Incremental seismic retrofitting of infill walls using plastic joints and fiber-reinforced mortars: LCA, analytical modeling and size effect assessment

In high-seismicity areas, the behavior of non-structural components like double-layer infill walls is critical to building safety and post-earthquake functionality. This study introduces an incremental seismic retrofitting strategy that combines plastic dissipative joints and fiber-reinforced mortars (FRMs) to restore and enhance wall performance after significant in-plane (IP) and out-of-plane (OoP) damage. Plastic joints preserve panel integrity through controlled sliding and crack mitigation, while FRMs recover safety levels without requiring the removal of damaged infill. The incremental approach consists of a sequential intervention strategy carried out in distinct stages: i) plastic joints for damage prevention under moderate-to-high seismic events, and ii) FRMs for post-event reinforcement when damage exceeds the effectiveness of joints. This approach allows performance-based upgrades with reduced demolition, cost, and environmental impact. Experimental results are supported by analytical models and a Life Cycle Assessment (LCA) is proposed to evaluate the effectiveness of the Incremental Retrofitting Technique (IRT). Experimental results highlighted an out-of-plane size effect, with the flexural strength of fiber-reinforced mortar layers decreasing markedly when applied to full-scale masonry elements compared to standard laboratory prisms. To account for this behavior, an empirical bivariate fitting was performed, introducing two dimensionless parameters to represent the effect of structural scale and partial section utilization. The fitting expression enables a rational estimate of the nominal flexural strength in full-scale structures. Key findings indicate a full recovery of IP strength (C/NC = 1.13), a 50 % improvement in OoP capacity, and significant environmental and economic benefits of IRT over reconstruction, with savings up to 61 % in LCA indicators. The proposed size-effect model accurately predicts flexural behavior, with a deviation of only 4 % from experimental results.