Ilhwan You

Concrete has been the most widely used construction material for civil infrastructure and buildings for the past several decades. Because of its excellent mechanical strength, low cost, and durability, it has been effectively applied to major structural elements, including columns, beams, slabs, etc., subjected to external loading. However, it has relatively poor tensile strength and toughness compared to those under compression, such that steel reinforcements, that is, reinforcing bars or prestressing strands, are generally incorporated, particularly where tensile stress occurs. This is because steel 250reinforcements show very ductile tensile behavior due to their yielding plateaus, have a similar coefficient of thermal expansion, and provide good bond performance with concrete. Thus, they have been broadly adopted for concrete structures. Such reinforced-concrete (RC) structures, however, deteriorate when steel reinforcements are corroded, mainly due to penetration of detrimental materials from outside concrete through cracks. In addition, concrete creep results in secondary stresses generated in RC structures, causing damage and structural integrity problems. Accordingly, structural health monitoring (SHM) techniques have attracted attention from engineers and researchers in order to monitor and investigate the structural integrity of existing large-scale structures [1].