Risk Based Asset Management
Risk Based Asset Management

Eurocode 1 – Basis of design and actions on structures”, like previous codes, is based upon the principles of limit state design. It is recommended that this limit state design should be achieved by the partial factor method, similar to many other international codes of practice.  However, the new Eurocode explicitly states that “As an alternative, a design directly based on probabilistic methods may be used”. Therefore, it is not necessarily a requirement of the Eurocodes that structures fulfil the generalised aspects of the Code once it can be demonstrated that the overall safety levels are achieved. This “safety level” is formally defined in terms of the acceptable probability of failure of a structure as a function of the consequence and mode of failure.

 

Risk Based Asset Management adopts this probabilistic approach to design and provides infrastructure owners and managers with the ability to optimise the way in which they spend their budgets in the provision and/or maintenance of new and existing infrastructural elements/networks. Adoption of a risk based approach ensures that those actions/decisions which have the greatest effect on the overall operational efficiency/performance of the system, in terms of whole life performance, are prioritised in a robust manner which is beyond the capabilities of traditional deterministic approaches.

 
ROD-IS expertise in this field covers
  • Probabilistic Design and Assessment of Bridges
  • Infrastructure Asset Management
 

The “generic” approach to the design and assessment of bridges structures using traditional codes is based on the following:

  • Adoption of partial safety factor format (for loads and resistances);

  • Load & limit state generalisation;

  • Application to a large number of bridge structures.

The benefits of using this approach are that it is efficient and easy to use, though the outcome is often conservative. In terms of the design of new bridge structures, the disadvantage of using this method is increased costs (particularly associated with long-span bridges). In terms of assessment of existing structures, the disadvantages lies in an underestimation of the load carrying capacity, remaining life and ultimately, the safety level of existing bridges. By adopting a probabilistic approach, the safe working lives of bridges can be considerably extended, often by decades with considerable monetary savings accruing to owners/managers.

For new bridge structures, the benefits of using a “Probabilistic” approach are as follows:

  • Structure specific information can be incorporated in a statistically consistent/robust manner to provide material and cost savings;

  • The safety level of the bridge and all constituent elements can be determined and documented at the end of construction and computed going forward for the service life of the structure. This will assist in planning Structural Health Monitoring strategies for structures over their lifetime;

  •  There are no practical or technical obstacles in applying probabilistic based design techniques.

For existing bridge structures, the benefits of using a “Probabilistic” approach for the assessment and rehabilitation of existing structures are as follows;

  • Probability based assessment using Structural Reliability theory has demonstrated, in many cases, greater inherent reserves of safety, thereby reducing maintenance interventions and/or replacement without compromise on the required level of safety. This results in significant capital cost savings by avoiding the need for strengthening and/or replacement of existing structures.

  • In cases where the structure is in a state of deterioration probabilistic based modelling can be used to; determine the optimal rehabilitation methodology by using a Cost Benefit Analysis; and monitor the safety of the structure during repair/rehabilitation.

  • For probabilistically assessed structures, the implication of proposed changes in legal load limits or of use during their life can be quickly assessed in terms of their effect on the structures safety.

 

Asset Management is defined in the International Infrastructure Management Manual as “the combination of management, financial, economic, engineering and other practices applied to physical assets with the objective of providing the required level of service in the most cost effective manner”. Central to this process is multi-objective optimisation incorporating probabilistic approaches. ROD-IS staff has extensive international experience in this area.

 

ROD-IS’s bases its analysis on the principles of Structural Reliability Theory.  This ensures that the structure under consideration has optimised performance throughout its lifetime, based on the estimation of its specific probability of failure at critical component and/or global levels. Whilst Structural Reliability theory is directly applicable to the assessment of existing structures (as information can be readily determined on the structural loads and resistances), the design of new structures using probabilistic techniques can also be employed to optimise whole life performance. Whilst the methodology may be applied to the design of any structure, its principal application lies in the design of long span or special structures.