► Sensitivity of the seismic response parameters of the infilled RC frames was investigated. ► Characteristics of the masonry infills has the greatest impact on the response parameters. ► ...Near-collapse state is most sensitive to the ultimate rotation of the columns.
The sensitivity of the seismic response parameters to the uncertain modelling variables of the infills and frame of four infilled reinforced concrete frames was investigated using a simplified nonlinear method for the seismic performance assessment of such buildings. This method involves pushover analysis of the structural model and inelastic spectra that are appropriate for infilled reinforced concrete frames. Structural response was simulated by using nonlinear structural models that employ one-component lumped plasticity elements for the beams and columns, and compressive diagonal struts to represent the masonry infills. The results indicated that uncertainty in the characteristics of the masonry infills has the greatest impact on the response parameters corresponding to the limit states of damage limitation and significant damage, whereas the structural response at the near-collapse limit state is most sensitive to the ultimate rotation of the columns or to the cracking strength of the masonry infills. Based on the adopted methodology for the seismic performance assessment of infilled reinforced concrete frames, it is also shown, that masonry infills with reduced strength may have a beneficial effect on the near-collapse capacity, expressed in terms of the peak ground acceleration.
A computing environment for the seismic performance assessment of reinforced concrete frames has been developed in Matlab in combination with OpenSees. It includes several functions which provide ...calculations of the moment-rotation relationship of plastic hinges in columns and beams, rapid determination of simplified nonlinear structural models, the post-processing of the results of analyses and structural performance assessment with different methods. The user can add new functions to the PBEE toolbox in order to support additional procedures for the seismic performance assessment of RC frames, or can just change the rules for determining the moment-rotation relationship of plastic hinges in columns and beams, which are the main source of uncertainty in simplified nonlinear models. In the paper, the capabilities of the computing environment (PBEE toolbox) are first explained by focusing on the procedures for determining the moment-rotation relationship of plastic hinges. Different examples are then presented, starting with a comparison between the calculated response of a four-storey RC frame building and the response obtained in a pseudo-dynamic experiment. The calculated response was determined with the two different structural models which are later on used for the demonstration of the seismic performance assessment of the same structure by the N2 method. Lastly, seismic performance assessment of an eight-storey frame is performed by using incremental dynamic analysis with consideration of the modelling uncertainties.
Analytical, closed-form solutions are derived for the computation of equivalent constant rates of limit-state exceedance for structures under seismic loads whose capacity is degrading with time. ...Seismic guidelines currently designate constant, time-independent probabilities or mean annual frequencies of exceedance that are assumed to remain invariable for the entire design life. These are at odds with the time-dependent, ever-increasing exceedance rates of ageing structures. Based on the concept of social equity and discounting of societal investments, the equivalent constant rate provides a basis for judging the safety of structures with time-dependent capacity by allowing comparisons with the code-mandated rates of limit-state exceedance. Starting from the simple SAC/FEMA solution and assuming a power-law degradation of capacity with time and a linear change in the combined epistemic and aleatory variability of capacity, we provide general solutions for the equivalent constant rate and for the limiting case of the average rate over the design life of the structure. The solutions are formulated both in the demand-based and in the intensity-based format, the latter being suitable for all limit-states, even close to global collapse. By using a 7-story reinforced concrete building as an example, we demonstrate the accuracy and the practicality of these approximations for the assessment of an existing structure.
A simplified method for seismic risk assessment with consideration of aleatory and epistemic uncertainties is proposed based on the widely used closed-form solution for estimating the mean annual ...frequency of exceeding a limit state (LS). The method for the determination of fragility parameters involves a non-linear static analysis of a set of structural models, which is defined by utilising Latin hypercube sampling, and non-linear dynamic analyses of equivalent single degree-of-freedom models. The set of structural models captures the epistemic uncertainties, whereas the aleatory uncertainty due to the random nature of the ground motion is, as usual, simulated by a set of ground motion records. Although the method is very simple to implement, it goes beyond the widely used assumption of independent effects due to aleatory and epistemic uncertainty. Thus, epistemic uncertainty has a potential influence on both fragility parameters, and not only on dispersion, as has been assumed in some other approximate methods. The proposed method is applied to an example of a four-storey reinforced concrete building, where it is shown that the effects of epistemic uncertainties, in addition to aleatory uncertainty, increase with the severity of the LS, so that, for the near collapse LS, the risk with consideration of both sources of uncertainty is more than double if compared to the risk, which was determined solely by the consideration of aleatory uncertainty.
The lack of empirical data regarding earthquake damage or losses has propelled the development of dozens of analytical methodologies for the derivation of fragility and vulnerability functions. Each ...method will naturally have its strengths and weaknesses, which will consequently affect the associated risk estimates. With the purpose of sharing knowledge on vulnerability modeling, identifying shortcomings in the existing methods, and recommending improvements to the current practice, a group of vulnerability experts met in Pavia (Italy) in April 2017. Critical topics related to the selection of ground motion records, modeling of complex real structures through simplified approaches, propagation of aleatory and epistemic uncertainties, and validation of vulnerability results were discussed, and suggestions were proposed to improve the reliability and accuracy in vulnerability modeling.
Abstract The design of structures depends on the performance requirements that are usually defined through structural codes for single units. This approach may not be optimal because major ...earthquakes affect the built environment and can also trigger domino effects due to fires, explosions or toxic dispersion. To overcome this issue, we introduce a probabilistic framework for defining unit performance requirements by means of risk‐targeted fragility functions that account for potential domino effects and an overall system performance requirement. The system performance requirement is demonstrated by the potential loss of life, which represents the tolerated number of fatalities per year expected in the earthquake‐affected area. The proposed framework decomposes the problem into a damage‐based fatality analysis, population analysis and seismic hazard analysis, which can be performed and improved independently by engineers with the relevant expertise. The damage‐based fatality analysis includes a series of Monte Carlo simulations using logic trees to account for domino effects. These analyses are then coupled with an iterative risk estimation aimed at identifying the critical units in a system and estimating their risk‐targeted fragility functions, which can then be used for the design of a single unit. The methodology is demonstrated by estimating the potential loss of life due to a seismic event in an urban industrial area. It is shown that the risk‐targeted fragility functions of hazardous storage tanks can be estimated in a few iterations based on disaggregating the potential loss of life. The pilot research presented in the paper provides new possibilities for defining seismic design parameters of structures.
•Fatality risk is affected by multi-hazard domino triggered by earthquakes•Multi-hazard risk for industrialized urban areas is assessed by fatality risk maps•Domino effects are simulated by event ...trees and associated probabilistic models•Probabilistic models of intermediate events are coupled by Monte Carlo method•Disregarding multi-hazard domino effects could underestimate fatality risk
The rapid expansion of the built environment has resulted in the coexistence of industrial facilities and urban centres. Following recent major earthquakes throughout the world, it has become clear that multi-hazard domino effects can significantly increase the risk of fatalities, environmental problems and losses. This complex phenomenon is not yet well understood. In this paper, the problem is treated by decomposing it into several subproblems which are described by simplified probabilistic models. These models are then coupled with the Monte Carlo method to estimate the annual probability of fatality for an individual who is continuously standing in a location of interest and to estimate fatality risk maps for an area of interest. Emphasis is placed on considering multi-hazard domino effects, which can be triggered within an industrial area due to the damage caused by earthquakes. Thus it is considered that fatalities can be caused: a) as a direct consequence of seismic damage to a unit b) as a direct physical and/or chemical consequence due to the loss of containment of hazardous material, and c) as a consequence of domino triggered by physical and chemical events such as fire, explosion, and toxic dispersion. The capabilities of the proposed methodology are demonstrated by calculating fatality risk maps for a hypothetical industrialized urban area. It is shown that disregarding multi-hazard domino effects in the estimation of fatality risk could lead to significant underestimation of the fatality risk in an industrialized urban area. Thus, it is necessary to account for multi-hazard domino effects. However, different teams of engineers can enhance the models for the probability of fatality due to various phenomena, which will improve the accuracy of the proposed methodology.
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