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In the last years, many research efforts have been focusing on the development of fragility and risk models of different building classes and structural typologies for large-scale seismic risk applications. Although the role of masonry infills is well recognised, less attention has been paid to the quantification of the variability surrounding their mechanical properties and how this might affect the collapse fragility curves and loss estimates. This study investigates and quantifies, in a thorough manner, the impact of the variability in the characteristics of masonry infill on the expected annual losses (EALs) of existing infilled reinforced concrete frames of different configurations. To do so, a fully integrated portfolio, representative of buildings designed according to the Italian codes in force between 1970 and 1980, is used as case-study. Infill-related variability is accounted for by means of a macro-level distinction of five common infill types, defined in terms of stiffness and shear strength. Moreover, building-to-building variability is also included through different geometrical configurations. Multiple-stripe analyses are carried out and fragility curves are developed for buildings with different heights, in-plan layouts and structural typologies. Finally, EALs are computed and analysed in a statistical fashion in order to quantify, in a simplified manner, the uncertainty induced by the variability of the masonry infill properties, as a function of the number of storeys and masonry infill typology. [ABSTRACT FROM AUTHOR]

Past earthquake evidence has shown the high vulnerability of Italian school buildings, given by the extensive damage observed to structural and non-structural elements. Such vulnerability demonstrates the need to undertake a seismic risk assessment and reduction strategies for critical facilities and allocation of national funds for retrofit interventions to those regions where seismic risk is higher. To do so, Expected Annual Losses (EAL) are evermore considered one of the main seismic risk metrics, which can, however, be largely affected by the epistemic uncertainty that typically characterizes the material and geometrical properties of existing buildings, particularly masonry-infilled reinforced concrete (RC) ones. This paper investigates the implications of accounting for a thorough identification of sources and characterization of uncertainty in seismic loss estimates on the risk assessment of a typical Italian masonry-infilled RC school building. The variability in masonry infill properties and modeling assumptions, as well as the subsequent epistemic uncertainty, are explicitly considered in the loss estimation of the RC school building. Specifically, the impact on the expected annual loss ratio is quantified in terms of both structural and non-structural components, depending on the engineering demand parameter to which they are sensitive. The results show that, when considering the uncertainty related to the variability in masonry infills, higher loss ratios of up to 30% are obtained with respect to the available literature estimates. [ABSTRACT FROM AUTHOR]

Robust performance‐based earthquake assessment should consider the effects of both aleatory and epistemic uncertainty on seismic response parameters. While the effects of modelling uncertainty on specific engineering demand parameters and collapse fragility curves have been widely investigated to date on bare frame structural typologies, little attention has been paid to the impact of masonry infill properties variability on the uncertainty estimation in existing infilled RC frames. Previous studies available in the literature are mainly related to seismically designed RC buildings and the suggestions provided in international guidelines cannot be reasonably adopted for poorly detailed RC existing frames. As regards the uncertainty in existing RC frames, the role of masonry infills was often neglected or their interaction with the surrounding frames was not rigorously accounted for in the uncertainty estimation. With such limitations in mind, the aim of this study is to provide more realistic modelling uncertainty quantities to be adopted in seismic assessment of existing infilled RC frames, including, in a thorough manner, the impact of the variability of the masonry infill typologies and the occurrence of RC frame shear failure. Both the aleatory and epistemic uncertainties are estimated, in terms of the overall dispersion on specific engineering demand parameters and collapse fragility curves. Finally, the impact of such uncertainties on seismic risk estimates, quantified through expected annual losses, is also thoroughly investigated. The inclusion of additional random variables, not considered so far, in the uncertainty estimation framework, led to importantly higher modelling uncertainty quantities than those currently available from previous studies. [ABSTRACT FROM AUTHOR]

The existence of torsion, as well as consideration of the Soil-Structure Interaction (SSI), increase the natural periods of the structure resulting from a subsequent decrease in the seismic demand of the system. This paper summarizes the probabilistic assessment in order to evaluate the collapse fragility curves in concrete moment resisting structure with different mass center eccentricities. A 12-story, 3-D, moment resisting concrete structure with fixed-base and deliberating SSI, both types of one- and two-way eccentricities is employed to estimate the collapse fragility curve by the IM-based approach. In consonance with the obtained results, increasing the torsion as a result of shifting the mass centers decreases the median of the collapse fragility curve. In addition, it was observed that the SSI consideration for soil type D with shear wave velocity of 180m/s to 360m/s leads to reduction of the median of collapse capacity by in the presence of torsion effect due to one- and two-way mass center eccentricities in range of 0-20% of the building's plan dimensions respectively. Put it differently, the fixed-base assumption overestimates the median of collapse capacity and leads to unsafe design. Moreover, shifting the mass centers of all the stories up to 20% of the building's plan dimensions, with or without the consideration of the SSI, decreases the median of collapse capacities and increases the seismic vulnerability of the building. Accordingly, the fixed-base assumption can be underestimated the dispersion range of the collapse fragility curve. The result reveals that the mentioned differences cannot be neglected.

On 16 April 2016, an earthquake of Mw 7.8 shook the coast of Ecuador, causing the destruction of buildings and a significant number of casualties. Following a visit by the authors to the city of Portoviejo during the debris removal and recovery stage, it was noted that several reinforced concrete buildings located on corners had collapsed in the central part of the city. These buildings were characterized by the presence of masonry at the edges of the buildings but not between the two mostly open-plan facades on the corner for practical reasons. This article reviews the effect of masonry infill panels on the seismic response of reinforced concrete structures. For this, a model that contains the geometric and mechanical characteristics typical of collapsed buildings was generated and subjected to nonlinear analysis, with both static and dynamic increments. The results show the clear influence of the masonry infill panels on the structural response through the torsional behavior that is reflected in the evolution of the floor rotations. Finally, dynamic incremental analysis is used to obtain the collapse fragility curve of the building, and a new damage measure based on floor rotations is proposed. [ABSTRACT FROM AUTHOR]

Past earthquake evidence has shown the high vulnerability of Italian school buildings, given by the extensive damage observed to structural and non-structural elements. Such vulnerability demonstrates the need to undertake a seismic risk assessment and reduction strategies for critical facilities and allocation of national funds for retrofit interventions to those regions where seismic risk is higher. To do so, Expected Annual Losses (EAL) are evermore considered one of the main seismic risk metrics, which can, however, be largely affected by the epistemic uncertainty that typically characterizes the material and geometrical properties of existing buildings, particularly masonry-infilled reinforced concrete (RC) ones. This paper investigates the implications of accounting for a thorough identification of sources and characterization of uncertainty in seismic loss estimates on the risk assessment of a typical Italian masonry-infilled RC school building. The variability in masonry infill properties and modeling assumptions, as well as the subsequent epistemic uncertainty, are explicitly considered in the loss estimation of the RC school building. Specifically, the impact on the expected annual loss ratio is quantified in terms of both structural and non-structural components, depending on the engineering demand parameter to which they are sensitive. The results show that, when considering the uncertainty related to the variability in masonry infills, higher loss ratios of up to 30% are obtained with respect to the available literature estimates.

One important issue in compiling siesmic fragility curves is blending and incorporating uncertainties into the model under seismic conditions. Methods used in this regard are either approximate, costly and time-consuming. To address this, the optimized fuzzy method is used. To compile the fragility curve, epistemic and aleatory uncertainties have been incorporated in which model parameters are fuzzy values and FCM-PSO method is used to estimate mean and standard deviation of fragility curve. The FCM-PSO algorithm is trained using scenarios compiled via the IDA method. Results obtained from the full Monte Carlo method were used for verification. The method employed here is advantageous with regard to both accuracy and execution time. [ABSTRACT FROM AUTHOR]

On 16 April 2016, an earthquake of Mw 7.8 shook the coast of Ecuador, causing the destruction of buildings and a significant number of casualties. Following a visit by the authors to the city of Portoviejo during the debris removal and recovery stage, it was noted that several reinforced concrete buildings located on corners had collapsed in the central part of the city. These buildings were characterized by the presence of masonry at the edges of the buildings but not between the two mostly open-plan facades on the corner for practical reasons. This article reviews the effect of masonry infill panels on the seismic response of reinforced concrete structures. For this, a model that contains the geometric and mechanical characteristics typical of collapsed buildings was generated and subjected to nonlinear analysis, with both static and dynamic increments. The results show the clear influence of the masonry infill panels on the structural response through the torsional behavior that is reflected in the evolution of the floor rotations. Finally, dynamic incremental analysis is used to obtain the collapse fragility curve of the building, and a new damage measure based on floor rotations is proposed.

Earthquake accelerograms recorded in the near-fault regions have special characteristics including the long-period pulse in velocity records as well as high frequency content in acceleration records. In the present study, by using a wavelet analysis, the long period pulses exist in the velocity records of 28 near-fault ground motions, selected from the PEER NGA database, were first separated from the original records. Subsequently, an incremental non-linear dynamic analysis (IDA) was conducted to evaluate the non-elastic response of an example frame subjected to these original records and their extracted pulses to examine the efficiency of the extracted pulse of the records instead of the original accelerograms in dynamic analysis. The results of this study revealed that the efficiency of the extracted pulses to estimate the structure capacity depends on the structural performance levels. From the numerical analysis performed in the present study, it is found that if a given structure is designed for immediate occupancy (IO) performance level (low drift), the application of the extracted pulses overestimates the structure capacity, which is in the unsafe side. Nevertheless, if the structure is designed for collapse prevention (CP) performance level and experiences high level of non-elastic displacements, the extracted pulses provide a conservative estimation of the collapse capacity, which is in the safe side. [ABSTRACT FROM AUTHOR]

Progressive collapse is a form of disproportionate damage, which is induced by an initial local failure that propagates throughout a large portion or the entirety of structural systems. The initial local failure may occur anywhere in a structural system, which consequently exhibits different collapse behaviors. However, the progressive collapse resistance is an inherent property of the entire structural system regardless of any specific initial local failure. This article proposes a collapse probability index to assess the progressive collapse resistance of reinforced concrete frame structures. Such an index is capable of measuring all typical initial local failures instead of any specific ones. The collapse fragility curve is further established based on the collapse probability index, which varies with an increase in the nominal gravity. The structural redundant resistance to progressive collapse can be assessed by the fragility curve. Furthermore, a simplified assessment method is proposed to measure the collapse probability indices feasibly of reinforced concrete frames under different nominal gravity levels. The proposed method based on the collapse probability index can comprehensively evaluate the progressive collapse resistance of reinforced concrete frames which is validated through analysis of a single four-story and a group of eight-story reinforced concrete frame structures. [ABSTRACT FROM AUTHOR]

Highlights: [•] Finite element models of two high-rise steel frames are provided and calibrated. [•] Seismic performance of the structures is compared using ETA, IDA, and THA. [•] Advantages and disadvantages of ETA are compared with IDA in the structural collapse assessment. [•] A new method is proposed to drive the collapse fragility curve for structures. [•] Progressive collapse analysis of the frames is investigated using ETA method. [Copyright &y& Elsevier]