Supplemental Energy Dissipation Research Articles

Controlled Rocking CLT Walls for Buildings in Regions of Moderate Seismicity: Design Procedure and Numerical Collapse Assessment

ABSTRACTControlled rocking heavy timber walls are designed to rock on their foundations in response to earthquakes. For regions of moderate seismicity, it is proposed that this rocking behaviour can be adequately controlled using only post-tensioning, even with a large force-reduction factor and no supplemental energy dissipation. This article presents a force-based design procedure for controlled rocking cross-laminated timber walls without supplemental energy dissipation, including a method for estimating higher mode effects. Fragility analyses of three prototype walls demonstrate that the procedure can limit the probability of collapse to <10% during a maximum considered earthquake in a region of moderate seismicity.

01.12: Development and validation of design criteria for free from damage steel joints

ABSTRACTSeismic response of steel structures in case of destructive events strongly depends on their ability to dissipate seismic energy. Traditional design of steel Moment Resisting Frames (MRFs) is based on the assumption that this energy is dissipated by steel members or connections. In the former case, full strength joints are adopted and plastic hinges are developed in beam ends while, in the latter case, partial strength connections are adopted, promoting the plastic engagement of some of the connections’ components. In both cases, the design for rare seismic events concedes high levels of damage in some structural parts, requiring high costs for the retrofit. In order to overcome this drawback, recently, the FREE from DAMage design strategy has been proposed as a combination of partial strength and supplementary energy dissipation strategies. Indeed, in previous works, a new joint typology called FREEDAM, has been conceived with the aim to avoid the structural damage (even in case of rare seismic events), thanks to the capacity of the connection to withstand high rotations without developing any plasticization of the steel parts. More specifically, a FREEDAM connection is a connection where friction dampers are introduced at the level of the beam bottom flange. The main feature of this connection is that its resistance and rotational capacity are very easy to control by means of a proper calibration of preload applied to the friction pads with high strength bolts and length of slotted holes, designed to allow the relative movement between the beam and the column. Within this framework, in this paper, the attention is focused on the behaviour of two possible types of FREEDAM connections. In addition, design rules for the friction components of the connections are also discussed. The design procedure is developed in view of application of a hierarchical design, applied at the level of the joint components, able to concentrate energy dissipation in the friction damper and to avoid any damage to all the other parts. The effectiveness of FREEDAM connections is subsequently verified by means of finite element simulations under both monotonic and cyclic loading.

Dynamic Response Evaluation of Damped-Outrigger Systems with Various Heights

Outriggers are a proven and effective system used to reduce the dynamic response of tall buildings. By inserting dampers into the outriggers, providing supplementary energy dissipation, further improvements in the dynamic response can be achieved. The aim of this study is to develop analytical methods for the dynamic response evaluation of a single-damped-outrigger system and determine the optimal outrigger locations and damper sizes to minimize response. Changes in the mode shape, damping, natural period and seismic response were studied parametrically using complex eigenvalue analysis of a continuous cantilever model, and the accuracy verified by comparison with a member-by-member model. A simplified single-degree-of-freedom model was then constructed and studied using an assumed lateral displacement curve and the principle of virtual work. Finally, a practical method for determining optimal outrigger location and damper size based on this simplified model was proposed.

Collapse risk of controlled rocking steel braced frames with different post‐tensioning and energy dissipation designs

SummaryControlled rocking steel braced frames (CRSBFs) are low‐damage self‐centring lateral force resisting systems. Previous studies have shown that designing the energy dissipation (ED) and post‐tensioning (PT) in CRSBFs using a response modification factor of R=8 can prevent collapse of structures during earthquakes beyond the design level. However, designers have unique control over the hysteretic behaviour of the system, even after the response modification factor is selected. Additionally, recent studies have suggested that CRSBFs could also be designed using R&gt;8 while still satisfying performance limits. This paper examines how the response modification factor and the design of the ED and PT influence the collapse performance of CRSBFs with three and six storeys where collapse occurs because of over‐rotation of the base rocking joint. In addition, the influence of using an additional rocking joint above the base to mitigate higher‐mode forces is evaluated for a 12‐storey frame. A total of 18 different designs are considered for the three buildings using different ED and PT design parameters, including different response modification factors. A suite of 44 ground motions is scaled until at least 50% of the records cause collapse, and fragility curves are generated using the truncated incremental dynamic analysis curves. The results from two different assessment methodologies show that the parameters selected have a marked influence on the collapse performance of a CRSBF. Nevertheless, even CRSBFs designed using R&gt;8 or without supplemental ED can have acceptably low probabilities of collapse, provided that the frame members are designed to remain elastic. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Performance of RC Structures Equipped with Steel and Aluminium X-Plate Dampers

The supplementary energy dissipation using dampers represents an efficient technique for the seismic protection of structural system. Also, the optimal damper location in the building helps in reducing damper cost along with maximum response reduction. In this work, an effort has been made to use the X-plate metallic damper made of steel and aluminium for seismic response control. In the first phase of work, the building has been analysed without and with full dampers under real earthquake ground motion. The response quantities such as maximum displacement, max interstory drift, axial force, shear force and bending moment are compared. The results obtained after the analysis shows that the response quantities are reduced significantly thus establishing the effectiveness of damper to dissipate the input seismic energy. It is important to find out the optimal damper location format in the building to improve its efficiency and reduce total cost of dampers to accomplish the max reduction in the response of the building. Therefore, the second phase of work focuses on the optimal location of the damper in the building. To obtain the optimal damper location, the concept of genetic algorithm is used.

Lateral Isolation System of a Long-Span Cable-Stayed Bridge with Heavyweight Concrete Girder in a High Seismic Region

AbstractThis paper primarily introduces a new lateral isolation system proposed for the seismic control of a long-span cable-stayed bridge, namely, the Yongning Yellow River Bridge, with high seismic activity and a heavyweight concrete girder. Elastic cables (used in pairs to provide a uniaxial tension/compression constraint) in association with a fluid viscous damper (FVD) for supplemental energy dissipation were employed to form a new lateral isolation system at the girder–tower connections. The cable pairs provided the essential lateral stiffness in service conditions, the desired flexibility and sufficient deformation capacity for seismic isolation, and the ability to recenter the girder following an earthquake. At the pier locations, buckling restrained braces (BRBs) were used for lateral isolation of the piers. A three-dimensional nonlinear finite-element model was developed, and three lateral earthquake-resisting systems (i.e., the traditional fixed system, an isolation system using steel dampers, ...

An investigation of the effects of structural nonlinearity on the seismic performance degradation of active and passive control systems used for supplemental energy dissipation

It is generally accepted that active control systems provide better structural performance when compared to their passive counterparts. On the other hand, the design of active control systems based on linear control theory is highly dependent on the structural properties. For this reason, their performance is expected to be affected more severely by variations in structural properties compared to those of passive systems. These variations can occur due to nonlinear structural behavior, or even before that due to uncertainties in the estimation of these properties and in numerical modeling. The present work is an investigation of the dependency of various control systems used for supplemental energy dissipation to the changes in structural properties. For this purpose, the performance degradations of most common control systems are studied for structures entering their nonlinear response range. The considered control systems include active control using linear quadratic regulator algorithm and passive control using viscous fluid dampers and yielding devices. These control systems are optimized separately for linear and nonlinear structures by minimizing performance indices based on inter-story drift and absolute acceleration response. It is shown that among these control systems, viscous dampers are affected the least by the alteration of structural properties, which may further support their utilization contrary to the more costly active control systems. It is also shown that the amount of performance degradation depends on the selected structural performance index, and more importantly, the severity of the earthquake excitation.

Investigations of the application of gyro-mass dampers with various types of supplemental dampers for vibration control of building structures

A gyro-mass damper (GMD) is an inertia-based passive control device. It has a gear assembly that amplifies the rotational inertias developed in the gears and generates a resultant resisting force that is proportional to the relative acceleration at the end terminals of the GMD. The amplification provided by the gear assembly can be adjusted by changing the gear masses or the gear ratios of the compound gears. Although similar inertia-based devices have been successfully used for vibration mitigation of motor vehicles and optical tables, there are only a few studies that investigated their application in building structures. This number is even lower for the particular type of inertial damper that has been considered in this study, i.e., GMD. Unlike other types of inertial dampers, the supplemental energy dissipation component of GMDs is not built-in to the device and can be independently attached as an external component. This allows the design engineers to use this cost-effective device and select any available energy dissipation device to use in parallel. In this study, using a small-scale GMD, by considering the rotational inertias of the intermediate gears, characteristic equation which describes the relationship between the applied relative acceleration and the resulting resisting force is derived and experimentally verified. For the introduction of GMDs into building structures, three different configurations are evaluated: (i) stand-alone GMD, (ii) GMD-brace system, and (iii) GMD–Viscous damper–Brace (GVB) system. The structure-GMD interaction, considering these three configurations, is investigated in frequency domain and in time domain through energy balance equations and time history analyses. It is shown that by selecting the system parameters properly, GVB systems with nonlinear viscous dampers can effectively improve the seismic behaviour of the structure. This is discussed in more detail when the effects of the damper nonlinearities, as well as the various GMD equivalent mass, brace stiffness, damping values and selected ground motions are investigated. The key findings related to the design, implementation and performance considerations of these systems are provided.

Design and performance of autonomous chevron-brace systems with elastomeric-dampers for steel frames

This paper presents an innovative use of natural rubber pads for seismic control of multistory low- and medium-rise steel braced frames. Such pads have always been used as supplemental energy dissipation devices in structures that already have their own and independent seismic force resisting system. This paper investigates the use of such devices in series with chevron braces as an autonomous seismic force resisting system, which provides not only additional damping to the structure but also a period shift. The damping and isolation material is a fiber reinforced natural rubber exhibiting strong nonlinear dependence with respect to strain. First, a design procedure based on numerical studies is illustrated for a typical one-story building. Pseudo-linear models of the structures are used for the final evaluation of the seismic response. Cyclic tests on a full scale frame were conducted to calibrate the models and showed the reliability of the autonomous rubber-based system under full loading and real assembly conditions. Then a 1/3-scale 3-story chevron braced steel frame with and without rubber devices was used to evaluate the seismic performances of the system. The application was studied numerically and experimentally through shake table tests of the 1/3 reduced-scale model at different seismic intensities. Results show the efficiency of the system to significantly reduce linear seismic forces induced on the structure without devices. Control of displacements is also achieved but is highly dependant on the initial value of damping in the structure without devices.

Beyond Ductility: Parametric Testing of a Jointed Rocking Beam-Column Connection Designed for Damage Avoidance

AbstractDespite their good performance in terms of their design objectives, many modern code-prescriptive buildings built in Christchurch, New Zealand, had to be razed after the 2010–2011 Canterbury earthquakes because repairs were deemed too costly due to widespread sacrificial damage. Clearly, a more effective design paradigm is needed to create more resilient structures. Rocking, posttensioned connections with supplemental energy dissipation can contribute to damage avoidance designs (DAD). However, few have achieved all three key design objectives of damage-resistant rocking, inherent recentering ability, and repeatable, damage-free energy dissipation for all cycles, which together offer a response that is independent of loading history. Results of experimental tests are presented for a near full-scale rocking beam-column subassemblage. A matrix of test results is presented for the system under varying levels of posttensioning, with and without supplemental dampers. Importantly, this parametric study ...

Development and experimental evaluation of a passive gap damper device to prevent pounding in base‐isolated structures

SummaryStudies have shown the effectiveness of providing supplemental energy dissipation in base‐isolated structures to reduce displacements at the isolation level. A previous analytical study demonstrated the benefits of providing this energy dissipation at a specified gap larger than the design displacement. The gap before engagement allows the base isolation system to meet performance criteria in varying levels of ground excitation. Use of this ‘gap damper’ device eliminates undesirable effects often exhibited with large amounts of supplemental damping at lower intensity motions. Using results from an analytical study, the primary purpose of this research was to develop devices for practical implementation. Development of the devices demanded simplicity, feasibility, economy, and reliability to be an effective option in building design and construction. Multiple designs were proposed, and a final design was chosen based on selection criteria and finite element analyses. The device was designed and tested in Auburn University's Structural Research Lab. Experimental results were compared with theoretical models to verify behavior and make necessary adjustments for a shake table experiment. The design parameters were selected to accommodate re‐use of the device for the shake table test. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Performance-based Design of RC Frame Buildings with Metallic and Friction Dampers

Supplemental energy dissipation is a technique of earthquake resistant design and for improving the seismic performance of existing buildings. In the present study, a comprehensive design methodology for performance based design of frame buildings with metallic and friction dampers has been proposed. In this study, the target performance level is aimed to achieve both in terms of inter-storey drift and plastic hinge rotation. A non-iterative step-by-step design procedure is proposed to achieve the target performance level. The methodology provides the design yield forces in case of metallic dampers, and slip forces in case of friction dampers. A satisfactory distribution of both types of dampers along the height of the building is also provided in the methodology. The efficiency of the proposed design methodology is validated by applying to a ten storey building and performing nonlinear time history analysis. The building, with and without dampers, is subjected to five spectrum compatible time histories with peak ground acceleration of 0.24 g and the relative performance of the building with the two types of dampers is studied.

Numerical study and practical design of beam-to-column connections with shape memory alloys

This paper reports a comprehensive numerical study on end-plate beam-to-column connections equipped with NiTi shape memory alloys (SMAs). The numerical modelling strategy is first validated through comparisons with seven full scale tests conducted by the authors. The FE predictions correlate well with the test results, especially in terms of the deformation mode, strain reading, moment–rotation response, residual deformation, and equivalent viscous damping. Following the validation study, a parametric study is performed considering the effects of bolt layout, bolt length/diameter, beam-to-connection strength ratio, end-plate thickness, column web panel deformation, and shear resisting mechanism. In order to overcome a major issue identified from the parametric study, i.e. shear slippage, an improved HS-SMA hybrid solution is proposed. One of the novel concepts is the employment of HS bolts in collaboration with SMA Belleville washers, where the latter are used to absorb the bolt row deformation, to enable connection recentring, and to offer supplementary energy dissipation. A detailed FE model is established to confirm the feasibility of the HS-SMA hybrid connection, and an analytical model is also developed for normal design of such connections. A set of design rules for practical use are also proposed, and the required future studies are finally identified.

Rocking isolation of nonductile moderately tall buildings subjected to bidirectional near-fault ground motions

Recent studies show that slender structures with shallow foundations located on soil medium can benefit from rocking isolation effects during strong earthquakes. In such condition, foundation uplifting and soil yielding provide supplemental energy dissipation potential at substructure level. As a result, the structural demands would be significantly reduced. In this study, building structures with various geometrical properties mounted on surface raft foundations are examined. A set of 91 component pairs of near-fault forward-directivity ground motions recorded at soft as well as dense sites are selected. Three dimensional nonlinear soil–structure interaction (SSI) including foundation uplifting and soil yielding is considered. The results show that the protective effects of rocking isolation can play vital role in survival of medium-to-high-rise building structures subject to catastrophic earthquakes which are excessively greater than design limits. Evidently, rocking isolation has enhanced the elastic structural demands up to 50% for low-aspect-ratio as well as 75% for high-aspect-ratio structures. Such beneficial effects keep the superstructure in significantly larger safety margins. In addition, site effects on seismic demands of rocking structures, as well as liquefaction potential in case of buildings located on soft site are investigated.

Viscous Dampers Utilized at an Operating Electronic Facility for Reducing Seismic Risk

Using supplemental energy dissipation devices into the structure to increase the damping ratio for reducing the responses of seismic activity has become more and more popular. This paper presents a case study of seismic retrofit strategy, utilizing a type of passive energy dissipation device, namely, the viscous damper, in order to make an ongoing chips produced facility resistant to seismic activity. The building in question was a chips produced facility belonging to a semiconductor manufacturing company. This was a double FAB where the structure system was divided into an island building and an RC shell. The retrofit involved installing 44 non-linear dampers between the island building and the RC shell. This was due to the significant differences in the fundamental vibration periods. This paper will present the rationale of making a decision on the parameters of the dampers to give the optimum retrofit strategy.

Seismic Behavior of Posttensioned Self-Centering Precast Concrete Dual-Shell Steel Columns

This paper describes an innovative bridge column technology for application in seismic regions. The proposed technology combines a precast posttensioned composite steel-concrete hollow-core column, with supplemental energy dissipation, in a way to minimize postearthquake residual lateral displacements. The column consists of two steel cylindrical shells, with high-performance concrete cast in between. Both shells act as permanent formwork; the outer shell substitutes for the longitudinal and transverse reinforcement, because it works in composite action with the concrete, whereas the inner shell removes unnecessary concrete volume from the column, prevents concrete implosion, and prevents buckling of energy dissipating dowels when embedded in the concrete. Large inelastic rotations can be accommodated at the end joints with minimal structural damage, since gaps are allowed to open at these locations and to close upon load reversal. Longitudinal posttensioned high-strength steel threaded bars, designed to respond elastically, in combination with gravity forces ensure self-centering behavior. Internal or external steel devices provide energy dissipation by axial yielding. This paper describes the main requirements for the design of these columns and also discusses the experimental findings from two quasi-static tests.

등방성 이력형 강재댐퍼를 이용한 RC 라멘조 아파트건물의 지진응답 개선

수동형 제진장치를 이용하는 제진구조는 수년간 개발이 지속되고 있으며, 1990년대 중반이후로 여러 나라들에서 실무적인 적용이 빠르게 증가되고 있다. 국내의 경우 이러한 제진장치 중 강재이력형 댐퍼가 비교적 저렴한 비용과 설치와 관리가 용이하다는 이유로 건물의 내진설계를 위하여 보편적으로 많이 적용되고 있다. 이 논문에서는 건물의 지진응답을 개선하기 위하여 적용된 소위 카고메댐퍼로 불리우는 등방성 강재이력형 댐퍼(Isotropic Hysteretic Metallic Damper, IHMD)의 유효성에 대한 해석적인 사례연구를 제시하고 있다. 연구대상 건물은 18층 규모의 철근콘크리트 라멘조 아파트건물로 해석결과를 통하여 IHMD의 실효성을 실증적으로 보여주고 있다. 해석결과는 IHMD가 건물의 지진응답을 줄일 수 있는 매우 효과적인 방법임을 검증하고 있다. Passive energy dissipation systems for seismic applications have been under development for a number of years with a rapid increase in implementations starting in the mid-1990s in many countries. A metallic hysteretic damper has most commonly been used for seismic protection of structures in domestic area because they present high energy-dissipation potential at relatively low cost and easy to install and maintain. This paper presents an analytical case study of the effectiveness of isotropic hysteretic metallic damper(IHMD) called Kagome as a passive dissipative device in reducing structural response during seismic excitation. An eighteen-story RC framed apartment building is studied with and without IHMD. Results demonstrate the feasibility of these techniques for seismic mitigation. The inclusion of supplemental passive energy dissipation devices in the form of IHMD proved to be a very effective method for significantly reducing the seismic response of the building investigated.

Energy dissipation system for earthquake protection of cable-stayed bridge towers

For economical earthquake resistant design of cable-stayed bridge tower, the use of energy dissipation systems for the earthquake protection of steel structures represents an alternative seismic design method where the tower structure could be constructed to dissipate a large amount of earthquake input energy through inelastic deformations in certain positions, which could be easily retrofitted after damage. The design of energy dissipation systems for bridges could be achieved as the result of two conflicting requirements: no damage under serviceability limit state load condition and maximum dissipation under ultimate limit state load condition. A new concept for cable-stayed bridge tower seismic design that incorporates sacrificial link scheme of low yield point steel horizontal beam is introduced to enable the tower frame structure to remain elastic under large seismic excitation. A nonlinear dynamic analysis for the tower model with the proposed energy dissipation systems is carried out and compared to the response obtained for the tower with its original configuration. The improvement in seismic performance of the tower with supplemental passive energy dissipation system has been measured in terms of the reduction achieved in different response quantities. Obtained results show that the proposed energy dissipation system of low yield point steel seismic link could strongly enhance the seismic performance of the tower structure where the tower and the overall bridge demands are significantly reduced. Low yield point steel seismic link effectively reduces the damage of main structural members under earthquake loading as seismic link yield level decreases due their exceptional behavior as well as its ability to undergo early plastic deformations achieving the concentration of inelastic deformation at tower horizontal beam.

Theory of plastic mechanism control for the seismic design of braced frames equipped with friction dampers

An innovative approach for the design of a seismic resistant system composed by the combination of a MR-Frame and a bracing system equipped with friction dampers is presented. From a multi-scale point of view, at local scale, supplementary energy dissipation is provided by means of friction dampers, while, at global scale, the development of a global type mechanism is assured involving all the friction dampers equipping the structure. The activation of all the friction dampers requires an advanced design procedure. Toward this end, the theory of plastic mechanism control, which is based on the application of the kinematic theorem of plastic collapse is extended to the concept of mechanism equilibrium curve, is applied. The fulfillment of the design goal has been pointed out by means of both pushover and dynamic non linear analyses whose results are herein presented and discussed.

Design and evaluation of seismic strengthening techniques for reinforced concrete frames with soft ground story

This paper presents a design procedure and analytical evaluation of two strengthening techniques to improve the seismic performance of the existing non-ductile RC frames with soft-story at the ground story level. The first technique, termed as column retrofit (CR), uses only partial steel jacketing (or caging) to enhance the lateral strength and plastic rotational capacities of the deficient columns at the ground story level. The later technique, termed as full retrofit (FR), considers the aluminum shear links as supplemental energy dissipation devices in addition to the strengthened ground story columns. Steel collector beams and chevron braces are used to transfer the lateral load from the RC frame to these dissipating devices. Performance-based plastic design approach is used to proportion various elements of the strengthening techniques. Nonlinear static and dynamic analyses are carried out to evaluate the performance of the existing and the strengthened frames. The main parameters investigated are (a) interstory drift, (b) residual drift, (c) yield mechanism, (d) energy dissipation, and (e) lateral strength. The FR frame effectively controlled the drift response by avoiding the soft-story collapse because of the significant energy dissipation in the shear links. Moreover, the FR frame achieved the desired yield mechanism without exceeding the design target drift level.