Southern Romania is a geographic region with alluvial deposits. This soil type leads to rather long corner periods and provides as a particularity of the response spectrum an enlarged plateau. These conditions produce large displacement demands. Moreover, pulse-type ground acceleration records make this seismic area more unique. Research on the seismic behaviour of structures built under such unusual conditions is limited and Romanian engineers are not confident to apply alternative solutions such as base isolation. Although capacity design is still the regular design method applied in Romania, modern base isolation solutions may overcome the large displacement demand expectation produced by seismic events and fulfil immediate occupancy requirements. This study presents the seismic performance of an existing hospital from Bucharest, for which two seismic design solutions were applied: (i) classical approach based on capacity design and (ii) base isolation. Both approaches are compared in terms of drift, acceleration and base shear values. Static as well as non-linear dynamic analysis methods were applied.

A plan irregular hospital building, having one underground floor and five overground levels has been analysed. The frame type building is part of a hospital ensemble built in Bucharest, in a high corner period seismic area. For these challenging seismic conditions the efficacy of base isolation is investigated. Two design attempts are considered: base isolation and strengthening. Advantages and disadvantages of both solutions are discussed.

This paper reports on a series of shaking table tests on a full-scale flat-bottom steel silo filled with soft wheat, characterized by aspect ratio of around 0.9. The specimen was a 3.64-m diameter and 5.50-m high corrugated-wall cylindrical silo. Multiple sensors were used to monitor the static and dynamic response of the filled silo system, including accelerometers and pressure cells. Numerous unidirectional dynamic tests were performed consisting of random signals, sinusoidal inputs, and both artificial and real earthquake records. The objectives of this paper are (i) to provide a general overview of the whole experimental campaign and (ii) to present selected results obtained for the fixed-base configuration. The measured data were processed to assess the static pressures, the dynamic overpressures (related to the effective mass) and the accelerations of monitored points on the silo wall, and to identify the basic dynamic properties (fundamental frequency of vibration, damping ratio, dynamic amplification factors) of the filled silo. The main findings are discussed and compared with the predictions given by available theoretical models and code provisions. It is found that the fundamental frequency slightly decreases with increasing acceleration, while it slightly increases with increasing compaction of the granular material. For close-to-resonance input, the dynamic amplification (in terms of peak values of accelerations) increases along the height of the silo wall up to values of around 1.4 at the top surface of the solid content. The dynamic overpressures appear to increase with depth (differently from the EN1998-4 expectations), and to be proportional to the acceleration.

The TMD system of the footbridge "Inwilerstrasse" near Zug in Switzerland was model-based designed for the first vertical bending mode, the expected human excitation, assuming the inherent damping of 0.3 % and ensuring the acceleration limit CL1 (0.50 m/s²) of HIVOSS. After the installation of the locked TMDs, first, the TMD frequency was optimized based on the identified bridge eigenfrequency by adjusting the TMD mass. Then, the bridge with locked and activated TMDs was excited by five synchronized persons. These tests were re-computed adopting the experimentally identified eigenfrequency and damping ratio of the first bending mode and the optimized TMD mass. The re-computation demonstrates that the excitation force amplitude of one bouncing person must be set to approximately 600 N in order to obtain the measured acceleration of 0.117 m/s² of the bridge with activated TMDs. The value of 600 N seems reasonable as this corresponds to approximately 80 % of the average body weight (76 kg) of one person. The very low acceleration of 0.117 m/s² of the bridge with activated TMD demonstrates the effectiveness of TMDs.

The design of conventional curved surface sliders (CSSs) uses appropriate selections of effective radius and friction coefficient. These two design parameters are commonly optimized for the design basis earthquake (DBE). As a consequence efficient structural isolation for weak and frequent earthquakes is hardly possible on the one hand and the isolator relative motion due to the maximum considered earthquake (MCE) becomes unacceptable large on the other hand. This trade-off problem is solved by adaptive stiffness and damping behaviors. The concept of the adaptive CSS is described, and its seismic performance is computed by nonlinear time history analysis using a nonlinear and experimentally validated model. The results demonstrate that the adaptive CSS significantly enhances seismic structural performance. (C) 2021 American Society of Civil Engineers.

This paper investigates the isolation performance of curved surface sliders (CSSs) with different damping mechanisms. The following passive damping mechanisms are considered: passive friction damping as commonly present in CSSs, linear viscous damping as linear damping mechanism, and bow tie friction as adaptive, that is, position-dependent, but passive approach; CSSs with adaptive behaviour based on different sliding regimes are not considered. From the field of CSSs with semiactive dampers, two control strategies are considered: amplitude proportional friction damping aiming at linearizing the friction damping over one cycle and semiactively controlled damping and stiffness properties to enhance the decoupling between ground and structure by the emulation of zero dynamic stiffness. The CSSs under consideration are assessed in terms of peak structural acceleration, peak CSS horizontal force and displacement, and recentring error as function of peak ground acceleration (PGA) of the accelerograms. The results demonstrate that (a) friction damping can be optimized at one PGA only due to its nonlinearity, (b) the optimization of linear viscous damping does not depend on PGA, (c) optimized bow tie friction improves the isolation at low PGA while the isolation at medium to high PGAs worsens, (d) optimized amplitude proportional friction damping does not improve the isolation compared with optimized linear viscous damping, and (e) zero dynamic stiffness is preferably emulated only for a certain range of CSS relative motion amplitude to keep the recentring error within acceptable limits.

A new type of an adaptive curved surface slider (CSS) is presented. The SIP-Adaptive (SIP: spherical isolation pendulum) consists of two concave plates with an articulated slider in between to decouple the relative motions on the two sliding surfaces. The friction coefficient of surface 1 is selected low to initiate relative motion on surface 1 at peak ground accelerations (PGA) significantly below the PGA of the Design Basis Earthquake (DBE) which improves the isolation of the structure in this PGA range compared to the conventional CSS. The friction coefficient of surface 2 is designed to generate at least the same isolation of the structure for PGAs in the vicinity of the DBE as for the conventional CSS. The design of the effective radii 1 and 2, which takes into account that the total bearing relative motion is composed of sliding on surface 1 only and simultaneous sliding on surfaces 1 and 2, guarantees the envisaged isolation time period. By nonlinear time history analysis of the SIP-Adaptive with structure and PGA-scaled accelerograms the performance of the SIP-Adaptive in terms of peak structural acceleration, peak horizontal isolator force and displacement and re-centring error is optimized within the entire expected PGA range up to the PGA of the Maximum Credible Earthquake (MCE). The results demonstrate that the SIP-Adaptive reduces structural acceleration, isolator horizontal force and displacement compared to the conventional CSS and that the re-centring condition is fulfilled. The characterization tests on two SIP-Adaptive confirm the functioning of this new isolator.

The adaptive curved surface slider "SIP-Adaptive" represents a new isolator with adaptive behaviour. Due to the articulated slider the relative motions on both sliding surfaces are de coupled whereby the two sliding surfaces can be designed independently for different ground shaking levels. The model-based design and the experimental validation of the SIP-Adaptive are described. The numerical results demonstrate that the SIP-Adaptive significantly reduces structural peak acceleration, displacement capacity and maximum base shear.

The design of curved surface sliders (CSS) based on the elastic response spectrum is done by iteration to find the combination of friction coefficient and displacement capacity which satisfies the condition that the maximum horizontal CSS force is equal to the horizontal force of the structure. Although this CSS design is valid it does not necessarily minimize structural acceleration. This paper therefore describes the optimum CSS design for minimum structural acceleration. All valid CSS designs and the optimum CSS design are represented by their associated trajectory in the elastic response spectrum plane which visualizes the optimization problem. The results demonstrate that the optimum CSS design is not obtained at maximum tolerated effective damping ratio. The subsequent sensitivity analysis describes how much the structural acceleration increases if the actual friction coefficient of the real CSS deviates from its optimum design value. The analysis points out that the increase in structural acceleration is approximately one order of magnitude smaller than the deviation in friction. The sensitivity data may be used by structural engineer to determine tolerable deviations in friction coefficient which still results in acceptable structural accelerations.

This study performs an experimental investigation of a novel, semi-active control strategy for effective vibration mitigation. The implemented approach comprises a combination of the linear quadratic regulator with a nonlinear observer, namely, the unscented Kalman filter, for the control of systems described by uncertainties. Indeed, numerical models of structural systems often result as inadequate because of inherent uncertainties, such as noise, modeling errors, unknown system properties, or influence of varying operational and environmental conditions. In tackling this issue, the unscented Kalman filter is herein employed for adaptive joint state and parameter estimation refining the accuracy of the model employed by the controller and resulting in enhanced vibration mitigation. A scaled five-story shear frame attached to a hydraulic cylinder comprises the tested structure, where actuation is provided by means of a rotational magnetorheological damper operating on the relative motion between the ground floor and the first floor plate. The experimentally obtained results demonstrate a good agreement with simulations and encourage further implementation of the proposed framework in field applications of structural control. Copyright (C) 2016 John Wiley & Sons, Ltd.

This paper investigates the seismic soil-structure-interaction (SSI) effects on the design of curved surface sliders (CSS) for base isolation and re-centering capability of rectangular shear-wall structures isolated by CSS. Typically, the design of CSS follows a three-step process: First, the effective radius is selected to significantly increase the natural period of the isolated structure to values in the region of 3 s and higher whereby the structure is shifted out of the time period range of greatest excitation energy of most earthquakes. Second, the friction coefficient is selected to add maximum damping to the structure, which further reduces the structural acceleration response. Finally, the design of the CSS is double-checked for the re-centering condition given by the norm EN 15129. This three-step process and the required design parameters are commonly analyzed without considering the effects of soil-structure-interaction. However, existence of non-vertically propagating and surface incident waves is a concern for the base isolated structures since the effect of the motion incoherency resulting from the spatial variation of the ground motion in the horizontal plane potentially introduces: (1) a global torsional excitation of the structure on isolators, and (2) increased vertical forces on isolators due to small local differential ground motions especially coming from the vertical directions and due to rocking response of the structure. This paper presents a parametric study to demonstrate how the incoherency of the seismic motion affects the forces acting on the isolators and the calculated design parameters of the isolators. In this study a 3D soilstructure-interaction model of a typical nuclear shear-wall structure is developed in the ACS SASSI software that uses an efficient hybrid time/frequency domain approach for nonlinear analysis. The CSS are idealized by nonlinear hysteretic springs distributed uniformly on the mat foundation. The nonlinear response of the CSS is modelled using an iterative equivalent-linearization algorithm. The properties of the springs are iteratively changed to determine the equivalent stiffness and damping level in the CSS. The case study analysis results show that incoherent motion increases the relative displacement and horizontal force of the CSS. Based on these results it is concluded that a careful SSI modelling of base isolated structure is mandatory in order to take into consideration incoherency effects that may result in the spatial variation in the ground motion and therefore non-vertically propagating waves. 24 Conference on Structural Mechanics in Reactor Technology BEXCO, Busan, Korea August 20-25, 2017 Division V INTRODUCTION The seismic base isolation technologies have been widely used in conventional structures and bridges. However only a few nuclear power plants are equipped with seismic base isolation systems. Application of seismic isolation systems was extended to nuclear power plant facilities in early 80s in Koeberg NPP in South Africa and Cruas NPP in France. The first new seismic isolation applications following Cruas and Koeberg NPPs are Jules Horowitz Research Reactor and International Thermonuclear Experimental Reactor, currently under construction in France [1]. Elastomeric bearings are used in these nuclear power plants. The limited number of existing seismically isolated nuclear plants is probably due to the fact that theoretical studies are still in progress and experimental results about the behaviour of large isolators under severe seismic conditions are insufficient. There are recent research efforts in order to develop a methodology to extend the base isolation technology to the NPP structures in Japan [2]. In this study, the seismic soil-structure-interaction (SSI) effects on design of curved surface sliders (CSS) for base isolation and re-centering capability of typical NPP structures are investigated. Typically, design of curved surface sliders follows a three-step process: First, the effective radius is selected to significantly increase the natural period of the isolated structure to values in the region of 3 s and higher whereby the structure is shifted out of the time period range of greatest excitation energy of most earthquakes. Second, the friction coefficient is selected to add maximum damping to the structure which further reduces the structural acceleration response. Finally, the design of the curved surface slider is doublechecked for the re-centering condition given by the norm EN 15129. This three-step process and the required design parameters are commonly analysed without considering the effects of soil-structureinteraction. However, existence of non-vertically propagating and surface incident waves is a concern for the base isolated structures since the effect of the motion incoherency resulting from the spatial variation of the ground motion in the horizontal plane potentially introduces: (1) a global torsional excitation of the structure on isolators, and (2) an increased, local vertical forces on isolators due to small local differential ground motions especially coming from the vertical directions and due to rocking response of the structure. This paper presents a parametric study to demonstrate how the incoherency of the seismic motion affects the forces acting on isolators and the calculated design parameters of the isolators. The paper is organized as follows: the next section presents the methodology used in the study and the following section provides information about the structure and CSS considered in the study. Seismic response calculation methods applied in the study are presented in the last two sections; namely simplified approach and soil-structure interaction analysis approach. A brief summary of the main outcomes of the study concludes the paper.

The working philosophy of the triple friction pendulum (FP) is to generate low friction in the region of 1.5–2% combined with high stiffness due to the small effective radii of the articulated slider assembly at low peak ground accelerations (PGAs), to produce medium friction around 3–5% and medium stiffness by simultaneous sliding on surfaces 1 and 4 at PGAs corresponding to the design basis earthquake (DBE), to generate increasing friction with further increasing PGAs up to the maximum credible earthquake (MCE) by the high friction of surface 4 in the region of 10% and, eventually, to produce considerably increased stiffness at PGAs beyond of MCE in order to reduce the maximum required displacement capacity of the triple FP. This study first investigates if this design philosophy results in enhanced isolation of the primary structure compared to the conventional FP. For this, the triple FP according to the above mentioned design concept is numerically tested for several earthquakes that are scaled to various PGAs in order to operate the triple FP within all its sliding regimes with associated isolation efficiencies. These results are compared to those of the conventional non-adaptive double FP with equal friction coefficients on its sliding surfaces and same effective radii as those of concave plates 1 and 4 of the triple FP to ensure equal isolation time periods. The first study demonstrates that the conventional FP outperforms the triple FP for most of the PGAs except for very small PGAs below 1–2 m/s2 depending on the earthquake. This finding is explained by the facts that the small effective radii of the articulated slider assembly reduce the isolation time period and therefore the isolation of the structure and splitting the friction into medium and high values on surfaces 1 and 4 cannot improve the isolation performance since the relative motion amplitudes on surfaces 1 and 4 are reverse whereby the energy dissipation is not enhanced compared to the conventional double FP with equal friction coefficients. The second study shows a way how the triple FP with four friction coefficients, four effective radii and four displacement capacities can be optimized for maximum isolation of the primary structure. This study points out that the optimized triple FP converges to the optimized double FP which explains the similar isolation performances. Thus, the triple FP does not improve the isolation of the structure compared to the conventional friction pendulum.

This article deals with the development of a long-stroke MR-damper aimed to control, by reacting on a tuned mass (TM), the earthquake performance of an existing 21-story office building located in Santiago, Chile. The +/- 1 m stroke MR-damper was designed using the nominal response of the building equipped with two 160 ton pendular masses tuned to the fundamental lateral vibration mode of the structure. An extended physical on-off controller, a special current driver, a new real-time structural displacement sensor, and an MR-damper force sensor were all developed for this application. The physical damper and control were experimentally validated using a suite of cyclic and seismic signals. The real-time displacement sensor developed was validated by first using a scaled down building prototype subjected to shaking table tests, and then a real-scale free vibration test on the sensor installed horizontally at the foundation level of a building. It is concluded that the proposed TM and MR-damper solution is technically feasible, and for an equivalent key performance index also defined herein, more economical than a solution based on passive viscous dampers.

A 3-storey residential building with OSB-sheathed light-frame timber walls and timber-concrete composite slabs was subjected to dynamic excitation in two different stages of construction. The experiments consisted of measurements of the accelerations resulting from forced horizontal vibrations which were excited by means of a hydraulic actuator shaking a mass of 940 kg. The exciter was positioned on the second floor of the building and rigidly anchored in the slab. It excited the building in its two main directions to vibrations with frequencies within a range of 0.2–14 Hz. Natural frequencies, modal damping ratios and mode shapes of the building were estimated using accelerations of the building measured in the four external corners of each upper floor. For increasing displacement amplitude (1/8000 mm → 0.7 mm) the natural frequencies decreased moderately (−15 %) whereas the modal damping ratios increased markedly (+100 %). Modal damping ratios computed using ambient vibration data were generally smaller than modal damping ratios obtained from forced vibration tests, which suggests that modal damping for the levels of vibration in interest in design might be significantly underestimated if based on results from ambient vibration tests. However, the mode shapes computed using ambient vibration data turned out to be reliable. The differences in dynamic properties assessed in the different stages of construction were much smaller than expected. Compared to the natural frequencies estimated by the designer by applying a simple single degree of freedom model, the measured natural frequencies were considerably higher. This may be attributed to the impact of non-structural internal walls and walls with openings not accounted for in the designer’s model.

This paper describes a novel force tracking control scheme for magnetorheological (MR) dampers. The feed forward, which is derived by a control‐oriented mapping approach to reduce modelling effort of the inverse MR damper behaviour, compensates for the main steady‐state nonlinearity of the MR damper force and thereby linearizes the plant. The resulting force tracking error due to model imperfections and parameter uncertainties is reduced by parallel proportional and integral feedback gains that are formulated based on the absolute values of actual MR damper force and desired control force due to the semi‐active constraint of the MR damper force. The feedback is enriched by an anti‐reset windup to account for MR damper current constraints and the concept of current reversal to accelerate demagnetization. The experimental validations of the force tracking control scheme on a rotational and a long‐stroke MR damper demonstrate its robustness and efficacy. Copyright © 2015 John Wiley & Sons, Ltd.

This paper discusses the damping measurements on cables with real-time controlled MR dampers that were performed on a laboratory scale single strand cable and on cables of the Sutong Bridge, China. The control approach aims at producing amplitude and frequency independent cable damping which is confirmed by the tests. The experimentally obtained cable damping in comparison to the theoretical value due to optimal linear viscous damping reveals that support conditions of the cable anchors, force tracking errors in the actual MR damper force, energy spillover to higher modes, and excitation and sensor cables hanging on the stay cable must be taken into consideration for the interpretation of the identified cable damping values.

StahlbauVolume 84, Issue 4 InhaltFree Access Inhalt: Stahlbau 4/2015 First published: 02 April 2015 https://doi.org/10.1002/stab.201590035AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume84, Issue4April 2015 RelatedInformation

This study introduces a novel semi-active control scheme, where the linear-quadratic regulator (LQR) is combined with an unscented Kalman filter (UKF) observer, for the real-time mitigation of structural vibration. Due to a number of factors, such as environmental effects and ageing processes, the controlled system may be characterized by uncertainties. The UKF, which comprises a nonlinear observer, is employed herein for devising an adaptive semi-active control scheme capable of tackling such a challenge. This is achieved through the real-time realization of joint state and parameter estimation during the structural control process via the proposed LQR-UKF approach. The behavior of the introduced scheme is exemplified through two numerical applications. The efficacy of the devised methodology is firstly compared against the standard LQR-KF approach in a linear benchmark application where the system model is assumed known a priori, and secondly, the method is validated on a joint state and parameter estimation problem where the system model is assumed uncertain, formulated as nonlinear, and updated in real-time.