Multistory Building Structures Research Articles

The Seismic Shear Demand in Ductile Cantilever Wall Systems and the EC8 Provisions

The seismic shear provisions of EC8 for ductile reinforced concrete walls, serving as the lateral load resisting system in multistorey building structures are re-examined. Two aspects are considered (1) single walls, or a system comprising a number of equal-length walls, (2) a resisting system comprising walls of different lengths. It is demonstrated, in light of recent parametric studies, that the EC8 provisions for walls in the medium- and high-ductility classes (DC-M and DC-H, respectively) are both in need of revision. Possible revisions of requirements and a design procedure for a wall system are presented.

건축구조물의 층전단력 분포에 기초한 마찰감쇠기의 최적설계

본 연구에서는 지진하중을 받는 탄성구조물을 대상으로 층전단력 분포에 기초한 마찰감쇠기의 설계방법을 제시하였다. 먼저 마찰감쇠기의 슬립하중(slip-load)을 정규화하는 방법 별로 단자유도 시스템의 수치해석을 수행하고 비교하였다. 이를 통해 슬립하중과 가새 강성의 영향을 파악하였으며, 설치용 가새와 원구조물의 최적강성비를 찾았다. 다음으로는 다양한 고유주기와 층수를 갖는 구조물을 대상으로 수치해석을 통해 마찰감쇠기의 설치 층수와 위치의 결정방법 및 슬립하중의 분배 방법을 도출하였다. 이 과정에서 설치 층수가 포함된 성능지수를 사용하여 슬립하중의 총합으로부터 최적의 설치 층수를 도출하는 경험식을 제시하였다. 마지막으로 실제 지진하중을 사용한 수치해석을 통해 기존의 최적설계 방법과 비교하여 제안된 방법의 우수성을 입증하였다. In this study, a seismic design methodology for friction dampers based on the story shear force distribution of an elastic building structure is proposed. First, using two normalization methods for the slip-load of a friction damper, numerical analyses of various single-degree-of-freedom systems are peformed. From those analyses, the effect of the slip-load and the brace stiffness was investigated and the optimal silliness ratio of the brace versus original structure was found. Second, from the numerical analysis for five multi-story building structures with different natural frequency and the number of story, reasonable decision method for the total number of installation floor, location of installation and distribution of the slip-loads are drawn. In addition, an empirical equation on the optimal number of installation floor is proposed. Finally, the superiority of the proposed method compared to the existing design method is verified from the numerical analysis using real earthquake data.

Evaluation of seismic performance of multistory building structures based on the equivalent responses

The prediction of inelastic seismic responses and the evaluation of seismic performance of a building structure are very important subjects in performance-based seismic design. Currently, the inelastic time history analysis method and the pushover analysis method such as the displacement coefficient method (FEMA-273) and the capacity spectrum method (ATC-40) can be adapted to evaluate the seismic performance of a building structure. However, the pushover analysis methods have some drawbacks in estimating the accurate inelastic seismic responses. In this study, an improved analytical method based on the equivalent responses of multistory building structures is proposed to estimate the inelastic seismic responses efficiently and accurately. The proposed method can be used to accurately evaluate the seismic performance not only for the global inelastic behavior of a building but also for its local inelastic seismic responses. In order to demonstrate the accuracy and validity of the proposed method, inelastic seismic responses estimated by the proposed method are compared with those obtained from other existing methods. When the proposed method is applied in the pushover analysis more improved analytical results could be obtained than those from the conventional capacity spectrum method (CSM).

A soft post-earthquake damage identification methodology using vibration timeseries

A neural-network-based post-earthquake damage identification methodology for smartstructures with the direct use of vibration measurements is developed. Two neuralnetworks are constructed to facilitate the process of post-earthquake damageidentification. The rationality of the proposed methodology is explained and thetheory basis for the construction of an emulator neural network (ENN) and aparametric evaluation neural network (PENN) are described according to thediscrete time solution of the structural state space equation. An evaluation indexcalled the root mean square of the prediction difference vector (RMSPDV) ispresented to evaluate the condition of different associated structures. Based onthe trained ENN, which is a non-parametric model of the object structure ina healthy state, and the PENN that describes the relation between structuralparameters and the components of the corresponding RMSPDVs, the inter-storeystiffness of the damaged object structure is identified. The accuracy, sensibilityand efficacy of the proposed strategy for different ground excitations are alsoexamined using a multi-storey shear building structure by numerical simulations.Since the methodology does not require the extraction of structural dynamiccharacteristics such as frequencies and mode shapes from measurements, it has thepotential of being a practical tool for health monitoring of smart engineeringstructures.

Hybrid control of irregular steel highrise building structures under seismic excitations

Control of irregular highrise building structures under various seismic excitations is investigated using a hybrid control system consisting of a passive supplementary damping system and a semi-active tuned liquid column damper (TLCD) system. Equations of motion for the combined building and the TLCD system are derived for multistorey building structures with rigid floors and plan and elevation irregularities. Major steps involved in optimal control of three-dimensional irregular buildings equipped with a hybrid damper-TLCD system are delineated. A wavelet-based optimal control algorithm is applied to find the optimum control forces. Simulation results for control of two multistorey moment-resisting space steel structures with vertical and plan irregularities show clearly that the hybrid damper-TLCD control system significantly reduces responses of irregular buildings subjected to various earthquake ground motions as well as increases reliability and maximum operability during power failure.

Approximate analysis of building structures with identical stories subjected to earthquakes

In this paper an approximate earthquake analysis is presented for multistory building structures. The building is stiffened by an arbitrary combination of lateral load-resisting subsystems (shear walls, frames, trusses, coupled shear walls, cores). We consider stories with identical stiffnesses and masses, however the mass at the top floor may be different. The analysis is based on the continuum method. The spatial vibration problem of the replacement beam is solved approximately. Simple formulas are given to calculate the periods of vibration and internal forces of a building structure subjected to earthquakes. The utility and accuracy of the method is demonstrated by two numerical examples, in which the approximate solution is compared with finite element calculations.

비선형 변위모드법을 적용한 복합구조물의 내진성능평가

구조물의 내진 성능을 정확히 평가하기 위해서는 비선형 시각 이력 해석이 필요하지만 실용성과 단순성 측면에서 약산법이 대안이 될 수 있으며, 다층 구조물을 등가 단자유도계로 치환할 때 다층 구조물의 모드벡터는 구조물이 탄성 또는 탄소성 상태에 상관없이 탄성 상태에서의 모드 형상으로 가정되지만, 항복이 발생한 후 증가하는 하중단계에서 구조물은 비탄성으로 되기 때문에 변위 모드 특성들도 변화된다. 본 논문은 항복 이후의 구조물의 모드 변화를 고려한 비선형 변위모드를 이용하여 다자유도계를 등가 단자유도계로 변환하는 방법을 제시하였으며, 변환된 등가 단자유도계의 변위응답을 근거로 추정한 복합 구조물의 최상층 변위와 실제 지진교란을 받는 복합 구조물의 비선형 동적해석에 의한 최상층 변위를 비교함으로서 복합구조물의 지진응답예측을 위한 비선형 변위모드법의 적용성과 신뢰성을 검토하였다. Though a nonlinear time history analysis may be provided to estimate more exactly the seismic performance of building structure, approximation methods are still needed in the aspect of practicality and simplicity, In converting a multi-story structure to an equivalent SDOF system, the mode vectors of the multi-story structure are assumed as the mode shape in elastic state regardless of elastic or elastic-plastic state. However, the characteristics of displacement mode are also changed after the yielding made in the structural elements, because the structure becomes inelastic in each incremental load step. In this research, a method of converting MDOF system to ESDOF system is presented by using nonlinear displacement mode considering the mode change of structures after the yielding. Also, the accuracy and efficiency of the method of the nonlinear displacement mode method of the estimate of seismic response of Mixed Building Structures were examined by comparing the displacements of the roof level of the multi-story building structures estimated from this converted displacement response of ESDOF with the displacement of the roof level through the nonlinear dynamic analysis of the multi-story building structures subjected to an actual earthquake excitation.

Optimal drift design model for multi‐story buildings subjected to dynamic lateral forces

AbstractAn optimal drift design model for a linear multi‐story building structure under dynamic lateral forces is presented. The drift design model is formulated into a minimum weight design problem subjected to constraints on stresses, the displacement at the top of a building, and inter‐story drift. The optimal drift design model consists of three main components: an optimizer, a response spectrum analysis module, and a sensitivity analysis module. Using a small example, the validation of the proposed model has been tested by a comparison of optimal solutions. Then, the performance of the optimal drift design model is demonstrated by application to three steel frame structures including a 40‐story building. Various structural responses including lateral displacement and inter‐story drift distributions along the height of the structure at the initial and final design stages are presented in figures and tables. Time‐consuming trial‐and‐error processes related to drift control of a tall building subjected to lateral loads is avoided by the proposed optimal drift design method. Copyright © 2003 John Wiley & Sons, Ltd.

Semi-active control of 3D coupled response of building structures

The semi-active tuned liquid column damper (TLCD) system is investigated for control of coupled responses of 3D irregular buildings under seismic excitations. The TLCD system is a special type of tuned mass damper (TMD) system providing a performance similar to a TMD system but offers a number of practical advantages over the traditional TMD system. The equations of motion for the combined building and TLCD system are derived for multistory building structures with rigid floors and plan and elevation irregularities. Simulation results for control of two multistory moment-resisting space structures with vertical and plan irregularities show clearly that the semi-active TLCD control system reduces the responses of 3D irregular buildings subjected to earthquake ground motions efficiently.

Semiactive Structural-Control Based on Variable Slip-Force Level Dampers

This paper presents a semiactive control strategy based on variable slip-force level dampers. The proposed scheme controls only the slip-force level of the friction damper in such a way that the damper exhibits bilinear hysteresis with a ductility factor equal to two regardless of the level of seismic excitation. With a constant ductility factor maintained in any seismic event, the damper behaves like a linear system in response to any seismic excitation. For implementation of this scheme in multistory buildings, an autonomous-decentralized type of control system is constructed. In such a control system, a number of subcontrol systems are present, each of which is controlled by the decentralizing or local controller utilizing local response information. The fundamental idea is first presented through the application of this control scheme to a single-degree-of-freedom structure. The extension of the scheme to a multistory building structure is then discussed. Finally, the feasibility of utilizing oil dampers for the proposed control strategy is experimentally examined.

등가 1 자유도계에 의한 철근콘크리트 모멘트 골조구조의 비선형 지진응답 평가법의 검토

건축구조물의 내진성능을 효율적으로 평가하기 위해서는 다자유도계 구조물을 등가 1자유도계로 표현하는 것이 필요하다. 본 연구는 다층 철근콘크리트 골조구조를 등가 1자유도계로 치환하는 방법을 제시하였다. 다층 철근콘크리트 모멘트 골조를 등가 1자유도계로 치환하여 모델화에 따른 비선형 시간이력해석을 통하여 다자유도계 구조물의 축약 방법의 타당성을 검토하는 것이 목적이다. 다층 골조구조의 정적 비선형 해석을 수행하여, 등가 1자유도계의 복원력 모델을 설정하였다. 다층 골조 구조의 비선형 시간이력해석 응답치와 등가 1자유도계의 시간이력해석 응답치를 비교하여, 등가 1자유도계 모델의 타당성을 검증하였다. 다층 철근콘크리트 골조구조를 등가 1자유도계로 치환하여 비선형 지진응답을 구하는 방법은 충분히 그 타당성이 있다는 것이 확인되었다. 다층 철근콘크리트 골조구조의 대표변위로서 1차모드참여 yector<TEX>$_1$</TEX>,<TEX>$\beta$</TEX>{<TEX>$_1$</TEX><TEX>$\mu$</TEX>}= 1인 높이가 등가 1자유도계의 응답을 가장 근사하게 나타내는 것을 알 수 있었다. 등가 1자유도계의 지진응답해석에 사용하는 복원력 모델의 이력곡선에 따라 응답파형에 차이가 생기므로, 실제 frame 구조의 복원력 특성을 반영한 이력모델을 선정하는 것이 중요하다. To evaluate the seismic performance of multistory building structures use an equivalent SDOF model to represent the resistance of the structure to deformation as it respond in its predominant mode. This paper presents a method of converting a MDOF system into an equivalent SDOF model. The principal objective of this investigation is to evaluate appropriateness of converting method through perform nonlinear time history analysis of a multistory building structures and an equivalent SDOF model. The hysteresis rules to be used an equivalent SDOF model is obtained from the pushover analysis. Comparing the peak inelastic response of a moment resisting reinforced concrete frames and an equivalent SDOF model, the adequacy and the validity of the converting method is verified. The conclusion of this study is following; A method of converting a MDOF system into an equivalent SDOF model through the nonlinear time history response analysis is valid. The representative lateral displacement of a moment resisting reinforced concrete frames is close to the height of the first modal participation vector \ulcorner<TEX>$_1{\beta}$</TEX><TEX>${_1{\mu}}=1$</TEX>. It can be found that the hysteresis rule of an equivalent SDOF model have influence on the time history response. Therefore, it necessary for selecting hysteresis rules to consider hysteresis characteristics of a moment resisting reinforced concrete frames.

Bending and shear stiffness optimization for rigid and braced multi-story steel frames

The response of multi-story building structures to lateral loads, mainly due to earthquake and wind, is investigated for preliminary design purposes. Emphasis is placed on structural systems consisting of rigid and braced steel frames. An attempt to gain a qualitative understanding of the influence of bending and shear stiffness distribution on the deformations of such structures is made. This is achieved by modeling the structure with a stiffness equivalent Timoshenko beam. It is observed that the conventional stiffness distribution, dictated by strength constraints, may not be the best to satisfy deflection criteria. This is particularly the case for slender structural systems with prevailing bending deformations, such as flexible braced frames. This suggests that a new approach to the design of such frames may be appropriate when serviceability governs. A pertinent strategy for preliminary design purposes is proposed.

An evaluation ofP-Δ amplification factors in multistorey steel moment resisting frames

Three different amplification factors that have been proposed to account for P-Δ effects in the seismic design of multistorey building structures are described and compared. Nonlinear dynamic analyses of a typical 20-storey steel moment resisting frame are carried out under earthquake ground motions typical of eastern and western Canada to evaluate the gravity load effects and to assess the effectiveness of each type of amplification factor in accounting for these effects. All three approaches maintain the ductility demand within the level computed without P-Δ effects, but lateral deformations are generally larger than those obtained neglecting the gravity loads. Nonlinear dynamic analyses are also performed on a shear-beam (stick) model of the same building to examine the possibility of using such simple models for studying the dynamic stability of buildings subjected to ground motions. The shear-beam model does not predict adequately the seismic behaviour of steel moment resisting frames for which P-Δ effects are significant.Key words: ductility, earthquake, ground motion, lateral deformation, moment resisting frame, P-Δ effects, push-over analysis, seismic, shear-beam model, stability coefficient, amplification factor.

Optimal control of adaptive building structures under blast loading

>Creation of a new generation of high-performance adaptive⧹smart structures with self-modification capability is advanced to resist dynamic loadings due to both nature such as wind and earthquake loadings and man such as blast and bomb loadings. The general computational models and high-performance parallel algorithms developed recently by the authors for optimal control of large structures are applied to multistorey building structures subjected to blast loadings. Both internal blast loading at different floor levels and external blast loading from outside the structure are considered. Results are presented for several regular and irregular moment-resisting steel space frame structures. It is demonstrated that the response of a building structure to blast loadings can be reduced substantially to a fraction of the response of the uncontrolled structure. © 1998 Elsevier Science Ltd. All rights reserved.

Optimal Control of Adaptive/Smart Multistory Building Structures

This research advances creation of a new generation of adaptive/smart structures with self‐modification capability by designing a predetermined number of members as actively controlled members. The computational model and high‐performance parallel algorithms for optimal control of large structures recently developed by the authors are applied to multistory buildings. Four different schemes for placement of controllers are investigated. Three types of dynamic loadings are considered: earthquake ground motion, periodic impulsive horizontal wind loading on the exterior joints of the structure, and asymmetric periodic impulsive wind loading on the exterior of the structure modeling a twister. Results are presented for three multistory building structures with curved beams and setback representing both space moment‐resisting and braced frames. It is demonstrated that through a proper selection of the weighting factor, the response of a multistory building structure can be reduced substantially to a fraction of the response of the uncontrolled structure at a practically feasible maximum required actuator force. Recommendations are made on the placement of the controllers for various types of structural configurations.

Three-dimensional finite element analysis of shear wall buildings

A three-dimensional finite element computer analysis of multistorey building structures, made of pierced shear walls of open and/or closed cross-sections and flat plates, is presented. The computer program developed for this purpose provides a special and powerful mesh generation subroutine. A graphic program is also developed to prepare the data interactively by utilizing a screen graphic option. The structure model can be created or modified very easily with the use of the present mesh generation program. The beams or columns can be added or cancelled with no difficulty at all. The plate finite element developed can represent the membrane as well as the bending behaviour of the shear wall and the floor components. The program developed is used to obtain solutions to some realistic structures to determine the bounds of the simplifying assumptions commonly made for the analysis of multistorey building structures. The program is also capable of performing analysis by using conventional simplified models of multistorey structures and of verifying the bounds set for the assumptions.

SEISMIC TESTING OF A BUILDING STRUCTURE WITH A SEMI-ACTIVE FLUID DAMPER CONTROL SYSTEM

This paper describes shaking table tests of a multi-storey scale-model building structure subjected to seismic excitation and controlled by a semi-active fluid damper control system. The semi-active dampers were installed in the lateral bracing of the structure and the mechanical properties of the dampers were modified according to control algorithms which utilized the measured response of the structure. A simplified time-delay compensation method was developed to account for delays within the control system. The results of the shaking table tests are presented and interpreted and analytical predictions are shown to compare reasonably well with the experimental results. © 1997 John Wiley & Sons, Ltd.

Seismic response of irregular multi‐storey buildings with flexible inelastic diaphragms

The effectiveness of rigid floor modelling in the seismic design of multi-storey building structures as well as the influence of some structural parameters are deeply investigated through an extensive parametric study. The nonlinear behaviour of 216 structures has been simulated. The basic structural model consists of a symmetrical two-storey system which is supported by seven lateral load-resisting vertical elements with degrading stiffness properties. Different stiffness and strength distributions in the lateral load resisting system and in the floors are considered. The elastic design analysis is carried out by modelling floors as rigid diaphragms or, alternatively, as flexible beams, while the seismic inelastic analyses take into account the real in-plane stiffness and strength of floors. Diagrams show the behaviour of the most important structural element in detail, while statistical techniques are used to identify the most important structural parameters. The results of this study show that the rigid floor hypothesis generally leads to a conservative design for multi-storey buildings, thus confirming the findings of some previous studies on single-storey building structures. Moreover floors need to be adequately designed for strength when they have re-entrances and the stiffness distributions of the lateral-force resisting system is markedly non-uniform. © 1997 John Wiley & Sons, Ltd.

Seismic response of irregular multi-storey buildings with flexible inelastic diaphragms

SUMMARY The effectiveness of rigid floor modelling in the seismic design of multi-storey building structures as well as the influence of some structural parameters are deeply investigated through an extensive parametric study. The nonlinear behaviour of 216 structures has been simulated. The basic structural model consists of a symmetrical two-storey system which is supported by seven lateral load-resisting vertical elements with degrading stiffness properties. Different stiffness and strength distributions in the lateral load resisting system and in the floors are considered. The elastic design analysis is carried out by modelling floors as rigid diaphragms or, alternatively, as flexible beams, while the seismic inelastic analyses take into account the real in-plane stiffness and strength of floors. Diagrams show the behaviour of the most important structural element in detail, while statistical techniques are used to identify the most important structural parameters. The results of this study show that the rigid floor hypothesis generally leads to a conservative design for multi-storey buildings, thus confirming the findings of some previous studies on single-storey building structures. Moreover floors need to be adequately designed for strength when they have re-entrances and the stiffness distributions of the lateral-force resisting system is markedly non-uniform. 1997 by John Wiley & Sons, Ltd.

Assessment of Translational-Torsional Coupling in Asymmetric Uniform Wall-Frame Structures

A method to predict the degree of translational-torsional coupling of mixed-bent-type multistory building structures subject to dynamic loading is presented. The method is based on the treatment of nonproportionate structures as a particular class of regular proportionate ones, and on the generalized representation of asymmetric structures by shear-flexure, torsion-warping cantilevers. The method is applicable to structures consisting of any combination of walls and frames that are uniform over their height. The concept and location of the significant centers of reference, such as the shear centers and the centers of resistance, of mixed-bent-type multistory building structures are clarified, and the significance of the coupled-period ratio for the assessment of the coupling effect is discussed. The derivation of the method, and comparisons of results with those obtained by three-dimensional (3D) finite-element dynamic analyses of discrete member models, are given. A worked example illustrates the applica...