基于损伤塑性模型的地下洞室结构地震作用分析

基于损伤力学原理,通过引入损伤变量的方法,详细推导了ABAQUS中的损伤塑性本构模型,描述混凝土后继屈服阶段及其卸荷后的损伤机制和力学行为。此本构模型可考虑循环荷载条件下材料刚度退化和应变率的影响,适用于类似混凝土材料的脆性材料,如岩石等。以某水电站地下厂房洞室结构为例,进行二维动力时程非线性分析,考虑不同的刚度恢复权重因子和应变率相关性对结构损伤的影响。多个数值算例表明：洞室混凝土结构和其周围一定深度的围岩的损伤是一个渐进积累的过程;材料的率相关性效应并不是在地震动作用开始时就立即产生,而是在一段时间后,结构经历一定程度的损伤后才慢慢体现出来;此损伤塑性模型适合地震荷载等循环荷载作用下地下洞室结构的动力时程非线性分析,尤其是强震下采用此损伤塑性模型是合理和必要的。     

基于功能的混凝土重力坝抗震风险模型研究

抗震风险评价是基于功能的抗震设计的关键问题之一。通过对大坝可能出现的抗震风险进行分析论证,在技术和经济上进行风险评估,为大坝业主提供决策依据,也可对抗震风险提出优化措施或对策。在重力坝抗震风险分析中,采用已给出的抗震破损程度划分标准,利用地震危险性分析和坝体地震易损性计算,建立了抗震风险分析模型,进行了抗震措施分析。通过金安桥混凝土重力坝抗震风险实例研究,计算得出抗震优化前后的风险概率,说明了抗震风险模型可用于混凝土重力坝的抗震风险评价。     

岩石低周疲劳损伤模型与损伤变量表达方法

在岩石（体）工程领域,周期荷载作用下岩石的疲劳破坏特性与岩体的长期稳定性密切相关。针对目前对混凝土疲劳损伤研究较多,但对岩石疲劳损伤研究相对较少这一现状,运用损伤力学方法对以累积塑性应变表达的损伤变量进行了分析,指出了目前常用的以累积塑性应变表达的损伤变量表达式存在的理论上的缺点,建立了一种新的岩石疲劳损伤变量表达方法。为研究岩石在疲劳荷载作用下力学性能不断劣化的过程,从连续介质损伤力学的基本理论出发,分析岩石在疲劳荷载下的损伤发展和变形规律,并考虑岩石材料的硬化特性,推导了低周疲劳损伤演化方程,经低周疲劳试验数据分析,所建模型可以较好地反映岩石的疲劳损伤演化规律,可用于岩石在低周疲劳荷载作用下的有限元分析。     

堆石坝地震响应和地基液化分析

利用冶勒大坝已经获得的强震监测资料进行大坝坝体及覆盖层动力参数反演,采用三维非线性有限元动力分析方法,分析冶勒大坝在其已经遭遇的最大地震,即4级地震作用下的坝体动力加速度状况,并根据计算结果判别坝基覆盖层的液化情况,进而对冶勒大坝在所遭受的4级地震下的抗震安全性作出评价。其中坝体堆石料及覆盖层砂粒料静力计算时采用邓肯E-B模型,动力计算是采用Hardin模型,地震响应分析采用等价线性法。     

基于地表冲击荷载作用下的城市地下空间结构动力响应分析

由于地震效应、重载车辆的震动效应或由于不同爆炸物引起的强烈冲击效应,都会给城市地下空间结构带来较大的影响。通过土体的混凝土改进剑桥动力本构模型和混凝土塑性损伤本构模型,建立地表爆炸冲压荷载简化计算模型,对城市地下空间结构在TNT当量100 kg的炸药爆炸冲压荷载作用下进行了动力分析,研究了结构埋深、土体刚度对结构动力响应的影响,分析了远场爆炸地震波作用下地下空间结构的动力响应。计算结果表明,地下空间结构中部顶板产生了轻微的拉伸损伤;当埋深小于5 m时,结构动应力响应较大;结构覆盖土刚度越小,土对爆炸能量的吸收作用越显著;由于爆炸产生的地震波频率高,其对结构动应力的影响较小。研究结果对地下结构的抗爆设计具有一定的参考意义     

基于Coulomb准则的混凝土塑性损伤本构模型及其数值验证

以连续介质不可逆热力学为基础,采用了Mohr-Coulomb屈服准则,提出混凝土塑性损伤耦合的新的本构方程。在该模型中采用了塑性应变 、各向同性损伤标量D作为内变量。这个新的本构关系模型严格满足热力学的基本方程。以不同围压作用下混凝土试件的单轴压缩行为为例,采用开发的程序进行了局部水平上本构模型数值验证。结果表明,模型损伤演化数值结果符合试验趋势。     

走滑断层位错作用下城市地铁隧道损伤分析

为了能够较快速、较准确地估计出穿越活断层城市地铁隧道的抗震薄弱部位,基于拟静力弹塑性有限元方法,以北京地铁7号线工程的区间隧道作为研究对象,采用数值模拟的方法研究了在走滑断层位错作用下地铁隧道的非线性反应。通过在数值计算模型中嵌入合理的损伤塑性本构模型,利用损伤指标研究了走滑断层下衬砌结构的破坏形式,重点分析了结构损伤的开始部位、发展过程以及最终的损伤程度,并建立了能够估计结构损伤范围及破坏最严重位置的统计关系式。结果表明,在走滑断层作用下衬砌结构出现损伤的区域主要发生在活断层附近一定范围内,拱腰部位的损伤最为严重;增加基岩上覆土层厚度能够减轻衬砌结构的破坏程度,当基岩上覆土层厚度大于等于临界覆盖土层厚度时可以不考虑走滑断层断裂对于浅埋隧道的影响。衬砌结构损伤区域长度与震级的大小和土层厚度有关,损伤最严重的位置随土层厚度的变化而改变。研究成果为穿越活断层地铁隧道的抗震设计和安全性评价提供了参考依据。     

主震和余震联合作用下复杂地基上重力坝的稳定性分析

大地震主震发生之后通常伴随强余震,多次余震下大坝的结构损伤破坏累积效应明显。为了解复杂地基上重力坝在主、余地震联合作用下的变形和稳定性,以紧邻汶川地震震中的某大型水利工程重力坝典型坝段A#坝段为研究对象进行研究分析。首先,仅考虑主震作用的影响,采用拟静力法模拟地震主震荷载,运用地质力学模型试验方法,研究主震作用下A#坝段坝与地基的变形特征和模型最终破坏形态;再考虑主、余地震联合作用的影响,采用动力法（即时程分析法）基于ANSYS有限元软件进行计算。研究结果表明,主震作用下模型试验与有限元计算结果基本一致,坝与地基均发生了大变形,且通过模型试验得到了A#坝段最终破坏形态;在主、余地震联合作用下,A#坝段坝与地基的变形的累积增加效应明显,变位特征值比主震作用下明显增大,其坝体最大变形处（坝顶）变位值增幅约为37%,对坝与地基稳定性影响较大。因此,对位于地震高发带复杂地基上的重力坝,应考虑主、余地震联合作用的影响,这样更利于工程的安全。     

地震作用下水平层状岩质边坡累积损伤与破坏模式研究

研究边坡在反复地震作用下的累积损伤对于库区岩质边坡的长期稳定性分析具有重要意义。结合振动台试验与理论分析方法,对水平层状岩质边坡在反复地震作用下的累积损伤与破坏模式进行了深入研究。结果表明:采用混凝土疲劳裂纹扩展的双K准则可以很好地解释边坡的累积损伤曲线的变化趋势,完整的累积损伤演化曲线表现出初始损伤、细观裂纹扩展、宏观裂缝扩展3个阶段;分别采用三次多项式和幂指数建立了微小地震和强震作用下边坡岩体累积损伤演化模型并取得了良好的拟合效果,微小地震作用下边坡岩体累积损伤曲线表现出初期略微下降、中期线性增长、后期平缓增长的正"S"型的3段式特征,强震作用下边坡岩体累积损伤相比微震作用下有较为快速的增长,且在边坡破坏前增速加快。频发微震作用下,水平层状岩质边坡在坡体上部形成阶梯型破坏面并向坡面出露,在坡体下部形成平直的剪切破坏面,坡体最终的破坏面呈阶梯状。     

河湖堤坝在地震作用下稳定性计算分析

以京杭运河扬州段典型堤坝为例,利用极限平衡分析法、地震拟静力数值分析法和地震动力数值分析法计算分析地震作用下堤坝的稳定性,分析这三种方法计算分析地震作用下堤坝稳定性得到的结果的差异及产生差异性的原因,评价该段堤坝地震作用下的稳定性。结果表明:在天然工况下堤坝稳定性状态良好,在基本地震动工况处于明显不稳定状态,可能出现明显局部塑性破坏,罕遇地震动工况下处于严重不稳定状态,可能会出现垮塌性破坏。该研究为河湖堤坝的地震灾害预测提供依据,也为今后类似地区地震作用下堤坝的稳定性分析计算提供借鉴。     

Seismic performance evaluation of dam-reservoir-foundation systems to near-fault ground motions

Ground motion records obtained in recent major strong earthquakes have provided evidence that ground motions recorded near the near-fault regions differ in many cases from those observed further away from the seismic source. As the forward directivity and fling effect characteristics of the near-fault ground motions, they have the potential to cause more considerable damage to structures during an earthquake. Therefore, understanding the influence of near-fault ground motions on the performance of structures is critical to mitigate damage and perform effective response. This paper presents results of a study aimed at evaluating the effects of near-fault and far-fault ground motions on seismic performance of concrete gravity dams including dam-reservoir-foundation interaction. Koyna gravity dam is selected as a numerical application. Four different near-fault ground motion records with an apparent velocity pulse are used in the analyses. The earthquake ground motions recorded at the same site from other events that the epicenter far away from the site are employed as the far-fault ground motions. The seismic performance evaluation method based on the demand-capacity ratio, the cumulative overstress duration and the spatial extent of overstressed regions is presented. The concrete damaged plasticity model including the strain hardening or softening behavior is employed in nonlinear analyses. Nonlinear seismic damage analyses of the selected concrete dam subjected to both near-fault and far-fault ground motions are performed. The results obtained from the analyses show the effects of near-fault ground motions on seismic performance of concrete gravity dams and demonstrate the importance of considering the near-fault ground excitations.     

Strong ground motion estimation in the Sea of Marmara region (Turkey) based on a scenario earthquake

We perform a broadband frequency bedrock strong ground motion simulation in the Marmara Sea region (Turkey), based on several fault rupture scenarios and a source asperity model. The technique combines a deterministic simulation of seismic wave propagation at low frequencies with a semi-stochastic procedure for the high frequencies. To model the high frequencies, we applied a frequency-dependent radiation pattern model, which efficiently removes the effective dependence of the pattern coefficient on the azimuth and take-off angle as the frequency increases. The earthquake scenarios considered consist of the rupture of the closest segments of the North Anatolian Fault System to the city of Istanbul. Our scenario earthquakes involve the rupture of the entire North Anatolian Fault beneath the Sea of Marmara, namely the combined rupture of the Central Marmara Fault and North Boundary Fault segments. We defined three fault rupture scenarios based on the location of the hypocenter, selecting a preferred hypocentral location near a fault bend for each case. We analysed the effect of location of the asperity, within the Central Marmara Fault, on the subsequent ground motion, as well as the influence of anelasticity on the high-frequency attenuation characteristics. The fault and asperity parameters for each scenario were determined from empirical scalings and from results of kinematic and dynamic models of fault rupture. We calculated the resulting time series and spectra for ground motion at Istanbul and evaluated the sensitivity of the predictions to choice of model parameters. The location of the hypocenter is thus shown to be a critical parameter for determining the worst scenario earthquake at Istanbul. We also found that anelasticity has a significant effect on the regional attenuation of peak ground accelerations. Our simulated ground motions result in large values of acceleration response spectra at long periods, which could be critical for building damage at Istanbul during an actual earthquake.     

场地条件对地震动和震害影响的研究进展与建议

场地条件对地震动和震害有重要影响。本文简要回顾了场地条件对地震动和震害影响的研究历史,总结和评述了这一领域的研究进展。重点对地形地貌、岩土类型、覆盖层厚度、土层结构、地下水、岩土动力性质及物理地质现象等对地震动和震害的影响进行了总结和评述。提炼和概括了目前场地条件对地震动和震害影响研究中比较一致的几点认识。在此基础上,提出了这一领域当前应进一步研究的问题,主要包括地震现场资料调查、局部地形几何尺度、场地分类、覆盖层安全厚度界限、近断层地震动参数分布规律、活断层避让距离,以及强震资料积累等关键问题。     

Numerical simulation of the seismic response of the Zipingpu concrete face rockfill dam during the Wenchuan earthquake based on a generalized plasticity model

The strong ground motion of the 2008 Wenchuan earthquake in China caused considerable damage to the Zipingpu concrete face rockfill dam (CFRD). The maximum crest settlement was approximately 1.0 m, and compressive failure and joint dislocations were observed in the face slabs. This damage has made it necessary to understand the damage pattern and safety of high CFRDs subjected to strong earthquake shaking, and the response of the Zipingpu CFRD during the Wenchuan earthquake can be used as a benchmark for this purpose. In this study, a 3D dynamic procedure was employed to simulate the dynamic responses of the Zipingpu CFRD. The rockfill materials were described using a generalized plasticity model, while the interfaces between the face slabs and cushions were modeled using zero-thickness interface elements that follow a perfect elasto-plastic stress–strain model in the tangential direction using Coulomb’s friction law. Dam deformation, face-slab stress, and face joint dislocations were simulated, and the results were compared with the field measurements. Using the generalized plastic model, the residual deformation of the dam during the earthquake could be directly obtained without being complemented by separate, semi-empirical procedures. The rockfill materials shrank to the center of the valley due to the strong shaking, causing crushing damage in the zone of the slabs. The dislocation of construction joints was also duplicated by the numerical procedure. The results of this study indicate that a 3D finite element procedure based on a generalized plasticity model can be used to evaluate the dynamic responses of CFRDs during strong earthquakes.     

黄土塬地震动响应特征分析

2008年汶川Ms8.0级强烈地震对远离震中的黄土塬地区造成了较为严重的破坏,局部场地的震害和地震动放大效应显著。以典型黄土塬场地为对象,应用地形台阵流动观测和有限元计算方法,系统开展强震动作用下黄土塬边坡场地动力响应特征研究;应用大型振动台模拟试验和数值计算方法,重点探讨黄土塬平台场地在汶川地震作用下地表加速度响应随覆盖层厚度、地震动强度的变化规律以及对建筑结构的潜在影响。结果表明：黄土塬边坡顶部存在低频但较高放大系数的现象,可能与斜坡高差与入射波波长之比密切相关;大角度（60°～70°）黄土塬边坡对地震动的放大效应十分显著,坡顶加速度峰值（PGA）放大可达2倍,反应谱卓越周期放大可达5倍;较厚黄土塬平台场地加速度放大可达2倍以上,地震烈度增加1度,对于场地上固有周期0.7～2.0 s和周期大于3.0 s的建筑物地震反应将显著增加。     

Structural damages of the May 19, 2011, Kütahya–Simav earthquake in Turkey

Reconnaissance observations are presented on the building damage caused by the May 19, 2011, Kütahya–Simav earthquake in Western Turkey as well as an overview of strong ground motion data recorded during the earthquake is given. According to Disaster and Emergency Management Presidency of Turkey, the magnitude of the earthquake is 5.7 in local magnitude scale. Although the earthquake can be regarded as a moderate event when considering its magnitude and strong motion recordings, it caused excessive structural damage to buildings in Simav district and several villages in the near vicinity. During the field investigation, different types of structural damage were observed mainly in the reinforced concrete frame buildings with infill walls and masonry buildings with various types of construction materials. Observed damage resulted from several deficiencies in structural and non-structural components of the buildings. Poor construction materials and workmanship, non-conforming earthquake-resistant design and construction techniques and non-ductile detailing are the main reasons for such an extensive damage, as observed in many past earthquakes in Turkey.     

液化与非液化场地加速度反应谱对比

通过对2011年新西兰发生的6.3级地震中获取的硬土场地、软土场地和液化场地强震记录实测资料进行分析,研究包括3种类型场地的地震动特征及其相互关系。分析的强震记录为震中距小于50 km,且峰值大于0.05g的23个场地上的加速度记录,其中含3个硬场地、11个软场地和9个液化场地。3种类型场地上的放大系数谱对比分析表明,硬土场地、软土场地和液化场地上的地震动特征具有明显区别,三者层次清晰,差别显著,从地震动表现上液化场地已构成一个与常规场地并列的独立单元;液化场地减少地震动高频分量但同时对低频分量显著放大,与非液化场地相比,液化场地可使其上短周期结构反应减小一半,但同时可使其上长周期结构反应放大2.5～5.0倍;土层的液化对此次地震中克莱斯特彻奇市中心CTV大楼的破坏应有很大影响,大楼自振周期约为0.7 s,地震中土层液化使场地加速度反应谱卓越周期由0.1～0.3 s增到0.5～1.0 s,与大楼的自振周期趋于吻合,加重了大楼震害。以此为鉴,按现有规范中地震动的设计方法,如遇液化场地将对长周期结构给出明显危险的结果,因此从振动角度今后进行结构抗震设计时,可液化场地上的地震动应给予特殊考虑。     

金沙江阿海水电站混凝土重力坝地震抗滑稳定性的时程法分析

通过动力有限元时程法分析了金沙江阿海混凝土重力坝在设计地震动(0.344g)作用下的动态响应,计算模型考虑了动水压力作用、大坝-岩基相互作用,用黏弹性吸波边界模拟了地震动能量向无限远域逸散的地基“辐射阻尼”效应。通过将坝体惯性力时程极大值与振型分解反应谱法的惯性力极值对比,从而验证了复杂动力数值模拟结果的正确性,为后续分析打下了基础。采用沿滑面的应力积分法得到了大坝沿建基面的瞬态抗滑安全系数时程。计算结果表明：阿海重力坝在设计地震动(0.344g)作用下的安全系数时程的极小值为1.146,大坝整体稳定性良好,可不采取提高整体抗滑     

Simulation of large earthquakes and its implications on earthquake insurance rates: a case study in Bursa region (Turkey)

Ground motion intensity parameters of past and potential earthquakes are required for a range of purposes including earthquake insurance practice. In regions with no or sparse earthquake recordings, most of the available methods generate only peak ground motion parameters. For cases where full ground motion time histories are required, simulations that consider fault rupture processes become necessary. In this study, a major novel use of simulated ground motions is presented in insurance premium calculations which also require ground motion intensity measures that are not always available through observations. For this purpose, potential earthquakes in Bursa are simulated using stochastic finite-fault simulation method with dynamic corner frequency model. To ensure simulations with reliable synthetic ground motions, input parameters are derived from regional data. Regional model parameters are verified by comparisons against the observations as well as ground motion prediction equations. Next, a potential large magnitude event in Bursa is simulated. Distribution of peak ground motion parameters and time histories at selected locations are obtained. From these parameters, the corresponding Modified Mercalli Intensities (MMI) are estimated. Later, these MMIs are used as the main ground motion parameter in damage probability matrices (DPM). Return period of the scenario earthquake is obtained from the previous regional seismic hazard studies. Finally, insurance rates for Bursa region are determined with implementation of two new approaches in the literature. The probability of the scenario event and the expected mean damage ratios (MDR) from the corresponding DPMs are used, and the results are compared to Turkish Catastrophe Insurance Pool (TCIP) rates. Results show that insurance premiums can be effectively computed using simulated ground motions in the absence of real data.     

Nonlinear Analysis of Local Site Effects on Seismic Ground Response in the Bam Earthquake

The influence of local geologic and soil conditions on the intensity of ground shaking is addressed in this study. The amplification of the ground motion due to local site effects resulted in severe damage to dwellings in the Bam area during the 2003 Bam Earthquake. A unique set of strong motion acceleration recordings was obtained at the Bam accelerograph station. Although the highest peak ground acceleration recorded was the vertical component (nearly 1 g), the longitudinal component (fault-parallel motion) clearly had the largest maximum velocity as well as maximum ground displacement. Subsurface geotechnical and geophysical (down-hole) data in two different sites have been obtained and used to estimate the local site condition on earthquake ground motion in the area. The ground response analyses have been conducted considering the nonlinear behavior of the soil deposits using both equivalent linear and nonlinear approaches. The fully nonlinear method embodied in FLAC was used to evaluate the nonlinear soil properties on earthquake wave propagation through the soil layer, and compare with the response from the equivalent linear approach. It is shown that thick alluvium deposits amplified the ground motion and resulted in significant damage in residential buildings in the earthquake stricken region. The comparison of results indicated similar response spectra of the motions for both equivalent and nonlinear analyses, showing peaks in the period range of 0.3–1.5 s. However, the amplification levels of nonlinear analysis were less than the equivalent linear method especially in long periods. The observed response spectra are shown to be above the NEHRP building code design requirements, especially at high frequencies.