# Risk-Based Selection of Inspection Method for External Post-Tensioning System of Bridges
###### Abstract  
The increasing complexity associated with the maintenance of bridges with post-tensioning tendons, along with growing public awareness to ensure higher levels of safety in bridges, has put additional pressure on the designers and the owners to find innovative solutions to ensure safe as well as economically viable solutions. Risk-based inspection and maintenance helps in finding such solutions and, thus, it is gaining more importance in the field of infrastructure management. Within the framework of current risk-based inspection methodologies, it is normally assumed that the method by which the inspection is performed is known beforehand. However, the selection of the inspection method by itself should be given importance and viewed as the first key step for any inspection. The lack of quantitative data in the initiation step makes this selection uncertain and the decision making rather subjective. Despite recent release of comprehensive reports and other publications on condition assessment of bridges with post-tensioning systems, a quantitative approach and a decision-making framework for the selection of the inspection method and associated protocol are still missing, and the inspection strategy and methods are determined purely by the experience of the inspector or the owner. In this paper, a simple and structured risk-based selection methodology is presented that can bridge the existing knowledge gap. The proposed methodology uses a statistical approach to quantify the likelihood of the inspection error utilizing a variety of applicable NDE (Non-destructive Evaluation) methods. To give the methodology both accuracy and practicality, the specifications for the national bridge inventory (SNBI) condition rating was incorporated in this methodology and the accuracy of the inspection methods are measured against determining the correct SNBI condition. Application and effectiveness of the proposed methodology are demonstrated using a case study inspection conducted earlier by the authors. The results, in this case, converged to the selection of one of the NDE methods, which consequently was accepted by the bridge stakeholders. risk-based inspection; NDE Methods; risk-based maintenance; aggregative risk analysis; bridges; post-tensioning system; post-tensioning elements +
Footnote †: journal: Applied  
framework for risk analysis and decision-making, which is used in developing inspection and maintenance programs. Risk-based selection of inspection method can be used to identify the methods by which the inspections will provide the most benefit in reducing the overall risk. The complexity of a post-tensioning system and tendons in relation to installation, maintenance, and operation has been increasing steadily. This, combined with the growing usage of post-tensioned structures owing to the efficiency of structural cables and tendons, has motivated the designers and operators to find innovative solutions to ensure a safe as well as an economically viable operation. Risk-based selection of the inspection method can help in finding such solutions. Accuracy of the inspection method generally plays an important role in ensuring safety as well as providing the necessary information for secondary structural analysis and bridge condition rating. Employing techniques with a low accuracy may incur a lower initial cost but may produce higher maintenance and failure rates in time and vice versa. The trade-off between the accuracy of the inspection (maintenance cost) and the risk resulting from the associated lower safety level is achieved through the principle of 'as low as reasonably practicable (ALARP)'. Risk is considered to be ALARP once the cost of further risk reduction can be shown to be grossly disproportionate to the benefits accrued [5]. In the last two decades, a wealth of literature has become available that addresses this subject extensively. Different methodologies were developed and applied within different industries.