Bridges

This paper outlines the philosophy and engineering principles underpinning the new Austroads Guideline to Bridge Assessment.

Devotees of engineering history will observe that the fundamental engineering principles contained within the Guideline have not changed since Roman times. While our understanding of uncertainties has improved over time, the approach to understanding and managing uncertainties has not. Since engineers are designing and managing structures in the physical environment, using materials with variable properties to carry future unknown loads, and using mathematical models to describe complex structures, uncertainties will always be present.

The focus of bridge assessment in the context of the Guideline, is the management of access to bridges by heavy vehicles. The distinct roles of the road agency and assessor are set out in the Guideline. While an assessor is typically focussed on analysis and calculations, the road agency must consider other issues being managed by the road agency. The Guideline will assist assessors to prepare more reliable bridge assessments and road agencies to understand and manage risk, so encouraging better decision making.

The Guideline adopts risk-informed decision-making as outlined in AS 5104:2017, General principles on reliability for structures, as its basis for bridge assessment. While the Guideline utilises much of AS 5100:2017, Bridge design, which is familiar to engineers, the standard is unsuitable for bridge assessment due to its design focus and restrictions due to its format as an Australian Standard. Risk-informed decision making provides a richer basis for engineers to understand and manage bridges.

The paper will inform bridge asset owners and assessors about what to expect in the new Guideline and why it is so different to what they may currently be familiar with, despite the timeless underpinning principles.