Reliability and variance-based sensitivity analysis of arch dams during construction and reservoir impoundment

The static performance of arch dams during construction and reservoir impoundment is assessed taking into account the effects of uncertainties presented in the model properties as well as the loading conditions. Dez arch dam is chosen as the case study; it is modeled along with its rock foundation using the finite element method considering the stage construction. Since previous studies concentrated on simplified models and approaches, comprehensive study of the arch dam model along with efficient and state-of-the-art uncertainty methods are incorporated in this investigation. The reliability method is performed to assess the safety level and the sensitivity analyses for identifying critical input factors and their interaction effects on the response of the dam. Global sensitivity analysis based on improved Latin hypercube sampling is employed in this study to indicate the influence of each random variable and their interaction on variance of the responses. Four levels of model advancement are considered for the dam-foundation system: 1) Monolithic dam without any joint founded on the homogeneous rock foundation, 2) monolithic dam founded on the inhomogeneous foundation including soft rock layers, 3) jointed dam including the peripheral and contraction joints founded on the homogeneous foundation, and 4) jointed dam founded on the inhomogeneous foundation. For each model, proper performance indices are defined through limit-state functions. In this manner, the effects of input parameters in each performance level of the dam are investigated. The outcome of this study is defining the importance of input factors in each stage and model based on the variance of the dam response. Moreover, the results of sampling are computed in order to assess the safety level of the dam in miscellaneous loading and modeling conditions.     

混凝土坝-基岩地震动力相互作用时域有限元分析

混凝土坝地震响应分析是坝工安全评估的关键一步。坝与基岩动力相互作用对混凝土坝地震响应具有重要影响。因此,建立一个可考虑坝与基岩动力相互作用影响的数值分析方法是十分必要的。给出了分析混凝土坝–基岩系统地震响应的时域有限元法。在时域有限元分析中,地震波的输入以及地基辐射阻尼的模拟常常是2个十分重要的课题。基于柱面波动方程提出了能同时实现地震动输入和模拟地基辐射阻尼的方法,这种方法非常简单有效,几个数值算例验证了方法的精度和有效性。最后,对混凝土重力坝地震响应进行了数值分析,结果表明无限地基辐射阻尼的影响是显著的。     

基于非线性剪胀模型的面板堆石坝应力变形分析

介绍了一种力学概念明确、简单实用的非线性剪胀模型,给出了本构关系的刚度系数矩阵,应用该模型对某堆石坝工程的堆石料真三轴试验进行了计算模拟,并与试验成果进行比较,验证了模型的合理性。在此基础上,分别采用非线性剪胀模型和邓肯E–B模型完整模拟了坝体分层填筑、面板分期以及分期蓄水全过程,对坝体应力与变形、面板应力与变形计算成果进行对比分析,验证了非线性剪胀模型在面板堆石坝静力有限元分析中的适用性。     

In-plane transversal normal stresses in the concrete face of CFRD induced by the first-dam reservoir filling

To evaluate the effects of dam height, valley narrowness and width of concrete slabs on the first-dam reservoir filling in-plane transversal normal stresses in the concrete face of CFRD´s, 3D finite difference analyses were carried out. Behavior of rockfill dams considered in this study was defined from the monitoring of a number of 3D sets of pressure cells and extensometers installed in three large dams in Mexico. The 3D analyses results show that high in-plane transversal compressive stresses develop within the concrete panels located in the central concrete face zone upon dam reservoir filling loading. Likewise, in-plane induced tensile transversal stresses in the zones near the abutments increase the potential of slabs cracking and damaging the waterstops in-between the vertical and perimetral joints. From the results of the 3D finite difference analyses, a simple method to estimate in-plane normal stresses in the concrete face is advanced and through comparisons with the results of a 3D case numerical study, its accuracy assessed.     

动载作用下钢筋混凝土梁非线性有限元分析

利用大型通用有限元软件ANSYS对钢筋混凝土梁在爆炸荷载作用下的动力响应进行数值模拟，其中，混凝土采用ANSYS软件中特有的SOLID65单元类型和专门的材料模型CONCRETE，钢筋采用LINK8杆单元和随动硬化双线性弹塑性(Kinematic Hardening Bilinear Plasticity)模型来实现，并与Suidan和Schnobrich[1]的方法进行比较，计算结果与Suidan和Schnobrich预示的响应十分吻合。     

Earthquake performance assessment of concrete gravity dams subjected to spatially varying seismic ground motions

This paper investigates the earthquake performance of concrete gravity dams under spatially variable seismic excitations. A nonlinear finite element model is developed and validated using shake table experimental results. The model is then subjected to spatially varying earthquake ground motions incorporating the wave passage effect, with values for apparent propagation velocities consistent with the source-site geometry and the shear wave velocity in the foundation rock. The evaluation reveals that different response patterns occur when spatially non-uniform and uniform seismic ground motions are applied as input excitations to the model, because spatially non-uniform excitations induce the quasi-static response, whereas uniform excitations do not, and, in addition, the dynamic response caused by different input motions varies. Notably, spatially non-uniform excitations produce larger opening at the heel of the dam and severer slipping at its toe; this latter observation can have a significant effect on the global equilibrium and stability of the dam during an earthquake.     

高拱坝基础大垫座及周边缝设置研究

 提出高拱坝基础承载力对建基面的要求,讨论坝肩与河床基础大垫座及周边缝的工作机制、大垫座及周边缝设置的非线性分析特点以及其与高坝整体稳定的关系。指出大垫座设置对基础刚度的对称性、大坝整体稳定性有显著提高的效应。结合高拱坝(英古里、李家峡拱坝和锦屏I级拱坝)实例,详细讨论高拱坝在基础设置垫座后的安全度及坝踵、坝址应力分布优化情况。拱坝所提出的问题对我国目前的高拱坝建设具有指导意义。     

Risk-based probabilistic thermal-stress analysis of concrete arch dams

The probabilistic risk of arch dam failure under thermal loading is studied. The incorporated uncertainties, which are defined as random variables, are associated with the most affecting structural (material) properties of concrete and thermal loading conditions. Karaj arch dam is selected as case study. The dam is numerically modeled along with its foundation in three-dimensional space; the temperature and thermal stress distribution is investigated during the operating phase. The deterministic thermal finite element analysis of the dam is combined with the structural reliability methods in order to obtain thermal response predictions, and estimate the probability of failure in the risk analysis context. The tensile overstressing failure mode is considered for the reliability analysis. The thermal loading includes ambient air and reservoir temperature variations. The effect of solar radiation is considered by an increase in the ambient temperatures. Three reliability methods are employed: the first-order second-moment method, the first-order reliability method, and the Monte-Carlo simulation with Latin Hypercube sampling. The estimated failure probabilities are discussed and the sensitivity of random variables is investigated. Although most of the studies in this line of research are used only for academic purposes, the results of this investigation can be used for both academic and engineering purposes.     

碧口土石坝与混凝土防渗墙在各运用期的应力与位移的分析

国内最高的碧口土石坝及其坝下尚有国内最宽与最深的两道混凝土防渗墙,蓄水七年多来运行良好。应用改进的邓肯模型,对其作了施工期、蓄水期和稳定渗流期的有限元分析,获得了应力与位移场在运用过程中的演变情况,说明建筑物是安全的,也与尚有效的防渗墙观测资料基本相符。提出:今后在高土石坝设计中,应注意坝体中的荷载传递;混凝土防渗墙是强度接近临界状态的承压构件。     

地基刚度和不均匀性对混凝土大坝地震响应的影响

应用比例边界有限元方法进行了坝-水库-无限地基的动力相互作用分析。深入研究了无限地基刚度变化以及地基非均匀性对大坝地震响应的影响。计算了不同的均匀地基刚度和地基刚度随深度变化情况下Koyna大坝的频响曲线以及地震作用下大坝的时程响应。计算结果表明,地基刚度和不均匀性对大坝地震响应产生重要影响。对于均质地基刚度增加时,坝的地震响应随之增加;对于地基刚度随深度增加的不均匀地基,坝的地震响应增加迅速。此外还讨论了工程中广泛应用的无质量地基模型对于相互作用分析的适用性问题。     

Comparison of the expected damage patterns from two- and three-dimensional nonlinear dynamic analyses of a roller compacted concrete dam

The seismic performance of the tallest roller-compacted concrete gravity dam in Turkey is investigated in this study. For this purpose, two- and three-dimensional nonlinear dynamic finite element analyses were conducted to investigate the expected damage under simulated ground motions. Based on the results of finite element simulations, it was found that the three-dimensional behaviour of the dam is substantially different from the idealised two-dimensional monolith behaviour, even for a dam having monoliths separated with transverse joints. In addition, it was determined that in order to limit the cracking at the base of the dam, higher strength grout-enriched concrete must be used on the upstream and downstream faces. This study demonstrates the importance of three-dimensional modelling for gravity dams built in relatively narrow valleys along with the significance of the modelling of the nonlinear response for seismic performance assessment.     

300m级超高面板堆石坝变形规律的研究

采用三维有限元数值分析方法研究了300m级超高混凝土面板堆石坝的变形规律。指出坝体分区、筑坝材料特性特别是流变特性是影响超高面板堆石坝变形性状的主要因素,要重视超高面板堆石坝上游部分坝体变形的鼓肚现象。建议了合理选择筑坝材料,适当提高下游堆石区填筑标准、全断面均衡填筑、上部1/3左右坝体采用变形模量较高的坝料,待坝体变形基本趋于稳定才浇筑面板以及考虑设置面板永久水平缝等工程措施来改善超高面板堆石坝的应力变形性状。     

高心墙堆石坝坝基廊道受力特性研究

在中国水资源最为丰富的西部地区,河床覆盖层厚达数十米甚至百米,一大批土石坝正在和将在这些大江大河上建设。坝体心墙与坝基防渗墙多采用廊道这种结构型式进行连接,廊道受力条件复杂,是工程成败的关键,但是有些已建工程却出现了廊道漏水的现象,廊道开裂和结构缝破坏成为亟待解决的问题。为了对廊道受力情况和开裂规律有一个清楚的认识,分析总结了几个工程廊道的监测资料,同时基于混凝土非线性本构理论,建立有限元模型对廊道进行了数值模拟。对监测结果和数值计算结果进行对比分析之后,探讨了廊道中的结构缝问题和廊道整体的受力规律,指明了廊道中需要重点关注的易开裂部位,为廊道合理配筋提供了指导,同时为类似工程的决策提供参考。     

Performance of soft-hard-soft (SHS) cement based composite subjected to blast loading with consideration of interface properties

This paper presents a combined experimental and numerical study on the damage and performance of a soft-hard-soft (SHS) multi-layer cement based composite subjected to blast loading which can be used for protective structures and infrastructures to resist extreme loadings, and the composite consists of three layers of construction materials including asphalt concrete (AC) on the top, high strength concrete (HSC) in the middle, and engineered cementitious composites (ECC) at the bottom. To better characterize the material properties under dynamic loading, interface properties of the composite were investigated through direct shear test and also used to validate the interface model. Strain rate effects of the asphalt concrete were also studied and both compressive and tensile dynamic increase factor (DIF) curves were improved based on split Hopkinson pressure bar (SHPB) test. A full-scale field blast test investigated the blast behavior of the composite materials. The numerical model was established by taking into account the strain rate effect of all concrete materials. Furthermore, the interface properties were also considered into the model. The numerical simulation using nonlinear finite element software LS-DYNA agrees closely with the experimental data. Both the numerical and field blast test indicated that the SHS composite exhibited high resistance against blast loading.     

深覆盖层上土石坝心墙与防渗墙连接型式研究

深厚覆盖层上建造的土石坝常采用封闭式防渗系统。当心墙坝防渗系统坝体采用沥青混凝土心墙、坝基采用封闭式防渗墙时,心墙混凝土基座、防渗墙与相邻土体之间将产生不均匀沉降,易引起基座混凝土断裂和坝壳及覆盖层土体剪切破坏。针对心墙坝坝体心墙与坝基防渗墙合理的连接型式问题,结合某水库工程,采用非线性有限元法,建立三维有限元模型,分析研究了心墙基座与防渗墙不同连接型式下坝体与坝基的变形和应力。通过坝体和坝基的变形协调分析以及心墙基座和防渗墙的应力分析,推荐了合理的连接型式,即深厚覆盖层上沥青混凝土心墙坝坝基采用封闭式防渗墙时,宜采用心墙基座与防渗墙间预留空隙的连接型式,其空隙大小与坝基覆盖层厚度及其力学特性以及防渗墙弹性模量有关,需经计算分析确定。     

Numerical analysis of nonlinear dynamic behavior of earth dams

A numerical study is conducted to investigate the dynamic behavior of earth dams. The numerical investigation employs a fully nonlinear dynamic finite difference analysis incorporating a simple elastic perfectly plastic constitutive model to describe the stress-strain response of the soil and the Rayleigh damping to increase the level of hysteretic damping. The extended Masing rules are implemented into the constitutive model to explain more accurately the soil response under general cyclic loading. The soil stiffness and hysteretic damping change with loading history. The procedures for calibrating the constructed numerical model with centrifuge test data and also a real case history are explained. For the latter, the Long Valley (LV) earth dam subjected to the 1980 Mammoth Lake earthquake as a real case-history is analyzed and the obtained numerical results are compared with the real measurements at the site in both the time and frequency domains. Relatively good agreement is observed between computed and measured quantities. It seems that the Masing rules combined with a simple elasto-plastic model gives reasonable numerical predictions. Afterwards, a comprehensive parametric study is carried out to identify the effects of dam height, input motion characteristics, soil behavior, strength of the shell materials and dam reservoir condition on the dynamic response of earth dams. Three real earthquake records with different levels and peak acceleration values (PGAs) are used as input motions. The results show that the crest acceleration decreases when the dam height increases and no amplification is observed. Further, more inelastic behavior and more earthquake energy absorption are observed in higher dams.     

严寒、高震、深覆盖层混凝土面板坝关键技术研究综述

自 20 世纪 90 年代以来,新疆的水库建设已从平原水库转入山区水库建设,以混凝土面板砂砾石坝为主要的当地材料坝,得到了迅速发展。新疆于 20 世纪 70 年代末,开始引进混凝土面板坝筑坝技术,采用天然砂砾石填筑百米级高坝,是区别于一般面板堆石坝的主要特点。针对严寒地区、深覆盖层、高地震区等不良环境地质条件,全面总结基础上系统地建立了混凝土面板砂砾石坝筑坝关键技术体系,阐述了在抗震结构设计、坝体变形控制、坝体渗流控制等方面取得的创新突破,研究指出施工工艺的不断改进,大型机械压实功能的不断增强,为该坝型推广应用和安全性能提高,提供了重要的技术保障。对于提高混凝土面板砂砾石坝建设和运行管理水平具有重要意义。     

爆炸荷载作用下钢筋混凝土构件动力响应的数值模拟

考虑了高应变率下混凝土和钢筋的动态本构模型,根据已有试验资料对炸药、钢筋混凝土构件和两者之间的空气建立数值模型,使用显式动力有限元软件LS-DYNA模拟了空气中点源炸药爆炸产生的爆轰冲击作用于钢筋混凝土构件和爆炸荷载作用下构件动力响应的全过程。结果表明,钢筋混凝土构件受到爆轰冲击的作用区域主要集中在构件迎爆面,构件背爆面受到的绕射冲击作用相比可以忽略;构件内应力波的传播不规则,同一位置处剪切应力波峰值早于弯曲应力波出现,构件的易损部位和爆轰冲击的主要作用位置有关,构件中部较端部更易发生弯曲破坏,而端部较中部更易发生剪切破坏。数值模拟结果和试验数据具有较好的一致性。成果表明,本文的数值模拟方法可以更准确地模拟爆炸荷载作用下钢筋混凝土构件的破坏机理和研究构件抗爆能力。     

Modelling autogenous expansion for magnesia concrete in arch dams

Magnesia Concrete is a kind of expansive concrete used in Chinese hydraulic engineering more and more widely. To evaluate the effects of autogenous expansion on the stresses of arch dams, a simple model of autogenous expansion for Magnesia Concrete in dam engineering is presented. This model is based on three assumptions: 1) the total amount of autogenous expansion of Magnesia Concrete is related only to the properties of materials and mixing of concrete; 2) the autogenous expansion of Magnesia Concrete is irreversible due to the irreversibility of hydration reaction of Magnesia in the concrete; 3) the autogenous expansion strain rates of Magnesia Concrete bear a relation between temperature and residual Magnesia per unit volume of concrete. The model is verified by some experimental data of autogenous expansion of Magnesia Concrete and field-measured data of an arch dam in China. Embedded into finite element arch dam simulation software, this model is employed to simulate the effects of autogenous expansion of Magnesia Concrete in hydraulic engineering.