• Journal of the Earthquake Engineering Society of Korea
• /
• v.27 no.4
• /
• pp.187-192
• /
• 2023

An elastic bearing must be strong against vertical loads and flexible against horizontal loads. However, due to the material characteristics of rubber, it may show variability due to the manufacturing process and environmental factors. If the value applied in the bridge design stage and the actual measured value have different values or if the performance during operation changes, the performance required in the design stage may not be achieved. In this paper, the seismic response of bridges was compared and analyzed by assuming a case where quality deviation occurs during construction compared to the design value for elastic bearings, which have not only always served as traditional bearings but also have had many applications in recent seismic reinforcement. The bearing's vertical stiffness and shear stiffness deviation were considered separately for the quality deviation. In order to investigate the seismic response, a time history analysis was performed using artificial seismic waves. The results confirmed that the change in the bearing's shear stiffness affects the natural period and response of the structure.

• Earthquakes and Structures
• /
• v.15 no.3
• /
• pp.319-334
• /
• 2018

In this paper, an analytical study was carried out to propose an optimum base-isolated system for the design of steel structures equipped with lead rubber bearings (LRB). For this, 5 and 10-storey steel moment resisting frames (MRFs) were designed as Special Moment Frame (SMF). These two-dimensional and three-bay frames equipped with a set of isolation systems within a predefined range that minimizes the response of the base-isolated frames subjected to a series of earthquakes. In the design of LRB, two main parameters, namely, isolation period (T) and the ratio of strength to weight (Q/W) supported by isolators were considered as 2.25, 2.5, 2.75 and 3 s, 0.05, 0.10 and 0.15, respectively. The Force-deformation behavior of the isolators was modelled by the bi-linear behavior which could reflect the nonlinear characteristics of the lead-plug bearings. The base-isolated frames were modelled using a finite element program and those performances were evaluated in the light of the nonlinear time history analyses by six natural accelerograms compatible with seismic hazard levels of 2% probability of exceedance in 50 years. The performance of the isolated frames was assessed in terms of roof displacement, relative displacement, interstorey drift, absolute acceleration, base shear and hysteretic curve.

• Earthquakes and Structures
• /
• v.7 no.6
• /
• pp.1223-1240
• /
• 2014

Seismic isolation has been established as an effective earthquake-resistant design method and the lead rubber bearings (LRBs) are among the most commonly used seismic isolation systems. In the scientific literature, a sharp bilinear model is often used for capturing the hysteretic behaviour of the LRBs in the analysis of seismically isolated structures, although the actual behaviour of the LRBs can be more accurately represented utilizing smoothed plasticity, as captured by the Bouc-Wen model. Discrepancies between these two models are quantified in terms of the computed peak relative displacements at the isolation level, as well as the peak inter-storey deflections and the absolute top-floor accelerations, for the case of base-isolated buildings modelled as multi degree-of-freedom systems. Numerical simulations under pulse-like ground motions have been performed to assess the effect of non-linear parameters of the seismic isolation system and characteristics of both the superstructure and the earthquake excitation, on the accuracy of the computed peak structural responses. Through parametric analyses, this paper assesses potential inaccuracies of the computed peak seismic response when the sharp bilinear model is employed for modelling the LRBs instead of the more accurate and smoother Bouc-Wen model.

• Structural Engineering and Mechanics
• /
• v.29 no.6
• /
• pp.689-707
• /
• 2008

This study presents a method to evaluate the seismic risk of an extradosed bridge with seismic isolators of lead rubber bearings (LRBs), and also to show the effectiveness of the LRB isolators on the extradosed bridge, which is one of the relatively flexible and lightly damped structures in terms of seismic risk. Initially, the seismic vulnerability of a structure is evaluated, and then the seismic hazard of a specific site is rated using an earthquake data set and seismic hazard maps in Korea. Then, the seismic risk of the structure is assessed. The nonlinear seismic analyses are carried out to consider plastic deformation of bridge columns and the nonlinear characteristics of soil foundation. To describe the nonlinear behaviour of a column, the ductility demand is adopted, and the moment-curvature relation of a column is assumed to be bilinear hysteretic. The fragility curves are represented as a log-normal distribution function for column damage, movement of superstructure, and cable yielding. And the seismic hazard at a specific site is estimated using the available seismic hazard maps. The results show that in seismically-isolated extradosed bridges under earthquakes, the effectiveness of the isolators is much more noticeable in the columns than the cables and girders.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2003.04a
• /
• pp.193-200
• /
• 2003

This paper presents a hybrid (i.e., integrated passive-active) system for seismic response control of a cable-stayed bridge. Because multiple control devices are operating, a hybrid control system could alleviate some of the restrictions and limitations that exist when each system is acting alone. Lead rubber bearings are used as passive control devices to reduce the earthquake-induced forces in the bridge and hydraulic actuators are used as active control devices to further reduce the bridge responses, especially deck displacements. In the proposed hybrid control system, a linear quadratic Gaussian control algorithm is adopted as a primary controller. In addition, a secondary bang-bang type (i.e., on-off type) controller according to the responses of lead rubber bearings is considered to increase the controller robustness. Numerical simulation results show that control performances of the hybrid control system are superior to those of the passive control system and slightly better than those of the fully active control system. Furthermore, it is verified that the hybrid control system with a bang-bang type controller is more robust for stiffness perturbation than the active controller with μ-synthesis method and there are no signs of instability in the overall system whereas the active control system with linear quadratic Gaussian algorithm shows instabilities in the perturbed system. Therefore, the proposed hybrid protective system could effectively be used to seismically excited cable-stayed bridges.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2002.10a
• /
• pp.338-345
• /
• 2002

This paper presents a hybrid control strategy for seismic protection of a benchmark cable-stayed bridge, which is provided as a testbed structure for the development of strategies for the control of cable-stayed bridges. In this study, a hybrid control system is composed of a passive control system to reduce the earthquake-induced forces in the structure and an active control system to further reduce the bridge responses, especially deck displacements. Lead rubber bearings and ideal hydraulic actuators are used fur the passive and active control systems. Bouc-Wen model is used to simulate the nonlinear behavior of lead rubber bearings and an H₂/LQG control algorithm is adopted as an active control algorithm. Numerical simulation results show that the performance of the proposed hybrid control strategy is superior to that of the passive control strategy and slightly better than that of the active control strategy. The proposed control method is also more reliable than the fully active control method due to the passive control part. Therefore, the proposed hybrid control strategy can effectively be used to seismically excited cable-stayed bridges.

• Journal of Korean Society of Steel Construction
• /
• v.17 no.3 s.76
• /
• pp.307-316
• /
• 2005

This study analyzed the characteristics of four kinds of bridge rubber pads and suggested a method of determining the stiffness and the damping ratio of the pads.The stiffness of rubber pads can be estimated by a direct static test and a dynamic test indirectly.This study used both methods to determine the pad's stiffness.The damping ratio of pads can be obtained using the dynamic test and the damping ratio of polyurethane rubber pads was estimated to aproximate that of natural and chloroprene rubber pads.The polyurethane rubber pads are harder than natural and chloroprene rubber pads and thus carry larger load bearing capacity.In addition, they showed higher stiffness with the same shape factor than the others and thus are more available for bridge bearings.Although natural and chloroprene rubber pads are elongated to large deformation in the horizontal direction due to vertical loads, polyurethane rubber pads almost do not generate horizontal deformation due to vertical loads regardless of the thickness and hardness of the pads.Therefore, they do not need reinforced plate to restrict horizontal deformation.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.13 no.2
• /
• pp.85-93
• /
• 1993

Base isolation systems are economic and efficient for the control of structural vibration. In this study, the base isolators of LRB(laminated rubber bearing) type which have been generally used are fabricated and tested. From the static and dynamic tests, the characteristics of the base isolators, considering strain-hardening, hysteretic damping and horizontal stiffnesses, etc., are verified and particularly the feasibility as base isolation devices is discussed. Consequently, the test results are compared with the analytical ones that are derived from idealization as a bilinear model.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2002.09a
• /
• pp.379-386
• /
• 2002

The objective of this study is to investigate the seismic demand on the isolated slab-on-steel girder bridge under cold climate conditions. To this end comparative test results are presented of laminated elastomeric and lead-rubber seismic isolators in warm and cold temperature conditions. At extremely cold temperatures, rubber "glass-harden" and as a result rubber bearings that may be used for seating bridges behave in a significantly non-linear fashion. From the nonlinear time history analysis of the isolated slab-on-steel girder bridge, larger forces are transferred to the substructures. however smaller displacement at superstructure is obtained under cold climate conditions. These phenomenons might need to be considered in design stage of the seismically isolated bridges.

• Nuclear Engineering and Technology
• /
• v.30 no.5
• /
• pp.387-395
• /
• 1998

In general, the laminated rubber bearing (LRB), a composite structure laminated with the elastic rubber and steel plates, has a complex hysteretic nonlinear characteristics in relationships between the restoring force and shear deflection. The representative nonlinear characteristics of LRB include the change of hysteresis loop with cyclic shear deflections and the hardening effects at large shear deflection regions. Changes of the hysteresis loop of LRB with cyclic shear deflections affect the horizontal stiffness and the damping characteristics. The hardening behavior of LRB in large shear deflection region results in an increased horizontal stiffness and therefore, has a great impacton the seismic responses. In this paper, the seismic response analysis is carried out using the modified hysteretic bi-linear model of LRB, which takes into account the hysteresis loop change and the hardening behavior with cyclic shear deflection. The results on seismic responses are compared with those obtained using the widely used hysteretic hi-linear model. The new model is found to reveal the greater amount of peak acceleration response.