Shear strengthening of existing reinforced concrete columns by pre-stressed steel strips: experimental outcomes

Existing Reinforced Concrete (RC) buildings generally are vulnerable to seismic actions worldwide, often exhibiting shear failures, especially in high-seismicity areas, like Italy. According to obsolete technical or seismic codes in force in Italy until ‘80s, columns generally have a minimum amount of transverse reinforcement, thus often requiring a seismic improvement. Different strengthening techniques are nowadays spread in common practice to solve such critical failure typology, by means of FRP wrapping, RC or steel jacketing. This paper experimentally analyses the effectiveness of pre-stressed stainless steel strips (CAM ® technology), which are externally applied on shear-critical RC columns to increase their shear strength without changing lateral stiffness. Cyclic pseudo-static tests are carried out under increasing top displacement on nominally identical cantilever columns, comparing the as-built condition with different retrofitting layout. Experimental results are described in terms of damage evolution and global response. Code prescriptions about the design of this technique are assessed based on the main experimental outcomes to provide suggestions for future optimization in the retrofitting design.