Cyclic behavior of twisted stainless-steel bar for masonry retrofitting

The demand for reversibility, compatibility and limited damage in masonry retrofitting led to the use of twisted stainless steel bars in many applications. However, limited studies are available in literature both on monotonic and cyclic behaviour. The study focuses on the comparison between performances under monotonic and cyclic loading, not only in terms of maximum load but also focusing on the ductility. Displacement controlled cyclic tests showed large residual displacement in the unloading phase, therefore a second test protocol without residual displacement (applying compression) were conducted. The performances were assessed considering bars installed in the middle of the brick and in mortar joint. Results showed very good performance with reliable results associated to low coefficient of variation of the loads and with a very limited damage of the base material. The load-displacement curves showed a good ductility, an excellent superposition between monotonic and cyclic tests, with an extended plateau. Among the different investigated parameters, the position within the wall was the most influential one, with higher loads and higher ductility associated to the location of the bar in the middle of the brick.