ABSTRACT Simulated ground motions are increasingly used in earthquake engineering, particularly in regions with sparse strong‐motion recordings where constraining non‐ergodic ground‐motion models (GMMs) remains challenging. Physics‐based simulations (PBS) can reproduce key source and wave‐propagation effects but are often limited to low frequencies, whereas stochastic methods are computationally efficient but typically lack physically coherent three‐component behaviour and realistic near‐fault features. Here we develop a hybrid broadband framework with three main innovations. These comprise: (i) an enhanced artificial neural network (ANN) that predicts short‐period spectral accelerations (SAs) from long‐period PBS SAs and scalar source‐site predictor variables while jointly modelling the three ground‐motion components; (ii) a transfer learning strategy that enables regional calibration in data‐limited settings; and (iii) an explicit multivariate correlation model for within‐event residuals that introduces realistic broadband dependence across space, periods, and components. The approach is validated using regional 3D PBS of the M w 6.5 and M w 6.4 June 2000 South Iceland earthquakes. For this case study, the resulting broadband fields reproduce observed short‐period attenuation and near‐fault saturation, are consistent with local Icelandic GMM trends, and preserve physically plausible directionality and component ratios comparable to empirical models. Inter‐period correlations of within‐event residuals follow established empirical trends and, importantly, remain continuous across the stochastic–PBS transition, while spatial correlation ranges are comparable to published observations. Owing to its computational efficiency, the framework provides a practical basis for generating spatially and spectrally coherent broadband ground‐motion fields for scenario‐based hazard and risk applications.
ABSTRACT Although drywall partitions are generally regarded as non‐structural elements, they interact with the primary structural frame and can significantly influence the structural response during seismic events. This study presents a full‐scale experimental investigation to quantify this seismic interaction and validate a novel polymer‐based isolation strategy, denoted as SISPYL. Two identical full‐scale, two‐story reinforced concrete buildings were subjected to quasi‐static cyclic loading. One building featured standard rigid drywall partitions, while the other incorporated the isolation system, replacing specific sections of the rigid gypsum core with a deformable polyurethane polymer at both perimeter and connection interfaces. The standard rigid installation exhibited an initial lateral stiffness of 20.93 kN/mm. This rigid composite action triggered a dominant membrane behaviour, transferring severe localised shear forces to the structural connections. This induced a premature soft‐story mechanism at the ground level, culminating in widespread structural and non‐structural failure before a roof drift ratio of 1.62%. Conversely, the deformation decoupling achieved by the SISPYL system reduced the initial lateral stiffness by 32.4% (to 14.15 kN/mm) compared to the standard configuration. This isolation prevented the transfer of damaging membrane forces, mitigated shear damage in the reinforced concrete joints, and restored a uniform story drift distribution. Consequently, the isolated frame accommodated lateral deformations up to a roof drift ratio of 2.39% while developing its intended distributed flexural yielding. Finally, the isolated configuration exhibited a stable equivalent viscous damping ratio between 5% and 6%, aligning the structural response more closely with code design assumptions for non‐interacting infills.
ABSTRACT Equivalent‐frame modeling is a common approach for assessing the seismic response of unreinforced masonry buildings, given its ability to capture the main failure mechanisms of masonry panels without the complexity of micro‐modeling techniques and the associated computational burdens. Typically, the equivalent‐frame strategy assumes that the out‐of‐plane response of walls is negligible, and the analysis focuses on the global building response governed by in‐plane panel mechanisms, reproduced through macroelements corresponding to vertical piers and horizontal spandrels. However, there might be cases where accounting for the coupled in‐plane and out‐of‐plane response is essential for a comprehensive description of the nonlinear behavior of the structure, even when local out‐of‐plane overturning mechanisms are inhibited through adequate structural details. For this reason, this paper presents a two‐node three‐dimensional macroelement that enhances the capabilities of the well‐established bidimensional formulations already implemented in computer programs, effectively and efficiently capturing the bidirectional axial‐flexural response in both elastic and nonlinear regimes. Two sectional integration approaches are proposed for the axial‐flexural response: a stripe formulation that optimizes computational efficiency through bidimensional analytical stress integrations, and a fiber discretization that allows versatility in defining constitutive laws. Three independent shear failure criteria are also implemented. The presentation of the macroelement is completed by an explicit demonstration of the energetic equivalence with a force‐based beam‐column element and by a detailed discussion on the inclusion of second‐order geometrical effects. The capabilities of the proposed macroelement are validated through the simulation of in‐plane and out‐of‐plane quasi‐static cyclic shear‐compression tests on masonry piers characterized by different masonry typologies, aspect ratios, and axial‐load ratios, demonstrating its accuracy and reliability. Moreover, numerical simulations carried out with the proposed formulation demonstrate the opportunity of including in‐ and out‐of‐plane interaction in numerical simulations.
ABSTRACT Actuator saturation forces two controller‐design choices: how to impose the force limit and how to represent post‐yield softening. We isolate the two choices on a reproducible OpenSeesPy reimplementation of the 3‐story and 9‐story Ohtori SAC steel‐frame benchmark structures, checked against published modal frequencies and selected uncontrolled response peaks. A matched finite‐horizon two‐by‐two factorial crosses elastic versus softened design models with post‐hoc clipping versus in‐QP actuator bounds. Across 44 3‐story evaluations using 22 FEMA P695 far‐field records at two intensity tiers, constraint handling accounts for 82% of the descriptive variance among four pooled cell‐mean costs, frequency tuning for 14%, and interaction for 4%; in the 9‐story 10‐case common‐finite‐score canonical subset the constraint‐handling share is 99.5%. Elastic in‐QP has the lowest mean under all five weight sets, yet under the primary score it loses to matched elastic clipping in 12 of 44 cases, with losses more frequent at larger uncontrolled drifts. Design‐frequency retuning stays small and inconsistent (elastic‐minus‐softened mean margin ); yield‐adaptive updating gives no consistent improvement, and a softening‐capable constitutive branch retains the principal ordering. In the transferred magnetorheological‐device comparison, powered operation reduces casewise peak drift by 19.9% on average but has a higher mean cost than zero‐current operation, and separate collapse‐limit analyses do not establish a consistent advantage for either allocation rule. For the primary score, the results prioritize actuator‐bound handling over the tested frequency retuning within the two planar frames, retaining clipping as a high‐demand comparator rather than a validated switching fallback.
ABSTRACT Torsional response remains an important concern in the seismic performance of base‐isolated structures. In this study, a full‐scale shake table test was conducted on a three‐layer FPB‐isolated structure, together with numerical simulations and bearing component tests, to investigate its torsional behavior and three potential sources of torsion: superstructure flexibility, pressure dependence of the friction coefficient, and bearing‐to‐bearing variability in the friction coefficient. The results show that, compared with the transient eccentricity ( ε k ), the proposed effective transient eccentricity ( ε s ) provides a clearer indication of torsional response because it directly represents the effective lever arm producing torsion. Superstructure flexibility increases ε s by altering the instantaneous distribution of inertia forces, although the resulting torsional displacement amplification remains limited. The torsional response observed in the shake table tests is mainly associated with variability in the friction coefficient, whereas the pressure dependence of the friction coefficient has a relatively limited influence. These findings provide a mechanical interpretation of the torsional response of FPB‐isolated structures and highlight the importance of considering variability in individual bearing properties in torsional assessment.
