Approach to Robust and Elegant Bridge Design

Abstract

In bridge planning, the successful translation of the many conditioning factors into a solution that meets all safety requirements while also addressing considerations such as economy and elegance is essentially a matter of conceptual design. Despite the utmost importance of that stage, which in addition to an intuitive understanding of load-bearing mechanisms calls for imagination and a sense of form and beauty, creative conceptual thinking is systematically underestimated both in engineering training and everyday practice. The resulting impoverishment of the profession stems not only from growing, need-driven and hardly reversible specialisation, but also from inexorably extensive and opaque standardisation and control. The rules for ensuring robustness reflect the increasing complexity and opacity characterising structural design codes. While the practical importance of designing and building robust structures is universally acknowledged, the codes presently in place are often vague or confusing. Cross-referencing, in turn, may lead to loops around rules that, confounding engineers, are counterproductive. At the same time, however, that lack of clarity may afford opportunities for innovative solutions by building items that ensure robustness into the conceptual design of a structure. This paper proposes an operational design process that deals appropriately with all factors of structural performance, including robustness, without compromising bridge economy or elegance. That process, which combines a number of robustness strategies, including risk-based considerations, is illustrated with a case study of a proposal submitted to a design competition for a viaduct.

New or existing, does it matter?

“…/ New or existing, does it matter? a) b) structural performance for some hazard scenarios and worsen it for others [16]. Given this situation, even for apparently robust solutions, it is of the utmost importance to unequivocally identify all relevant hazards and hazard scenarios and to take them into account appropriately in the analysis.…”

“…In such cases, the target reliability index should therefore be taken as the greater of β t,LR and β t,code . Under an operational criterion suggested [16], reliability requirements for human safety, β t,LR , are inferred from current best practices and represented in Figure 4 for a reference period of one year, varying with the area affected by the collapse, A col , and the respective Consequence Class, CC1 to CC3, as defined in the Eurocode [5].…”

“…They may be identified, then, as members in whose absence an anticipated load-bearing mechanism will develop only if suitable measures are adopted, i.e., if the corresponding structural behaviour can be verified with sufficient reliability. In terms of the remaining structural system left standing after key member failure, both the relevant design situations and the performance requirements depend on the design goal, e.g., rescuing any endangered people [16]. Given that in robustness verifications the possible failure of a key member is assumed to be due to an unidentified accidental situation, the required reliability for the remaining system, β t,rs , may be lower than calculated for persistent and identified accidental situations, since conditional reliability is envisaged [5].…”