Seismic Isolation, Energy Dissipation and Active Vibration Control of Structures

Mitigation of structural damages or structural collapse due to seismic events is of major importance to avoid fatalities and grants immediate occupancy after the earthquake. Therefore, new and existing structures are studied if these are adequate to fulfill stability criteria while regional seismic conditions and soil types must be considered. An essential technical tool to achieve stability, better seismic performance and to avoid structural damages is to increase significantly structural inherent damping. An economic and extremely effective way of increasing damping is with hysteretic dampers within wall bracing arrangements of buildings and other facilities, where seismic isolation cannot be applied properly. A newly developed hysteretic device called SHARK^® is rather promising, as it can provide reliable energy dissipation over many cycles even during a long earthquake duration and it is still a very economic approach compared to other damper solutions like viscous dampers. This device is consisting of specially shaped serially and parallelly arranged lamellas. The lamella shape is similar to the gills of a shark. This specific shape allows excellent energy dissipation, reliable initial stiffness, is redundant and accepts many movement cycles until device may fail. The entire device consists of one single unit, which is easy to handle and to install into a wall bracing. Inspection is simple and functionality status can be properly checked compared to other systems like BRBs. The SHARK^® can be used for retrofitting, too. In a first approach a case study for a regular building structure has been carried out to verify and quantify the efficiency of the device. Then excessive testing of regular and adaptive devices at EUCENTRE in Pavia was performed, to proof reliability and consistency with numerical approach strategy. With the adaptive approach the energy dissipation capacity is strongly depending on seismic intensity and displacement amplitude, what opens new doors for modern but still economic design concepts.

A building mass damper (BMD) is used to suppress structural responses of high-rise buildings. In a building with BMD, the upper and lower structures are connected by a “connecting layer,” and the BMD utilizes the upper structure as a tuned mass damper. Because a BMD uses part of a building, an elevator may be installed through the connecting layer. Thus, the displacement of the connecting layer must be small so that the elevator can operate during strong winds or small earthquakes. To achieve this, the initial stiffness of the connecting layer is large which results in the BMD not being optimally tuned to the lower structure and having less-than-optimal damping effect during small earthquakes. Therefore, in this study, an active mass damper (AMD) was installed on the suboptimal BMD, and the AMD was designed with model reference predictive control (MRPC), which compensates for the reduced damping effect of the suboptimal BMD, especially during small earthquakes. In the MRPC method, the response of the control target (the building with a suboptimal BMD) and the reference model (the optimal BMD) are predicted, and the control input is calculated to minimize the difference between them. In this paper, first, the proposed method is formulated and explained. Second, an experiment performed to verify the method is described. In this experiment, the model used was a six-story building that employed a BMD and an AMD. The results of the experiment verified the validity of the method.

Tuned mass dampers (TMD) are used primarily for reduction of seismic and wind oscillations in high-rise buildings. It is well-known that the base isolation isn’t effective in tall buildings. In general, TMD can reduce seismic loads in tall building but it needs a large mass of TMD. In addition, TMD can’t reduce vertical oscillations, which can be very destructive due to P-delta effect. This paper presents an engineering solution for mitigation of response of structure caused by seismic excitations. An approach of using the upper part of the building as a TMD can significantly reduce horizontal accelerations and stresses in building elements up to 50% along the entire height. Also proposed TMD can siginficantly reduce vertical oscillations in a primary building up to 30% in comparison with building without TMD. This solution can be used both in existing and in new built buildings. This solution doesn’t require any additional mass and its transportation to the installation place. Optimization criterion for defining optimal TMD’s properties was developed. Criterion presents the aim’s function of maximum difference between accelerations of floors with and without TMD along the entire height. For analytical studies matrix of stiffness and dissipation matrix were developed. Matrix of stiffness considers bending and sliding motions and dissipation matrix consider damping ratio for soil, TMD’s constructions and constructions of the building.

Tuned mass dampers (TMD) are widely used as passive countermeasure devices for vibration problems, but that have many limitations. As an example, the ability of a TMD depends on the mass of the weight, but there is a limit to the mass of the weight that can be installed as a damping target structure. Therefore, there are cases where TMD cannot obtain the necessary effect due to the limitations of the target structure. TMD-Booster was proposed as a device to solve the limitation of TMD, and its effect was confirmed by experiments. However, it was not possible to achieve the expected effect due to the effects of friction in the drive unit, when it was operated in an actual environment. In this paper, we implemented displacement feedback control to solve the above problem. As a result, the effect of TMD-Booster was improved.

Energy dissipation and use of this concept in the form of a variety of devices with different mechanical and dynamic properties are representing state of the art approach of engineering and design, to reach targeted seismic resilience for structures. There are various methods of adding extra damping to structures that may be used to reduce structural and non-structural damage. Metal yielding type damping systems are sometimes selected among many other alternatives because they have stable hysteretic behavior characteristics, they are less affected by environmental factors, and they clearly have less cost in comparison to other types of damping systems. To use metallic yielding dampers in the seismic design of structures, detailed mechanical behavior of these fuse elements must be known very well. This FEM based numerical modelling study will concentrate on optimization for energy dissipation. Specially designed and detailed various geometries of a metallic fuse elements will be used, that will be sacrificed before the structure is damaged and will convert seismic energy into various other energies and will help to reach resilience targets.

Numerical comparisons of the mechanical behavior (yield deformation, ultimate deformation capacity, absorbed energy and effective stiffness) of metallic yielding damper components of triangular plate and X-type plate will be given and results will be discussed, to reach resilience objectives.

Earthquakes pose significant threats to human lives and structures, making the study of seismic-resistant foundation systems crucial. This paper investigates the seismic performance of the historical foundation system at the Bulguksa Temple in Korea, which utilizes natural stones stacked in layers for energy dissipation. The system allows controlled movement during earthquakes, dissipating seismic energy through friction and reducing damaging forces transmitted to the superstructures. A test specimen replicating the temple’s foundation was subjected to shake table tests with varying scales of ground motions. The specimen exhibited elastic behavior at lower excitation scales but demonstrated inelastic behavior after reaching the friction force. It showed enhanced energy dissipation capacity at higher scales, effectively reducing response acceleration during seismic events. The results highlight the foundation system’s potential in minimizing structural damage and ensuring the safety of historical buildings. This study provides valuable insights for seismic-resistant design strategies in traditional structures, promoting earthquake resilience and cultural heritage preservation. Further investigations will be conducted to explore response of superstructures affected by this foundation system.

The prestressed lead damper is an energy-dissipative device with a high damping capacity and is used for seismic response control in the earthquake-resistant design of structures. The device works as a friction damper and utilizes the friction losses between lead and a moving shaft while prestressing on the lead controls the behavior. This study experimentally investigates the effect of prestressing level on the characteristics of a lead damper. After producing the lead damper with a straight shaft, different prestressing levels were applied to the lead, i.e., 0.0%, 0.5%, 1.0%, 1.5%, 2.0%, 3.0% and 4.0%. The dampers were experimentally tested by applying a three-step displacement protocol to the shaft: five cycles of 5.0 mm target displacement with a rate of 0.5 mm/s, five cycles of 10.0 mm target displacement with a rate of 1.0 mm/s, and ten cycles of 20.0 mm target displacement with a rate of 2.0 mm/s. The cyclic tests showed that the lead damper’s characteristics, e.g., damper force, initial stiffness, hysteretic behavior, and damping properties, were considerably affected by the amount of prestressing on lead. Increasing the lead prestressing levels resulted in more stable hysteretic curves. In addition, the damper force and, consequently, the damping properties were significantly improved.

Previous earthquakes have demonstrated that collapse of RC precast frame buildings is mostly due to failure of beam-column joints. The precast beam-column joints exhibited insufficient strength, ductility, stiffness, and energy dissipating capacity of the connection region. Use of passive energy dissipation systems at beam-column joint of RC precast frame buildings is an effective and reliable solution to improve seismic performance of these buildings. Energy dissipation through these systems can be accomplished in various mechanisms such as friction sliding, yielding of metal, and deformation of viscoelastic fluids. The most popular mechanism for the dissipation of input energy is through metallic yielding. In the available study, the metallic slit dampers are tested for yielding of steel slits through bending or shear deformation modes under shear action. Studies were also carried out using the dedicated shear and flexural steel plate arrangement to combine bending and shear deformation modes for the yielding of steel. This paper discussed development of slit damper for dissipation of input seismic energy through combined bending and shear deformations in RC precast frame buildings. The proposed damper comprises multiple steel slits cut from steel plate. The steel slits will yield under combined shear and flexural actions and consumes the portion of the input seismic energy. The energy dissipation characteristics of the proposed passive devices are studied using experimental testing. The seismic performance is evaluated in terms of strength degradation ratio, equivalent viscous damping ratio, strength index ratio, displacement ductility, and the failure modes.

The identification of structural systems using vibration measurements has garnered a lot of interest in the field of structural dynamics over the last few decades. System identification is the process of modelling dynamical systems mathematically using measurements of input and output signals. Extended Kalman filter (EKF) or unscented Kalman filter (UKF) are commonly used to identify the structural properties. EKF cannot estimate the state and parameters of the structure when nonlinearity is present in the system. On the other hand, UKF takes a lot of computational time for state and parameter estimation. With this in view, in this study, a Fourier neural network (FNN) has been used to solve the identification problem. A neural network establishes a mapping between infinite-dimensional spaces. For state estimation, FNN uses the advantages of Fourier transformation. In this study, a single-story steel moment-resisting frame coupled with a nonlinear energy sink with nonlinear stiffness is considered for the numerical demonstration purpose. Results show the effectiveness of the proposed approach, whose performance is compared with UKF in terms of accuracy, robustness to noise level, and computational efficiency.

Viscous dampers (VDs) are remarkably effective passive energy dissipation devices successfully implemented in building structures to reduce seismic demands during earthquake excitations. Viscous dampers can be utilized to enhance the resilience of structures against earthquake excitations. Besides that, they can be used for seismic rehabilitation of existing structures. Viscous dampers influence the dynamic response of the building structures that they are attached to; therefore, their allocation is vital. Furthermore, the optimum design of viscous dampers is another critical concept since they are expensive devices; thus, their optimum distribution results in a more economical method. This study suggests a methodology to rehabilitate existing building structures with soft story irregularities via optimum viscous damper distribution using the Particle Swarm Optimization (PSO) algorithm. Soft story irregularity causes significantly large peak inter-story drift ratios (IDR) and abrupt changes in peak inter-story drift ratios between adjacent stories. The primary objective of this study is to limit the peak inter-story drift ratios to an allowable limit. In the scope of this study, the suggested procedure was tested on shear buildings with soft story irregularity under different earthquake ground motions. The results of this study show that it is possible to keep peak inter-story drift ratios at an allowable limit with an optimum viscous damper distribution for shear buildings with soft story irregularity. Moreover, this study shows that the Particle Swarm Optimization algorithm can be successfully implemented on optimum viscous damper design problems in building structures.

Knee bracing system is a lateral earthquake resisting system which combines the feature of lateral stiffness and energy dissipation capacity. The concept relies on the strategic placement of hysteresis dissipative elements to yield (form plastic hinges) in the first instance and absorb energy to protect the main frame. This paper proposes an intelligent procedure to optimise the seismic performance of knee braced frames. For this purpose, a genetic algorithm (GA) is elaborated to determine the strength distribution of the knee elements to optimise the energy dissipation through the building height. The strength limits of the knee elements are considered as the individual genes, and a first population is randomly generated within a predefined range of variation. The population is evolved through adequate crossover and mutation operations. The objective function is the total hysteresis energy dissipated by the knee elements. The results show that the algorithm is efficient and robust in generating optimal distributions of the knee elements strengths for different frame configurations.

One of the most widely used practical structural analysis approaches to evaluate the maximum seismic response of structures is the capacity spectrum method (CSM). Based on the CSM, this paper presents a new procedure for predicting the structural response of passively controlled suspended ceiling structures named “Pulley Damper Ceiling System (PDCS)” based on the CSM. The PDCS employs the displacement amplification mechanism of a block and tackle pulley system, and the supplemental damping element comprises a rotary damper and a friction damper. The single-degree-of-freedom model of the PDCS is initially constructed. Then the reliability of the simplified calculation to obtain an equivalent damping coefficient of the PDCS, which is determined by the sum of the inherent damping and the square root of the sum of squares of each damping provided by the nonlinear viscous damper and the bilinear hysteretic damper, is validated by comparison with the full-scale shake table test results of the PDCS. In this study, the capacity curve of the system was generated by continuously plotting the transition of maximum force and displacement values under different amplitudes of sinusoidal waves. Finally, the availability of the proposed CSM to predict the peak response during earthquake excitations was assessed by comparing it with results from time history analyses. In addition, because the target structure of the PDCS is suspended ceilings, the floor response spectrum was also examined, and accuracy sufficient to evaluate the seismic response was confirmed.

Lessons learned from the Turkey 2023 earthquake and other strong earthquakes in the past underlined importance of safe operation of energy facilities, such as conventional (fossil) power plants (FPP) to provide energy and heat during and after earthquake. Usually FPP consists of steel frame, steam boiler and a number of critical components, equipment and piping. Therefore, design and analysis justification of actual FPP seismic margin is associated with consideration of the complex dynamic systems “frame structure - boiler - equipment”. In conventional design of the powerful FPP the boiler is suspended to the ceiling of the steel frame by special flexible and very elongated hangers in order to provide free thermal expansion of the boiler. Due to that the boiler usually has very low natural frequency that presumes big seismic displacements in the gap between boiler body and steel frame. As a result, the boiler under strong seismic impact closes the gap and all the system experiences shocks and large overloads that could lead to disruption of normal operation and even complete destruction of the boiler. The paper investigates different seismic measures and devices that could efficiently upgrade seismic capacity of FPP and provide necessary seismic margin. High efficiency is demonstrated by using of hysteresis (elastic-plastic) elements and viscous dampers, rationally distributed along the system. It is shown that using investigated approach it is possible to achieve very high seismic capacity for the new and the old one FPPs with their location in high seismic zones.

The recent earthquakes in Türkiye have caused massive destruction to many buildings and structures, particularly reinforced concrete buildings which were not sufficiently engineered to withstand major seismic events. This paper presents a seismic retrofit using Rotational Friction Dampers, a supplemental energy dissipation device that can be installed during the normal function of the structures. The most effective damper configuration and capacities were selected after an iterative trial-and-error linear study using simplified methods developed by authors. Nonlinear push-over and time-history analyses are also conducted for confirmation of results. The proposed retrofit scheme satisfies desired performance goals for both DBE and MCE events. It provides the optimal solution for stakeholders from a performance, design, constructability, and economical point of view. The paper includes application photos and explanations of the retrofit methods used. Overall, rotational friction dampers provide passive energy dissipation and protect buildings from structural and nonstructural damage during moderate and severe earthquakes. It is worth noting that testing of dampers of this type with different slip capacities has been carried out at the Technical University of Denmark and other Japanese and USA laboratories over the last two decades, providing a solid basis for their use in seismic retrofitting. Additionally, at the time of this paper, more than 25 different structures and buildings in Türkiye have been retrofitted with Rotational Friction Dampers. The paper concludes that retrofitting with Rotational Friction Dampers is a viable solution for earthquake protection of precast reinforced concrete structures.

Self-centering (SC) precast concrete wall structures are recognized as a highly effective earthquake-resilient system, displaying remarkable structural integrity with minimal damage and manageable residual drift. However, achieving optimal seismic performance necessitates the harmonization of both structural and non-structural elements. This paper focuses on the infill wall and studies the self-centering precast concrete wall structure incorporating infill walls from two perspectives. Firstly, it provides an evaluation of SC precast concrete wall structures incorporating existing masonry infill walls, which included conventional infill walls and new slippage infill walls. The results demonstrate that while the SC wall remains undamaged, evident damage can occur in the integral system due to the condition of the attached infills. Specifically, stronger traditional infill walls tend to lead to more severe damage in the integral system, whereas the system with slippage joints exhibits the best performance in terms of damage. However, the benefit of reduced damage with slippage joint infills comes at the cost of larger drift responses compared to conventional infills. Therefore, there is a need to develop a new infill that not only effectively reduces damage and displacement but also minimizes acceleration. Secondly, in addressing the aforementioned concerns, this study introduces a novel set of infill walls that integrate sliding mechanisms and higher damping. An experimental investigation of self-centering wall structures with these new infills is conducted. The test outcomes demonstrate the remarkable qualities of the proposed infill walls, exhibiting low damage levels and substantial energy dissipation capacity.

Mass dampers (MD) are theoretically very effective for decreasing dynamic loads on structures, but two fundamental difficulties arise in their implementation. First, the MD is sensitive to tuning, and small deviations in the stiffness or mass of the MD stop its working. Second, the damper displacement exceeds the structure displacement by as many times as the mass of the structure exceeds the MD mass. To eliminate these difficulties, it is necessary to significantly increase the MD mass. For the MD of large mass, there is a critical mass value, above which the damping effect disappears. In the studies of the authors, the connection between the critical mass and damping in the protected structure is shown. The greater is damping in a structure, the smaller is critical mass of the MD. Another feature of a large mass MD is the significant influence of the type of damping in the structure and in the MD spring on the tuning parameters. The applied methods of damping setting lead to significantly different optimal characteristics of the MD. In addition to these features, there may be a question of combining loads in the selection of the MD. In addition to the classical MD, the two-mass MD with consecutive or parallel additions of mass are considered. This solution makes it possible to expand the area of effective operation of the MD and reduce the force in the main damper spring.

To improve the energy dissipated ability and reduce seismic deformation of the bolt-connected precast shear wall structural system, a friction-strip coupled damper that could provide sufficient energy dissipation for main structures was proposed to be installed at the toes of wall panel. To evaluate the seismic performance of the structural system, a shaking table test of a full-scale two-story model was conducted. Seismic capacities of the precast structure without dampers (Model I) and with dampers (Model II) were compared in the test. The results showed that the two models had the similar lateral stiffnesses, indicating the installation of a few dampers exerted slight effects on the stiffness of the structure. Besides, the two models underwent ground motions until to 0.22 g with slight damage, and indicated commonly high seismic capacity against design-basis earthquake. Compared with the Model I, the Model II showed a fewer inter-story drift ratio under the same PGA, which suggested that the friction-strip coupled dampers could effectively reduce the inter-story drift response of the structure.

When performing seismic calculations of civil structures, it is necessary to take into account the effects of the soil structure interaction effect (SSI). At the same time, it is allowed to simulate the soil with impedances from ASCE 4–16, and the civil structure in a geometrically similar way, taking into account the deformation of the foundation slab. However, in the classical modal superposition method, the “ground” damper is not reliably modeled. This is due to the assumption that the damping matrix projected on the basis of eigenvectors has a diagonal appearance, which leads to inaccurate accounting of the energy outflow into the ground during fluctuations of the structure. In view of this, the non-classical modal superposition method is used in this paper, which allows for reliable consideration of the “ground” damper, since the designed damping matrix is taken into account as completely filled. Also in the paper, an approach is presented that takes into account the distribution of equivalent stiffness and damping along the bottom of the foundation slab, which ensures that its flexibility is taken into account. In conclusion, a number of test tasks are presented, demonstrating the advantage of the presented methodology and the accuracy of the results obtained in comparison with calculations using an alternative program. The authors recommend including the non-classical modal superposition method, taking into account the deformation of the foundation slab, in the standards for earthquake resistance of civil structures.

In this study, performance of viscous dampers as an alternative retrofitting technique in a building is evaluated. Büyük Halkalı Primary School Building in İstanbul is considered as a case study. The building was constructed in 1997 and retrofitted in 2006 using conventional methods. In 2019, the building was reassessed according to the Turkish Building Seismic Code (TBDY-2018) and strengthening was achieved by additional shear walls. In this study, different from the previous approach, directivity effects of the ground motion were also considered in addition to the code specific design spectrum. Nonlinear time-history analyses were performed according to TBDY-2018. The retrofit design aimed to enhance the building's seismic performance and reduce potential damage during a seismic event. The design included the installation of seismic dampers, which are devices that dissipate seismic energy and reduce the building's response to ground motion. The seismic dampers were strategically placed to control the building's response to seismic forces and limit the structural damage. Both retrofit options (conventional method and the viscous dampers alternative) were compared in terms of cost, serviceability, architectural benefits, and construction time.

Base isolation and energy dissipative bracing systems are the most used passive control techniques for seismic retrofitting of existing structures. The main goal of this research is the assessment and the comparison of seismic fragility functions of a case study of existing reinforced concrete (RC) building retrofitted with isolation systems based on double concave curved surface sliders (DCCSS) isolators or with dissipative braces based on hysteretic damper (HD) devices. The alternative retrofit applications have been designed conforming to the Italian seismic code considering equivalent single degree of freedom (SDOF) systems with similar global performances and the same anti-seismic devices overstrength level. Multi-stripe nonlinear time-history analysis has been performed on multi degree of freedom (MDOF) numerical models, considering a set of 20 spectra-compatible earthquakes at 10 increasing intensity measure levels. Seismic fragility analysis of the retrofitted building has been evaluated considering a design (minor) damage state and a collapse damage state. The structure drift and the HDs ductility and DCCSSs displacement have been considered as the main engineering demand parameters (EDPs) for the global and local seismic performances. Results of design damage state highlighted that seismic isolation and energy dissipation systems are almost equivalent, coherently with the design assumptions. Results of collapse damage state show the same safety margin for earthquakes bigger than the design one.

This study introduces an energy-based design approach for retrofitting existing reinforced concrete (RC) buildings through passive Energy Dissipative Bracing (EDB) systems. The proposed method is particularly suitable for low - to medium-rise buildings characterized by column-driven failure. It is grounded in the principle of optimizing strength distribution, facilitating a well-balanced damage distribution and energy dissipation throughout the structure to prevent concentration at any single storey. The efficacy of this method is assessed through non-linear dynamic analyses conducted on three reinforced concrete frames originally designed using outdated codes. Furthermore, a comparative analysis is carried out, comparing the results obtained from the proposed approach with those derived from two alternative procedures from the existing literature..