Earthquake Engineering & Structural Dynamics最新文献

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.

Repairs were carried out on a full-scale, single-story specimen of a traditional Ottoman-period Greek structure, comprising a stone masonry wall with timber ties and three timber-framed ones with fired clay brick infill, which had been subjected to biaxial shaking table tests. The connection between the walls was enhanced, as was the roof-level diaphragm. The timber-framed walls were clad with plywood panels and the cracks in the stone wall were repaired. The repaired specimen was then subjected to biaxial seismic tests, while its dynamic characteristics before and after seismic testing were determined with sine sweep tests. The repaired specimen safely withstood 22% increased base acceleration (0.44 g compared to 0.36 g for the As-built one), with damages concentrating in the stone wall, while the rocking mechanism of the timber-framed ones changed.

To study the seismic behavior of horizontal-hole interlocking concrete block-confined masonry walls with openings, in-plane cyclic loading tests were conducted on specimens with no openings, a window opening, and a door opening. The results indicated that the specimens with no openings and window openings exhibited typical diagonal shear failures of the entire wall. However, the structure and bearing mode were changed by including a door opening. The door-opening specimen could no longer be analyzed as an entire confined masonry wall owing to its lateral resistance and failure modes. The tie columns on both sides and the adjacent masonry formed wall columns, and the lintel beam and masonry above the opening formed a wall beam. Under a horizontal force, localized shear failure occurred in the wall beam, which resembled the shear failure of the coupling beam of double-limb shear walls and was an expected failure mode. Finally, this study proposes a new method for analyzing the lateral resistance of confined masonry walls with openings, called the force transmission path method, with a maximum calculated difference of 8.51%. This reflected the lateral resistance contribution of the reinforced concrete lintel beams.

Free rocking isolation systems (FRIS), characterized by negative post-uplift stiffness, have demonstrated favorable seismic performance such as resonance avoidance and gravity-driven self-centering (SC); however, a key design challenge lies in simultaneously ensuring sufficient deformability of the rocking isolation story while effectively mitigating the seismic demand on the superstructure. To address this challenge, this study investigates controlled rocking isolation systems (CRIS) with flag-shaped (FS) hysteretic devices. An analytical model is developed for elastic single-degree-of-freedom (SDOF) oscillators (representing elastic low-to-medium rise frames) fixed on CRIS with FS hysteresis. A practical application using NiTi shape-memory alloy (SMA)-based rocking columns is proposed to realize the intended FS behavior. The analytical model is validated through comparisons with a newly developed finite element model in OpenSees. Dimensional analysis is employed to reduce the number of governing variables in the equations of motion, thereby facilitating the identification of fundamental similarities in seismic responses across different structural scales and loading conditions. Both case-to-case and statistical comparisons confirm the accuracy of the proposed model. Based on the validated model, parametric studies are performed to examine the effects of varying FS hysteretic parameters and seismic input characteristics on the structural seismic performance. The results further confirm that CRIS exhibit enhanced dynamic stability relative to FRIS. Furthermore, it is possible to achieve a balance between controlled rocking and minimized superstructure demand for CRIS with FS hysteresis.

Due to the structural parameters diversity, material attributes nonlinearity, and ground motions uncertainty, predicting the elastic-plastic seismic response of columns is challenging and crucial, particularly in near-fault areas where significant damage can occur. Traditional machine learning (ML) models have demonstrated powerful capabilities for predicting structural seismic demand. However, their difficulty in accurately capturing latent system nonlinearity and the challenges associated with quantifying the impact of pulse effects on structural seismic demand complicate their application in practical engineering. This study proposes an efficient, high-precision, and highly interpretable physic-law-integrated neural network (PLNN) method. It introduces a novel physic-law model (PLM), which establishes the relationship between the normalized period (pulse to structural fundamental period ratio) and seismic demand. In addition, this research examines and quantifies the effects of column properties and pulse attributes on the characteristic coefficients of the PLM using an artificial neural network model (ANN). This method provides a PLNN model for estimating seismic demand based on the structural parameters, material attributes, and seismic characteristics by integrating the ANN model with the PLM. The ability and stability of the PLNN are evaluated by comparing its prediction performance with that of a traditional ML model. The results indicated that the proposed PLNN model maintains high prediction accuracy and significantly enhances computational efficiency. The PLNN model in this research requires 10 neurons to achieve optimal fitting goodness, one-third of the number required by the corresponding ANN model. In addition, the accuracy of the PLNN model is twice that of the ANN model in small sample settings, indicating the stability of the PLNN.