Evolution of cumulative Coulomb failure stress in northeastern Qinghai-Xizang (Tibetan) Plateau and its effect on large earthquake occurrence

We simulate accumulative Coulomb failure stress change in a layered Maxwell viscoelastic media in the northeastern Qinghai-Xizang （Tibetan） Plateau since 1920. Lithospheric stress/strain evolution is assumed to be driven by dislocations of large earthquakes （M≥7.0） and secular tectonic loading. The earthquake rupture parameters such as the fault rupture length, width, and slip are either adopted from field investigations or estimated from their statistic relationships with the earthquake magnitudes and seismic moments. Our study shows that among 20 large earthquakes （M≥7.0） investigated, 17 occurred in areas where the Coulomb failure stress change is positive, with a triggering rate of 85%. This study provides essential data for the intermediate to long-term likelihood estimation of large earthquakes in the northeastern Tibetan Plateau.

Fatigue behavior and cumulative damage rule of concrete under cycli ccompression with constant confined stress

The effects of different lateral confinement stress on the fatigue behavior and cumulative damage of plain concrete were investigated experimentally. Eighty 100mm×100mm×100mm specimens of ordinary strength concrete were tested with constant-or variable-amplitude cyclic compression and lateral confinement pressure in two orthogonal directions. A fatigue equation was gained by modifying the classical Aas-Jakobsen S-N equation and used for taking into account the effect of the confined stress on fatigue strength of plain concrete. The present study indicates that the fatigue failure is greatly influenced by the sequence of applied variable-amplitude fatigue loading, and Miner’s rule is inapplicable to predict the residual fatigue life, especially in the sequence of low to high. The present research also shows that the exponent d of the Corten-Dolan’s damage formula is a constant depending on the materials and the levels of load spectrum, and d can be determined through the two-stage fatigue tests. The residual fatigue lives predicted by Corten-Dolan’s damage formula are found to be in good agreement with the results of the experiments.

Cumulative Coulomb Failure Stress Change in the Basin- range Region of West Beijing and Its Effect on Strong Earthquakes

Since 231 B. C.,a total of 15 M6.0 - 7.5 earthquakes have been recorded in the west Beijing basin-range tectonic region( 38.3°- 41.5° E,112°- 116.2° N),a region mainly under the action of tensional normal faulting. In this paper,we calculate the Coulomb stress change of each earthquake and the cumulative Coulomb stress change,and on this basis we analyze the stress triggering of strong earthquakes. The research shows that there are 10 of 14 earthquakes that occurred in the trigger zones,in which the Coulomb stress change is positive,and the trigger rate is 71%. The positive areas of cumulative Coulomb stress change caused by these 15 earthquakes are: middle of northern Liulengshan fault,Northern Huaizhuo basin fault,Xinbaoan-Shacheng fault,Sangganhe fault and Southern Yuxian basin fault. This necessarily increases the seismic risk of these faults and can be used as a reference for future seismic risk analysis in this area.

基于CLD的风电叶片挥舞疲劳试验寿命预测方法

随着风电叶片长度的不断增加,挥舞疲劳测试时叶片自重和夹具重量对叶片产生的影响已无法忽略。本文以株洲时代新材料科技股份有限公司某90 m级叶片挥舞疲劳试验主梁失效为研究对象,测试了主梁拉挤板在不同应力比情况下的疲劳S-N曲线,基于Goodman等寿命图提出一种新的复合材料疲劳寿命预测方法。通过考虑平均应力对主梁疲劳寿命的影响,文章对比分析理论试验预测损伤及疲劳试验实际损伤,得出两个重要结论:(1)现有不考虑叶片自重的挥舞疲劳试验载荷等效方法已不能反映叶片的实际受载情况;(2)本文提出的考虑均值的Goodman疲劳寿命计算方法能够较准确地预测叶片的疲劳试验寿命。

重塑黄土的往返加卸载真三轴试验研究

针对不同应力路径往返加卸载条件下黄土累积塑性应变发展特性,以重塑黄土为研究对象,利用真三轴仪开展不同应力路径的往返加卸载试验研究,探究不同应力路径、应力幅值下黄土的循环应力时程曲线、滞回曲线、骨干曲线及累积塑性应变曲线的影响规律。揭示了应力路径对重塑黄土力学特性的影响,描述了各主应力与中主应力比b和应力幅值的相关性,提出了重塑黄土的滞回曲线近似呈椭圆形,长轴斜率随中主应力比b值的增大而增大,随应力幅值的增大而减小;随着中主应力比b值的增大,循环应力-应变骨干曲线随之硬化,累积塑性应变曲线依次降低,且累积塑性应变发展更早的进入平缓阶段,为解决相关黄土工程问题提供了参考。

列车荷载作用下压实花岗岩残积土累积变形特性试验研究

为研究列车荷载作用下应力及湿化条件对压实花岗岩残积土累积变形特性的影响,以围压、动应力幅值、含水率为变量,对压实花岗岩残积土进行循环空心扭剪和循环定向加载试验。结果表明:循环扭剪应力路径下主应力轴旋转效应增加了试样的累积变形量,甚至改变了累积变形的发展模式,该影响程度随试样含水率的增大而增大;试样的累积应变发展速率在加载初期(N<100)时完成大幅度衰减,围压增大可加快累积应变发展速率的衰减,动应力幅值的增加会延长累积应变发展速率的衰减时间,循环扭剪加载时试样的累积应变发展速率衰减程度小于循环定向加载试验,含水率越高该效应越显著。通过预测模型能够对两种动力加载应力路径下的稳定型和发展型累积应变发展曲线能够进行拟合,对压实花岗岩残积土的累积变形作出较好预测。

考虑不同损伤模型的转向架构架疲劳寿命研究

【目的】为了更好地分析动车组转向架构架的疲劳寿命。【方法】对某型转向架构架的疲劳关注测点进行了动应力实测,并对其数据进行后处理,通过雨流计数法和波动中心法进行了一维应力谱的编制;通过Miner线性累积损伤模型、一种考虑载荷相互作用及其固有属性损伤的非线性累积损伤模型和Cotern-Dolan非线性累积损伤模型分别对其进行分析计算,推断其疲劳寿命并进行三方对比。【结果】考虑固有损伤的非线性模型分析结果与线性模型计算结果差别微小。【结论】固有属性损伤的非线性属性不明显,Cotern-Dolan非线性累积损伤模型的寿命分析结果与前两种相比整体偏小,但趋势相同,表明其用于疲劳寿命评估更偏保守。

Mechanical responses of anchoring structure under triaxial cyclic loading

Dynamic load on anchoring structures(AS)within deep roadways can result in cumulative damage and failure.This study develops an experimental device designed to test AS under triaxial loads.The device enables the investigation of the mechanical response,failure mode,instability assessment criteria,and anchorage effect of AS subjected to combined cyclic dynamic-static triaxial stress paths.The results show that the peak bearing strength is positively correlated with the anchoring matrix strength,anchorage length,and edgewise compressive strength.The bearing capacity decreases significantly when the anchorage direction is severely inclined.The free face failure modes are typically transverse cracking,concave fracturing,V-shaped slipping and detachment,and spallation detachment.Besides,when the anchoring matrix strength and the anchorage length decrease while the edgewise compressive strength,loading rate,and anchorage inclination angle increase,the failure intensity rises.Instability is determined by a negative tangent modulus of the displacement-strength curve or the continued deformation increase against the general downward trend.Under cyclic loads,the driving force that breaks the rock mass along the normal vector and the rigidity of the AS are the two factors that determine roadway stability.Finally,a control measure for surrounding rock stability is proposed to reduce the internal driving force via a pressure relief method and improve the rigidity of the AS by full-length anchorage and grouting modification.

铁路基床底层风积沙填料长期动力稳定性研究

为了研究铁路基床底层风积沙填料的长期动力稳定性,以和若铁路某试验段路基为研究对象,开展现场动力响应试验,试验车速分别为5,20和30 km/h,轴重分别为14.5 t和23.5 t,分析动应力随列车速度、轴重及沿深度的变化规律,基于现场测试和以往动三轴试验成果,将临界动应力和累积塑性变形作为评价参数,分别从动强度和动变形2个方面评价和若铁路基床底层风积沙填料的长期动力稳定性。研究结果表明:1)当列车以不大于30 km/h的速度运行时,车速对基床动应力值的影响很小,但轴重的影响十分显著,不同轴重作用下动应力衰减系数沿深度的变化曲线基本重合,动应力经过基床表层衰减约39.7%,传递至基床底层底面衰减约84.6%。2)在和若铁路基床底层范围内,列车荷载产生的动应力为12.86~53.05 kPa,小于风积沙临界动应力66.02~100.21 kPa,从动强度角度来说,风积沙用作铁路基床底层填料满足长期动力稳定性要求。3)基于基床填料的累积塑性应变模型,采用分层总和法计算了和若铁路基床层的累积塑性变形,结果发现列车荷载作用下基床变形主要集中在第1个月,累积变形量为13.59 mm,小于规范允许的月沉降量25 mm,从动变形角度来说,风积沙用作铁路基床底层填料满足长期动力稳定性要求。研究成果可为沙漠地区路基填料选择及基床结构设计提供参考。

冻融循环作用下黄土累积塑性应变演变规律

为探究黄土路基在冻融循环和交通荷载耦合作用下的累积塑性应变变化规律,选取西宁地区重塑黄土为研究对象,采用GDS双向动三轴测试系统对其进行一系列动三轴试验,研究不同冻融循环次数、围压、动应力幅值以及频率对累积塑性应变的影响规律,并通过引入拟合参数建立考虑多因素的累积塑性应变预测模型。结果表明:累积塑性应变随冻融循环次数的增大而增大,在6次冻融循环后增长速率减缓且趋于稳定;减小动应力幅值和增大围压能显著抑制累积塑性应变的发展;加载初期累积塑性应变随频率变化不明显,随着振次的增加,频率作用凸显,累积塑性应变随着频率的增大而减小;基于试样的累积塑性应变演变规律,分别采用幂指数模型和对数模型进行拟合,发现后者拟合效果好;综合考虑4种因素对累积塑性应变的影响,建立累积塑性应变预测模型,并对试验的实测值与预测值进行对比,验证模型的可行性。研究成果可为季冻区黄土路基永久变形的计算提供理论参考依据。

Fatigue Crack Propagation Law of Corroded Steel Box Girders in Long Span Bridges

In order to investigate the fatigue performance of orthotropic anisotropic steel bridge decks,this study realizes the simulation of the welding process through elastic-plastic finite element theory,thermal-structural sequential coupling,and the birth-death element method.The simulated welding residual stresses are introduced into the multiscale finite element model of the bridge as the initial stress.Furthermore,the study explores the impact of residual stress on crack propagation in the fatigue-vulnerable components of the corroded steel box girder.The results indicate that fatigue cracks at the weld toe of the top deck,the weld root of the top deck,and the opening of the transverse diaphragm will not propagate under the action of a standard vehicle load.However,the inclusion of residual stress leads to the propagation of these cracks.When considering residual stress,the fatigue crack propagation paths at the weld toe of the transverse diaphragm and the U-rib weld toe align with those observed in actual bridges.In the absence of residual stress,the cracks at the toe of the transverse diaphragm with a 15%mass loss rate are categorized as type I cracks.Conversely,when residual stress is considered,these cracks become I-II composite cracks.Residual stress significantly alters the cumulative energy release rate of the three fracturemodes.Therefore,incorporating the influence of residual stress is essential when assessing the fatigue performance of corroded steel box girders in long-span bridges.

累积生态风险与留守儿童心理健康:应对方式的中介作用和积极心理资本的调节作用

目的:探讨累积生态风险对留守儿童心理健康的影响及内在作用机制。方法:采用累积生态风险量表、消极应对方式量表、积极心理资本量表及抑郁-焦虑-压力量表,对5所乡村中小学共905名留守儿童进行调查。结果:①累积生态风险正向预测留守儿童抑郁-焦虑-压力水平(β=0.15,P<0.001);②消极应对方式在累积生态风险对留守儿童抑郁-焦虑-压力的影响中起部分中介作用(β=0.59,95%CI=0.50~0.61),中介效应值是0.05;③积极心理资本在消极应对方式对留守儿童抑郁-焦虑-压力的影响中起调节作用(β=-0.06,P<0.05),即消极应对方式对高/低积极心理资本留守儿童的影响作用均显著,但相比积极心理资本水平高的个体,消极应对方式对低积极心理资本留守儿童抑郁-焦虑-压力的影响更大。结论:降低留守儿童消极应对方式、提高积极心理资本可有效预防抑郁-焦虑-压力发生。

风积沙填筑铁路路基累积塑性变形及临界动应力试验研究

目前用于铁路基床的填料大多数为级配优良的填料,而对风积沙作为路基填料在列车荷载作用下的累积塑性变形特性和临界动应力研究不多,但风积沙作为路基填料已在沙漠铁路建设中得到运用。为探究列车荷载作用下风积沙填料填筑铁路路基的累积塑性变形演变特性及临界动应力,考虑围压、动应力幅值、压实系数和含水率等因素的影响,开展一系列动三轴试验。试验结果表明:风积沙累积塑性应变随压实系数、围压的增大而减小,随动应力幅值的增大而增大。以最优含水率为分界点,低于最优含水率时,风积沙累积塑性应变随含水率的增加而减小;高于最优含水率时,风积沙累积塑性应变随含水率的增加而增大。风积沙试样的累积塑性应变曲线可分为:稳定型、临界型和破坏型。根据对累积塑性应变曲线的分类,获得了不同条件下风积沙填料的临界动应力。风积沙临界动应力随围压和压实系数的增大而增大,饱和含水率下风积沙填料的临界动应力明显小于天然含水率和最优含水率下风积沙填料的临界动应力。临界动应力和围压具有较好的线性关系。构建了可考虑围压和含水率影响的风积沙临界动应力经验公式,通过临界动应力公式确定了不同工况下风积沙作为路基填料的适用范围。试验结果可为沙漠铁路的设计、施工以及运营提供经验和理论依据。

Effect of Band Width on Fatigue Life under Random Stress Response

A fatigue life estimation method for offshore structures under random stress response is studied in this paper. The method of broad band cumulative frequency number is used to determine the effect of band width of stress frequency spectra on fatigue. A formula of correction factor for fatigue under broad band stress spectra is suggested and compared with that given by P. H. Wirsching.

Crustal Stress Evolution over the Past 700 Years in North China and Earthquake Occurrence

Fault interaction and earthquake occurrence have attracted much attention in seismological community during recent years. Many studies have shown that the rupture of one fault could encourage or discourage earthquake nucleation on a neighboring fault, depending on the relative geometry of the two faults and the earthquake rupture mechanisms. In this paper, we simulate the evolutionary process of cumulative Coulomb failure stress change （ CCFSC ） in North China since 1303, manifested by secular tectonic stress loading and occurrence of large earthquakes. Secular tectonic stress loading is averaged from crustal strain rates derived from GPS. Fault rupture parameters of historical earthquakes are estimated as follows： the earthquake rupture length and the amount of slip are derived based on their statistical relationships with the earthquake intensity distribution and magnitude, calibrated using parameters of instrumentally measured contemporary earthquakes. The earthquake rake angle is derived based on geologically determined fault orientational parameters and seismically estimated orientation of regional tectonic stresses. Assuming a layered visco-elastic medium, we calculate stress evolution resulting from secular tectonic loading and coseismic and postseismic deformation. On the eve of each large earthquake, the accumulated stress field is projected to the fault surface of that earthquake and the CCFSC is evaluated to assess the triggering effect of CCFSC. Forty-nine earthquakes with M≥6.5 have occurred in North China since 1303. Statistics shows that 39 out of the 48 subsequent events were triggered by positive CCFSC, yielding a triggering rate of 81.3%. If we use the accumulative stress field to evaluate the CCFSC for the M ≥ 5.0 earthquakes that occurred in North China since 1303, we find that 75.5% of those events were triggered. The triggering rate for the M ≥ 5.0 earthquakes after the 1976 Ninghe earthquake is up to 82.1%. The triggering rates can be higher if corrections are made for some aftershocks which were wrongly identified as occurring in stress shadow zones because of errors in parameter estimates of historical earthquakes. Our study shows a very high correlation between positive CCFSC and earthquake occurrences. Relatively high CCFSC in North China at present is concentrated around the Bohai Sea, the west segment of the Northern Qinling fault, the western end of the Zhangjiakou-Bohai Sea seismic zone, and the shiyuan basin, Shanxi graben, suggesting relatively higher earthquake potential in these areas.

生活事件与中学生学业拖延:一个有调节的中介模型

本研究旨在考察近端压力(生活事件)与学业拖延的关系,并检验状态焦虑的中介和远端压力(童年期虐待)的调节作用。以750名初中生为被试,采用青少年生活事件量表、状态-特质焦虑量表、Aitken拖延问卷(中学生版)和儿童虐待问卷进行测试。结果显示:(1)在控制年级后,生活事件能够显著正向预测学业拖延;(2)状态焦虑在生活事件和学业拖延的关系中起中介作用;(3)“生活事件→状态焦虑→学业拖延”这一中介效应的前半路径受到童年期虐待的调节。具体来说,相对于童年期受虐程度较高的个体,生活事件对童年期受虐程度较低的个体的状态焦虑正向预测作用更大。

温度应力对机场道面板疲劳损伤的影响

目前,中国机场水泥混凝土道面设计中并未单独计算温度应力。参考传热学研究成果在道路工程和场道工程中的应用,采用华北地区某机场实例及其气象数据,建立有限元模型模拟道面结构温度场,并计算分析该机场道面板温度场和温度应力情况。结果表明,温度荷载造成的板底应力曲线与气温、辐射曲线之间存在较大的相位差,板底最大拉应力出现在19—20时。将随时间变化的温度应力与随横向位置变化的飞机轮载应力叠加,并将轮载作用次数按横向、月度、时刻分布,计算机场道面板的累计损伤和剩余寿命。结果表明,采用该方法预测的机场跑道剩余寿命与钻芯取样检测、FAARFIELD软件预测结果,以及跑道实际继续运营时长较为接近。可通过所提方法计算厚度较大的机场道面板的温度应力,对既有机场水泥混凝土道面结构的剩余寿命进行预测评估,并为大尺寸机场水泥混凝土道面板的研究和设计提供参考。

循环荷载下楔形劲芯水泥土复合桩工作特性试验研究

楔形劲芯水泥土复合桩作为一种新型组合桩,为探究其在公路、铁路等长期承受循环荷载下工程应用的工作性状,对4根不同桩芯楔角、静荷载比和循环荷载比的复合桩进行模型试验,研究了静载极限承载力及循环荷载下累计沉降、桩身轴力分布、桩端阻力和侧摩阻力。试验结果表明:静载作用下楔形内芯复合桩的承载能力要优于等截面内芯复合桩;复合桩累计沉降会随着静荷载比和循环荷载比的增大而增大,并在不同动静荷载组合下可分为稳定型、发展型和破坏型3种类型,同时给出满足各类型的荷载取值范围;芯桩与水泥土外桩之间的相互作用并未发生明显弱化现象,楔形芯桩复合桩能充分发挥桩侧上部土体的侧摩阻力,并能有效减弱芯桩端部应力集中现象,因此其抵抗循环荷载的能力要优于等截面芯桩的复合桩。

磷石膏稳定土临界动应力及累积变形特性研究

针对磷石膏的资源浪费和红黏土的特殊工程特性,以水泥(石灰)为固化剂,采用SDT-20动三轴试验研究了磷石膏稳定土的疲劳特性和改良机理,建立了累积变形模型和临界动应力模型,得到了混合料动强度指标。结果表明:随着动应力幅值与围压提高,累积变形特征显著增大,且素红黏土与磷石膏稳定土变形均经历稳定型、临界型与破坏型三阶段;临界动应力随围压的增大而线性增大,降低动应力水平和提高围压可提升路基抵抗失稳的能力;石灰磷石膏稳定土和水泥磷石膏稳定土动抗剪强度相比素红黏土有大幅提升,且水泥磷石膏稳定土的动抗剪强度增加值比石灰磷石膏稳定土更大;磷石膏稳定土强度提升是由水泥(石灰)和磷石膏共同作用引起的,水泥(石灰)反应生成水化硅酸钙(C—S—H凝胶),磷石膏反应生成钙矾石,两者相互交织形成空间网状结构。

胸腔镜肺亚叶切除术及肺叶切除术对肺癌患者的疗效

目的 探讨胸腔镜肺亚叶切除术及肺叶切除术对肺癌患者的影响,为临床治疗提供参考。方法 将濮阳市人民医院2017年3月至2019年3月收治的86例肺癌患者纳入研究,通过随机数字表法将其分为观察组与对照组,每组43例。观察组接受胸腔镜肺亚叶切除术,对照组接受胸腔镜肺叶切除术。记录并比较两组围手术期指标,检测并比较两组术前及术后7 d免疫指标(CD4^(+)、CD8^(+)、CD4^(+)/CD8^(+))水平,检测并比较两组术前及术后7 d创伤应激指标[皮质醇(COR)、促肾上腺皮质激素(ACTH)、生长激素(GH)]水平,比较两组并发症发生情况,对患者进行为期3 a随访,记录并比较两组3 a生存情况。结果 两组手术时长组间比较差异无统计学意义(P>0.05);观察组术中出血量、镇痛药物使用量低于对照组,术后引流时长、住院时长短于对照组(P<0.05)。术后7 d,观察组CD4^(+)、CD8^(+)及对照组CD4^(+)、CD8^(+)、CD4^(+)/CD8^(+)水平较术前均有下降(P<0.05),同时观察组CD4^(+)、CD4^(+)/CD8^(+)水平高于对照组(P<0.05),两组CD8^(+)水平组间比较差异无统计学意义(P>0.05)。术后7 d,观察组与对照组COR、ACTH、GH水平较术前均有上升(P<0.05),观察组COR、ACTH、GH水平低于对照组(P<0.05)。观察组并发症总发生率低于对照组(P<0.05)。经Kaplan-Meier检验两组累积生存率差异无统计学意义(χ^(2)=0.343,P=0.558)。结论 胸腔镜肺亚叶切除术能够减少肺癌患者围手术期术中出血量、镇痛药物用量,缩短术后引流时长及住院时长,并且对机体免疫及创伤应激反应的影响较小,同时具有较高安全性,且不会降低患者累积生存率,具有临床应用价值。