods before production commences for a particular customer. This can often limit full understanding of the structural performance, key structural features or critical failure modes, ultimately limiting the potential for producing buses with minimum structural mass. The proposed method in this paper aims to develop a design tool capable of rapidly informing structural design engineers with respect to the structural limitations of various vehicle components using performance envelopes. Vehicle performance envelopes define the combinations of global vehicle accelerations (lateral, vertical and longitudinal) that cause structural failure of any feature or component included in the envelope. Additionally, envelopes will enable definition of the critical (non-redundant) and redundant structural failure modes for each feature considered, e.g. material yielding, buckling or fatigue. For a section of an integral double-deck bus, this paper will demonstrate how these vehicle performance envelopes can be generated for shell panels, and how interrogation of these envelopes can enable a designer to rapidly identify the non-redundant and redundant loading constraints. In doing so, it is also possible to identify the critical failure modes that could cause failure of structural features, as well as quickly evaluating margins of safety for variable route or passenger loading to highlight particular structural features that may fail. This rapid evaluation of structural performance will not only support identification of redundant, or non-critical, components which can potentially be made lighter, but also quantitatively estimate the potential weight saving.