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1.
Conventional shake tables employ linear controllers such as proportional‐integral‐derivative or loop shaping to regulate the movement. However, it is difficult to tune a linear controller to achieve accurate and robust tracking of different reference signals under payloads. The challenges are mainly due to the nonlinearity in hydraulic actuator dynamics and specimen behavior. Moreover, tracking a high‐frequency reference signal using a linear controller tends to cause actuator saturation and instability. In this paper, a hierarchical control strategy is proposed to develop a high‐performance shake table. A unidirectional shake table is constructed at the University of British Columbia to implement and evaluate the proposed control framework, which consists of a high‐level controller and one or multiple low‐level controller(s). The high‐level controller utilizes the sliding mode control (SMC) technique to provide robustness to compensate for model nonlinearity and uncertainties experienced in experimental tests. The performance of the proposed controller is compared with a state‐of‐the‐art loop‐shaping displacement‐based controller. The experimental results show that the proposed hierarchical shake table control system with SMC can provide superior displacement, velocity and acceleration tracking performance and improved robustness against modeling uncertainty and nonlinearities. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

2.
The interest in shake tables stems from a need to simulate earthquake behavior in laboratory settings. However, the inherent properties and nonlinearities associated with electromechanical and servohydraulic shake tables, combined with issues of table-structure interaction, make accurate reproduction of earthquake acceleration time histories a challenging problem. The classical approach to control shake tables has been the Transfer Function Iteration (TFI) method. The tuning of the TFI controller is an offline iterative process, conducted using small amplitude ground motions. Effective compensation is not achievable for system nonlinearities that are not projected in the iterative tuning process. To address this problem, researchers have developed online compensation techniques, which can maintain tracking performance for the earthquake signals more effectively. Model-based controllers (MBC) are a class of online controllers which use an identified model of the shake table-structure for compensation. The MBC employs feedforward and feedback controllers to ensure that the shake table tracks a specified earthquake ground motion despite the presence of table and structural nonlinearities. However, the feedback controllers in MBC do not always maintain tracking accuracy and can result in loss of robustness when changes occur in the shake table and structure dynamics. This paper introduces a modified model-based controller (mMBC) for acceleration tracking as an improvement on the existing MBC architecture. A stability condition is introduced to assess the robustness of the new modified control architecture. Through numerical and experimental studies, the improved tracking robustness of the mMBC architecture is demonstrated.  相似文献   

3.
Among several different experimental techniques, used to test the response of structures and to verify their seismic performance, the shake table testing allows to reproduce the conditions of true effects of earthquake ground motions in order to challenge complex model structures and systems. However, the reproduction of dynamic signals, due to the dynamics of the shake table and of the specimen, is usually imperfect even though closed‐loop control in a shake table system is used to reduce these errors and obtain the best fidelity reproduction. Furthermore, because of the dynamic amplifications in the specimen, the signal recorded at desired locations could be completely different from the expected effect of shake table motion. This paper focuses on the development of practical shake table simulations using additional ‘open loop’ feedforward compensation in form of inverse transfer functions (i.e. the ratio of the output structural response to an input base motion in the frequency domain) in order to obtain an acceptable reproduction of desired acceleration histories at specific locations in the specimen. As the first step, a well‐known global feedforward procedure is reformulated for the compensation of the table motion distortions due to the servo‐hydraulic system. Subsequently, the same concept is extended to the table‐structure system to adjust the shake table input in order to achieve a desired response spectrum at any floor of the specimen. Implementations show how such a method can be used in any experimental facility. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

4.
This paper presents a detailed study on feasibility of un‐bonded fiber reinforced elastomeric isolator (U‐FREI) as an alternative to steel reinforced elastomeric isolator (SREI) for seismic isolation of un‐reinforced masonry buildings. Un‐reinforced masonry buildings are inherently vulnerable under seismic excitation, and U‐FREIs are used for seismic isolation of such buildings in the present study. Shake table testing of a base isolated two storey un‐reinforced masonry building model subjected to four prescribed input excitations is carried out to ascertain its effectiveness in controlling seismic response. To compare the performance of U‐FREI, same building is placed directly on the shake table without isolator, and fixed base (FB) condition is simulated by restraining the base of the building with the shake table. Dynamic response characteristic of base isolated (BI) masonry building subjected to different intensities of input earthquakes is compared with the response of the same building without base isolation system. Acceleration response amplification and peak response values of test model with and without base isolation system are compared for different intensities of table acceleration. Distribution of shear forces and moment along the height of the structure and response time histories indicates significant reduction of dynamic responses of the structure with U‐FREI system. This study clearly demonstrates the improved seismic performance of un‐reinforced masonry building model supported on U‐FREIs under the action of considered ground motions. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

5.
Large‐scale, servo‐hydraulic shake tables are a central fixture of many earthquake engineering and structural dynamics laboratories. Wear and component failure from frequent use may lead to control problems resulting in reduced motion fidelity, necessitating repairs and replacement of major components. This paper presents a methodology to evaluate shake table performance pre‐ and post‐repair, including the definition of important performance metrics. The strategy suggested is presented in the context of the rebuilding of a 4.9 × 3.1 m, 350‐kN‐capacity uniaxial shake table. In this case, the rebuild consisted of characterization of wear to table components, replacement of worn bearing surfaces, and replacement of hydraulic accumulators. To assess the effectiveness of the repair actions, sinusoidal and triangular waves, white noise, and earthquake histories were run on the table before and after the rebuild. The repair actions were successful in reducing the position and velocity dependence of friction, improving the ability of control algorithms to accurately reproduce earthquake motions. The maximum and average response spectral misfits in the period range of 0.1–2 seconds were reduced from approximately 50% to 15%, and from 5% to less than 2.5%, respectively.  相似文献   

6.
This paper presents the shake‐table tests of a 2/3‐scale, three‐story, two‐bay, reinforced concrete frame infilled with unreinforced masonry walls. The specimen is representative of the construction practice in California in the 1920s. The reinforced concrete frame had nonductile reinforcement details and it was infilled with solid masonry walls in one bay and infill walls with window openings in the other bay. The structure was subjected to a sequence of dynamic tests including white‐noise base excitations and 14 scaled historical earthquake ground motion records of increasing intensity. The performance of the structure was satisfactory considering the seismic loads it was subjected to. The paper summarizes the design of the specimen and the major findings from the shake‐table tests, including the dynamic response, the load resistance, the evolution of damage, and the final failure mechanism. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

7.
This paper investigates the seismic performance of a functional traction elevator as part of a full‐scale five‐story building shake table test program. The test building was subjected to a suite of earthquake input motions of increasing intensity, first while the building was isolated at its base and subsequently while it was fixed to the shake table platen. In addition, low‐amplitude white noise base excitation tests were conducted while the elevator system was placed in three different configurations, namely, by varying the vertical location of its cabin and counterweight, to study the acceleration amplifications of the elevator components due to dynamic excitations. During the earthquake tests, detailed observation of the physical damage and operability of the elevator as well as its measured response are reported. Although the cabin and counterweight sustained large accelerations because of impact during these tests, the use of well‐restrained guide shoes demonstrated its effectiveness in preventing the cabin and counterweight from derailment during high‐intensity earthquake shaking. However, differential displacements induced by the building imposed undesirable distortion of the elevator components and their surrounding support structure, which caused damage and inoperability of the elevator doors. It is recommended that these aspects be explicitly considered in elevator seismic design. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

8.
The concentrically braced frame (CBF) structure is one of the most efficient steel structural systems to resist earthquakes. This system can dissipate energy during earthquakes through braces, which are expected to yield in tension and buckle in compression, while all other elements such as columns, beams and connections are expected to behave elastically. In this paper, the performance of single‐storey CBFs is assessed with nonlinear time‐history analysis, where a robust numerical model that simulates the behaviour of shake table tests is developed. The numerical model of the brace element used in the analysis was calibrated using data measured in physical tests on brace members subjected to cyclic loading. The model is then validated by comparing predictions from nonlinear time‐history analysis to measured performance of brace members in full scale shake table tests. Furthermore, the sensitivity of the performance of the CBF to different earthquake ground motions is investigated by subjecting the CBF to eight ground motions that have been scaled to have similar displacement response spectra. The comparative assessments presented in this work indicate that these developed numerical models can accurately capture the salient features related to the seismic behaviour of CBFs. A good agreement is found between the performance of the numerical and physical models in terms of maximum displacement, base shear force, energy dissipated and the equivalent viscous damping. The energy dissipated and, more particular, the equivalent viscous damping, are important parameters required when developing an accurate displacement‐based design methodology for CBFs subjected to earthquake loading. In this study, a relatively good prediction of the equivalent viscous damping is obtained from the numerical model when compared with data measured during the shake table tests. However, it was found that already established equations to determine the equivalent viscous damping of CBFs may give closer values to those obtained from the physical tests. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

9.
A hypothetical 5‐storey prototype structure with reinforced concrete (RC) frame and unreinforced masonry (URM) wall is considered. The paper focuses on a shake‐table experiment conducted on a substructure of this prototype consisting of the middle bays of its first storey. A test structure is constructed to represent the selected substructure and the relationship between demand parameters of the test structure and those of the prototype structure is established using computational modelling. The dynamic properties of the test structure are determined using a number of preliminary tests before performing the shake‐table experiments. Based on these tests and results obtained from computational modelling of the test structure, the test ground motions and the sequence of shakings are determined. The results of the shake‐table tests in terms of the global and local responses and the effects of the URM infill wall on the structural behaviour and the dynamic properties of the RC test structure are presented. Finally, the test results are compared to analytical ones obtained from further computational modelling of the test structure subjected to the measured shake‐table accelerations. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

10.
This study presents results from shake table experiments of a wood‐frame building conducted at the University of California, Berkeley. A 13.5‐ft × 19.5‐ft two‐story wood‐frame building representing San Francisco 1940s design of a residential building with a garage space on the first story (house‐over‐garage) was tested. The test building was subjected to scaled ground motion based on Los Gatos record from Loma Prieta 1989 earthquake. The strong motion time history was scaled to match design spectra of a site in Richmond district of San Francisco. The test results demonstrated the seismic vulnerability of the test building due to soft story mechanism and significant twisting when shaken in two horizontal directions. In addition to conventional instrumentation for measuring acceleration and position of selected points of the test building, high‐definition laser scanning technology was employed to assess global and local anomalies of the building after the shake table tests. The analysis conducted in this study showed very good correlation between conventional data recorded from position transducers and the laser scans. These laser scans expanded limits of conventional data at discrete points and allowed analyzing the whole building after shaking. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

11.
A full‐scale shake table test on a six‐story reinforced concrete wall frame structure was carried out at E‐Defense, the world's largest three‐dimensional earthquake simulation facility, in January 2006. Story collapse induced from shear failure of shear critical members (e.g., short columns and shear walls) was successfully produced in the test. Insights gained into the seismic behavior of a full‐scale specimen subjected to severe earthquake loads are presented in this paper. To reproduce the collapse process of the specimen and evaluate the ability of analytical tools to predict post‐peak behavior, numerical simulation was also conducted, modeling the seismic behavior of each member with different kinds of models, which differ primarily in their ability to simulate strength decay. Simulated results showed good agreement with the strength‐degrading features observed in post‐peak regions where shear failure of members and concentrated deformation occurred in the first story. The simulated results tended to underestimate observed values such as maximum base shear and maximum displacement. The effects of member model characteristics, torsional response, and earthquake load dimensions (i.e., three‐dimensional effects) on the collapse process of the specimen were also investigated through comprehensive dynamic analyses, which highlighted the following seismic characteristics of the full‐scale specimen: (i) a model that is incapable of simulating a specimen's strength deterioration is inadequate to simulate the post‐peak behavior of the specimen; (ii) the torsional response generated from uniaxial eccentricity in the longitudinal direction was more significant in the elastic range than in the inelastic range; and (iii) three‐dimensional earthquake loads (X–Y–Z axes) generated larger maximum displacement than any other loading cases such as two‐dimensional (X–Y or Y–Z axes) or one‐dimensional (Y axis only) excitation. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

12.
Results from real‐time dynamic substructuring (RTDS) tests are compared with results from shake table tests performed on a two‐storey steel building structure model. At each storey, the structural system consists of a cantilevered steel column resisting lateral loads in bending. In two tests, a slender diagonal tension‐only steel bracing member was added at the first floor to obtain an unsymmetrical system with highly variable stiffness. Only the first‐storey structural components were included in the RTDS test program and a Rosenbrock‐W linearly implicit integration scheme was adopted for the numerical solution. The tests were performed under seismic ground motions exhibiting various amplitude levels and frequency contents to develop first and second mode‐dominated responses as well as elastic and inelastic responses. A chirp signal was also used. Coherent results were obtained between the shake table and the RTDS testing techniques, indicating that RTDS testing methods can be used to successfully reproduce both the linear and nonlinear seismic responses of ductile structural steel seismic force resisting systems. The time delay introduced by actuator‐control systems was also studied and a novel adaptive compensation scheme is proposed. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

13.
Two models are tested on a shake‐table. One of the models is a normal reinforced concrete megaframe structure and the other is a multifunctional vibration‐absorption reinforced concrete megaframe structure in which the laminated rubber bearings are placed between the major frame and the minor frames. Two earthquake motions (the El Centro wave and the Taft wave) are used during the test. This paper presents the dynamic characteristic, the seismic responses and the failure mechanism of these two models under varying peak acceleration levels for each of the earthquake motions. The test results demonstrate that the aseismic behavior of a multifunctional vibration‐absorption reinforced concrete megaframe structure is much better than that of a normal reinforced concrete megaframe structure. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

14.
This study proposes an innovative passive vibration mitigation device employing essentially nonlinear elastomeric springs as its most critical component. Essential nonlinearity denotes the absence (or near absence) of a linear component in the stiffness characteristics of these elastomeric springs. These devices were implemented and tested on a large‐scale nine‐story model building structure. The main focus of these devices is to mitigate structural response under impulse‐like and seismic loading when the structure remains elastic. During the design process of the device, numerical simulations, optimizations, and parametric studies of the structure‐device system were performed to obtain stiffness parameters for the devices so that they can maximize the apparent damping of the fundamental mode of the structure. Pyramidal elastomeric springs were employed to physically realize the optimized essentially nonlinear spring components. Component‐level finite element analyses and experiments were conducted to design the nonlinear springs. Finally, shake table tests using impulse‐like and seismic excitation with different loading levels were performed to experimentally evaluate the performance of the device. Experimental results demonstrate that the properly designed devices can mitigate structural vibration responses, including floor acceleration, displacement, and column strain in an effective, rapid, and robust fashion. Comparison between numerical and experimental results verified the computational model of the nonlinear system and provided a comprehensive verification for the proposed device. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

15.
This paper proposes a simple conceptual mathematical model for the mechanical components of the NEES‐UCSD large high‐performance outdoor shaking table and focuses on the identification of the parameters of the model by using an extensive set of experimental data. An identification approach based on the measured hysteresis response is used to determine the fundamental model parameters including the effective horizontal mass, effective horizontal stiffness of the table, and the coefficients of the classical Coulomb friction and viscous damping elements representing the various dissipative forces in the system. The effectiveness of the proposed conceptual model is verified through a comparison of analytical predictions with experimental results for various tests conducted on the system. The resulting mathematical model will be used in future studies to model the mechanical components of the shake table in a comprehensive physics‐based model of the entire mechanical, hydraulic, and electronic system. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

16.
This paper investigates the dynamic characteristics and seismic behavior of prefabricated steel stairs in a full‐scale five‐story building shake table test program. The test building was subjected to a suite of earthquake input motions and low‐amplitude white noise base excitations first, while the building was isolated at its base, and subsequently while it was fixed to the shake table platen. This paper presents the modal characteristics of the stairs identified using the data recorded from white noise base excitation tests as well as the physical and measured responses of the stairs from the earthquake tests. The observed damage to the stairs is categorized into three distinct damage states and is correlated with the interstory drift demands of the building. These shake table tests highlight the seismic vulnerability of modern designed stair systems and in particular identifies as a key research need the importance of improving the deformability of flight‐to‐building connections. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

17.
This paper presents a non‐linear, kinematic model for triple friction pendulum isolation bearings. The model, which incorporates coupled plasticity and circular restraining surfaces for all sliding surfaces, is capable of capturing bi‐directional behavior and is able to explicitly track the movement of each internal component. The model is general so that no conditions regarding bearing properties, which effect the sequence of sliding stages, are required for the validity of the model. Controlled‐displacement and seismic‐input experiments were conducted using the shake table at the University of California, Berkeley to assess the fidelity of the proposed model under bi‐directional motion. Comparison of the experimental data with the corresponding results of the kinematic model shows good agreement. Additionally, experiments showed that the performance of TFP bearings is reliable over many motions, and the behavior is repeatable even when initial slider offsets are present. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

18.
This paper presents shake‐table tests conducted on a two‐fifths‐scale reinforced concrete frame representing a conventional construction design under current building code provisions in the Mediterranean area. The structure was subjected to a sequence of dynamic tests including free vibrations and four seismic simulations in which a historical ground motion record was scaled to levels of increasing intensity until collapse. Each seismic simulation was associated with a different level of seismic hazard, representing very frequent, frequent, rare and very rare earthquakes. The structure remained basically undamaged and within the inter‐story drift limits of the ‘immediate occupancy’ performance level for the very frequent and frequent earthquakes. For the rare earthquake, the specimen sustained significant damage with chord rotations of up to 28% of its ultimate capacity and approached the upper bound limit of inter‐story drift associated with ‘life safety’. The specimen collapsed at the beginning of the ‘very rare’ seismic simulation. Besides summarizing the experimental program, this paper evaluates the damage quantitatively at the global and local levels in terms of chord rotation and other damage indexes, together with the energy dissipation demands for each level of seismic hazard. Further, the ratios of column‐to‐beam moment capacity recommended by Eurocode 8 and ACI‐318 to guarantee the formation of a strong column‐weak beam mechanism are examined. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

19.
Reinforced concrete waffle‐flat plate (WFP) structures present 2 important drawbacks for use as a main seismic resisting system: low lateral stiffness and limited ductility. Yet the former can serve a positive purpose when, in parallel, the flexible WFP structure is combined with a stiff system lending high‐energy dissipation capacity, to form a “flexible‐stiff mixed structure.” This paper experimentally investigates the seismic performance of WFP structures (flexible system) equipped with hysteretic dampers (stiff system) through shake‐table tests conducted on a 2/5‐scale test specimen. The WFP structure was designed only for gravitational loads. The lateral strength and stiffness provided by the dampers at each story were, respectively, about 3 and 7 times greater than those of the bare WFP structure. The mixed system was subjected to a sequence of seismic simulations representing frequent to very rare ground motions. Under the seismic simulations associated with earthquakes having return periods ranging from 93 to 1894 years, the WFP structure performed in the level of “immediate occupancy,” with maximum interstory drifts up to about 1%. The dampers dissipated most (75%) of the energy input by the earthquake.  相似文献   

20.
This paper reports on the investigation of novel fiber reinforced elastomeric isolator (FREI) bearings, which do not have thick end plates, and are used in an unbonded application. Owing to the stable lateral load‐displacement response exhibited by the unbonded FREI bearings, the proposed bearings are referred to as stable unbonded (SU)‐FREIs. A shake table test program was conducted on a two‐story test‐structure having well‐defined elastic response characteristics. Compared with the results for the corresponding fixed base (FB) structure, the peak response values, distribution of lateral response throughout the height of the structure, and response time histories of the tested base isolated (BI) structure indicate that significantly improved response can be achieved. This study clearly indicates that SU‐FREI bearings can provide an effective seismic isolation system. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

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