Reliability-Based Design Optimisation of Bridge Systems Within BIM—Robustness, Redundancy and Safety Metrics

Research shows that structures are often over designed in reliability-based calculations compared to code requirements. To address the knowledge gap in applying Reliability Based Design Optimisation (RBDO) within Building Information Modelling (BIM), this paper presents a novel BIM-integrated RBDO system for highway structures aimed at reducing over design. The approach is aimed at optimising the system reliability index. This value is then applied to the BIM model of the structure as a direct safety metric describing the probability of failure. In addition, minimum robustness and redundancy indices can be derived using this approach to ensure overall compliance with structural design codes, (Eurocodes), yielding key BIM model safety metrics. The system reliability index was optimised by utilising target limit state reliability indices to derive system difference target limits. System element reliability indices were effectively increased or reduced by manipulating element resistance parameters. An optimisation algorithm was employed to ensure compliance with the minimum system difference target limits. A secondary verification was undertaken to ensure minimal element target reliability indices were not compromised. The system reliability-based case studies on one-span bridge structures demonstrated that optimisation resulted in an overall 15% reduction in design resistance compared with the Eurocodes design method. In addition to highlighting element overdesign, the balance between safety and economy is improved by yielding comprehensive structural system safety metrics as a safer approach than direct element reliability-based optimisation.