Seismic Isolation, Energy Dissipation and Active Vibration Control of Structures

The development and application of seismic isolation in Italy are presented in this paper. The absence of a suitable technical code limited the use of seismic isolation until the Molise earthquake of October 31st 2002. A great impulse was given by the 2009 L’Aquila earthquake, when the Italian Civil Protection Department realised buildings with seismic isolation for the homeless, the so-called C.A.S.E. project, using sliding pendulum isolators. After that, seismic isolation has always been considered, especially for public buildings, in the reconstruction after seismic events but not only. The evolution of seismic isolation application in Italy is analysed and represented in different diagrams. The structural type, the new or retrofit application and the type of isolation device are distinguished. A summary of the Italian technical code is also provided. Despite the mentioned problems, research has always been very active and advanced in Italy, thanks to the work of several universities and research institutions as well as producer companies. Among the most interesting subjects, here are reported the application for the retrofit of existing buildings, keeping them operational during the works, and the observed behaviour under far fault earthquakes, when the onset of motion could not be guaranteed, especially for friction based devices.

This paper summarizes the passive structural control system applications and other related developments in Turkey, emphasizing the period between 2019 and 2022. The country hosts state-of-the-art seismic isolation applications, relatively greater in size, and use more isolators in each project (415 isolators per building on average) compared to the other seismic isolation projects worldwide. Construction of the world's largest seismic isolated building, Istanbul Başakşehir Pine and Sakura City Hospital, covering more than 1 million square meters of area and employing more than 2000 seismic isolators, was completed and has been in service since May 2020. 1915 Çanakkale Bridge, constructed in memory of the great war of Çanakkale during World War I, is now the world's longest suspension bridge with a 2023m main span length. Eight massive hydraulic dampers were used at the main deck and 48 at the approach viaducts in combination with 72 seismic isolators. Construction of a residential building complex in Istanbul consisting of 16 isolated blocks covering more than 170,000 m2 area and having 454 seismic isolators is coming to an end very soon. Historical Nusretiye Clock Tower in Istanbul was relocated a few meters over seismic isolators. Historical Goztepe Railway Station in Istanbul was retrofitted to accommodate an additional railway line using seismic isolation technology. Seismic codes for buildings and bridges now include rules for the seismically isolated design of structures. Additionally, all seismic isolation designs must be peer-reviewed by law. A new seismic isolator testing facility was established in Eskişehir to respond to the demand for the large number of isolators that need to be tested.

Romania is one of the most seismic prone countries in Europe, as it has the Vrancea point source producing intermediate depth earthquakes and affecting a vast territory. The last big earthquake was in 1977 with a magnitude of 7.5 Mw on Richter scale. While the building stock is gradually aging, since most of it was built during the communist period (more than 40 years ago), many buildings, heritage or not, are now considered vulnerable to strong earthquakes and need urgent interventions. The conventional strengthening solutions, such as adding shear walls or jacketing, are usually being used due to economic reasons, but there are situations in which the disruption of the building’s functionality is the most important factor when deciding how to strengthen/retrofit a building. For such situations, recent technology such as seismic isolation is suitable. In Romania, there are few applications of seismic isolation, only applied at existing heritage buildings. The case studies will be briefly presented, with a special focus on the latest one, which is now under construction, the Fire Tower (Foisorul de Foc) Building, where 18 rubber bearings and 5 viscous dampers were used to seismically isolate the masonry tower from the foundation.

Structures that use seismic isolation technology have been built since the 1970s. The effectiveness of seismic isolation technology has been verified in many earthquakes. By adopting the seismic isolation technology, the inertial force acting on the building can be dramatically reduced, so that not only the structural safety of the building but also the function of the building can be secured by preventing the fall of the indoor contents. There is no other such excellent seismic technology other than the seismically isolated structure. However, existing design standards of seismically isolated structures such as Eurocode, ASCE, Japanese Design Guide, etc. are not consistent even in their basic philosophy. Also, promotion of good quality seismically isolated structures is needed in all earthquake prone countries. In order to spread the seismic isolation technology more widely and internationally, it is necessary to develop internationally harmonized standards for ensuring the performance of the seismically isolated structure. It should include 1) the design method for the seismically isolated structure to achieve the target performance of the building, 2) the construction and maintenance method for the seismically isolated structure, 3) the manufacturing and testing method for the seismic isolation devices. In 2018, a WG (working group) was established within ISO (International Organization for Standardization) to create an international standard for seismically isolated structures. After active discussions in the committee, a standard has been developed that summarizes the basic concepts that will encompass the seismic isolation standards of various countries.

China is a seismic country which 100% of the territory locates in seismic zone. Most of strong earthquakes are over prediction. Most people dead caused by structures collapse. Earthquakes not only cause severe damages for structures, but also cause non-structural elements and inside facilities, cause to stop the city’s life, such as hospital, airport, bridge, and power plant, etc. Designers need to use the new techniques to protect the structures, non-structures, and inside facilities. Therefore, the structural isolation, energy dissipation and control are more and more widely used in recent years in China. There are nearly 16000 large or complex structures with isolation, and about 9000 structures with passive energy dissipation or hybrid control in China until 2021. The fields of application include house buildings, schools, hospitals, airports, bridges, power plant, historical or cultural relic protection, industries facilities, retrofit for existed structures, and immersed tunnel under sea or river. China has got some new progress and established relating systems of isolation, energy dissipation and vibration, which include 3D Seismic Isolation system (3DSI), Seismic and Vibration Control system (SVC), immersed Tunnel with Isolation and Energy Dissipation system (TIED), Hybrid TMD Control system for high rise buildings (HTMD), Eddy-Current Damping system (ECD) and Vortex Vibration Control system for bridges (VVC). Paper also introduces the systems of design codes and device standards, and three large scale and advanced testing systems for isolation, energy dissipation and vibration control. Paper also makes discussion for the tendency of development on seismic resistance, seismic isolation, passive and active control technique in the future in China and in the world.

The number of seismically-isolated building projects continues to grow at a steady, albeit slow rate in the U.S., and applications in Canada are starting to appear. Many projects are architecturally notable, and many also involve increasingly large isolation displacements. The use of isolation for sensitive and critical equipment is becoming more common, and in some cases is extending to state-of-the-art three-dimensional protection. The paper gives an overview of a selection of recent notable projects and discusses recent trends in design and applications.

The application of seismic protection technologies has continued expanding in Chile and other South and Central American countries. This paper presents some selected projects recently designed or built. Most countries in the region have developed local codes or considered the requirements presented in ASCE/SEI 7 for designing seismically isolated structures. Chile is not the exception. Nevertheless, the most recent versions of the Chilean standard, including its current revision, deviates from the US standard because of the recent experience in large earthquakes (Mw 8.8 in 2010, Mw 8.2 in 2014, and Mw 8.3 in 2015), the occurrence of frequent Mw 6.0 or larger (approximately one every month and a half) and economic aspects during construction and maintenance. The main differences include: i) structural system designed for a design basis earthquake; ii) limits to minimum vertical isolation frequency; iii) stricter limits for structure story drifts; iv) requirements for testing 100% production bearings; v) explicit protocol for production bearings testing; vi) explicit requirements for fire protection system; and vii) considerations for minimum safety factors for loads and deformations. In addition, most public hospitals currently under design and construction are incorporating structural health monitoring systems to verify the conditions of the isolation system and the safety of the structure after events with Mercalli Intensity larger than VI. With several seismic events having moment magnitudes larger than 6 every year, it is expected that the Chilean standard becomes empirically validated within the next 10 years.

Scientific research within seismic protection techniques is still nowadays an actual and vibrant field. The main goal of earthquake protection is to alleviate the effects of seismic events on civil structures and infrastructures to reduce both human losses and socio-economical impacts in the medium and long-term. Seismic protection techniques are mainly related to the base isolation systems for buildings or bridges, and to energy dissipation-based solutions with the adoption of special devices, e.g. metal hysteretic dampers, viscous dampers, and friction dampers. The optimization procedures play a fundamental role in the dynamic parametric identification of such devices. Current trends in the optimization field are the adoption of computational intelligence meta-heuristic algorithms, which have been inspired by a conjunction of the artificial intelligence community and nature-inspired phenomena. Specifically, the widespread use of meta-heuristic techniques combined with proper seismic protection optimization problem formulations leads to more cost-effective, high-performing, and innovative design solutions. In the present study, a brief review is argued presenting some optimization procedures to accomplish seismic protection tasks.

Seismic isolation is one of the most reliable passive structural control techniques with adequately established standards for the earthquake protection of structures from earthquakes. However, it has been shown that the seismic isolation systems may not function the best for the near-fault ground motions, since in the proximity of a capable fault, the ground motions are significantly affected by the rupture mechanism and may generate high demands on the isolation system and the structure. In fact, several earthquake resistant design codes state that the seismically isolated structures located at near-fault sites should be designed by considering larger seismic demands than the demand on structures at far-field sites. When the fault ruptures in forward direction to the site most of the seismic energy arrives in coherent long-period ground velocity pulses. The ground-motion prediction equations (GMPEs) typically cannot account for such effects with limited distance metrics and lack adequate data at large magnitudes and near distances. For the reliable earthquake design of the isolated structure in near fault conditions that meets the performance objectives, the 3D design basis ground motion(s) need to be appropriately assessed. Measures in the design of the isolation system, such as modifications in the stiffness and damping characteristics, as well as in the limitation of vertical effects are needed. The behavior of the base-isolated buildings under near-fault (NF) ground motions with fling-step and forward-directivity characteristics are investigated with a rational assessment of design-basis near-fault ground motion, are investigated in a parametric format. The parametric study includes several variables, including the structural system flexibility; number of stories; isolation system characteristic (yield) strength, and the isolation periods related to the post-elastic stiffness. Furthermore, the effect of additional damping by viscous dampers were tested for some selected cases. Important findings observed from the parametric performance results and the overall conclusions of the study are provided.

Italian seismicity is generated by the ongoing subduction of the European lithosphere beneath the Alps, and the Adriatic lithosphere beneath the Apennines. The two belts are extremely different due to their opposite polarity relative to the inferred underlying ‘eastward’ mantle flow. Contractional tectonics is concentrated in low topography areas, whereas extensional tectonics and the larger magnitude seismicity due to normal faulting is preferentially located along the Apennines ridge, where the brittle crustal layer is thicker and the lithostatic load is maximum. Seismicity is the result of dissipation of energy along passive faults but stored mostly in crustal volumes located in the hangingwall of the faults. The 2–5 mm/yr deformation in all Italian tectonic settings prevents the occurrence of great earthquakes (Mw 8) that rather occur in other areas of the world where deformation rates are at least one order of magnitude faster. The maximum event so far recorded in Italy is Mw 7.3, 1693 southeast Sicily. InSAR data nowadays provide a precise definition of the epicentral area of an earthquake, which can be several hundred km2. The epicentral area is defined as the ‘active’ domain where the hangingwall is moving along the fault and it is contemporaneously crossed by the seismic waves radiated by the fault plane due to the friction in it. Within the active domain occur the strongest coseismic shaking, both vertical and horizontal. The vertical coseismic motion allows the horizontal shaking to be much more effective.

Resiliency is an important consideration while designing critical buildings, bridges, and industrial structures in earthquake prone regions of the world. This is necessary for minimizing post-earthquake disruption to society. Major earthquakes that have occurred every year in the world are a constant reminder that critical structures must remain operational post-earthquake, so that community needs are met. Hospitals need to remain operational in order to treat injured people and save lives. Bridges classified as lifeline structures also need to remain functional so that rescue and recovery operations can be performed. Gas, water and electric facilities also need to remain functional post-earthquake so that basic services are not interrupted. Code provisions (ductility based) for seismic design of structures all over the world have focused primarily on achieving “Collapse Prevention” within acceptable limits, at the expense of inflicting damage to structural, non-structural, architectural elements, and contents. After a major earthquake this results in loss of use and function, as observed in recent Japan, New Zealand and Chile earthquakes. One of the approach to achieve resiliency is through continued functionality design objectives for minimizing damage in structures by absorbing seismic displacement in isolation bearings, maintaining an elastic structure, and minimizing in-structure accelerations and drifts. The paper presents the current pitfalls of code compliant seismic isolation provisions, and a way forward for the right approach for implementing seismic isolation following the “Continued-Functionality Standard (CFS)” to meet the owner’s expectation. Examples of resilient isolated structures worldwide designed and constructed at lower costs than conventional ductile structures are presented. Real earthquake performance of CFS designed seismically isolated structures are also presented.

As the construction of over-track buildings has increased, the need for reducing vertical vibrations caused by subways has emerged. Thick rubber bearings (TRBs) can provide both horizontal and vertical isolation. However, there is still uncertainty about the mechanical properties of TRBs which causes a difficulty in evaluating their performance. In this study, a full-scale TRB with a low first shape factor was designed, manufactured, and then tested under compressive, tensile, and shear loads. Its vertical and horizontal characteristics were identified through experiments. The effects of the vertical pressure, shear strain, and loading frequency on the mechanical behavior of the TRB were explored. Based on the experimentally determined properties, simplified multiple-degree-of-freedom systems were established to evaluate the performance of the TRB in terms of mitigating the vertical vibrations caused by the subway. Under a subway-induced excitation, the acceleration responses of the isolated system using TRBs were substantially reduced. Therefore, TRBs could be used to mitigate vertical vibrations and improve the seismic safety of over-track buildings.

Seismic isolation has become increasingly popular due to the excellent performance observed in buildings during past earthquakes. The seismic response of isolated structures to earthquake input is strongly controlled by the force-deformation constitutive behavior of the isolators. High Damping Rubber Bearings (HDRBs) are one of the most widely manufactured and used isolation systems in practice. Because of the large shear flexibility, the stress-strain constitutive behavior of the elastomeric material controls the overall behavior of the device. Thus, the behavior of HDRBs is highly nonlinear and characterized by the same phenomena as the elastomeric material, which is challenging to model analytically. Consequently, this article describes a simple but sufficiently accurate numerical model for simulating the bi-directional shear behavior of HDRBs under large shear deformations. A brief description of the experimental test data of HDRBs is presented, as well as the importance of including the observed phenomena in the numerical model proposed. The mathematical formulation of the proposed model is summarized, based on a hyperelastic spring and dissipative element connected in parallel. The former considers anisotropic degradation (scragging and Mullins effect), while the latter includes the isotropic hardening phenomenon. The proposed model was validated using experimental results of bi-directional shear tests of cylindrical disks of high damping natural rubber, unidirectional shear cyclic tests, and a bi-directional shear loading history applied to an HDRBs. Since the proposed model is capable of simulating the bi-directional cyclic behavior of HDRBs by considering anisotropic degradation instead of the classical isotropic behavior, which improves the numerical predictions, it can be used in dynamic analyses of buildings isolated with HDRBs.

Deformation history integral type hysteresis (DHI) model is a numerical model for seismic isolation bearing which has high non-linearity in restoring force characteristics, such as high-damping rubber bearing (HDR). While the model can represent the complex behavior of HDR including performance change by temperature, aging and manufacturing variation, the scragging effect, which is generally considered in practical design of seismic isolation system, is not taken into account in the conventional model. In this study, the model was improved by defining scragging effect as a function of performance change ratio. In order to confirm the accuracy of the proposed model, time history analysis was carried out and the results of analysis were compared with those of substructure real-time online testing (SROLT) using scaled model of HDR. The analysis results showed good agreement with those of SROLT and the applicability of improved DHI model was verified.

This paper presents the application of long, complicated isolated buildings in large scale infrastructure in cold region in China, and carried out quantitative study on the effect of low temperature and shrinkage on long isolated buildings. To investigate how low temperature and shrinkage affect the mechanical behavior of the rubber bearing, a microscopic observation of the effect of low temperature on the rubber isolator is carried out using differential scanning calorimeter (DSC) to determine the scope of freezing low temperature for the isolator to achieve. A mesomechanics model is employed to analyze the effect of micro damage on rubber bearings due to large displacement under low temperature. The dividing of construction elements of isolation layer in several long isolated buildings has been studied using such FEM software tool as Abaqus and SAP2000. The optimum construction scheme of several long isolated buildings has been suggested and verified through machine vision based monitoring in airports and urban complex buildings in typical cold regions in China.

A novel variable friction pendulum isolator (VFPI) and a novel variable curvature and friction-friction pendulum isolator (VCF-FPI) are developed in this study, which introduces variable mechanical properties into the conventional friction pendulum isolator (FPI). The mechanical behavior and operating principles of the VFPI and VCF-FPI are illustrated. The theoretical constitutive models are subsequently derived based on the mechanical behavior of the VFPI and VCF-FPI. A numerical modeling scheme of VFPI for response-history analysis, composed of existing elements, is proposed, which can be easily achieved in the currently available analysis software. Mechanical property tests for the full-scale VFPI and VCF-FPI are carried out to verify the force-displacement relationships obtained from theoretical analysis and numerical modeling. These investigations conclude that both VFPI and VCF-FPI provide desired changeable stiffness and damping with increasing isolator deformation. The hysteresis loops of VFPI and VCF-FPI are thin in the middle and thick at both ends, which indicates the energy dissipation capability of VFPI and VCF-FPI increases with increasing isolator deformation.

The hysteretic behavior of a sliding seismic isolation system is basically a function of its friction properties. Thus, identification of the coefficient of friction at the sliding interface of the isolator is crucial. It requires displacement controlled dynamic tests to determine friction properties considering loading conditions representative of seismic actions. In these tests, the number of loading cycles is mostly three, and deterioration in friction coefficient, which is mostly due to frictional heating at the sliding interface, is assessed from cycle to cycle. The aim of this experimental study is to investigate the effect of vertical force and loading velocity on friction properties of a full-scale double friction pendulum. During the tests, by means of thermocouples mounted on the isolator, the change in temperature at the sliding interface was monitored too. Isolator tests were conducted at ESQUAKE Seismic Isolator Test Laboratory of Eskişehir Technical University. Results showed that the amplitude of frictional heating is highly dependent on the vertical force and the loading velocity. It is also revealed that the corresponding temperature rise at the sliding interface is not uniform. This is especially more pronounced for high loading velocities.

Pendulum dampers, which are the subject of this study, are a type of tuned mass damper (TMD). In general, TMDs are effective since they are designed according to the first mode behavior of the buildings. In this study, the effects of pendulum dampers on the structural behavior are investigated by performing vibration experiments on a 3-storey shear frame model with reduced dimensions. Harmonic loads are applied to the test models with and without pendulums on a one-way shaking table. Firstly, experiments without dampers were performed on the selected 3-storey reduced building model, and structural responses were found. The mass of pendulum dampers is chosen to be around 3% of the total mass of the structural model. One of the main aims of this study is to reveal the effects of the different placements of the dampers on the dynamic behavior. Accordingly, a single pendulum is independently placed on the top floor, the second floor, and finally on the first floor. In addition, experiments are carried out by establishing double damper models and then a triple damper model. By creating seven different damper models, the experiments are repeated under harmonic loads with different frequencies. Tests under a harmonic load equal to the first mode frequency of the undamped model reveal the behavior of the models in the resonant state. Experiments show that the pendulums used are highly effective in the resonance state. Some models with more than one damper have also been shown to be effective at reducing dynamic response.

Acceptable probabilities of collapse for seismically isolated buildings could be achieved by an appropriate isolator displacement capacity. This paper investigates the effects of the over-stroke capacity, in addition with the displacement capacity of the isolation system, on the seismic response of a structure isolated with double concave curved surface slider isolators. The case study is a moment resisting steel framed building in which the isolation system assumes different displacement limits. Results from nonlinear static analysis and nonlinear time history analysis demonstrate that over-stroke displacement of the isolators may significantly increase the safety factor in case of earthquakes bigger than the design ones, without drawing on the plastic resources of the structure and changing the construction costs.

The present work explores the use of a curved hysteretic steel device, known as Crescent Shaped Brace, to strengthen pinned beam-column connections in order to obtain semi-rigid joints. The kinematics and mechanical behavior of the semi-rigid joint is investigated by introducing a simplified analytical model. The model is then validated through Finite Element analysis. Finally, the possibility of optimizing the joint geometry and mechanical performances using novel metal 3D printing techniques (such as Wire-and-Arc Additive Manufacturing) is briefly presented.

This study presents a reliability analysis of stochastic system using the probability density evolution method (PDEM). The PDEM is formulated according to the principle of probability conservation where generalized density evolution equations (GDEEs) are completely decoupled. To estimate the probability density function accurately, a set of representative points of random variables are generated using the GF-discrepancy scheme. A large number of representative points is needed to obtain satisfactory accuracy, which becomes computationally expensive. To reduce the computation burden, a stochastic spectral embedding (SSE) is used as a surrogate model which approximates the original response surface. To illustrate the proposed SSE-based PDEM, two numerical examples are investigated, including the reliability analysis of four-branch problem, and the reliability-based design optimization of a shape memory alloy based damped outrigger tall timber building. Numerical results show that the proposed SSE-based PDEM can estimate failure probability using a very small number of representative points without compromising accuracy compared with Monte Carlo simulation, which leads to a reduction in computational costs.

In the seismic isolation structure, the seismic isolation device is designed to have low horizontal rigidity and high vertical rigidity for obtaining a long horizontal period and stable vertical support capacity. However, due to this, the seismic isolation structure cannot be expected to have a seismic isolation effect in the vertical direction. For protecting human and physical safety from earthquakes, it is necessary to consider the vertical component of the earthquake. In this research, after confirming the mechanical performance of the existing seismic isolation device, a three-dimensional seismic isolation system will be constructed by combining the horizontal seismic isolation device and the vertical seismic isolation device. The purpose is to analyse the seismic response at the building level using the constructed three-dimensional seismic isolation system and propose a three-dimensional seismic isolation system which can provide the better seismic isolation effect.

Long period seismic ground motions are known to cause large amplitude cyclic deformation in the energy dissipation devices installed in high-rise structures. Low cycle fatigue damage due to the large amplitude cyclic deformation in energy dissipation devices is of great concern. In this study, ultra-low cycle fatigue performance of buckling restrained aluminum shear yielding dampers (BR-AlSYDs) is assessed through numerical investigation on finite element program ABAQUS. Material properties of annealed Al-6063 alloy shear yielding devices are calibrated using ABAQUS platform against the cyclic experiment results. These calibrated material properties are adopted to design and investigate the BR-AlSYDs for their low cycle fatigue performance numerically. Two geometrical profiles of energy dissipator core plates are adopted in BR-AlSYD specimens which are hourglass and rectangular shapes. It is observed that the hourglass shaped energy dissipator core plates show better low cycle fatigue performance than rectangular shaped energy dissipator core plates. Further, fatigue performance parameters of Coffin-Manson relation are calibrated for BR-AlSYDs and accordingly Miner’s rule is proposed to assess the fatigue performance of these dampers for any random seismic excitation.

The design of seismic isolators as specified by building code requirements is well defined and well established. However, there is still some refinement required for these design practices, especially in terms of estimating the yield strength and confinement of lead cores. The Lead Core is a key component in a Lead Rubber Bearing (LRB) that provides energy absorption resulting in the damping of a unit/system. Historically, designers have used a standard value for lead yield (7–10 MPa) depending on individual preferences. However, based on prototype test results, it has been shown that lead yielding is variable and strongly influenced by a number of physical parameters. This piece of research has focused on validating a newly developed equation to estimate the yield strength of lead rubber bearing regarding the confinement category of the lead cores. The yield strength results from prototype tests were compared with the predicted yield strengths from the proposed equation. The output trends present an appropriate match between the prototype test and the proposed equation so that the difference for most cases falls within ±5%.

More and more seismically isolated buildings have been constructed in the world. One of the reasons for the dramatic increase is the stipulation of design standards. In October 2021, “ISO/FDIS 23618-2022 Bases for design of structures - General principles for seismically isolated structures” was approved.In this paper, seismic isolation design and devices testing standards of Japan, China, the United States of America and Eurocode, are compared using the same building model. For seismic loads, design response spectra were calculated and compared. The locations of the buildings were assumed to be Tokyo, Beijing, San Francisco and Reggio Calabria, Italy, respectively, in order to take into account the seismicity.The building model is a 7-story RC building supported by lead rubber bearings. In each analysis case, the weight, height, super-structure and ground conditions of the building were all the same. In Japan, China and Eurocode, the same LRB devices were used. However, the seismic load in USA was quite large, larger size devices were used. Both the equivalent linearization method and the time history response analysis method were used for the response analysis of the building. The response analysis results such as the response displacement of the seismic isolation system, the shear force coefficients of the super-structure, and the story drift were used as comparison parameters.

Rubber compounds are extensively used for manufacturing rubber bearings for seismic isolation. Current seismic codes prescribe the use of design properties of seismic isolators derived from experimental evaluations to account for the effects of strain rate representative of the design seismic condition, cyclic degradation, frequency and environmental conditions (especially the temperature variation). Moreover, ageing phenomena, which such devices undergo during their service life, should be taken into account. Such tests should be carried out on devices, even though the European Standard on seismic devices (EN 15129) allows for both high and low damping rubber bearings the use of data from material tests performed on the elastomer used in their manufacture, (although extrapolation the results of materials tests to the scale of isolation devices is not always straightforward). In this study a set of experimental data obtained from type tests performed by different manufacturers on both low and high damping compounds with nominal stiffness ranging from 0.4 MPa to 1.3 MPa is statistically analysed. The effects of shear deformation, cyclic degradation, ageing, frequency and temperature on equivalent shear stiffness and equivalent damping are shown, providing also a view of the intra-supplier variability and inter-supplier variability. As general modification factors, also known as λ-factors, are provided by the codes in case of unavailability of experimental data, a comparison between the codes values and the obtained experimental results is shown.

Most of the current seismic codes on seismic isolation prescribe upper and lower bound analyses to account for the variability of mechanical properties of seismic isolators. This procedure should be based on experimental data provided by manufacturers during qualification tests. When such data are not available, codes provide the so-called property modification factors or λ-factors for different kind of devices, giving maximum upper and lower bound coefficients to apply to nominal properties of bearings. Different sources of variability are considered, from the variability due to the bearing production to environmental or behavioural effects (such as temperature, contamination, ageing or repeated cycles). However, the origin of these values is not straightforward: some of them are based on wide experimental data, whereas others are based on few and old indications given by technical literature. The aim of this paper is to illustrate in detail such factors, especially for HDRBs (High Damping Rubber Bearings). In particular, it is shown that in the European context, both the EN 1998—part 2 (on bridges) and the EN 15129 (on anti-seismic devices), provide values deriving (with some transcription inconsistencies) from the second version of the AASHTO guide specification, which in turn proposes values derived from the MCEER-99-0012 report written in 1999 and never updated. The aim of this paper is to illustrate in detail such factors and to make the reader aware that most of factors derive from limited and/or old data, especially for HDRBs (High Damping Rubber Bearings).

Detailed design of a base-isolated building as per Indian code provisions and practices is made and described here to facilitate corroboration of the design with other international codes and standards. Upon reviewing the latest developments and applications of the base isolation technology in India, the code development is presented. Particularly, the code provisions and practices in India have been elaborated in light of the state-of-the-art and state-of-the-practice. Then, by taking an example building, base isolation system has been designed and provided to achieve higher seismic performance. Assessment of the design outcomes is made to understand the implications of the code recommendation, especially from techno-economics viewpoints.

Seismic isolation technology has become a practical strategy for seismic-resistant design. Several studies have also been proposed to promote the applications of seismic isolation technology in structural engineering and the corresponding design procedures. This study introduces the newly issued Building Seismic Isolation Design Standards of China, in which the framework of an integrated direct design method(IDM) for seismically seismically isolated structures is proposed based on the concept of the Complex-mode-superposition response spectrum. The proposed method is different from the traditional two-stage seismic reduction coefficient design method. The new standard design spectrum for the seismically isolated building is given in the issued Standard. The dynamic history analysis method, the IDM, and the divisional design method(DDM) are employed to conduct the seismic isolation design using the seismically isolated benchmark model. The critical design parameters and analysis results from the China standard are reported and evaluated to facilitate the comprehensive comparisons of the seismic isolation design codes from various countries.

Dr. Victor Zayas invented and patented the seismic isolator that is known under the Trade Name “Friction Pendulum Bearing®” in 1985, which together with Lead Rubber Bearing revolutionized modern seismic hardware. Prior to the expiration of Dr. Zayas’s patent, Prof. Chong-Shien Tsai filed a patent in Taiwan (R.O.C.) in 1991, which represents an interesting evolution thereof. In all the seven (7) versions illustrated in the Prof. Tsai’s Patent a hinged slider separates the two concave surfaces. At the turn of the last century, a further version of Double Curved Surface Slider (DCSS) appeared in Japan, in which the intermediate slider is solid, in that the hinge has been removed. Being constructively much simpler, it has met with success with all seismic hardware manufacturers. However, this simplified version has produced serious anomalies. These consist of high eccentricities that cause significant deformations at the edges of the sliding material (liner) with its consequent wearing, as well as strong vibrations transmitted to the structure and even the phenomenon of “banging”. The paper elaborates the mathematical models of the Kinematics of the two types of Double Curved Surface Sliders, identifies the critical parameters and quantifies the values thereof that produce the observed adverse phenomena. Finally, the paper reports the list of factors, the concomitant presence of which suggests not adopting the simplified solution.

Full scale dynamic testing of seismic isolation devices in combined compression and shear is nowadays required by all international standards on seismically isolated structures and/or on anti-seismic devices, for prototype tests, and sometimes for production control (or acceptance) tests. The Type tests aim at understanding the effects on the isolator's hysteretic behavior of different actions, such as vertical loads, amplitude and velocity of the horizontal displacements, and at introducing such effects in proper modelling of seismically isolated structures. The dynamic tests required by the standards are usually cyclic sinusoidal tests under different vertical loads, with different amplitude, frequency and number of cycles, thus resulting very demanding, in terms of global energy dissipation and cumulated displacement. Testing protocols for production control are usually simpler. As a contribution to future revision of the testing protocols in the standards, this paper presents a comparison between cyclic loading tests and Time History (TH) tests performed under the design vertical load on a pendulum isolator characterized by ±450mm maximum displacement capacity. The input of TH tests is the displacement TH resulting as output of non-linear dynamic analyses on the structure in which the isolator are installed. A total of 9 time-history tests were performed: 3 couples of records of Turkish earthquakes, scaled to the MCE spectrum, and 3 generated earthquakes compatible with the same spectrum. The results are compared with that of cyclic sinusoidal tests similar to those required by standards, in terms of energy dissipation and cumulated displacement.

Seismic isolation is an effective method to control seismic forces, seismic displacements and to govern modal shapes on a structure or a part of it. Seismic isolation devices are widely used in the design of new bridges and retrofit of existing structures due to their effectiveness in the reduction of seismic forces and the relatively simple methods of installation. This work aims to provide practical considerations to be included when dealing with the design of new bridges equipped with seismic isolator devices and in particular the paper focuses on the study of seismic isolator stiffness variation and inclusion of soil-structure interaction. The purposes of the paper are a) to set a fast design procedure for the design of seismically isolated bridges b) to investigate how the stiffness of an equivalent system composed of foundations, piers and bearings can be affected by varying the stiffness of the individual components. Both these objectives will be described following a sort of flow chart containing the different main steps to be included for the design of seismically isolated bridges. This study can provide practical oriented considerations to the designers dealing with seismic design of isolated bridges and can help to understand how stiffness variations of the single components might affect the global behavior of the structure and thus the sizing of the structural elements.

Water and ice contamination in Friction Pendulum System (FPS) bearings has been observed on several seismically isolated bridges in Alaska. However, there have been few studies on how water and ice contamination affect FPS bearings frictional properties. In this study, two formerly in-service double pendulum, a new double pendulum and a new single pendulum bearing were tested. Each bearing was subjected to displacement controlled loading using a single bearing test assembly that supports the bearing between the earthquake simulator and a stabilizing A-shaped steel frame that loads the bearing axially and restrains the bearings top plate from horizontal movement. An idealized bilinear loop was fitted to the data points of each test, excluding the first and last cycle. Uneven sliding between both sliding surfaces was observed on tests on double pendulum bearings subjected to water, ice or soil contamination. Sliding restricted to one surface results in approximately twice the post yield stiffness compared to balanced sliding on two surfaces. Also, lower coefficient of friction was observed during wet tests compared to dry tests. Furthermore, ice resistance was calculated by comparing the first cycle on frozen tests with the idealized bilinear loops of the subsequent cycles. Ice resistance is hypothesized to be a function of ice volume and doesn’t seem to have a big impact on heavily loaded bearings.

This study investigates the variation in structural response of a bridge seismically isolated with lead rubber bearings (LRBs), when subjected to ground motion excitations at low ambient temperature. For this purpose, first, a full-scale LRB was conditioned at −20 °C, −10 °C, 0 °C and 20 °C temperatures for 24 h and tested under dynamic conditions in order to determine the change in its characteristic strength and post-yield stiffness. Recorded force-displacement curves were then utilized to represent the deteriorating hysteretic behavior of the LRB in case of different temperatures. Seismically isolated bridge was idealized by a single-degree-of-freedom model and analyses were performed by OpenSees structural analysis program. Nonlinear response history analyses (NRHA) were conducted considering the strength deterioration of the LRB due to the lead core heating during cyclic motion. In the analyses, eleven pairs of ground motion records, selected and scaled to represent a target spectrum, were used. Response quantities assessed in the analyses were maximum isolator displacement and maximum isolator force for the isolation system and maximum acceleration for the bridge deck. It is revealed that as the ambient temperature decreases, the amount of amplification in maximum isolator forces and accelerations can be up to 30%.

Post-tensioned (PT) rocking piers have emerged as a promising solution for bridge substructures, significantly increasing their seismic performance and resilience. These piers are characterized by unbonded PT tendon and energy dissipation (ED) components providing, respectively, self-centering and dissipating capacities. Despite the potential advantages, their practical applications are still limited due to the lack of design standards and guidelines. In this context, developing a simple design procedure represents an essential step in making the use of such systems more accessible to the bridge design community. The present study introduces a design procedure for PT bridge piers by defining a performance index λ related to both initial PT force level and ED device amount. The design process is based on the improvement of a conventional monolithic bridge pier (i.e., similar dimensions and steel amount with superior self-centering behavior and load resistance). For illustration purposes, the design procedure is applied to a case study bridge pier, and its seismic performance is compared with the corresponding conventional monolithic pier. The results show that a PT bridge pier that satisfies the design objectives of residual drift and lateral force (i.e., superior self-centering behavior and load resistance) can be conceived and designed through the proposed simple design approach.

Seismic isolation is a proven strategy for protecting critical infrastructures from the damaging effects of design-level earthquake shaking. For seismically isolated highway bridges, the expected seismic performance is to provide limited service under a safety evaluation-level ground shaking with minimal to moderate damage. The behavior under extreme shaking, corresponding to a large return period seismic hazard, is not well understood and could induce significant damage. In these rare events, the seismic isolation system can be subjected to displacement demands beyond its design capacity, resulting in failure of the bearings or exceeding the clearance and pounding against the abutment backwalls. To better assess the seismic performance of a prototype highway bridge subjected to earthquakes beyond design considerations, this study examines the bridge lateral displacement, the transfer of forces to the substructure, and potential failure modes of seismically isolated bridges. Advanced modeling approaches are considered to capture bearing characteristics such as hardening for large strain, and a pounding macro-elements is implemented. Results show that for beyond design shaking, the bearings can reach the maximum shear strain capacity, significant residual deformation of the abutment can result from pounding, and the columns can experience moderate damage. The progression of damage is identified and interpreted to assess downtime.

The 6 km toll road “Via Puente Industrial” represents one of the major public infrastructure under development in Chile, linking the Municipality of Hualpén to San Pedro de la Paz [1]. The total investment of the project, about 160 million dollars, includes the construction of the main section “Puente Industrial”, that is the fourth viaduct over the Biobio River in the Conception region, which also incorporates various complementary works at intersections at different levels and railway overpass. The bridge will have a total length of 2.5 km, 2 abutments and 55 piers. Due to the high seismicity of the site, the structure will be seismically isolated with Lead Rubber Bearings (LRB). For this project Freyssinet designed, produced and finally tested a total of 784 ISOSISM® LRB. The high number of devices to produce, together with the very demanding performance and testing requirements, asking to test full scale all the 784 isolators with a maximum variation of 10% on the average performance, represented a real challenge. Freyssinet successfully achieved it, going even beyond the requirement providing an overall variation close to half of the required value, thanks to strict quality and production processes, allowing to control all the steps from characterization of incoming materials, up to vulcanization and test of the isolators. This paper aims at analyzing the performance characteristics of the lead rubber bearings provided for this important project with special focus on the quality control processes that Freyssinet carries on during the full production cycle. This was a mandatory gate to guarantee the performances beyond the requirements of the applicable standard.

Çanakkale-1915 is the longest mid-span suspension bridge in the world and it is part of a mega-scale investment in transportation and infrastructure in Turkey. The bridge across the Dardanelle (Çanakkale) Strait carries a new highway connecting Europe and Asia and it will represent a new alternative to the Bosporus passage. The approach bridges are seismically isolated with high-friction curved surface sliders to accommodate the high displacement demand while dissipating the seismic energy transmitted to the piers and foundations which otherwise would be very large and costly due to the extreme seismic excitation foreseen for that region. This paper gives a complete overview of the seismic isolation system of both Asian and European approach bridges. More than 70 isolators were designed and manufactured by Freyssinet. In addition, two viaducts of the approaching highway will be presented, both equipped with viscous dampers to dissipate a huge quantity of energy and designed and tested for extremely high performances. These structures represent an application of mega anti-seismic devices, with displacement capacity up to more than one meter and design velocity above one meter per second.

The 1915 Çanakkale Bridge is a recently completed suspension bridge, characterized by a main span of 2023 m which is the world’s record. The bridge restraint system is quite complex in order to guarantee safety under traffic, wind and seismic actions. It comprises 8 fluid viscous dampers, 4 large bearings designed to withstand compression load as well as tension load and horizontal displacement, 8 lateral elastomeric bearings for transversal restraint and 8 hydraulic end-stop devices. This paper focuses on the eight special fluid viscous dampers that give large energy dissipation capacity to the bridge under earthquake. They are characterized by a load capacity of 5000 kN, a stroke of ± 1.25 m and a maximum design velocity of 1 m/s. The paper describes the dynamic and static tests carried out on two full scale viscous dampers according to the test protocol that includes the European Standard EN 15129:2009 type tests and additional contract specifications.

Even though there are so many studies upon optimization of supplemental damping devices integrated to structural systems, the vast majority of them remain only as a subject of the research articles of the Journals and cannot find a place itself in common practice due to lack of the regulations about the issue in codes and standards. In this paper, the issue is dealt with the most fundamental inputs and outputs of a general problem. All efforts are made to show how the procedure could frequently be used in common practice and what the attained benefits could be from the design and application point of view. The analysis of the structural systems in which the “seismic response control systems” have been adapted requires considering the special numerical analysis techniques which provide “solutions in frequency domain”. By this means, not only the “dynamic response characteristics” of the structure shall be determined but also the variation of this response with the change of the “design parameters forming the structural control systems” shall be able to be investigated from the optimization point of view. Since conventional analysis tools and methods are not capable of providing such information, advanced numerical analysis method based on the “state-space approach” is considered along with the “gradient based optimization algorithm” in the proposed study. In this paper, viscous fluid dampers are examined as a supplemental damping devices in the analysis of a multi degree of freedom structure. Dampers are modelled with the Maxwell model in which the spring and the dashpot are placed in series. For a given brace stiffness, viscous damping coefficients and the distribution of the damping devices between stories are optimized by a procedure to reach a “target performance level”. The optimization is achieved by minimizing an “objective function” which rates the structural responses of the controlled system with the uncontrolled one. Generally, mean square responses of the inter-story drift, floor acceleration and base shear are among the structural response quantities considered for this procedure.

The Site C Clean Energy Project is a new, 1,100 MW hydroelectric generating station on the Peace River in northeastern British Columbia, Canada. Seismic isolation has been adopted to protect more than 150 pieces of equipment deemed critical for dam safety and to meet the project’s operational requirements. Three-dimensional seismic isolation platforms are being used to protect the critical equipment, with a total of 39 platforms throughout the spillway headworks structure. The design of the isolation systems followed the framework of IEEE 693-2018, Annex W, with nonlinear analyses and shake table testing of the equipment and the isolation platforms to confirm their performance. Seismic isolation is also being used to protect seismically-vulnerable electrical equipment at the interface of the powerhouse generator step-up transformers and the 500 kV transmission system. The paper will describe the design and testing of the isolation systems being implemented on the project and key aspects of their benefits and effectiveness.

Due to the complexity in the development of highly nonlinear models, engineers tend to use more practical ones such as smoothed or sharp bilinear models. It has been shown that differences in hysteresis characteristics may lead to variance in performance parameters, resulting in possible overdesign or underdesign. In this study, to assess the effect of the modelling approach on seismic performance, high damping rubber bearing was designed and evaluated in terms of structural performance for a selected hospital building. Commonly used bilinear and highly nonlinear isolator hysteresis models from the literature were adopted, and structural models were created for 2475 years return period earthquake level. Three-dimensional nonlinear time history analyses were conducted on the 10-story building model under a set of 11 ground motions. For each model, structural performance is evaluated and compared in terms of maximum isolator displacements, base shear reactions, story accelerations, and inter-story drifts. The results show that when bilinear models are used instead of more accurate nonlinear models, there is significant variation in the superstructural response, especially for sharply bilinear models for the considered building.

Historic masonry buildings are often heavily damaged by earthquakes, resulting in huge losses of cultural heritage. Several studies have shown the effectiveness of seismic vulnerability mitigation strategies based on base isolation systems (BISs), which allow damage to masonry buildings and their contents to be significantly reduced or even avoided. This paper presents preparatory activities and base isolation project for seismic retrofitting of an existing strategic masonry building with historical-architectural value, which is located in Perugia (Italy) and hosts the headquarters of Umbria Region, Perugia public prosecutor’s office and some offices of the Italian Ministry of Infrastructure and Transportation. The building consists of five floor levels and has an L-shaped plan with size equal to approximately 1600 m2. The structure was built in the early 1950s using different materials and construction technologies. The BIS design started from a historical investigation on the original design, fabrication and modifications of the masonry building, based on archival data and available literature. An extensive investigation was carried out through on-site experimental tests on both subsoil and masonry structure, as well as geometric surveys with laser scanner technology, allowing an excellent knowledge of the building (including the development of a building information model) and the calibration of two three-dimensional structural models based on both finite element method (FEM) and equivalent frame method (EFM). The structural characteristics, historical value and public function of the building delineate a case study with considerable importance in the field of seismic isolation of existing masonry buildings.

An alternative passive energy-based retrofit design is proposed for a reinforced concrete building, seismically retrofitted in 2013 and damaged by the 2016 Central Italy earthquake. An evaluation analysis carried out by referring to the pre-2013 conditions shows unsafe stress states in most structural members and severe damage in the masonry partitions and perimeter infills. The alternative retrofit strategy of the building, which consists in the incorporation of a dissipative bracing system equipped with pressurized fluid viscous spring-dampers, allows attaining a substantial seismic performance improvement. This is assessed by a safe response of all columns and beams, and at most a very slight damage in the masonry panels, in post-intervention conditions.

Tuned Mass Dampers (TMD) have been widely used in the passive vibration control of engineering structures, both under wind and seismic loads. Under wind loads, a proper frequency tuning ensures a significant response reduction of the primary structure. While under wind loads the structure is likely to remain in the elastic range of behaviour, when large earthquakes occur it can experience inelastic deformations and damage, with a consequent de-tuning effect. In this paper, nonconventional TMDs with large mass ratios, realized through Inter-story Isolation Systems (IIS), are considered and the influence of the inelastic behaviour of the primary system on the overall structure response is analysed. In detail, IIS is employed for retrofitting existing masonry buildings through a vertical extension, isolated at its base and built up on the roof of the existing structure. Pivot-type hysteretic models are used to grasp the mechanical behaviour of the masonry structure. Based on a case-study building, time history analyses on 3D Finite Element models are implemented. The results of nonlinear time history analyses show that in the building with the vertical extension both displacements and hysteretic energy dissipated by the masonry piers, are lower than in the as-is building, confirming that, although a de-tuning effect can occur, the inelastic engagement of the original structure is significantly reduced.

The effects of seismic attacks, especially in ancient or historical district of hit towns, depend not only on the intensity of the seismic action, but most of all on the quality of materials and construction technique. The negative consequences of traditional design and construction approaches appeared in all their negative evidence in many areas of Central Italy affected by recent seismic sequences of medium intensity (M5-M6) in 2016–2017 where entire villages were destroyed. Now the reconstruction should solve the problem to rebuild with safety but preserving the historical aspect of buildings and landscape. This paper presents a particular application of the known technique of seismic isolation for the reconstruction with integral seismic protection of the worldwide known village of Castelluccio di Norcia in Umbria (Central Italy). The adoption of a seismic isolation system at city scale involves the construction of a large floating slab, having the dimensions of the entire compartment, stepped due to the site orography, and supported by seismic isolators, above which to construct buildings that will present the aesthetic and constructive characteristics of the collapsed original ones. The solution allows a correct interpretation of the objective to rebuild “as it was, where it was”, safeguarding the landscape, prolonging the lifetime, saving the expected cost.

It is well known the low capacity of unreinforced masonry (URM) buildings to withstand seismic excitations. Thus, many reinforcement techniques (tie rods, buttresses, collar beams, etc.) have been developed, aiming at improving their dynamic response. Such techniques increase the strength and sometimes the ductility of the structural members. However, in the last two decades, vibration control techniques have been tested and applied as an alternative to reduce the seismic response of URM buildings. These techniques, based on performance approaches, rely on the dissipation of kinematic energy by placing passive devices able to add damping into the structure. Among them, viscoelastic (VE) devices can supply self-centring capacity and dissipate energy through the shear deformation of viscoelastic layers. In contrast with other dampers, VE devices can have linear behaviour which simplifies their design and application to URM structures. This paper presents the results of a parametric analysis comparing the dynamic response of a URM building strengthened with a traditional technique and with VE devices. A FEM model was generated using a prototype based on viceregal buildings (18th century) located in Mexico. The response was evaluated in terms of displacements and energy.

The interest in the concept of Resilience in the scientific community has been growing consistently over the past few years to study the functionality and behavior of systems against natural and man-made hazards. This is reflected by the number of journal articles that can be accessed in the Web of Science database. In this paper, a bibliometric and visualization method is applied to explore the status of resilience research in civil engineering applications by analyzing the journal papers published from 1996 to 2020. The bibliometric analysis aims at consolidating the state of the art by identifying influential journals, most cited articles, the geographic distribution of resilience publications including the research institutions by country, the author keywords distribution, and the co-authorship status. The concept of resilience is investigated through eight subject categories identified by the authors in the literature: Recovery time strategies and Downtime, Critical infrastructures, Probabilistic approaches, Fuzzy logic approaches, Structural health monitoring, Health Care facilities, Emergency management and Decision-making, Community and Urban Resilience. Results show that resilience research has increased rapidly since its introduction, most notably in the last seven years. In terms of the geographical region of the studies, most of them have been carried out in the USA, the United Kingdom, China, and Italy. Finally, based on the author keywords analysis, it is possible to observe that recovery strategies, critical infrastructures, vulnerability, and community resilience have attracted prominent attention during the past decade.

The observed behaviour of seismically isolated structures in different countries allowed testifying the suitability of this technique to protect structures against strong earthquakes. In Italy, up to now, base isolated buildings have been subjected only to low energy earthquakes. This paper describes and compares the observed behaviours under a low energy earthquake of three buildings with different isolation systems. In the first one, seismically isolated by means of HDRBs, the structure showed resonance frequencies higher than the design ones but the decoupling was always guaranteed also thanks to the high stiffness of the superstructure. In the second one, seismically isolated with CSSs, the onset of motion was governed by the friction, which was much higher than the design one. Finally, in a building seismically isolated with HDRBs and SDs, the onset of motion was governed by the SDs and the successive motion by the HDRBs.

Effective protection against earthquakes has always challenged humanity. Aseismic isolation (AI) has provided an excellent solution and isolation systems (ISs) have improved seismic safety of the built environment. However, this improving impact of AI on seismic resilience is not appropriate to its capabilities and further attempts are required. Advanced materials provide great opportunities to make AI more effective in sustainable seismic resilience. Shape memory alloys (SMAs) are known as the most favorable advanced materials for this purpose. SMA-based superelasticity-assisted slider (SSS) brings the advantages of SMAs in the practice of AI by innovatively combining them with the technically preferred sliding ISs. SSS is pioneered to seismically protect a broad variety of structures using a single platform. This IS can be implemented both traditionally by its construction-industry-friendly structure and in the industrialized style by means of isolation units. It is also facilitated by SSS to utilize other advanced materials such as nanomaterials and metamaterials. All these are discussed in this paper. The versatility of SSS is demonstrated by explanatory technical drawings and roles of alternative configurations that result in various hysteretic behaviors are investigated. Possible design strategies are studied for a typical office building and a sensitive medical equipment. Applications of other advanced materials are suggested and seismic performances of SSS are compared with those of currently used ISs in earthquake protection of a typical reinforced concrete building. It is shown that high seismic performances can be obtained by the practical applications of the advanced materials in the AI technology to obtain sustainability in seismic resilience.

The Terminal Core Redevelopment project is an approximately 1.6 billion USD project to functionally expand and seismically upgrade the existing main terminal at the Portland International Airport in Portland, Oregon, USA. At the center of the project is the seismic isolation of a new approximately 350,000 square foot (32,500 m2) mass timber roof. A total of 68 double-concave friction pendulum isolators with displacement capacities ranging between 16 and 22.5 in. (406–572 mm) sit on top of each tine of 34, approximately 53-foot (16.2-m) tall concrete-filled steel Y-Columns on which the mass timber roof is supported. Performance-based seismic design for both a Risk-Targeted Maximum Considered Earthquake (approximately equal to the 2500 year return period event) and a deterministic event on the Cascadia Subduction Zone was pursued. Extensive nonlinear response history analyses considered multiple cases of foundation stiffness and seismic isolator coefficients of friction as well as explicit, time-step-by-time-step assessment of isolator-induced P-Delta and V-h moments. Full-scale, dynamic testing of prototype seismic isolators was performed at EUCENTRE. Quasi-static testing of 100% of production isolators was conducted at either EUCENTRE or SISMALAB prior to shipping to the project site.

In the present paper, additions in structural steelwork are utilized for giving new life to old buildings in regions characterized by medium/high seismic hazard. Two models are here proposed, i.e.: vertical addition for masonry buildings and lateral addition for r.c. buildings. For the model of vertical addition, the connection between the masonry and steel structures is realized by means of an Intermediate Isolation System (IIS). For the model of lateral addition, an exoskeleton (EXO) is connected to the existing building by means of rigid or flexible and dissipative link. Two buildings, representative of the heterogeneous Italian building stock, are selected as case studies. Parametric analyses are firstly performed on lumped mass models to explore the feasibility and effectiveness of the IIS and EXO systems in reducing the seismic response of the case studies; then, once selected the design configurations of the new additions, more refined 3D FE models are adopted for the detailed analysis of the two solutions.

Amid increasing concerns about the occurrence of mega earthquakes, recent studies have shown that the deformation of conventional seismic isolators may exceed their expected design range. To address this issue, we have been developing a displacement-control system for seismic isolation equipped with high-static-low-dynamic stiffness and rotational inertia. In this paper, we report the results of large shaking-table experiments involving a comparison of the response of a seismic-isolation model of our displacement control system we developed to that of a time-response analysis model we constructed on the basis of our model.

In order to enhance the serviceability of civil structures during seismic action base isolators and dampers need to perform at high efficiency independent of the ground shaking level. However, base isolators and dampers are commonly designed to the shaking level of the Design Basis Earthquake (DBE) whereby their efficiencies are poor for earthquakes with lower peak ground accelerations (PGAs). This shortcoming can only be improved if the friction of curved surface sliders is not constant and if hysteretic dampers can produce hysteretic behaviour at various yielding levels. This article presents two new types of curved surface sliders and hysteretic dampers which operate at high efficiency over a wide range of PGAs. This makes it possible to enhance structural serviceability for weak and frequent earthquakes and ensure structural safety for strong motion earthquakes. The dynamic behaviours of the new adaptive curved surface slider and hysteretic damper types are presented. The isolation performance computed by non-linear time history analysis confirms their improved functioning.

Recent years have seen an increasing demand in the use of glass partition walls in office buildings, with major concerns regarding their behaviour and safety in case of strong seismic events. This study illustrates the development of an innovative solution for aluminium-glass partition walls that can resist, without any damage, horizontal accelerations as those measured during strong earthquakes. The proposed solution is based on a highly dissipative interface rubber between the aluminium frame and the glass plate, the latter constituting the largest portion of the mass of the partition wall. During a seismic event the glass plate moves relatively to the aluminium frames, thus, activating a dissipative mechanism that is basically a scaled-down version of what is seen in rubber bearings used in seismic isolation. In this article the initial structural concept is presented, preliminary numerical analyses illustrated, the preparation of preliminary small-scale prototypes followed by full-scale prototypes, and the execution of shake-table tests to simulate extreme seismic events are discussed. It is shown that very encouraging structural performances can be achieved in a product that is economically comparable to currently non-earthquake proof solutions, without problems or limitations in its every-day use.

This study illustrates the development of innovative solutions for school furniture designed to protect children and teachers in school buildings that cannot guarantee sufficient level of safety in case of seismic events. Attention is given to school desks and shelving units, the former having as objective the protection against falling debris from the ceilings, the latter the protection against damages and overturning of partition walls. In the past, school desks were the focus of seismic designs resulting in expensive and heavy solutions that, for these reasons, have not found practical application. Shelving units, on the other hand, did not receive special attention in their seismic design, other than a stronger connection to the walls. However, partition walls play a very important role during a seismic event due to the different interaction with the structure that can lead to anticipated damages and danger for people, even for moderate seismic events. In this article briefly presents the initial structural concept, preliminary numerical analyses, the preparation of full-scale prototypes, and the execution of experimental tests to simulate extreme loading conditions following structural collapse. It is concluded that very encouraging structural performances against extreme loading conditions and impacts can be achieved using products that are economically affordable with no constraints in their every-day use.

Ventilated façades are complex non-structural elements composing the building system, the latter being intended as a unique system integrating both structural skeleton/components and non-structural items, owing for instance to issues of seismic performance and loss. In light of this, experimental response characterisation is of paramount importance, leading indeed to data gathering for key components or sub-systems, which in turn could inform numerical modelling efforts, with a view to design methodology definition. Thus, this paper presents testing efforts meant to characterise the cyclic behaviour of brackets – connecting the panel elements in the façade system of interest – for both in-plane and out-of-plane earthquake-induced actions, assuming prescriptions by FEMA461 for the displacement-controlled loading protocol that relies upon monotonic test counterparts for reliable definition of ultimate target displacement. Test outcomes are presented with emphasis placed on stiffness and dissipation capacity for the case-study bracket typology.

Passive response control systems have been adopted as a common practice to mitigate the seismic response of structures. Meantime, suspended ceiling systems (SCS) have frequently suffered severe damage among nonstructural elements during earthquakes in the last decade. This paper presents the shake table test results on a new passive control system developed for indirect-SCSs employing a damped cable system equipped with pulley tackle amplification mechanisms, named “Pulley Damper Ceiling System (PDCS)”. In this study, the seismic performance of the SCSs with and without the presence of the proposed system is investigated based on a series of full-scale shake table tests. In particular, one-direction shake table tests on a total of six SCSs, a non-damped SCS, a steel-braced-SCS, and four SCSs with different PDCS configurations, are primarily tested to evaluate the fundamental response reduction effect of the PDCS. Additionally, two-directions shake table tests on the SCSs with PDCS are carried out to confirm the seismic response reduction efficiency and dynamic behavior of the PDCS under bidirectional earthquake motions. The experimental observations showed that the PDCS successfully amplified the damper displacements and velocities. Besides, the PDCS sufficiently mitigates both displacement and acceleration response by comparing to the conventional and braced SCSs.

A preliminary characterization of the input vibrations and of the dynamic behavior of the Sarcophagus of the Spouses at the National Etruscan Museum in Rome by advanced digital videos analyses is illustrated. This activity focuses on the development of a protection system for museum assets in order to reduce potential damage due to traffic and earthquakes. The vibrations induced by roads, tramways and an underground train line were measured by seismometers and analyzed to characterize the base excitation to the Sarcophagus. Given the high vulnerability of the Sarcophagus, no instrumentation could be placed on it, so that conventional contact sensors could not be used. Consequently, non-contact video-based techniques were considered and, in particular, high-speed and high-resolution video camera footage was recorded. The video was analyzed by advanced algorithms derived from the motion magnification method, which is a video signal elaboration method able to enormously amplify the tiniest movements of the acquired objects. A preliminary estimation of the main dynamic characteristics of the Sarcophagus was performed. The associated frequencies will be used to calibrate the numerical models and to optimize the design of the base-isolation system. The used digital video analysis technique is also discussed in terms of its many advantages and its application criticalities.

Monuments and historic structures have been extensively damaged by major seismic events that occurred in the Mediterranean area in the last decades. A large research activity has been devoted to the mitigation of seismic effects in historic buildings, but also the museums contents deserves the attention of scholars due to their inestimable values and cultural significance. In particular, statue-like objects revealed a poor dynamic behaviour during past earthquakes and are prone to overturn if seismic excitations overcame an acceleration threshold. In scientific literature a lot of analytical research are present in non-linear dynamic field but experimental works in this area still remain limited. In this research work, the results of an extensive test campaign, aiming at characterizing the dynamical behaviour and assessing the seismic protection level of an innovative bidirectional base-isolation device is presented and commented. The isolator consists in a series of multiple articulated quadrilateral mechanism elements, patented as KSJ (Kinematic Steel Joint), that allows the free movements of a rigid base in both horizontal directions, providing pendulum-like behaviour and re-centring capabilities. Shake-table tests on a full-scale replica of the statue of the Goddess of Morgantina have been carried out at the L.E.D.A. Research Institute at the Kore University of Enna, with varying load conditions, acceleration time-histories and intensities.

The rocking response of rigid blocks, such as statues, storage systems, and slender structures in general, was documented both in the field and in the laboratory. These objects/structures must be protected from earthquakes, as their value may be inestimable in some cases. The use of base isolation devices for this structural typology was already studied and successfully applied to real cases. Previous research has focused on the isolation of a single rigid block system, although there are circumstances in which the use of a single block is insufficient to define the response. Configurations in which one block is stacked on top of another, such as ancient Greek and Roman structures composed of large heavy members or statues placed on a pedestal, are examples. In this paper the rocking response of two stacked rigid blocks placed on a seismic isolation device is investigated. The dynamics of this multi-degree of freedom system is briefly summarized, together with the conditions associated to an impact or a change in the rocking configuration. Many parameters govern the response of the system and to understand their influence on the dynamic behavior, analysis of the response to a pulse-type ground motion is carried out. In general, the seismic isolation device is shown to be effective for a wide range of scenarios. However, the study also highlights how, for large period pulses or short period devices, the response of the isolated system can be amplified compared to the scenario where the blocks are placed on a rigid foundation. This phenomenon is due to the amplification of the acceleration of the isolation device for specific ratios between the period of the pulse and that of the isolator; the need of a careful design of the device is evident.

Non-structural elements such as electrical cabinets play a key role in determining the seismic performance of buildings. Seismic qualification shake table testing of non-structural elements is a relatively simple way to evaluate their expected seismic performance. This paper presents a shake table testing campaign performed on several electrical cabinet specimens using the 6DLAB laboratories at the EUCENTRE Foundation located in Pavia, Italy. These shake table tests were performed as part of the research project Creazione di un Ambiente Domestico Sicuro (CADS). The physical properties of all the tested electrical cabinet archetypes varied considerably including: base-mounted electrical cabinets, wall-mounted electrical cabinets, electrical cabinets with different attachment strengths, and electrical cabinets with different framing structure strengths. The shake table tests were carried out using two seismic testing protocols, one of which is commonly used for the seismic qualification of non-structural elements, whereas the second one was proposed within the scope of the CADS Project. The performance of selected electrical cabinet archetypes during the shake table tests are presented and discussed in this paper.

Piping networks are complex systems in a building and their seismic response assessment may be challenging. Different types of seismic analyses have been increasingly conducted on such non-structural components, due to their importance from a building serviceability standpoint, as well as the effect of their failure on economic losses. On the other hand, further studies are still required, due to the peculiar geometry of each network. This study aims to analyse the effect of the vertical and horizontal component of the seismic acceleration on the performance of piping networks with irregular geometry. Non-linear dynamic analyses are performed and the response of different types of piping networks is analysed in terms of maximum accelerations and maximum displacements. The dynamic behaviour of the systems is defined accounting for the non-linear response of pipe joints and suspended piping restraint installations. The analysis results are used to provide design optimization and analysis criteria for piping systems.

In the last decade, increasing attention has been paid to the seismic vulnerability of steel pallet racks, mainly due to the catastrophic effects recorded in recent earthquakes and the increased use of these systems in the production and e-commerce sectors. For example, in May 2012 the Italian region of Emilia-Romagna was hit by a seismic swarm that affected many industrial buildings, causing significant damage to the structures as well as to the storage systems inside. In this paper, a parametric analysis to assess the vulnerability of these systems is presented. First, a small stock of 6-levels 7-spans pallet racks is generated by varying the upright section’s properties and considering the unbraced and braced configurations. Then, the seismic vulnerability of this stock of structure is evaluated through nonlinear time history analyses and a Cloud-like approach. For this purpose, a specific code was developed in the OpenSees framework. The rack modelling includes the main geometric and material non-linearities, both for elements and connections, as well as the pallet-to-beam friction. Fragility curves are derived as a function of the spectral acceleration (Sa) for two engineering demand parameters, significant in representing the damage condition of these structures. Finally, fragility results are presented, discussed, and compared, in order to provide useful information on the vulnerability of these structural systems.

Non-structural components play a significant role in the definition of economic losses produced by seismic events. Gypsum partition walls represent a significant portion of the non-structural components and can manifest considerable damage even at low-intensity seismic events. Nonetheless, the non-structural partition walls are generally not taken into account in the context of traditional analysis and design. This is also a consequence of the lack of knowledge related to a clear definition of performance limit states, owing also to the wide range of partitions’ typologies available on the market. To deal with this issue, a database collecting the results of quasi-static experimental tests was developed. The database was used to collect data useful to identify performance parameters and drift levels at which the different limit states are attained. The hysteretic curves collected in the database were used to develop a single-degree-of-freedom model for each partition typology. This paper briefly presents a general framework to calculate fragility functions for internal partitions using the data available in the experimental database. A database of floor displacement time histories evaluated by analyzing a building portfolio composed of reinforced concrete moment resisting frames was used to perform the multi-stripe analyses required to generate the fragility functions. The proposed framework is illustrated by calculating the fragility functions for one of the gypsum partition typologies collected in the experimental database.

The vulnerability assessment of glazing systems and partitions under dynamic loads is still an open topic, requiring huge efforts. Especially in terms of dynamic-related effects, the use of Finite Element (FE) software packages can represent an efficient tool for design but special care should be spent for the definition of key input parameters, such as for example the restraints features. Moreover, boundary conditions could also modify, during the lifetime of a given glazed partition, due to external factors or materials degradation, hence resulting in possible unsafe structural performances or premature damage. In this paper, the dynamic characterization of two types of glazed partition is presented based on Operational Modal Analysis (OMA) techniques and Finite Element (FE) numerical simulations. The dynamic in situ tests have been carried out in the framework of the PON research project CADS- “Creating a Safe Home Environment”. It is shown, in particular, how the actual restraint condition with respect to ideal boundaries can affect the vibration parameters (frequency, modal shape) of a given glazed partition.

Recent earthquakes worldwide have proven that losses result not only from damage to building structures but also from nonstructural components. Therefore, a correct design of these components can ensure not only the functionality and the life safety but also reduce the economical losses. Among nonstructural components fire-protection piping systems play an important role for critical facilities such as hospitals that are required to guarantee the immediate operation after a seismic event. In order to conduct a more accurate seismic analysis or damage assessment of the piping systems, it is necessary to establish reliable numerical models. In this work, the results of an experimental ambient vibration test are reported to determine the dynamic properties of a piping system, such as the natural frequencies and mode shapes, to establish the constraints that are uncertain in case of existing constructions, and upload a numerical model implemented by MIDAS FEA NX software. Most of the numerical natural frequencies achieve a good correlation with the measured frequencies, allowing a calibration of the effective constraints. Finally the preliminary results related to the efficiency of the test layout for damage detection are reported and discussed.

Non-structural elements (NSEs) represent most of the total construction cost of typical buildings. A significant portion of the total losses in recent earthquakes worldwide has been attributed to damage to NSEs, demonstrating the need for the harmonization of the seismic performance of the NSEs and of the seismic force-resisting systems. Unfortunately, lack of research results on the seismic performance of NSEs available in the public domain has, and continues to hamper, the development of efficient performance-based seismic design methods for buildings. Even though recent research continues to develop new and improved seismic design methodologies for NSEs, significant efforts are still required, particularly for existing building for which seismic mitigation detailing for NSEs are generally not adopted. To deal with this issue, and to reduce non-structural related seismic losses in existing buildings, simplified tools, which allow to quantify the seismic risk at which NSEs are prone, should be developed. This paper presents a rapid visual screening procedure useful to perform a large-scale classification of the seismic vulnerability of NSEs installed in critical facilities. The methodology is based on questionnaire forms that are used to calculate a nonstructural index and to identify the most vulnerable NSE category. The methodology has been applied to some case study buildings focusing the attention on critical facilities.

Nonstructural elements are typically associated with high seismic risk, regarding functioning interruption, economic losses, and casualties. Architectural elements such as infills and internal partitions are often associated with major construction costs, and, even in case of relatively frequent earthquakes, the post-event repair costs might be critical, due to poor seismic performance. Moreover, damage of architectural elements typically affects functioning and operativity of the facilities. The present study focuses on seismic response of internal partitions, with particular regard to economic losses. Seismic losses associated with both traditional and innovative internal partitions are assessed and compared, considering code-conforming reinforced concrete frame buildings as a case study. Both traditional and innovative partition systems are investigated, considering hollow brick and plasterboard solutions. Seismic demand is assessed through multiple stripe analyses, considering advanced nonlinear modeling and including low-to-high seismicity sites in Italy. Seismic capacity of investigated partition systems is derived from literature experimental data, considering multiple damage states (and performance levels) as a reference. The study quantifies seismic losses associated with the investigated partition systems, shedding lights on their strengths and weaknesses in terms of seismic performance and economic efficiency. Technical insights regarding the efficient use of the investigated partitions are also supplied in the light of the loss comparison analysis.

Infills are one of the most common non-structural elements worldwide adopted to build external and internal partition walls in framed structures. Many types of infills can be encountered in practical applications, characterized by different construction typologies and materials, but the most adopted ones are those realized with masonry. It is well known that infill masonry walls suffered lot of damage in the past as a consequence of earthquake excitations and, moreover, they were cause of undesirable effects on the structural seismic performance, such as the activation of soft story mechanisms and shear failure of short columns. For these reasons, the infill contribution on the seismic behaviour of buildings should be investigated both during the design process of new structures and the assessment of the existing ones. The aim of this paper is to investigate the usefulness of vibration data for the damage detection in infilled frame structures starting from the tracking of both the stiffness and modal properties. To this aim, an experimental campaign was performed on a laboratory steel-concrete composite frame with infill masonry walls. The tested mock-up was subjected to stepped-increasing cyclic displacements that produced a progressive in-plane damage of infills, up to their complete damage. In the meantime, vibration-based tests characterized by different level of input excitation provided to the structure, were performed to capture the effects of the infill damage on the mock-up global dynamic response. Results provide useful information for the detection and tracking of damage to non-structural elements during and after low and moderate seismic events, contributing to a better interpretation of data provided by structural health monitoring systems. Finally, a monitoring strategy suitable for new infilled buildings is proposed, with the main aim of providing a contribution in the context of differentiating between structural and non-structural damage, especially in case of blind monitoring.

The seismic risk associated with the freestanding elements can be high, especially if they are housed within critical buildings (e.g., hospitals and nuclear plants) or have historical/cultural significance (e.g., museum objects or artifacts). In many cases, these systems exhibit a seismic response governed by rigid motion that is typically critical. In this study, an experimental testing campaign is carried out to assess the dynamic properties and seismic performance of museum objects and artifacts. Shake table tests of a typical museum display case containing a representative art object are performed. The specimen was provided by the National Archaeological Museum of Naples (MANN), Italy. Seismic assessment of the test specimen was performed through two types of testing: dynamic identification and seismic performance assessment. The dynamic identification of the display case was carried out, and both natural frequencies and damping ratios of the specimens were evaluated by reliable and consistent methods. The seismic performance tests were conducted by the international seismic certification protocol for nonstructural elements ICC-ES AC156. Both accelerations and displacements of the display case were assessed, as well as the response of the art object was characterized. The study sheds light on the critical behavior of the tested specimen, stressing the need for further studies toward a more comprehensive assessment of freestanding museum objects and artifacts.

The Great East Japan Earthquake of 2011 reaffirmed ceilings, which had been regarded as the finishing touch to architectural spaces, as an entity that can cause serious damage to occupants when they fall. The control of damage from falling ceilings was treated as an urgent issue, and in 2013, the “Notice on Specified Ceilings and Specified Ceilings with Structurally Safe Structural Methods (hereinafter referred to as “Ceiling Notice”)” was enacted. This defined ceilings that meet certain conditions as “specified ceilings,” and required that they be earthquake-resistant and that fall prevention measures be installed in existing buildings as well. Since then, there has been much research on fall prevention measures for ceilings, but there is still an urgent need to develop better materials and construction methods. Against this background, an experimental study was conducted to propose a method of repairing ceiling surfaces that have deteriorated over time and whose safety has not been confirmed. Tensile tests showed that polyurea resin and aramid fiber are effective for repairing suspension bolts inserted in concrete frames. In addition, the ceiling surface (plasterboard) was dropped to confirm its impact resistance against falling impact, and its effectiveness as a ceiling fall prevention measure was confirmed.

This paper discusses the experimental results from dynamic shake-table tests conducted at the University of Pavia and at the EUCENTRE Foundation (Pavia, Italy) on an industrial steel rack seismically isolated with innovative devices. Despite the undeniable effectiveness of common isolators in reducing seismic demands on superstructures, their application to non-structural systems can be hindered by cost, durability, and mechanical issues. To overcome these drawbacks, an innovative isolator has been patented by Kyneprox S.r.l., based on a multiple articulated quadrilateral mechanism and named “Kinematic Steel Joint (KSJ)”. This device can be manufactured from steel sheets, possibly stainless or galvanized to mitigate corrosion issues. The KSJ imposes to the superstructure a pendulum-type motion with self-centering behavior, and its modular nature allows tailoring it to different masses. Friction within pinned joints grants some energy dissipation to the device, and replaceable fuses can be added to act as brakes before reaching the maximum displacement range. KSJ devices were installed at the base of a five-shelf, two-bay industrial steel rack, isolated in the cross-aisle direction and braced in the down-aisle one. Incremental uniaxial shake-table tests were conducted in the isolated direction under three different loading scenarios. The beneficial effects of the isolators on the dynamic response of the rack are demonstrated by the elastic response spectra of the input signal imposed to its base.

Cross-Laminated Timber (CLT) panels allow nowadays to design and realize high-rise timber-based buildings with different construction systems and have shown potential to be used as a sustainable strengthening system for reinforced concrete (RC), steel and masonry structures. Among the various applications of CLT panels in hybrid structures is the very recent interest of the scientific community in using them as infill panels. This paper presents a numerical study aimed at investigating the lateral response of RC frames with traditional masonry and innovative CLT infills. The role of CLT infills and their capability to improve the structural performance of RC structures is investigated. Pushover analyses of RC frames with different number of stories and bays are presented in the study. Results of the analyses show that introducing CLT panel infills in RC frames leads to higher structural performance compared to traditional masonry infills. Given their high in-plane mechanical properties, CLT panel infills allow to reach lower inter-story drifts, resulting in lower structural and non-structural damages and economic losses.

The assessment of the seismic performance of nonstructural elements (NEs) is typically required by the current international codes, regulations, and guidelines. Required response spectra (RRS) and acceleration testing inputs are the key parameters for defining shake table testing protocols suitable for both assessment and qualification of acceleration-sensitive NEs. However, international codes and guidelines define RRS and acceleration time histories that are not necessarily consistent with seismic demands associated with Italian and European territories. In this study, novel RRS and acceleration time histories are developed for a consistent shake table assessment of acceleration-sensitive NEs according to the Italian building code. A critical review of existing protocols was carried out to define new approaches for developing code-consistent assessment and qualification protocols. The approach used to develop RRS and testing inputs is widely applicable and easily extendable to different case studies as the process is highly flexible and adaptable. The application of the developed methodology lays the foundations for the development of code-consistent shake table protocols for both assessment and qualification purposes.

The behaviour of Buckling-Restrained Braces (BRBs) is characterised by steady and nearly symmetrical hysteretic loops that provide large energy dissipation capacity. However, their low post-yielding stiffness may result in large residual deformations at the end of the earthquake motion. Moreover, the cumulative ductility demand due to repeated plastic excursions can lead to low-cycle fatigue failure. These two unfavourable conditions could be exacerbated by the occurrence of subsequent earthquakes (e.g., mainshock-aftershock sequences or multiple earthquakes during the design lifetime). Therefore, their assessment requires a framework that considers ground motion (GM) sequences. In this paper, a case study structure subjected to GM sequences is analysed, considering three Engineering Demand Parameters (EDPs) relevant to the performance evaluation of the BRBs and of the frame, namely the maximum ductility demand in the BRBs, the cumulative ductility demand in the BRBs, and the residual inter-storey-drift in the frame. These EDPs are assessed both independently and simultaneously, in order to establish the risk of overpassing any capacity limit that may lead to the collapse or demolition of the structure.

This contribution examines the application of modern systems for increasing damping in regard to protect structures against wind and seismic induced vibrations. The Tuned Mass Control System, presented as the first of two systems, consist of an additional mass, elastically connected to the main structure—in general quite similar to the well-known tuned mass systems that are applied at high rise structures against wind-induced effects. Dampers are installed in parallel to the elastic devices to widen the operating frequency band of the system and to reduce the relative displacements between mass and main structure. This passive seismic protection system yields a significant reduction of induced acceleration, displacement levels as well as internal stresses, support reactions and interstory drift. An important advantage is the possibility to use the inside of the building as there is no disturbance by the upgrade activities, if these systems are used as retrofitting systems. Corresponding project examples are presented and results of numerical investigations are described to verify the effectiveness of the mitigation measures. Just as these systems are suitable for new buildings and for existing structures, viscous wall dampers are also appropriate for both cases. They are using the shear resistance force of a highly viscous fluid. The devices consist of an outer steel dashpot, filled with liquid and an internal shearing piston. The extension of a two-story building by seven new floors is presented as corresponding example, where the increase of structural damping was required to protect the existing structure against seismic demands.

Throughout the last decades, the idea of substituting conventional steel shear wall structural systems with perforated shear wall panels has been explored. Extending this concept, cellular shear wall systems have been proposed. Such systems demonstrate an enhanced dynamic behavior due to their lightweight properties and their ability to avoid out-of-plane buckling. The existing gaps within the body of the cellular shear wall system, allow for viscoelastic infills to be introduced, providing both stiffness and damping into the structural element. The purpose of this paper is to describe the performance of such cellular shear wall systems with viscoelastic fillers under dynamic loading. Considering the steel matrix of the shear wall system, two types of cell architectures are discussed: (a) 8hexagonal honeycomb cells and (b) chiral cells. A harmonic excitation is imposed on full-scaled shear wall panels of any of the previous cell types, with and without viscoelastic infills. The effectiveness of the proposed shear wall system is verified. Comparative results in terms of stress-strain curves provide better understanding of the proposed concept’s behavior.

In this paper, derived from a M.Sc. thesis jointly developed at Politecnico di Milano and TU Wien, an innovative design strategy for the well known Tuned Mass Damper (TMD) passive structural control device is presented. Linear TMDs need to stay properly tuned to the principal structure in order to be effective. The newly proposed “NextGenTMD” incarnation aims at overcoming the detuning by implementing a hysteretic version of the TMD, able to remain tuned despite the hysteretic response of the primary structure itself. The usage of Genetic Algorithms introduced in the design process of the NextGenTMD is at the basis of the proposed approach. Within this context, the design phase of the TMD is presented as a multi-objective minimization problem. The proposed design methodology is applied on a reduced numerical model of a four story building, of which full scale seismic pseudo-dynamic test results were available. The calibration of this reduced hysteretic model is carried out as well as a minimization problem exploiting Genetic Algorithms. The capabilities of the NextGenTMD, designed according to the proposed procedure, is assessed with respect to a set of spectrum compatible time histories, according to the Eurocode 8. The very promising results obtained, from numerical simulations, show that the NextGenTMD can be effective in a seismic setting while the simplicity of the installation is promising for its large scale diffusion and, consequently, for a more effective reduction of the seismic vulnerability of the built environment.

There is an increased desire for higher levels of building performance during and after seismic events for life science and biotechnology facilities due to the potential for loss of valuable research data, product inventory, or manufacturing capability of critical and high-value products. Methods for increasing building performance include the incorporation of passive energy dissipation systems in the form of viscous damping devices or a seismic base isolation system. Several challenges exist with the structural design of laboratory facilities, including a desire to maintain long spans free of columns for better space planning and tall stories to accommodate demanding ventilation and air filtration requirements associated with clean room spaces. The authors describe these challenges and a set of novel design and detailing solutions implemented to facilitate efficient incorporation of a damped moment frame lateral system for a production laboratory facility in the San Francisco Bay Area in Northern California. The improved structural performance supported the client’s campus-wide goals to minimize downtime after a severe seismic event.

There is an increased desire for higher levels of building performance during and after seismic events in the mission critical and data center industries due to the costs associated with non-structural damage and uptime losses. Conventional industry-accepted approaches such as voluntary use of a larger importance factor may increase the robustness of the structure itself, but does not result in reduced floor accelerations or reductions of negative impacts on both computer servers and the extensive mechanical and electrical distribution systems associated with data centers. Seismic isolation remains the premier solution for increasing both structural and non-structural performance during a seismic event. The authors describe the project challenges in the design of two base isolated facilities located in California. The first project is located in Northern California and was for a client operating their data center in a “Colocation” format. This project was located on a site with tight space constraints, necessitating the use of fluid viscous dampers as part of the isolation system to limit building displacements to an acceptable level. The second project is located in Southern California and was for a single “Enterprise” client. The larger site for this project allowed the team to design for a larger displacement to maximize the effectiveness of the isolation system and minimize the demands imparted on to the building.

Damper failures are generally brittle mechanisms, which can compromise the capacity of the structure to withstand the seismic action, leading to a lack of robustness of the overall system. The brittle failure is due to the attainment of the maximum force capacity, because of end-stroke impacts, which causes an arising of the forces, or to an excessive velocity of the piston (over-velocity). Moreover, anti-seismic devices need to be designed with proper safety margins against their failure in order to reach a target safety level. Seismic standards generally prescribe safety factors (reliability factors), that in the case of Fluid Viscous Dampers (FVDs) are applied to stroke and velocity, with values that are not homogenous among seismic codes. The effect of damper failure and different reliability factors on both the fragility and the seismic risk of the structural system is investigated by performing multiple-stripe analysis and monitoring different global and local demand parameters of a medium-rise steel moment-resisting frame building, widely studied in literature, thanks to an advanced model implemented in OpenSees, which considers the brittle mechanism. Moreover, the problem of damper failure is also analysed in terms of fragility functions, providing information about the dependency of the probability of failure with the seismic intensity.

Seismic isolation is a passive control methodology widely used for the mitigation of the dynamic response of structures. However, significant seismic actions can induce considerable displacements in these structures, which in turn can cause damage to the isolation system or impacts against adjacent structures in the event of insufficient seismic gap. A technique to prevent the occurrence of these negative phenomena can be obtained by interposing dissipative and deformable devices, called bumpers between the structure and the adjacent ones. Therefore, in this work the response, from a numerical point of view, of single-degree-of-freedom, SDOF, system isolated at the base subjected to known seismic actions and whose displacements are limited by bumpers has been studied. The system was designed according to an optimality relationship that relates the mechanical parameters of the isolator with those of the bumper, and is independent of the gap.The SDOF system investigated is representative of a typical base-isolated structure, therefore, the system exhibits a damping ratio ξ = 10% and a system natural period Tn = 3.00 s. The dynamic response of the system obtained by impact with an appropriately designed bumper is compared with the response of the same system obtained without the impact and with an impact whit rigid bumper. Finally, the influence of the stiffness of the bumper, designed with the optimality relationship, and the gap is evaluated. The results show a considerable reduction in displacements compared to a modest increase in accelerations with respect to the no-impact condition, evidence that highlights the effectiveness of the optimality relationship used.

Seismic isolation is today largely used as a passive mitigation system for seismic actions. While this technique can be easily implemented in new structures, more difficult, whenever possible, is the implementation in existing buildings, which can become a real challenge especially in countries where maintenance of old structures, sometimes of historical importance, is an important issue, like Italy. The use of seismic isolation in existing buildings presents interesting features. Using a base isolation system, the period of vibration can be chosen in order to allow input of low spectral amplitude, so that the superstructure can substantially remain in the elastic range. This possibility allows for limiting or even avoiding the conventional retrofit intervention in the superstructure. In fact, the intervention can be concentrated at the lowest level, while no intervention is necessary in the superstructure, so it is not necessary to demolish non-structural elements. As a result, an “operational seismic retrofit” would be possible, that is the superstructure could remain operative during the retrofit works. In order to do that, at least a safety degree not lower than the existing one should be guaranteed. This can be obtained by using temporary fixing systems for the isolation devices or temporary structures for the columns. After a brief overview of the available research in this field, the paper proposes and discusses different solutions for “operational seismic retrofit”, pointing out also the convenience in terms of costs. Furthermore, a case study is presented, in which some solutions are implemented.

In recent years, the use of static non-linear analysis, the so-called pushover analysis, is increasingly common when dealing with seismic vulnerability assessment and mitigation of existing buildings.The pushover analysis has the final goal to determine the relation between the base shear and the displacement of a control node to determine the capacity curve of the structure, together with the evaluation of the maximum displacement reached after a seismic event. Finally, by post-processing such information, it is possible to perform comparisons in terms of displacements or acceleration to evaluate vulnerability index of the structure.Many Finite Element software include this type of analysis among their various features. Therefore, computational algorithms are becoming useful tools to deal with seismic vulnerability issues, thanks to their robustness.Non-linear static analyses are usually performed on masonry and reinforced concrete structures, by assigning plastic material properties to the main elements of the structure.In this paper, an advanced constitutive law is presented, the Concrete Damage Plasticity model, highlighting the main features and the parameters involved in its implementation.Finally, the application of this constitutive model is presented on a real existing concrete-masonry structure, by means of the software Midas Gen.

The severe seismic events affecting urban areas may have disastrous consequences if buildings are designed without appropriate seismic standards. On 24 August 2016, an earthquake of a magnitude Mw 6.0 caused severe damages, casualties, and collapses in four regions of Central Italy. Due to the high level of observed ground motion and not regular damage distribution, in-depth studies have been conducted on the Amatrice earthquake. In this context, the paper investigates the seismic demand affecting the buildings of the Amatrice during the earthquake focusing on evaluating if the registered seismic actions exceed design spectra. Processing both accelerations acquired by the National Accelerometric Network (RAN) stations and Osservatorio Sismico delle Strutture (OSS) operated by the Italian Dipartimento della Protezione Civile (DPC) and considering available results on site amplification, conclusions on the return period of the seismic event are derived. Moreover, an interpolation method has been introduced to define an Amplification function (Af) to use the information contained in microzoning maps evidencing the enormous amplified elastic demand induced by the peculiar site of Amatrice. Finally, the computed elastic response spectra were compared with the elastic demand spectra provided by the Italian Building Standard (DMIT 2018) in three different manners: (i) taking the response spectra of the registration components directly at AMT and AMTS, (ii) evaluating through realistic de-amplification effects these components at the bedrock, and (iii) considering a realistic average of the two registration AMT and AMTS corrected by possible underestimation errors occurred at AMTS.

Artworks represent a priceless asset to the economic and cultural features of communities. Most art collections are hosted in Museums, which can be new buildings, appositely made for expositive purposes, or monumental buildings, whose high artistic and historical value enhances the exposed art pieces. In this latter case, however, the Museums can disregard the seismic safety requirements provided for new constructions, becoming the main source of hazard for the precious contents they should preserve. In this paper, the dynamic behavior of the National Museum of Bargello in Florence is studied by means of a dynamic identification, focusing the attention on the “Sala Donatello”. An experimental campaign was performed by simultaneously installing two sets of three seismometric stations in the mentioned room and in the “Sala Michelangelo”, placed at the lower level. Analysis of the recorded data via Operational Modal Analysis techniques has furnished the structure’s natural frequencies, damping ratio and mode shapes allowing the assessment of the amplification of the seismic acceleration experienced by the art works exposed in “Sala Donatello”. The effect of the seismic acceleration on the artifacts has been checked on a case-study, i.e. the masterpiece “Marzocco”. It is the statue of the lion considered the symbol of Florence, realized by Donatello in 1420, placed on a marble pedestal made by Benedetto da Maiano in 1480, which is a work of art as well. The assessment has been made by performing a simplified rigid-block analysis. The geometrical data of Marzocco has been stated based on a detailed photogrammetric survey, which provided a reliable representation of the mass distribution.

The existing reinforced concrete frame structures built before the 1970s were designed only for gravity loads, and they were mainly built using smooth steel rebars. The behaviour of these kinds of structures is different with respect to that exhibited by structures reinforced with deformed rebars. Low bond capacity and the associated slip of the anchorages characterise a more flexible structural response and a lower energy dissipation of the elements. The contribution of rebar slip to structural deformability is often not considered in traditional lumped plasticity models used for the assessment of existing structures. An innovative modelling approach has been recently proposed to directly account for smooth rebar slip, so the characterization of the cyclic behaviour of different types of anchorages is of primary importance. A first experimental campaign was conducted on straight, hooked-end, and bent anchorages to evaluate their hysteretic behaviour and their strength capacity. Some aspects highlighted by the first campaign were investigated in the second one, the main results are here presented. The influence of the bond conditions and of the embedded length on the anchorage performance of plain rebars was investigated, and the mean bond strength was thus evaluated. Finally, the cyclic behaviour of bent anchorages for different bond conditions is analysed.

This paper focuses on the dynamic identification and the seismic vulnerability assessment of an existing masonry port structure located in Livorno (Italy), which is a former railway station bombed and reconstructed after WWII. To this end, a historical-critical analysis, and an investigation and testing campaign has been carried out, along with a number of Ambient Vibration Tests (AVT). According to the Operational Modal Analysis (OMA), a Frequency Domain Decomposition (FDD) algorithm has been leveraged for dynamic identification. The severe noise around the harbour area and the poor soil quality make it difficult to identify the modal parameters of the structure, even if specific signal processing techniques were applied to remove the interferences. Although a ground sensor is not needed for output-only identification, it has been useful to identify a local phenomenon that it would have been arduous to figure out without its support. The investigations and the test outputs have been the baseline to create a finite element model, although not reproducing the real structural behaviour of some simplifying assumptions. However, the dynamic Structural Health Monitoring (SHM) outcomes have not been leveraged to calibrate it. A Modal Response Spectrum Analysis (MRSA) and a non-linear static (Pushover) analysis (POA) have been carried out to determine the structure capacity, and thus the Seismic Vulnerability Index (SVI) of the simplified model.

A vital task of this millennium is to protect the existing heritage, also through the adoption of resilient management systems. In this framework, the organization of knowledge remains one of the critical points. For this reason, new methodologies and cross-disciplinary technologies are increasingly being chosen to optimize resources toward more sustainable interventions. Therefore, the ability to model the building geometry and behavior must be maximized through interoperable processes between Building Information Modeling and Finite Element Modeling methods aimed at the seismic vulnerability assessment. Setting up an integrated digitalization process is undoubtedly challenging initially but returns more significant benefits during the infrastructure life cycle. The interoperability tests’ bi-directionality is essential for constantly evaluating activities to update data following facilities’ modifications. The Modal Assurance Criterion indicator is used to assess the coherence of the models after possible simplifications introduced for non-linear state analyses.

Infrastructures are degrading rapidly, which necessitates the application of automated dynamic characterization in damage identification schemes. The Operational Modal Analysis (OMA) is an effective tool to process monitoring data of structural assets. In this study, the Frequency Domain Decomposition (FDD) technique is automated based on two different criteria, the Discrimination Factor (DF) and Modal Assurance Criterion (MAC). The recorded ambient vibration response of a cable-stayed bridge was used as input to the proposed method to extract its modal properties automatically. The method was also tested on a calibrated finite element model of the cable-stayed bridge for validation purposes. The optimal automation performance is achieved by establishing the best range of each criterion.