Search Results (38)

When large liquefied natural gas (LNG) storage tanks are constructed on deep non-rock sites, soil–foundation–structure interaction (SFSI) alters the dynamic characteristics of the system and affects the actual control effectiveness of the isolation layer. However, the current understanding of the coupling mechanism between the two remains insufficient. This paper takes a 220,000 m³ full-containment LNG storage tank as the study object and establishes a three-dimensional finite element model of the tank-pile group-site system in ABAQUS. Through comparative analyses of three model configurations, namely a rigid foundation model, a non-isolated model considering SFSI, and a lead-rubber bearing (LRB) isolated model considering SFSI, the SFSI effects and LRB isolation effectiveness are systematically separated. For the SFSI effects, the deep site attenuates medium- and high-frequency content while amplifying the response around approximately 1.6 Hz through site–foundation flexibility, transforming the heightwise acceleration amplification profile from an approximately linear pattern to a curvilinear one that bulges at mid-height, with peak pile-cap accelerations increasing by 25.1–76.9% relative to the rigid-base values. For the LRB isolation performance, the introduction of LRBs shifts the dominant system frequency below 1.0 Hz and reduces the maximum tank-wall acceleration amplification factor from 2.64 to 0.81. The resulting attenuation of superstructural inertial forces leads to reductions of 49.6–82.0% in pile-head shear and 57.4–78.0% in near-head bending moment, while the outer-to-inner pile-head moment ratio decreases from 2.94 to 1.13, indicating substantially improved pile-group force uniformity. Nevertheless, the beneficial effect of isolation diminishes with depth, and internal forces at abrupt soil-stiffness interfaces remain governed by kinematic interaction that the isolation layer cannot mitigate. The findings of this study can provide references for the seismic isolation design and pile foundation seismic optimization of super-large LNG storage tanks on deep overburden sites. Full article

A novel two-stage friction damper (semi-metal composite material) proposed and tested in the paper, some of which can be connected in parallel with regular isolation bearing to form a new composite type combined isolation bearing. It can significantly improve the matching of isolation parameters under multi-level earthquakes (helping to improve the applicability and sustainability of the structure) and enhance the isolation effect. Traditional methods, such as adding lead cores to laminated rubber bearings (LNR) to obtain LRB, or adding metal dampers, viscous dampers, etc., often encounter problems such as insufficient matching of isolation parameters (such as excessive slice force under frequent earthquakes and insufficient damping ratio under rare earthquakes), or space limitations due to the addition of dampers. To address these limitations, this paper proposes this new structure and uses the theory of elasticity mechanics to establish a set of methods for calculating the internal force and deformation of the damper, which can be used for the compact design of the internal structure and connecting components of the damper. After assembly and testing, it shows the damper can ensure reliable operation with a compact size and providing satisfactory damping performance. Independent mechanical performance tests confirm the shape characteristics of the force–displacement hysteresis curve, the appropriate preload torque value, and the technical parameters under variable displacement and variable speed loading conditions. The full-scale combined isolation bearing (LNRF) test verifies the working principle of the damper and the stable bone-shaped force–displacement hysteresis curve output, and compared with LNR, the equivalent viscous damping ratio increases by −14.8% (due to the increase in stiffness), 7.1%, 20.2%, and 24.0% at shear angles of 100%, 200%, 250%, and 300%, respectively. This indicates that the new combined isolation bearing structure and damper design method proposed in this paper can assist in the design of combined bearing structures and the development of products of various specifications, and suits for application in isolation buildings, bridges, and other engineering projects. Full article

This study investigates the comparative effectiveness of Lead Rubber Bearing (LRB) and Friction Pendulum System (FPS) isolation units under varying seismic hazard levels and soil classes, within the framework of the Turkish Building Earthquake Code (TBEC 2018). The assessment was conducted in two stages. First, keeping the site class constant, multiple locations characterized by different seismic hazard levels are examined. Second, a fixed geographical location is considered to evaluate the influence of different site classes on isolator response. The performance of the isolation systems is evaluated in terms of displacement demand, base shear ratio, and code-based verification criteria. Additional sensitivity checks were performed using selected limit values to better understand the response trends under changing hazard and soil parameters. The findings highlight how soil amplification effects and seismic intensity levels influence the relative advantages of LRB and FPSs. The results provide practical insight for the selection of seismic isolation systems in hazard-prone regions, contributing to improved performance-based decision-making in earthquake-resistant design. The isolator parameter choices were set based on average catalogue values provided by manufacturers to make this research an example. As a result of the analysis of the isolators’ performance, it was concluded that the FPS-type isolator performed better as acceleration values increased. Full article

Seismic isolation systems are widely adopted in bridge engineering to reduce earthquake-induced force transfer and improve structural resilience. Conventional lead rubber bearings (LRBs) provide effective energy dissipation and period elongation; however, their limited recentering capability may result in significant residual displacement after strong ground motions. This study investigates the seismic performance of a two-level shape memory alloy–lead rubber bearing (TL-LRB-SMA) hybrid isolation system for multi-span bridges considering structural flexibility, support compliance, and geometric irregularity. A nonlinear analytical model of the hybrid isolator was developed and validated under cyclic loading using benchmark hysteretic behavior from the literature. Subsequently, a multi-degree-of-freedom numerical model of an eleven-span benchmark bridge was established and verified through modal analysis, equivalent static analysis, and comparison with MSBridge software (MSBridge Beta 1.0.1). Nonlinear time-history analyses were performed using multiple excitation scenarios, including the 1940 El-Centro record, Kobe ground motion, oblique seismic incidence, and combined loading cases. Flexible foundation conditions were represented using equivalent translational soil springs. The results indicate that the TL-LRB-SMA system consistently improves self-centering performance and significantly reduces residual displacement relative to conventional LRBs. For the regular bridge with 48 ft piers, residual displacement decreased from 0.786 inches to 0.268 inches under El-Centro excitation, while under combined excitation it reduced from 0.264 inches to 0.087 inches. For irregular bridge configurations, substantial residual displacement reductions were also observed under both longitudinal and oblique loading. Although moderate increases in peak displacement occurred in some cases due to staged SMA activation, the overall recentering performance improved markedly. Overall, the proposed TL-LRB-SMA system demonstrates strong potential for enhancing seismic resilience and post-earthquake serviceability of bridge structures, particularly in flexible and irregular configurations. Full article

The mechanical behavior of lead/rubber bearings (LRBs) is strongly influenced by both ambient temperature and hysteretic heating under seismic loading; however, their coupled effects and underlying mechanisms remain insufficiently understood. This study presents a systematic investigation of the thermo-mechanical response of LRBs through combined experimental and numerical approaches. Dynamic cyclic tests were conducted on full-scale LRBs (700 mm in diameter) over a wide range of ambient temperatures, revealing that ambient temperature and hysteretic heating jointly govern the evolution of key mechanical properties, including stiffness, characteristic strength, and energy dissipation capacity. Specifically, decreasing temperature leads to stiffness and strength enhancement, whereas hysteretic heating induced by cyclic plastic deformation of the lead core results in progressive softening and degradation of restoring force. Based on the experimental observations, a modified uniaxial Bouc–Wen constitutive model is developed, incorporating the coupled effects of ambient temperature, hysteretic heating, and large-strain hardening. The proposed model is implemented in a single-degree-of-freedom (SDOF) base-isolated system to evaluate the seismic response under different temperature conditions. The results reveal a competing mechanism between ambient temperature and hysteretic heating: low temperatures tend to increase base shear and reduce displacement, while hysteretic heating produces the opposite effect, with their relative dominance depending on temperature level and ground motion intensity. Neglecting such thermo-mechanical coupling may lead to significant misestimation of structural response, particularly under long-duration strong ground motions. This study provides new insights into the coupled temperature-dependent behavior of LRBs and establishes a robust modeling framework for the seismic analysis and design of isolation systems under complex service conditions. Full article

This paper aims to quantify the change in seismic response of a reinforced concrete (RC) building retrofitted by the seismic isolation technique when reinforcement corrosion is considered. In this regard, an 8-story RC building that possesses the characteristics of the existing fixed-base building stock in Türkiye has been identified and hypothetically retrofitted with lead rubber bearings (LRBs). In the numerical models, four different corrosion scenarios to represent the spatial distribution of corrosion on the frame elements of the superstructure and three different corrosion levels considering the mass losses (5, 10 and 20%) due to corrosion are considered; the corresponding reductions in (i) the cross-sectional areas of both the longitudinal and transverse reinforcements and (ii) the mechanical properties of steel and concrete are taken into account. Code-based bidirectional nonlinear response history analyses (NRHAs) are performed by considering the nonlinearity not only in the seismic isolation system but also in the superstructure. Furthermore, LRBs are represented by a force–displacement relation that enables modeling of the deterioration in strength of isolators due to lead core heating during cyclic motion. The results revealed that the spatial distribution of the corrosion is highly effective in amplification of inter-story drift ratios (ISDRs), which can be in the order of 2-fold depending on the level of mass loss. It is found that the seismic isolation technique is still effective in protecting the superstructure against earthquakes even though there is a corrosion problem in frame members. Full article

Seismic design for multi-span simply supported to continuous (SSC) bridges is complicated by the vulnerability of continuity joints and the interaction between substructure stiffness and superstructure dynamics. Although Lead Rubber Bearings (LRB) are standard in current practice, the optimization of their spatial layout to balance displacement demands against force mitigation is often overlooked. This study evaluates the efficacy of hybrid bearing configurations that integrate LRBs with sliding bearings on the same pier. Using a 3D finite element model of a representative five-span prestressed concrete box girder bridge, 20 distinct layout schemes utilizing five different types of LRBs were systematically evaluated under El-Centro ground motions. Results show that a hybrid bearing configuration outperforms uniform isolation strategies. The fundamental efficacy of the proposed hybrid layout configuration is rooted in the establishment of a spatial stiffness gradient. This configuration concentrates hysteretic energy dissipation centrally while releasing transverse edge constraints. This also results in a higher seismic reduction rate for the transverse pier bottom bending moment compared to the longitudinal direction in the same pier. Compared to the non-isolated baseline, this hybrid scheme achieved a maximum reduction of 67.4% and 90.0% in longitudinal and transverse pier bottom bending moments, respectively. Main girder displacements, while increased by isolation, remained strictly within safe serviceability limits (peak 174.8 mm). This study provides a cost-effective optimization strategy for the seismic resilience design of SSC bridges. Full article

The increasing integration of Chinese-engineered infrastructure in Pakistan under the China–Pakistan Economic Corridor (CPEC) necessitates a comparative evaluation of seismic resilience between the Chinese and Pakistani building codes. This study focused on the seismic performance of reinforced concrete (RC) frames designed according to these two codes. Fragility curves were generated for 4-story, 8-story, and 12-story buildings subjected to varying seismic intensities using Incremental Dynamic Analysis (IDA). The results indicate that structures designed under the Chinese code exhibit up to 12% lower fragility values, suggesting enhanced seismic resilience, particularly at higher seismic intensities. Additionally, the study investigates the effectiveness of Lead Rubber Bearings (LRBs) for seismic isolation, demonstrating that their integration improves the seismic performance of RC frames by enhancing energy dissipation and reducing the likelihood of exceeding various damage states by up to 25%. These findings underscore the importance of adopting stringent seismic design provisions, such as those found in the Chinese code, to enhance the resilience and safety of infrastructure, especially in seismic-prone regions. Full article

As the rubber constituting laminated rubber isolation bearings is a temperature-sensitive material, its performance is susceptible to temperature disturbances. Firstly, this study systematically analyzed the effects of temperature on the mechanical properties of natural rubber bearings (LNR), lead–rubber bearings (LRB), and high–damping rubber bearings (HDR), including horizontal equivalent stiffness, equivalent damping ratio, and yield load. The variation trends of the mechanical property parameters of the three types of bearings with temperature are basically the same. LNR exhibits a strong linear variation law, while the mechanical properties of HDR bearings are the most sensitive to temperature changes. Secondly, based on the analysis of the temperature characteristics of the mechanical properties of the bearings, the temperature dependence of the seismic mitigation effect of the bearings was further studied. The results show that the displacement response of the isolation layer has the best temperature stability when using LRB bearings, and the displacement response of the superstructure is most susceptible to temperature changes when using HDR bearings. When the temperature is lower than the normal temperature, the displacement responses of isolation systems with different types of bearings all show the characteristic that the lower the temperature, the greater the deviation from the displacement response at normal temperature. Finally, to overcome the influence of temperature, a temperature-controlled isolation rubber bearing integrating laminated rubber isolation bearings with a temperature regulation system was proposed. This can solve the problems that the mechanical properties of rubber bearings deteriorate and the aging rate accelerates in a wide temperature range, which affect their isolation effect and service life. Thus, it endows new theoretical connotations to rubber isolation bearings and has practical application value for engineering seismic resistance. Full article

Earthquakes can cause significant damage to structures, resulting in considerable financial and social losses. Enhancing the seismic capacity of existing structures through retrofitting is essential. Traditional seismic retrofitting techniques, such as reinforced concrete (RC) jacketing and steel jacketing, primarily aim to increase structural resistance. But RC jacketing is intrusive and increases mass and stiffness, steel jacketing increases cost and demands careful detailing and both approaches are often inadequate for addressing the dynamic complexities of seismic loading. As an alternative, base isolation systems provide a promising solution by concentrating deformation and energy dissipation within isolation bearings, thereby protecting the superstructure from seismic forces. This study evaluates the effectiveness of base isolation compared with conventional retrofitting methods in enhancing the seismic performance of existing structures. The experimental program included cyclic testing of four RC frame structures: one control specimen and three others retrofitted with RC jacketing, steel jacketing, and lead rubber bearings (LRB). The results indicate that the base-isolated specimen demonstrates superior energy dissipation capacity due to the favorable deformation characteristics of the LRB. Moreover, structural damage is redirected from the original columns to the newly installed transition beams, effectively preserving the integrity of the primary structure. These findings highlight the advantages of base isolation in improving seismic performance and provide valuable experimental evidence supporting its application in the retrofitting of existing structures. Full article

Small-diameter lead-rubber bearings (LRBs) are widely employed in shaking table tests of isolated structures, particularly reinforced concrete base-isolated structures. Accurately determining their mechanical properties and identifying their restoring force model parameters are essential for seismic response analysis and numerical simulation of scaled models. In this study, quasi-static tests and shaking table tests were conducted to obtain the compression–shear hysteresis curves of LRBs under various loading amplitudes and frequencies, as well as the hysteresis curves under seismic wave excitation. The variation patterns of mechanical performance indicators were systematically analyzed. A parameter identification method was developed to determine the restoring force model of small-diameter LRBs using a genetic algorithm, and the effects of pre-yield stiffness and yield force of the isolation layer on structural response were investigated based on an equivalent two-degree-of-freedom model. By incorporating appropriately identified restoring force model parameters, a damping modeling method for the reinforced concrete high-rise over-track structures with an inter-story isolation system was proposed. The results indicate that, when the maximum bearing deformation reached 150% shear strain, the post-yield stiffness and horizontal equivalent stiffness under seismic excitation increased by 11.97% and 19.40%, respectively, compared with the compression–shear test results, while the equivalent damping ratio increased by 18.18%. Directly adopting mechanical parameters obtained from quasi-static tests would lead to an overestimation of the isolation layer displacement response. The discrepancies in the mechanical indicators of the small-diameter LRB between the theoretical hysteresis curve, obtained using the identified Bouc–Wen model parameters, and the compression–shear test results are less than 10%. In OpenSees, the seismic response of the scaled model can be accurately simulated by combining a segmented damping model with an isolation-layer hysteresis model in which the pre-yield stiffness is amplified by a factor of 1.15. Full article

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

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

In this study, the effects of ambient temperature on the horizontal mechanical performance of isolated rubber bearings were investigated using high-speed reciprocating loading methods. A comprehensive series of 54 experimental trials are performed on the full-scale (900 mm-diameter) isolation rubber bearings, encompassing a range of temperatures (−20 °C, 0 °C, and 23 °C), shear pressures (50%, 100%, and 250%), and frequencies (0.20 Hz, 0.25 Hz, and 0.30 Hz). Because the compression-shear tests were conducted at high velocities and pressures (specifically, vertical compressive stress of 15 MPa), the equipment used in these tests was capable of generating substantial inertial and frictional forces. Appropriate correction methodologies for the precise determination of mechanical performance metrics for bearings are presented. Then, a comprehensive investigation of the effects of various loading conditions on the characteristic strength, post-yield stiffness, horizontal equivalent stiffness, and equivalent damping ratio of LRB900 (lead-core rubber bearings 900 mm-diameter) and LNR900 (linear natural rubber bearings 900 mm-diameter) is conducted. The empirical results show a discernible relationship between these characteristics and ambient temperature as the number of loading cycles increases, except for the equivalent damping ratio. Finally, empirical fitting formulations incorporating the influence of ambient temperature are presented for each performance indicator. These formulas are intended to assist designers in performing seismic design analyses by allowing them to take into consideration the effects of ambient temperature comprehensively. Full article