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This paper presents an insight on the seismic response and seismic risk of base-isolated structures performed within the RINTC project, considering different configurations of rubber-based isolatio...

Past earthquakes have repeatedly shown that damage to masonry infills can produce large economic losses and even jeopardize human lives. Nevertheless, in current design practice masonry infills are ignored, while available macro-models for nonlinear analysis focus the attention on the In-Plane (IP) behavior of masonry infills only, while neglecting the Out-Of-Plane (OOP) collapse mechanism. The main objective of this study is to investigate the seismic performance of RC frame buildings accounting for the interaction between IP and OOP behavior of masonry infills. To this end, a suitable nonlinear model, able to capture the IP stiffness and strength reduction due to the OOP displacement demand (and vice versa) is implemented. The selected model incorporates a routine that removes infills from the structural model when either IP or OOP collapse occurs. Different building models, representative of typical residential buildings, realized in Italy (and other European countries) from 50’s to 90’s, are examined through nonlinear response-time history analysis at different earthquake intensity levels, with return period ranging from 30 to 5000 years. Two alternative infill configurations (single layer and double layer with inner cavity) are considered, in accordance with the construction practice of the time. The comparison between the models with and without IP/OOP interaction points out the relevance of the OOP behavior towards an accurate evaluation of the seismic performance of RC frame buildings. A set of fragility curves is tentatively proposed, for different building performance levels, ranging from immediate occupancy to life safety.

A Displacement-Based framework for the Simplified Seismic Loss Assessment of pre-70 RC buildings is presented. The attention is focused on the calculation of the Expected Annual Loss using results ...

A new approach, referred to as the DEAL (Direct estimation of Expected Annual Losses) method, is developed to evaluate the Expected Annual Loss (EAL) of RC buildings using results of traditional st...

This paper builds on the results of in-situ release tests carried out on a 3-storey base-isolated reinforced concrete frame building located in the city of Augusta (Sicily). The isolation system consists of a combination of High Damping Rubber Bearings and Low Friction Flat Sliding Bearings. Suitable practice-oriented nonlinear models have been considered to describe the cyclic behavior of the isolation system and the infill panels. The results of ambient vibration and release tests have been used to calibrate the numerical models of superstructure and isolation system, respectively. Nonlinear response-history analyses of the calibrated model are then performed to compare the seismic response of the structure with the expected (design) seismic performance.

A device prototype, based on the superelastic properties of Shape Memory Alloys (SMAs), is proposed to enhance the thermal and seismic behavior of steel tie-rods. First, the thermal behavior of ste...

In seismic risk assessment, fragility (or vulnerability) curves are commonly used to express the likelihood that constructions (e.g. buildings) will sustain different degrees of loss over a range of earthquake ground motion intensities. In the paper, fragility curves for typical older residential RC buildings, realized in Italy and other southern Europe countries from the 50s to the early 70s, are derived following a hybrid approach. Fragility curves are expressed in terms of spectral acceleration. Median values for each damage state (or performance limit state) are estimated based on the results of comprehensive loss assessment analysis and the definition of a suitable loss index. Dispersions are evaluated based on the results of accurate inelastic dynamic analyses carried out for a number of archetype buildings at increasing levels of seismic intensity. A detailed discussion on the parameters that influence most the fragility curves, such as the number of storeys of the building, is provided.

UnReinforced Masonry (URM) infills can significantly affect the seismic response of frame buildings. Typical numerical models, however, do not account for the In-Plane/Out-Of-Plane (IP/OOP) interaction that characterizes the damage/collapse mechanism of masonry infills. The main objective of this study is to investigate the seismic performance of RC frame buildings accounting for the IP/OOP interaction of URM infill walls, using a refined nonlinear macro-model recently implemented in OpenSees. To this end, the seismic performance of a case-study building, representative of typical residential buildings realized in Italy before ‘70 s, is examined, at different earthquake intensity levels, with return period ranging from 30 to 2500 years. A set of fragility curves is then derived to express the probability of exceedance of given building performance levels as a function of the earthquake intensity level, considering (or neglecting) the IP/OOP interaction of masonry infill walls.

The seismic vulnerability assessment of masonry built heritage is an importance issue in Italy, due to the high seismic hazard of the territory and the huge amount of masonry buildings located in the exposed areas. The evaluation of the seismic performance of buildings can be useful to assess possible damages occurred after an earthquake, the direct costs which would result from it, the “pre” and “post” loss distribution in an urban area and the most vulnerable buildings. At urban scale, a building-specific assessment approach appears extremely difficult and time-consuming because of the large number of constructions. Therefore, being able to classify the built heritage in a limited number of territorial-specific structural typologies with similar characteristics would significantly simplify the vulnerability assessment.

The seismic vulnerability assessment of the built heritage located on a specific area represents an important starting point for both the evaluation of the consequences in the aftermath of significant seismic events and a proper management of the post-seismic reconstruction phase. In other words, the vulnerability assessment represents one of the main input elements for resilience analysis at urban scale. However, facing with a large-scale study, a building-specific assessment approach appears extremely difficult and time-consuming. In this optic, the definition of territorial-specific structural typologies and corresponding vulnerability classes represent a powerful tool for a rapid estimation of the “global vulnerability” of an examined area. As a matter of fact, the classification of the built heritage in a limited number of structural typologies (featuring similar characteristics) could sensibly reduce the complexity of the vulnerability assessment, hence resilience analysis, at urban scale.

This paper reports on results of nonlinear analyses performed within the RINTC project on an RC building isolated with different systems (High Damping Rubber Bearings, High Damping Rubber Bearings ...

Monetary losses induced by earthquakes in Reinforced Concrete (RC) buildings are mainly due to damage to non-structural elements (infills, partitions, finishes, etc.). In this study, alternative re...

This paper presents the results of an extensive parametric study aimed at investigating the influence of residual displacements on the design displacement of spherical friction-based isolation systems. Residual displacements may significantly jeopardize the displacement capacity of spherical friction-based isolation systems thus causing extensive damage or even triggering structural collapse. For that reason, they must be properly taken into account in the design. The study builds on the results of thousands of nonlinear response-time history analyses of SDOF systems, using almost one hundred ground motions pairs. Residual displacements arising from both individual earthquakes and sequences of seismic ground motions are considered. Based on regression analysis of results, a closed-form equation is derived to predict residual displacements of spherical friction-based isolation systems as a function of the main parameters governing their mechanical behavior. The proposed relationship is compared with state-of-the-art relationships and current seismic code provisions.

In the last decade, a number of methodologies for the seismic performance assessment of existing buildings have been proposed. They are based on comprehensive probabilistic procedures where uncertainties related to ground motions, construction and material quality are explicitly accounted for. Structural analysis is performed to evaluate the seismic demand to the structure through a number of Engineering Demand Parameters (EDPs) (i.e.: inter-story drift ratios, floor accelerations, etc.). In this respect, the use of Nonlinear Response History Analyses (NRHAs) appears to be computationally expensive, time demanding and potentially tricky for most practicing engineers. On the other hand, simplified approaches, based on linear static analysis, are affected by strong limitations of use and loss of accuracy towards seismic performance assessment. In this paper, an alternative approach, referred to as Multiple Inelastic Mechanisms Analysis (MIMA), based on the principles of the Displacement-based Assessment (DBA) method, is proposed in the attempt of reducing the complexity related to NRHAs, while maintaining a sufficient accurateness in the estimation of expected losses. MIMA is a practice-oriented approach that provides the seismic response of a structure at different intensity levels. The most important novelties of MIMA with respect to the current state-of-the-art are the possibility of accounting for the contribution of different inelastic mechanisms, the record-to-record variability, and the effects of infills and stairs. In the current version, the proposed approach is specialized for pre-70 RC frame buildings. However, it could be extended to other building types with minor efforts. In this paper, MIMA is applied on a six-stories building, representative of typical RC frame buildings realized in Italy (and other European countries) in the 60’s and 70’s. A good accordance between approximate predictions and accurate results (from NRHAs) is observed.

The superelastic properties of Shape Memory Alloys (SMAs) can be used to improve the thermal and seismic behavior of steel tie-rods, which are often used in historical constructions. In this paper, a device prototype based on SMAs is presented, whose performances have been assessed through extensive experimental tests in thermal chamber and shaking table tests on reduced-scale testing models. The functioning principles of the device and the main steps for its implementation are first illustrated. The experimental behavior of the device is then examined. Finally, a recent example of application of the proposed technology to a historic single-aisle church, realized in the 13th century in Brindisi (southern Italy), and equipped with inadequate and deteriorated steel tied rods, is shown.

Past earthquakes have shown that seismic events may incur large economic losses in buildings. FEMA P-58 provides engineers a practical tool for the performance seismic assessment of buildings. In this article, FEMA P-58 is applied to a typical Italian pre-1970 reinforced concrete frame building, characterized by plain rebars as steel reinforcement and masonry infills and partitions. Given that suitable tools for these buildings are missing in FEMA P-58, in the first part of the article, specific fragility curves and loss functions for the main structural and non-structural components of the building type under consideration are proposed. In the second part, building performance is evaluated following a time-based assessment approach. Expected economic losses in form of repair costs are then derived. Finally, results are compared with those from past applications to old RC frame buildings.

Fragility and loss functions are developed to predict damage and economic losses due to earthquake loading in Reinforced Concrete (RC) structural components with smooth rebars. The attention is focused on external/internal beam-column joints and ductile/brittle weak columns, designed for gravity loads only, using low-strength concrete and plain steel reinforcing bars. First, a number of damage states are proposed and linked deterministically with commonly employed methods of repair and related activities. Results from previous experimental studies are used to develop empirical relationships between damage states and engineering demand parameters, such as interstory and column drift ratios. Probability distributions are fit to the empirical data and the associated statistical parameters are evaluated using statistical methods. Repair costs for damaged RC components are then estimated based on detailed quantity survey of a number of pre-70 RC buildings, using Italian costing manuals. Finally, loss functions are derived to predict the level of monetary losses to individual RC components as a function of the experienced response demand.

Few studies have investigated so far the collapse capacity of buildings with base-isolation. In such studies, preliminary considerations have been drawn based on a number of assumptions regarding: (i) the methodology used for assessing the collapse capacity, (ii) the collapse conditions and failure modes assumed for both superstructure and isolation system, and (iii) the numerical modeling assumptions. The main results pointed out that the collapse conditions of base-isolated buildings may occur for intensity levels slightly higher than those associated with the design earthquake. In this paper, further developments are made through the use of enhanced models for the description of the behavior of a rubber-based isolation system and the assumption of more rational collapse conditions. Collapse fragility functions, in terms of mean and dispersion values, are proposed for two archetypes representative of existing buildings retrofitted using the seismic isolation technique. The collapse margin ratio (median collapse capacity Sa,C, namely the spectral acceleration associated to a probability of exceedance equal to 50%, divided by the design spectral acceleration at the collapse prevention limit state) has been evaluated for each examined case-study. Values ranging from 1.10 to 1.45 were found.

The primary objective of this study is to summarize results from previous experimental tests on laboratory specimens of RC/steel frames with masonry infills, in order to develop fragility functions that permit the estimation of damage in typical non-structural components of RC frame buildings, as a function of attained peak interstory drift. The secondary objective is to derive loss functions for such non-structural components, which provide information on the probability of experiencing a certain level of monetary loss when a given damage state is attained. Fragility curves and loss function developed in this study can be directly used within the FEMA P-58 framework for the seismic performance assessment of RC frame buildings with masonry infills.

The restoring (or re-centring) capability is an important feature of any isolation system and a fundamental requirement of current standards and guideline specifications for the design of seismically isolated structures. In this paper, the restoring capability of spherical sliding isolation systems, often referred to as friction pendulum systems (FPSs), is investigated through an extensive parametric study involving thousands of non-linear response history analyses of SDOF systems. The dynamic behavior of the isolation system is described with the visco-plastic model of Constantinou et al. (J Struct Eng 116(2):455–474, 1990), considering the variability of the friction coefficient with sliding velocity and contact pressure. Numerical analyses have been carried out using a set of approximately three hundred natural seismic ground motions recorded during different earthquakes and differing in seismic intensity, frequency content characteristics, magnitude, epicentral distance and soil characteristics. Regression analysis has been performed to derive the dependency of the residual displacement from the parameters governing the dynamic response of FPS. The influence of near-fault earthquakes and the accumulation of residual displacements due to real sequences of seismic ground motions have been also investigated. Finally, the restoring compliance criteria proposed in this study are compared to the lateral restoring force requirements of current seismic codes. Based on the results of this study, useful recommendations for a (more) rational design of FPSs are outlined.

Summary Performance-based earthquake engineering procedures have now developed to the point that it is possible to evaluate a range of possible decision variables, including the expected annual monetary loss (EAL). Quantification of the EAL is considered to be particularly useful because it could assist with the identification of effective design and retrofit measures that consider seismic performance over a range of intensity levels. Recognizing, however, that existing procedures for the evaluation of EAL tends to be quite time consuming, this paper builds on a recent proposal to use simplified limit state loss versus intensity relationships to compute EAL via a closed-form equation, without the need to compile an inventory of damageable components and with freedom in the choice of structural analysis method. Various developments to the simplified approach are made in this paper to allow consideration of loss thresholds, non-uniform damage distributions and the impact of differences in seismic performance in orthogonal directions. In addition, means of accounting for uncertainties in the simplified EAL assessment are described. The work has focused on the assessment of EAL for reinforced concrete frame buildings with details representative of construction practice adopted in Italy in the 1950s through to the early 1970s. By comparing loss assessment results obtained using a refined methodology with those obtained using the new guidelines developed here for two case study buildings, it is concluded that the simplified approach works well. Future research should therefore aim to further validate the approach and extend it to other building typologies and construction eras. Copyright © 2017 John Wiley & Sons, Ltd.

The use of seismic isolation for the seismic rehabilitation of existing buildings is very attractive but often very tricky due to several aspects related to its implementation. In this paper, a case study of seismic rehabilitation of a high-rise residential building with seismic isolation is presented. The building under consideration is located in southern Italy and it is placed next to another building from which it is separated by a gap of 400 mm. In the paper, all the steps of the seismic rehabilitation process are described. First, the target objective of the seismic rehabilitation and the choice of isolation system type and location are discussed. The design of the isolation system, carried out following a direct displacement-based approach, is then examined. Finally, the main phases followed in the installation of the isolation system are described. Some comments on costs and time needed to complete the intervention are also reported.

The seismic retrofitting of a high-rise RC building, recently realized in Italy using the seismic isolation technique, is examined in terms of cost of the intervention (compared to the replacement cost of the building), seismic performances and expected benefits (compared to the building in the as-built configuration), expressed in terms of reduction of direct and indirect seismic losses in case of attainment of different limit states. In the paper, the comparison of the building performance before and after seismic retrofitting is performed in terms of Expected Annual Loss (EAL), applying a direct displacement-based loss assessment approach. The results show a considerable reduction of the EAL (approximately of 70%), passing from the as-built to the retrofitted configuration. The time needed to get the balance between costs of the intervention and benefits due to EAL reduction turns out to be of the order of 13 years.

Steel cables, tendons and tie-rods are the key components of many structures including masonry arches and vaults, timber roof trusses and several post-tensioned structures. In this paper, a device prototype based on the superelastic properties of Cu-based Shape Memory Alloys (SMAs), is proposed to enhance the thermal behavior of such structural elements. The thermal behavior of steel tie-rods with and without SMA is evaluated through comprehensive experimental tests in thermal room. During the tests, different temperature–time histories are considered, with air temperature varied between −10 °C and 40 °C. The results of the experimental tests confirm the great effectiveness of the proposed SMA device, with reductions of force changes due to air temperature variations of the order of 80–90%, compared to steel tie-rods without SMA. In the paper, the main structural components and basic functioning principles of a SMA-based device prototype for masonry arches and vaults are presented and aspects related to its implementation in practice are discussed in detail.

The downtime due to earthquake damage in RC buildings is examined. The rational component of downtime is evaluated based on the results of probabilistic seismic loss assessment analyses, using suitable time estimating manuals for civil construction works. The irrational component of downtime is derived from empirical data relevant to post-earthquake reconstruction in Italy. Suitable criteria are then adopted to monetize the downtime for indirect loss estimation. Finally, a simplified model, expressing indirect monetary loss as a function of the earthquake intensity level, is tentatively proposed, to be incorporated in practice-oriented procedures for the estimation of the expected annual loss of residential RC buildings.

A comprehensive experimental program of cyclic tests on 1:3-scale models of bridge piers is going to be carried out at the Laboratory of Structures and Materials of the University of Basilicata. The testing models include eight RC single shaft piers with hollow circular cross section. Four piers have been realised using corroded steel rebars. In this paper, the results of preliminary numerical simulation analyses of the cyclic behaviour of the piers, carried out with Opensees using fiber-based models, are presented. Pull-out and lap-splice effects of steel rebars have been taken into account in the numerical analyses. First, the experimental specimens and the test set up are presented. Next, the results of the numerical analyses are discussed. In the numerical analyses, different configurations and levels of corrosion have been considered. The effective stiffness and equivalent damping of the piers is reported as a function of pier ductility and pier drift.

This paper presents the results of an experimental study aimed at investigating the sensitivity of the cyclic behavior of elastomeric materials to air temperature variations. The experimental tests have been performed on several elastomeric specimens, purchased from two different Italian manufacturers of structural bearings and seismic isolation devices. Six different types of elastomers, with shear modulus (G) ranging from 0.5 MPa to 1.2 MPa at 100% shear strain, have been examined. During the tests, the specimens have been cycled under shear strains of increasing amplitude (from 25% to 125%), at three different frequencies of loading (0.01 Hz, 0.1 Hz and 0.5 Hz). The tests have been carried out at six different air temperatures, ranging between −20 °C and 40 °C. The effects of prolonged exposure to low temperatures have been also investigated. The cyclic behavior of the specimens is described in terms of (i) shear stress at zero cyclic strain, (ii) maximum shear stress, (iii) secant shear modulus at the maximum strain amplitude, (iv) energy loss in one fully reversed cycle and (v) corresponding equivalent viscous damping ratio. In the paper, the most important results of the experimental investigation are described.

Metallic tie-rods are currently used in many historical buildings for absorbing the out-of-plane horizontal forces of arches, vaults and roof trusses, despite they exhibit several limitations under service and seismic conditions. In this paper, a post-tensioned system based on the superelastic properties of Ni-Ti shape memory alloys is proposed for improving the structural performances of traditional metallic tie-rods. First, the thermal behavior under service conditions is investigated based on the results of numerical and experimental studies. Subsequently, the seismic performances under strong earthquakes are verified trough a number of shaking table tests on a 1:4-scale timber roof truss model. The outcomes of these studies fully confirm the achievement of the design objectives of the proposed prototype device.

SUMMARY A comprehensive parametric study on the inelastic seismic response of seismically isolated RC frame buildings, designed for gravity loads only, is presented. Four building prototypes, with 23 m × 10 m floor plan dimensions and number of storeys ranging from 2 to 8, are considered. All the buildings present internal resistant frames in one direction only, identified as the strong direction of the building. In the orthogonal weak direction, the buildings present outer resistant frames only, with infilled masonry panels. This structural configuration is typical of many existing RC buildings, realized in Italy and other European countries in the 60s and 70s. The parametric study is based on the results of extensive nonlinear response-time history analyses of 2-DOF systems, using a set of seven artificial and natural seismic ground motions. In the parametric study, buildings with strength ratio (Fy/W) ranging from 0.03 to 0.15 and post-yield stiffness ratio ranging from 0% to 6% are examined. Three different types of isolation systems are considered, that is, high damping rubber bearings, lead rubber bearings and friction pendulum bearings. The isolation systems have been designed accepting the occurrence of plastic hinges in the superstructure during the design earthquake. The nonlinear response-time history analyses results show that structures with seismic isolation experience fewer inelastic cycles compared with fixed-base structures. As a consequence, although limited plastic deformations can be accepted, the collapse limit state of seismically isolated structures should be based on the lateral capacity of the superstructure without significant reliance on its inherent hysteretic damping or ductility capacity. Copyright © 2012 John Wiley & Sons, Ltd.

One of the most important aspects of the seismic response of elastomeric isolators is their stability under large shear strains. The bearing capacity of elastomeric isolators, indeed, progressively degrades while increasing horizontal displacement. This may greatly influence the design of elastomeric isolators, especially in high seismicity regions, where slender elastomeric isolators subjected to large horizontal displacements are a common practice. In the current design approach the critical load is evaluated based on the Haringx theory, modified to account for large shear strains by approximate correction factors. In this paper the critical behavior of a pair of slender elastomeric devices is experimentally evaluated at different strain amplitudes, ranging from approximately 50% to 150%. The experimental results are then compared to the predictions of a number of semi-empirical and theoretical formulations. The main conclusion of this study is that current design approaches are overly conservative for slender elastomeric seismic isolators, since they underestimate their critical load capacity at moderate-to-large shear strain amplitudes.

The re-centring capability is identified by the current design codes as a fundamental feature of seismic isolation systems. In this paper, the re-centring capability of seismic isolation systems characterised by a flag-shaped hysteretic cyclic behaviour is investigated through an extensive parametric study of single-degree-of-freedom hysteretic systems subjected to different natural records. A remarkable example of this kind of isolation system derives from the combination of flat steel-PTFE sliding bearings with auxiliary re-centring devices based on the superelastic properties of Shape Memory Alloys. The results of the parametric analyses are processed statistically and regression analysis relations are derived that show the dependence of the residual displacement after the earthquake on the governing parameters of the isolation system. Based on the analysis results, the features of the flag-shaped system that guarantee sufficient re-centring capability are identified.

In this paper, the effectiveness of Shape Memory Alloys (SMA) restrainers for the seismic retrofit of multi-span simply supported deck bridges is investigated through a series of numerical nonlinear dynamic analyses and shaking table tests on an experimental mock-up of a typical bridge structure. Both numerical analyses and experimental tests have been carried out on the structure with and without seismic restrainers. The results of these studies clearly prove the effectiveness of the SMA-based restrainers in controlling the displacement response of simply supported deck bridges.

Recent earthquakes have highlighted the seismic vulnerability of bridges due to excessive movements at the joints (in simply supported deck bridges) or concentration of seismic forces in a few piers (in multi-span continuous deck bridges). Steel-based seismic restrainers and viscous shock transmitters are used to limit the joint openings in simply supported deck bridges or to redistribute the seismic force among all piers in continuous deck bridges, respectively. Currently used devices, however, have some limitations such as large dimensions, no energy dissipation, possible large residual displacements, bad control of the force transmitted to the substructure (steel restrainers), large dimensions, difficulty of installation in existing structures, need of maintenance, and sensitivity to the earthquake characteristics (viscous shock transmitters). Shape memory alloys (SMAs) with superelastic behavior show the potential to overcome the limitations involved in the current technologies. In this article, a multi-performance seismic device based on superelastic SMA wires is proposed for the seismic retrofit of multi-span simply supported and continuous deck bridges. The effectiveness of the SMA devices is assessed through a number of nonlinear time-history analyses on two bridge structures representative of existing Italian highway bridges. Results are compared to the seismic response of the bridges in the as-built configuration.

A performance-based adaptive methodology for the seismic assessment of highway bridges is proposed. The proposed methodology is based on an Inverse (I), Adaptive (A) application of the Capacity Spectrum Method (CSM), with the capacity curve of the bridge derived through a Displacement-based Adaptive Pushover (DAP) analysis. For this reason, the acronym IACSM is used to identify the proposed methodology. A number of Performance Levels (PLs), for which the seismic vulnerability and seismic risk of the bridge shall be evaluated, are identified. Each PL is associated to a number of Damage States (DSs) of the critical members of the bridge (piers, abutments, joints and bearing devices). The IACSM provides the earthquake intensity level (PGA) corresponding to the attainment of the selected DSs, using over-damped elastic response spectra as demand curves. The seismic vulnerability of the bridge is described by means of fragility curves, derived based on the PGA values associated to each DS. The seismic risk of the bridge is evaluated as convolution integral of the product between the fragility curves and the seismic hazard curve of the bridge site. In this paper, the key aspects and basic assumptions of the proposed methodology are presented first. The IACSM is then applied to nine existing simply supported deck bridges, characterized by different types of piers and bearing devices. Finally, the IACSM predictions are compared with the results of nonlinear response time-history analysis, carried out using a set of seven ground motions scaled to the expected PGA values.

The mechanical properties of elastomers can change significantly due to air temperature variations. In particular, prolonged exposure to subzero temperatures can result in rubber crystallization, with a considerable increase in the shear stiffness of the material. As a result, the seismic response of structures with elastomeric isolators can be strongly influenced by air temperature. Current seismic codes, indeed, require an upper and lower bound analysis, using suitable modification factors, to account for the changes in the cyclic behavior of elastomeric isolators due to air temperature variations. In this study, the sensitivity of the cyclic behavior of elastomeric isolators to air temperature variations is investigated based on the experimental results of an extensive test program on six different elastomeric compounds for seismic isolators, characterized by a shear modulus ranging from 0.5 to 1.2 MPa at 100% shear strain and 20°C. The cyclic tests have been performed on small-size specimens, subjected to shear strain amplitudes and frequency of loading typical for elastomeric seismic isolators, at seven different air temperatures, ranging from 40 to −20°C. The effects of rubber crystallization due to prolonged exposure to low-temperatures have been also investigated. A finite element model for the evaluation of the temperature contour map inside a full-size elastomeric isolator exposed to low air temperatures has been also developed. In the paper, the experimental outcomes are compared with the modification factors provided by the current seismic codes to account for the temperature effects on the mechanical properties of elastomeric isolators.

A modern base isolation system is proposed for the aseismic control of structures. It is composed of steel-Teflon Flat Sliding Bearings, to support the gravity loads while allowing large horizontal displacements, and simply connected Shape Memory Alloy (SMA) truss elements, to provide the necessary horizontal stiffness as well as a proper restoring capability. The system is referred to as Smart Restorable Sliding Base Isolation System (SRSBIS). Depending on the arrangement of the auxiliary SMA elements, SRSBIS can exhibit a geometric nonlinearity in addition to the nonlinearity of materials. In this paper, the dynamic characteristics of SRSBIS are first examined in terms of the force-displacement behavior, effective period of vibration, and equivalent damping. After that, the earthquake response of buildings equipped with SRSBIS, designed in accordance with a direct displacement-based approach, is evaluated through extensive nonlinear time-history analyses. The effects of the design parameters on the system behavior are then investigated within a comprehensive parametric study and the seismic performances of SRSBIS are finally compared to those of similar practical isolation systems. Based on the results, it is shown that SRSBIS can be suitably used for the seismic protection of structures.