Retrofitting performance of steel connectors in masonry: experimental study & numerical modelling

The multi-leaf wall is widely used in ancient masonry structures. The capacity is low due to the weak physical and mechanical properties of the infills and the weak adhesion between leaves. Out-of-plane instability is prone to occur under earthquakes, so it is necessary to reinforce the multi-leaf masonry structure. For experimental study, material characterization and a total number of 20 pull-out tests were carried out. The bond – slip curves of helical connectors inserted in masonry blocks were obtained. Linear regression analysis was performed. The FEA software ABAQUS was used for numerical simulation of the pull-out test. The constitutive law of the masonry was simulated by concrete damaged plasticity model. The complex contact surface between the helical connectors and the masonry is simulated by translator element. Furthermore, a FEA model of single panel of multi-leaf masonry wall was established, considering 7 various configurations of reinforcement, and was subjected to vertical compression and horizontal pushover, respectively. For vertical compression, the transversal connectors effectively control the lateral displacement of the external leaf and reduce the second-order effect, thereby improving the compressive bearing capacity. For horizontal pushover, the transversal connectors strengthen the integrity of the multi-leaf wall. As the reinforcement density increases, its out-of-plane stability is improved. Finally, the Civic Tower of Ravenna, Italy was selected for case study. The vibration modes were obtained by modal analysis, and the design response spectrum was obtained based on Italian seismic code. Pushover analysis was carried out, considering 5 configurations of reinforcement. It was found that the transversal connectors can significantly improve the seismic resistance. As the reinforcement density increases, the failure mode gradually transforms from local overturning of external leaf to shear failure of the side walls.