考虑轴力弯矩耦合的截面随动强化恢复力模型     

陈永盛  吴斌  潘天林 《地震学刊》2014,(3):336-341

截面层次的恢复力模型能兼顾计算精度与计算效率,为此在梁-柱单元中得到了广泛的应用。但目前给定＂轴力-弯矩-曲率＂的截面恢复力模型无法灵活考虑轴力与弯矩的耦合作用;采用屈服面的截面恢复力模型尚未考虑截面强化效应。提出了基于屈服面的截面随动强化恢复力模型及其积分方法,首先依据截面屈服面建立了截面随动强化恢复力模型,然后依托塑性理论,进行截面状态确定和本构关系积分。最后利用所提出的恢复力模型进行了悬臂柱的静力往复分析。结果表明：（1）所选用的截面恢复力模型能很好考虑轴力存在对弯矩的影响;（2）该模型具有随动强化的特性;（3）在精度上接近纤维截面所用的单轴材料随动强化模型。  相似文献   

The effect of dissolved magnesium on creep of calcite II: transition from diffusion creep to dislocation creep     

Lili Xu  Jörg Renner  Marco Herwegh  Brian Evans 《Contributions to Mineralogy and Petrology》2009,157(3):339-358

We extended a previous study on the influence of Mg solute impurity on diffusion creep in calcite to include deformation under a broader range of stress conditions and over a wider range of Mg contents. Synthetic marbles were produced by hot isostatic pressing (HIP) mixtures of calcite and dolomite powders for different intervals (2–30 h) at 850°C and 300 MPa confining pressure. The HIP treatment resulted in high-magnesian calcite aggregates with Mg content ranging from 0.5 to 17 mol%. Both back-scattered electron images and chemical analysis suggested that the dolomite phase was completely dissolved, and that Mg distribution was homogeneous throughout the samples at the scale of about two micrometers. The grain size after HIP varied from 8 to 31 μm, increased with time at temperature, and decreased with increasing Mg content (>3.0 mol%). Grain size and time were consistent with a normal grain growth equation, with exponents from 2.4 to 4.7, for samples containing 0.5–17.0 mol% Mg, respectively. We deformed samples after HIP at the same confining pressure with differential stresses between 20 and 200 MPa using either constant strain rate or stepping intervals of loading at constant stresses in a Paterson gas-medium deformation apparatus. The deformation tests took place at between 700 and 800°C and at strain rates between 10⁻⁶ and 10⁻³ s⁻¹. After deformation to strains of about 25%, a bimodal distribution of large protoblasts and small recrystallized neoblasts coexisted in some samples loaded at higher stresses. The deformation data indicated a transition in mechanism from diffusion creep to dislocation creep. At stresses below 40 MPa, the strength was directly proportional to grain size and decreased with increasing Mg content due to the reductions in grain size. At about 40 MPa, the sensitivity of log strain rate to log stress, (n), became greater than 1 and eventually exceeded 3 for stresses above 80 MPa. At a given strain rate and temperature, the stress at which that transition occurred was larger for samples with higher Mg content and smaller grain size. At given strain rates, constant temperature, and fixed grain size, the strength of calcite in the dislocation creep regime increased with solute content, while the strength in the diffusion creep regime was independent of Mg content. The results suggest that chemical composition will be an important element to consider when solid substitution can occur during natural deformation.  相似文献   

进一步加强地震知识的普及与宣传汶川“5·12”大地震的教训与启示   总被引：1，自引：0，他引：1  

马凤霞 《国际地震动态》2010,(9):37-40

本文从吸取2008年5月12日四川汶川大地震的经验和教训出发,从贯彻"预防为主"的防震减灾工作方针着眼,阐述了地震宣传在防震减灾工作中的重要地位和作用,对防震减灾工作的宣传内容进行了详细的诠释,提出了进一步做好防震减灾宣传工作的对策和建议,对于保障防震减灾宣传工作的顺利开展具有一定的参考意义。  相似文献   

土石混填料台背回填柔性加筋注浆技术加固试验研究     

赵炼恒  罗恒  李亮  但汉成  邹金锋 《岩土力学》2010,31(1):199-205

通过采用柔性加筋注浆技术处理台后回填土现场试验研究并结合室内试验的方式,研究了柔性加筋注浆新技术处理湘西红砂岩土石混填台背的施工工艺特性、加固实现机制和加固效果。现场试验及质量测试表明,水平柔性加筋注浆新技术处理湘西红砂岩土石混填台背施工工艺简单、加固效果良好,具有较好的开发应用价值。同时,现场试验过程取得大量施工参数和试验数据,为改进该新技术的设计计算及施工参数、完善施工工艺获得素材; 对有效预防和减少桥头跳车现象的发生,保证行车的舒适和安全也提供了可供选择的新方式。  相似文献   

Twin lintel belt in steel for seismic strengthening of brick masonry buildings   总被引：2，自引：1，他引：1  

C.V.R.Murty JayantaDutta S.K.Agrawal 《地震工程与工程振动(英文版)》2004,3(2):215-222

A single-room, single-storey full-scale brick masonry building with precast RC roofing system was tested thric eunder displacement controlled lateral cyclic loading, to assess the effectiveness of the basic repair and seismic strengthening techniques. Initially, the virgin building specimen was loaded laterally to failure, In the second stage, the damaged building was repaired by stitching across the cracks, and tested under the same lateral loading. In the third stage, the twice-damaged structure was repaired once more by stitching and strengthened by twin lintel belt in steel and vertical corner reinforcement,and re-tested. The building strengthened by twin lintel belt in steel showed about 28% higher strength under lateral loading than the virgin building.  相似文献   

An improved implicit numerical integration of a non‐associated,three‐invariant cap plasticity model with mixed isotropic–kinematic hardening for geomaterials          下载免费PDF全文

M. H. Motamedi  C. D. Foster 《国际地质力学数值与分析法杂志》2015,39(17):1853-1883

The Sandia GeoModel is a continuum elastoplastic constitutive model that captures many features of the mechanical response for geological materials over a wide range of porosities and strain rates. Among the specific features incorporated into the formulation are a smooth compression cap, isotropic/kinematic hardening, nonlinear pressure dependence, strength differential effect, and rate sensitivity. This study attempts to provide enhancements regarding computational tractability, domain of applicability, and robustness of the model. A new functional form is presented for the yield and plastic potential functions. This reformulation renders a more accurate, robust, and efficient model as it eliminates spurious solutions attributed to the original form. In addition, we achieve a high‐performance implementation, because the local iterative method is allowed to recast residual vectors with a uniform dimensionality. The model is also furnished with a smooth, elliptical tension cap to account for the tensile yielding. Moreover, an efficient algorithm is introduced, which decreases the computational cost by differentiating the updated shear yield surface from the cap surface based on the trial relative stress state. Finally, various numerical examples including a large‐scale boundary value problem are presented to demonstrate the fidelity of the modified model and to analyze its numerical performance. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

超长桩荷载传递性状研究   总被引：30，自引：4，他引：26  

钟闻华  石名磊  刘松玉 《岩土力学》2005,26(2):307-310

根据超长桩的现场静载荷试验资料,分析了超长桩的单桩荷载传递特性。结果表明,超长桩表现出端承摩擦桩的特性,桩顶以下l/3桩长及桩端以上l/6范围内的桩侧摩阻力极限值接近规范推荐值,而中间部分的桩侧摩阻力远远大于规范值,表现出强化效应,桩端注浆桩的侧摩阻力强化效应更加明显。根据其荷载传递特性,提出了单桩极限承载力的估算公式,实例计算结果和实测结果较吻合。  相似文献   

钻孔灌注桩后压浆法在渭南某工地应用     

赵跃文  王佳武  李敏杰  王锋涛  张少林  张波 《陕西地质》2012,30(1):65-69

近年来我国的高层建筑迅猛发展,对地基承载力的要求越来越高,高层建筑的基础形式一般采用灌注桩基础。为了满足设计要求;灌注桩的持力层要求是较为完整的岩石层或承载力较高的卵石层,桩长和桩径尺寸往往很大,使得地下部分的造价在整个工程总造价中占较大的比例;同时;由于桩长很长,也给施工造成很大的困难。渭南市某工地采用φ300mm桩径,桩长30m,试桩施工完成后,经过桩基检测,桩的承载力不能满足上部荷载的要求,其后采用后压浆法来提高桩的侧摩阻力和桩端承载力,从而使灌注桩达到提高基桩承载力、减少基桩沉降的结果。  相似文献   

金属耗能器在结构抗震加固中的应用   总被引：1，自引：0，他引：1  

乐登  邓雪松  周云 《震灾防御技术》2006,1(4):309-318

采用金属耗能器进行结构抗震加固是一种较经济、简单、又可靠的耗能减震加固方法。本文介绍了几种常用金属耗能器的构造、原理与性能及其在建筑、桥梁抗震加固工程中应用的概况,给出了典型工程实例,并提出了金属耗能器在加固工程应用中应解决的一些问题。  相似文献   

大体积混凝土裂缝的分析及控制措施     

张金凤 《中国勘察设计》2010,(3):37-39

随着高层建筑和工业建筑的发展,大型的筏式基础、箱形基础、桩基承台以及大型的设备基础,一般是大体积混凝土,在施工过程中都有一个温度控制和温度应力问题,这些问题如果解决不好,都会引起混凝土表面裂缝和收缩裂缝的发生。为了解决这个问题我们通过分析原因、现场实践得出一些实际有效的措施。  相似文献