Earthquake Engineering & Structural Dynamics最新文献

Simulation-based seismic assessments rely on large ensembles of ground motions to represent site-specific hazards and evaluate structural performance, leading to high computational demands from both simulations and response evaluations. In practice, ground motion selection algorithms are used to extract a manageable subset for response evaluations, an arguably counterintuitive step in this framework with its own limitations. To address these challenges, this article introduces the MC-ROM approach, a two-step method that reduces the computational demands of simulation-based assessments, specifically adapted for the CyberShake framework. First, the Monte Carlo catalog method limits the number of simulations by selecting a smaller subset of earthquake scenarios that capture the site-specific hazard, reducing simulation time. Then, Reduced-Order Models (ROMs) are constructed for intensity measures that characterize the seismic hazard, selecting a small, representative subset of ground motions from the Monte Carlo catalog—thereby reducing response evaluations and associated computational effort. The effectiveness of MC-ROM is demonstrated through case studies at three CyberShake sites in Southern California. Hazard curves for elastic pseudospectral accelerations and inelastic demands generated using MC-ROM are similar to those from full CyberShake simulations, with maximum relative errors less than 5% and 9% at a 2% probability of exceedance in 50 years, respectively. Using only 2000 ground motions, the approach demonstrates a 94.9% reduction in required simulation workload and a 99.9% reduction in response evaluations compared to CyberShake. Both methods yield similar hazard disaggregation patterns, demonstrating the MC-ROM approach as an efficient tool for simulation-based seismic assessments and an alternative ground motion selection method for seismic demand analyses.

The 2021 Magnitude 7.4 Maduo earthquake resulted in complete damage to typical seat-type abutments and severe collapse of girders along the longitudinal direction of Yematan Bridge, a representative multi-span, multi-frame girder bridge. To address an urgent need for unveiling abutment failure mechanisms, this study performs comprehensive field investigations coupled with in-depth numerical analyses. Moreover, as an important boundary component for full bridge collapse analyses, a practical macro constitutive model of abutment is eagerly required for computational efficiency. To this end, this study introduces a refined abutment modeling and an associated adaptive quasi-static pushover analysis approach, which features three innovations: (1) a coupled flexural-shear model of the backwall to identify failure modes (flexural, flexural-shear, or shear); (2) distributed p-y springs, modified from traditional API p-y springs, to simulate backfill-abutment interactions; and (3) an adaptive pushover load pattern to capture variations of girder-backwall contact points. Accordingly, elastoplastic damage mechanisms, critical load paths, and abutment component-wise resistance contributions against longitudinal seismic loading exerted by adjacent girders are systematically uncovered. Numerical results confirm a predominant flexural-shear failure mechanism of the backwall and verify the integrity of the pile foundations, aligning closely with the observed earthquake-induced damage. The originality and strength of the macro constitutive modeling lie in its ability to succinctly encapsulate complex nonlinear girder-abutment-backfill interactions into an efficient, transferable, and practical model, advancing seismic collapse analysis capabilities of full bridge-abutment systems.

This study provides a novel approach to minimizing elevator cable oscillations in a coupled model including a building and a cable-guided hoisting mechanism under seismic excitation. A crucial component of this study is the inclusion of building vibrations that impact the cable system, which improves the model's actual usefulness. In this study, mathematical models of both the building and the elevator cable system are developed and thoroughly analyzed. An active damping device is proposed, connecting the ground and the elevator cabin, playing a crucial role in controlling oscillations. A control law is designed to regulate the oscillations of the elevator cable, with the system's stability rigorously proven using the Lyapunov Theory. The effectiveness of the proposed control law is evaluated through various earthquake scenarios. Furthermore, the system's stability is validated under four cases of operational states of the elevator, such as ascending, descending, and stopping at the lowest position, where the cable length is at its maximum.

Equivalent-lateral-force (ELF) procedure of seismic design considers accidental torsion by applying the design lateral force profile at an offset equal to accidental eccentricity from the CM. This paper evaluates the required accidental eccentricity in a median sense to account for the torsional ground motion, arguably the most dominant contributor of accidental torsion. The proposed recommendation of accidental eccentricity is based on the analysis of a wide range of one-storey torsionally coupled buildings subject to a suite of seismic events comprising the recorded orthogonal pair of horizontal accelerograms and the recorded torsional accelerogram. Demands from the simultaneous incidence of horizontal pair and torsional ground motions are met with those from the base shear of bidirectional horizontal excitations applied conforming to the required accidental eccentricity. The resulting accidental eccentricity depends on the triplet of uncoupled horizontal and torsional periods if the natural eccentricities are small, and otherwise, contingent on the natural eccentricities as well. Further, accidental eccentricity is observed to vary linearly with the radius of gyration beyond a threshold. A system with a threshold radius of gyration is defined as the reference system. Accidental eccentricity of any system with an arbitrary radius of gyration may be obtained using an amplification or deamplification of that recommended for the reference system. The proposal also considers all possible directionality of the horizontal pair given the same recorded torsional accelerogram. One example is also included, demonstrating the computation of system properties that are required to implement the proposed recommendation of accidental eccentricity in a multistorey building.

The study of unbonded post-tensioned (PT) bridge piers continues to gain momentum, as they can produce self-centering lateral force behavior with limited structural damage; however, little attention has been given to the dynamic responses of these controlled rocking systems. This paper presents an experimental study to investigate the motion pattern and assess the seismic performance of unbonded post-tensioned reinforced concrete (PRC) rocking bridge piers under uni- and bi-directional earthquake excitation. A conventional PRC pier and two improved versions with end segments enhanced, respectively, by a steel tube and ultra-high performance concrete (UHPC) were investigated through shaking table tests. The experimental outcomes highlighted the potential limitations of the two enhanced strategies in terms of damage-tolerance and rotation-dominance. Tests also revealed that the bi-directional displacement of PRC piers can be estimated from the individual uniaxial responses using the square root of the sum of the squares (SRSS) rule. In contrast, the force responses are overestimated by SRSS. Moreover, it has been observed that PRC piers are characterized by a three-dimensional (3D) wobbling motion with a contact region around the circular base instead of the sudden point impact during in-plane rocking. An analytical model is presented for the 3D rigid motion of PRC piers subjected to bi-directional earthquakes, which accounts for variations in the contact region at the pier-to-footing interface and relevant energy loss. The model's predicted responses aligned closely with the rotation-induced results derived from experimental data, provided the interface's contact properties were properly calibrated. The findings and results provide significant insights into the seismic response of PRC rocking piers, as well as further refinement of damage-tolerant solutions.