软土加固过程中微结构变化的分形研究

土体内部孔隙的特征及分布情况是土体微结构变化的内因,也是决定土体物理力学性质的主要因素。在软土性质发生改变时,孔隙的变化是最直接、最显著的。所以,对土体微观结构进行研究,应着重研究土中孔隙的变化。由于土中孔隙的复杂性及非确定性,很难用传统的几何方法对其研究和描述。为研究加固前后软黏土微结构的变化情况,在珠江三角洲某高速公路软土路基利用动力排水固结法加固的施工现场,取不同深度内加固前后土样进行压汞测试,用分形理论对压汞测试数据进行分析,探讨软土中孔隙的分布特征,在此基础上提出了土中孔径划分的方法,进而探讨动力排水固结法加固软土地基的微结构变化,建立了加固后土样的孔隙度分维数与土体固结度之间的关系,研究结果表明土中孔隙分布具有分形特征,用孔隙度分维数可以实现对地基加固程度的预测。     

软土固结过程中的孔隙分形特征及渗透性影响研究

基于Sierpinski分形模型,对珠江三角洲地区软土固结过程中的ESEM图片进行测试,对孔径及孔隙分布分维值进行计算。研究表明:软土孔隙具有明显的分形特征,测试得到的Sierpinski分形模型的线性相关系数均达到了95%以上,且重塑土的孔隙分布分维及孔径分维值均较原状土小;固结初期孔隙分布分维值变化不明显,当荷载增大时,孔隙分布分维及孔径分维均明显减小,此时孔径大小逐渐变得均匀,大孔隙变成了中小孔隙;当荷载继续增大时,软土孔隙较难向颗粒间超微孔隙发展,软土孔隙分维值也趋于稳定;研究还发现,软土的渗透性随着孔径分维和孔隙分布分维值的减小而减小。     

广东科学中心饱和软土微结构定量分析

通过利用液氮制样技术制备饱和软土试样,借助扫描电子显微镜技术,本文对广东科学中心强夯试验区进行了软土微结构特性定量分析。通过比较试样的孔隙度、孔隙总面积、孔隙总个数、平均孔隙周长、孔隙平均直径及孔洞的复杂度,初步探讨了动力排水固结技术对饱和软土地基处理的影响。     

广州南沙软土的工程性质与微结构定量化研究

分析和总结了广州南沙软土的物理力学性质指标,采用数理统计、数据回归方法,建立了各指标与天然孔隙比、含水量之间的回归方程,通过分析微结构参数,获得了分维特征,对于认识软土的工程性质具有重要的意义。     

广州软土固结过程微观结构的显微观测与分析

 利用环境扫描电子显微镜(ESEM)对珠三角典型的广州金沙洲软土固结过程土样的微观结构进行观测,基于观测所得的显微照片分析软土在不同固结压力下微结构的尺度、形状、定向性等微结构特征及其变化规律,并采用计算机图像处理软件定量分析软土的微孔隙率、结构单元体分布角等微结构参数随固结压力的变化规律。根据显微观测照片的分析获得随着固结压力的增加结构单元体不断变大、微孔隙率减小、垂直于固结压力方向的集合体形状增长、结构单元体的定向性有所提高以及孔隙分布分维呈下降趋势并逐步稳定等有价值的结论。     

软岩与水相互作用的非线性动力学过程分析

软岩与水相互作用的非线性动力学过程的研究不仅对软岩软化的研究方法具有探索价值,而且对于合理确定软化的参数及其应用具有重要的实践意义。结合东深供水改造工程中灰白色泥质粉砂岩不同饱水时间后的试验数据分析,发现该类软岩的软化具有非线性特点。将时间序列的分维分析方法应用于软岩与水相互作用系统中,通过重建相空间,确定了描述该系统所需的最少变量数。试验中发现,软岩的微观结构、力学参数是反映软岩软化的控制性因素,因而取微结构孔隙分布分维值Ds、粘聚力c和内摩擦角?值作为描述该系统的3个变量。在此基础上,应用反演分析理论,确定了软岩软化的非线性动力学模型,再将以上3个变量的时间序列值通过求残差平方和极小值的方法与模型进行逼近,得到模型中各个未确定的参数,从而对软岩与水相互作用过程进行非线性动力学分析。结果表明:所给出的非线性动力学模型计算得到的微结构孔隙分布分维值Ds、粘聚力c和内摩擦角?值与试验获得的相应参数值的分布曲线非常接近,说明软岩与水相互作用具有显著的非线性动力学特点;同时,利用所建立的模型可较好地预测软岩在饱水条件下,一定时间后的微观结构参数和力学性质变化规律。     

某地区饱和黏性土静力触探参数的相关性研究

在分析某地饱和黏性土基本工程性质的基础上,对黏性土静力触探测试参数和物理力学性质参数进行相关性研究,并建立推算饱和黏性土物理力学性质参数的经验回归公式。结果表明:黏性土双桥静力触探与其他原位试验结果具有较显著的关联性;锥尖阻力和十字板剪切强度、标准贯入击数之间具有较显著的正相关关系,与土体孔隙比、含水量和压缩系数等物理量之间则具有一定的负相关关系。本文结果可为类似软土地区岩土工程勘察设计中饱和黏性土的参数取值和可靠性分析提供有益参考。     

土的微结构特征对其电阻率的影响试验研究

土的电阻率是土的固有物性参数之一,可反映土的基本物理力学性质指标及结构特征等,具有重要的理论意义和应用价值。利用课题组研制的ESEU-1型土电阻率测试仪对膨胀土与黄土的电阻率进行测试,主要研究了孔隙率、孔隙结构等土的微结构特征对电阻率的影响规律。研究结果表明:孔隙率与孔隙结构等土的微结构特征对土的电阻率存在显著的影响,微结构不同、其他条件相同的土样的电阻率存在较大差别,且在水与导电性良好的NaCl溶液中饱和后的大小与变化规律也不一致。     

软土地基的力学特性及其处治方法

介绍了软土含水量高、孔隙比大、渗透性小、压缩性高、抗剪强度低和灵敏度高等工程性质,分析了软土地基对高速公路路堤工程的影响,汇总了常见的软土地基处理方法,对有关工程施工具有一定的参考价值。     

海洋饱和软土UU测试值与原位测试值相关性分析

海洋饱和软土的力学性质对海洋工程建设具有重要作用,但由于海洋软土土样易扰动,试验数据可靠性低,而原位测试由于受到海洋环境的影响实施较为困难。通过珠海横琴某工程的原状饱和软土的UU测试值,与相同位置、相同深度处的原位十字板测试值和双桥静力触探试验测得的锥尖阻力值进行比较分析,得出饱和软土UU测试值与十字板测试值、双桥静力触探锥尖阻力值具有很好的一致性;折减后的十字板测试值与UU测试值较为接近,可作为海洋工程中相关参数选取的参考。     

黏塑流变本构模型力学参数辨识研究

伴随着各种复杂地质条件,大型地下洞室围岩流变特性与其长期稳定性密切相关,流变本构模型是认识围岩流变力学特性非常重要的一个方面。流变本构模型力学参数是流变本构模型准确应用的一个首要条件。本文主要开展了三个方面的工作:(1)研究推导了岩体黏塑流变本构模型,对其力学参数进行了理论分析;(2)对砂岩进行了不同围压下瞬时三轴压缩试验和三轴流变压缩试验,得到了砂岩相关试验数据,其可以较好的反映砂岩的瞬时力学特性和流变力学特性;(3)基于不同围压下瞬时三轴压缩试验和三轴流变压缩试验,结合改进粒子群优化算法,对流变本构模型的力学参数进行了拟合优化,得到了不同围压下整体流变力学参数。与试验数据对比发现,拟合得到的流变模型力学参数可以较好的反映岩体的流变力学特性,可以为流变本构模型实际应用提供参考。     

Optimisation of process parameters for electroless nickel plating on SS316L for refrigeration systems

Nowadays, refrigeration systems are important for industrial and domestic applications. The coefficient of performance of a vapour compression refrigeration system can be improved if a reduction in the work of compression can be achieved by a suitable technique for a specified heat removal rate. The present study investigates the effect of material coating of electroless nickel (EN) plating. The friction and wear experiments were performed using a four-ball machine tribo tester. Controlling the EN plating parameters plays an important role in the quality of coating. It depends on the wear scar rate of the coated material. So it is necessary to optimise the process parameters of EN plating. The experimental studies have been conducted under varying pressure, load and time on quality characteristics. In this paper, optimisation of process parameters using response surface methodology technique for EN plating was discussed.     

Research on mechanical behaviour of overlapped CHS-to-SHS welded N-joints

An experimental programme and associated parametric analysis of overlapped CHS-to-SHS welded N-joints were carried out. Two partially overlapped CHS-to-SHS welded N-joints were tested to failure under overlapping brace axial compression and chord axial loading. Elastic-plastic large deflection finite element analysis (FEA) of the experimental joints was performed and the FEA results for the failure mode and ultimate capacity are found to be in good agreement with the tests results. A detailed parametric study is subsequently conducted to examine the failure modes and to study the effect of geometric parameters and chord forces on the ultimate bearing capacity of the joints. The analytical results show that there are four possible failure modes of the joint under overlapping brace axial compression. It also reveals that brace-to-chord width ratio, chord width-to-its thickness ratio and brace-to-chord thickness ratio have a large effect on the failure mechanism and ultimate bearing capacity of overlapped CHS-to-SHS N-joints. Furthermore, the effect of chord compression force on the ultimate bearing capacity of the joints cannot be neglected.     

偏心受压冷弯薄壁槽钢的卷边角度优化设计

为了使得钢结构的性能与用钢量比达到最优,前人对槽型钢的截面尺寸优化进行了较为充分的研究。但是,涉及卷边角度的优化特别是偏心受压工况下的优化分析却很缺乏。以Yao-Teng偏心受压计算公式,结合遗传算法,以冷弯卷边槽钢柱偏心受压为例,将槽钢卷边角度与偏心距作为设计变量,寻找在不同偏心距受压情况下,达到最大畸变屈曲临界应力的卷边角度。基于有限条分析程序,对两端简支与两端固支情况下不同截面尺寸构件的畸变屈曲临界应力进行了计算分析,最终得出不同偏心距受压下统一的最优卷边角度。为了方便工程设计人员设计时参考,建议卷边角度统一取为100°。     

Influence of autoclaving process parameters on the buckling and postbuckling behaviour of thin-walled channel section beams

The postbuckling behaviour and load carrying capacity of thin-walled composite channel sections subjected to uniform compression are presented. An analysis of the influence of parameters of the composite manufacturing process on strength properties and load carrying capacity of the thin-walled structure made of this composite has been conducted. The microstructure characteristics of composites is presented and discussed. The postbuckling behaviour and load carrying capacity of thin-walled channel section columns subjected to compression have been determined with the finite element method. The ANSYS software has been employed.     

Experimental study on the determination of strength of masonry walls

The results of a research project carried out on masonry panels obtained from structures struck by the Umbria-Marchigiano earthquake of 1997–1998 are presented. The project consists of two parts: tests were performed in the laboratory, and in situ in order to determine the correct parameters describing masonry behavior. With regard to the laboratory tests, several compression tests were performed on cylindrical stone samples. Stone samples were obtained from the panels on which in situ tests had been previously carried out. Depending on the three types of in situ tests carried out (compression test, diagonal compression test, shear–compression test), different dimensions of panels were used using an appropriate cutting technique in order to leave the panels undisturbed. The shear strength and the Young and shear elastic modulus were measured. These results were compared with the values suggested by different standards. The experimental research allowed to characterize the mechanical properties of some typical masonry walls in old buildings of Umbria. These results are reported, together with an analysis of the masonry textures and sections.     

Recent advances on postbuckling analyses of thin-walled structures: Beams, frames and cylindrical shells

The lateral postbuckling response of thin-walled structures such as bars and frames with members having steel rolled shapes as well as circular cylindrical shells under axial compression is thoroughly reconsidered. More specifically via a simple and very efficient technique it is found that beams with rolled shapes (symmetric or non symmetric) under uniform bending and axial compression exhibit a stable lateral-torsional secondary path with limited margins of postbuckling strength. New findings for the static and dynamic stability of frames with crooked steel members-due to the presence of residual stresses-are also reported. It is comprehensively established that the coupling effect due to initial crookedness and loading eccentricity may have a beneficial effect on the load-carrying capacity of the frames. Moreover, simple mechanical models are proposed for simulating the buckling mechanism of axially compressed circular cylindrical shells. Very recently Bodner and Rubin proposed an 1-DOF mechanical model whose buckling parameters correlated to those of the shells by using an empirical formula based on experimentally observed shell buckling loads. In the present analysis a new 2-DOF model for the static and dynamic buckling of axially compressed circular cylindrical shells, which can include mode coupling, is presented.     

Eutrophication research of West Lake,Hangzhou, China: modeling under uncertainty

The models such as the eutrophication ecosystem model of West Lake, Hangzhou (EEM), are always used to make policy decisions for eutrophication management. Thus it is important to know the uncertainty in the model predictions due to the combined effects of uncertainty in the full set of input variables, and the individual input parameters whose variations have the greatest effect on variations in model predictions. In this study, randomized methods based on Monte Carlo technique have been developed and applied to the model (EEM). The technique consists of parameter sensitivity analysis, randomly sampling from underlying probability distributions and multivariate regression analysis. With this technique, model uncertainties during modeling are clarified and their propagation evaluated. Results show that among the five input parameters selected for uncertainty analysis, the settling rate of algae SVS and water temperature TEM have the largest contribution to model prediction uncertainty of the model outputs (PC, PS and PHYT).     

天津津塔施工过程结构分析及预变形技术

重力荷载下,75层的天津津塔超高层建筑竖向构件会出现较明显的压缩变形以及相互之间的差异压缩变形。通过施工过程结构分析及预变形技术,确定出构件加工预调值和施工安装预调值,使得建造完成后的结构实际位形能符合预期目标位形。为提高精度,分析时计入了地基不均匀沉降、混凝土收缩徐变对施工模拟和预变形值的影响。     

不封口钢管混凝土柱脚支承混凝土局部受压性能试验研究

针对端部不封口钢管混凝土的局部受压性能进行单调轴压试验研究及有限元分析。试件参数设置包括钢管的规格、支承体的混凝土尺寸、垫块的设置和配筋率等。试验及有限元分析表明：端部不封口钢管混凝土支承体顶面有压陷现象,其压陷现象与支承体的配筋率大小、不同局部受压面积比、垫块设置与否有关;对素混凝土支承体,其顶面压陷现象明显,并严重降低素混凝土的局部受压承载力;对配有间接钢筋的混凝土支承体,其顶面压陷现象不明显,对局部受压承载力影响不大,仍可按GB 50010-2010《混凝土结构设计规范》局部受压公式进行验算;当局部受压荷载满足GB 50010-2010中的要求时,不封口钢管混凝土支承体的压陷现象可以得到有效控制;局部受压截面通过局部承载力实测值与GB 50936-2014《钢管混凝土结构设计规范》公式对比可知,GB 50936-2014中建议的局部受压公式结果偏保守,柱脚环板下混凝土承载力也偏于保守。