Life-cycle cost simulation and optimization modeling for coastal structures using Markov Chains and Genetic Algorithms

Abstract

While extensive research has been carried out on the management of various types of infrastructure assets, limited research was allocated to coastal structures. The rapid world demographic growth especially in low-lying areas within close range to the shoreline over the past centuryas well as global climate change have given more importance to coastal infrastructure management. Climate change has increased storm intensities while decreasing storm return periods; imposing further risks to life and property. The aim of this research is to provide a modeling methodology for deterioration prediction, and optimization of repair, maintenance, and rehabilitation costs of various sorts of coastal protection structures. The coastal protection structures in Alexandria, Egypt, represent the case study. An Asset Inventory Database for Alexandria's coastal assets was developed, comprising 43 structures occupying an approximate length of 18.50 km. Established visual inspection and condition rating procedures were followed to obtain a current Structural Condition Index and a Structural Condition Matrix for each reach and each structure, considering a single inspection point in 2013. Structural Indices and Structural Condition Matrices (SCM's) are classified into severity ranges. Transition probabilities between structural condition ranges were calculated using backward analysis considering an excellent structural condition at the year of construction. Such probabilities were then utilized to formulate the structure's Markov Chain transition probability matrix, enabling the prediction of future deterioration. Integration of single-time random events, namely intermediate and design storms; was also performed on the future deterioration forecast. Maintenance and repair policies and their associated costs were determined, according to which a Genetic-Algorithm-based Life-Cycle Cost (LCC) optimization modeling was constructed with the aim to optimize maintenance and repair cost for the next 50 years, all while achieving the minimum reliability of structures. Results of the optimization are then presented collectively for the entire group of coastal structures within the study area.