Probabilistic behavior of semi-active isolated buildings under pulse-like earthquakes

Seda Öncü-Davas,Cenk Alhan 국제구조공학회 2019 Smart Structures and Systems, An International Jou Vol.23 No.3

Seismic isolation systems employ structural control that protect both buildings and vibration-sensitive contents from destructive effects of earthquakes. Structural control is divided into three main groups: passive, active, and semi-active. Among them, semi-active isolation systems, which can reduce floor displacements and accelerations concurrently, has gained importance in recent years since they don’t require large power or pose stability problems like active ones. However, their seismic performance may vary depending on the variations that may be observed in the mechanical properties of semi-active devices and/or seismic isolators. Uncertainties relating to isolators can arise from variations in geometry, boundary conditions, material behavior, or temperature, or aging whereas those relating to semi-active control devices can be due to thermal changes, inefficiencies in calibrations, manufacturing errors, etc. For a more realistic evaluation of the seismic behavior of semi-active isolated buildings, such uncertainties must be taken into account. Here, the probabilistic behavior of semi-active isolated buildings under historical pulse-like near-fault earthquakes is evaluated in terms of their performance in preserving structural integrity and protecting vibration-sensitive contents considering aforementioned uncertainties via Monte-Carlo simulations of 3-story and 9-story semi-active isolated benchmark buildings. The results are presented in the form of fragility curves and probability of failure profiles.

준공공공간에서의 이용자 행동 분석을 통한 장소 활성화에 관한 연구

이민영,이현성,김주연 한국공간디자인학회 2022 한국공간디자인학회논문집 Vol.17 No.5

(Background and Purpose) The semi-public space mainly comprises the walking environment, and it is a transition space connected to public, internal, and private spaces. This study aims to identify the effects of user behavior for activating a particular place and to develop basic data on the role of sustainable semi-public spaces for future research and policymaking. (Method) The researcher utilized four research methods considering the three forms of semi-public spaces, which comprised 13 components. First a behavioral analysis of users was conducted through direct observation. Second, their additional opinions were confirmed through online questionnaires; third, instances of activation of local commercial areas and their connection toe semi-public spaces were identified by analyzing users; consumption behavior. Finally, the evaluation items were defined by capturing and classifying the status of semi-public spaces based on their components. In addition, behavioral analysis was conducted using five classification criteria of semi-public spaces, based on their the components. This study aimed at conceptualizing a street space that is walkable and usable with rather than being the center of various functions. However, it is necessary to activate public functions by strengthening cooperation between various functions to activate public and private spaces. Consequently, the study aimed at redefining public space outside buildings, the transition space between buildings, and walkways built inside buildings, and to organically link the interior and exterior spaces by securing various public facilities and defining the semi-public space. (Results) Three observation sites were selected based on the existing classification semi-public spaces. Most spaces had a proportional number of users who exhibited various behavioral characteristics. Given the social importance of semi-public spaces, they should serve as an effective meeting place, rather than merely a transit space for people to come and go. (Conclusions) Shopping and culture centers are most common commercial facilities linked to semi-public spaces , which contribute to the vitality of the city and help activate the surrounding facilities. The public and private spaces should be transformed into a space that can be activated through continuous management and systemic improvement. This will enable such spaces to provide users with an integrated spatial experience by securing visual and behavioral connectivity and can positively improve the image urban spaces. In terms of public and public spatial design, future studies should focus on improving the public value of semi-public spaces.

Semi-active control of seismic response of a building using MR fluid-based tuned mass damper

Ashutosh Bagchi,Kambiz Esteki,Ramin Sedaghati 국제구조공학회 2015 Smart Structures and Systems, An International Jou Vol.16 No.5

While tuned mass dampers are found to be effective in suppressing vibration in a tall building, integrating it with a semi-active control system enables it to perform more efficiently. In this paper a forty-story tall steel-frame building designed according to the Canadian standard, has been studied with and without semi-active and passive tuned mass dampers. The building is assumed to be located in the Vancouver, Canada. A magneto-rheological fluid based semi-active tuned mass damper has been optimally designed to suppress the vibration of the structure against seismic excitation, and an appropriate control procedure has been implemented to optimize the building\'s semi-active tuned mass system to reduce the seismic response. Furthermore, the control system parameters have been adjusted to yield the maximum reduction in the structural displacements at different floor levels. The response of the structure has been studied with a variety of ground motions with low, medium and high frequency contents to investigate the performance of the semi-active tuned mass damper in comparison to that of a passive tuned mass damper. It has been shown that the semi-active control system modifies structural response more effectively than the classic passive tuned mass damper in both mitigation of maximum displacement and reduction of the settling time of the building.

Control Performance Evaluation of Semi-active TMD Subjected to Various Types of Loads

김현수,장준호,강주원 한국강구조학회 2015 International Journal of Steel Structures Vol.15 No.3

Many types of tuned mass dampers (TMDs), such as active TMDs, multiple TMDs, hybrid TMDs, semi-active TMDs etc., have been proposed to effectively reduce the dynamic responses of a structure. Control performance of a conventional TMD subjected to various types of dynamic loads has been widely studied to date. Although it is known that control performance of a semi-active TMD is better than that of a conventional TMD, control performance of a semi-active TMD subjected to various types of dynamic loads has not been fully studied. Therefore, control performance of a semi-active TMD has been systematically evaluated in this study. To this end, an idealized variable damping device and a magnetorheological (MR) damper are used as semi-active dampers. These semi-active dampers can change the properties of TMDs in real time based on the dynamic responses of a structure. The control performance of STMD is investigated with respect to various types of excitation by numerical simulation. Groundhook control algorithm is used to appropriately modulate the damping force of semiactive dampers. The control effectiveness between STMD and a conventional passive TMD, both under harmonic and random excitations, is evaluated and compared for a single-degree-of-freedom (SDOF) structure. Excitations are applied to the structure as a dynamic force and ground motion, respectively. The numerical studies showed that the control effectiveness of STMD is significantly superior to that of the passive TMD, regardless of the type of excitations.

Influence of Semi-active Suspension on Running Safety of Vehicles

Hong-You Liu,Da-Lian Yu 한국철도학회 2010 International Journal of Railway Vol.3 No.2

Railway vehicles equipped with semi-active suspension system can improve the ride quality of car bodies. Semi-active suspension system is usually applied onto high speed train, and therefore higher running safety requirement is desirable. The influence of semi-active suspension system on safety of vehicles running on straight line and curve line is studied, and the influences of sky hook damping coefficient and system time-delay on operational safety of cars fitted with semiactive suspension system is analyzed. The results show that in vehicles equipped with semi-active suspension system, while the vibration of car body is decreased, the running safety of cars is not affected to any significant degree. As a result, the ride quality is much improved with negligible deterioration of the running safety of cars.

A semi-active stochastic optimal control strategy for nonlinear structural systems with MR dampers

Z. G. Ying,Y. Q. Ni,J. M. Ko 국제구조공학회 2009 Smart Structures and Systems, An International Jou Vol.5 No.1

A non-clipped semi-active stochastic optimal control strategy for nonlinear structural systems with MR dampers is developed based on the stochastic averaging method and stochastic dynamical programming principle. A nonlinear stochastic control structure is first modeled as a semi-actively controlled, stochastically excited and dissipated Hamiltonian system. The control force of an MR damper is separated into passive and semiactive parts. The passive control force components, coupled in structural mode space, are incorporated in the drift coefficients by directly using the stochastic averaging method. Then the stochastic dynamical programming principle is applied to establish a dynamical programming equation, from which the semi-active optimal control law is determined and implementable by MR dampers without clipping in terms of the Bingham model. Under the condition on the control performance function given in section 3, the expressions of nonlinear and linear nonclipped semi-active optimal control force components are obtained as well as the non-clipped semi-active LQG control force, and thus the value function and semi-active nonlinear optimal control force are actually existent according to the developed strategy. An example of the controlled stochastic hysteretic column is given to illustrate the application and effectiveness of the developed semi-active optimal control strategy.

A semi-active stochastic optimal control strategy for nonlinear structural systems with MR dampers

Ying, Z.G.,Ni, Y.Q.,Ko, J.M. Techno-Press 2009 Smart Structures and Systems, An International Jou Vol.5 No.1

A non-clipped semi-active stochastic optimal control strategy for nonlinear structural systems with MR dampers is developed based on the stochastic averaging method and stochastic dynamical programming principle. A nonlinear stochastic control structure is first modeled as a semi-actively controlled, stochastically excited and dissipated Hamiltonian system. The control force of an MR damper is separated into passive and semi-active parts. The passive control force components, coupled in structural mode space, are incorporated in the drift coefficients by directly using the stochastic averaging method. Then the stochastic dynamical programming principle is applied to establish a dynamical programming equation, from which the semi-active optimal control law is determined and implementable by MR dampers without clipping in terms of the Bingham model. Under the condition on the control performance function given in section 3, the expressions of nonlinear and linear non-clipped semi-active optimal control force components are obtained as well as the non-clipped semi-active LQG control force, and thus the value function and semi-active nonlinear optimal control force are actually existent according to the developed strategy. An example of the controlled stochastic hysteretic column is given to illustrate the application and effectiveness of the developed semi-active optimal control strategy.

Comparison of semi-active and passive tuned mass damper systems for vibration control of a wind turbine

Eric R. Lalonde,Kaoshan Dai,Girma Bitsuamlak,Wensheng Lu,Zhi Zhao 한국풍공학회 2020 Wind and Structures, An International Journal (WAS Vol.30 No.6

Robust semi-active vibration control of wind turbines using tuned mass dampers (TMDs) is a promising technique. This study investigates a 1.5 megawatt wind turbine controlled by eight different types of tuned mass damper systems of equal mass: a passive TMD, a semi-active varying-spring TMD, a semi-active varying-damper TMD, a semi-active varying-damper-and-spring TMD, as well as these four damper systems paired with an additional smaller passive TMD near the mid-point of the tower. The mechanism and controllers for each of these TMD systems are explained, such as employing magnetorheological dampers for the varying-damper TMD cases. The turbine is modelled as a lumped-mass 3D finite element model. The uncontrolled and controlled turbines are subjected to loading and operational cases including service wind loads on operational turbines, seismic loading with service wind on operational turbines, and high-intensity storm wind loads on parked turbines. The displacement and acceleration responses of the tower at the first and second mode shape maxima were used as the performance indicators. Ultimately, it was found that while all the semi-active TMD systems outperformed the passive systems, it was the semi-active varying-damper-and-spring system that was found to be the most effective overall – capable of controlling vibrations about as effectively with only half the mass as a passive TMD. It was also shown that by reducing the mass of the TMD and adding a second smaller TMD below, the vibrations near the mid-point could be greatly reduced at the cost of slightly increased vibrations at the tower top.

자기 유변 유체를 이용한 반능동 감쇠기의 개발

정병보,권순우,김상화,박영진 한국유변학회 1999 Korea-Australia rheology journal Vol.11 No.2

감쇠기는 기계 시스템에서 에너지를 소모하는데 사용되는 요소이다. 이러한 감쇠기에는 수동 감쇠기, 능동 감쇠기, 반능동 감쇠기 등의 종류가 있다. 반능동 감쇠기는 수동 감쇠기에 비해서 더 좋은 성능을 내면서 능동 감쇠기보다는 더 작은 동력원을 필요로 하는 장치로 상황에 따라서 그 감쇠력 특성을 변화 시킬 수 있다. 본 논문은, 자기 유변 유체를 이용한 반능동 감쇠기의 개발에 관한 것이다. 자기 유변 유체는 가제어성 유체의 일종으로 인가 자기장에 대해서 그 유동학적 성질이 변하며 높은 항복응력, 낮은 점성계수, 불순물에 대한 안정성과 넓은 사용 온도 범위 등의 장점을 가진 재료이다. 이를 이용할 경우 간단한 구조로 반능동 감쇠기를 설계할 수 있을 뿐만 아니라 빠른 응답성 등의 효과도 기대할 수 있다. 본 연구에서는 자기 유변 유체를 이용하여 설계·제작된 몇 가지 종류의 감쇠기들을 통하여 그 응용 방법과 범위 그리고 응용 시 수반되는 문제점 등을 제시하였다. Dampers have been used to dissipate energy in mechanical systems. There are several types of dampers such as passive, active, and semi-active damper. Semi-active dampers have higher performance than passive ones and require less power to operate than active ones. Their damping characteristics can be changed properly for varying conditions. In this paper, we investigated the semi-active damper using Magneto-Rheological fluid. Magneto-Rheological fluid, which is one of controllable fluids, changes its damping and rheological characteristics from Newtonian fluid to Bingham fluid as the magnetic field is applied. It has several advantages such as high yield strength, low viscosity, robustness to impurities and wide temperature range of stability. If we designe a semi-active damper by using this material, we can not only design a simply structured damper but also expect rapid response. In this study, we propose several types of semi-active dampers which are designed and manufactured using Magneto-Rheological fluid and some problems encountered during their applications.

지도학습과 강화학습을 이용한 준능동 중간층면진시스템의 최적설계

강주원,김현수,Kang, Joo-Won,Kim, Hyun-Su 한국공간구조학회 2021 한국공간구조학회지 Vol.21 No.4

A mid-story isolation system was proposed for seismic response reduction of high-rise buildings and presented good control performance. Control performance of a mid-story isolation system was enhanced by introducing semi-active control devices into isolation systems. Seismic response reduction capacity of a semi-active mid-story isolation system mainly depends on effect of control algorithm. AI(Artificial Intelligence)-based control algorithm was developed for control of a semi-active mid-story isolation system in this study. For this research, an practical structure of Shiodome Sumitomo building in Japan which has a mid-story isolation system was used as an example structure. An MR (magnetorheological) damper was used to make a semi-active mid-story isolation system in example model. In numerical simulation, seismic response prediction model was generated by one of supervised learning model, i.e. an RNN (Recurrent Neural Network). Deep Q-network (DQN) out of reinforcement learning algorithms was employed to develop control algorithm The numerical simulation results presented that the DQN algorithm can effectively control a semi-active mid-story isolation system resulting in successful reduction of seismic responses.