Injected tie-rods improve out-of-plane masonry wall capacity

What the study found: Full-length injected tie-rods (FIT), a strengthening method for unreinforced masonry (URM) walls, improved out-of-plane (OOP) capacity and post-peak stiffness in the U-shaped walls studied, while initial stiffness changed little.
Why the authors say this matters: The authors say FIT is promising because it has practical feasibility and minimal visual impact on heritage masonry structures, and the study suggests it can provide a useful basis for designing retrofitted masonry walls.
What the researchers tested: The researchers used validated finite element (FE) modeling, parametric analyses, dynamic simulations, and a design-oriented kinematic approach to study U-shaped URM walls retrofitted with FIT. They compared solid-element and truss-element modeling strategies and calibrated the models against literature experimental data.
What worked and what didn't: Multiple tie-rods at two different heights and larger rod diameters were most effective, although the benefits decreased beyond a threshold diameter. Dynamic simulations showed better drift control and delayed failure across different excitations, and the modified kinematic method matched FE predictions with an average error of about 7%.
What to keep in mind: The abstract describes results for U-shaped URM walls and the specific FIT configurations tested. Limitations are not otherwise described in the available summary.

Key points

• FIT increased out-of-plane capacity and post-peak stiffness, but not initial stiffness.
• Multiple tie-rods at two heights and larger diameters performed best, with diminishing returns beyond a threshold diameter.
• Dynamic simulations showed improved drift control and delayed failure under different excitations.
• A modified kinematic method matched finite element predictions with an average error of about 7%.
• Truss-element modeling was as accurate as solid-element modeling and simpler for large-scale analyses.