Mid-story Isolation Research Articles

Seismic Response Evaluation of Mid-Story Isolation System According to the Change of Characteristics of the Seismic Isolation Device

Seismic Response Evaluation of Mid-Story Isolation System According to the Change of Characteristics of the Seismic Isolation Device

Seismic Response Evaluation of High-Rise Buildings Considering Installation Story of the Mid-Story Isolation System

Seismic Response Evaluation of High-Rise Buildings Considering Installation Story of the Mid-Story Isolation System

主系と副系から成る建物を対象とした動的縮約モデルによる層間変位分布の復元

A two degree-of-freedom (2-DOF) model is employed for mid-story isolation buildings or a tuned mass damper mounted on buildings in practical design. These systems are classified into a primary-secondary structural system. A seismic response analysis using this model is an empirical evaluation method in design practice. However, the accuracy of the peak response distribution computed by the 2-DOF model has not been clarified. The objective of this study is to investigate the error in the inter-story drift calculated by the 2-DOF model. The employed 2-DOF model is derived from its original multi-degree of freedom system (MDOF) based on dynamic reduction technique. Parameters of interest are a tuning ratio and mass ratio. The tuning ratio is a frequency ratio to secondary to the primary system. The mass ratio is a ratio of the secondary mass to the effective mass of the primary system. The mass ratio is set within the parameter of 0.02 to 0.5. The inter-story drifts in primary system are recovered from generalized displacements (modal displacements) of the 2-DOF model and classical modal vectors with respect to the primary system. A stochastic vibration analysis is conducted in both original MDOF model and corresponding the 2-DOF model. RMS responses are obtained by solving a Lyapunov equation governing the stochastic process. The displacement responses of the MDOF model are decomposed into coupled and decoupled components. The decoupled components are the higher modal responses. The coupled component is the remaining response and corresponds to a controlled response. The controlled mode is limited to the fundamental mode in this study. The response of the controlled mode is compared to the one from the 2-DOF model. The analysis reveals that the 2-DOF model estimates accurate floor displacements. The relative errors are ten percent at most. However, the 2-DOF model underestimates inter-story drifts in the upper story of the primary system. As the mass ratio becomes larger, the error becomes large. A convenient modal superposition technique is proposed to improve the accuracy of inter-story drift obtained by the 2-DOF model. The method is as follows. The CQC modal combination is applied with modal damping factors evaluated by classical modal vectors. Then, amplitude of the response is slightly corrected to be consistent with the one obtained from the MDOF model. It is confirmed that reasonable accuracy is obtained by the proposed method.

Application of Mid-story Isolation System for Seismic Response Reducing of Dome Structure

Application of Mid-story Isolation System for Seismic Response Reducing of Dome Structure

Model reduction and optimal parameters of mid-story isolation systems

The paper presents a modal synthesis-based approach to develop a reduced two, three, or higher order model to represent a mid-story isolated building structure. Herein, the approach is utilized to obtain a simple two-degree of freedom model which can effectively capture the response characteristics of the full system well. This reduced order model is used to formulate analytical approaches for calculating the optimal parameters of a mid-story isolation system that either minimize the (a) maximum base shear force amplitudes for harmonic base excitations or (b) base shear force variance for a band-limited white noise random base excitation. Numerical examples are, then, presented to study the influence of the placement of an optimal mid-story isolation system at different levels in a building as well as to show the structural response reducing effects of the isolators.

Seismic Performance of Midstory Isolated Structures under Near-Field Pulse-Like Ground Motion and Limiting Deformation of Isolation Layers

Excessive deformation of the isolation layer in midstory isolated structures may occur under strong near-field pulse-like ground motion, which would result in the overturning collapse of the superstructure. The objective of the present research is to limit excessive deformation of the isolation layer and to reduce nonlinear response of midstory isolated structures. To this end, a protective system is presented to limit deformation of the isolation layer by soft pounding. Based on the Kelvin pounding model, a mechanical model is put forward for this protective system. In addition, a new method has been proposed that synthesizes artificial near-field pulse-like ground motion by combining the real near-field nonpulse ground motion with simple equivalent pulses. Also, the impact of artificial near-field pulse-like ground motion on the nonlinear response of midstory isolated structures and the deformation of the isolation layer has been investigated. The effectiveness of the midstory isolation with the protective system has been validated. The results show that the maximum deformation of the isolation layer significantly exceeds the allowable deformation of lead-rubber bearings when subjected to near-field pulse-like ground motion, and it causes the lead-rubber bearings destruction. The proposed protective system is effective in restricting the excessive deformation of the isolation layer and reducing nonlinear responses of the isolated structure, preventing collapse of the superstructure.

Seismic Fragility Analysis of Mid-Story Isolation and Reduction Structures Based Two Directions

This study focus on derivation of such fragility curves using classic mid-story isolation and reduction structures (MIRS) in China metropolis. This study focus on derivation of such fragility curves using conventional industrial frames with masonry infill wall. A set of stochastic earthquake waves compatible with the response spectrum of China seismic code selected to represent the variability in ground motion. Dynamic inelastic time history analysis was used to analyze the random sample of structures. MIRS seismic capability of longitudinal and transversal orientation is different. Stochastic damage scatter diagrams based different seismic intensity index are obtained. Seismic fragility of longitudinal axis (Y axis) is larger than transversal axis (X axis) of frames under major earthquake obviously.

스마트 최상층 면진시스템의 중약진지역 적용성 평가

Because a smart isolation system cannot be used as a base isolation system for tall buildings, top-story or mid-story isolation systems are required. In this study, adaptability of a smart top-story isolation system for reduction of seismic responses of tall buildings in regions of low-to-moderate seismicity has been investigated. To this end, 20-story example building structure was selected and an MR damper and low damping elastomeric bearings were used to compose a smart base isolation system. Artificial earthquakes generated based on design spectrum of low-to-moderate seismicity regions are used for structural analyses. Based on numerical simulation results, it has been shown that a smart top-story isolation system can effectively reduce both structural responses and isolation story drifts of the building structure in low-to-moderate seismicity regions in comparison with a passive top-story isolation system.

Shaking Table Test Study on Mid-Story Isolation Structures with Viscous Damper

Mid-story isolation structure is developing from base isolation structures. As a complex structural system, the work mechanism of base isolation structure is not entirely appropriate for mid-story isolation structure, and the prolonging of structural natural period may not be able to decrease the seismic response of substructure and superstructure simultaneously. In this paper, for a four-story steel frame model, whose prototype first natural period is about 1s without seismic isolation design, the seismic responses and isolation effectiveness of mid-story isolation system with linear natural rubber bearing and viscous damper are studied experimentally by changing the location of isolation layer. Respectively, the locations of isolation layer are set at bottom of the first story, top of the first story, top of the second story and top of the third story. The results show that mid-story isolation can reduce seismic response in general, and substructure acceleration may be amplified.

Dynamic behavior of a building structure tested with base and mid-story isolation systems

The discrepancies of dynamic behavior in base-isolated and mid-story isolated buildings are investigated experimentally in this study. In a mid-story isolated building, the isolation system is incorporated into the mid-story rather than the base of the building. The shaking table test results disclose that with the same design of the isolated superstructure and isolation system, a mid-story isolated building has smaller fundamental modal quantities than a base-isolated building. Besides, the seismic response at the superstructure is mainly attributed to the fundamental mode response, while the higher mode responses contribute significantly to the seismic responses at the substructure below the isolation system. Therefore, the modal response spectrum analysis appropriately considering the contribution of higher modes, rather than the equivalent lateral force procedure only considering the fundamental mode, is suggested for the preliminary design of mid-story isolated buildings prior to performing nonlinear responses history analyses.

Analytical and experimental studies on midstory isolated buildings with modal coupling effect

SUMMARYIn a midstory isolated building, the isolation system is incorporated into the midstory rather than the base of the building. Because of the flexibility of the substructure below the isolation system in a midstory isolated building, the contribution of higher modes to the seismic responses of the midstory isolated structure may not be negligible, especially when the coupling of higher modes exists. To investigate this modal coupling effect, a simplified three‐lumped‐mass structural model of the midstory isolated building is assumed in this study. Through the equivalent linear analysis and shaking table tests, it is found that the coupling of higher modes may lead to enlarged acceleration responses at the super‐floor and superstructure above the isolation layer. Accordingly, a simple method to prevent the midstory isolation design from the coupling of higher modes attributed to the improper design of the substructure and superstructure is proposed in this paper. Copyright © 2012 John Wiley & Sons, Ltd.

Shaking Table Test Study on Mid-Story Isolation Structures

Mid-story isolation structure is developing from base isolation structures. As a complex structural system, the work mechanism of base isolation structure is not entirely appropriate for mid-story isolation structure, and the prolonging of structural natural period may not be able to decrease the seismic response of substructure and superstructure simultaneously. In this paper, for a four-story steel frame model, whose prototype first natural period is about 1s without seismic isolation design, the seismic responses and isolation effectiveness of mid-story isolation system with lead rubber bearing are studied experimentally by changing the location of isolation layer. Respectively, the locations of isolation layer are set at bottom of the first story, top of the first story, top of the second story and top of the third story. The results show that mid-story isolation can reduce seismic response in general, and substructure acceleration may be amplified.

Shaking Table Test Study on Mid-Story Isolation Structures

Mid-story isolation structure is developing from base isolation structures. As a complex structural system, the work mechanism of base isolation structure is not entirely appropriate for mid-story isolation structure, and the prolonging of structural natural period may not be able to decrease the seismic response of substructure and superstructure simultaneously. In this paper, for a four-story steel frame model, whose prototype first natural period is about 1s without seismic isolation design, the seismic responses and isolation effectiveness of mid-story isolation system with lead rubber bearing are studied experimentally by changing the location of isolation layer. Respectively, the locations of isolation layer are set at bottom of the first story, top of the first story, top of the second story and top of the third story. The results show that mid-story isolation can reduce seismic response in general, and substructure acceleration may be amplified.

System identification of mid-story isolation building using both ambient and earthquake response data

SUMMARY The behavior of story-isolated structures during an earthquake is highly affected by the characteristics of the isolation system and its location along the height of the building. Interaction between the super-structure and the sub-structure with mid-story isolation as nonlinear connector makes the mid-story isolation building even more complicated during the earthquake excitation. In this paper, two different identification techniques are applied to identify the time-varying dynamic characteristics of the mid-story isolation building using the ambient vibration test data as well as the earthquake response data. For the ambient vibration measurements, the recursive stochastic subspace identification method is used, whereas for the earthquake response data the recursive subspace identification is used. Comparison on dynamic characteristics of the story-isolated building from the results of identification is made, and the effect of nonlinear behavior of the mid-isolation system to the response of the building during the earthquake is discussed. Copyright © 2011 John Wiley & Sons, Ltd.

Seismic Vulnerability Analysis of Mid-Story Isolation and Reduction Structures Based Stochastic Vibration

This study focus on derivation of such fragility curves using classic mid-story isolation and reduction structures (MIRS) in China metropolis. A set of stochastic earthquake waves compatible with the response spectrum of China seismic code selected to represent the variability in ground motion. Dynamic inelastic time history analysis was used to analyze the random sample of structures. The result reveal that good effect for superstructure and reduction effect for substructure of MIRS is favorable and obvious under major earthquake, Weak position of MIRS was be pointed out and fragility curves of typical MIRS of China was obtained finally.

Experimental Investigation on Mid-Story Isolated Structures

Isolation technique has been acceded as a part of the China Seismic Code for Design of Buildings. In this code, the limitations for using isolation design are very strict, superstructure must be regular and the isolation layer must be located on the top of base (base isolated structure). Because of the needs of architecture and function or the feasibility of technique, some limitations have been broken in recent projects. Sometimes isolated layer can be set on the intermediate story, so-called the mid-story isolated structure. According to the characteristic of structure, isolation layer of mid-story isolated structure is set on a place where the structure’s vertical stiffness is suddenly changed, as like the top of the first story, middle story, conversion story of the structure. Laminated rubber bearings (LRB) are adopted as an isolation layer. Because the isolation layer is set on intermediate story, the whole structure is divided into superstructure and substructure; the structure’s dynamic characteristics are changed. The mechanism of mid-story isolated structure appears different characteristic compared with base isolation. The aim of mid-story isolation is not only to reduce seismic responses of superstructure, but also to reduce seismic responses of the substructure. Theoretical analysis and the shaking table test of the mid-story isolated structure were carried. And the response of mid-story isolated structure is discussed by comparing with the response of base-isolated structure and base fixed structure. The key problems of mid-story isolated structure are the force condition and the interaction of the structure up and below the isolation layer. Many factors, such as the number of story, mass, stiffness of superstructure and substructure, parameter of the isolation layer, have influence on the seismic behavior of the mid-story isolated structure. The optimum combination relationship of these factors is presented and dynamic characteristics and dynamic responses are investigated.

多質点系構造物モデルにおける遺伝的アルゴリズムによる免震装置の最適選択計画 : その2 中間層免震の場合

This study proposes an optimal selection method for base-isolation devices in a mid-story isolation structure using a genetic algorithm. Parameters employed in the genetic algorithm's evaluation functions are: A) eccentricity ratio, B) vertical load on each isolator, C) temporary load on each isolator, D) natural period, E) yield force coefficient of base isolation devices, F) the maximum response displacement of isolation devices, G) storey shear force coefficient and H) base isolation displacement. We employed three groups of parameters: (1). A-B-C-D-E, (2). A-B-C-E-F, (3). A-B-C-G-H. We did time history response analyses with buildings designed by the proposed method. As the result, the response value was suppressed in case of (3). Therefore, the proposed method is effective for selection isolation devices for mid-story isolation buildings.

中間層免震建物の地震応答

As arise great demands for maintenance of functions and protection of properties, recently many base isolated buildings have been constructed. Depending on the geometrical shape and occupancy type of buildings, mid-story isolation system is more suitable than conventional base isolation system for some buildings. Therefore, it is necessary to shed light on the seismic behavior for buildings with the mid-story isolation system. For the mid-story isolated buildings, nonlinear time history analyses as well as modal analyses with equivalent linear model were carried out. As the results, it is concluded that the mid-story isolation system is effective in reducing the seismic response and if the effect of higher modes related to the location of isolation devices can be properly evaluated, the proposed system is considered to be one of the efficient choices in the seismic design.