桩土共同作用下的复合基础沉降计算

桩土共同作用下的复合基础是介于常规桩基与天然基础之间的一种基础形式,对其作用与机理作了简单探讨.关于桩土复合基础的沉降计算方法目前较少,按上海地基基础设计规范提供的方法在荷载较大时沉降值计算偏小,在保证结构安全度与设计减少桩数用量的前提下,本文提出计算复合基础沉降的一种改进方法,并给出一工程实例,可供同行设计参考.     

大底盘高层对单层地下室的沉降影响及内力分析

大底盘建筑的地下室经常为不分缝设计,整个地下室连成一个整体,其单层地下室部分也通常设计为天然基础.在高层的影响下,单层地下室必然发生沉降,从而承受一定的基底反力.用目前的设计手段,无法确切计算单层地下室的沉降量,也不能准确计算沉降对于基础结构的内力影响.通过工程实例,由建筑完成后的沉降量推算承受的底板反力,结果表明,由...     

上部结构-地基基础协同作用分析及设计优化

在常规的高层结构设计中,一般将上部结构和基础部分分开设计,既分析上部结构时认为基地固定,忽略基础和地基土的变形对其内力的影响。而实际上地基基础-上部结构三者共同工作、协同变形,基础和地基变形会引起上部结构内力的重新分布,上部结构对基础的变形也具有一定的限制作用。因此,设计常用方法与实际情况存在一定的差异。本文以某高层建筑为例,运用MIDAS-GTS软件建立地基-基础-上部结构协同分析模型,计算了三者共同作用时,多种荷载组合情况下的基础沉降量、桩基内力及桩身强度,对比了是否考虑协同分析两种情况下的结构内力分布情况,最后依据桩基础内力分布及沉降特征、建筑与裙房的差异变形量等模拟结果,提出合理的桩长、布桩方式、差异沉降控制措施等优化方案为工程设计提供参考。     

大底盘建筑主裙楼基础整体连接的可行性与适用性研究

随着现代化建设的发展,大底盘建筑越来越多。为解决主裙楼的差异沉降问题,主裙楼之间的连接方式有三种:沉降缝、沉降后浇带、主裙楼整体连接,目前工程中较多采用后两种连接方式。模型试验、共同作用分析及工程实践表明:大底盘高层建筑随着主楼外裙房面积的增大,厚筏基础的变形特征由刚性、半刚性特征逐渐表现为柔性特征;裙房结构和厚筏基础可以起到一定的扩散荷载及调整不均匀沉降的作用;通过合理的设计,当主裙楼的差异沉降控制在规范许可的范围内时,可以实现主裙楼基础的整体连接。工程实践中可以根据工程具体情况,有针对性地调整地基刚度、筏板刚度或结构刚度,达到控制主裙楼差异沉降的目的,从而实现主裙楼基础的整体连接。     

矩形筏基筏土刚度的确定方法

引言 在筏式基础的设计中,由于基础的变形导致上部结构的破坏,因此差异沉降是比绝对沉降更重要的控制因素.一旦差异沉降不符合要求,设计者所面临的选择是在基础下加桩,或是增大筏板的厚度,在不考虑桩支承的情况下,筏基的绝对沉降是不与筏基厚度相关的,并且其值可利用弹性理论或非线性理论进行计算.而差异沉降与绝对沉降可以表示成比例关系.这个比例与筏基的尺寸和筏土之间的相对刚度相关.     

考虑共同作用地基的沉降计算

针对目前结构设计中将上部结构与地基基础分开考虑,忽略上部结构刚度对基础内力及沉降的影响的现状,提出一种考虑上部结构与地基共同作用时基础沉降差的计算方法,据此可进一步考虑基础沉降差在上部结构中引起的附加内力.     

跨越地铁高层建筑桩筏基础数值模拟研究

基于某跨越地铁高层建筑的设计实践,利用ABAQUS建立剪力墙与桩筏基础和地基共同作用的三维有限元数值模型,研究了跨越地铁隧道的桩筏基础受力和变形性状,并分析了上部结构刚度、逐层施工、地铁隧道跨度、跨越地铁隧道方式等因素对其影响。结果表明,上部为剪力墙结构的高层建筑,考虑上部结构刚度作用可显著减小筏板的差异沉降和弯矩。当上部结构刚度达到一定程度后,其对筏板差异沉降和弯矩的调节能力减弱,表现出上部结构刚度贡献的有限性。随着地铁隧道跨度的增加,筏板最大沉降、差异沉降和弯矩都增大。桩筏基础以筏板对角线与地铁隧道中心线重合的方式跨越地铁隧道对筏板的内力和变形影响最小。桩顶反力数值计算结果与实测数据较为吻合。     

上海通用汽车有限公司某大型工业厂房基础设计

大型工业厂房轴网大、结构受力工况复杂.同时,由于工艺特殊、设备布置错综繁复、荷载重且沉降控制严格,给基础设计增加了难度.结合上海通用汽车有限公司某油漆车间基础和设备基础设计,分析其应注意的问题和技巧.     

带裙房高层建筑桩基设计与沉降计算的研究

一、立项背景 高层建筑桩筏基础设计中,桩多采用等长、等直径均匀布桩、即等刚度设计.实测沉降表明,等刚度设计情况下,带裙房的高层建筑物主楼的差异沉降及与裙房间的不均匀沉降问题比较普遍,特别是框剪、框筒、筒中筒结构,主楼碟形沉降明显.现有的全国性和地方性规范对桩箱或桩筏基础设计问题涉及较少.带裙房高层建筑桩基优化设计与沉降计算的研究很有必要. 基于上述问题,如何寻求在提高承载力和控制沉降之间找到一个契合点,是设计工作的重点.桩与筏板分担荷载的比例与沉降分析也是目前桩筏基础设计中的难点.     

考虑上部结构作用的沉降控制复合桩基设计

介绍了上海中学体育馆微型桩复合基础的设计情况。针对其受力特点以及沉降控制的 设计要求,在设计中采用了一种适合这种基础的计算方法,桩基计算考虑了与上部结构的共同作 用。使分析的结果更能反应实际的情况。     

均质土地基上埋深条形基础 极限承载力系数数值研究

 以K. Terzaghi提出的叠加公式为基础计算均质地基上埋深条形基础的极限承载力,需要确定承载力系数及相应的埋深修正系数。一般情况是采用极限平衡法、滑移线法及上限分析法进行承载力问题的研究,但受假定破坏模式的影响,不同的研究成果具有较大差异,而有限元法并不事先假定破坏模式,其计算结果具有较高精度。通过在基础与地基土接触面及基础边缘土体内数值奇异点引入接触面单元,建立适用于埋深条形基础的理想弹塑性有限元数值计算模型。利用在ABAQUS平台上开发的计算模块,对饱和不排水黏土地基、砂土地基及土体摩擦角与黏聚力均不为0的地基承载力问题进行系统的有限元计算,分析各系数随基础侧面粗糙程度、地基土强度参数、超载大小等影响因素的变化规律,并与已有结果进行对比,所给出的承载力系数及相应埋深修正系数的计算图表,可供基础工程设计参考。     

Bearing capacity of square footings on geosynthetic reinforced sand

The results from laboratory model tests and numerical simulations on square footings resting on sand are presented. Bearing capacity of footings on geosynthetic reinforced sand is evaluated and the effect of various reinforcement parameters like the type and tensile strength of geosynthetic material, amount of reinforcement, layout and configuration of geosynthetic layers below the footing on the bearing capacity improvement of the footings is studied through systematic model studies. A steel tank of size 900 × 900 × 600 mm is used for conducting model tests. Four types of grids, namely strong biaxial geogrid, weak biaxial geogrid, uniaxial geogrid and a geonet, each with different tensile strength, are used in the tests. Geosynthetic reinforcement is provided in the form of planar layers, varying the depth of reinforced zone below the footing, number of geosynthetic layers within the reinforced zone and the width of geosynthetic layers in different tests. Influence of all these parameters on the bearing capacity improvement of square footing and its settlement is studied by comparing with the test on unreinforced sand. Results show that the effective depth of reinforcement is twice the width of the footing and optimum spacing of geosynthetic layers is half the width of the footing. It is observed that the layout and configuration of reinforcement play a vital role in bearing capacity improvement rather than the tensile strength of the geosynthetic material. Experimental observations are supported by the findings from numerical analyses.     

基于摇摆柱的古建筑木结构柱脚节点力学模型研究

在古建筑木结构中,木柱通常直接平摆浮搁于础石之上,形成只有受压而无受拉能力的柱脚节点。在地震作用下,木柱会发生摇摆,柱脚为半刚性节点。为研究地震作用下古建筑木结构柱脚节点的摇摆机理,对柱脚节点的受压状态进行分析,并对木柱的摇摆过程进行分类,给出了不同摇摆过程的判定条件,建立了柱脚节点的弯矩-转角（M-θ）力学模型;通过与柱脚节点的弯矩-转角曲线试验结果进行对比,验证了该力学模型的正确性;将该M-θ力学模型应用于古建筑木结构的地震分析中,分别建立了柱脚半刚性连接和铰接的数值模型,并与振动台试验结果进行对比。研究结果表明：木柱的摇摆过程可分为全截面弹性摇摆、小截面弹塑性摇摆、大截面弹塑性摇摆以及全截面弹塑性摇摆等4类;采用M-θ力学模型得到的柱脚节点弯矩-转角曲线计算结果与拟静力试验结果的差异在10%以内;与铰接的柱脚节点相比,采用柱脚半刚性连接计算的古建筑木结构在地震作用下的动力响应更接近振动台试验结果,结构的加速度峰值、位移峰值与振动台试验结果的差异均在20%以内。     

Load-settlement characteristics of large-scale square footing on sand reinforced with opening geocell reinforcement

This paper describes load-carrying characteristics of a series of large-scale steel square footing tests performed on sand reinforced with two types of reinforcement methods. These are full geocell reinforcement (FGR) and geocell with an opening reinforcement (GOR). A thick steel square plate with 500?mm by 500?mm dimensions and 30?mm thickness was used as foundation. The parameters varying in the tests include the depth of geocell mattress (u), width of opening in geocell in the GOR type (w), relative density of sand (D_r) and number of geocell layers (N). The results revealed that the use of GOR and FGR methods enhances significantly the footing load carrying capacity, decreases the footing settlement and decreases the surface heave. It has been found that the use of GOR with an opening width of w/B?<?0.92, has the same improvement effect on the footing load-carrying response as the FGR has (B?=?footing width). Furthermore, with increasing the number of geocell layers from 1 to 2 in both GOR and FGR methods, the footing bearing pressure increases and footing settlement, surface heave and difference of performance between FGR and GOR mattress decrease.     

浅基础承载力离心模型试验研究

笔者利用容量为10gt的离心机对砂基上的浅基础进行了较为系统的试验,用以研究基础的尺寸、形状、埋深和砂土相对密度对浅基础承载力、承载力因数（Nr,Nq）、形状因数（ζr,ζq）及破坏型式的影响。笔者提出一种利用浅基础离心模拟试验资料确定浅基础的承载力因数和形状因数的方法。利用此方法确定的44T-4砂的承载力因数,形状因数与已有的各种理论解和试验解进行了对比。研究工作得出了一些有意义的结论。     

溶洞上方圆形基础地基极限承载力有限元分析

针对 3 种典型围岩条件,采用有限元方法对岩溶地区圆形基础下溶洞顶板稳定性进行了分析计算,讨论岩石地基极限承载力的确定方法,得出不同围岩、溶洞顶板跨度、顶板厚度条件下地基的极限承载力,并分析极限承载力与各影响因素之间的关系。     

Experimental and numerical investigations of the behaviour of footing on geosynthetic reinforced fill slope under cyclic loading

This paper investigates the cyclic loading responses of a strip footing supported by a geosynthetic reinforced fill embankment. A series of large-scale model footing tests were conducted first to investigate the accumulation of permanent footing displacement and residual vertical soil stress over large number of load cycles. The embankment fill was a heavily compacted silty sand and the reinforcement was a flexible geogrid, so that the model test configurations were representative of actual field conditions. Both permanent displacement and residual stress accumulated asymptotically with load cycles and majority of the build-up occurred over the first few hundred cycles. The potential effect of load interruptions was part of the study. Depending on how cyclic load interruption was implemented, it may or may not induce a trailing effect on subsequent cyclic loading responses. To have more in-depth understanding, these footing tests were also investigated numerically based on a soil model that can capture the unload-reload stress-strain loop over large number of load cycles. Reasonably good agreement between experimental observations and numerical predictions was also achieved.     

热管及保温材料在青藏直流联网工程中的应用研究

针对青藏直流联网工程塔基热管措施应用效果,通过现场实测资料确定了热管年内工作周期及混凝土桩基表面热效应,考虑无绝热段热管传热过程组成,建立空气-热管-土体耦合传热数学模型,利用有限元方法系统模拟不同年平均地温分区锥柱式塔基传热过程及气候变暖背景下基础周围多年冻土热状况发展变化趋势。结果表明：冷季热管工作期间,其对周围土体冷却降温效果显著,同时由于混凝土塔基为热的良导体,热管产生的“冷量”通过基础及其底座快速向基础周围传递,使得基础下形成大范围低温冻土。暖季,热管停止工作期间,由于基础埋设较浅,混凝土塔基良好的导热性能使得其周围浅层土体温度升温较快,量值基本与天然地表下同一深度接近,而基础下部深层地温则主要受热管作用控制,温度较低。在单一塔腿4根热管及50 a气温升高2.6℃背景下,-1.0℃、-1.5℃两种年平均地温条件下,桩基础下部多年冻土仍保持冻结状态,满足工程对于冻土地基热状况的要求。-0.5℃年平均地温条件下,运营后期桩基础周围土体季节融化深度已大于桩基埋深。在该地温条件下,通过热管-保温板复合措施的采用,可有效发挥热管的“冷却降温”及保温板的“隔热保冷”效能,在大幅减小基础周围土体的最大季节融化深度的同时降低锥柱式基础底部深层地温,进而满足工程需求。     

钢筋混凝土锥形基础的优化设计

以基础总造价为目标函数,以国家规范要求的地基承载力、抗弯和抗冲切强度等为约束条件,给出了钢筋混凝土锥形基础优化设计的数学模型;借助于MATLAB优化工具箱,通过编程,实现了此类基础的优化设计。算例表明,该优化设计方法经济效益显著,可推广应用于工程设计。     

Full-scale mechanically stabilized earth (MSE) walls under strip footing load

This study analyses two full-scale model tests on mechanically stabilized earth (MSE) walls. One test was conducted with a rigid and one with a flexible wall face. Other parameters were the same in these two tests, like the number and type of geogrid layers, the vertical distance between the layers and the soil type. The loads and strains on the reinforcement are measured as function of the horizontal and vertical earth pressure and compared with analytical models. Specifics regarding the behavior of the geogrids under the compaction load during the construction of the model and under strip footing load are included in the study. Results are compared with AASHTO and the empirical K-stiffness method. In this study, an analytical method is developed for the MSE walls taking into account the facing panel rigidity both after backfill construction and after strip footing load. There is good agreement between the proposed analytical method and the experimental results considering the facing panel rigidity. The results indicate that the tensile force on reinforcement layers for rigid facing is less than the flexible facing. The maximum strains in the reinforcement layers occurred in the upper layers right below the strip footing load. The maximum wall deflection for the flexible facing is more than for the rigid facing. The maximum deflection was at the top of the wall for the rigid facing and occurred at z/H?=?0.81 from top of the wall for the flexible facing.