Retrofitting method using fiber with high tensile strength namely Aramid and Carbon has successfully proven increasing both shear strength and ductility of reinforced concrete structural members. The drawback of these fibers is its low fracturing strain property which causes brittle failure at the time the fiber breaks. This book focuses on fiber with high fracturing strain and low tensile strength such as PET as retrofitting material for reinforced concrete specimens representing bridge piers tested under reversed cyclic loading. PET fiber breakage did not occur and higher shear capacity and ductility were obtained compared to that of specimens retrofitted with Aramid and Carbon. The high fracturing strain property allows bigger tolerance of fiber breakage resulting in slower decrease of shear strength capacity. Models to predict shear strength capacity and deformation with the key variable of increasing fiber strain as a representation of structural member deterioration are proposed and show good prediction of experimental result. The results should provide valuable information for civil engineer, construction company and industry specializing in structural retrofitting.