Development of medium- and low-rise reinforced concrete building fragility curves based on Chi-Chi Earthquake data

In this paper, a grid-based cluster division procedure, in combination with a novel maximum likelihood estimate based on multinomial distribution, is proposed to derive fragility curves for medium- and low-rise reinforced concrete (RC) buildings in Taiwan. This new grid-based method generates higher-quality vulnerability data for reducing the dispersion of datasets than does the district-based method. The medium- and low-rise RC buildings are classified into six typologies according to both the number of floors and the design code, based on the complete building damage records collected after the 1999 Chi-Chi Earthquake in Taiwan. The results of the grid-based method show that the fragility curves are more stable and convergent than those from the district-based method. The numerical results demonstrate that the proposed method can reasonably be implemented for fragility analysis and can be used for assessing seismic risk in the future.     

Seismic risk assessment of buildings in Izmir,Turkey

Izmir, the third largest city and a major economic center in Turkey, has more than three million residents and half million buildings. In this study, the seismic risk in reinforced concrete buildings that dominate the building inventory in Izmir is investigated through multiple approaches. Five typical reinforced concrete buildings were designed, modeled and assessed for seismic vulnerability. The sample structures represent typical existing reinforced concrete hospital, school, public, and residential buildings in Izmir. The seismic assessments of the considered structures indicate that they are vulnerable to damage during expected future earthquakes.     

Scenario-based earthquake loss estimation for the city of Cairo,Egypt

This paper describes a multi-tiered loss assessment methodology to estimate seismic monetary implications resulting from structural damage to the building population in Greater Cairo. After outlining a ground-shaking model, data on geological structures and surface soil conditions are collated using a considerable number of boreholes to produce a classification of different soil deposits. An inventory database for the existing building stock is also prepared. The seismic vulnerability of representative reinforced concrete building models, designed according to prevalent codes and construction practices, is evaluated. Capacity spectrum methods are utilised for assessing the structural performance through a multi-level damage scale. A simplified methodology for deriving fragility curves for non-ductile reinforced concrete building classes that typically constitute the building population of the city is adopted. In addition, suitable fragility functions for unreinforced masonry constructions are selected and used for completing the loss model for the study area. The results are finally used to build an event-based loss model caused by possible earthquakes in the region.     

悬臂式抗滑桩加固黏土边坡地震永久位移算法

为了有效地确定悬臂式抗滑桩加固的黏土边坡地震永久位移,基于极限分析上限定理,针对圆弧滑动式土坡破坏模式,通过对设置抗滑桩条件下土坡进行外力功率和内能耗散率的计算,按严格力学定义推导出坡体在地震作用下的安全系数,进而导出与安全系数相对应的边坡地震屈服加速度计算公式,并结合Newmark滑块位移法对边坡产生的转动加速度进行二次积分,推导出与边坡设计安全系数密切相关的坡体地震永久位移的详细计算公式。以5.12汶川地震卧龙测站东向地震波为例,通过对一算例边坡进行分析,给出了边坡永久位移时程曲线以及不同设计安全系数与永久位移的关系,分析了算法与Ambraseys算法的结果,验证了所提计算方法的有效性,并得到不同设计安全系数时边坡土体黏聚力和内摩擦角对坡体永久位移的影响规律。研究结果表明,坡体永久位移随着设计安全系数的增加逐渐呈指数函数式减小变化,在较低设计安全系数下,坡体永久位移受土体抗剪强度参数影响较为敏感,随着设计安全系数的提高,这种敏感性则逐渐降低。     

Seismic stability analysis of soil nail reinforced slope using kinematic approach of limit analysis

Prediction of the critical seismic yield acceleration coefficient and the seismic permanent displacement of soil nail reinforced slope under seismic loading has been playing an important role in helping design in the earthquake-prone areas. In this paper, the seismic stability of soil nail reinforced slope is analyzed using the kinematic theorem of limit analysis. The log-spiral failure mechanism is considered and the corresponding analytical expressions are derived to calculate the critical seismic yield acceleration coefficient and the permanent displacement of slope subjected to earthquake loading. A series of calculations are carried out to illustrate the influence of inertial force on the stability of a nail-reinforced slope. Parametric studies indicate that the strength and geometry of slope as well as characteristic parameters of soil nail have a significant effect on the critical seismic yield acceleration coefficient and the permanent displacement of soil nail reinforced slope.     

基于静动力有限元的边坡抗震稳定分析方法

由人工截断边界输入地震波,通过时程积分法确定地震荷载作用下边坡的应力和变形,在人工截断边界上采用黏-弹性人工边界条件模拟地基辐射阻尼的影响。采用有限元强度折减法求解边坡稳定安全系数,以塑性区贯通时刻特征点的位移突变作为边坡失稳的评判标准。非线性有限元和黏-弹性人工边界条件结合运用,建立了基于静动力有限元的边坡抗震稳定分析方法。该方法在稳定安全系数的定义上和传统的刚体极限平衡法是一致的。以十里铺水电站为工程实例,分析了库区边坡的抗震稳定性,得出了边坡动力位移时程和动力稳定安全系数,计算结果合理评价了实际工程在地震荷载下的稳定性。     

Stochastic seismic slope stability assessment using polynomial chaos expansions combined with relevance vector machine

This paper presents probabilistic assessment of seismically-induced slope displacements considering uncertainties of seismic ground motions and soil properties.A stochastic ground motion model representing both the temporal and spectral non-stationarity of earthquake shakings and a three-dimensional rotational failure mechanism are integrated to assess Newmark-type slope displacements.A new probabilistic approach that incorporates machine learning in metamodeling technique is proposed,by combining relevance vector machine with polynomial chaos expansions(RVM-PCE).Compared with other PCE methods,the proposed RVM-PCE is shown to be more effective in estimating failure probabilities.The sensitivity and relative influence of each random input parameter to the slope displacements are discussed.Finally,the fragility curves for slope displacements are established for sitespecific soil conditions and earthquake hazard levels.The results indicate that the slope displacement is more sensitive to the intensities and strong shaking durations of seismic ground motions than the frequency contents,and a critical Arias intensity that leads to the maximum annual failure probabilities can be identified by the proposed approach.     

Empirical fragility and vulnerability curves for buildings exposed to slow-moving landslides at medium and large scales

Slow-moving landslides yearly induce huge economic losses worldwide in terms of damage to facilities and interruption of human activities. Within the landslide risk management framework, the consequence analysis is a key step entailing procedures mainly based on identifying and quantifying the exposed elements, defining an intensity criterion and assessing the expected losses. This paper presents a two-scale (medium and large) procedure for vulnerability assessment of buildings located in areas affected by slow-moving landslides. Their intensity derives from Differential Interferometric Synthetic Aperture Radar (DInSAR) satellite data analysis, which in the last decade proved to be capable of providing cost-effective long-term displacement archives. The analyses carried out on two study areas of southern Italy (one per each of the addressed scales) lead to the generation, as an absolute novelty, of both empirical fragility and vulnerability curves for buildings in slow-moving landslide-affected areas. These curves, once further validated, can be valuably used as tools for consequence forecasting purposes and, more in general, for planning the most suitable slow-moving landslide risk mitigation strategies.     

Building damage characteristics based on surveyed data and fragility curves of the 2011 Great East Japan tsunami

A large amount of buildings was damaged or destroyed by the 2011 Great East Japan tsunami. Numerous field surveys were conducted in order to collect the tsunami inundation extents and building damage data in the affected areas. Therefore, this event provides us with one of the most complete data set among tsunami events in history. In this study, fragility functions are derived using data provided by the Ministry of Land, Infrastructure and Transportation of Japan, with more than 250,000 structures surveyed. The set of data has details on damage level, structural material, number of stories per building and location (town). This information is crucial to the understanding of the causes of building damage, as differences in structural characteristics and building location can be taken into account in the damage probability analysis. Using least squares regression, different sets of fragility curves are derived to demonstrate the influence of structural material, number of stories and coastal topography on building damage levels. The results show a better resistant performance of reinforced concrete and steel buildings over wood or masonry buildings. Also, buildings taller than two stories were confirmed to be much stronger than the buildings of one or two stories. The damage characteristic due to the coastal topography based on limited number of data in town locations is also shortly discussed here. At the same tsunami inundation depth, buildings along the Sanriku ria coast were much greater damaged than buildings from the plain coast in Sendai. The difference in damage states can be explained by the faster flow velocities in the ria coast at the same inundation depth. These findings are key to support better future building damage assessments, land use management and disaster planning.     

既有深坑边坡、结构共同作用的动力响应研究

城市周边废弃矿坑逐渐被利用起来以建设大型公共服务项目,建筑群以边坡作为基础将引起新的技术难题。采用大型振动台试验对地震作用下既有深坑边坡、单跨和多跨框架结构的动位移及结构动内力进行了研究。研究结果表明：地震波类型、幅值和激振方向对模型动力响应均有影响,不同地震波对模型动位移和内力的影响存在差异,动位移随激振幅值的增加而增加,双向激振比单向激振引起的动位移大,与激振同方向的位移较其他方向大;单跨和多跨结构控制位移的能力在高强度地震激振下才有差异,后者比前者控制位移的能力强,但柱子内力较前者大;由于结构与地基的共同作用,整体性好、刚度大的结构可提高地基的抗震性能,多跨结构地基较自由场动峰值位移小2.5%～8.8%,永久位移小13.6%～62.1%。试验结果有助于揭示深坑边坡在地震作用下的失稳机制,为深坑边坡及构筑物的抗震设计提供有益的参考。     

Expansion of the Nishinomiya Built Environment Database

The Nishinomiya Built Environment Database, which can be used to analyze the disaster process of the 1995 Hanshin-Awaji Earthquake Disaster in Nishinomiya City, has been expanded with new data entries. The database contains the following very detailed datasets: (1) the urbanization area base map, (2) casualty data, (3) three sets of building damage data surveyed by the Nishinomiya City, the Architectural Institute of Japan and the City Planning Institute of Japan, and the Kobe University, (4) building property data based on the real estate tax roll, (5) photographs of the damaged buildings with the information on the place and orientation of the picture, and (6) the estimated distribution of the seismic ground motion. The seismic ground motion was simulated for the southern part of Nishinomiya City and two verification sites in Kobe City and Amagasaki City. In the simulation, the borehole data of public facilities were used to model the surface soils as one-dimensional layers, taking into consideration the fact that the spatial distribution of the sediment/basement interface forms a slope. The model of the fault rupture process simulated the characteristics of the seismic motion at basement level, and amplification effects of the surface layers were evaluated based on multiple reflection theory. The distribution of peak ground acceleration and peak ground velocity was estimated from acceleration response spectra at each borehole point. In addition, the relationship between simulated seismic ground motion and building damage was studied based on newly proposed band-passed spectrum intensity using the expanded database. This confirmed that detailed categorization is necessary in order to evaluate the fragility functions, especially for reinforced concrete structures. The database should provide fundamental information for identifying the relationship between the ground motions and the extent and pattern of building damage, or the pattern of the occurrence of casualties.Presently     

地震作用下堆积体边坡的坡面变形与失稳机制

地震作用下堆积体边坡的动力响应特性十分复杂,单一抗震安全系数不足以评价其动力稳定性。通过大型振动台试验,研究了连续多级地震荷载作用下,地震波的类型、卓越频率及峰值加速度对堆积体边坡坡面永久位移的影响,并初步分析其失稳机制。试验结果表明,相同峰值加速度下振动型地震波比冲击型地震波更容易产生坡面永久位移,地震波卓越频率对坡面永久位移也有重要影响;堆积体边坡在峰值加速度apeak=0.2g时开始有大颗粒石砾滚落,对应的坡面永久位移在apeak=0.2g～0.3g之间开始产生并显著增大,另外利用考虑坡面几何形态变化的改进Newmark法对坡顶的永久位移进行了估算。通过坡面永久位移评价堆积体边坡的动力稳定性有一定合理性。     

不良地质环境中基坑边坡加固技术分析及其应用

结合现有边坡加固理论和加固经验,对一紧临道路和8层老楼房且下部有厚度达14 m淤泥软弱土层的基坑边坡进行了复合加固设计。通过对边坡稳定性计算、分析,加固后的边坡满足最小安全系数的要求。按照本设计进行施工后,基坑边坡的变形和周围建筑物的沉降均在安全允许的范围之内,保证了地下室结构部分的顺利施工。所提供的加固技术对同类深基坑支护工程具有重要的参考价值。     

多级边坡平台宽度对边坡地震动力响应 及破坏机制的影响

以典型工程边坡为原型,利用FLAC3D有限差分软件建立一个三维土坡模型,分析地震作用下多级边坡平台宽度对边坡动力响应特性和动力失稳机制的影响。计算结果表明,边坡设置平台可以有效地提高地震动力条件下边坡的稳定性,且平台宽度越大则稳定性越显著;PGA放大系数随着平台宽度的增大而减小。结合频谱分析得到第一级边坡坡顶的动力响应较第二级边坡坡脚的大,边坡岩土体剪应变增量和位移响应也减小;地震作用下边坡塑性区从坡脚部位向坡体内部发展,随地震持时的增加,坡顶出现拉张变形,坡面及其浅表层发生拉张剪切变形,坡体内部一定部位发生剪切变形;坡面监测点位移时程曲线表明,地震作用下边坡坡脚位移向上,发生剪出变形或破坏,坡脚和变坡点均为薄弱部位,应加强支护。研究结果对多级土质边坡抗震设计具有一定指导意义。     

考虑波浪与地震动力效应的曹妃甸海底斜坡稳定性探讨

波浪和地震等动力荷载容易引起斜坡海床失稳,进而引发海底滑坡,危及港口码头安全和海洋工程建设。本文以曹妃甸港南部深槽处海底斜坡为研究对象,考虑真实波浪荷载和地震荷载,采用有限元法和极限平衡法相结合的研究手段对海底斜坡的动态稳定性进行了定量化计算,探讨了动力效应对特殊环境下海底斜坡稳定性的影响机制。结果表明: (1)极端波浪荷载和地震动力荷载对海底斜坡稳定性影响很大,重现期为50a的波浪荷载和峰值加速度为0.15 g的地震动力荷载将引发海底斜坡失稳,且地震荷载将诱发海底斜坡产生较大位移; (2)动力效应会引发海床侵蚀和岩土体强度弱化,进而降低斜坡安全系数,这是稳定性分析中不可忽略的重要因素。     

建筑边距对岩坡地基及上部结构影响数值分析

为节约用地,山地城镇建设中有些建筑建于岩坡地基上,岩坡地基与上部建筑结构之间的共同作用分析成为山区岩土工程实践中的一个课题。基于有限元分析的数值方法,对均质岩坡上建筑边距(建筑距坡顶边缘的距离)对上部建筑结构与地基基础相互作用的影响进行了计算分析,其中边坡地基为10 m高的直立岩坡,基础为平板式筏基,建筑边距分别考虑了2、5、8 m的3种情况。研究了3种建筑边距情况下边坡地基的强度变形情况及上部框架结构、筏板基础的内力和变形情况,分析中上部结构、基础与边坡地基满足三者的受力平衡和变形协调条件。得出了相关结论,对工程实践有一定参考意义     

Regression analysis for seismic slope instability based on a double phase viscoplastic sliding model of the rigid block

Semi-empirical models based on Newmark’s sliding block permit the estimation of expected co-seismic displacements in relation to one or more parameters which characterize the ground motion that theoretically caused them. Taking this into consideration, a regression analysis, based on a double-phase viscoplastic (DPV) model, was developed using 96 Italian ground motion accelerograms for a total of 1,448 combinations obtained for different parametric conditions of the indefinite slope model. Repeated stability analysis, performed by means of the DPV model, allows for the assessment of the seismic instability of a slope in relation to different reached behaviour levels, as well as seismically induced permanent displacements. At these behaviour levels, co-seismic increases and possible subsequent decreases of viscoplastic shear strengths are associated. This implies that the post-seismic persistent mobility (collapse) of the slope can be obtained from the computation. On the other hand, coherently with the increasing of shear resistances during fast sliding displacements in clay soils, the seismic-forced displacements result substantially lower than corresponding values obtained by means of the rigorous Newmark’s sliding block. In addition, in relation to some seismic ground motion parameters, regression and functional border and separation curves were obtained with the aim of providing an expeditious seismic slope stability evaluation in reference to the co-seismic and post-seismic behaviour of clayey slopes. Regarding this, the real behaviour of two historical landslide events is discussed in the light of the results of the regression analysis outlined in this work.     

考虑填土强度的加筋土挡墙动位移计算

加筋土挡墙在地震荷载作用下的位移大小对结构的抗震性能影响显著。为了计算地震荷载作用下加筋土挡墙的位移,Newmark滑块法通常被用于设计中。由于传统的Newmark滑块法在计算中忽略了填土强度的变化,因而采用单一峰值或残余强度的计算将可能导致计算得到的位移小于或大于实际位移值。在二楔块破坏模式的假定条件下,根据楔块的力学平衡条件,建立了加筋土挡墙滑动安全系数计算式,同时通过引入位移阈值考虑了填土的应变软化特点。通过将计算结果与模型试验结果对比,得到以下结论：相较于单楔块法,二楔块法更能真实地反映出墙体的实际破坏模式,且计算得到的屈服加速度系数更接近试验值;相较于采用单一峰值或残余强度计算的位移,考虑填土应变软化的计算解更接近于模型测试值。     

A simplified approach for studying the influence of vertical accelerations on seismic response of slopes

ABSTRACT

A simplified approach is presented for estimating permanent displacements in slopes as a result of both vertical and horizontal seismic accelerations. A study of 52 earthquake records showed that the time difference between maximum horizontal and vertical accelerations varied between 0 and 10.3 s. The approach is illustrated for an earth dam embankment by analysing the effects of five of the above earthquake records. The approach combines a pseudo-static slope stability analysis for estimation of the critical (or yield) horizontal-vertical acceleration combinations, and a Newmark type displacement analysis. Guidelines are presented for conservative choice of soil strength parameters of saturated clays for use in the stability analysis. While permanent displacements of up to 40 cm were predicted without considering the vertical acceleration component, no additional displacement above 3.5 cm resulted when this component was included. The predicted additional displacement was consistently less than 10%, and in 50% of the analyses, vertical acceleration led to smaller predicted displacements. The simple approach may be applied in analysis for any slope using real earthquake records. Using existing, empirical expressions for permanent displacement, based only on horizontal accelerations, the effect of the vertical accelerations may be conservatively estimated by increasing the displacement by 10%.