Das Magnitude 8.8 Maule (Chile)‐Erdbeben vom 27. Februar 2010 — Ingenieuranalyse der Tsunamischäden,Teil 2

Das Maule (Chile)‐Erdbeben vom 27. Februar 2010 gehört zu den stärksten, weltweit jemals registrierten Erdbeben. Das seismische Ereignis löste einen Tsunami aus, der durch mehrere Wellenfronten verheerende Schäden an der Küste Chiles verursachte. Ereignisspezifische Besonderheiten aus der überlagerung der Effekte aus Erdbeben und darauffolgenden Flutwellen (Tsunami) waren Motivation, im Rahmen einer Erkundungsmission der Ingenieurgruppe der Deutschen Task Force im betroffenen Gebiet die Bauwerksschäden aufzunehmen und ihre regionale Verteilung zu dokumentieren. Der Beitrag vermittelt einen Eindruck von den durch den Tsunami bedingten Schäden; es wird der Versuch unternommen, das Verhalten der typischen Bauweisen unter den zeitlich sequentiell auftretenden extremen Einwirkungen aufzuzeigen. Die Auswertungen schließen an die Ingenieuranalyse der Erdbebenschäden an, so dass auf die im vorangegangenen 1. Teil des Beitrags vom August 2010 [1] gegebene allgemeine übersicht zum Gebäudebestand in Chile und zur Typisierung der Bauweisen verwiesen werden kann. Die Schäden aus dem Tsunami konzentrieren sich auf die eher ländlichen und ohnehin weniger tauglichen traditionellen Bauweisen in den Küstenregionen. An den wesentlichen Wirkungsmechanismen eines Tsunami werden die Verletzbarkeit der Bauweisen und die Effizienz einfacher baulicher Schutzmaßnahmen herausgearbeitet. Wie gezeigt werden kann, tragen Schäden aus Treibgut erheblich zum Schadensbild bei. The Magnitude 8.8 Maule (Chile) earthquake of February 27, 2010 — Engineering analysis of tsunami damages. The Maule (Chile) February 27, 2010 earthquake is regarded as one of the strongest earthquakes ever recorded world‐wide. The seismic event triggered a tsunami which caused by several wave fronts serious damage alongside the coastal border. Event‐specific characteristics from the overlay of the effects from earthquakes and following flood wave (Tsunami) were motivation to examine building damage and to document their regional distribution, in the context of a reconnaissance mission of the engineering group of the German Task Force for earthquakes. The paper provides an impression from the tsunami induced damage to the different building types under the impact of time‐varying sequence of extreme natural events. First results of the studies in [1] are related to the engineering analysis of earthquake damage. Therefore it can be referred to the overview of the building stock and the predominant structural systems in Chile given there. Damage caused by the tsunami is concentrated on rural and often less resistant traditional buildings in coastal areas. The main loading and impact components induced by the tsunami are used to explain the vulnerability of building types and the efficiency of simple structural measures. As the damage cases demonstrate, debris in its general sense has contributed to the observed effects.     

A computational framework for fluid–structure interaction with applications on stability evaluation of breakwater under combined tsunami–earthquake activity

In this article, an improved impervious solid boundary condition of the coupled method called smooth particle hydrodynamics and discrete element method (SPH-DEM) is proposed, which prevents the fluid particles from penetrating solid boundary under earthquake action. And an improved transmitting boundary condition of SPH-DEM is designed in order to conquer the reflection of seismic waves on the boundary. Meanwhile, the effective stress method is proposed to be applied to the SPH-DEM for simulating seabed liquefaction. Based on these, a new computational framework for the SPH-DEM is put forward. Dynamic triaxial test of seabed soil samples indicate that our proposed computational framework can well reproduce the seismic liquefaction process of the seabed soil. Moreover, our proposed computational framework is used to numerically reproduce the failure mechanisms of a breakwater built in liquefied seabed under combined tsunami–earthquake activity and meantime the centrifuge test is carried out. And the experimental results demonstrate the effectiveness of our proposed computational framework, in which numerical results of it are consistent with results of the centrifuge test.     

Collapse safety margin-oriented seismic retrofit strategy for corroded reinforced concrete frames using fibre reinforced plastics

Considering residual service life, this paper presents a collapse safety margin-oriented seismic retrofit strategy for corroded reinforced concrete (RC) frames using fibre reinforced plastics (FRP). With the assumed uniform corrosion model, corrosion-induced initial damage combined with subsequent earthquake-induced damage is identified by the multi-mode-based global damage model developed previously. The collapse-level earthquake intensity determined by incremental dynamic analyses (IDA) with the damage model and the maximum considered earthquake (MCE)-level intensity considering residual service life are combined to generate the time-variant collapse safety margin assessment of corroded RC structures. Based on this assessment, the collapse safety margin-oriented FRP seismic retrofit strategy is proposed and demonstrated on a 4-storey frame. The damage model originally developed for earthquake scenarios has also exhibited its rationality for characterising corrosion-induced initial damage and its influence on coupled damage development with subsequent earthquake excitation. Seismic retrofitting with FRP composites should consider the effects of the corrosion development stage, target collapse safety margin and residual service life. FRP retrofits can cause decreases in the MCE-level collapse probability and increases in the collapse resistance of corroded RC structures. Retrofitting carried out at different times achieves different efficiencies and different time-variant collapse safety margins within the residual service life.     

Seismic collapse analysis of high‐rise reinforced concrete frames under long‐period ground motions

Structural damages associated with buckling of longitudinal reinforcing steel and crushing of concrete induce strength and stiffness degradation in reinforced concrete (RC) beams and columns. This paper presents a numerical investigation on earthquake‐induced damages and collapse of typical high‐rise RC buildings model incorporating strength degradation (SD) effects. In a simple finite‐element analysis program with the generalized stress fiber discretization, hysteretic constitutive models primarily dominate the inelastic behavior. Buckling of reinforcing steel and crushing of confined concrete are taken into accounted to the stress–strain relationship of fiber elements. The SD effect in components with small hoop ratio tends to amplify the seismic responses high‐rise RC moment‐resisting frames when the intensity of ground motions exceeds the design level. Buckling of steel rebar and crushing of concrete should be fully considered together with the P‐Δ effect for collapse simulations.     

钢筋混凝土结构课程教学中抗震概念和思想贯彻方法研究

钢筋混凝土结构作为土木工程、水利工程等专业的技术基础课程,包含许多结构抗震设计的概念和思想。5·12汶川地震造成大量钢筋混凝土结构不同程度的开裂、损坏,甚至倒塌。在课堂教学中,通过对不同类型构件破坏形态的分析,从结构延性、约束混凝土、"强柱弱梁"等方面,对学生开展了抗震概念和思想的引导和教育,增强了学生对结构抗震设计重要性的认识,培养了对钢筋混凝土结构学习的兴趣,为后续课程,如建筑结构抗震和高层建筑等课程的学习打下了基础。     

Toward an economic design of reinforced concrete structures against progressive collapse

A three-dimensional discrete crack model based on the Applied Element Method is used to perform economic design for reinforced concrete structures against progressive collapse. The model adopts fully nonlinear path-dependent constitutive models for concrete and reinforcing bars. The model applies a dynamic solver in which post-failure behavior, element separation, falling and collision are predicted. First, the model is used to study the behavior of multi-story reinforced concrete buildings designed in a traditional manner according to the ACI 318-08 and subjected to accidental removal of one or two central columns at the ground level. In an iterative way, the model is then used to investigate a safe design against progressive collapse for such extreme loading case. Based on the analytical results of the AEM, it can be concluded that the collapse of only one column would not lead to any progressive collapse of the studied reinforced concrete structure. However, the collapse of more than one column may lead to a progressive collapse of a considerable part of it. It is concluded also that the AEM could be successfully used as an analytical tool to suggest economical designs that are safe against progressive collapse of reinforced concrete structures.     

天然地基浅基础的震害分析

本文总结了天然地基浅基础的震害经验，从宏观上讨论了地基基础的震害机理，以及相应的发生条件。并指出，除了含饱和砂土或粉土地基，软粘性土地基和严重不均匀地基外，一般低层房屋的天然地基浅基础抗震性能良好，不易产生地基震害，只要静力设计合理，可不作抗震验算。最后，指出了天然地基浅基础抗震研究应着重注意的几个问题。     

Independent Reinforced Soil Structure with Pile Foundation—Piled Geo-Wall: An Experimental Study on the Application to Seismic Measure for Embankment—

Our aim in this study was to achieve an independent reinforced soil structure with pile foundation that can be applied to such structures as earth retaining walls and countermeasures against the collapse of embankments or rockfall impact built on narrow construction sites, such as on slopes. In order to confirm the effectiveness of the application of pile foundation to reinforced soil structures by geogrid for improvement of the lateral resistance of the structure and to investigate the interaction between pile and reinforced soil structure, a dynamic centrifuge model test (25 G) was carried out. Two geogrid reinforced soil, one with piles and one without, were used in a countermeasure to reduce the deformation of a road embankment built on a slope in the event of an earthquake, and the effectiveness of the pile foundation to the reinforced soil structure was considered with regard to it affected the road surface. The details and the results of the dynamic centrifuge model test, as well as the interaction between pile and reinforced soil structure are described, and the effectiveness of the application of pile foundation to reinforced soil structure is discussed in this paper.     

近断层向前方向性地震动作用下RC框架结构易损性研究#br#

向前方向性效应是近断层地震动的重要特征之一，使得在垂直于断层方向上表现出明显的速度脉冲分量，引起结构的严重破坏。为考察该类特殊地震动作用下RC框架结构的损伤程度，基于传统的增量动力分析方法，建立考虑材料不确定性和输入地震动不确定性的结构-地震动样本，对一个12层框架结构进行地震易损性研究。利用易损性分析结果计算出结构的破坏状态概率，结合群体结构震害评估中的震害指数经验值，得到多遇地震、设防地震和罕遇地震的易损性指数。研究结果表明：近断层向前方向性地震动作用下，依据我国抗震规范设计的RC框架结构能够满足小震不坏、中震可修、大震不倒的抗震设防目标。尤其在大震作用下，结构仍处于中等破坏水平，表明结构在发生倒塌之前具备充分的富裕度。     

Collapse of concrete-covered levee under composite effect of overflow and seepage

During the Great East Japan Earthquake and Tsunami of 2011, enormous coastal levees collapsed as a result of tsunami overflows. Concrete-covered levees, where concrete blocks are used to protect levees made of soil, showed a specific failure mode in which back slope blocks and internal soils were dislodged. Although several hydraulic experiments have been conducted in an attempt to understand the failure mechanism, the complexity of the failure requires that both hydro-dynamical and geotechnical points of view be taken into account for a deeper understanding. This study uses a centrifuge to identify the failure behavior of levees from those points of view. The centrifuge can reproduce the stress, water pressure, and overflow velocity of the prototype-scale ground. Overflowing at sufficient time periods was produced in the centrifuge by generating differences in water height for seaside and landside areas. The test results showed that the levees collapsed due to a combination of the effect of water flow on the back slope and seepage inside the levees. In addition, the effectiveness of several proposed countermeasures for preventing collapse was confirmed.     

钢筋混凝土框架结构抗地震倒塌破坏的研究现状与对策分析

总结了罕遇地震作用下结构倒塌破坏的研究现状,重点分析了建筑物倒塌破坏的系统性和不确定性,对比了不同的倒塌破坏准则和倒塌破坏分析方法,给出了建筑物倒塌的临界状态定义。研究结果表明:现有的倒塌破坏准则无法准确定义结构的倒塌破坏;时程分析法更为精确,且较少地引入了地震动随机性影响,更适于结构倒塌研究;建议的倒塌破坏区间能够更好地反映倒塌破坏特性;塑性变形集中是框架倒塌的主要原因,应重视柱端塑性铰发育导致的结构整体性能退化;相关研究成果可为定量研究建筑结构的倒塌破坏提供理论基础。     

衡重式挡墙处治山区公路路基垮塌病害实例

以国道319线黔江段山区公路路基垮塌应急处治工程为例,分析了衡重式挡土墙用于处治山区公路路基病害的可行性。处治工程竣工后投入使用已近三年,期间经历了2007年重庆百年一遇降雨和2008年汶川特大地震,工程完好无损,表明处治工程措施科学合理,工程效果良好。     

Damage to railway earth structures and foundations caused by the 2011 off the Pacific Coast of Tohoku Earthquake

Statistics are compiled on the damage to railway earth structures, soil retaining walls and bridge foundations caused by the 2011 off the Pacific Coast of Tohoku Earthquake in Japan and the subsequent tsunami. Several case histories are reported on the damage they created and the rehabilitation works implemented, including the collapse of a high cut slope, the excessive settlement of embankments in lowland areas, the significant scoring of the backfill soil of bridge abutments, the restoration works of tilted bridge foundations and the tsunami-induced collapse of soil-retaining walls and bridge foundations. The good performance of well-designed foundations, which were able to survive the impact of the earthquake, particularly the effects of the earthquake-induced liquefaction of the subsoil layers, is also described.     

考虑倒塌概率修正的钢筋混凝土框架结构地震易损性分析

为研究倒塌概率对非倒塌极限状态的影响,提出了考虑倒塌概率修正的结构地震易损性分析方法。基于全概率定理,将结构极限状态划分为倒塌状态和非倒塌状态两类,若结构发生倒塌则认为结构发生非倒塌极限状态破坏的概率为100%。考虑倒塌概率修正的地震易损性分析方法包含直接方法和间接方法,其中,直接方法是直接对传统地震易损性函数进行修正,而间接方法仅修正地震易损性函数中的概率地震需求参数。以4榀不同高度不同设防烈度的钢筋混凝土平面框架结构作为研究对象,选择100条实际地震动记录作为输入,分别采用直接方法和间接方法开展考虑倒塌概率修正的地震易损性分析。结果表明：倒塌概率对轻微破坏和中等破坏极限状态的影响较小,而对严重破坏极限状态的影响较大;在地震动强度较小时,两种方法对地震易损性的修正结果相差较小;随着地震动强度的提高,两种方法对地震易损性修正结果的差距逐渐增大。     

柔性连接填充墙框架结构模型振动台试验研究

通过对一典型的框架结构1/8整体模型模拟地震振动台试验,测试了模型结构的动力特性、阻尼比及其在7度多遇、7度基本、7度罕遇、8度罕遇烈度地震作用下的加速度和位移反应等,研究了模型结构的破坏机理和破坏模式,运用有限元分析程序对原型结构进行了地震作用下的时程分析,并与试验数据进行了对比分析。对比结果表明,试验与理论分析结果吻合良好。研究得到:该结构体系在7度多遇烈度至设防烈度地震作用下结构自振频率基本不变,结构基本处于弹性阶段;在7度大震作用下,结构自振频率有所下降,最大层间位移角满足规范的弹塑性变形要求;在8度大震作用下,结构局部出现混凝土开裂和压碎现象,但能维持结构不倒塌的工作状态。综合研究结果表明该结构能满足小震不坏、中震可修、大震不倒的抗震设防要求。     

Stability of caisson-type breakwater foundation under tsunami-induced seepage

A tsunami-induced difference between the water levels of the seaward and the landward sides of breakwaters generates one-way seepage in the rubble foundation under the breakwaters. Such seepage may decrease the bearing capacity of the rubble foundation, trigger the piping and/or boiling of the foundation, and cause the scouring of the sandy seabed. In this paper, we describe the stability of a breakwater foundation under the action of seepage based on the results of model tests and FEM analyses. The main feature of our study is the application of the centrifuge technique to such composite hydrodynamic and geotechnical problems. The centrifuge technique can be used to produce high-water pressure and ground stress corresponding to those of prototype-scale breakwaters. The experimental results show that seepage-induced scouring and boiling occur, and that the seepage force decreases the bearing capacity of the rubble foundation. The results of the numerical analyses also reveal the effect of the reduction in bearing capacity in the presence of seepage.     

少剪力墙框架结构在多遇地震下的抗震性能计算分析

纯框架结构的整体侧向刚度较小,在强烈地震作用下侧向变形大,易造成结构整体倒塌破坏。从增加结构整体冗余度的角度出发,考虑添加少量钢筋混凝土剪力墙来提高框架结构的整体抗倒塌能力。并对添加少量剪力墙的各种布置方式及数量进行分析比较,得出可行的平面布置形式及其对框架结构变形形态的影响。分析增设少量剪力墙在多遇地震作用下对框架结构弹性层间位移角的改善情况,在此基础上,进一步得出承担不同倾覆力矩比例的墙体与弹性层间位移角的对应关系。     

Numerical modelling of the cyclic behaviour of RC elements built with plain reinforcing bars

The bond-slip mechanism is one of the features that significantly controls the response as well as damage evolution of reinforced concrete structures when subjected to severe cyclic loadings, such as those induced by earthquakes. Its effect is particularly important in structures built with plain reinforcing bars. For a rigorous simulation of the response of existing RC structures, built mainly with plain bars, the bond-slip mechanism should be considered. However, the majority of the available concrete-steel bond numerical models were developed and calibrated for elements with deformed reinforcing bars. Moreover, the available experimental data on the cyclic behaviour of RC elements built with plain bars is still limited. In this framework, the objective of the present paper is to calibrate a numerical model based on results of a cyclic test performed on a two-span RC beam built with plain bars, which was collected from an existing structure. The numerical modelling was carried out with the nonlinear OpenSees software platform. Particular awareness was devoted to the bond-slip mechanism. The numerical results obtained with the calibrated nonlinear model are presented and compared with the experimental results. The consideration of the bond-slip effect in the numerical model was fundamental to achieve a good agreement between the numerical simulation and the test results.     

Incremental dynamic collapse analysis of RC core‐wall tall buildings considering spatial seismic response distributions

Despite wide‐ranging studies on fragility analysis and collapse safety assessment of short to medium‐rise reinforced concrete (RC) structures, a new interest in the topic is still valuable and even necessary for tall RC buildings. This study aims at establishing fragility relationships as well as collapse probability of high‐rise RC core‐wall buildings under maximum considered earthquake ground motions. This study is carried out in a probabilistic framework on a case study of a fully 3‐dimensional numerical model developed to simulate seismic behavior of a 42‐story building having a RC core‐wall system. Proposing planar and vertical distributions of ductility and damage indices, the incremental dynamic analysis, and the multi‐direction nonlinear static (pushover) analyses were employed to reach the research goal. Median collapse‐level capacities were defined in terms of seismic responses (e.g., ductility/damage indices) as well as several intensity measures by employing statistical analyses and cumulative density functions. Available and acceptable collapse margin ratios were next estimated to quantify collapse safety at maximum considered earthquake shaking level. On an average basis, the statistics indicated 9%–10% and 5%–6% collapse probability of the building subjected to near‐ and far‐field ground motions, respectively.