Discrete‐like crack simulation by smeared crack‐based FEM for reinforced concrete

A numerical process that simulates crack propagation in reinforced concrete through post‐crack stress redistribution is presented. This process is developed within the context of the smeared crack approach. Continuity and orientation of the reinforcing bar components are automatically recognized in the pre‐processing stage. The process explicitly outputs crack widths by computing the bond slips along reinforcement, without imposing any additional nodes between the reinforcement and concrete. The process is incorporated with a finite element algorithm, and the validation is investigated through sample 3D static analyses of nine concrete specimens subjected to monotonic shear and flexure loads. These specimens contain relatively well‐distributed steel bars and fiber reinforced polymer (FRP) sheets of reinforcement ratio from 0.11 to 0.57%. The analyses predict the crack patterns and crack widths well, although some disagreements are found between the test and the analysis results. The proposed process outputs discrete, continuous in crack directions, and element boundary‐free crack patterns. Copyright © 2007 John Wiley & Sons, Ltd.     

钻杆失效理论分析方法初探

从有限元分析构件裂纹周围的应力分布出发,导出钻杆中常出现的Ⅰ－Ⅲ型复合裂纹的失稳条件,通过编程计算了不同深度秒同倾角裂纹尖端处的应力强度因子,计算得到的临界裂纹深度可作为钻杆检测仪精度选择的参考,同时也为钻杆寿命评估提供了理论依据。     

埃塞俄比亚欧泊充填处理及鉴定特征研究

埃塞俄比亚WOLLO地区产出的欧泊品种丰富,但火欧泊和水欧泊不稳定,易因外界温度或水分变化形成较多裂纹,严重影响其稳定性及加工性能。因此,本实验对埃塞俄比亚WOLLO地区产出的多裂纹火欧泊、水欧泊样品进行了充填处理,并对充填前、后的样品进行了显微放大观察和红外光谱、相对密度、紫外荧光的测试及分析,总结出了有机充填欧泊的一些鉴定特征。测试及分析结果显示,在2800-3100cm叫范围内红外吸收峰为有机充填欧泊的主要鉴定特征,表面及内部显微充填特征、偏小的相对密度、裂隙处的蠕虫状及空洞缺陷处的斑块状强蓝白色荧光可作为辅助鉴定特征。从样品的充填及测试分析结果可见,埃塞俄比亚WOLLO地区产出欧泊的有机充填方案可行,比较明显的开放裂隙易被充填。     

PHC管桩在基坑工程中应用的实例

就PHC管桩替代钻孔灌注桩在某基坑中的设计应用进行了分析,探讨了设计中几个取值问题.     

甘肃黑方台地区灌溉型黄土滑坡形成机理 与运动学特征 ——以焦家崖头13号滑坡为例

甘肃黑方台地区常年农业灌溉导致塬边产生大量的黄土滑坡,灌溉水长期入渗引起灌区地下水位上升,因地下水作用造成水敏性黄土遇水乃至饱水后强度劣化,进而产生斜坡失稳,因黄土滑坡剪出口高悬于上缓下陡的坡体中部,其成灾模式呈现出高位剪出后高速滑动,并产生远程运移,波及范围大,致灾后果严重。以甘肃省永靖县黑方台焦家崖头滑坡为例,在现场调查和地下水动态监测的基础上,对灌溉型黄土滑坡塑流-拉裂形成机理进行分析,并运用离散元模拟方法,对地下水位上升过程中模型底部饱水黄土软弱层的形成、演化过程和滑坡运动学特征进行模拟研究。结果表明,随地下水位的上升,模型底部软弱层范围不断增大;孔隙水压力主要作用于滑坡底部软弱层饱水黄土;地下水位高程上升至标高1682m时,滑坡产生整体破坏。     

砂岩和大理岩纵波速度及Q值实验研究

利用新近完成的弹性波参数测量系统,我们在静水压力(常压—32MPa)范围内,对不同饱和度砂岩和大理岩的纵波速度和Q 值进行了测试.结果表明,随着静水压力和饱和度的增加,砂岩和大理岩的纵波速度均增加;砂岩的Q 值随静水压力增加,但随饱和度减小.有关静水压力、孔隙流体对岩石纵波和Q 值的影响机理也作了简要论述.     

Non-parametric machine learning methods for interpolation of spatially varying non-stationary and non-Gaussian geotechnical properties

Spatial interpolation has been frequently encountered in earth sciences and engineering.A reasonable appraisal of subsurface heterogeneity plays a significant role in planning,risk assessment and decision making for geotechnical practice.Geostatistics is commonly used to interpolate spatially varying properties at un-sampled locations from scatter measurements.However,successful application of classic geostatistical models requires prior characterization of spatial auto-correlation structures,which poses a great challenge for unexperienced engineers,particularly when only limited measurements are available.Data-driven machine learning methods,such as radial basis function network(RBFN),require minimal human intervention and provide effective alternatives for spatial interpolation of non-stationary and non-Gaussian data,particularly when measurements are sparse.Conventional RBFN,however,is direction independent(i.e.isotropic)and cannot quantify prediction uncertainty in spatial interpolation.In this study,an ensemble RBFN method is proposed that not only allows geotechnical anisotropy to be properly incorporated,but also quantifies uncertainty in spatial interpolation.The proposed method is illustrated using numerical examples of cone penetration test(CPT)data,which involve interpolation of a 2D CPT cross-section from limited continuous 1D CPT soundings in the vertical direction.In addition,a comparative study is performed to benchmark the proposed ensemble RBFN with two other non-parametric data-driven approaches,namely,Multiple Point Statistics(MPS)and Bayesian Compressive Sensing(BCS).The results reveal that the proposed ensemble RBFN provides a better estimation of spatial patterns and associated prediction uncertainty at un-sampled locations when a reasonable amount of data is available as input.Moreover,the prediction accuracy of all the three methods improves as the number of measurements increases,and vice versa.It is also found that BCS prediction is less sensitive to the number of measurement data and outperforms RBFN and MPS when only limited point observations are available.     

Fatigue crack growth investigation on offshore pipelines with three-dimensional interacting cracks

Due to high cost of full-scale experimental setup, this study presents a numerical model on fatigue behaviours of offshore pipeline with multiple coplanar cracks under cyclic tensile loadings. The validation on numerical results is made by other researchers' experimental results, and significant parameters affecting fatigue crack growth are studied.     

A rock damage constitutive model and damage energy dissipation rate analysis for characterising the crack closure effect

Due to the insufficiency of the previous damage constitutive model for rock, an improved damage mechanics model for rock is proposed with characterising the crack closure effect. Otherwise, the effective methods of determining the model parameters and crack closure coefficient are proposed. The results represent that the model can reflect the damage evolution of rocks in the deformation process in the crack closure stage and this improved model is more reasonable than the previous model. Crack closure coefficient also has great effect on distribution parameters. The calculation formula of damage energy dissipation rate considered that crack closure effect is derived and the relationships between damage energy dissipation rate and crack closure coefficient are analysed. Crack closure coefficient has great effect on damage dissipation energy rate. Damage energy dissipation rate increases with the decrease of crack closure coefficient and damage energy dissipation rate increases quickly in the post-peak stage.     

叶巴滩水电站深部破裂岩体波速特征

揭示深部破裂岩体波速特征及深部破裂对岩体卸荷、损伤、完整性及弹性模量的影响,以叶巴滩水电站岸坡深部破裂为典型实例,开展深部破裂现象精细测绘与声波测试。研究表明:根据宏观地质特征与波速,可将深部破裂划分为轻微松弛型、中等松弛型、强烈松弛型;轻微松弛型深部破裂岩体纵波波速大于4 200m/s,中等松弛型深部破裂岩体纵波波速3 000~4 500m/s,强烈松弛型深部破裂岩体纵波波速小于3 000m/s;轻微松弛型深部破裂对岩体卸荷程度、损伤程度、强度弱化影响较小,中等松弛型深部破裂次之,强烈松弛型深部破裂影响最为显著;轻微松弛型深部破裂岩体较完整,中等松弛型深部破裂岩体完整性差-较破碎;强烈松弛型深部破裂岩体已处于较破碎-破碎状态。