Earthquake Engineering & Structural Dynamics最新文献

Surrogate modeling using Probabilistic Learning on Manifolds (PLoM) was found to be an effective and efficient approach for predicting site-specific or structure-specific collapse fragility and non-collapse response demand distributions. This study extends the application of PLoM surrogate modeling to site-and-structure specific problems, which is a promising alternative to the computationally expensive ground motion selection and nonlinear response history analysis when assessing the seismic performance of highway bridges (e.g., peak response demand, cumulative damage, and collapse risk). A systematic procedure is proposed to train parameterized PLoM surrogate models from incremental dynamic analysis (IDA) data and predict site-and-structure-specific collapse fragility and non-collapse engineering demand parameter (EDP) distributions for highway bridges. A quasi-stripe training approach is illustrated to effectively tune two PLoM hyperparameters $�{\epsilon }_{�d�b�}$ and $�{\epsilon }_k$ as functions of spectral acceleration intensity $��S�a�$, which yields good model prediction accuracy at varying $��S�a�$ intensity levels. A comprehensive validation study is conducted on both the collapse and non-collapse EDP predictions for nine different site-bridge combinations of three California sites and three pre-1971 two-span single column bridges. The proposed training and prediction procedure is implemented to obtain PLoM prediction results, which are found to be in good agreement with multiple stripe analysis (MSA) results regarding (1) mean annual frequency of collapse, (2) probabilistic distribution of individual non-collapse EDPs, and (3) correlation coefficients and empirical copulas between data dimensions.

Floating roof tanks, which are utilized in a multitude of industrial facilities for the storage of volatile and flammable products, are particularly susceptible to seismic events. These events can result in substantial structural damage and hazardous material releases due to roof sinking and leading to rim fires. The metallic contact between the floating roof and the tank wall, induced by seismic roof oscillations, has been shown to generate sparks. These sparks, in the presence of flammable vapors, pose a significant risk during seismic events. This study investigates the interaction between the floating roof and the tank walls, with a focus on the role of the sealing system and the pounding dynamics during seismic events. Based on experimental findings of mechanical characterization of a spring in a typical sealing system, with a single-degree-of-freedom system with rigid pounding, the horizontal dynamics of the floating roof under seismic excitation were investigated. Then, a gap and a deformable, dissipative bumper system were designed to control the roof's oscillations and protect the sealing system. Seismic analyses demonstrated that the proposed bumpers significantly reduce the number and contact force of impacts, thereby mitigating the risk of generating sparks during the critical phase of maximum seismic energy. The optimized bumper design was found to be fully compatible with the operational conditions of the case study tank, offering an effective solution to improve the seismic safety of floating roof tanks in seismic-prone areas.

Summary:

• Identifies fire hazards from roof-shell pounding in floating roof tanks, an issue overlooked in regulations.
• Provides experimental characterization of sealing system stiffness and damping properties.
• Demonstrates that conventional sealing systems lead to excessive oscillations and high contact forces (∼10⁴ kN) under seismic excitation, with an SDOF system.
• Proposes deformable and dissipative bumpers to control displacements.
• Conducts a parametric analysis to optimize bumper stiffness, damping, and gap size.
• Confirms, through seismic simulations, that optimized bumpers dissipate energy effectively, minimizing impact velocities and enhancing seismic safety.

Rapid functional recovery and minimal structural damage have become critical objectives in modern seismic design. To address this need, a Low-Prestressed Self-Centering (LPSC) brace was developed, providing reliable re-centering capacity with a low level of prestressing force. This study evaluates its structure-level seismic performance through shake-table tests on a 1/3-scale, two-story LPSC Braced Frame (LPSC-BF). The test building featured hinged column bases with pinned beam-to-column joints in one direction, and rotational-restrained column bases with shear beam-to-column joints in the other. A total of 60 tests, including unidirectional and bidirectional excitations of varying intensities, were conducted. The test building consistently achieved immediate occupancy performance, with plastic deformations confined to the steel dissipaters in the LPSC braces. These steel dissipaters were easily replaceable, enabling rapid post-earthquake repair. Despite a minor loss in prestressing force, the residual drift remained minimal throughout testing. The direction with hinged column bases exhibited a uniform drift distribution, whereas the direction with rotationally restrained bases showed a concentration of drift at the first story. Floor acceleration responses were generally lower than the code-predicted values. Overall, the test results demonstrate that the LPSC-BF is an attractive seismic resilient structural system.