焦散线法在压剪裂纹应力强度因子测量中的应用

从理论上分析了焦散线法在压剪裂纹应力强度因子测量中的应用,并利用焦散线法测量了有机玻璃标本中两组预制裂纹的应力强度因子. 该方法可综合考虑裂纹面上的摩擦作用、裂纹之间的相互影响和外载荷. 由于不需要了解边界条件,从而提高了测量的可信度.      

工程结构三维疲劳裂纹最大应力强度因子计算

介绍了裂纹的类型、裂纹尖端应力场的奇异性。以一维问题为例,推导论证了奇异单元能够很好的反映裂纹尖端应力场的奇异性。应力强度因子一般表达式表明应力强度因子与载荷呈线性关系,并依赖于物体和裂纹的几何形状和尺寸。本文借助大型通用有限元软件ANSYS,采用位移外插法计算了三维表面裂纹前沿不同位置处的应力强度因子,并与《应力强度因子手册》基于实验的理论公式计算结果相比较。结果表明:有限元结果与理论解误差较小,裂纹最深处应力强度因子最大。     

Analysis of crack movements observed in an alpine bedrock cliff

Crack widths and rock temperatures were monitored on an andestic bedrock cliff in the summit area of the Daisetsu Mountains, Hokkaido, northern Japan. Sequential data recorded the gradual widening of a crack to the point of critical crack extension, which resulted in catastrophic rock breakage. The data indicate that a combination of liquid water in?ltration into crack tip and subsequent freezing is the most signi?cant factor contributing to critical crack extension. The recorded sub‐critical crack movements involved a number of minor crack extensions and contractions, the timing of which correlates well with the magnitude of the reconstructed thermal stresses at the crack tip derived from thermal deformation of the plate‐shaped rock fragment. Larger crack extensions occurred when stress at the crack tip exceeded a threshold value, possibly re?ecting the control of rock fracture mechanics by which cracks are thought to propagate when the stress intensity factor at the crack tip exceeds the threshold values for stress corrosion cracking and the fracture toughness of the material. Copyright © 2004 John Wiley & Sons, Ltd.     

On the propagation of an in-plane shear fault with super-S-wave velocity

The speedv, especially the problem whether super S-wave velocity in the classical model (linear elasticity fracture mechanics) exists, of spontaneous propagation of a shear fault is investigated theoretically. An in-plane shear crack propagating in the crack plane is taken as the model of the shear fault. The results obtained firstly by Kostrov (1975) is extended from sub-Rayleigh wave velocity to super S-wave velocity, and the analytical expression for the stress intensity factorK ₂ in the case ofα>v>β is derived. It is proved that for Poisson mediumK ₂ is positive and real in the velocity range (β, 1.70β). This demonstrates that (β, 1.70β) is the velocity range which fulfils the conditions for spontaneous crack propagation. The existence, convergence and positiveness or negativeness ofK ₂ forv in individual sections are examined, and it is found that for an in-plane shear crack: 1. There are three sections forv, i.e., [0.v _R], (β, 1.70β), andα, respectively, and 2. There are two physically reasonable sections forv, the first is [v _R, β], and the second is [1.70β, α]. These two forbidden sections behave as barriers to fault propagation. The analytical expressions derived in this paper are not only suitable to classical model, but also to the other derivative models (e. g., the slip-weakening model and the renomalization model etc.). The model considered in this paper is more realistic than the static model employed by previous authors. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica, 15, 9–14, 1993.     

Nonlinear shear mass participation factor (rd) for cyclic shear stress ratio evaluation

Most methods for assessment of in situ seismic soil liquefaction potential require evaluation of the earthquake-induced cyclic shear stress ratio (CSR). Estimates of the in situ CSR can be developed directly, using dynamic response analyses, but it is common in ‘simplified’ analysis methods to develop estimates of the in situ CSR using empirical relationships. Unfortunately, the most widely used existing empirical relationships are based on limited response analyses and do not take full advantage of current knowledge of factors affecting this response problem. As a result, they are both biased and unnecessarily imprecise. This paper presents the results of a relatively comprehensive suite of site response studies (2153 site response analyses), performed using carefully selected suites of site conditions and input time histories, to provide an improved basis for development of estimates of in situ CSR using the r_d-approach. The resulting empirical correlations, developed using the Bayesian updating method, provide a much improved basis for simplified empirical evaluation of CSR as a function of (1) depth; (2) earthquake magnitude; (3) intensity of shaking; and (4) site stiffness.     

夹层橡胶隔震支座全刚性性能、回转刚性及高压缩应力性能试验研究

本文详细地研究了夹层橡胶隔震支座的全刚性性能,同时还研究了夹层 橡胶隔震支座的回刚性,并给出了竖向压力及剪切变形对隔震支座回转刚性的影响结果,文末给出了隔震支座在高压缩应力作用下的基本力学性能,研究结果显示在竖向压缩压力达到30MPa时,隔震支座仍可具有良好的力学性能。     

横波各向异性在裂缝和应力分析中的应用

针对裂缝性和低孔低渗地层的横波各向异性特征,反演得到横波各向异性参数,研究了裂缝的发育程度、方位和有效性,并对低孔低渗地层的应力场分布状态和方位进行了综合评价;通过对反演得到的快、慢弯曲波形进行频散分析以及计算单极横波各向异性大小,确定了引起横波各向异性的原因,并结合常规测井资料、岩心及FMI成像资料对分析结果进行了验证和对比,最后对研究区8口典型井的横波各向异性进行了综合处理和评价,得到了该区的横波各向异性特征以及和总的应力场走向.结果表明,利用横波的各向异性参数可以有效的评价裂缝的发育程度、走向及有效性,并能准确的确定地应力分布状态和最大水平应力方位.     

青岛崂山地区环境应力与视应力变化分析

利用青岛市地震监测中心数字台网的地震波形记录,选取震级下限为ML1.0,计算了2003~2004年崂山地震序列过程中青岛地区地震视应力aσpp和环境剪应力τ0值的变化,结果表明,崂山地震序列的中等地震发生前相近震级小震所反映出来的应力增强变化并不明显,2003年以来青岛地区背景应力场也不存在明显的趋势性变化。对青岛崂山地震序列中261个小震的数字化波形记录计算分析后发现,环境剪应力0τ值和视应力aσpp值与震级明显相关,并且相同震级的地震事件所计算出二者的变化与地震序列的活动状态密切相关。     

桅杆结构纤绳连接拉耳孔边裂纹扩展形状变化特性研究

本文采用两自由度的裂纹扩展模型,以桅杆结构纤绳拉耳孔边裂纹前缘最深点和表面点的裂纹扩展增长量来追踪裂纹扩展。基于最小二乘法原理对通过有限元法所获得的各种裂纹形状所对应的裂纹前缘最深点和表面点的无因次形状因子进行多项式曲线拟合,用拟合曲线上的值代替离散的无因次形状因子扩充插值数据库,采用拉格朗日插值法计算任意形状裂纹前缘最深点和表面点无因次形状因子,并计算得到确定裂纹扩展速率所需要的应力强度因子幅度。最后根据裂纹前缘最深点和表面点的裂纹扩展速率确定桅杆结构纤绳连接拉耳孔边裂纹的扩展特性。     

压缩感知技术在地震数据重建中的应用

地震资料室内处理过程要求野外采集的地震资料越多越好,而地震数据远距离快速传输又要求野外地震数据量越少越好.为解决这一矛盾,将基于曲波变换与压缩感知的数据重建技术引入到地震资料处理中,对实际的野外不完整数据进行压缩重建.结果表明,曲波变换相对于傅里叶变换在数据压缩采样方法中占有一定的优势.但是,在对实际资料进行处理时,首先要对资料中的面波进行处理,同时还要在一定曲波基元尺寸的情况下,考虑缺失道数量的影响.最终,得到的重建数据图像纹理清晰、连接自然,从而验证了该方法的实用性和有效性.     

Shear-wave splitting in the crust: Regional compressive stress from polarizations of fast shear-waves

When propagating through anisotropic rocks in the crust, shear-waves split into faster and slower components with almost orthogonal polarizations. For nearly vertical propagation the polarization of fast shearwave (PFS) is parallel to both the strike of the cracks and the direction of maximum horizontal stress, therefore it is possible to use PFS to study stress in the crust. This study discusses several examples in which PFS is applied to deduce the compressive stress in North China, Longmenshan fault zone of east edge of Tibetan plateau and Yunnan zone of southeast edge of Tibetan plateau, also discusses temporal variations of PFS orientations of 1999 Xiuyan earthquake sequences of northeastern China. The results are consistent to those of other independent traditional stress measurements. There is a bridge between crustal PFS and the crustal principal compressive stress although there are many unclear disturbance sources. This study suggests the PFS results could be used to deduce regional and in situ principal compressive stress in the crust only if there are enough seismic stations and enough data. At least, PFS is a useful choice in the zone where there are a large number of dense seismic stations.     

Experimental study of extreme shear stress for shallow flow under simulated rainfall

The raindrop impact and overland flow are two major factors causing soil detachment and particle transportation. In this study, the turbulent characteristics of the shallow rain‐impacted water flow were investigated using a 2‐D fibre‐optic laser Doppler velocimetry (FLDV) and an artificial rainfall simulator. The fluctuating turbulent shear stress was computed using digital data processing techniques. The experimental data showed that the Reynolds shear stress follows a probability distribution with heavy tails. The tail probability increases with an increase of rainfall intensity or raindrop diameter, and it decreases with an increase of Reynolds number. A modified empirical equation was derived using both the raindrop diameter and rainfall intensity as independent variables to provide a better prediction of the Darcy‐Weisbach friction coefficient f under rainfall conditions. Copyright © 2009 John Wiley & Sons, Ltd.     

Comparing different methods of bed shear stress estimates in simple and complex flow fields

Bed shear stress is a fundamental variable in river studies to link ?ow conditions to sediment transport. It is, however, dif?cult to estimate this variable accurately, particularly in complex ?ow ?elds. This study compares shear stress estimated from the log pro?le, drag, Reynolds and turbulent kinetic energy (TKE) approaches in a laboratory ?ume in a simple boundary layer, over plexiglas and over sand, and in a complex ?ow ?eld around de?ectors. Results show that in a simple boundary layer, the log pro?le estimate is always the highest. Over plexiglas, the TKE estimate was the second largest with a value 30 per cent less than the log estimate. However, over sand, the TKE estimate did not show the expected increase in shear stress. In a simple boundary layer, the Reynolds shear stress seems the most appropriate method, particularly the extrapolated value at the bed obtained from a turbulent pro?le. In a complex ?ow ?eld around de?ectors, the TKE method provided the best estimate of shear stress as it is not affected by local streamline variations and it takes into account the increased streamwise turbulent ?uctuations close to the de?ectors. It is suggested that when single‐point measurements are used to estimate shear stress, the instrument should be positioned close to 0·1 of the ?ow depth, which corresponds to the peak value height in pro?les of Reynolds and TKE shear stress. Copyright © 2004 John Wiley & Sons, Ltd.     

Use of Large-Eddy Simulation for the bed shear stress estimation over a dune

Environmental flows are generally characterized by complex bed morphology and high current speeds. Such configurations favor the formation of vortex structures that strongly affect hydrody-namics and sediment transport. Large-Eddy Simulation (LES) enables investigation of the dynam-ics of the largest turbulence scales and, thanks to enhanced calculation resources, has now become applicable for simulating environmental flows. In this paper, a LES approach is developed in a CFD code (TELEMAC-3D), which was originally developed to simulate free surface flows using RANS methods. The present developments involve implementing subgrid models, boundary con-ditions and numerical schemes suitable for LES. The LES version of TELEMAC-3D was validated by comparing results on the model with experimental data for flow past a cylinder. Then, the model was applied to a test case representing flow over dunes. After validating the hydrodynamics, the model was used to assess the bottom shear stress, using both a RANS and a LES approach. Com-parison highlighted the potential contribution of LES to investigating the hydrodynamic forces acting on the bottom.     

基于增量动力法的剪力墙结构地震易损性分析

地震易损性分析是评估结构地震灾害损失的关键。应用PKPM软件设计了不同设防烈度的6个16层剪力墙结构。应用增量动力法求得各结构在不同罕遇烈度地震作用下的最大层间位移角,回归分析给出了最大层间位移角与地震作用加速度峰值的关系式。以最大层间位移角为整体性能指标,进行结构地震易损性分析,给出了结构地震失效概率关于地震作用加速度峰值的计算公式。计算得到了不同设防烈度剪力墙结构在罕遇地震作用下的震害矩阵,为评估框架-剪力墙结构的地震灾害损失,提供了基础数据。     

Dependence of the energy released during earthquake on ambient shear stress

Starting with dislocation model, using the result of the fracture mechanics: the slip displacement at the crack tip is proportional to the length of the crack and the applied ambient shear stressτ ₀ ² , we consider the dislocation in the earthquake to be the slip displacement at the crack tip and have obtained the analysis expresses of displacement and velocity pulse for the circular crack and have calculated the seismic wave energy radiated by earthquake. The seismic wave energyE ∞M ₀ τ ₀ ² f(v) _r , i. e.E is proportional to the seismic momentM ₀ and the square of the ambient shear stressτ ₀ ² and increases with the rupture velocityv _r . In frequency domain, integrating the square of source velocity spectrum derived from our the scaling law model, we have also obtained the seismic wave energyE released by earthquake and earthquake radiated effficiencyη.E ∞M ₀ τ ₀ ² also. If takingτ ₀ = 10.0 MPa, E=4.79M ₀. This result is consistent with the estimate by Vassiliou and Kanamori (1982). Theη=5.26%. The distribution of the seismic wave energy is that most of the energy contains in the frequency range between the first corner frequencyf _c1 and thirdf _c3, amount to 92.3% the energy in the rangef<f _c1 is about 3.85% and 3.85% whenf>f _c3. Thef _c3 is about 8Hz forM ⩾ 6, thus most of radiated energy is below 2Hz. This phenomenon had been verified by Vassiliou Kanamori. Previous results show the energy radiated by earthquake to be strongly dependent on ambient shear stress. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 146–152, 1993. This work was supported by the Deutsche Forschungsgemeinschaft, Bonn, F. R. Germany. The support is grateful acknowledged. The authors are also grateful to Professor Klussmann and Mr. Hasthoff for their lots of help.     

Wave- and current-induced bottom shear stress distribution in the Gulf of Lions

Simulations of both currents and waves were performed throughout the year 2001 to assess the relative contribution of each to their overall erosive potential on the Gulf of Lions shelf. Statistical analysis of bottom shear stress (BSS) was compared to sediment grain-size distribution on the bottom. The hydrodynamic features of the bottom layer coincide with the distribution of surficial sediments, and three areas with different hydro-sedimentary characteristics were revealed. (i) The sandy inner shelf (<30 m) area is a high-energy-wave dominated area but may be subjected to intense current-induced BSS during on-shore winds along the coast and during continental winds mainly in the up-welling cells. (ii) The middle shelf (30–100 m) is a low-energy environment characterised by deposition of cohesive sediments, where the wave effect decreases with depth and current-induced BSS cannot reach the critical value for erosion of fine-grained sediments. (iii) The outer shelf, which has a higher bottom sand fraction than the middle shelf, may be affected by strong south-westward currents generated by on-shore winds, which can have an erosive effect on the fine-grained sediments.     

应用数字地震台网资料求解广东地区的环境剪应力场

应用广东数字地震台网的数字化地震资料,经过预处理,获得每次小地震在观测点处的峰值加速度、峰值速度和峰值位移,再利用适当的衰减模式,将其换算成震源处的值。最后利用它们与构造环境剪应力场的关系,计算出广东地区的构造剪应力场。结果表明,广东地区的总体剪应力值较低,未来发生中强地震的可能性不大。     

广东地区4级左右地震前环境剪应力场的变化

根据1993年陈培善等导出的峰值加速度、峰值速度和峰值位移与构造环境剪应力场τ0的关系，利用广东省数字地震记录研究了广东地区4级左右地震前后环境剪应力场的变化。结果显示，地震前并未观察到中短期异常变化，以短临变化为主，震前3～15天应力等级显著上升，应力等级相对主震后余震以及较早前的小震都要高，且个别小震平均应力等级大于3这一异常现象。