A probabilistic framework for multi-hazard risk mitigation for electric power transmission systems subjected to seismic and hurricane hazards

Abstract

Many areas of the world are prone to multiple hazards that can be concurrent/non-concurrent and dependent/independent. Infrastructure systems located in such areas will likely be subjected to more than one hazard in their lifetime. The damage due to such hazards on electric power systems is well documented. Over the years, strategies to mitigate single hazards have been proposed for electric power systems. However, accurate long-term decisions on investment in risk mitigation strategies require the consideration of multiple hazards that can impact a system over its lifespan. Therefore, there is a need to investigate the cost-effectiveness of mitigation strategies in reducing risks to infrastructure systems that are vulnerable to multiple hazards given the constraints on resources. This requires a comprehensive multi-hazard risk assessment approach. This paper presents a framework for investigating the effectiveness of multi-hazard risk mitigation strategies for electric power systems subjected to seismic and hurricane wind hazards. The framework includes probabilistically weighted deterministic hazard analysis model, component vulnerability models, topologically based system performance model, component importance measure appropriate for networked systems, and life cycle cost analysis. A notional electric power network assumed to be located in Charleston, SC, and New York, NY, is used to demonstrate the proposed framework.     

Proposal of a probabilistic assessment of structural collapse concomitantly subject to earthquake and gas explosion

In recent decades, many public buildings, located in seismic-prone residential areas, had to grapple with abnormal loads against which the structures were unguarded. In this piece of research, an ordinary three dimensional reinforced concrete building is selected as case study. The building is located in an earthquake-prone region; however, it is designed according to seismic building codes. Yet, it is not shielded against abnormal loads, such as blasts. It is assumed that the building suffers a blast load, due to mechanical/thermal installation failure during or after intense seismic oscillations. These two critical incidents are regarded codependent and compatible. So the researchers developed scenarios and tried to assess different probabilities for each scenario and carried out an analysis to ensure if progressive collapse had set in or not. In the first step, two analysis models were used for each scenario; a non-linear dynamic time history analysis and a blast local dynamic analysis. In the second step, having the structural destructions of the first step in view, a pushdown analysis was carried out to determine the severity of progressive collapse and assess building robustness. Finally, the annual probability of structural collapse under simultaneous earthquake and blast loads was estimated and offered.     

基于文献调研的我国建筑结构地震倒塌风险概率评估

基于文献调研,搜集和整理了我国近年来关于建筑结构地震倒塌易损性方面的研究成果,建立了我国建筑结构地震倒塌易损性数据库。基于经典的Cornell地震风险概率计算公式,分别以谱加速度和峰值加速度为地震动强度参数,计算了我国建筑结构的地震倒塌风险概率。通过与美国抗震设计规范FEMA P750和欧洲学者建议的关于建筑结构地震倒塌风险的相关要求进行对比,对我国建筑结构的地震倒塌风险水平进行了评估。分析结果表明:由于我国现行抗震设计规范GB 50011—2010中并未对结构地震倒塌风险做一致性要求,因此,我国建筑结构的地震倒塌风险概率结果分布较广;随着建筑结构抗震设防等级的提高,其地震倒塌风险概率也随之增加;相比于美国规范和欧洲学者研究成果,我国现行抗震设计规范尚不能对结构的地震倒塌风险进行有效控制。     

Sensitivity analysis of steel buildings subjected to column loss

In this study, the sensitivity of design parameters of steel buildings subjected to progressive collapse is studied. To this end, design parameters such as yield strengths of beams, columns, and braces, live load, elastic modulus, and damping ratio were considered as random variables. The Monte Carlo simulation, the Tornado Diagram analysis, and the First-Order Second Moment method were applied to deal with the uncertainties involved in the design parameters. The analysis results showed that among the design variables beam yield strength was ultimately the most important design parameter in the moment-resisting frame buildings while the column yield strength was the most important design parameter in the dual system building. Sensitivity of the vertical displacement to uncertain member strength showed that progressive collapse mechanisms of the moment-resisting frame buildings and the dual system building completely differed due to different patterns of the vertical load redistribution.     

Sensitivity analysis for failure assessment of concrete pipes subjected to sulphide corrosion

Sulphide corrosion in concrete sewers is the most common form of deterioration and should be investigated in failure assessment of sewage systems. Corrosion parameters are considered as random variables because of data scarcity and uncertainties involved in the corrosion affected concrete sewers. Sensitivity analysis is widely accepted as a necessary part of failure assessment of structures and infrastructure, in which the effect of random variables on the failure can be analysed.

In the current study, the results of sensitivity analysis of a corrosion affected concrete sewer in the UK showed that among eight random variables, alkalinity of concrete and relative depth of the flow have the most effect on the probability of sewer failure. The analysis showed less significant contribution of some variables in failure functions. Therefore, it would not be necessary to consider those parameters as random variables and they can be treated as deterministic constant values for further studies.     

Stochastic seismic collapse and reliability assessment of high‐rise reinforced concrete structures

To provide knowledge beyond the conventional engineering insights, attention in this work is focused on a comprehensive framework for the stochastic seismic collapse analysis and reliability assessment of large complex reinforced concrete (RC) structures. Three key notions are emphasized: the refined finite element modeling and analysis approach towards structural collapse, a physical random ground motion model, and an energy‐based structural collapse criterion. First, the softening of concrete material, which substantially contributes to the collapse of RC structures, is modeled by the stochastic damage constitutive model. Second, the physical random ground motion model is introduced to quantitatively describe the stochastic properties of the earthquake ground motions. And then the collapse‐resistance performance of a certain RC structure can be systematically evaluated on the basis of the probability density evolution method combining with the proposed structural collapse criterion. Numerical results regarding a prototype RC frame‐shear wall structure indicate that the randomness from ground motions dramatically affects the collapse behaviors of the structure and even leads to entirely different collapse modes. The proposed methodology is applicable in better understanding of the anti‐collapse design and collapse prediction of large complex RC buildings.     

Evaluation of progressive collapse alternate load path analyses in designing for blast resistance of steel columns

The alternate load path method is a convenient, “threat-independent” method used in progressive collapse analysis and design. Because no actual loadings are considered in this method, the resistance provided by the alternate load path method for specific extreme events is not well quantified. However, such quantification allows for an understanding of what real scenarios can be efficiently represented by alternate load path analyses. As blast loading is one of the abnormal loading events typically motivating an alternate path analysis, this load type is selected for evaluation in the present work. In order to find the blast threat that is representative of the alternate load path method in steel-framed buildings, finite element analyses of steel columns being subjected to blast loads were analyzed in the program LS-Dyna. Prior to this, sensitivity and validation studies were also completed, which are described herein. The results of the column analyses show that failure is governed by a stability-based deflection criterion. Conclusions regarding the charge sizes that the alternate load path method may be considered to be representative of, as well as the influence of column spacing, size, and end fixity on these results are given.     

A probabilistic approach for economic analysis of a shopping center in seismic zone

The occurrence of an earthquake causes direct and indirect losses in economy. Performance of the built environment can determine both the magnitude of the losses and the speed of recovery from earthquakes. Earthquake losses can be minimized by the use of planning techniques. This paper presents a probabilistic approach for economic evaluation of a shopping center constructed in a seismic zone. Decision-makers can benefit from this approach, before and after an earthquake occurrence, by considering the probability distribution and variability. Life cycle cost concept is taken into account in the formulation of future worth estimation. Therefore, the approach simulates all the benefits and costs, which are prone to variation within Monte Carlo framework. The probabilistic approach can be used to assess the effects of recovery periods.     

Application of system reliability‐based assessment for collapse fragility of braced moment‐resisting frames

This paper presents a system reliability‐based framework for collapse fragility assessment of steel braced moment‐resisting frames (BMRFs). The conditional failure of intermediate events is calculated, considering two important features in the design of BMRFs: (i) different failure scenarios (FSs) with multiple sequences of components failure formation and (ii) structural reliability analysis based on the failure propagation from components to system. The system collapse reliability‐based assessment of BMRFs is developed with an efficient algorithm using the Monte Carlo simulation procedure incorporated into a nonlinear finite element (FE) analysis program. An appropriate nonlinear FE model of such systems is demonstrated, and the probability of various predefined components' failure over the most likely FSs in the presence of both epistemic and inherent uncertainties is calculated. Then, a system‐simulated reliability index (SSRI) is computed by lower and upper bounds in the probability of BMRF system collapse. Finally, fragility curves based on the SSRI is compared with the ones from incremental dynamic analysis, and later, the outcomes from multiple FSs are compared with the codified main collapse criterion. For the BMRFs analyzed herein, it is shown that the existing allowable story drift for the collapse limit state is conservative, and a new criterion is appraised. Copyright © 2015 John Wiley & Sons, Ltd.     

A new proxy for ground motion selection in seismic collapse assessment of tall buildings

Tall buildings are long‐period structures that are sensitive to the long‐period content of ground motions. Selection of appropriate ground motions is an important step in seismic collapse assessment of tall buildings using nonlinear dynamic analyses. Epsilon (ε_Sa) and eta (η) are two spectral shape indicators, which have been recently proposed for ground motion selection in the technical literature. In this study, a new parameter gamma (γ) is proposed, which has considerable correlation with the collapse capacity of long‐period structures having a fundamental period greater than 1 s. This parameter is a linear combination of ε_Sa and the displacement spectrum intensity epsilon (ε_DSI). The parameter γ is obtained and optimized by applying the particle swarm optimization algorithm. Since γ has significant correlation with the collapse capacity of long‐period structures, it can be used as an efficient proxy for ground motion selection in seismic collapse assessment of tall buildings. The results of this study show that ground motion selection considering the new proxy γ causes reduction in the dispersion of structural response and also decrease in the mean annual frequency of collapse, when compared with ground motion selection based on ε_Sa and η. Copyright © 2013 John Wiley & Sons, Ltd.     

Calibration of the equivalent linearization gaussian approach applied to simple hysteretic systems subjected to narrow band seismic motions

A calibration of the equivalent linearization approach (EL) applied to simple hysteretic systems subjected to narrow band seismic motions is reported. The results obtained through this method are compared with those derived using the Monte Carlo simulation technique. An evaluation is presented of the influence of the ductility demand of the system, as well as of the degradation parameters, hardening ratio and smoothness of the hysteretic behavior on the accuracy of the EL approach. The computational efficiency of the approach is estimated for the cases analyzed.     

Probabilistic loss assessment of light-frame wood construction subjected to combined seismic and snow loads

In some areas, e.g., mountainous areas in the western United States, both seismic and snow loads are significant. Limited research has been conducted to investigate the seismic risk of light-frame wood construction in those areas considering the combined loads, particularly the snow accumulation. An object-oriented framework of the risk assessment for light-frame wood construction subjected to combined seismic and snow hazards is proposed in this paper. A typical one-story light-frame wood residential building is selected to demonstrate the proposed framework. Economic losses of the building due to the combined hazards are evaluated using the proposed framework. It is found that in areas with significant snow accumulation, the snow load has significant effects on the seismic risk assessment for light-frame wood construction.     

Numerical studies on the effect of plan irregularities in the progressive collapse of steel structures

This research examines the effect of plan irregularities on the progressive collapse of four steel structures located in regions with different seismic activity. The plans of the first and second structure are irregular, whilst those of the third and fourth structures are regular. The collapse patterns of the four buildings are examined and compared under seven loading scenarios using non-linear dynamic and static analyses. In the non-linear dynamic analyses, node displacements above the removed columns and the additional force on the columns adjacent to them are discussed. Furthermore, the strength and capacities of the columns are compared to determine their susceptibility to collapse. In the non-linear static analyses, the pushdown curve and yield load factor of the structures are obtained after column removal. The results indicate that an irregular structure designed in site class C seismic zone, collapses in most of the column-removal scenarios. Moreover, when comparing regular and irregular structures designed in site class E seismic zone, the demand force to capacity ratio (D/C) of the columns in the irregular structures is on average between 1.5 and 2 times that of the regular ones.     

A design-oriented model for the collapse resistance of composite floors subjected to column loss

A design-oriented model is proposed for computing the load-resisting capacity of composite steel-concrete floors subjected to interior column loss. The model is based on the premise that floor collapse is resisted through the development of membrane action in the slab elements and catenary forces in the steel beams. A number of simplifying assumptions are made in the model pertaining to the deformed shape of the system, development of failure-resisting mechanisms, and overall system behavior. The proposed model is incremental in nature and tracks the evolution of damage in a floor system loaded up to failure. The model is shown to be able to capture the effect of influential variables on collapse resistance. Key limitations on the model are highlighted and discussed.     

钢结构建筑柱失效的敏感度分析

研究钢结构建筑连续倒塌对各设计参数的敏感度,包括:梁、柱和支撑的屈服强度,活荷载取值,弹性模型及阻尼比等。应用MonteCarlo模拟,Tornado表分析和一次二阶矩方法确定设计参数的不确定性。分析结果表明,在抗弯框架中,梁屈服强度在各设计参数中影响最大,而在双重系统建筑中,柱屈服强度在各设计参数中影响最大。强度不确定构件的竖向位移敏感度表明,抗弯框架和双重系统建筑的连续倒塌机构因为竖向荷载分布模式不同而完全不同。     

水中爆炸条件下结构毁伤评估方法研究

水中爆炸会引起水中结构如码头、船坞等产生构件变形、局部破坏乃至整体损毁。为合理确定水中爆炸条件下作用在水中结构上的荷载及其毁伤特性,通过分析比较现有理论及方法,提卅了不同工况下的荷载计算方法、水中结构毁伤等级划分标准,以及简化计算法、数值模拟法等2种毁伤评估方法;通过对某型高桩码头的响应及毁伤情况进行验算,综合给出了给定当量下高桩码头的安全阈值,对比验证了分析方法的适用性和准确性,为进一步研究水中结构的动态响应及毁伤提供了基础。     

The probabilistic time and cost risk analysis of a challenging part of an urban tunneling project

A predominant characteristic of geotechnical works and more particularly tunneling projects, is the uncertainty that surrounds the geologic medium in which the construction is to be performed. This paper is dealing with the risk analysis of both the construction time and cost of a challenging part of Tehran Metro Line 7, an urban tunneling project which is currently being under development. The Decision Aids for Tunneling (DAT) has been utilized for this assessment, concerning the risk analysis by taking into account different scenarios relating to the measures implemented to prevent surface subsidence problems. The results have shown that selection of different sorts of methods will help control the risk of escalating the project’s total construction cost and time to completion. This research delivers useful information to concurrently help the owner, the contractor as well as the designer of the project in making the most appropriate decisions under such a highly uncertain and challenging geological environment.     

Consideration of uncertainties in LCA for infrastructure using probabilistic methods

The construction and usage of transport infrastructure are major causes of greenhouse gas emissions and energy consumption. The effects of resource consumption and pollutant emissions are often quantified through Life Cycle Assessment (LCA) models. All decisions made in infrastructure projects during the whole life cycle are afflicted by uncertainty, e.g. physical properties of materials or amount of pollutants emitted by certain processes. The pervasive role of uncertainty is reflected in LCA models, which therefore should consider uncertainty from various sources and provide a sound quantification of their effects. The aim of the work presented in this paper is to give an overview of different sources of uncertainty in LCA of infrastructure projects and to describe systematic methods to evaluate their influence on the results. The possibility of including uncertainty in a LCA-tool for infrastructure is presented, studying the sensitivity of the model output to the input parameters and two alternative approaches for propagation of uncertainty using two case studies. It is shown that, besides the influence of uncertainty in emission factors, other inputs such as material amounts and service life could contribute significantly to the variability of model output and has to be considered if reliable results are sought.     

Quantifying and reducing uncertainty in life cycle assessment using the Bayesian Monte Carlo method

The traditional life cycle assessment (LCA) does not perform quantitative uncertainty analysis. However, without characterizing the associated uncertainty, the reliability of assessment results cannot be understood or ascertained. In this study, the Bayesian method, in combination with the Monte Carlo technique, is used to quantify and update the uncertainty in LCA results. A case study of applying the method to comparison of alternative waste treatment options in terms of global warming potential due to greenhouse gas emissions is presented. In the case study, the prior distributions of the parameters used for estimating emission inventory and environmental impact in LCA were based on the expert judgment from the intergovernmental panel on climate change (IPCC) guideline and were subsequently updated using the likelihood distributions resulting from both national statistic and site-specific data. The posterior uncertainty distribution of the LCA results was generated using Monte Carlo simulations with posterior parameter probability distributions. The results indicated that the incorporation of quantitative uncertainty analysis into LCA revealed more information than the deterministic LCA method, and the resulting decision may thus be different. In addition, in combination with the Monte Carlo simulation, calculations of correlation coefficients facilitated the identification of important parameters that had major influence to LCA results. Finally, by using national statistic data and site-specific information to update the prior uncertainty distribution, the resultant uncertainty associated with the LCA results could be reduced. A better informed decision can therefore be made based on the clearer and more complete comparison of options.     

Probabilistic approach for failure assessment of steel structures in fire by means of plastic limit analysis

The issue of fire scenarios approach to fire protection is often subject of ongoing discussions within the fire safety engineering community. The choice of an adequate number and type of fire scenarios is not always univocal and straightforward. The fire scenarios to be used in structural assessment are quite complicated to obtain. Their definition often involves significant large-scale fire tests and sophisticated numerical simulations, taking into account numerous factors. For this reason, it seems appropriate to introduce probabilistic tools to assess the most probable fire scenarios. This work proposes a probabilistic approach integrating the Monte Carlo simulation with plastic limit analysis in order to assess the probability of failure of a structure subjected to fire. The underlying assumptions related to spatial–temporal evolution of the fire action and the response of materials and structural members comply with Eurocode provisions. The procedure, mainly devoted to identify the most critical fire scenarios for the structural response, is illustrated by means of a case study represented by a steel braced structure, used as parking. Beyond the limitations related to the simplified assumptions, the outcomes of the analyses demonstrate the potential of the approach for choosing fire scenarios by means of a probabilistic procedure and for evaluating the probability of fire-induced progressive collapse.