This study investigates the contribution of rubber and lead core to amplification in mechanical properties of lead rubber bearings (LRBs) when subjected to cyclic motion after low temperature ...exposure. In the experimental program, both large- and small-size LRBs were tested in order to observe the effect of bearing size on the results. For both sizes, tests were conducted with two identical bearings in terms of geometry. One of the bearings had a lead core while the other one did not. Displacement controlled cyclic tests were performed at a frequency of 0.1 Hz and a rubber shear strain of 100% after the bearings were conditioned at 0, −10 and −20 °C for a period of 24 h. Force-displacement loops recorded during the tests were used to compute hysteretic properties of bearings with and without a lead core. Comparison of hysteretic properties provides the contribution of the lead core to modification in post-yield stiffness of both large- and small-size LRBs. Test results showed that variation in post-yield stiffness of both large- and small-size LRBs has a similar trend which is to increase with decreasing temperature. It is also found that the contribution of lead core to post-yield stiffness depends on the size of LRB. In small-size LRB, the amount of lead core contribution to post-yield stiffness decreases with decreasing temperature while it remains almost unchanged for large-size LRB.
•Full-scale LRB tests were conducted for several low temperatures.•Changes in rubber and lead contributions to post-yield stiffness of LRBs in case of low temperature exposure were determined.•Large- and small-size LRBs were tested to observe the size effect.•The amount of lead core contribution to post-yield stiffness depends on both LRB size and temperature.
•Developed a new type of fiber-reinforced seismic isolator with low cost and high-performance features.•Tensile and bending performance tests were conducted on the fiber-reinforced plastic ...plates.•Evaluated FRP seismic isolators’ mechanical properties, including the vertical compressive performance, horizontal shear performance, ultimate performance, shear strain correlation, compressive stress correlation and loading frequency correlation by mechanical properties tests.•Studied the distributions of horizontal normal stress, vertical normal stress and interfacial shear stress in the isolator by numerical analysis.•Studied the effects of changing the plane size of the FRP seismic isolator and the plate/rubber thickness ratio on the isolator’s performance.
Seismic isolators are widely used in the field of seismic mitigation. But the disadvantage of the high cost limits the promotion of seismic isolators in underdeveloped areas. Therefore, the development of a new type of low-cost seismic isolator will facilitate the application of seismic isolation technology. This paper proposes a fiber-reinforced plastic (FRP) seismic isolator with cost-effective and stable mechanical performance features, which uses a synthetic material of alkali-free fabrics and vinyl resin instead of the steel plate in the traditional laminated isolator. The design and manufacturing process of the bearing makes it have higher stability and integrity than the traditional bearing. A series of mechanical properties tests were conducted to investigate the mechanical behavior of the FRP seismic isolator and to determine the boundary properties of the FRP seismic isolator. The stress distributions inside the FRP seismic isolator are analyzed detailly by the finite element model. The effects of changing the plane size of the FRP seismic isolator and the plate/rubber thickness ratio (P/RTR) on the isolator performance were studied to provide technical support for the subsequent design and manufacture of FRP seismic isolators. The experimental and numerical analyses show that the FRP seismic isolators developed in this paper have good performance and are beneficial for application in low-rise building structures.
Seismic isolators such as rubber bearings and other dampers are critical components of seismic design. The hysteresis behavior of such bearings is complicated, and engineers are using a bilinear ...model or equivalent linearization method in design practice. The response evaluation and initial design parameter assumptions are highly dependent on engineers' expertise and need repeated analysis. Therefore, this study proposed a machine learning‐based approach to conduct bridge seismic isolation performance evaluation and design parameters proposal without repeating the nonlinear simulations. The training data were generated by conducting a nonlinear time history analysis of the bridge structure model with input design earthquakes. Four trained three‐layer neural network models could perform bridge seismic response evaluation, predict the structure's seismic response, and suggest design proposal using some input parameters.
Bridge seismic isolation design is complicated and highly dependent on the engineer's expertise, as the seismic response is related to both the bridge's dynamic characteristics and the seismic isolator's nonlinear characteristics, in which both the seismic performance evaluation and initial design parameters proposal should be conducted simultaneously. Therefore, this study proposed an AI‐enhanced bridge seismic isolation performance evaluation and design proposal using an artificial neural network, which aims to reduce the computation time in analysis during the design process without repeating the time history analysis and repeated adjustment of the initial design parameters.
The expansion of earthquake zones over the past decade motivates scholars and researchers to find appropriate solutions to reduce demolishing and disaster risk. Base Isolation is one of the modern ...engineering solutions to dampen the earthquake force transmitted to the building. This paper estimates the effect of replacing the lead core of a lead rubber bearing (LRB) with the same size of rubber core on the mechanical properties of the seismic isolator using Finite Element Analysis (FEA). The Mooney-Rivlin was used to define the rubber hyperelastic and the Mullins effect was used to determine the rubber damage. The isolator, 700 mm in diameter with a lead core of 200 mm, using 24 rubber shims of 10 mm thickness, was simulated from a manufacturing company brochure. The shear strain of 150% was adopted with 3 hysteric loops for each model. Results presented that the rubber core increased 22% of the horizontal stiffness but decreased 5% of both horizontal force and stability. The Mullins Effect presented the rubber damage behaviour without a hysteresis loop, in which the horizontal stiffness had reduced because of rubber damage.
The research objective is to develop a rubber mixture for the High Damping Rubber Bearing HDRB type of seismic base isolation system to resist seismic loads, and compare it with international ...companies’ brochures. Experiments were conducted on three HDRB models of 150 mm in diameter and 12 cm in height. These models were manufactured locally from natural rubber with other chemical additives and steel sheets. Load and unload tests (quasi-static) were conducted on the models simulating earthquake loads, first loaded with a vertical load of 110 kN, and then the base cyclic horizontally with an increasing amplitude of 25 % until 125 % of the shear strain. The vertical stiffness was 44,027 kN/m, the effective horizontal stiffness was 334 kN/m, and the damping ratio was 20.1 % experimentally. The results were within satisfactory ranges of the parametric values in the manufacturing design brochure, indicating the developed rubber mixture is convenient, giving a great motivation to manufacture seismic isolators locally at suitable prices.
Summary
The influences of design parameters, including sloping angles of bearing plates and friction damping forces, together with seismic parameters, including corner periods and effective peak ...accelerations that are usually used for characterizing a design response spectrum, on the maximum horizontal displacement responses of sloped rolling‐type seismic isolators are numerically discussed in this study. Because the seismic isolators feature the constant acceleration control (or zero postelastic stiffness) performance, the equivalent linear model conventionally adopted in the equivalent lateral force procedure might not be adequate for predicting their maximum horizontal displacement response under a given seismic demand. Therefore, considering a small number to a large number of coefficients, several statistics‐based empirical formulas that are able to approximate their maximum horizontal displacement response are proposed. Not only the accuracy but also the conservative property of the proposed empirical formulas are discussed by comparing their predictions with the nonlinear response history analysis results. To efficiently determine the horizontal displacement capacity of sloped rolling‐type seismic isolators during the preliminary design stage, the statistics‐based empirical formula considering a reasonable number of coefficients is recommended.
This paper is focused on the modelling, the system identification and the adaptive control design of an unidirectional hydraulically actuated seismic isolator test rig.
The plant, constituted by the ...hydraulic actuation system and the isolator under test, is characterized by a non-linear behaviour and parametric uncertainties caused by the operating conditions and the unknown characteristics of the device to be tested. Therefore, a model reference adaptive approach is adopted for the position controller synthesis. To this end, a first order non-linear model is proposed and its structure identified.
Experimental results and simulations highlight the goodness of the proposed model and the effectiveness of the designed control for the hydraulically actuated isolator test rig.
•A system structure identification is performed.•A non-linear first order model of the seismic isolator test rig is derived.•A parameter sensitivity analysis is carried out.•A non-linear adaptive control is designed.
Seismic base isolators and dampers are commonly used as control tools in building frames to mitigate earthquake damage. This study proposes and investigates a structural system consisting of a ...central fixed core and an isolated section, the two parts of which are connected to each other by a damper. In new structures, called partially isolated (PI) structures, the interaction between conventional frames with fixed bases and frames equipped with control tools including isolators and dampers is measured using a three-mass model by three simplified differential equations of motion. Validating the proposed model provided good results. The model with various modes of partial isolation and certain mass ratios was subjected to seven near-fault and seven far-fault earthquakes to be evaluated. The mean displacement, acceleration, and shear responses of the structural-isolating-damping model were compared with those of fully isolated (FI) and fully fixed (FF) structures. The results showed that by connecting the two parts, responses of the fixed part to FF structure and those of the isolated part to FI structure significantly improved. Under near-fault earthquakes, the displacement response reduction of the fixed part to FF model was estimated to be about 20% and the response of the isolated part to FI model was about 50%. Due to the functional weaknesses observed in FI structures including large displacement of the structure base, poor performance of the isolator in near-fault earthquakes, and high costs of preparing and installing the isolation system, these points were significantly resolved in PI structures.
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