低周反复荷载下Q460钢材框架柱抗震性能分析     

刘宽  马煜东  黄娇  刘笑笑  苏佶智 《震灾防御技术》2019,14(3):535-554

为了进一步完善Q460钢材在抗震设计规范中相关限值的要求，本文利用有限元软件ABAQUS，以轴压比、翼缘宽厚比、腹板高厚比和壁板宽厚比为变量，建立了共48根“工”字型框架柱和“箱”型框架柱，分析了其抗震性能。结果表明:翼缘宽厚比对框架柱的能量耗散系数影响较小；能量耗散系数随轴压比、腹板高厚比（“工”字型）和壁板宽厚比（“箱”型）增大而明显减小；框架柱的极限承载力随轴压比的减小及壁板宽厚比和翼缘宽厚比的增大而逐渐增大，当腹板高厚比接近规范限值时，承载力下降趋势明显增大。与采用Q235钢材的框架柱相比，Q460钢材框架柱的延性较小，仅为2左右；当采用Q460钢材时，“工”字型框架柱的极限位移角限值建议取为0.03，“箱”型框架柱的极限位移角限值建议取为0.032。规范中对翼缘宽厚比限值的规定偏于保守，其值最大可取至9。无论是“工”字型框架柱还是“箱”型框架柱，其腹板高厚比均不宜过大。Q460钢材框架柱的刚度退化率随轴压比的增大而增强，且翼缘宽厚比越大，腹板高厚比越小，柱的初始刚度越大，刚度退化程度越明显。  相似文献   

Strength matters: Resisting erosion across upland landscapes     

Arjun M. Heimsath  Kelin X. Whipple 《地球表面变化过程与地形》2019,44(9):1748-1754

Soil-covered upland landscapes comprise a critical part of the habitable world and our understanding of their evolution as a function of different climatic, tectonic, and geologic regimes is important across a wide range of disciplines. Soil production and transport play essential roles in controlling the spatial variation of soil depth and therefore hillslope hydrological processes, distribution of vegetation, and soil biological activity. Field-based confirmation of the hypothesized relationship between soil thickness and soil production is relatively recent, however, and here we quantify a direct, material strength-based influence on variable soil production across landscapes. We report clear empirical linkages between the shear strength of the parent material (its erodibility) and the overlying soil thickness. Specifically, we use a cone penetrometer and a shear vane to determine saprolite resistance to shear. We find that saprolite shear strength increases systematically with overlying soil thickness across three very different field sites where we previously quantified soil production rates. At these sites, soil production rates, determined from in situ produced beryllium-10 (¹⁰Be) and aluminum-26 (²⁶Al), decrease with overlying soil thickness and we therefore infer that the efficiency of soil production must decrease with increasing parent material shear strength. We use our field-based data to help explain the linkages between biogenic processes, chemical weathering, hillslope hydrology, and the evolution of the Earth's surface. © 2019 John Wiley & Sons, Ltd.  相似文献   

冻融循环对土体强度变形参数的影响          下载免费PDF全文

张渭军 《探矿工程》2020,47(6):86-91

在寒区工程建设中，冻融循环会引起土强度和变形特性发生改变。为了研究多次冻融循环后土的强度和变形参数的变化量，本文以冻融和非冻融的粉质粘土饱和试样为研究对象，通过固结排水三轴剪切试验、三轴等向压缩试验和弹性模量试验，比较了冻融循环对土样强度参数和变形参数的影响。试验结果显示：冻融和非冻融试样的应力—应变关系曲线均呈应变硬化型，对于原状试样冻融作用破坏了其结构性；冻融作用导致土体强度的降低，主要体现在粘聚力的降低，约降低了55.6%；冻融循环对变形参数有明显的影响，其中最明显的是弹性模量的降低，降低了31.2%。该研究结论可为工程冻害处理提供参考，也可为相关研究的数值计算提供试验参数。  相似文献   

Predicting gravel bed river response to environmental change: the strengths and limitations of a regime‐based approach          下载免费PDF全文

Brett Eaton  Robert Millar 《地球表面变化过程与地形》2017,42(6):994-1008

Rivers respond to environmental changes such as climate shifts, land use changes and the construction of hydro‐power dams in a variety of ways. Often there are multiple potential responses to any given change. Traditionally, potential stream channel response has been assessed using simple, qualitative frameworks based largely on professional judgement and field experience, or using some form of regime theory. Regime theory represents an attempt to use a physically based approach to predict the configuration of stable channels that can transport the imposed sediment supply with the available discharge. We review the development of regime theory, and then present a specific regime model that we have created as a stand‐alone computer program, called the UBC Regime Model (UBCRM). UBCRM differs from other regime models in that it constrains its predictions using a bank stability criterion, as well as a pattern stability criterion; it predicts both the stable channel cross‐sectional dimensions as well as the number of anabranches that the stream must have in order to establish a stable channel pattern. UBCRM also differs from other models in that it can be used in a stochastic modelling mode that translates uncertainty in the input variables into uncertainty in the predicted channel characteristics. However, since regime models are fundamentally based on the concept of grade, there are circumstances in which the model does not perform well. We explore the strengths and weaknesses of the UBCRM in this paper, and we attempt to illustrate how the UBCRM can be used to augment the existing qualitative frameworks, and to help guide professionals in their assessments. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Mechanical transitional behavior of binary mixtures via DEM: Effect of differences in contact-type friction coefficients     

《Computers and Geotechnics》2017

This report presents a numerical investigation of the shear behavior of binary mixtures via a two-dimensional discrete element method. The effect of the coarse particle content on the peak shear strength of mixtures is investigated for different contact-type friction coefficients. A detailed analysis on the anisotropies enables us to understand the microscopic mechanisms that result in the dependency of the peak shear strengths on the coarse particle content. The contributions of different contact types to the peak shear strength are quantified. Lastly, the inter-particles structures are examined when the binary mixtures become coarse-particle-supported structures.  相似文献   

Stability analysis of tunnels driven in jointed rocks by means of a homogenized limit analysis approach     

Samir Maghous  José E. B. Winiawer  Vanessa F. Pasa Dutra 《国际地质力学数值与分析法杂志》2014,38(18):2009-2032

Conceived as a potential alternative to the classical design methods employed for analyzing the stability of underground structures driven in jointed rocks, the homogenization approach stems from the heuristic idea that, from a macroscopic point of view, a rock mass cut by a network of joints may be perceived as a homogenized continuum. The strength properties of the latter can be theoretically obtained from the failure conditions of its individual constituents: rock matrix and joint interfaces. At the material level, the limit analysis reasoning is used in the context of homogenization to formulate the homogenized strength criterion of a jointed rock mass in the particular situation of a single set of parallel joints. As it could be expected, the obtained closed‐form expressions show the strength anisotropy induced by joint preferential orientation. The support functions (π functions) associated with the homogenized strength criterion are also determined in both plane strain and three‐dimensional cases. This criterion is then applied to the investigation of stability analysis of a tunnel excavated in a jointed rock mass. Upper bounds estimated of the stability factor are derived from the implementation of the kinematic approach directly on the homogenized underground structure. Finally, the approach is applied to analyze and discuss the collapse of the Pinheiros subway station (São Paulo, Brazil). Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Dynamic propagation criteria for catastrophic failure in planar landslides          下载免费PDF全文

Wangcheng Zhang  Dong Wang  Mark F. Randolph  Alexander M. Puzrin 《国际地质力学数值与分析法杂志》2016,40(17):2312-2338

Quantitative assessment of the risk of submarine landslides is an essential part of the design process for offshore oil and gas developments in deep water, beyond the continental shelf. Landslides may be triggered by a reduction in shear strength of subsea sediments over a given zone, caused for example by seismic activity. Simple criteria are then needed to identify critical conditions whereby the zone of weakness could grow catastrophically to cause a landslide. A number of such criteria have been developed over the last decade, based either on ideas drawn from fracture mechanics, or considering the equilibrium of the initial weakened zone and adjacent process zones of gradually softening material. Accounting for the history of the weak zone initiation is critical for derivation of reliable propagation criteria, in particular considering dynamic effects arising from accumulating kinetic energy of the failing material, which will allow the failure to propagate from a smaller initial zone of weakened sediments. Criteria are developed here for planar conditions, taking full account of such dynamic effects, which are shown to be capable of reducing the critical length of the softened zone by 20% or more compared with criteria based on static conditions. A numerical approach is used to solve the governing dynamic equations for the sliding material, the results from which justify assumptions that allow analytical criteria to be developed for the case where the initial softening occurs instantaneously. The effect of more gradual softening is also explored. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Macroscopic criteria for Green type porous materials with spheroidal voids: application to double porous materials          下载免费PDF全文

W. Q. Shen  J.‐F. Shao  D. Kondo 《国际地质力学数值与分析法杂志》2017,41(13):1453-1473

Combined effects of matrix plastic compressibility and void shape are investigated for ductile porous materials. To this end, a spheroidal volume containing a confocal spheroidal (prolate or oblate) void subjected to uniform strain rate boundary conditions has been first studied. A Green type matrix is chosen as a prototype for investigating effects of plastic compressibility. This is carried out by using a kinematics limit analysis theory from which a closed‐form expression of the macroscopic criterion is established for the considered class of materials. These results are then extended to ductile porous materials made up of a green matrix containing randomly oriented spheroidal voids. In the framework of a two‐step homogenization procedure, the obtained results are implemented to describe the macroscopic behavior of double porous materials involving spherical voids at the microscale and randomly oriented and distributed spheroidal voids at the mesoscale. For validation purpose, the new derived criteria are assessed and validated by comparing their predictions to available upper bounds and numerical data from literature. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Strength and deformation behavior of the Shimanto accretionary complex across the Nobeoka thrust          下载免费PDF全文

Hiroko Kitajima  Miki Takahashi  Makoto Otsubo  Demian Saffer  Gaku Kimura 《Island Arc》2017,26(4)

A rapid reduction in sediment porosity from 60 to 70 % at seafloor to less than 10 % at several kilometers depth can play an important role in deformation and seismicity in the shallow portion of subduction zones. We conducted deformation experiments on rocks from an ancient accretionary complex, the Shimanto Belt, across the Nobeoka Thrust to understand the deformation behaviors of rocks along plate boundary faults at seismogenic depth. Our experimental results for phyllites in the hanging wall and shale‐tuff mélanges in the footwall of the Nobeoka Thrust indicate that the Shimanto Belt rocks fail brittlely accompanied by a stress drop at effective pressures < 80 MPa, whereas they exhibit strain hardening at higher effective pressures. The transition from brittle to ductile behavior in the shale–tuff mélanges lies on the same trend in effective stress–porosity space as that for clay‐rich and tuffaceous sediments subducting into the modern Nankai subduction zone. Both the absolute yield strength and the effective pressure at the brittle–ductile transition for the phyllosilicate‐rich materials are much lower than for sandstones. These results suggest that as the clay‐rich or tuffaceous sediments subduct and their porosities are reduced, their deformation behavior gradually transitions from ductile to brittle and their yield strength increases. Our results also suggest that samples of the ancient Shimanto accretionary prism can serve as an analog for underthrust rocks at seismogenic depth in the modern Nankai Trough.  相似文献   

岩石锚桩基础的承压力与抗拔力之应用   总被引：1，自引：0，他引：1  

黄皖平 《安徽地质》2005,15(4):318-320

根据“110kV绩溪-旌德”线路现场设计及施工情况,系统总结了岩石锚桩基础在中风化、强风化的山区中的应用经验,分析了工程设计中锚筋内力、锚桩承载力和粘结力之间关系,合理采用计算公式,获得较好效果。  相似文献