Vertical accelerations in seismic analysis: A numerical investigation of their effects on URM structures

This article presents a numerical investigation into the influence of vertical ground motion on the global seismic response of unreinforced brick-masonry buildings. Vertical accelerations of significant intensity can cause variations in gravity-induced loads, affecting the in-plane lateral capacity of masonry piers. This study employs a suite of numerical structural models to explore the damage potential of vertical accelerations on a masonry building through earthquake simulations. The building features piers with varying aspect ratios, axial loads, and shear resistance. The models are developed using the equivalent-frame modeling approach and nonlinear macroelement within the TREMURI software. Initially, the study demonstrates the capability of the numerical models to replicate dynamic responses under combined horizontal and vertical seismic inputs. The predictive accuracy is validated through simulations of multidirectional shake-table tests on full-scale structures under near-source ground motions. Subsequently, the validated models undergo cloud analysis using unscaled three-component ground motions from earthquakes with moment magnitudes 5–7 and short epicentral distances (below 30 km). The findings indicate that vertical accelerations do not cause considerable differences in global seismic behavior. Any effect on maximum displacement demands for walls with varying geometric and mechanical properties appears random and negligible. Vertical accelerations may only become relevant under certain synchronization scenarios between horizontal and vertical motions, which are rarely encountered in natural settings. This study underscores the importance of considering vertical earthquake motion in seismic analysis yet highlights its generally limited effects on regular masonry structures.