Probabilistic seismic risk assessment of hall buildings in Turkey

Steel space framed hall buildings are dedicated as shelters for people suffering from earthquakes. In general construction, steel space frames are built on reinforced concrete (R/C) frames or wall structures above the bottom side. For this reason, the bottom side has higher rigidity comparing with the upper side. In Turkey, where there is a very high earthquake risk, earthquake‐resistant steel space framed structures is an important issue. In this current research, hall buildings in Turkey, involving two different rigidity parts as R/C and steel, are taken into consideration regarding earthquake effect. In this study, three different hall structures were modeled with different elastic moduli for the analysis part. Nonlinear time history analyses were applied with 25 different earthquake data for performance estimation. After the time history analyses, probabilistic seismic assessment was carried out for the model buildings through fragility analyses. For each model, analysis results were evaluated and compared. As a result, the hall buildings were found to be vulnerable to damage during expected future earthquakes. Moreover, elastic moduli have significant effect on the structural response. Copyright © 2011 John Wiley & Sons, Ltd.     

Multihazard resilience of highway bridges and bridge networks: a review

Abstract

Assessment of resilience for engineered systems has drawn ample attention from the engineering community in recent years. It has resulted in a significantly large body of literature focusing on pertinent areas of resilience. This article provides a systematic and comprehensive review of the literature addressing resilience assessment of bridges and bridge networks under single hazard and multihazard conditions. Though not much work been performed yet on multihazard resilience of bridges, relevant aspects including combinations of multiple hazards for bridge performance evaluation, methods for loss assessment and approaches taken for post-event recovery are discussed. Furthermore, maintenance is a key component if resilience is assessed in a life-cycle framework. Hence, available maintenance plans and strategies and their probable applications for bridges and bridge networks are discussed. The article concludes with a discussion on the need for further research in the focus area and challenges involved with the same.     

Multi-hazard loss analysis of tall buildings under wind and seismic loads

This paper presents a framework for life-cycle loss estimation for non-structural damage in tall buildings under wind and seismic loads. Life-cycle cost analysis is a useful design tool for decision- makers, aimed at predicting monetary losses over the lifetime of a structure, accounting for uncertainties involved in the problem definition. For tall buildings, sensitive to dynamic excitations like earthquake and wind, it can be particularly suitable to base design decisions not only on initial cost and performance but also on future repair expenses. The proposed approach harmonises the procedures for intervention costs evaluation of structures subjected to multiple-hazards, taking into account the peculiar differences of wind and earthquake, in terms of load characterisation, type and evolution of damage. Relative effect of the two hazards on damage to drift- and acceleration-sensitive non-structural elements are examined. The influence of uncertainty in structural damping is also taken into account. It is shown that, although it is commonly believed that the design of a given structure is usually dominated by either winds or earthquakes, when LCC-based design is performed, both winds and earthquakes may be important.     

Seismic risk assessment of reinforced concrete bridges in flood-prone regions

This article presents a conditional seismic risk evaluation framework of bridges located in seismically active flood-prone regions. Flood-induced bridge scour causes loss of lateral support at bridge foundations and thus the effect of seismic hazard on bridge performance gets amplified. Two example reinforced concrete bridges located in Sacramento County in California are considered. The regional multihazard scenario is characterised by combining scour resulted from regional flood events of different intensities with a suite of earthquake ground motions that represents regional seismicity. Uncertainties in the hazard models are discussed and their influences on bridge performance are investigated. A separate set of analysis is performed to evaluate the bridge performance only under earthquake ground motions. Seismic fragility curves and risk curves for the example bridges are generated. Result shows higher seismic risk of bridges when the impact of regional flood hazard on bridges is considered in the analysis framework. This suggests the use of a combined seismic and flood hazard model for reliable seismic risk evaluation of bridges located in flood-prone regions.     

Monte Carlo simulation of extreme traffic loading on short and medium span bridges

The accurate estimation of site-specific lifetime extreme traffic load effects is an important element in the cost-effective assessment of bridges. A common approach is to use statistical distributions derived from weigh-in-motion measurements as the basis for Monte Carlo simulation of traffic loading. However, results are highly sensitive to the assumptions made, not just with regard to vehicle weights but also to axle configurations and gaps between vehicles. This paper presents a comprehensive model for Monte Carlo simulation of bridge loading for free-flowing traffic and shows how the model matches results from measurements on five European highways. The model has been optimised to allow the simulation of many years of traffic and this greatly reduces the variance in calculating estimates for lifetime loading from the model. The approach described here does not remove the uncertainty inherent in estimating lifetime maximum loading from data collected over relatively short time periods.     

Contribution of in situ and laboratory investigations for assessing seismic vulnerability of existing bridges

This work describes the main results of an in situ experimental campaign carried out in the context of the seismic assessment of 71 existing road bridges as representative of the main structural typologies located in the Veneto region and pertaining to the regional roadway managing authority Veneto Strade SpA. An initial in situ and laboratory experimental campaign on basic materials and an overall geometrical survey were carried out for each bridge, using different tests according to the construction typologies, with the aim of characterising the main mechanical parameters of the significant structural elements. Structural assessment has been subsequently carried out according to the parameters derived from the above campaign and the design ground motion action. The results have been compared with those deriving from a preliminary analysis conducted on the basis of some assumptions on materials’ mechanical characteristics related to the original design documents and the construction practice at the time of the structures’ edification. This comparative analysis could give some insights on appropriate and rational planning of inspections on existing bridges and reliability of basic assumptions for their seismic assessment.     

The directionality effect in the seismic risk assessment of highway networks

This study introduces the directionality effect of the ground motion in the probabilistic seismic risk assessment (PSRA) of lifeline systems. Given an earthquake scenario, the seismic wave strikes each component of the system with a different angle. The angle may vary significantly depending on the shape, the location and the orientation of the structure. An appropriate example of a lifeline system is a highway transportation network, in which under earthquake conditions the bridges are considered the most vulnerable components. The proposed PSRA model requires that the seismic fragility model is a function of a ground motion intensity measure (IM), as in the traditional risk analysis, and the angle of seismic incidence. The model was implemented in a new framework for the PSRA of highway transportation network. In addition, the framework includes new algorithms. One reduces the confidence interval of the results and one increases the computational efficiency. The example used is the highway transportation network serving the Los Angeles area, which has more than 3000 bridges. The results show a considerable difference in the system resilience with or without the seismic directionality taken into consideration. This is important for benefit/cost analysis and it represents a clear departure from the current risk analysis.     

不同抗力水平公路桥梁限载分析模型

针对钢筋混凝土中、小跨径简支梁桥,提出一种适用于不同设计荷载等级或抗力衰减桥梁的限载取值简化分析方法。首先,通过引入抗力修正系数, 构造钢筋混凝土梁受弯破坏极限状态函数。进而,以规范建议的钢筋混凝土受弯抗力、恒载效应概率密度函数为依据,提出考虑抗力修正系数的桥梁限载简 化分析模型。在此基础上,以04规范桥梁的设计抗力水平为基准,以设计采用的活恒载比值为基本参数,计算与不同抗力修正系数对应的桥梁限载系数。最 后,以13m钢筋混凝土空心板梁为例验证限载分析模型,通过分析限载系数和典型车辆限载取值,给出了限载取值的修正方法。结果表明,按所提限载分析 模型推算的限载值均有一定的安全储备,可用于不同抗力水平桥梁的限载分析。     

路堤震害风险概率评价与管理研究

 路堤震害在破坏性地震中十分普遍,开展路堤震害风险概率评价并提出合理的震害风险管理方法对提高公路抗震能力和区域防灾减灾能力具有重要意义。进行路堤震害等级划分,选取路堤震害损伤参数,建立路堤震害等级与震害损伤参数的对应关系;以连霍高速公路西宝段K1125+470处路堤为例开展基于CPSHA的公路地震危险性评价,基于IDA和PSDA的路堤震害易损性评价以及基于危险性曲线的路堤震害风险概率评价;在明确路堤震害风险可接受度的基础上提出路堤震害风险管理方法,验证挡土墙对提高路堤抗震性能的积极作用。研究结果表明：连霍高速公路西宝段地震危险性评价结果比第四代地震区划图略高,这与目前渭河断陷盆地地震活跃的现实是一致的;PGA(PGA为地震动峰值加速度)达到0.6 g时,路堤超越严重损伤的概率为65.910%,达到0.8 g时,超越严重损伤的概率为99.995%,说明路堤震害易损性较高;路堤未来50 a超越严重损伤的风险概率为36.46%,发生基本完好和轻微损伤的风险概率为28.49%;以路堤未来50 a发生毁坏的风险概率40%为风险可接受度,路堤震害风险管理方法适用于新建路堤的抗震设计和已建路堤的抗震加固;未来50 a有挡土墙路堤超越严重损伤的风险概率比无挡土墙路堤低15.29%,发生基本完好和轻微损伤的风险概率比无挡土墙路堤高15.62%。     

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。     

核电厂地震概率风险评估研究综述

日本福岛核事故之后,核电厂抗震安全评估受到广泛关注。地震概率风险评估方法是核电厂抗震安全评估方法之一。该文针对地震概率风险评估方法进展做了全面综述：首先介绍核工程领域地震概率风险评估方法的发展历史;并总结核电厂地震概率风险评估方法的基本原理和研究进展;然后论述三种改进的地震概率风险评估方法：基于SMA的地震概率风险评估方法、基于性能的概率地震风险评估方法和先进的地震概率风险评估方法;最后对全文做了总结和展望。     

Methodology for development of live load models for refined analysis of short and medium-span highway bridges

Abstract

The accuracy of bridge system safety evaluations and reliability assessments obtained through refined structural and finite element analyses depends not only on the accuracy of the structural model itself but also on the proper modelling of the maximum traffic loads. While current code-specified live load models were calibrated to properly reflect the safety levels of bridge structures analysed using the simplified methods adopted in bridge design and evaluation manuals, these load models may not lead to accurate results when implemented during refined structural analysis procedures. This paper describes a method to calibrate appropriate live load models that can be used for advanced analyses of bridges. The calibration procedure is demonstrated using actual traffic data collected at a representative weigh-in-motion station in New York State. The proposed calibration methodology is applicable for developing live load models for different bridge service periods, bridge types and design/assessment codes or standards. Live load models obtained using the proposed calibration procedure are readily implementable for deterministic refined analyses of highway bridges to produce similar results to those of complex traffic load simulations. Examples are presented that describe how results of such calibrated live load models would be used in engineering practice.     

Life cycle and performance based seismic design of major bridges in China

The idea of life cycle and performance based seismic design of major bridges is introduced. Based on the key components and non-key components of a bridge and the consideration of the inspectability, replaceability, reparability, controllability and retrofitability of the bridge components, different seismic design levels and expected performance objectives are suggested for the major bridges in China. The vulnerability analysis and progressive collapse analysis, as well as risk assessment, are also proposed to be the important issues to study in order to guide the seismic design of major bridges in the future.     

Evaluation of nonlinear static analysis methods and software tools for seismic analysis of highway bridges

The response of bridges when subjected to seismic excitation can be evaluated by a number of analysis methods. The traditional approach is to employ linear static or dynamic analyses coupled with appropriate modifiers to account for inelastic response while current design practice is moving towards an increased emphasis on nonlinear static analysis methods. In this study, a preliminary seismic response analysis of a two-span highway bridge was performed using linear dynamic analysis procedures to identify the potential for inelastic response. The bridge was subsequently analyzed in accordance with two nonlinear static analysis methods (capacity spectrum and inelastic demand spectrum methods) in an effort to evaluate the difference in global response predicted by the two methods and the effectiveness of various software programs for performing nonlinear static analysis. The results demonstrated that, for the two nonlinear static analysis methods used in this study, different predictions of nonlinear response occurred with neither method being regarded as producing correct results due to a number of simplifications inherent in the methods. Furthermore, the analysis revealed that some software programs are well suited to performing nonlinear static analysis, both from the point-of-view of performing comprehensive analyses and providing a graphical depiction of the evolution of damage (i.e. the behaviour of plastic hinges).     

Environmental risk of dissolved oxygen depletion of diverted flood waters in river polder systems - A quasi-2D flood modelling approach

River polders are retention basins contained by levees alongside rivers into which water from the main river channel is diverted during extreme floods in order to cap the peak discharge of the flood hydrograph and to alleviate downstream flood risk by reducing the water levels. The retained water, however, is stagnant and the organic material in the water and the bottom sediments imposes a strong oxygen demand on the water. This paper presents a quasi two-dimensional computer-based methodology to assess the environmental risk exhibited by the operation of polders with which the concentration of dissolved oxygen in river and polder water can be simulated. A Monte-Carlo analysis allows the probability distribution of all the outcomes of the minimum dissolved oxygen levels in the water to be derived. From this analysis, the environmental risk of the dissolved oxygen concentrations in the polder water falling below 2 mg O₂/L (the level considered critical for aquatic ecosystems) can be determined.The August 2002 extreme flood event on the Elbe River, Germany, with a proposed polder system variant was used to calibrate the model. A daily time step was used to for the simulations for a time frame 12-21 August 2008. The results show plausible spatial and temporal variations in the dissolved oxygen concentrations within the polders. The quasi-2D approach was successful in simulating the spatial distribution of water quality constituents in the polder system. There is up to approximately 20% risk that dissolved oxygen levels fall below 2 mg/L in the polders. This risk can potentially increase if sediment oxygen demand increases due to crop residue and water temperatures in polders increase. High nutrient transport in the river during flooding can cause a spurt of phytoplankton growth in the polders.     

A proactive and resilient seismic risk mitigation strategy for existing school buildings

Different methods and procedures have been developed to define prioritisation strategies of retrofit interventions aimed at reducing the seismic risk of school buildings on a large territorial scale. However, these approaches fail to demonstrate how risk analysis has been used successfully to quantitatively assess and select the optimal risk management decision. This article proposes innovative and useful metrics to measure the potential costs and benefits related to the prioritisation of retrofit intervention and the resilience of the analysed school system by directly integrating engineering, organisational, socio-economic and political aspects in the realm of seismic resilience assessment. Based on probabilistic risk assessments considering the new vulnerability of the prioritised school buildings, these measures could predict the expected economic and functional losses associated with a disastrous seismic event, as well as the possible post-disaster recovery of the system. In order to help decision-makers in selecting the optimal mitigation strategy with a multidisciplinary and multidimensional perspective, different political scenarios, the relative prioritisations of interventions and their intervention options are also defined. The proposed framework is demonstrated in a complex case study of 1,825 public schools in the Lima metropolitan area, Peru. Policymakers, planners and engineering professionals could benefit from results.     

Seismic fragility curves for mid-rise reinforced concrete frames in Kingdom of Saudi Arabia

This article is concerned with the development of seismic fragility curves for typical mid-rise plane reinforced concrete moment-resisting frames in Kingdom of Saudi Arabia (KSA), which is considered as low-seismicity area. Two structural models; four- and eight-storey moment-resisting frames were considered. Three cities with different seismic intensities, Abha, Jazan and Al-Sharaf, were selected to cover various values of mapped spectral accelerations in KSA. The 0.2-s spectral accelerations range from 0.21 to 0.66 g, while the 1.0-s spectral accelerations range from 0.061 to 0.23 g. The structural models were designed under dead, live and seismic loads of these cities according to the Saudi Building Code. Incremental dynamic analysis was performed under 12 ground motions using SeismoStruct. Five performance levels, namely, operational, immediate occupancy, damage control, life safety and collapse prevention were considered and monitored in the analysis. Fragility curves were developed for the structural models of the three cities considering the five selected performance levels.     

Wildlife vulnerability and risk maps for combined pollutants

Ecological risk and vulnerability maps can be used to improve the analysis of pollutant risks and communication to stakeholders. Often, such maps are made for one pollutant at the time. We used the results of wildlife vulnerability analysis, a novel trait-based risk assessment approach, to map overall vulnerability of habitats in Denmark to various metals and one insecticide. These maps were combined with maps of estimated soil concentrations for the same compounds divided by their Maximum Permissible Concentrations. This combination yielded relative risk maps that can be used to assess where the highest risk conditions to wildlife from these individual pollutants in Denmark occur (hot spot identification). In order to show how cumulative risk maps can be made, the maps of the individual pollutants were combined assuming different mechanisms of joint toxicity: no addition, concentration addition, antagonism and synergism. The study demonstrated that with an accurate set of geographical and ecological data one can use the results of vulnerability analysis to make relevant ecological risk maps that show hot spot areas for risks of single or cumulative risks from soil pollutants.     

山西省公路工程建设生产安全事故分析及对策

运用事故致因理论、MES风险评价方法等理论,从基础工程、桥隧管理、路基及路面工程等方面出发,对近几年山西省公路工程建设领域发生的生产安全事故进行了综合分析、系统评价,提出防范事故的对策与措施,以达到控制生产安全事故发生的目标。