Increasing the shear capacity of reinforced concrete beams using pretensioned stainless steel ribbons

In this work, the second part of an experimental campaign investigating the efficiency of an alternative retrofitting method for increasing the flexural and/or shear capacity in reinforced concrete beams, based on the use of prestressed stainless steel ribbons and steel angles, is presented and analytically reproduced. This group of tests focuses on the ability of the adopted retrofitting method to improve the shear strength and ultimate deformation of reinforced concrete structural elements. As described in a companion paper, the adopted retrofitting method is alternative to traditional techniques of reinforced concrete retrofitting, being easy to install and usually reversible, and characterized by high fire resistance and avoiding corrosion. The experimental results obtained from shear tests carried out on nine reinforced concrete beams are presented. The efficiency of stainless steel ribbons as shear reinforcement that wrap a portion of cross-sectional depth are analyzed, and the interaction between existing stirrups and stainless steel ribbons examined. The tests results are critically analyzed, highlighting the ability of the retrofitting method in increasing the shear strength and ductility of reinforced concrete beams. The experimental shear strength was also analytically evaluated by extending the theoretical approach of the fib Model Code 2010 formulation, originally suggested for reinforced concrete beams with or without stirrups.