Search Results (85)

A numerical investigation is conducted to examine the mechanical properties of a novel three-dimensional (3D) isolation bearing. This device is primarily composed of a lead rubber bearing (LRB), disc springs, and U-shaped dampers. A finite element model is developed and validated against the previous experimental results. Subsequently, comprehensive analyses are performed to evaluate the influence of vertical loadings, shear strains, and the number of U-shaped dampers on the horizontal behavior, as well as the effects of displacement amplitudes and the number of dampers on the vertical performance. Under horizontal loading conditions, the bearing demonstrates reliable energy dissipation capabilities. However, the small lead core design limits its energy dissipation capacity. Compared with the bearing without U-shaped dampers, the bearing’s energy dissipation capacity increases by 628%, 1300%, and 2581% when employing 1, 2, and 4 dampers on each side, respectively. Regarding vertical performance, the innovative disc spring group design effectively reduces the tensile displacement of the LRB under tension, thereby enhancing the overall tensile capacity of the bearing. Furthermore, in comparison to their contribution to horizontal energy dissipation, the U-shaped dampers play a relatively minor role in vertical energy dissipation. Full article

Seismic isolation is a vital strategy for improving the earthquake resilience of structures, utilizing flexible components such as lead–rubber bearings (LRBs) and curved surface sliders (CSSs) to attenuate ground motion effects. This paper presents a comprehensive comparative analysis of seismic isolation design methodologies prescribed in the U.S. code (ASCE 7-22) and the European code (EC8). The focus is on the equivalent lateral force method, also known as the simplified linear method, renowned for its simplicity and efficiency in seismic design applications. A six-story steel building serves as a case study to examine the discrepancies between the two codes. The structure was modeled and subjected to nonlinear time-history analysis (NTHA) using 20 ground motion records, selected and scaled to match a conditional mean spectrum (CMS). Key performance indicators—including displacement at the isolation level, base shear forces, story shear forces, and story drifts—were compared to assess the reliability and effectiveness of each code’s design approach. The findings reveal notable differences between ASCE 7-22 and EC8, particularly in seismic hazard characterization and the calculation of design displacements. ASCE 7-22 generally adopts a more conservative stance, especially for CSSs, resulting in overestimations of design displacements and lateral seismic forces. In contrast, EC8’s simplified method aligns more closely with observed performance for LRBs. However, when applied to CSSs, simplified methods prove less reliable, underscoring the need for more precise analytical techniques. Full article

Modeling seismic isolators, one of the most effective installations in the design of earthquake-resistant buildings, is a very important challenge. In this study, we propose a new energy-based approach for the optimization of seismic isolation parameters. The hysteretic energy represents the dissipation of isolated structures in the isolation system. The minimization of input energy ensures that structural components are exposed to reduced seismic energy. For these reasons, this study aims to minimize the input energy and maximize the hysteretic energy. Additionally, an objective function is also generated with the energy ratio obtained from the input and hysteretic energy. The gray wolf optimizer (GWO) was applied to the optimization process. A four-story, 3D, and reinforced concrete superstructure was prepared and lead rubber bearings were placed under the base story. The isolation system is modeled nonlinearly, which requires two parameters: isolation period and characteristic strength. The inter-story drift ratio was selected as the structure constraint, while the isolator displacement and effective damping ratio were selected as the isolator constraints in the optimization process. The prepared base-isolated structure was optimized using 11 scaled ground motions. Nonlinear time history analyses were run in ETABS finite element software. Firstly, the optimum isolation parameters were obtained using peak roof story acceleration (PRA), in accordance with the methodology in previous studies. The outcomes generated by the PRA and energy components are compared considering the isolation parameters and structural responses. The energy ratio produced better results in terms of inter-story drift ratio than the other energy components. Secondly, the energy ratio was re-optimized with different constraints and its effectiveness was examined. Full article

Under the action of near fault earthquakes, the LRB bearings of long-period isolated buildings are prone to significant deformation and failure under compression shear conditions. Therefore, it is necessary to analyze the damage of LRB and its impact on the superstructure. Finite element analysis methodology was selected and Abaqus was used to simulate hysteresis curve of LRB and the separation between rubber layer and steel layer when horizontal deformation reaches 400%. A simplified four-stiffness isolation bearing model is proposed and applied to seismic isolation damage analysis on 8-story seismic structure under near-fault earthquakes. Damage on different positions and numbers of bearings are also compared. It concludes that under the compressive and shearing state, when the horizontal deformation of the isolator exceeds 300%, the stiffness enhancement section appears. Moreover, it is found that the damage of all LRBs show the most significant scale-up effect on acceleration and story drift. Full article

Seismic isolation systems play a crucial role in enhancing structural resilience during earthquakes, with lead rubber bearings being a widely adopted solution. These bearings incorporate lead cores to effectively dissipate seismic energy. However, their widespread application is constrained by significant drawbacks, including high costs and environmental concerns associated with lead. This study introduces a novel sustainable S-shaped steel damper made from standard steel. The influence of key geometrical parameters—thickness, width, and the distance from the bolt hole to the arc’s start—on the cyclic behavior of the dampers was investigated. Seven prototypes were designed, manufactured, and experimentally tested to evaluate their horizontal stiffness and damping performance. Subsequentially, the experimental results were considered for the validation of a numerical model based on a full 3D Finite Element discretization. The model, calibrated using simple uniaxial steel material tests, facilitates the identification of optimal geometric features for the production of S-shaped steel dampers without the need for extensive prototype fabrication and experimental testing. Additionally, the model can be seamlessly integrated into future numerical structural analyses, enabling a comprehensive evaluation of performance characteristics. In conclusion, this research provides critical insights into the geometric optimization of S-shaped steel dampers as cost-effective and sustainable dissipation devices. It offers both experimental data and a robust numerical model to guide future designs for improved seismic mitigation performances. Full article

Given that numerous countries are located near active fault zones, this review paper assesses the seismic structural functionality of buildings subjected to dynamic loads. Earthquake-prone countries have implemented structural health monitoring (SHM) systems on base-isolated structures, focusing on modal parameters such as frequencies, mode shapes, and damping ratios related to isolation systems. However, many studies have investigated the dissipating energy capacity of isolation systems, particularly rubber bearings with different damping ratios, and demonstrated that changes in these parameters affect the seismic performance of structures. The main objective of this review is to evaluate the performance of damage detection computational tools and examine the impact of damage on structural functionality. This literature review’s strength lies in its comprehensive coverage of prominent studies on SHM and model updating for structures equipped with dampers. This is crucial for enhancing the safety and resilience of structures, particularly in mitigating dynamic loads like seismic forces. By consolidating key research findings, this review identifies technological advancements, best practices, and gaps in knowledge, enabling future innovation in structural health monitoring and design optimization. Various identification techniques, including modal analysis, model updating, non-destructive testing (NDT), and SHM, have been employed to extract modal parameters. The review highlights the most operational methods, such as Frequency Domain Decomposition (FDD) and Stochastic Subspace Identification (SSI). The review also summarizes damage identification methodologies for base-isolated systems, providing useful insights into the development of robust, trustworthy, and effective techniques for both researchers and engineers. Additionally, the review highlights the evolution of SHM and model updating techniques, distinguishing groundbreaking advancements from established methods. This distinction clarifies the trajectory of innovation while addressing the limitations of traditional techniques. Ultimately, the review promotes innovative solutions that enhance accuracy, reliability, and adaptability in modern engineering practices. Full article

The high-speed railway (HSR) system imposes stringent requirements for track smoothness. However, conventional seismic isolation bearings frequently fail to meet these demands. To address this challenge, a novel seismic isolation bearing was developed based on the principle of functional separation design. This innovative bearing effectively achieves the multistage control objectives, including amplitude limitation to ensure track smoothness during frequent earthquakes, energy dissipation to guarantee train running safety during design earthquakes, and structural integrity maintenance to prevent beam collapse during rare earthquakes. Firstly, an overview of the novel isolation bearing’s structural design and operational principle is provided. Subsequently, a corresponding mechanical model is formulated, with the parameters of the new bearing determined through finite element analysis. The study then compares the seismic performance of the general rubber bearing and the new bearing, using an HSR simply supported bridge as an engineering background. The dynamic response of the bridge under varying seismic waves, pier heights, and bridge spans is meticulously analyzed. The results indicate that the new bearing can achieve multistage control. Compared to general bearings, it reduces bridge displacement vibration by over 46.4% under frequent, design, and rare earthquakes. The bridge deformation under frequent earthquakes remains below 3 mm, thus meeting the track smoothness requirements for normal HSR operations. Additionally, the study reveals that higher pier heights increase the seismic response, peaking at 15 m. The vibration reduction provided by the new bearing varies but remains effective in most earthquake scenarios, with maximum reductions of 92.9% for displacement and 74.17% for bending moment. Furthermore, larger bridge spans also increase the seismic response, with the 24 m span bridge outperforming the 32 m span bridge. In conclusion, the novel seismic isolation bearing significantly enhances the seismic performance of HSR bridges, ensuring train running safety and operational reliability. Full article

Seismic accelerations and interlayer displacements can be reduced by Laminated Rubber Bearings (LRBs) efficiently. Isolators would amplify the displacement of the superstructure by extending the natural period, thereby reducing acceleration and seismic damage. However, as a result, the risk of pounding with adjacent structures would be raised. This study investigated the seismic responses and overturning resistance capacity of base-isolated structures subjected to pounding against an adjacent structure. Parameter studies were conducted to evaluate the effects of gap size, pounding stiffness, and horizontal stiffness of the isolation layer. Results show that poundings are characterized by intense, short forces causing acceleration spikes, amplifying the overturning coefficient and risk. The overturning risk initially decreases then increases with gap size under pulse-like earthquakes, while wider gaps mitigate effects during non-pulse events. Increased pounding stiffness intensifies poundings, heightening vulnerability. The structure’s overturning resistance initially improves with increased horizontal stiffness of the isolation layer but declines excessively with further stiffness increase. Full article

With advancements in seismic isolation and damping technology, high-damping rubber (HDR) bearings are now widely used. However, significant gaps remain in HDR-analysis model research, with few studies integrating multiple factors, the Mullins effect, and stiffness hardening for more accurate practical predictions. This study classifies the effective behavior of HDR and examines the stress–strain relationships of different behavioral types using more appropriate equations. Mathematical models were established based on pseudo-elasticity theory, which is an extension of continuum mechanics. Subsequently, parameter functions were developed through parameter determination tests and regression analysis, leading to the completion of the pseudo-elastic model for HDR. Finally, the model’s effectiveness was validated through validation tests. This study finds that behavior classification effectively examines phenomenological-based HDR stress–strain relationships, as distinct behavioral patterns are not adequately captured by a single approach. Incorporating tests to functionalize material parameters complements theoretical models. Additionally, accurately explaining HDR behavior requires considering the Mullins effect and stiffness hardening, influenced by the coupled effects of temperature, strain amplitude, and compressive stress. Consequently, this HDR pseudo-elastic model offers a comprehensive explanation of HDR behavior, including the Mullins effect and stiffness hardening, under various influencing factors based on clear mechanical principles and explicit computational procedures. Full article

Typical forms of seismic damage to laminated-rubber-bearing girder bridges in the transverse direction are falling beams, girder displacement, and bearing damage. However, the damage to piers and foundations is generally lighter. This is mainly due to slippage of the bearings. Therefore, we propose a new type of arc-shaped shear key to improve the lateral seismic performance. A 1/12-scale highway continuous-girder bridge isolated by different shear keys was tested utilizing a 4 m × 4 m shaking table with six DOFs. The seismic responses of the bridge were analyzed in terms of phenomenon, displacement, strain, and acceleration. The main girder and pier exhibited different seismic responses because the bridge had different stops. A numerical simulation based on FEM showed that the established finite element model can well reproduce the displacement time history of the main girder and the cap girder. By analyzing the finite element model, the relative displacement of the bearing under different seismic waves was obtained. A comparison between the measured and FEM responses showed that the arc-shaped shear key can well limit the displacement of the main girder and the bearing. In addition, it does not significantly amplify the seismic response of the substructure. The arc-shaped shear key dissipates more energy while limiting the displacement of the main girder, and the comprehensive seismic performance is better than that of the rubber pad shear key. Full article

High-damping rubber bearings play an essential role in isolated bridges. They can prolong the natural vibration period of a bridge and reduce its seismic response. In order to quantitatively study the isolation performance of high-damping rubber bearings, this paper investigates a concrete-filled steel tube-tied arch bridge as the research object and uses symmetrically arranged high-damping rubber bearings for isolation reconstruction. Nonlinear finite element analysis models for isolated and non-isolated bridges are built based on the structural properties of the actual bridge. Based on the structural deformation failure criterion, a bridge damage evaluation index system is established, the damage index of each component is defined, and a quantitative analysis of different damage states is carried out. Based on the incremental dynamic analysis method, the seismic vulnerability curves of bridge components and systems are established. By comparing the seismic vulnerability curves of the bridge before and after isolation, the isolation effect of the high-damping rubber bearings is quantitatively evaluated. The results of the analysis show that the high-damping rubber bearings have a significant isolation effect on the bridge structure and the effect is symmetrically distributed along the longitudinal symmetry plane of the bridge. After adopting the isolation measures, the exceedance probability of damage of each component of the bridge is reduced to varying degrees. Among them, the isolation effect on piers and arch ribs is the most significant, up to more than 90%. At the same time, the exceedance probability of damage of the bearing itself is less reduced. This result is also consistent with the original intention of the design of the isolation bearing; that is, through the energy dissipation of the isolation bearing, the seismic response of other components of the bridge is reduced. Full article

With the installation of rubber isolation bearings in the upper and lower ground layers, an isolated step-terrace structure was created. Considering the ultimate bearing capacity of the rubber bearing under tension as the critical condition, a comprehensive framework was established to evaluate the overturning failure mechanisms present in isolated step-terrace structures. The bound of nominal aspect ratio was identified as the principal control index within this framework, which incorporates critical parameters such as height ratio (α), width ratio (β), vertical tensile stiffness to compressive stiffness ratio (γ), seismic coefficient (k), and nominal vertical compressive stress (σ₀) to provide a thorough analysis of the structural responses and potential failure scenarios. In order to further investigate this matter, a scaled model of an isolated step-terrace concrete frame structure featuring two dropped layers and a single span within an 8° seismic fortification zone was meticulously crafted at a 1:10 similarity ratio. Subsequently, a series of shaking table tests were conducted to analyze the structural response under seismic excitation. The findings indicate that: utilizing the bound of nominal aspect ratio as a metric to gauge the anti-overturning capacity of isolated step-terrace structures is a justified approach. In instances where the height ratio remains constant, the bound of nominal aspect ratio for both positive and negative overturning trended upward with an increase in the width ratio. Notably, the bound of nominal aspect ratio for positive overturning consistently registered lower values compared to that of the negative overturning, underscoring the heightened susceptibility of step-terrace structures to positive overturning. Moreover, in scenarios characterized by higher height and width ratios, the structural integrity remained unscathed by any overturning effects arising from insufficient tensile strength in rubber bearings. Furthermore, the bound of nominal aspect ratio exhibited an ascending trend as the seismic coefficient, nominal vertical compressive stress, and vertical tensile stiffness to compressive stiffness ratio decreased. The outcomes derived from the shaking table test not only confirm the impressive seismic performance of the structure, but also, by closely examining the instantaneous stress variations within the upper and lower isolation layers of the model, substantiate the existence of a positive overturning hazard in scenarios marked by higher seismic coefficients (k). This observation aligns seamlessly with the theoretical projections, thereby substantiating the efficacy of the structural overturning failure theory through direct empirical verification. Full article

Flexible strain sensors have a wide range of applications in the field of health monitoring of seismic isolation bearings. However, the nonmonotonic response with shoulder peaks limits their application in practical engineering. Here we eliminate the shoulder peak phenomenon during the resistive-strain response by adjusting the dispersion of conductive nanofillers. In this paper, carbon black (CB)/methyl vinyl silicone rubber (VMQ) composites were modified by adding a silane coupling agent (KH550). The results show that the addition of KH550 eliminates the shoulder peak phenomenon in the resistive response signal of the composites. The reason for the disappearance of the shoulder peak phenomenon was explained, and at the same time, the mechanical properties of the composites were enhanced, the percolation threshold was reduced, and they had excellent strain-sensing properties. It also exhibited excellent stability and repeatability during 18,000 cycles of loading–unloading. The resistance-strain response mechanism was explained by the tunneling effect theoretical model analysis. It was shown that the sensor has a promising application in the health monitoring of seismic isolation bearings. Full article

A novel three-dimensional isolation system consisting of thick rubber bearing (TNRB), disc spring bearing (DSB), and laminated rubber bearing (LRB) in series combination was designed, and its composition, principle, and isolation effect were comprehensively analyzed. By combining numerical examples, the whole structure method is used to compare and analyze the dynamic characteristics, dynamic response, and structural damage of large-span isolation structures containing new three-dimensional systems, large-span horizontal isolation structures based on LRB, and corresponding non-isolation structures under multi-dimensional seismic excitation. The results show that compared with the horizontal isolation structure based on LRB, the structure of the new three-dimensional isolation system has a 33% longer vertical natural vibration period, a 17.85% attenuation in the overall damage index, and a 36.86% increase in vertical energy dissipation capacity. It can achieve good isolation effects in both horizontal and vertical directions, which can form a favorable complement to the horizontal isolation structure based on LRB in terms of vertical isolation and energy dissipation. Full article

Non-isolated structures have strong destructive effects and poor isolation effects when encountering earthquakes. Setting isolation bearings can prolong the natural vibration period of the structure, reduce the horizontal seismic response of the structure under the influence of variables such as acceleration, base reaction, and inter story displacement, and enhance the overall seismic performance of the structure. The new material—epoxy plate thick layer rubber isolation bearing—has unique advantages compared to other bearings, such as effective energy absorption, simple construction, and low cost. This study establishes a three-dimensional isolated nuclear power plant containment structure based on the principle of similarity ratio, and compares and analyzes the acceleration, base reaction, and displacement responses of non-isolated and isolated structures. At the same time, the incremental dynamic analysis method (IDA) is used to analyze the seismic vulnerability of the structure, and the isolation performance of the nuclear containment structure using epoxy plate thick layer rubber isolation bearings is comprehensively and deeply explored. The results show that the epoxy plate thick layer rubber isolation bearing effectively prolongs the natural vibration period of the structure, reduces the horizontal seismic response of the structure, reduces the dome acceleration response by 66.55%, and reduces the base horizontal shear force by 55.51%. Therefore, setting epoxy plate thick layer rubber isolation bearings in the isolation layer can effectively enhance the seismic performance of the structure, thereby improving the redundancy of the nuclear power plant containment structure. Full article