Parametric study on the in-plane performance of a steel frame retrofit solution for URM buildings using DEM

Significant advances in the field of innovative solutions for the seismic retrofit of existing buildings can be made by coordinating experimental testing with the development of reliable numerical models. In this work, numerical models based on the Distinct Element Method are employed to simulate the in-plane lateral response of unreinforced masonry piers strengthened with a novel retrofit solution consisting of modular steel frames fastened to the external surface of masonry walls. All masonry in-plane failure mechanisms as well as the contribution of the retrofit system are explicitly included in the modeling strategy. The developed numerical models, validated on available experimental data, are employed to achieve a comprehensive insight into the performance benefits of the proposed retrofit solution, numerically accounting for different masonry typologies, vertical overburden stresses, and pier aspect ratios, as well as alternative retrofit layouts and detailing. Time, size and mass scaling, and dynamic relaxation procedures, combined with the use of monotonic loading schemes, provided a significant reduction of computational effort, enabling the parametric study to be carried out in a reasonable amount of time. Overall, the results quantify the performance benefits of the investigated retrofit method, with particularly noticeable improvements in pier drift ratio capacities. The achieved outcomes serve as a benchmark for the development of design guidelines, facilitating the proper assessment of the retrofit contribution in real-practice applications.