Base-isolated High-rise Buildings Research Articles

Alongwind and crosswind response of friction-pendulum base-isolated high-rise buildings

Base isolation technology is widely accepted as an effective strategy for the seismic design of buildings. Although the elastomeric isolator is still extensively adopted for the base-isolation system in practice, there is a trend to use the frictional pendulum bearing (FPB) due to its high vertical bearing capacity, stable performance and good recentering capability. In this paper, the dynamic response of base-isolated high-rise buildings with FPB having a velocity-dependent friction coefficient subjected to uncoupled alongwind and crosswind loads is studied. The response characteristics calculated from response history analysis (RHA) are analyzed. Meanwhile, two statistical linearization methods are utilized to estimate the standard deviation (STD) of the structural response and to obtain the equivalent parameters of the linearized system. The time-varying mean of the base displacement under alongwind load with a non-zero mean is also discussed by the linearization method. Finally, a parameter analysis of the isolation bearing is performed to investigate the effects of the radius and friction coefficient of the sliding plate on the wind-induced vibration. This study highlights the strong nonlinear response characteristics of base-isolated high-rise buildings with FPB and offers design guidelines under strong winds.

High-performance isolation systems with rate-independent linear damping for seismic protection of high-rise buildings

There is currently growing concern within the earthquake engineering community regarding the potential for base-isolated structures to experience significant responses during extreme earthquakes. This concern is primarily driven by the observation that induced ground motions can contain influential long-period components, which may exacerbate the structural response. Supplementing damping using conventional damping devices contributed to a significant reduction in the responses whereas perhaps compromises the effects of base isolation itself when subjected to more frequently occurring short-period ground motions, particularly for base-isolated high-rise building structure. The present study employs rate-independent linear damping (RILD) to control the seismic response of high-rise building structures subjected to both short- and long-period ground motions. RILD is a damping mechanism that exerts a control force that is independent of the vibration frequency under harmonic deformation. This method is implemented in conjunction with isolators to achieve the desired control objectives. For passive realization of RILD, both the Maxwell-negative-stiffness (MNS) and modified tuned Maxwell–Wiechert (MTMW) models were considered. A regression technique is presented in this study to optimally design the properties of the MTMW model, and a recursive formulation is developed to conduct structural response history analyses efficiently. The proposed method for seismic protection of high-rise structures was demonstrated using a 20-story benchmark building structure as the analytical model. This approach serves to illustrate the advantages of the proposed method in a practical context. Both short- and long-period ground motions are used for examining the performance of rate-independent damping models incorporated into base-isolated high-rise structures. The findings suggest that the combined isolation systems, in conjunction with rate-independent linear damping (RILD), offer significantly enhanced protection against conventional short-period ground motions, without sacrificing performance during long-period ground motions. Compared to commonly utilized isolation systems, this approach demonstrates superior performance in safeguarding high-rise structures.

Enhancing the seismic performance of high-rise buildings with lead rubber bearing isolators

Recent earthquakes have enforced the engineering community to design seismically more efficient buildings through the energy dissipation systems. For this purpose, this paper investigates the seismic behavior of a high-rise building with a series of base isolation systems. Firstly, a 20-storey steel frame is selected as a fixed-base building, and then equipped with lead rubber bearings (LRBs). In the modelling of LRB, isolation period is alternatively varied as 4, 4.5, and 5 sec to evaluate the effectiveness of the isolator characteristic on the seismic performance of the high-rise base-isolated buildings. The seismic responses of the fixed-base and base-isolated buildings evaluated through a series of time-history analyses are performed using natural ground motion records. The analysis results are compared using engineering demand parameters such as storey displacement, isolator displacement, relative displacement, roof drift, interstorey drift ratio, absolute acceleration, base shear, base moment, input energy, and hysteretic curve. It is revealed that adjusting the isolation period in the design of LRB improved the seismic performance of the base-isolated high-rise steel buildings.

Wind-Induced Impact Behavior of Base-Isolated High-Rise Buildings with Adjacent Structures

The base-isolation technology has been increasingly applied in high-rise buildings in recent years. Previous studies have shown that the unfavorable wind-induced response can be effectively reduced by a certain degree of hysteretic energy dissipation after the yielding of the isolation system under strong wind load. However, a large relative inelastic displacement at the isolation level will occur under this condition, which is likely to exceed the width of seismic gap, and cause a structural impact with the adjacent structures (i.e. retaining wall or other barriers). Such wind-induced impacts may have detrimental consequences on the structural performance and have not been investigated much before. This study prospectively investigated the wind-induced impact behavior of base-isolated high-rise buildings with adjacent structures. The multi-story superstructure is modeled as a linear elastic shear building, while the isolation system is represented by bilinear hysteresis restoring force model. An impact element combined with linear spring and damper is used. The story wind load is determined by its cross power spectral density (PSD). Responses for two kinds of typical impact including crosswind and along-wind impact are examined by time history analysis. The results demonstrate that the impact will increase the fluctuation components of superstructure displacement, shear force and bending moment to some extent compared with that of the base-isolated building without impact. The floor accelerations, especially floors close to the base, are significantly increased during impact. The impact has no effect on the mean component of each response. At last, a parametric analysis is carried out to explore the influences of various impact parameters on the inelastic impact response. The results of this study can help to better understand the impact behavior of base-isolated high-rise buildings under strong wind excitation and be useful for performance-based wind resistance design.

The Influence of Wind Direction on the Inelastic Responses of a Base-Isolated Square Section High-Rise Building

Previous studies show that the largest wind-induced response of a square section fixed-base high-rise building occurs when the strong wind is blowing perpendicular onto a building face, and the greatest translational response is likely to occur in the crosswind direction. When it comes to a square section base-isolated high-rise building that allows the isolation system to yield under strong wind excitation, the inelastic response shows distinctive non-Gaussian characteristics under fluctuating wind excitation and mean drift phenomenon under non-zero mean wind load. These characteristics may lead to a quite different result when determining the most unfavorable wind direction. Thus, the influence of wind direction on the inelastic response of a square base-isolated high-rise building is discussed in this study based on synchronous pressure measurement. The multi-story superstructure is modeled as a linear elastic shear building, while the isolation system is represented in a bilinear hysteresis restoring force model. The peak value of the inelastic response is estimated through a moment-based Hermit model from an underlying standard Gaussian process. The results show that when the strong wind blows perpendicular onto a building face, the greatest inelastic displacement, both at the top and isolation level, occurs in the along-wind direction, which is different from the elastic response. With the change of wind direction, the largest combined inelastic displacement still occurs when the wind inclination angle is 0°, while the combined displacement in other directions is also very large, which is worthy of concern.

Optimization design of triple friction pendulums for Base-isolated High-rise buildings based on bearing displacement and collapse fragility

Although many studies have focused on the isolation performance of triple friction pendulum bearing (TFPB), but existing investigations are mainly for low-rise buildings and the TFPB design may not be utilized in all stages under the increasing earthquake levels (i.e. in some research the TFPB only slides at one stage and almost all research do not address this issue). To utilize all sliding stages of TFPB for high-rise buildings, a design method based on multi-objective optimization is proposed to determine the parameters of TFPB. In addition, the approach applied in this paper will guarantee the safety of the building (i.e. the collapse probability of the building can meet the requirement). Using the optimal parameters of TFPB, seismic responses and collapse probability under the maximum considered earthquake (MCE) level of the building are compared with those of the building isolated using the TFPB which the parameters are optimized by a genetic algorithm (GA). Based on the numerical results, it is found that the design method proposed in this paper is more effective in selecting the appropriate parameters to protect the structures.

On the Influence of the Vertical Earthquake Component on Structural Responses of High-Rise Buildings Isolated with Double Friction Pendulum Bearings

The double friction pendulum (DFP) bearing is adapted from the well-known single friction pendulum (SFP) bearing. This type of bearings has been widely used for structural vibration controls. The main advantage of the DFP is its capacity to accommodate larger displacements as compared with the SFP one. This paper aims to assess the effect of the vertical earthquake component on the seismic behaviour of a base-isolated high-rise building. In this respect, the mathematical model of the building subjected to earthquake excitations with an implementation of a DFP bearing system is established. The model presented herein considers earthquake excitations in horizontal (X and Y) and vertical (Z) directions. A series model of two friction elements is presented for the bearing, where the friction load of the bearing surface is governed by a modified Bouc-Wen model, which is dependent on the sliding velocity and the contact pressure. The numerical results of an example of a base-isolated 9-story steel building subjected to near-source and far-field earthquakes show the high effectiveness of the bearing system in reduction of the seismic response of the building, especially in the near-source region, as well as exhibit considerable effectiveness of the vertical earthquake component on the bearing and structural behaviour.

Design optimization of triple friction pendulums for base-isolated high-rise buildings

The triple friction pendulum bearing, as a novel seismic isolator, has received much attention due to its notable advantages such as variable stiffness and damping; however, existing investigations and applications are mainly for low-rise or medium-rise buildings. In order to determine optimal design parameters of triple friction pendulum bearings for high-rise buildings, equations of motion for an isolated high-rise building are derived, and an evaluation function is developed to indicate the isolation effect with different pendulum parameters. In the optimization analysis, seven ground motions are scaled to three levels (corresponding to the service level, the design basis, and the maximum considered earthquakes, respectively) and the genetic algorithm is applied to determine the optimal pendulum parameters. The optimization results are compared with those obtained by the single-degree-of-freedom model, where significant difference is observed, showing the necessity of the presented study. Using the optimal parameters of triple friction pendulum bearings, seismic responses of the isolated building are analyzed and compared with those of the building isolated using the single friction pendulum bearings and the base-fixed building, where it is observed that the triple friction pendulum bearing is more effective and reliable in reducing base shear, floor acceleration, and story drifts.

Robustness Evaluation of Elastoplastic Base-Isolated High-Rise Buildings Subjected to Critical Double Impulse

A new method of robustness evaluation is proposed for an elastoplastic base-isolated high-rise building considering simultaneous uncertainties of structural parameters. Since it is difficult to evaluate the robustness of elastoplastic structures due to heavy computational load on the time-history response analysis including elastoplastic response, a double impulse input is used to provide a closed-form solution of the critical response of a single-degree-of-freedom (SDOF) elastic-perfectly plastic structure under a near-field ground motion. Introducing an equivalent elastoplastic SDOF model of a base-isolated high-rise building, the worst combination of uncertain structural parameters, i.e. the stiffness and yield deformation at the base-isolation story and the stiffness of the superstructure, can be derived which leads to the upper bound of the critical elastoplastic response. It is shown that, by using the derived upper bound of the critical response, the robustness function, a measure of the robustness, of elastoplastic structures can be evaluated efficiently. In numerical examples, the robustness of a 30-story base-isolated high-rise building is compared with those of other models with different yield deformations at the base-isolation story to find a preferable design with larger robustness.

Seismic Response of Base-Isolated High-Rise Buildings under Fully Nonstationary Excitation

Stochastic seismic responses of base-isolated high-rise buildings subjected to fully nonstationary earthquake ground motion are computed by combining the pseudoexcitation and the equivalent linearization methods, and the accuracy of results obtained by the pseudoexcitation method is verified by the Monte Carlo method. The superstructure of a base-isolated high-rise building is represented by a finite element model and a shear-type multi-degree of freedom model, respectively. The influence of the model type and the number of the modes of the superstructure participating in the computation of the dynamic responses of the isolated system has been investigated. The results of a 20-storey, 3D-frame with height to width ratio of 4 show that storey drifts and absolute accelerations of the superstructure for such a high-rise building will be substantially underestimated if the shear-type multi-degree of freedom model is employed or the higher modes of the superstructure are neglected; however, this has nearly no influence on the drift of the base slab.

Stochastic Seismic Response Analysis of Base-Isolated High-Rise Buildings

Stochastic seismic responses of a base-isolated high-rise building subjected to non-stationary random seismic earthquake ground motion are investigated by combining the pseudo excitation method and equivalent linearization method, for which the superstructure is modeled as a multi-degree-of–freedom system considering the shear-flexural effect, the hysteretic restoring forces of the isolators are described by the Bouc-Wen differential equation model which has a good performance on the transition from elastic responses to plastic responses. With the linearization for such a Wen's model, a first order differential equation will be obtained, which will couple with the governing equations of the isolated structure and so make up the closed-form expressions for base-isolated high-rise buildings, thus the stochastic seismic responses of the simplified systems will be obtained conveniently. Consequently, the solution of the stochastic seismic responses of a base-isolated structure considering hysteretic nonlinear behavior is transformed to a deterministic step-by-step integration problem. The precision of the pseudo excitation method is verified by Monte-Carlo simulation, the results for a 17-storey frame with height:width ratio=5.1 show that the isolation technique greatly reduces the inter-storey drifts and absolute accelerations of the superstructure for high-rise buildings and that the responses are substantially underestimated if the flexural effect is neglected.

Theoretical Analysis for Effects on a Base-Isolated High-Rise Building

In this paper, three-Dimensional finite element analysis was used for the research of a base-isolated high-rise building. After studying the effects of different structural systems, action of bidirectional earthquake wave, P-Delta effect and acceleration responses on it, some useful conclusions are given as follows: in the same structural systems, the story shears of the isolated structure are one order of magnitude less than those of the non-isolated structure under the action of the same seismic waves; the story displacements of the isolated high-rise frame-shear structure and those of the isolated high-rise shear wall structure are different under the action of the same seismic waves; under the action of different seismic waves, the earthquake responses of the same structural system are quite different; the effects of bidirectional earthquake waves on some components should be considered; P-Delta effect can be ignored in the base-isolated building; and the acceleration responses of the isolated high-rise building are different from those of the non-isolated counterpart. Results show that the technology of base-isolation can be applied to the high-rise building system.

EARTHQUAKE RESPONSE CHARACTERISTICS ON UPLIFT OF MULTILAYERED ELASTOMERIC ISOLATOR OF BASE ISOLATED HIGH-RISE BUILDING WITH SETBACK ELEVATION

The earthquake response characteristics of the isolators in a base-isolated high-rise building with a set-back were examined numerically. A three-dimensional framework vibration model was subject to seismic response analysis using a software application that takes into account the bending stiffness of seismic shear walls and floor slabs. The tension and compression in the isolators was analyzed for three motion components, the two horizontal components as well as the vertical motion component, input simultaneously for each of 51 strong ground motion accelerograms recorded during actual earthquakes. The results showed that (1) axial stresses in isolators at the corners below the low-rise part are higher than those in isolators under the high-rise part, with more than a few of the strong motions inducing maximum tensile stresses exceeding σt = 1N/mm2 at these points, which is the conventional seismic performance design target in the design process, and also compressive stresses that exceed the critical stress; (2) the tension in these corner isolators under the low-rise section is affected more by the vertical component of strong motion than by the horizontal components; and (3) the effective maximum acceleration amplitudes of short-period vertical strong motion and of long-period horizontal strong motion can be adopted as suitable indexes for evaluating the strong-motion induced tension in these corner isolators of a base-isolated high-rise building with set-back.

STUDY ON ESTIMATION OF STRUCTURAL PARAMETERS OF BASE-ISOLATED HIGH-RISE BUILDINGS BY MEANS OF STOCHASTIC THEORY

This paper describes that the probabilities of exceedance is so effective to estimate safe and secure structural parameters under considering the incompatibility between the seismic performance and the wind-resistance performance. In this paper, a technique, which estimate the comprehensive safety for the earthquake loading and the wind loading based on the concept of probability, is indicated. It is tried that the structural parameters of base-isolated high-rise buildings are estimated by means of this technique. From the results, it is confirmed by estimating the probabilities of exceedance that the seismic performance and the wind-resistance performance have the incompatibility. It is also confirmed that the displacement in the base-isolator and the shear force in the first story have the incompatibility. The possibility to estimate safe and secure structural parameters for the design criteria based on the probability concept is indicated.

耐震壁及び床スラブの曲げ剛性を考慮した高層免震建物の地震応答解析 : 強震動水平・上下両成分同時入力が高層免震建物の地震応答性状に及ぼす効果に関する研究その1

耐震壁及び床スラブの曲げ剛性を考慮した高層免震建物の地震応答解析 : 強震動水平・上下両成分同時入力が高層免震建物の地震応答性状に及ぼす効果に関する研究その1

クリープ変形を伴う免震建物の風応答性状に関する研究

This study proposes analytical methods for determining wind responses of base-isolated high-rise buildings with creep deflection and clarifies characteristics of their modal forces and responses. The following results are derived. Modal forces on a base-isolated building are calculated easily by multiplying those on a conventional building with a linear mode shape function by the proposed mode shape correction factor. It is shown that the proposed methods for determining wind responses of base-isolated high-rise buildings with creep deflection are appropriate. Creep deflections are insensitive to fluctuating wind forces, so creep deflections and wind responses can be calculated separately. Shifts of the mean wind response of a base-isolated building due to plastic characteristics of isolation devices occur, but they behave almost elastically in the along-wind direction. However, the isolation layer moves inelastically in the across-wind and torsional directions. The standard deviation response calculated from the wind force for a certain direction is equal to or greater than that derived from 3 components of wind forces simultaneously. However, the mean response considering the former is smaller than that considering with the latter.

Resonant behaviour of base-isolated high-rise buildings under long-period ground motions

SUMMARY The resonant behaviour of base-isolated high-rise buildings under long-period ground motions is investigated. The long-period ground motions are known to be induced by surface waves. While the acceleration amplitude of such long-period ground motion is small, the velocity amplitude is fairly large. It is expected that high-rise buildings and base-isolated buildings with long fundamental natural periods are greatly influenced by these long-period ground motions. Especially base-isolated high-rise buildings with friction-type bearings may have remarkable mechanical characteristics unfavourable for these long-period ground motions. The purpose of this paper is to reveal that the long-period ground motions recorded in Japan have the intensity to make base-isolated high-rise buildings in resonance with long-period components and that careful treatment is inevitable in the structural design of these base-isolated high-rise buildings. It is pointed out that the friction-type bearings are effective in general in avoiding the resonance with ground motions with a narrow-range frequency characteristic, but are dangerous for ground motions with a wide-range frequency characteristic in the long period range. Copyright © 2005 John Wiley & Sons, Ltd.