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A soil–foundation–structure system (SFSS) often exhibits different responses compared to a fixed-base structure when subjected to earthquake ground motion. Both kinematic and inertial soil–foundation–structure interactions can significantly influence the structural performance of buildings. Numerous parameters within an SFSS affect its overall response, introducing inherent uncertainty into the solution. Performing time history analyses, even for a linear elastic coupled SFSS, requires considerable computational effort. To reduce the computational cost without compromising accuracy, the use of the Latin Hypercube Sampling (LHS) technique is proposed herein. Sampling techniques are rarely employed in soil–foundation–structure interaction analyses, yet they are highly beneficial. These methodologies allow analyses determined by sampling to be conducted using commercial codes designed for deterministic analyses, without requiring any modifications. The advantage is that the number of analyses determined by the sampling size is significantly reduced as compared to considering all combinations of input parameters. After identifying the important samples, one can evaluate the seismic demand of selected soil–foundation–bridge pier systems using finite element numerical software. This paper indicates that LHS reduces computational effort by 60%, whereas structural response components (translation, rocking) show distinct trends for different systems. [ABSTRACT FROM AUTHOR]

A shake table test using a full-scale 2-story steel moment frame was conducted to investigate the peak floor acceleration (PFA) and the peak component acceleration (PCA), which directly affect the seismic demand on nonstructural elements. The main focus of this study was to evaluate the effects of structural and component nonlinearity on the nonstructural seismic demand. The PFA reduction suggested by ASCE 7-22 to account for structural nonlinearity was shown to be larger than the experimental results for low-to-moderate ductility levels. The analysis on the resonant PCA showed the importance of structural nonlinearity on the elastic CAR (=PCA/PFA). The high resonant PCA around the fundamental period of the elastic test frame (7 times PFA) was effectively decreased as the test frame experienced a moderate level of ductility; PCA was lowered by 36% and 25% on the 2nd and roof floors, respectively. The effect of component yielding on the PCA was evaluated based on the test results of steel racks mounted on flexible and rigid access floors. The PCA reduction depending on the component ductility level was less than the relevant provisions of ASCE 7-22, and the reason was discussed from the perspective of the pinched hysteretic behavior of the tested specimens. [ABSTRACT FROM AUTHOR]

Non-structural elements play a crucial role in the overall seismic performance of buildings, as has been largely demonstrated in recent earthquakes that have stuck densely populated regions. Therefore, the development of performance-based seismic design and assessment methodologies for non-structural elements is becoming an important research topic within earthquake engineering. A crucial aspect in such methodologies is the accurate prediction of the seismic demands acting on non-structural elements in terms of consistent absolute acceleration and relative displacement floor response spectra for the most common types of structural seismic force resisting systems. Masonry-infilled reinforced concrete frames are one of the most common building typologies in high seismicity regions, such as the Mediterranean region. This study proposes a simplified procedure to estimate consistent absolute acceleration and relative displacement floor response spectra in masonry-infilled reinforced concrete frames based on an existing methodology to estimate consistent floor response spectra in bare reinforced concrete frames. Nine archetype masonry-infilled reinforced concrete buildings with different numbers of storeys and arranged with three masonry infill typologies were considered as case-study archetypes, and were used to validate the proposed methodology using nonlinear time history analyses. The proposed procedure can accurately estimate consistent absolute acceleration and relative displacement floor response spectra for masonry-infilled reinforced concrete buildings that respond both in the elastic and nonlinear ranges for all the non-structural period range. The estimates of floor response spectra given by the proposed procedure are fully consistent with the well-known pseudo-spectral relationship for the entire non-structural period range. [ABSTRACT FROM AUTHOR]

The steel in reinforced concrete (RC) members that form plastic hinges must possess sufficient strain capacity to dissipate seismic deformation demands. Unfortunately, there is limited information on the seismic strain demands of bridge column plastic hinges. Instead, designers rely on a perception of cyclic strain capacity that is an approximate rule of thumb. A standard methodology needs to be established for quantifying the strain demand on these structural members as a function of the expected seismic hazard. To develop this methodology, 1944 columns were analyzed with nonlinear time-history analyses (NLTHAs) using ground motions from a range of earthquakes. This study evaluates the strain demand on RC bridge columns by defining the relationship between the strain demand and earthquake intensity. The results of the model are defined in terms of the peak tensile strain of the reinforcing bar, ε t . The earthquake intensity with the highest correlation to the ε t was determined to be the elastic spectral displacement at the optimal period ( S de (T opt)), which is defined as 75% of the effective period. The relationship between ε t and S de (T opt) can be used to predict the strain demand for an RC bridge column at a given geographic location. Results are presented as a probability density function (PDF), representing strain demand, compared to a PDF of the column capacity. The intersection of the capacity curve and demand curve represents the maximum acceptable strain given as a function of S de (T opt). This methodology can help understand the demand placed on a structural system given a region's seismicity. [ABSTRACT FROM AUTHOR]

The endurance time (ET) method is an effective dynamic analysis method for seismic response analysis of structures. It has been recently used for analytical fragility analysis. However, the available ET-based fragility analysis methods have two limitations: 1) the prediction error of the structural median responses estimated by the ET method is ignored; and 2) the record-to-record variability inherent earthquake ground motions is not well considered. To overcome the above limitations, another ET-based fragility analysis method is proposed, where only three times of ET nonlinear analyses are required. To do this, three specific endurance time excitation functions (ETEFs) are generated in correspondence to the mean and 16% and 84% percentile of response spectra of a selected suite of ground motion records (i.e. ${\rm{ ETE}}{{\rm{F}}_m}$ ETE F m , ${\rm{ETE}}{{\rm{F}}_{v1}}{\rm{ }}$ ETE F v 1 and ${\rm{ETE}}{{\rm{F}}_{v2}}$ ETE F v 2 , respectively). The structural response under ${\rm{ ETE}}{{\rm{F}}_m}$ ETE F m is used to estimate the median response of structures under the selected suite of ground motion. Moreover, the structural responses under ${\rm{ETE}}{{\rm{F}}_{v1}}{\rm{ }}$ ETE F v 1 and ${\rm{ ETE}}{{\rm{F}}_{v2}}{\rm{ }}$ ETE F v 2 are used to quantify the record-to-record variability in earthquake ground motions. The fragility relationships are developed by both point and interval estimate methods since another logarithmic standard deviation is introduced to account for the difference between the median responses predicted using ${\rm{ ETE}}{{\rm{F}}_m}$ ETE F m and those predicted by the dynamic analysis. To validate the proposed method, two RC frame structures with six and nine stories are taken as the study cases. The fragility results based on the proposed ET-based method and those based on the cloud method are compared. It is found that the proposed ET-based fragility analysis method could generate reliable fragility estimation, whereas requiring limited computation cost. The proposed method would provide another simplified way for the rapid fragility assessment of structures. [ABSTRACT FROM AUTHOR]

The static nonlinear analysis has been developed for a reinforced concrete building to study the flexocompression behaviour of the shear walls and estimate the damage beginning when the structures reach the limit state defined in ACHISINA performance-based seismic design document. A refined fiber model has been incorporated throughout the entire height of the building considering the confined behaviour of the concrete from the detailing of the structural elements. A stiff diaphragm has been considered in the structure to model the behaviour of the reinforced concrete slab. The N2 method has been implemented considering a seismic demand in acceleration displacement format based on the displacement spectrum establish in the DS61, enacted after the Mw = 8.8 Maule Earthquake in 2010. Regarding this result, it is concluded that the building obtains an immediate occupancy performance level for drifts close to 5' in the symmetrical Y direction, a greater amount of structural damage, proportional to a life safety performance level, is observed. [ABSTRACT FROM AUTHOR]

A key component of infrastructure seismic risk assessment is the execution of nonlinear time-history analyses with a suite of selected ground motions scaled to site-specific spectra. When interested in the evaluation of distributed systems residing near major active faults, such an approach is challenged by the scarcity of records adequately incorporating region and site-specific features known to impact the nonlinear response of distributed infrastructure substantially (pulses, spectral shape, spatial variability). This paper assesses the differences in the seismic demand posed to a suspension bridge as obtained from real ground motions selected based on state-of-the-art methods and arrays of site-specific simulated ground motions generated from physics-based wave-propagation models. The objective is to characterize the biases in structural response estimates introduced by the use of real ground motions in code-compliant approaches. A total of 15 realizations of an M7 Hayward fault earthquake and a detailed nonlinear simulation model representative of the West San Francisco–Oakland Bay Bridge are utilized as a case study. Damage limit states associated with structural drifts are defined for each bridge component as a function of the spread of plasticity. The results indicate that the median and variability of the demands posed by the simulated motions and real ground motions scaled to the same site-specific spectra are markedly different. Evidence from this study highlights the sensitivity of complex structures to multiple characteristics of the ground motions that might be biased by current scaling methods. Finally, fundamental characteristics of the scaled records leading to differences in the bridge response are discussed providing the basis to inform current ground motion selection and scaling procedures. [ABSTRACT FROM AUTHOR]

This study employs a non-linear static analysis, known as pushover analysis, to explore the flexural-compressive behavior of complex shear walls within a reinforced concrete (R.C.) structure, adhering to contemporary design standards in Chile. The primary objective is to assess the initiation of damage as the building approaches the limit states outlined in Achisina's seminal "Performance Based Seismic Design" framework. To achieve this, a sophisticated fiber model, accounting for the confined behavior of concrete derived from the structural elements' detailing, has been uniformly integrated across the building's entire height. Furthermore, the analysis incorporates a rigid diaphragm to simulate the R.C. slab's response accurately. The study implements the N2 method, adjusting for seismic demands in an acceleration-displacement format, which leverages the displacement spectrum defined by Supreme Decree 61, a legislative response to the 8.8 Mw Maule earthquake in 2010. The findings reveal that the analyzed structure meets the immediate occupancy performance level with drifts nearing 5‰ in the symmetrical Y direction. This outcome aligns with prior assessments of Chilean R.C. wall buildings. However, in the asymmetric X direction, the structure exhibits a higher degree of structural damage, aligning with a life safety performance level. This differentiation underscores the critical need for nuanced understanding and modeling of structural behavior under seismic loads, contributing to the ongoing refinement of seismic design practices and standards. [ABSTRACT FROM AUTHOR]

This paper develops the probabilistic seismic demand models of circular tunnels under the transversal seismic load. The uncertainties of ground motion, soil profile, tunnel depth, and lining size are considered. Since the quasi-static analyses may significantly underestimate the seismic responses of tunnels, the results of dynamic numerical analyses are adopted to construct probabilistic models that are more accurate. The constructed model is unbiased and can facilitate the fragility analysis of tunnels. As a demonstration, the proposed probabilistic models are used to estimate the seismic fragility curves of a particular tunnel. [ABSTRACT FROM AUTHOR]

Recent research showed that the damage in non‐structural components significantly affects the seismic behaviour of structures, indeed it is crucial to evaluate the seismic behaviour of non‐structural components. For this purpose, the University of Naples "Federico II" started a cooperation with the Hilti Corporation, to evaluate the seismic demand on fasteners connecting drywalls to supporting elements. In particular, the seismic displacement demand on Power Actuated Fasteners (PAF) was obtained through quasi‐static in‐plane cyclic tests on full‐scale drywall partitions. Test specimens consisted of 2285 mm long and 2600 mm high partition walls and in total seven tests were carried‐out at the Lab of the Department of Structures for Engineering and Architecture. A specific test set‐up was developed for the experimental tests and the optimal instrumentation layout was studied to allow to capture the significant measurements on PAFs. A FEMA 461 protocol was employed for all the tests. The paper summarizes the experimental program, describing wall configurations, test set‐up, loading protocol and instrumentation layout. A special focus is dedicated to the comments of experimental results. [ABSTRACT FROM AUTHOR]

This article presents a numerical study on the influence of the anchorage shear hysteresis on the seismic response of nonstructural components (NSC) connected to multi-storey reinforced concrete (RC) buildings, and of the anchorage itself. To cover a variety of different types of shear hysteresis shapes, this contribution considered the experimental results obtained for five types of post-installed anchors. The results were used for calibrating the hysteresis model of the anchorage connecting an ideal NSC with rigid fixture and a 12-storey RC building host-structure. Using a suit of 40 earthquake records and assuming a single NSC at each storey level anchored by a single fastener, a series of non-linear dynamic analyses of the structure-fastener-nonstructural system was carried out. The results showed significant differences in terms of maximum acceleration and force of the NSC and anchorage, respectively, depending on the type of anchor. These seismic demands were sometimes larger than those required by the reviewed code provisions for rigid NSC, but also for the most restrictive code-case for flexible NSC. The results presented different amounts of scatter, mostly related to the size of the annular gap and of the loading stiffness of the anchorage. It is shown that the maximum force achieved by the anchorage is directly related to the peak relative velocity of the NSC within the gap region. It was concluded that the shape of the shear hysteresis of the anchorage highly influences the response of the NSC and the anchor itself and should not be neglected in practice. [ABSTRACT FROM AUTHOR]

Several aftershocks can occur after a strong mainshock and lead to additional structural damage. The investigation of the seismic response of bridges is more challenging when the effects of incident angles of mainshocks and subsequent aftershocks are considered. This study investigates the effects of the ground motion incident angle on the nonlinear structural responses of skewed bridge structures against mainshock–aftershock sequences. For this objective, the seismic performance of a 60° skewed bridge located in San Fernando, California, is examined under real bidirectional mainshock–aftershock sequences. In this study, ground motion directionality effects were investigated considering the relative difference between mainshock and corresponding aftershock incident angles. The results showed that taking into account the incident angles of both mainshock and the corresponding aftershock can significantly affect the seismic performance of skew bridges. In particular, when the difference between the angles of the mainshock and corresponding aftershock was considered, the nonlinear responses of the case study increased up to 65.56%. [ABSTRACT FROM AUTHOR]

This study employs a non-linear static analysis, known as pushover analysis, to explore the flexural-compressive behavior of complex shear walls within a reinforced concrete (R.C.) structure, adhering to contemporary design standards in Chile. The primary objective is to assess the initiation of damage as the building approaches the limit states outlined in Achisina’s seminal “Performance Based Seismic Design” framework. To achieve this, a sophisticated fiber model, accounting for the confined behavior of concrete derived from the structural elements’ detailing, has been uniformly integrated across the building’s entire height. Furthermore, the analysis incorporates a rigid diaphragm to simulate the R.C. slab’s response accurately. The study implements the N2 method, adjusting for seismic demands in an acceleration-displacement format, which leverages the displacement spectrum defined by Supreme Decree 61, a legislative response to the 8.8 Mw Maule earthquake in 2010. The findings reveal that the analyzed structure meets the immediate occupancy performance level with drifts nearing 5‰ in the symmetrical Y direction. This outcome aligns with prior assessments of Chilean R.C. wall buildings. However, in the asymmetric X direction, the structure exhibits a higher degree of structural damage, aligning with a life safety performance level. This differentiation underscores the critical need for nuanced understanding and modeling of structural behavior under seismic loads, contributing to the ongoing refinement of seismic design practices and standards.

The quantification of non‐structural seismic performance factors is a crucial step to improve the seismic performance of non‐structural elements (NSEs). Non‐structural seismic performance factors currently included in modern seismic design provisions are mainly based on engineering judgment and have not been calibrated to meet specific performance objectives. This makes the seismic performance of NSEs designed according to force‐based procedures uncertain at best. Previous studies have proposed a general framework for the quantification of non‐structural seismic performance factors. However, due to the necessity of considering the supporting structure dynamic properties in the estimation of the seismic demand, the required computational overhead can make the process unfeasible in some cases depending on the target supporting structure population and the pursued performance objectives. This paper proposes a procedure to estimate the seismic demand on NSEs for the quantification of non‐structural seismic performance factors that drastically reduces the required computational overhead. The proposed procedure makes use of synthetic floor accelerograms to describe in terms of seismic demand an entire population of supporting structures and ground motion sets. The proposed procedure is validated against a complete multiple‐stripe non‐linear time history analysis by deriving and comparing fragility curves. The results of the validation demonstrate that the proposed procedure is able to derive fragility curves that closely match the ones generated by using a multiple‐stripe analyses with remarkable savings in computational time and output storage size. [ABSTRACT FROM AUTHOR]

This study evaluates the seismic risk of weak first-story reinforced concrete (RC) structures retrofitted with inerter dampers at their ground level when subjected to narrow-band seismic excitations. The main advantages brought about by the ground-level inerters are the reductions in seismic demands (e.g., drifts, floor accelerations). This study shows that structures with inerters are reliable systems in terms of peak story drifts for large ground motions. For moderate ground-motion intensities, the opposite could occur, mainly for soft soil sites. The reliabilities of structures with inerter dampers at their ground level are in general higher for buildings under seismic intensities associated to limit state of incipient collapse, especially for low-height buildings. This could be reversed for intensities associated to the limit state of damage limitation. The findings of this study could guide practicing engineers to use inerter-based dampers in retrofitting ductile structures consisting of moment-resisting reinforced concrete (RC) frames subjected to narrow-band earthquake excitations in regions such as Mexico City. [ABSTRACT FROM AUTHOR]

Nonstructural components (NSCs) are the systems that are attached to the floors of a building structure. NSCs have become critical in sustaining post-earthquake functionality while constructing seismic-resilient structures. The seismic behavior of the NSCs primarily depends upon the behavior of the structure to which the NSC is attached. Building structures are subjected to earthquake loads and behave differently when the supporting soil type varies. In light of this, this study investigates the seismic demands on NSC attached to the floors of an elastic-reinforced concrete building frame supported by different soil types. The present study considered a regular building frame and a building frame with mass irregularity on the lower story. A total of 3 sets of 11 horizontal spectral-matched ground motions consistent with each soil type are considered. Floor response spectra (FRS) can be used to measure the seismic load on non-structural components. Primarily, it was found that the ordinates of FRS depend on the floor height, the vibration periods of the building, and the soil type. The presence of mass irregularity at the lower story amplified the floor response at all floor levels. Additionally, the values of floor spectral acceleration increase as soil flexibility increases. The amplification factors are critical for generating the floor response spectra, and their variation along the building height is discussed. The floor acceleration was found to vary non-linearly with the height of the building. Finally, artificial neural networks (ANNs) are employed to develop the prediction models for dynamic amplification factors. The results calculated by the dynamic time history analyses are utilized to validate the proposed prediction models. [ABSTRACT FROM AUTHOR]

An essential and emerging task in the area of performance-based seismic assessment of bridges is to improve the estimation of the seismic demands. Existing research proved that the bridge column is one of the dominant components in estimating the bridge system vulnerability. However, the seismic performance of bridges with tall piers is not deeply investigated yet. This study aims to address this problem through analysis of multi-span concrete box-girder bridges with tall piers. This study implements a clustering algorithm that identifies optimized groupings which can set up the basis to establish the best choice for generating MLPSDMs. The evaluation results implicate better performance of cluster-wise multiple models than a single model to represent the variation in the bridge demands. The insights gained from the findings of this study can pave the way toward a better realization of the seismic performance of bridges having tall piers. [ABSTRACT FROM AUTHOR]

The uplift effects on the seismic demands of flexible SDOF structures rocking on a stiff surface were numerically investigated, under impulse excitations. The final results were represented in the form of spectra for the seismic demands including the foundation rotation angle, structural drift and base shear. Comparing the results indicated that as the normalized natural frequency surpassed a specific threshold, the drift and base shear of the structure allowed to uplift were more than twice those of corresponding fixed-base structure. Moreover, an increase in structural damping did not necessarily reduce the seismic demands of uplifting systems. [ABSTRACT FROM AUTHOR]

In time-history analysis, considering the seismic characteristics and uncertainties of the site obviously leads to a more accurate assessment. Hence, in this study, an efficient method that can stochastically select earthquake records for structural time-history analysis was proposed. By using this method, the structure was subjected to the effects of many probable earthquakes based on the characteristics and design response spectrum of the site. In this way, first, a large number of earthquake records were selected based on the characteristics of the site. For each ground motion, the maximum elastic base shear of the structure (V max) and its equivalent response acceleration (S ae) were calculated. Afterward, the probability density function (PDF) of the maximum response acceleration (S a) was calculated based on the design response spectrum and annual exceedance probability of the site. Then, the selected records were stratified based on the S ae and PDF of S a. Eventually, some earthquake records were randomly selected using the Latin hypercube sampling (LHS) method. To better understand and assess the performance of the proposed method, the mentioned steps were utilized for a steel concentrically braced frame (CBF) building. The results showed the accuracy of the proposed method based on the hazard level and the design response spectrum of the site. Additionally, the results indicated that the number of analyses could be reduced with a satisfactory accuracy proportional to the uncertainty associated with the seismic parameters. • An efficient method that can stochastically select earthquake records for structural time-history analysis is proposed. • Random selection of earthquake records is based on the design response spectrum and the site hazard curve. • Selection of earthquake records is such that the probability of occurrence of earthquakes with a higher base shear is lower. • Number of analyses can be reduced with a satisfactory accuracy proportional to the uncertainty in the seismic parameters. [ABSTRACT FROM AUTHOR]

This paper presents a seismic fragility assessment of bridges commonly found in Northeastern Brazil. A generic three-dimensional nonlinear finite-element model is generated in OpenSees to enable variation of geometric features and component modeling. A parametric analysis is performed to evaluate the impact of the geometric and physical variations of the bridge inventory on the seismic behavior of the structures. Nonlinear time-history analyses using four sets of natural earthquake records are performed to obtain the Probabilistic Seismic Demand Model for the bridges. Capacity models are adopted according to previous studies to be combined with demand models to generate fragility functions. This article helps the decision markers to predict the seismic behavior of typical bridges in Northeastern Brazil, which enables the evaluation of risk mitigation methods. [ABSTRACT FROM AUTHOR]

Observations from past earthquakes in reinforced concrete buildings show that the masonry partitions can endanger the life of buildings occupants and lead to significant damage and loss. The most present codes of practice do not consider the effects of nonlinearity and higher modes of the structure and three-dimensional behavior of partitions on the out-of-plane seismic demands of these components simultaneously and the main purpose of this study is to investigate the effect of these cases together. This research involves assessing the seismic performance of partitions made of the hollow brick located in different stories of 3-, 7- and 11-story buildings containing 3D reinforced concrete special moment frames and subjected to a suite of 7 appropriate earthquakes. A finite element program, OpenSees, has been used for nonlinear seismic response history analysis. The average of the peak of responses of partition, under the seismic excitations, was computed for any model and the forces obtained using the analytical method, which some of them verified with existing studies results, were compared with the values from the code. For the majority of the models, the results show that the analytical seismic demands on partitions, in the lower half, are higher than those calculated using the code provisions because of the effect of higher modes of the structures and the peak values is even up to 1.54 times the computed value based on the code. The code provisions are conservative for the partitions in the upper half of the buildings.

In this study is investigated the performance of different glass fibre-reinforced polymer strengthening schemes on infilled reinforced concrete (RC) frames. The main objective was to limit the damage to beam–column joints and inter-storey drift ratios and to protect RC frames against the negative effects caused by infill-RC frame interaction. Five specimens were tested: one without infill and four infilled with full-scale hollow clay block masonry unit, three of which were strengthened with different schemes. Results showed that the beam–column joints could remain undamaged, lateral strength and stiffness were enhanced, inter-storey drift was limited, and new load carrying systems are generated. [ABSTRACT FROM AUTHOR]

Global sensitivity analysis is important for quantifying uncertainties in the design of civil infrastructure, which is taken as a crucial step towards structural reliability or fragility. Most global sensitivity analysis uses Monte Carlo simulation, but that has high computation demands since many nonlinear time-history analyses are required to obtain the unconditional and conditional probability density functions. To address this limitation, a more efficient entropy-based global sensitivity analysis technique is proposed and tested for its ability to rank the importance of random parameters. A bridge under seismic loading serves as an example of its use. The unconditional and conditional probability of bridge seismic demands can be obtained by reconstructing the probability density function through a parameterized probability distribution based on the proposed new three-point-estimate method. Two examples show that the proposed method can effectively rank the importance of uncertain parameters. One uses a linear polynomial and the Ishigami function as mathematical test cases. The other is a finite element model of a continuous girder bridge. The entropy-based global importance of the uncertain material and structural parameters are obtained with only a few nonlinear time-history analyses. The results are compared with those from Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

The purpose of this article is to contribute to the study of the seismic behavior of structures interacting with the ground and to offer new tools for the treatment of relevant problems, oriented towards the new seismic design philosophy of structures: the design performance-based design. The issue is part of the proposal for simplified models to address a complicated problem such as soil-structure interaction (ISS). The nonlinear behavior of the structure is determined by a capacitive approach based on the seismic performance such as the N2 method proposed by Peter Fajfar. In its original version, this method considers that the structure is fixed at its base, neglecting the ISS. Our contribution will be to make some modifications to this approach to introduce the effect of the soil on the nonlinear response.

This study evaluates the seismic risk of weak first-story reinforced concrete (RC) structures retrofitted with inerter dampers at their ground level when subjected to narrow-band seismic excitations. The main advantages brought about by the ground-level inerters are the reductions in seismic demands (e.g., drifts, floor accelerations). This study shows that structures with inerters are reliable systems in terms of peak story drifts for large ground motions. For moderate ground-motion intensities, the opposite could occur, mainly for soft soil sites. The reliabilities of structures with inerter dampers at their ground level are in general higher for buildings under seismic intensities associated to limit state of incipient collapse, especially for low-height buildings. This could be reversed for intensities associated to the limit state of damage limitation. The findings of this study could guide practicing engineers to use inerter-based dampers in retrofitting ductile structures consisting of moment-resisting reinforced concrete (RC) frames subjected to narrow-band earthquake excitations in regions such as Mexico City.

Moment-independent importance (MII) analysis is known as a global sensitivity measurement in qualifying the influence of uncertainties, which is taken as a crucial step towards seismic performance analysis. Most MII analysis is based on Monte Carlo simulation, which leads to a high computational cost since a large number of nonlinear time history analyses are required to obtain the probability density function. To address this limitation, this study presents a computational efficient MII analysis to investigate the uncertain parameters in the seismic demands of bridges. A modified four-point-estimate method is derived from Rosenblueth's two-point-estimate method. Thus, the statistical moments of a bridge's seismic demands can be obtained by several sampling points and their weights. Then, the shifted generalized lognormal distribution method is adopted to estimate the unconditional and conditional probability density functions of seismic demands, which are used for the MII analysis. The analysis of seismic demands based on piers and bearings in a finite element model of a continuous girder bridge is taken as a validation example. The MII measures of the uncertain parameters are estimated by just several nonlinear time history analyses at the point-estimate sampling points, and the results by the proposed method are compared with those found by Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

In a sample of 200 buildings built with the Great Soviet Panel prefabricated system in Santiago the Cuba, pathological damage and structural transformations carried out by the inhabitants are evidenced. Being necessary to evaluate a priori, the incidence of the aspects leading to potential seismic damages in the structural behavior of these buildings. To meet this objective, 16 hypothetical variants were elaborated, taking into account the statistical analysis of the diagnosis made, which are compared with the 4 variants of the original typologies. It is concluded that the aspects conducive to potential seismic damages have more repercussion in the change of the oscillation periods than in the seismic demand. Pathological damage is the one with the highest incidence in the increase in the fundamental periods of vibration, followed by the increase in weight and the openings of panels or slabs.

Nonstructural components (NSCs) are the systems that are attached to the floors of a building structure. NSCs have become critical in sustaining post-earthquake functionality while constructing seismic-resilient structures. The seismic behavior of the NSCs primarily depends upon the behavior of the structure to which the NSC is attached. Building structures are subjected to earthquake loads and behave differently when the supporting soil type varies. In light of this, this study investigates the seismic demands on NSC attached to the floors of an elastic-reinforced concrete building frame supported by different soil types. The present study considered a regular building frame and a building frame with mass irregularity on the lower story. A total of 3 sets of 11 horizontal spectral-matched ground motions consistent with each soil type are considered. Floor response spectra (FRS) can be used to measure the seismic load on non-structural components. Primarily, it was found that the ordinates of FRS depend on the floor height, the vibration periods of the building, and the soil type. The presence of mass irregularity at the lower story amplified the floor response at all floor levels. Additionally, the values of floor spectral acceleration increase as soil flexibility increases. The amplification factors are critical for generating the floor response spectra, and their variation along the building height is discussed. The floor acceleration was found to vary non-linearly with the height of the building. Finally, artificial neural networks (ANNs) are employed to develop the prediction models for dynamic amplification factors. The results calculated by the dynamic time history analyses are utilized to validate the proposed prediction models.

In a sample of 200 buildings built with the Great Soviet Panel prefabricated system in Santiago the Cuba, pathological damage and structural transformations carried out by the inhabitants are evidenced. Being necessary to evaluate a priori, the incidence of the aspects leading to potential seismic damages in the structural behavior of these buildings. To meet this objective, 16 hypothetical variants were elaborated, taking into account the statistical analysis of the diagnosis made, which are compared with the 4 variants of the original typologies. It is concluded that the aspects conducive to potential seismic damages have more repercussion in the change of the oscillation periods than in the seismic demand. Pathological damage is the one with the highest incidence in the increase in the fundamental periods of vibration, followed by the increase in weight and the openings of panels or slabs. [ABSTRACT FROM AUTHOR]

In this paper the seismic assessment of rocking masonry walls is evaluated through the displacement-based approach. In particular, a case study is selected to analyse the rocking failure mechanism of the façade of an ancient masonry church, damaged during the 2016–17 Central Italy seismic sequence. For this purpose, a non-linear kinematic analysis is developed to define the load factor at the activation of the failure mechanism and its evolution until collapse, at large displacements. An advanced macro-block model is adopted to take into account the stabilising contribution of frictional resistances exerted by the interlocked walls. The seismic input is described through acceleration-displacement response spectra (ADRS), provided both by seismic codes and selected real accelerograms, and the seismic analysis is addressed according to the capacity spectrum method (CSM), in the form incorporated into the latest Commentary to the Italian Technical Standard for Construction (CNTC19). The capacity is compared with the seismic demand through safety indexes, in terms of both forces and displacements, and the relevant influence of the frictional resistances on increasing the capacity is discussed. Incremental static analysis (ISA) curves are presented as another approach useful to highlight the relation between the peak ground acceleration (PGA) and the displacement demand. [ABSTRACT FROM AUTHOR]

This paper investigates the cyclic behavior of steel columns subjected to single‐sided cyclic loading protocols driven by residual deformations. First, nonlinear time‐history analyses are performed to steel framed structures using a set of repeated earthquakes. Then, based on the dynamic analysis results, a set of single‐sided loading protocols is developed to envelop the asymmetric seismic behavior of the examined frames. The developed protocols are used to identify the new single‐sided capacity margins of steel columns in terms of strength and ductility as well as evaluate the potential of using novel high‐strength materials. In this paper: (a) the new asymmetric loading protocols are proposed based on the seismic behavior of three medium‐rise frame buildings with different beam‐to‐column strength ratios (i.e. Mpc/Mpb) which are analyzed with the aid of the finite element analysis (FEA) software ABAQUS; (b) a computational databank of the inelastic responses of square tubular steel columns with high yield‐to‐tensile (YT) strength ratio is developed by subjecting column FEA models with various width‐to‐thickness ratio and axial loads to both conventional and asymmetric cyclic loading protocols. Due to the asymmetrical nature of the cyclic protocols, a lower post‐peak strength deterioration was observed in columns that enables the definition of new, extended, ductility capacity margins. The ductility capacity ratios under the asymmetric loading protocols were found to be 1.15 to 1.71 higher than those obtained under the conventional protocols enabling the use of high‐strength steels in steel columns of smaller width‐to‐thickness ratio. [ABSTRACT FROM AUTHOR]

Over the last few years, many studies were performed to investigate rubberized concrete's behavior as a sustainable alternative for conventional concrete by replacing natural aggregates with recycling old rubber tires. These studies have shown that the concrete's mechanical and durability properties are significantly reduced, while its ductility and damping ratio improved. Accordingly, using this material in RC structures could be a promising solution for improving their energy dissipation capabilities. Currently, the literature lacks a numerical study that can highlight the effectiveness of using high-strength rubberized concrete for retrofitting RC structures subject to earthquake loadings. Therefore, this research investigates the seismic performance of reinforced concrete buildings strengthened using different high-strength rubberized concrete mixtures under various ground motion excitations. As a part of the study, finite element models of reinforced concrete structure retrofitted with these concrete mixes will be analyzed using nonlinear response history analysis and compared against two different control models composed of a bare structure and a jacketed RC structure using the control concrete mixture. In general, using rubberized concrete jacketing improved the seismic performance of the bare structure significantly. Furthermore, utilizing high-strength rubberized concrete rather than the control one resulted in increasing the damping energy and slightly reducing the base shear forces of the structure. [ABSTRACT FROM AUTHOR]

Forces and displacements induced in a building due to structural responses to earthquake excitation are called seismic demands which depend upon the input motion, structural characteristics, site effects and the interaction of structure with soil. Structural response of three laterally non-controlled moment-resisting reinforced concrete frame structures with three different soil conditions are have been investigated in this paper. The soil conditions include loose soil, medium soil and rigid ground. The soil-structure interaction of low-, mid- and high-rise frame structures with the above mentioned soil types was analysed by performing nonlinear response history analyses. A set of eleven earthquake motions was employed in the analyses and maximum structural seismic demands for the frame structures were calculated. It was found that pressure-independent relatively loose sandy soils are not very critical for low-rise structures. On the other hand, pressure-independent relatively loose sandy soils and pressure-independent medium sandy soils are highly critical for mid-rise and high- rise structures, respectively. Categorisation of the soils is performed based on the value ranges of a series of constitutive parameters. Further, fixity of the base is most effective in controlling storey displacements until approximately one-third of the structure height. Medium soil leads to highest maximum base shears in low-rise structures while fixed-base and medium cases, and fixed base state control the behaviours of mid-rise and high-rise structures, respectively. [ABSTRACT FROM AUTHOR]

Summary: The achievement of adequate performance objectives for buildings under increasing seismic intensities is not only related to the performance of structural members but also to the behavior of nonstructural elements. The need to properly design nonstructural elements for earthquakes has been largely demonstrated in the last few years and has become an important objective within the earthquake engineering community. A crucial aspect in the proper design of nonstructural elements is the definition of the seismic demand in terms of both absolute acceleration and relative displacement floor response spectra. In the first part of this study, relative displacement and absolute acceleration floor response spectra were computed for four reinforced concrete moment‐resisting archetype frames via dynamic time‐history analyses and were compared with floor response spectra predicted by means of two recent simplified methodologies available in the literature. It was observed that one of the existing methodologies is generally unable to predict consistent absolute acceleration and relative displacement floor response spectra. An improved procedure is developed for estimating consistent floor response spectra for building structures subjected to low and medium‐high seismic intensities. This new procedure improves the predictions of a relative displacement floor response spectrum by constraining its ordinates at long nonstructural periods to the expected peak absolute displacement of the floor. The resulting acceleration and relative displacement response spectra are then consistently related by the well‐known pseudo‐spectral relationship over the entire nonstructural period range. The effectiveness of the proposed methodology was appraised against floor response spectra computed from nonlinear time‐history analyses. [ABSTRACT FROM AUTHOR]

Summary: Quasi‐static testing is one of the most commonly used experimental methods for examining the seismic performance of structural members. However, consistent loading protocols for experimental seismic qualification of members in emerging steel frames such as self‐centering braced frames (SCBFs) as well as in some conventional ones including buckling‐restrained braced frames (BRBFs) are still lacking. This paper aims to propose standardized loading protocols based on time‐history dynamic analysis on a series of prototype building frames, including steel SCBFs, BRBFs, and moment‐resisting frames (MRFs), where both far‐field and near‐fault earthquakes are considered. The methodology for the development of the loading protocols involves ground motion selection and scaling, design and analysis of prototype buildings, analysis results processing, and rainflow cycle counting, together with extra justification steps. The proposed loading protocols are consistently derived based on the MCE‐level seismic hazard and 84th percentile values of key seismic demand parameters. These parameters are number of damaging cycles Nt, maximum inter‐story drift θmax, inter‐story drift range Δθi, sum of inter‐story drift range ΣΔθi, and residual inter‐story drift θr. The analysis confirms the variations in these seismic demands imposed on the different structural systems under different types of ground motions, highlighting the necessity of developing separate loading protocols for the different cases. The assumptions, decisions, and judgments made during the development of the loading protocols are elaborated, and the conditions and restrictions are outlined. The rationality of the proposed loading protocols is further justified through demonstrating the cumulative distribution function and energy dissipation demand of the systems. [ABSTRACT FROM AUTHOR]

Urban highway bridges are crucial for regional economic development and population mobility, but they are vulnerable to seismic hazards. Accurately predicting the seismic demands of bridges is essential. Several commonly-used methods for seismic demand estimates, such as cloud analysis, incremental dynamic analysis, and multiple stripe analysis, are computationally expensive and subject to theoretical assumptions and convergence issues, especially for portfolios of bridges. Machine learning techniques can be effective, but their lack of interpretability hinders understanding of the surrogate model's predictions. To address these challenges, this study develops a Bayesian-optimized interpretable ensemble learning surrogate model for predicting and interpreting the critical seismic demands of urban highway bridges.Thousands of continuous prestressed concrete girder bridges with typical geometric configurations in China are generated, and 120 ground motion records with different frequency, waveform, and duration characteristics are chosen. The seismic demand dataset is established based on nonlinear time-history analyses for urban highway bridges, accounting for different types of uncertainties. The surrogate models are developed based on the XGBoost ensemble learning method, with hyperparameters automatically and efficiently determined by Bayesian optimization technique. Compared to the random search and grid search methods, Bayesian optimization is approximately 8 times and 29 times faster, respectively, and it also achieves the highest prediction accuracy. Meanwhile, the relationship of each hyperparameter in the surrogate model is also revealed. The prediction results of the proposed model are compared with other machine learning models. The SHAP algorithm is subsequently used to explain the model predictions regarding the feature importance, global interpretations, and feature dependency analysis. The study quantifies the contribution of each structural feature and seismic intensity measure to the selected critical seismic demand and identifies the interaction effects between different input variables in the prediction. • An interpretable surrogate model for seismic demand predictions of bridges is developed. • Bayesian-optimized model tuning is developed to determine the optimal hyperparameters. • Key structure and quake characteristics for demand predictions are quantified and interpretated. • Interaction effects between different input characteristics on demand predictions are revealed. [ABSTRACT FROM AUTHOR]

Moment-independent importance (MII) analysis is known as a global sensitivity measurement in qualifying the influence of uncertainties, which is taken as a crucial step towards seismic performance analysis. Most MII analysis is based on Monte Carlo simulation, which leads to a high computational cost since a large number of nonlinear time history analyses are required to obtain the probability density function. To address this limitation, this study presents a computational efficient MII analysis to investigate the uncertain parameters in the seismic demands of bridges. A modified four-point-estimate method is derived from Rosenblueth’s two-point-estimate method. Thus, the statistical moments of a bridge’s seismic demands can be obtained by several sampling points and their weights. Then, the shifted generalized lognormal distribution method is adopted to estimate the unconditional and conditional probability density functions of seismic demands, which are used for the MII analysis. The analysis of seismic demands based on piers and bearings in a finite element model of a continuous girder bridge is taken as a validation example. The MII measures of the uncertain parameters are estimated by just several nonlinear time history analyses at the point-estimate sampling points, and the results by the proposed method are compared with those found by Monte Carlo simulation.

The complex characteristics of explosion load as well as its increasingly high frequency in the civil environment highlight the need to develop models representing the behavior of structures under blast load. This work presents a probabilistic study of the performance of framed reinforced concrete buildings designed according to the current Italian NTC18 and European EC8 technical standards. First, a simplified single degree of freedom model representing the structural system under blast load has been developed. Then, a probabilistic approach based on Monte Carlo simulation analysis highlighted the influence of seismic demand on the behavior of Reinforced Concrete RC buildings subjected to blast load. [ABSTRACT FROM AUTHOR]

Summary: The selection of representative input ground motions (IGMs) is important for a proper nonlinear response time history analysis (NLRHA) of modern structures. The prevailing IGM selection procedure requires that the response spectra of selected ground motions are matched with the code‐specified design spectra, while the effect of the frequency contents combination in the time domain on the multimode interactions is not considered. Ignoring the effect of the frequency contents combination in the time domain of IGMs may cause significant variations in the analysis results for selected IGMs, although they are matched to the same design spectrum. In this paper, a modal‐based ground motion selection (MGMS) procedure is proposed as a supplement to spectrum matching‐based IGM selection procedures for selecting proper IGMs that can sufficiently induce the multimode interactions. In the proposed procedure, three equivalent single‐degree‐of‐freedom (ESDOF) systems are developed by pushover analysis. NLRHA is then conducted for these ESDOF systems with a set of 20 seed IGMs chosen by the spectrum‐matching–based selection procedure. Finally, seven IGMs are selected from the seed IGMs for NLRHA in the full structural model. To verify MGMS, seismic demands of high‐rise buildings were computed by NLRHA with seven MGMS‐selected IGMs, seven IGMs with closest spectrum matching, and groups of seven randomly selected IGMs derived from three different sets of 20 seed IGMs. The computed seismic demands with MGMS‐IGMs show very good agreement with the mean demands determined using the whole set of seed IGMs, while the deviation is much lesser compared with those groups of randomly selected IGMs. [ABSTRACT FROM AUTHOR]

The present paper deals with the analytical investigation of representative planar masonry-infilled reinforced concrete (MIRC) frames for seismic fragility, performance and demand. The study includes the effect of various patterns of layout for infills panels along the height of reinforced concrete frames. The analytical investigation has been done using non-linear dynamic time-history analysis under collection of forty SAC near-field ground motions using rational hysteretic models for structural components; the results are presented in terms of parameters such as peak inter-storey drift, residual drift and damage index. The outcomes of study are used to develop seismic fragility curves in probabilistic terms for the generic medium-rise MIRC frames. The developed fragility curves can be useful tools in predicting the life and economic losses in the future seismic event. In the current study, efforts are also made to develop curves demonstrating seismic performance and seismic demand for representative MIRC frames. [ABSTRACT FROM AUTHOR]