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This paper presents an experimental study on an innovative timber‐based retrofit solution for reinforced concrete (RC) framed buildings, with or without masonry infills. The intervention aims to enhance seismic resistance through a light, cost‐effective, sustainable, and reversible approach integrating energy efficiency upgrades. The method employs cross‐laminated timber (CLT) panels as infills or external retrofitting elements, mechanically connected to the RC frame through steel fasteners. The system is combined with thermal insulation for improved energy efficiency. The seismic performance of the proposed retrofit technique was assessed experimentally on a full‐scale building model at the European Laboratory for Structural Assessment (ELSA). The experiments included tests on two five‐story building configurations: a masonry‐infilled RC building as a reference and the same structure strengthened with CLT panels. Each building was subjected to unidirectional earthquake simulations of increasing intensity using the pseudodynamic (PsD) testing method with substructuring. The physical substructure of the hybrid model consisted of the first story of a two‐story mockup built and retrofitted in the laboratory, while stories two to five were simulated numerically. The paper discusses major observations from the tests, comparing the damage evolution and hysteretic responses of the two configurations. The experiments yielded promising results, showing that the suggested retrofit solution significantly increased displacement and energy dissipation capacity. The retrofitted building survived earthquake intensities up to 50% higher than the non‐retrofitted counterpart, exhibiting only slight structural damage. These pioneering experiments provide compelling data on the high effectiveness of the proposed CLT‐based retrofit system in enhancing the seismic performance of full‐scale RC buildings. [ABSTRACT FROM AUTHOR]

Many methods for seismic risk assessment rely on the selection of a seismic intensity measure (IM) and the development of models of the seismic demand conditional on the IM. The individual importance of these two features to accurately assess seismic performance is well known. In contrast, this study aims to evaluate the impact that the combined selection of IM and the demand model has on risk estimates. Using a hypothetical seismic source model and a non‐stationary stochastic ground‐motion model, we present risk estimates for a mid‐rise steel structure for 15 different IMs and five demand models derived by cloud analysis (four based on regression and a fifth based on an empirical binning approach). The impact of these choices is investigated through a novel method of model performance evaluation using a benchmark solution obtained via the unconditional approach (i.e., directly estimating demand exceedance frequencies from simulated ground motion time histories). The obtained results are also compared against traditional IM performance metrics, for example, efficiency and sufficiency. Finally, we demonstrate how risk estimate inaccuracies are propagated by performing a damage assessment on two example components. The results show that, for the scenario under investigation, Arias intensity combined with the binned demand model provides the best risk estimates, if sufficient samples are available, whilst ground displacement and duration‐based IMs ranked worst, irrespective of the demand model. The findings highlight the importance and interconnectedness of the selection of the IM and the demand model when using cloud analysis and present a clear method of determining the most accurate combination for risk assessments. [ABSTRACT FROM AUTHOR]

Nonstructural damage, usually predominates in buildings subjected to low to moderate seismic intensities and contributes significantly to business interruption and economic losses. It promotes a rapidly growing need for experimental research and qualification of various types of nonstructural elements in buildings in the recent decades. To provide a novel option of experimentally simulating the realistic boundary conditions for various nonstructural elements in labs, we developed the Nonstructural Element Simulator on Shake Table (NEST), a passively controlled three‐layer substructural testbed driven by existing shake tables. This paper presents the first experimental implementation of NEST on a challenging 42‐story archetype tall building. The dynamic properties of the substructure were tuned to adapt the archetype building and the required shake table motions were solved as a reverse problem by an open‐loop control algorithm. The test results proved the capability of NEST to replicate the history responses of the target floors in the archetype building under either recorded earthquake ground motion or artificial loading protocols for qualification purposes. In all cases, the synthetic relative error in the floor accelerations and the inter‐story drift within the frequency range of interest was less than 5% in the numerical domain and less than 30% in the physical realization. The seismic responses of a variety of nonstructural elements to the substructural motions show that, in the mid‐story of the archetype tall building, the ceiling sustained minimum damage because of the small floor acceleration while the indoor contents slid significantly and even overturned. [ABSTRACT FROM AUTHOR]

This paper presents results on what the conditions of testing for assessing the adequacy of seismic isolators in the maximum considered earthquake should be by utilizing an approach in which the cumulative dissipated energy history is used as the performance parameter. This test is what is described as Item 4 in section 17.8.2.2 of standard ASCE/SEI 7. The approach used follows the paradigm of another study in which the history of temperature at the sliding interfaces or in the bulk of the lead core of isolators was used. In conducting this work, many isolation systems (a total of 96 systems, single friction pendulum, triple friction pendulum, and lead‐rubber) were used, with isolator models capable of simulating the effects of heating on the strength of the isolators. The study utilized a large set of bi‐directional ground motions with short‐ and long‐duration characteristics (71 pairs of short‐ and long‐duration ground motions, 96 isolation systems, three seismic intensities, for a total of 40,896 ground motion pairs). The adequacy tests were designed to reproduce various percentile cumulative energy histories obtained in the response history analysis. The requirements of these tests are compared to the testing requirements obtained by the use of temperature history as the performance criterion, and the test currently prescribed as test item 4 of section 17.8.2.2 of standard ASCE/SEI‐7. The study shows that use of the cumulative dissipated energy as the performance criterion for designing tests to represent the effects of maximum earthquake results in onerous testing requirements. This is because the cumulative energy increases monotonically without accounting for fluctuations in the seismic ground motion intensity, unlike the history of temperature at the sliding interfaces or the lead core of isolators. Accordingly, tests designed using the temperature as the performance criterion are recommended for use in specifications for testing. [ABSTRACT FROM AUTHOR]

Current seismic design codes for bridge structures do not account for the influence of aftershock sequences, which, to some extent, overestimate the seismic performance for bridges subjected to mainshock‐aftershock (MS‐AS) scenarios. To address the great need for ground motion sequences tailored to specific research sites for fragility analysis, this study proposes a method for generating artificial MS‐AS ground motion sequences based on the evolutional bimodal Kanai–Tajimi model and the Epidemic–Type Aftershock Sequence model. We establish a framework for MS‐AS fragility analysis using an input–output Hidden Markov Model (IOHMM), where the damage states (DS) of bridge piers are considered unobservable and are inferred statistically through damage indices in an unsupervised manner. Model parameters are trained using intensity measure (IM) sequences and damage index (DI) sequences. Fragility curves for both the mainshock and state‐dependent aftershocks considering multiple aftershocks are formulated based on the initial state probability and state transition probabilities of the proposed IOHMM. The fragility analysis results reveal that as the initial seismic damage level increases, the probability of aftershocks causing higher damage levels in the structure also increases, highlighting the significant impact of aftershocks on structural damage increments. Furthermore, we extend the proposed model to a bivariate seismic intensity measure and develop fragility surfaces. The proposed framework provides a novel approach and insights for tackling seismic fragility under multiple aftershocks. [ABSTRACT FROM AUTHOR]

Most traditional passive friction dampers are limited to the design of single activated energy dissipation mechanism; therefore, when the seismic intensity is not strong enough to activate the mechanism, traditional friction dampers can only increase stiffness of the structure just like braces; only when the mechanism is activated will the energy dissipation elements perform energy absorption and assist the structure to absorb received seismic energy. The objective of this study is to improve this defect of traditional friction dampers, developing a Multi–Level Friction Damper (MFD) with a two‐stage energy dissipation mechanism, helping building structures (e.g., hospitals, high‐tech plants) reduce the acceleration responses of the superstructure. MFDs are proven to provide more comprehensive protection and have higher energy dissipation benefits than traditional friction dampers by the validation of numerical analysis and shaking table test. The study in turn performed parameter fitting with the results of the numerical simulation analysis and shaking table test, and the experimental results turned out to be satisfactory, validating the accuracy of the theoretical formulas. [ABSTRACT FROM AUTHOR]

In the probabilistic seismic performance assessment of structures, intensity measures (IMs) represent seismic characteristics and variations. Traditional fragility analysis method based on the assumption of linear regression requires selecting an optimal IM as input variable. By introducing machine learning (ML) techniques, nonparametric fragility analysis theoretically allows for considering all potential IMs as inputs. Nevertheless, to reduce input dimensionality and improve training efficiency, the feature selection of IMs remains imperative. This paper proposes a method to select optimal ground motion IMs for data‐driven surrogate modeling of structures. Specifically, the elastic net algorithm is employed to select the optimal multiple IMs based on the coefficient of determination and regression coefficient, differing from the efficiency and practicality emphasized in the traditional method. Using the optimal multiple IMs as input variables, several ML techniques are employed to construct surrogate models for seismic damage assessment of structures, thereby developing fragility functions, that is, the conditional probability of exceeding a damaged state given seismic intensity. A 3‐span, 6‐storey, reinforced concrete frame is utilized to illustrate the proposed methodology. The predictive performance of all ML models with the optimal multiple IMs outperforms that of the models with the commonly used IM (e.g., peak ground acceleration, PGA) as sole input and all candidate IMs as inputs. Additionally, the surrogate models with the optimal multiple IMs enable a more comprehensive seismic fragility modeling of structures under two or more IMs simultaneously, such as the fragility surface under spectral acceleration at 1.0s (Sa‐1.0s) and velocity spectrum intensity (VSI). [ABSTRACT FROM AUTHOR]

Traditional seismic evaluations for high‐voltage switchgear equipment, the critical power facilities, consider only structural failure mode and may underestimate the actual seismic risk. By additionally introducing a probable functional failure mode caused by the excessive deformation of the switchable blade of equipment, a novel copula‐based framework is proposed to utilize limited samples to generate simulation data and evaluate the joint failure probability (JFP). The correlation index and Akaike Information Criterion are employed to optimize the Copula function. For illustration, a disconnector, representative switchgear equipment, was selected as an example and modeled with the experiment validation. Model analysis results demonstrate the Clayton type is the most competent for evaluation. Neglecting functional failure can significantly underestimate the actual failure probability at various seismic intensities, up to 50%. Furthermore, it was found that the current equipment material strength level already meets the requirements, and enhancing strength alone does not effectively improve reliability under strong earthquakes. For PGA intensities ≥0.7 g, the blade deformation capacity plays the primary reliability constraint, independent of material stress. A cost‐effective seismic design should optimize the combination of allowable material stress and blade deformation based on the JFP considering seismic intensity and targeted reliability. [ABSTRACT FROM AUTHOR]

The behavior of short‐period reinforced concrete (RC) shear wall structures is often complicated and hard to predict accurately, even when the structure behaves in the elastic region, due to significant uncertainties in the material and the environment. Modeling assumptions used in finite element (FE) analyses often influence the accuracy of the dynamic response predictions. This paper discusses the numerical modeling of shaking table tests of a 3‐story RC shear wall specimen, which was carried out by Korea Atomic Energy Research Institute in July 2020. The experimental program is briefly introduced in this paper. Through nonlinear time history analyses using ABAQUS, the effect of modeling assumptions on the accuracy of the FE methods in predicting the linear and moderately nonlinear behavior of the RC structure is presented. Two commonly used modeling/model updating assumptions are considered: concrete Young's modulus and foundation flexibility. Influences of such modeling assumptions in predicting beyond design dynamic behavior (i.e., nonlinear responses and damage development) of the testing structure are also studied. The results showed that the accuracy of the dynamic response prediction of the structure could be improved significantly after calibrating the models against the white noise test results. Nevertheless, models established with different modeling assumptions can only capture the behavior of the structure at certain seismic intensity levels. Different models give results with a considerable variation in the structure's peak acceleration, floor response spectrum, acceleration amplification profile, damage pattern, and damage severity. [ABSTRACT FROM AUTHOR]

There has been no consensus on post‐earthquake operating plan for high‐speed railway trains. In this paper, two three‐dimensional coupling model of track‐bridge system without and with trains for high‐speed railways were developed, and their performance were verified based on shaking table tests. The equivalent method of design seismic track irregularity for random structures was discussed, and the amplitude response spectra of design seismic track irregularity for all levels of seismic intensity were proposed. In addition, the rationality of design seismic track irregularity was evaluated based on engineering case analysis, providing a theoretical foundation of formulating post‐earthquake contingency plans for high‐speed railways. The results show that when span number increases, the design seismic track irregularity amplitude increases and then tends to be stable; when the span number reaches 9, the train dynamic response gradually becomes stable; the random structures with arbitrary span numbers are equivalent to a specific 9‐span structure when constructing design seismic track irregularity. When the seismic intensity is low, there is no significant difference in shape and amplitude between the measured pre‐earthquake and post‐earthquake track alignment irregularities, and the train can normally run with no significant deceleration required. The train dynamic response under the design post‐earthquake track irregularity is greater than that under the measured post‐earthquake track irregularity, indicating that the design seismic track irregularity has a reasonable safety margin and a good feasibility in engineering practice. [ABSTRACT FROM AUTHOR]

To investigate the isolation effect of the friction pendulum system (FPS) horizontal isolation bearing and the air spring‐FPS three‐dimensional (3D) isolation bearing in truss structure and the influences of long‐period ground motions on the isolated structure, the shaking table test of a truss structure is designed and conducted. The ordinary ground motions, near‐fault pulse‐like ground motions, and far‐field long‐period ground motions with different spectral characteristics are chosen to input into the structure, and the dynamic characteristics such as the acceleration, displacement, and stress of the truss are compared and analyzed. The horizontal frequency of the horizontal isolated structure is reduced after the horizontal isolation, while the vertical frequency is further reduced after 3D isolation. The isolation effect of nodal acceleration, nodal displacement, and member stress under 3D isolation is better than that of horizontal isolation, especially the vertical seismic response is significantly improved. When the ground motion intensity is small, the FPS horizontal isolation bearing slides little, and reducing the seismic response of the structure is limited. There is a better isolation effect of 3D isolated structure. The vertical frequency ratio Rf under ordinary ground motions is far away from 1 and close to 3, basically avoiding the main energy segment of the ground motions. The advantage of 3D isolated structure is relatively reduced under long‐period ground motions, which lies in the rich low‐frequency components of long‐period ground motions which are difficult to isolate effectively. [ABSTRACT FROM AUTHOR]

Precariously balanced rocks (PBRs) are a type of naturally occurring freestanding structure that provides valuable information to constrain seismic hazard at return periods which are important for critical facilities such as nuclear power plants and nuclear repositories. Exposure ages have been established to be in excess of 10,000–30,000 years, which is why precarious rocks are one of the only available means to validate seismic hazard associated with long return periods. One critical component for constraining seismic hazard in this way is the overturning estimate of a given precarious rock as a function of earthquake intensity. However, current state‐of‐the‐art methods for modeling the seismic response of precarious rocks involve significant sources of uncertainty. One of the main sources of uncertainty stems from the interface of the rock, which is usually occluded during surveying and assumed during modeling. Through extensive shake table testing, this study analyzes the uncertainty in the overturning response of a granite precarious rock specimen incorporating various degrees of interface contact. The results indicate that a small variation in the contact geometry could result in a substantial increase in the stability of the specimen, which is significant given the difficulty of surveying the interface of PBRs in the field. Repeatability tests indicate that the overturning demand can vary up to nearly ±50%. The probabilistic overturning responses are compared across the interface changes to bound uncertainty; and, the effect of modeling parameters, namely the contact normal stiffness, is evaluated through a parametric study and comparison with experimental results. [ABSTRACT FROM AUTHOR]

Past earthquakes have highlighted the impact of prolonged downtime on community recovery. The introduction of performance objectives expressed in terms of recovery time has been identified as a key goal for the next generation of building codes. Recent development of downtime estimation frameworks now allows for the discussion of how to use recovery time estimates to (1) establish recovery‐targeted performance and (2) assess the functional recovery performance of buildings designed with modern code provisions. In this paper, we employ methods adapted from life‐safety provisions to evaluate building functional recovery performance using downtime simulation outputs. A scenario‐based, an intensity‐based and a risk‐targeted analysis of functional recovery performance objectives are presented. The functional recovery performance of a series of modern residential reinforced concrete shear wall archetype buildings, ranging from eight to 24 stories in height, at a site in downtown Seattle, Washington, are then assessed. Results of the scenario‐based assessment of an M9 Cascadia Subduction zone earthquake, comparable to an intensity‐based assessment at the 975‐year intensity level, show that the probability of achieving functional recovery within four months is close to zero, while the likelihood of achieving functional recovery by one year is approximately 60%. The results of the risk‐targeted assessment of the archetype buildings show a 50% probability in 50 years of the building downtime to functional recovery exceeding one month, a 43% in 50‐year probability of the downtime exceeding four months and an 8% in 50‐year probability of downtime exceeding one year. Finally, the expected annual downtime is approximately three days for all building heights considered. Disaggregation was used to identify intensity levels that contribute most of the downtime risk. The risk of downtime exceeding one month to one year is dominated by frequent, low‐intensity earthquakes (e.g., 100‐year return period). The risk of exceeding longer recovery times is dominated by less frequent, higher intensity earthquakes (i.e., return periods greater than 975 years). While the results of the analysis are sensitive to assumed damage thresholds and impeding factor delays triggered at low intensity levels, the findings suggest that reinforced concrete shear wall buildings designed following current building codes have a high risk of lengthy downtimes. Ultimately, the proposed methods and results illustrate the importance of introducing recovery‐based provisions into the next generation of building codes. [ABSTRACT FROM AUTHOR]

Efficient regional seismic risk assessment including ground motion prediction and damage risk estimation is needed for emergency response planning. However, a conventional regional assessment suffers from low data‐ and time‐ efficiency as it generally involves a large number of locations and infrastructure systems that have specific soil conditions, and geometric, material, and structural properties, requiring access to large data and massive individual calculations with complicated procedures. To achieve efficient regional seismic risk assessment, this work presents a deep generative learning framework to construct input–output surrogate models of regional seismic risk by learning the underlying complex relation between earthquake source parameters and regional seismic risk involving many locations and structures from data. The learned deep surrogate models directly output the ground motion intensity map and the risk map of a region given earthquake source parameters, circumventing massive individual calculations and data access to individual locations and structures. The presented framework is validated on the bridge network risk assessment using simulated scenario earthquakes of the San Francisco Bay Area. We observe that the obtained deep surrogate models perform well without the need of data access to locations and structures and are time‐efficient. We also discuss the applicability and limitations of the presented framework. [ABSTRACT FROM AUTHOR]

This study experimentally investigates a dynamic behavior of an end‐anchored floating bridge under the joint actions of earthquakes and water waves. A truncated model with a geometrical scale of 1:100 was utilized for the hydrodynamic test, and an actuator was used to generate the earthquake input. A series of trials were conducted for the floating bridge model under the combined action of two different sea states and three earthquake inputs with increasing intensity based on the concept of the incremental dynamic analysis method. For comparison, the dynamic responses of the floating bridge model under earthquake action in still water and pure wave action were also conducted. Based on the test data, the dynamic responses, particularly focused on the sway, heave, roll, and pitch motions of the pontoons, of the test model were experimentally analyzed. The experimental results showed that earthquake excitation along the longitudinal axis of the bridge girder would induce noticeable oscillation of the bridge pontoons in still water. The magnitude of the coupled effects of earthquakes and water waves is dependent on the intensity of the earthquake inputs and the sea state. [ABSTRACT FROM AUTHOR]

The hybrid self‐centering braced frames (HSBFs) with shape memory alloy‐based braces (SMABs) and viscous dampers (VDs) are an emerging structural system developed for improving the seismic resilience of traditional braced frames (e.g., buckling restrained braced frames [BRBFs]) and self‐centering braced frames (SCBFs) by reducing residual inter‐story drifts (RIDs) and floor acceleration responses simultaneously. Nevertheless, the excellent performance of HSBFs is captured by introducing high initial construction costs. This paper aims to highlight the benefits of HSBFs compared with BRBFs and SCBFs by investigating the earthquake‐induced life‐cycle costs. To this end, 6‐story BRBF, SCBF, and HSBF are designed separately to achieve the same maximum inter‐story drifts under design basis earthquakes (DBE) for a fair comparison. The advanced numerical models of the considered systems were developed, and nonlinear dynamic analyses were conducted to obtain the structural seismic responses under various intensities. Monte Carlo simulation (MCS) was adopted for considering the modeling uncertainty. The life‐cycle costs were subsequently estimated based on the revised HAZUS loss estimation method. The influence of RIDs, initial construction costs of SMABs and VDs, and values of contents inside buildings were comprehensively investigated. It has been found that HSBF can achieve better performance in reducing seismic loss than BRBF and SCBF due to its excellent capability of controlling structural and nonstructural damage. SCBF may show higher seismic loss than BRBFs, given high RID limits for demolition or high building contents' value, highlighting the importance of controlling floor acceleration responses of SCBFs. The life‐cycle benefits of BRBFs, SCBFs, and HSBFs are highly influenced by the RIDs, initial construction costs of SMABs and VDs, building contents' values, and building's lifetime. HSBFs show better life‐cycle benefits than SCBFs when the building's lifetime is not lower than 50 years. Compared to BRBF, the life‐cycle cost effectiveness of SCBF can be only achieved when the initial cost of SMABs is lower than 1.21 times that of BRBs for the building with 50 years' lifetime; the life‐cycle cost effectiveness of HSBF6 can be only achieved when the initial cost of SMABs or VDs is lower than 1.84 times that of BRBs for the building with 50 years' lifetime. It has been concluded that reducing the initial costs of SMABs and VDs is critical and essential for increasing the life‐cycle economic benefits of SCBFs and HSBFs and promoting their real‐world applications. [ABSTRACT FROM AUTHOR]

A bidirectional rocking isolation bearing system (Bi‐RIBS) is proposed to provide seismic protection for bridge structures. By using the 3‐D rocking motion of the Bi‐RIBS, this system acts as a mechanical fuse to limit the maximum force transmitted to the bridge piers and as a restoring component to control an excessive girder response. Possible applications in bridge structures were discussed. A simple analytical model was established to characterize the dynamics of an example bridge featuring such a Bi‐RIBS. A series of dynamic analyses were performed by using the proposed model to investigate the effects of several factors on controlling the seismic responses of the bridge, for example, the design parameters of Bi‐RIBS including inclined angle and size, the damping property at the support interface, and the mass ratio. The peak ground accelerations of the bidirectional ground motion record were scaled to various levels to evaluate the maximum performance indices of the bridge structure and the response control effectiveness of the Bi‐RIBS compared to the uncontrolled counterparts. The simulation results demonstrated that the proposed Bi‐RIBS could effectively control the maximum pier displacement while keeping the bearing from overturning if suitable parameters were selected. In particular, the control effectiveness on the maximum pier response becomes more significant as the seismic intensity increases, due to its distinctive negative stiffness property. [ABSTRACT FROM AUTHOR]

Lessons from recent earthquakes have provided a tough reality check of the traditional seismic design approach and technologies, highlighting the urgent need for a paradigm shift of performance‐based design criteria and objectives toward low‐damage design philosophy and technologies for the whole building system. Modern society is asking for "earthquake proof" resilient buildings that are able to withstand seismic events without compromising their functionality. The EU‐funded SERA (Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe Project) project discussed in this paper provided the opportunity to develop and validate within the European context an integrated seismic low‐damage prototype, including main structure and non‐structural elements, for the next generation of high‐performance buildings. This paper presents an overview of the research, involving three‐dimensional shake table tests of a two‐storey 1:2 scaled timber‐concrete post‐tensioned dissipative low‐damage structure "dressed" by earthquake‐resistant gypsum/masonry partitions and glass/concrete facades. Specimen details, construction and assembly phases, test setup, and experimental results are discussed. After many cycles of input motions at increasing levels of seismic intensity (higher than Collapse Prevention Limit State), the integrated building system exhibited a very high seismic performance. The experimental campaign carried out at the National Laboratory of Civil Engineering in Lisbon confirmed the unique potential of low‐damage technologies and the opportunity for their widespread implementation into design practice. [ABSTRACT FROM AUTHOR]

Site‐structure cluster interaction (SSCI) has a significant effect on the seismic response of densely distributed buildings, and rationally and effectively quantifying its effect when modelling the urban seismic damage can provide more optimal decisions to mitigate earthquake disasters. This paper focuses on the input motion of the structures, by extracting the main influential parameters of SSCI and adopting the loosely typed wavelet packet neural network to rapidly simulate the spatially varying ground motion in the urban environment. In the proposed framework, the wavelet packet energy ratio is presented to describe the variation of ground motion characteristics and used as the sole output to carry out the multi‐resolution spectral modulation, and the training samples were accumulated by a validated finite element simulation method. The developed surrogate model considers the effects of a series of factors, including the earthquake intensity, site condition, configuration of structure cluster, structural dynamic characteristics and spacing, and is superior to the one using conventional artificial neural network. It is verified by a virtual test that the waveshape and spectral features of the predicted ground motion agree well with the target result with an error of peak acceleration being only 1.23%. The suggested approach has the advantages of better modulation precision and lower sample size requirement. Moreover, it is almost zero cost to use the developed surrogate model to correct the ground motion of urban buildings and to consider the influence of SSCI, and the structural seismic response can be more factually displayed in the time and space domains. These specialties make it a promising technique in the rapid assessment of urban seismic damage. [ABSTRACT FROM AUTHOR]

In the context of performance‐based earthquake engineering (PBEE), response‐history analysis is currently considered an analytical tool for developing fragility curves. Typically, this involves subjecting a structural system to a large number of ground motion records (GMRs) representing seismic hazards at a site of interest and may be a time‐consuming task. To address this computational challenge, this study proposes a method for selecting a representative subset of GMRs that enables the reproduction of the fragility curve of the general GMR set. In this method, dimension reduction techniques are used to preferentially extract the principal features of earthquake intensity measures, which are applied to construct the feature space. Then, the divisive hierarchical clustering technique is applied to the feature space to obtain a subset of GMRs from the general set until the fragility curve converges. The performance of the proposed method is successfully demonstrated through various numerical examples that include a wide class of single‐degree‐of‐freedom systems and two steel‐frame buildings. The results confirm that the seismic hazard at a given site represented by a general GMR set can be covered in structural fragility estimation using a representative subset of GMRs selected based on the proposed method. The proposed method could contribute to significantly reducing the computational costs for structural fragility estimation without compromising the accuracy. [ABSTRACT FROM AUTHOR]

Using results from 57 large‐scale physics‐based fault‐rupture and wave propagation simulations, this research aims to evaluate the seismic risk, loss, and resilience of more than 16,000 reinforced concrete buildings in the Zeytinburnu district of Istanbul, Turkey. For each building and under each earthquake scenario, the spatially varying site‐specific simulated ground motions were used for performing three‐dimensional nonlinear time‐history analyses. The resulting structural responses—such as peak story drift ratios (PSDR) and peak floor accelerations (PFAs)—were utilized to conduct three region‐scale tasks: (i) building‐ and site‐specific seismic fragility analysis for both structural and nonstructural components of each building; (ii) intensity‐based seismic loss assessment using the FEMA P58 methodology and Monte Carlo simulations; and (iii) resilience evaluation based on the expected time of recovery predicted through FEMA P58. Moreover, both inertial and kinematic soil–structure interaction (SSI) effects were considered using a substructuring method for all three tasks. Site‐specific soil properties were utilized to compute the coefficients of soil springs and dashpots, as well as the foundation input motions. The SSI effects were investigated by comparing the fragility, loss, and resilience indices obtained with and without considering SSI. [ABSTRACT FROM AUTHOR]

This paper presents a new hybrid energy dissipation device and investigates experimentally its capability to improve the seismic response of an inherently very flexible structural system: a reinforced concrete waffle‐flat plate structure. The new device combines in parallel within a single device a low‐cost viscoelastic (VE) component and a metallic yielding (MY) component. The device has a gap that prevents deformations on the MY component in the range of displacements caused by wind or low intensity earthquakes, to avoid high‐cycle fatigue damage. The MY component is expected to activate under the design or the maximum credible earthquake, providing the main structure with lateral stiffness, and a reliable and large source of energy dissipation capacity. Six new hybrid energy dissipation devices (energy dissipation system) were installed in a scaled two‐story portion of a prototype RC waffle‐flat plate structure (main structure) designed only for gravity loads, without considering special ductility detailing or capacity design rules for the columns. The VE component of the hybrid energy dissipation devices reduced the translational periods with largest effective modal mass along the horizontal directions X and Y to 60%, and increased the fraction of damping to about 12%. The main structure with the energy dissipation system was subjected to bidirectional shake table tests that represented frequent, design and maximum credible earthquakes. In the tests, the main structure remained basically undamaged under the frequent and the design earthquakes, whereas it suffered minor (reparable) damage under the maximum credible earthquake. The MY component remained undeformed under low intensity earthquakes. [ABSTRACT FROM AUTHOR]

Application of Buckling Restrained Braces (BRBs) with Truss Moment Frames (TMFs) results in a robust seismic force‐resisting system, herein referred to as Buckling Restrained Knee Braced Truss Moment Frame (BRKB‐TMF), which utilizes the advantages of both BRBs and TMFs. Although steel is commonly used to make the core of BRBs, previous studies have demonstrated the efficacy of annealed aluminum as a preferred core material because of its high ductility and high over‐strength. However, the deformation compatibility of the truss members with the aluminum‐core BRB in BRKB‐TMFs at high drifts is not well studied in the literature. Hence, an experimental study is performed on a scaled sub‐assemblage of a BRKB‐TMF frame designed using the Performance‐Based Plastic Design method. Cyclic tests are performed on 1:3 scale models of aluminum‐core BRB and BRKB‐TMF to evaluate their performance at drifts corresponding to Maximum Considered Earthquake intensity. Also, to further compare the performance of steel and aluminum as suitable BRB core materials, cyclic tests are performed on BRBs with steel and aluminum cores designed using a consistent criterion. The experiments demonstrated the superior performance of aluminum core BRB over steel core BRB. The experimental studies on the BRKB‐TMF concluded that per the design intent, the BRB acted like a fuse for the frame by restricting all the inelastic deformations to itself and the study frame could successfully meet the target drift criteria. [ABSTRACT FROM AUTHOR]

Estimates of the earthquake ground motion intensity over a geographical area have multiple uses, that is, emergency management, civil protection and seismic fragility assessment. In particular, with reference to fragility assessment, it is of interest to have estimates of the values of different ground‐motion intensity measures in order to correlate them with the observed damage. To this purpose, the present paper uses a procedure recently proposed in the literature to estimate the ground‐motion intensity for the 2012 Emilia mainshocks, considering different ground motion intensity measures and directionality effects. Ground motion prediction equations based on different site effect models, and spatial correlation models are calibrated for the Emilia earthquakes. The paper discusses the accuracy of the shakemaps obtained using the different soil effect models considered and presents the obtained shakemaps as supplementary material. The procedure presented in the paper is aimed at providing ground motion intensity values for seismic fragility assessment and is not intended as a tool to estimate shakemaps for rapid emergency assessment. [ABSTRACT FROM AUTHOR]

This paper aims to assess the seismic fragility of vehicle‐bridge‐interaction (VBI) systems considering the effects of vehicle types, traffic conditions, and road surface qualities. A stochastic nonlinear mechanical model for the earthquake‐VBI system is developed, and the fragility functions for the proposed VBI model are derived by considering the relevant probabilistic seismic demand parameters. On the basis of a typical four‐span continuous prestressed concrete highway bridge in China, a complete numerical model for the VBI system is built considering multiple uncertainties from bridge and vehicle parameters, as well as the road surface qualities. A total of 120 real ground motion records with different combinations of magnitude‐source‐to‐site distance (M‐R) and earthquake intensity characteristics are selected. Meanwhile, 80 scenarios in terms of different combinations of vehicle types, vehicle speeds, and road surface irregularities are defined. In this context, 96,000 nonlinear time‐history analyses are performed, and the developed fragility models are applied to the VBI system at both component and system levels. Results indicate that the fragilities of pier drift, bearing shear strain, and the overall VBI system increase with the increase of the vehicle weight or the decrease of the vehicle speed, while the vertical deck displacement is dominated by the vehicle weight. It is also found that the road surface quality has a negligible effect on both component and system fragilities. [ABSTRACT FROM AUTHOR]

The interstory drift‐based scaling procedure (IDS) developed recently by the authors for plane frames under single component horizontal ground motions, has been extended to three‐dimensional structures possessing torsional coupling under bi‐axial ground motions which are represented by their geometric mean spectrum. The ground motion‐scaling factor is defined as the ratio of average interstory drift along building height under target spectrum versus that under the associated ground motion spectrum. Hence, scaling is conditioned on structural response, which is in turn a function of seismic intensity. IDS for 3D systems is applied to 20‐story and 3‐story concrete space frames with mass and stiffness eccentricity, respectively. Accuracy and efficiency of the IDS procedure is assessed under a set of near‐fault strong motion pairs from large magnitude events. The results revealed that the proposed procedure is accurate and noticeably more efficient as compared to conventional procedures suggested in seismic codes and in literature. Further, the intensity measure employed in the IDS procedure is proved as a good predictor of fundamental demand measures (maximum interstory drift ratio and maximum plastic rotations) obtained from nonlinear dynamic analyses under individual ground motion pairs. Hence, employing the intensity measure of IDS for ground motion scaling in intensity‐based evaluation of structures is proposed for reliable estimation of structural performance under code‐prescribed seismic hazard. [ABSTRACT FROM AUTHOR]

This paper explores the use of sliding friction dampers (SFDs) as dissipative floor connectors to mitigate higher mode effects and earthquake‐induced absolute acceleration demands on steel concentrically braced frame (CBF) buildings. The dampers connect each floor of the steel CBF system to the diaphragms of the gravity framing system (GFS) and they allow for a relative in‐plane movement between the two systems. For this purpose, a design methodology is first proposed to define the activation forces in the SFDs so as to ensure damage‐free seismic performance in the steel CBF and the diaphragms of the GFS. The efficiency of the design methodology is demonstrated through nonlinear response history analyses on a low‐ and high‐ductility six‐story steel CBF building. The simulation results suggest that (a) the determined activation forces of the SFDs are effective in mitigating higher mode effects and in preventing story drift concentrations regardless if capacity design is employed for the CBF system; (b) the absolute acceleration demands are reduced by approximately 50% relative to those in the rigid diaphragm counterpart. Similar reductions are achieved in the lateral drift demands of the GFS at seismic intensities with return periods of 475 and 2475 years. The reduction in the variability of seismic response, both in terms of absolute floor acceleration demands and story drift ratios (SDRs) in the CBF system, is noteworthy. Limitations as well as suggestions for future work are discussed. [ABSTRACT FROM AUTHOR]

Seismic risk assessment of new and existing structures has a long history, which is based on the development of specific methods for seismic hazard and vulnerability analyses. Performance‐based earthquake engineering is the natural evolution and integration of all these aspects that is nowadays implemented in several precodes. However, some critical aspects are not yet completely clarified. As a matter of fact, the vulnerability analysis suffers the so‐called record‐to‐record variability, which is usually controlled through different parameters used as seismic intensity measures (IMs), whose significance is still under discussion. Moreover, this variability represents an additional source of uncertainty, which is added to the dispersion derived from the ground motion prediction equation (GMPE), leading to an overconservatism. For these reasons, the present paper aims to propose a novel framework for the seismic risk assessment of structures, which is found on the idea to control the response variability in evaluating seismic hazard curves without taking into account the randomness (ε) of the GMPE, which instead is transferred to fragility curves. These latter are built by using groups of accelerograms, whose median and 84% fractile spectra fit well, for different return periods, the uniform hazard spectra for ε= 0 and 1, respectively. For this purpose, a new search algorithm for selecting natural records is formulated. The proposed method offers considerable advantages as it is no longer necessary to refer to a specific IM, and allows to select pairs of spectrum‐compatible natural records, which is enable to solve the problem of the seismic assessment of three‐dimensional structures. The procedure is then applied to assess seismic risk of a typical reinforced concrete frame, whose results demonstrate the robustness of the method and the practical independence from the record set used. [ABSTRACT FROM AUTHOR]

Electrical substations are critical elements of a power grid, enabling the transmission and distribution of electric power from power generators to the end‐users. Experiences from previous earthquakes have shown that electrical substations can be damaged due to ground shaking, reducing their functionality and potentially preventing the generated electric power from reaching end‐users. To assess the seismic vulnerability of a substation, a modular quantitative assessment method is proposed. In this method, the relation between the functionality state of a substation and the damage state of its components was established through the connection matrix technique. A substation is viewed as a network system, whose topology is defined by the connections among various pieces of electrical equipment (i.e., the components), represented in the connection matrix. The maximum allowable power transmission capacity of the substation after an earthquake is adopted as the system functionality metric, which is jointly determined by the power input, transform, and output capacity of the substation. The seismic vulnerability of an electrical substation is quantified by probabilistically calculating its postearthquake functionality when exposed to various earthquake intensities using Monte Carlo sampling. Finally, the risk of substation functionality loss is quantified by integrating the seismic hazard curve with the seismic vulnerability model of the substation. Two realistic case studies on a distribution substation and a transmission substation, with the same equipment configuration but different power delivery paths, were performed using the proposed method. Furthermore, a sensitivity analysis regarding the equipment fragility parameters is conducted, providing a risk‐informed basis for improving the seismic performance of the substation system. [ABSTRACT FROM AUTHOR]

A regional seismic risk assessment requires the estimation of ground‐motion intensities at multiple locations for a given event simultaneously. In this context, the spatial correlation of ground‐motion residuals plays an important role in characterizing the probability distribution of the field of shaking intensities. Over the last 20 years, the spatial correlation of ground‐motions has been widely studied and different models have been developed. In general, these models vary from each other depending on the ground‐motion database used to generate them, on the adopted intensity measure, on the selected ground‐motion model, and on the estimation methods, among others. This paper proposes a spatial correlation model for within‐event residuals of peak ground acceleration and spectral pseudo‐acceleration ordinates in the Chilean subduction zone. Although the database considered for this study has only a few well‐recorded earthquakes, it contains a large number of station pairs sharing several common events. Therefore, we compute non‐stationary correlations between station pairs and then fit a stationary spatial correlation model. Results of this paper are compared with previous models, concluding that, in general, subduction models show higher spatial correlations than those for active shallow crust events for long‐period spectral ordinates. Moreover, no evidence was found for a systematic effect of earthquake magnitude or site conditions on spatial correlation. Finally, the proposed model is compared with a model obtained assuming stationarity in spatial correlations, showing more reliable estimates when using the proposed model. [ABSTRACT FROM AUTHOR]

Steel moment resisting frames (MRFs) are drift‐sensitive structures and their design is largely influenced by code requirements to limit the lateral displacements and to control the second order effects. Current and next generation of Eurocode 8 recommend different rules to verify the lateral rigidity and resistance of steel MRFs that lead to structures that are substantially different in terms of size of members and overall performance. In order to investigate the influence of the design rules on the seismic behaviour of ductile steel MRFs a parametric numerical study was carried out on 48 structures designed according to Eurocodes as well as US codes, the latter analysed as benchmark, varying the number of storeys, moment resisting spans and seismic intensity. The results of non‐linear static and dynamic analyses show that the structures complaint with current Eurocode 8 are the most expensive and characterised by the greater lateral rigidity and resistance, while MRFs designed in accordance with ASCE7 rules have the smaller profiles and the lower overstrength. The frames designed with rules of the latest version of next generation of Eurocode 8 have an intermediate behaviour even if closer to ASCE7‐compliant structures. These results are also confirmed by the probability of collapse that is smaller than the minimum value specified by EN1990 for the considered consequence class of the examined buildings. [ABSTRACT FROM AUTHOR]

The evaluation of a bridge's structural damage state following a seismic event and the decision on whether or not to open it to traffic under the threat of aftershocks (ASs) can significantly benefit from information about the mainshock (MS) earthquake's intensity at the site, the bridge's structural response, and the resulting damage experienced by critical structural components. This paper illustrates a Bayesian network (BN)‐based probabilistic framework for updating the AS risk of bridges, allowing integration of such information to reduce the uncertainty in evaluating the risk of bridge failure. Specifically, a BN is developed for describing the probabilistic relationship among various random variables (e.g., earthquake‐induced ground‐motion intensity, bridge response parameters, seismic damage, etc.) involved in the seismic damage assessment. This configuration allows users to leverage data observations from seismic stations, structural health monitoring (SHM) sensors and visual inspections (VIs). The framework is applied to a hypothetical bridge in Central Italy exposed to earthquake sequences. The uncertainty reduction in the estimate of the AS damage risk is evaluated by utilising various sources of information. It is shown that the information from accelerometers and VIs can significantly impact bridge damage estimates, thus affecting decision‐making under the threat of future ASs. [ABSTRACT FROM AUTHOR]

This paper is motivated by the renewed interest in space exploration and the need to provide structurally sound and resource‐efficient shielding solutions for valuable assets and future habitable modules. We present, implement and test a methodology for the preliminary design and assessment of optimal arch forms subjected to self‐weight as well as seismically induced loads. The numerical framework, built around a limit thrust‐line analysis, previously published by the authors, is summarized first. This is followed by a detailed account of the form‐finding algorithm for arches of variable thickness. Special attention is placed on the physical feasibility of our assumptions and the justification of the engineering inputs adopted. The newly form‐found arches achieve material efficiencies between 10% and 50% in comparison with their constant minimum‐thickness circular or elliptical counterparts, depending on the relative intensity of the seismic action. The influence of the initial input geometry and the stabilising presence of additional shielding material against extreme radiation are also evaluated with emphasis on the effects of low‐gravity conditions. Finally, a case study is presented and Discrete Element Models of constant and varying thickness arches (VTAs) are assessed under a set of representative ground‐motions on a lunar setting. The significant over‐conservatism of constant thickness arches (CTAs) is made manifest and potential improvements of the optimally found arch shape are highlighted. Although developed with extraterrestrial applications in mind, the results and methods we present herein are also applicable to terrestrial conditions when material efficiency is of utmost concern. [ABSTRACT FROM AUTHOR]

Rapid urban growth has been paired with a rapid increase in the demand for high‐rise buildings, and has accelerated the need for developing more resilient high‐rise buildings in earthquake‐prone regions. Current best practices for the seismic design of high‐rise buildings follow a performance‐based design approach that allows the designer to use innovative structural systems, select performance objectives, and verify seismic performances targeted at multiple levels of seismic intensity. As shortcomings in conventional code‐designed high‐rise buildings continue to be revealed by strong earthquakes, the importance of more resilient high‐rise systems is increasingly evident. Several high‐performance systems have been proposed to limit the excessive seismic demands attributed to higher‐mode effects in high‐rise buildings. However, these systems still face design challenges associated with distributed damage and residual deformations. This paper proposes a novel self‐centering base mechanism for high‐rise buildings that independently limits both shear forces and overturning moments at the base to mitigate higher‐mode effects, while eliminating residual deformations and controlling concentrated stresses within the structure that otherwise would need to be designed for. The schematic overview of the proposed system is first introduced, followed by the detailed design of a physical embodiment developed based on a reference 42‐story RC core wall building. Results of a numerical case‐study comparison confirm that an enhanced seismic performance is achieved through the proposed system with minimum damage and negligible residual deformations even following major seismic loading. The proposed system, with further investigations, also has the potential to be applied to a wider range of structural systems. [ABSTRACT FROM AUTHOR]

In recent years, significant advancements have been made in the definition of innovative "minimal‐damage structures," chasing the need for more resilient societies against extreme seismic events. In this context, moment resisting frames (MRFs) equipped with self‐centering damage‐free (SCDF) devices in column bases and beam‐to‐column joints represent a viable solution to improve structural resilience and damage reduction. However, the extensive use of these devices significantly increases complexity and costs compared to conventional structures, thus limiting their practical application. To overcome this drawback, current research works are focusing on the definition of effective placement for SCDF devices, maximizing their beneficial effect on the seismic response and controlling their impact on the overall structural complexity. Within this context, the present study investigates the influence of the placement of SCDF devices in a steel MRF. An eight‐story MRF is designed, and 50 configurations with different locations of SCDF joints are considered. Numerical models are developed in OpenSees, and non‐linear static push–pull and incremental dynamic analyses (IDAs) are carried out. The influence of the placement of SCDF devices is assessed by considering residual and peak interstory drifts, residual top story drifts, peak story accelerations, and the total dissipated energy as performance parameters. The results of IDAs for a seismic intensity corresponding to the ultimate limit state (ULS) are analyzed and compared, and fragility curves are successively derived for some relevant configurations. The paper provides insights and observations to understand how including a different number of SCDF BCJs at different stories affects the seismic response. [ABSTRACT FROM AUTHOR]

The paper investigates the problem of Soil‐Foundation‐Structure Interaction (SFSI) for buildings supported on piles through the comparative analysis between the fixed base and the compliant base assumptions. The structure, a nine‐storey residential building (with or without infills), is modelled in non‐linear regime while the piled foundation is idealized by means of independent lumped parameters models, either linear or non‐linear. In this last case, the soil‐foundation system is replaced by an assembly of viscous‐dampers, fictitious masses and non‐linear springs modelled according to the classical Bouc‐Wen formulation, so as to account for the hysteretic behaviour of the foundation. A detailed calibration procedure for both linear and non‐linear foundation models is also presented and discussed. Two different natural soil deposits are considered, a pyroclastic deposit and a deep layer of lacustrine clay. The results undertaken in the context of a probabilistic analysis show that SFSI may lead to a significant reduction of the seismic demand in infilled buildings at low and intermediate earthquake intensity levels. Conversely, at higher intensity earthquakes the seismic demand is not affected by the non‐linear springs. It is shown that a proper modelling of radiation mechanism at foundation level is crucial for a reliable and sustainable prediction of SFSI effects. [ABSTRACT FROM AUTHOR]

This paper proposes surrogate models (or metamodels) mapping the parameters controlling the dynamic behaviour of inelastic single‐degree‐of‐freedom (SDoF) systems (i.e., force‐displacement capacity curve, hysteretic behaviour) and the parameters of their probabilistic seismic demand model (PSDM, i.e., conditional distribution of an engineering demand parameter [EDP] given a ground‐motion intensity measure [IM]). These metamodels allow the rapid derivation of fragility curves of SDoF representation of structures. Gaussian Process (GP) regression is selected as the metamodelling approach because of their flexibility in implementation, the resulting accuracy and computational efficiency. The metamodel training dataset includes 10,000 SDoF systems analysed via cloud‐based non‐linear time‐history analysis (NLTHA) using recorded ground motions. The proposed GP regressions are tested in predicting the PSDM of both the SDoF database (through ten‐fold cross validation) and eight realistic reinforced concrete (RC) frames, benchmarking the results against NLTHA. An application is conducted to propagate such modelling uncertainty to both fragility and vulnerability/loss estimations. Error levels are deemed satisfactory for practical applications, especially considering the low required modelling effort and analysis time. Regarding single‐building applications enabled by the proposed metamodel, this paper presents a first attempt at a direct loss‐based design procedure, which allows setting a target loss level for the designed structure (shown for a realistic RC frame). An earthquake risk model involving dynamic exposure and vulnerability modules is illustrated as an example of building portfolio applications. Specifically, the proposed application considers a retrofit‐based seismic risk‐reduction policy for a synthetic building portfolio, for which it is possible estimating the loss evolution over time. [ABSTRACT FROM AUTHOR]

A novel amplitude scaling procedure is proposed in this study where the ground motion scaling factors are defined as the ratio of interstory drift distributions under target spectrum versus under the associated ground motion spectrum. The advantage of employing interstory drift ratio in ground motion scaling, compared to employing spectral intensity directly, is that it provides a strong theoretical link between the target spectrum intensity and the fundamental dynamic characteristics of the structure. Hence, scaling is conditioned on structural response, which is in turn a function of seismic intensity. The interstory drift‐based scaling procedure (IDS) is presented herein for planar frames for brevity. Accuracy and efficiency of the IDS procedure is assessed under a set of near fault strong motions from large magnitude events. The results revealed that the proposed procedure is accurate since the resulting bias in estimating linear elastic interstory drifts is negligibly small. Further, it is noticeably more effective as compared to the conventional procedures suggested in recent seismic codes, yet it is simpler. [ABSTRACT FROM AUTHOR]

This study aims to assess, in a probabilistic manner, the effect of seismic excitation direction on the performance of a 638 m‐long, 12 span prestressed concrete bridge with significant curvature in plan on the basis of overall monetary repair loss. By means of a large number of nonlinear dynamic analyses, the optimum intensity measure (IM) was selected from a pool of twenty candidates considering the impact of seismic excitation direction. Next, the variability of bridge loss with respect to the seismic incidence angle under different groups of earthquake intensities was obtained. Finally, the applicability of combination rules for the seismic performance of curved bridges was evaluated based on the multidirectional loss assessment results. Meanwhile, the effects of seismic excitation direction and earthquake intensity on the evaluation of combination rules were also revealed. Results indicate that velocity‐related or/and structural‐dependent IMs are more appropriate for the probabilistic seismic demand analysis of curved bridges. It is also notable that the total bridge loss gradually turns out to be independent of the seismic excitation direction as the seismic intensity increases and the damage develops throughout the structure. Additionally, the widely used 100/30 and 100/40 rules may lead to an unconservative estimation for the loss of the curved bridge. The above findings highlight the necessity of addressing the issue of ground motion directionality in a rigorous probabilistic manner and pave the way for further research on qualifying the influences of geometric configuration, material parameters, soil type and the consequent soil‐structure interaction effect. [ABSTRACT FROM AUTHOR]

Rocking podium structures (RPSs) refer to a wide class of structural systems in which the base storey consisting of freestanding columns that can uplift during seismic excitations. Due to the rocking response, the base storey can be considered as a base isolation system on the condition that a rocking overturn is prevented. In the present study, the seismic response of RPSs is assessed within a probabilistic framework. For this purpose, synthetic pulse‐like acceleration records are generated. The performance of several ground motion intensity measures in predicting the rocking response of RPSs with different superstructure's fundamental period, lateral displacement profiles and rocking column configuration are examined. The effect of these structural parameters on the rocking response is evaluated in terms of seismic fragility. Finally, the seismic behaviour of the rocking storey, as a seismic isolation technique, is evaluated by examining both the rocking stability and the seismic demand reduction of the superstructure simultaneously. [ABSTRACT FROM AUTHOR]

In performance‐based earthquake wngineering, record selection comes into play at the interface of seismic hazard and structural analysis aiming to repair any loss of essential seismological dependencies caused by the choice of an insufficient intensity measure to be used for structural response prediction. Site‐specific selection is best exemplified by the prominent conditional spectrum (CS) approach that attempts to ensure a hazard‐consistent response prediction by involving site hazard disaggregation. Specifically, CS utilizes a target spectrum (with mean and dispersion) that, in its latest formulation, accounts for all the scenarios (in terms of magnitude, M, and closest to rupture distance, R) contributing to the hazard of the site at a given intensity level. The ground motion records, however, are selected to match this target spectrum–based solely on their spectral shape but with no explicit consideration to their underlying M‐R characteristics. The main focus of this study is to explore whether the reintroduction of M‐R criteria in the selection process preserves hidden dependencies that may otherwise be lost through a spectral‐shape‐only proxy. The proposed record selection method, termed CS‐MR, offers a simple approach to maintain a higher order of hazard consistency able to indirectly account for metrics that depend on M‐R (e.g., duration, Arias intensity) but are not captured in the response spectra. Herein the CS‐MR response prediction is favorably compared to CS and to the generalized conditional intensity measure methods that select records according to, respectively, spectral shape only and, for the case at hand, to spectral shape plus duration. [ABSTRACT FROM AUTHOR]

The study analyzes the influence of double concave friction pendulum (DCFP) isolator properties on the seismic performance of isolated multispan continuous deck bridges. The behavior of these systems is analyzed by employing an eight‐degree‐of‐freedom model accounting for the pier flexibility in addition to the rigid presence of both abutment and deck, whereas the DCFP isolator behavior is described combining two single FP devices in series. The uncertainty in the seismic input is taken into account by considering a set of nonfrequent natural records with different characteristics. The variation of the statistics of the response parameters relevant to the seismic performance of the isolated bridges is investigated through the proposal of a nondimensionalization of the motion equations, with respect to the seismic intensity, within an extensive parametric study carried out for different isolator and bridge properties. Moreover, two cases related to different ratios between the sliding friction coefficients of the two surfaces of the DCFP devices are analyzed with the aim also to evaluate the corresponding optimal values able to minimize the seismic demand to the pier. In this way, all the presented nondimensional results are useful for the preliminary design or retrofit of multispan continuous deck bridges, isolated with DCFP devices, located in any site and in relation, especially, to the seismic ultimate limit states. [ABSTRACT FROM AUTHOR]

Post‐earthquake damage reports have continuously highlighted the significant vulnerability of nonstructural elements to seismic events. Nonstructural damage has severe impact in the building recovery, increasing the socioeconomic losses even for low intensity events. In the last few years, research efforts have focused on the development of innovative nonstructural solutions, to be combined with damage‐resistant structural skeletons in order to obtain an overall high‐performance building. As part of a European Union (EU)‐funded project, the effectiveness of such integrated skeleton&envelope low‐damage system in reducing the earthquake related losses was investigated. Tridimensional shake table tests on a 1:2 scaled timber‐concrete low‐damage structural skeleton, "dressed" by different innovative nonstructural elements (glass/concrete facades, gypsum/masonry partitions), were performed at the National Laboratory for Civil Engineering (LNEC) in Lisbon, Portugal. The shake table tests were carried out at increasing seismic intensities to investigate the structural and nonstructural performance up to a higher‐than Collapse Prevention Limit State according to the Italian Code (975 years return period). This paper focuses on the dynamic behavior of nonstructural elements with detailed discussion on construction detailing, seismic demand and performance of the innovative solutions. The high performance of nonstructural elements proved the potential of the details introduced in the partitions/facades. Minimal or no damage was observed up to the end of the overall testing sequence, which reached moderate‐to‐high interstory drift ratios (more than 1.00%) ‐ typically expected to cause severe damage to traditional nonstructural partitions/infills/facades. [ABSTRACT FROM AUTHOR]

One of the main tasks in performance‐based seismic risk assessment and design of structures is the quantification of uncertainty due to earthquake ground motion (GM) records. Therefore, there is an optimal suite of GMs for each structure, selection of which can be an elusive task complicated by—among other things—the fact that structural behavior migrates into load‐path‐dependent inelastic regimes as damage begins to accumulate. To facilitate the selection of an optimal GM suite, the GM selection based on a generalized conditional single‐intensity‐measure approach will be enhanced herein to allow users to select GMs based on two and average of more‐than‐two conditioning intensity measures. To formulate this task, an intensity measure vector consisting of several intensity measures will be populated to represent earthquake's amplitude‐, duration‐based, and cumulative characteristics. The idea of two and average conditioning intensity measures will then be formulated by considering the correlation between the intensity measures in the vector with two and average of more‐than‐two intensity measures, simultaneously. The cross‐correlation between the intensity measures in the vector will also be considered to ultimately form a conditional multivariate distribution from which one could draw any number of realization samples to find matching earthquake records so that the hazard consistency concept can be fully enforced. [ABSTRACT FROM AUTHOR]

In performance‐based earthquake engineering, the suitability of an intensity measure (IM) is expressed through its efficiency and sufficiency. An efficient IM leads to a small record‐to‐record variability in the estimation of demand given seismic intensity. A sufficient IM is one that renders the estimation of demand for all intensity levels independent of all other ground motion parameters. Given that establishing sufficiency is not a trivial task, the relative sufficiency measure (RSM) has been proposed previously based on information theory concepts. RSM can be employed for quantifying the relative sufficiency of an IM with respect to another IM by the amount of extra information that it relays on average about the ground motion for the estimation of a demand parameter of interest. RSM has been so far conditioned on a linear logarithmic regression probability model, better known as the Cloud Analysis (CA), which relies on unscaled ground‐motion records. This work lays out the methodology for estimating both the efficiency and RSM in terms of the damage measure directly (instead of demand parameter) and by employing alternative nonlinear dynamic analysis procedures (NDAPs), such as, a modified version of CA that considers the collapse‐cases explicitly and the incremental dynamic analysis. It is demonstrated that the RSM can be sensitive to the NDAP employed, while it does not demonstrate significant sensitivity to the limit state of interest. An alternative measure of efficiency (known in literature as proficiency), directly measured as the dispersion in the fragility curve, shows more sensitivity to the limit state. [ABSTRACT FROM AUTHOR]

Simplified seismic assessment procedures relying on displacement‐based formulations have recently been implemented for the evaluation of the seismic performance in buildings and bridges. For bridges, displacement‐based assessment procedures have been formulated to predict the displacement response at several performance levels defined based on the expected damage on the structural elements. These displacement profiles have been subsequently used to estimate the performance level achieved under a given seismic hazard intensity and to develop damage fragility curves. For buildings, these concepts have been extended to compute economic losses in agreement with current performance‐based earthquake engineering procedures. In this study, existing displacement‐based formulations for the approximate seismic assessment of single‐column multi‐span continuous RC bridges, with non‐sacrificial shear keys for the pier‐to‐deck connections, are extended for the computation of expected annual losses under transverse direction excitation. Additionally, an iterative response spectrum analysis procedure, which directly considers higher mode effects, is proposed for computing the displacement response, and these results are also used to estimate direct expected annual losses. Results show that both procedures tend to compute higher losses when compared with those obtained with a fully probabilistic loss assessment framework, using demand estimations computed with nonlinear response history analysis. Results also show that the simplified loss assessment procedure is highly sensitive to the definition of the collapse fragility curve. [ABSTRACT FROM AUTHOR]

A framework to derive state‐dependent fragility relationships of structures subjected to ground‐motion sequences (e.g. mainshock‐aftershock (MS‐AS) or triggered earthquakes) is proposed. The hysteretic energy dissipated in the sequence is adopted as the main demand parameter, as it is a cumulative measure monotonically increasing with the length of the excitation. For a structure subjected to earthquake‐induced ground motions, it is not possible to define a closed‐form representation of the hysteretic energy as a function of the peak deformation. However, based on theoretical considerations, the hysteretic energy‐peak deformation trend is discussed, highlighting that (a) the significant duration of the ground motion explains the variability of the hysteretic energy for a given peak deformation; (b) the hysteretic energy dissipated in an AS decreases (for a given AS peak displacement) if the peak displacement in the MS increases. A vector‐valued probabilistic seismic demand model consistent with these considerations is proposed in the form of a surface relating the hysteretic energy in the sequence to the peak deformation in the MS and a ground‐motion intensity measure of the AS. This is calibrated via sequential cloud‐based time‐history analyses. The framework is demonstrated for 14 reinforced concrete frame buildings with different height, plastic mechanisms, and infill distributions. The results show the feasibility of the proposed approach, effectively capturing damage accumulation without inconsistencies in the obtained statistical model. The framework may be used for risk‐assessment applications explicitly incorporating ground‐motion sequences. The hysteretic energy versus peak deformation relationship may also be exploited in problems involving long‐duration ground motions or soft soils. [ABSTRACT FROM AUTHOR]

Summary: Studies of recorded ground motions and simulations have shown that deep sedimentary basins can greatly increase the intensity of earthquake ground motions within a period range of approximately 1–4 s, but the economic impacts of basin effects are uncertain. This paper estimates key economic indicators of seismic performance, expressed in terms of earthquake‐induced repair costs, using empirical and simulated seismic hazard characterizations that account for the effects of basins. The methodology used is general, but the estimates are made for a series of eight‐ to 24‐story residential reinforced concrete shear wall archetype buildings in Seattle, WA, whose design neglects basin effects. All buildings are designed to comply with code‐minimum requirements (i.e., reference archetypes), as well as a series of design enhancements, which include (a) increasing design forces, (b) decreasing drift limits, and (c) a combination of these strategies. As an additional reference point, a performance‐based design is also assessed. The performance of the archetype buildings is evaluated for the seismic hazard level in Seattle according to the 2018 National Seismic Hazard Model (2018 NSHM), which explicitly considers basin effects. Inclusion of basin effects results in an average threefold increase in annualized losses for all archetypes. Incorporating physics‐based ground motion simulations to represent the large‐magnitude Cascadia subduction interface earthquake contribution to the hazard results in a further increase of 22% relative to the 2018 NSHM. The most effective of the design strategies considered combines a 25% increase in strength with a reduction in drift limits to 1.5%. [ABSTRACT FROM AUTHOR]

Summary: Ground shaking intensity varies spatially in earthquakes, and many studies have estimated correlations of intensity from past earthquake data. This paper presents a framework for quantifying uncertainty in the estimation of correlations and true variability in correlations from earthquake to earthquake. A procedure for evaluating estimation uncertainty is proposed and used to evaluate several methods that have been used in past studies to estimate correlations. The results indicate that a weighted least squares algorithm is most effective in estimating spatial correlation models and that earthquakes with at least 100 recordings are needed to produce informative earthquake‐specific estimates of spatial correlations. The proposed procedure is also used to distinguish between estimation uncertainty and the true variability in model parameters that exist in a given data set. The estimation uncertainty is seen to vary between well‐recorded and poorly recorded earthquakes, whereas the true variability is more stable. [ABSTRACT FROM AUTHOR]

Summary: This study investigates the correlation properties of integral ground‐motion intensity measures (IMs) from Italian strong‐motion records. The considered integral IMs include 5–95% significant duration, Housner intensity, cumulative absolute velocity, and Arias intensity. Both IM spatial correlation and the correlation between different integral and amplitude‐based IMs (i.e., cross‐IM correlation) are addressed in this study. To this aim, a new Italian ground‐motion model (GMM) with spatial correlation for integral IMs is first introduced. Based on the newly developed GMM, the empirical correlation coefficients from interevent and intraevent residuals are investigated and various analytical correlation models between integral IMs and amplitude‐based IMs are proposed. The effective range parameter representing spatial correlation properties and the trend in the cross‐IM correlations are compared with existing models in the literature. The variability of the effective range parameters with respect to event‐specific features is also discussed. Modeling ground‐motion spatial and cross‐IM correlations is an important step in seismic hazard and risk assessment of spatially distributed systems. Investigating region‐specific correlation properties based on Italian strong‐motion records is of special interest as several correlation models have been developed based on global datasets, often lacking earthquakes in extensional regions such as Italy. [ABSTRACT FROM AUTHOR]