A Local Authority’s Risk-Based Approach to Principal Inspection Frequency of Structures

Gary McGregor, Slobodan B. Mickovski

Last modified: 2017-02-28


Scotland’s bridges are an integral part of its infrastructure, therefore it is imperative that they are inspected and maintained correctly. Current standards state that general inspections (GI’s) are carried out every 2 years and principal inspections (PI’s) every 6 years. This study examines a risk-based approach to principal inspection frequency and development of a tool for relevant structures. The current inspection practices were investigated with regards to the research behind the existing inspection intervals. A full literature review was carried out on a number of case studies and documents to ascertain all options that could be utilised for a risk-based approach of this type. The major factors that could affect the structural stability of highway structures were explored and a shortlist of factors was finalised. These factors were weighted against each other, e.g. Bridge Condition Index (BCIcrit) weighted higher than span length of the structure. Individual variables were researched for each factor and rated in accordance to perceived risks. All factors are used and an inspection frequency score is output from the assessment as well as a risk score for the structure. The results presented will assist the Bridge Manager of a Local Authority (LA) to organise PI’s on each structure within their stock based on its risk profile. Engineering judgement and knowledge of the structures will require to be used to complete the assessment tool for risk-based approach to PI frequency of structures. The main benefits of establishing a risk-based principal inspection frequency are reduced cost, higher level of safety and best value optimisation of resources.


Risk; inspection; frequency; reliability; local authority; structures

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