砂土中桩循环打入过程大变形数值模拟

深入认识桩打入过程引起的桩周土体应力场变化对准确计算打入桩的竖向承载力十分重要。在有限元分析软件ABAQUS中采用大变形任意拉格朗日-欧拉（ALE）方法以及状态相关莫尔-库仑砂土本构模型，模拟了室内标准模型槽试验，得到了桩循环打入过程中桩周砂土全阶段的应力变化规律，并重点分析了径向应力，验证了桩侧砂土应力水平的h/R效应（h为测点与桩尖竖向距离，向上为正；R为桩半径），获得了应力与桩尖和桩中心线相对位置的分布规律。数值模拟结果与室内模型试验实测结果较一致，验证了数值模拟方法的可靠性；有效补充了试验中难以测量的近桩侧区域的应力分布数据，可为打入桩的承载力设计理论和设计方法研究提供依据。     

群桩沉降预测的简化非线性分析法

本文介绍国外一种在竖向荷载作用下的群桩非线性反应近似计算方法。该方法采用双曲荷载传递函数来模拟非线性的桩-土-桩相互作用。根据一些已有文献中的单桩荷载试验数据的分析,可以评估所介绍方法的可行性。该方法通过计算分析,可以得到主要模型参数的近似值。在单桩分析的基础上,采用等效墩概念并根据桩-土相互作用修正单桩荷载传递函数可以将单桩的荷载-沉降反应推广到群桩。文中研究了两例群桩的现场测试性能,并将试验结果与所介绍方法的计算结果进行了比较。研究表明群桩的荷载-变形性能是可以较合理的预测的。     

水平受荷桩桩-土作用的有限元分析

采用有限元方法对水平荷载作用下单桩试验进行数值模拟,以土弹簧取代桩周土体作用,提出了由实测试验桩数据推导求得土弹簧刚度的方法,此方法可应用于各种荷栽作用、泥面坡度情况下桩的桩-土相互作用.计算结果表明有限元模拟结果与试验实测数据基本吻合,可以为工程实践与设计提供重要理论依据.     

承台对群桩-承台结构水动力特性的影响研究

以往对海上结构物下部结构水动力特性的研究,大多仅针对群桩结构进行分析。对于跨海桥梁而言,实际情况是群桩-承台结构受到波浪力荷载的作用,因此对群桩-承台结构在波浪作用下的水动力特性进行系统研究十分必要。文章首先运用数值模拟的方法分析群桩结构的水动力特性,计算结果与相同工况下的实测数据高度吻合,充分证明所采用数值模拟方法是可靠的。其后通过建立群桩-承台结构三维数值波浪水槽,研究承台结构对桩柱群桩效应的影响,绘出了群桩在横向并列和纵向串列两种布置形式下群桩-承台结构的群桩效应系数KG随KC数的变化曲线,并通过改变承台淹没系数以进一步研究其对群桩-承台结构的水动力特性的影响。     

扩顶CFG桩复合地基加固效果数值模拟研究

扩顶CFG桩复合地基是在CFG桩复合地基基础上发展的一种地基处理方法,其借鉴桩-承台-土相互作用理论,充分利用扩顶"荷载收集"作用以及桩间土的承载和变形协调能力。以河南省某高速公路为工程背景,通过有限元数值方法对常规CFG桩和扩顶CFG桩复合地基进行模拟分析,讨论不同因素对扩顶CFG桩控沉效果的影响;分析桩帽下土体的竖向位移;研究桩身应力、桩帽下土体的应力等的变化规律,并结合现场监测结果比较分析,对扩顶CFG桩数值模拟给出若干结论。     

分层土-桩-结构动力相互作用数值模拟试验分析

采用有限元法分析桩-土-结构动力相互作用是当前工程与学术界解决此类问题的惯用方法。应用数值试验对桩一土一结构弹塑性动力相互作用中相关的问题进行了研究,采用整体有限元方法分析桩-土-结构动力相互作用,上部结构以框架结构为研究对象,上部结构、承台以及桩均采用二维梁单元进行模拟;土体采用二维平面应变单元进行模拟。讨论了土体分层对桩-土-结构动力相互作用体系的影响,得到一些对工程实际有益的结论。     

整体桥扩孔桩-土相互作用有限元分析

为研究整体桥桥台扩孔桩-土相互作用,建立整体桥扩孔桩-土相互作用p-y曲线,以深圳某整体桥为原型,用有限元分析软件ABAQUS建立单桩有限元分析模型,并用试验结果验证分析模型的正确性,研究扩孔桩-土相互作用机理。分析结果表明:所建立的有限元分析模型能够很好地模拟扩桩-土相互作用,有限元分析结果与试验结果吻合较好,并根据分析结果建立了整体桥扩孔桩-土相互作用p-y曲线,研究结果可为国内整体桥设计提供参考。     

劲芯水泥土桩单桩竖向承载性能与破坏模式研究

劲芯水泥土桩是一种新型的复合桩,目前国内外对于劲芯水泥土桩单桩承载-破坏模式尚缺乏统一认识。基于相似理论,设计了室内劲芯水泥土单桩静载荷模型试验。采用反映桩体材料破坏后特征的应变软化模型,模拟室内单桩竖向承载模型试验过程。研究表明,相比于莫尔-库仑模型,应变软化模型能够更好地反映桩体材料破坏后的性状,模拟的破坏模式与试验结果接近。基于应变软化模型,讨论了芯长比、含芯率和端承条件对劲芯水泥土桩的竖向承载特性和破坏模式的影响。劲芯水泥土桩单桩竖向受荷时存在3种破坏模式:芯桩桩顶受压破坏、芯桩刺入外桩破坏、桩周土体破坏。采用现行规范中劲芯水泥土桩极限承载力计算方法进行对比分析,发现大部分工况下计算的承载力与数值模拟结果较为接近,但其适用性还需做进一步研究。     

砂土中大直径开口桩打入过程的有限元模拟

文中采用Abaqus软件中的耦合欧拉-拉格朗日法(CEL)模拟了砂土中大直径开口桩的打入过程。通过数值分析得到的土塞变化规律与现场试验结果较为一致,表明了CEL方法能够较好地模拟打桩过程。同时还得到了桩侧砂土的应力分布规律,并验证了应力的h/R效应。     

海上风电高桩承台基础钢管桩可打入性探析

主要应用GRLWEAP软件,对高桩承台基础钢管桩沉桩过程进行模拟。将模拟沉桩过程的贯入度随深度变化曲线和沉桩结果统计表与实际沉桩记录对比,验证软件模拟方法和结果的正确性和准确性。模拟结果能够为基础设计中预制桩桩长、桩底标高确定等过程提供依据。     

桥梁动力弹塑性分析方法对比研究

为明确纤维模型和分离式模型在应用于桥梁抗震分析中的差异,本文利用通用有限元软件ABAQUS,采用混凝土弹塑性损伤模型,对某连续剐构桥建立了分离式模型。考虑桥墩高宽比变化,进行了罕遇地震下的弹性与弹塑性动力时程分析,并将结果与纤维模型分析的结果进行对比研究。分析表明：在弹性状态,两种模型的分析结果受桥墩高宽比影响较小,能得到较一致的解答;在弹塑性阶段,纤维模型具有更高的计算效率．但对于弯曲破坏不明显的桥梁结构其分析结果并不能反应桥墩的真实损伤情况,对于弯曲破坏显著的桥梁结构却不失为一种有效的工程分析方法;应用分离式模型进行弹塑性动力分析,能够直观地反映桥梁结构的损伤分布,是一种更为合理更为精细的弹塑性动力分析方法。     

Ventilation performance prediction for buildings: Model assessment

Designing ventilation systems for buildings requires a suitable tool to assess the system performance. This investigation assessed seven types of models (analytical, empirical, small-scale experimental, full-scale experimental, multizone network, zonal, and CFD) for predicting ventilation performance in buildings, which can be different in details according to the model type. The analytical model can give an overall assessment of a ventilation system if the flow could be approximated to obtain an analytical solution. The empirical model is similar to the analytical model in terms of its capacities but is developed with a database. The small-scale model can be useful to examine complex ventilation problems if flow similarity can be maintained between the scaled model and reality. The full-scale model is the most reliable in predicting ventilation performance, but is expensive and time consuming. The multizone model is a useful tool for ventilation design in a whole building, but cannot provide detailed flow information in a room. The zonal model can be useful when a user has prior knowledge of the flow in a room. The CFD model provides the most detailed information about ventilation performance and is the most sophisticated. However, the model needs to be validated by corresponding experimental data and the user should have solid knowledge of fluid mechanics and numerical technique. Thus, the choice for an appropriate model is problem-dependent.     

A simplified two-phase macroscopic model for reinforced soils

This paper presents the formulation of a macroscopic model for reinforced soil structures in which the interface is taken into consideration as a rigid-plastic contact. The model is formulated in the framework of a so-called multiphase model recently introduced for reinforced soil masses. The proposed simplified two-phase model can be considered as an optimal solution between extremely simplified perfect bonding model on one hand, and using a third phase for the interface on the other hand, which results in a more complicated and time-consuming model. The introduced platform is implemented in a numerical code. The proposed model is evaluated by simulating (a) the failure of laboratorial plane strain compression tests; (b) the behavior of a 1-g reinforced soil retaining wall model under external loading, and (c) the deformation of a reinforced soil structure under its own weight, which has been analyzed by another homogenization approach including elastoplastic interface model. The results indicate that the deformation of reinforced soil structures can be satisfactorily predicted by the proposed model.     

岩土流变模型的比较研究

基于岩土流变模型的研究现状,把各种流变模型分成4类：元件模型、屈服面模型、内时模型和经验模型。从横向和纵向两个方面对各类模型进行了比较研究;各类模型都有其自身的特点,元件模型较适用于岩石,屈服面模型适用于软土,内时模型适用于循环与振动加载,经验模型适用于实际工程。同时各类模型也有限制,有街待进一步研究。     

模型盾构隧道管片纵缝接头设计方法

考虑到拼装的缩尺模型管片环与原型管片环的纵缝接头刚度相似性难以满足要求,建议缩尺模型隧道采用开槽模型接头,并分别得到了采用两侧同时开槽、内侧开槽及外侧开槽的模型接头设计计算方法。通过开槽模型接头的管片环模型与梁—弹簧模型的计算结果比较,表明开槽模型接头的设计方法可行,开槽模型接头能很好地模拟拼装管片接头。在综合考虑开槽模型接头的开槽宽度对管片环结构内力与变形的影响与开槽模型接头的加工可行性的基础上,建议开槽模型接头对应的管片环中心角取值为3°~5°。提出的开槽模型接头设计计算理论可用于缩尺模型管片环的纵缝接头设计及在惯用法均质圆环的基础上进行局部抗弯刚度折减的数值模型隧道的建模。     

砂土的UH模型

在UH(Unified Hardening,统一硬化)模型的基础上,通过分析砂土特性,建立了砂土的本构模型。该模型具有以下几个特点:1通过引入压硬性参量,模型可以描述在e–lnp空间内砂土的等向压缩线为曲线的特性;2通过引入剪胀性参数,模型可以合理描述砂土的剪胀特性,即松砂的特征状态应力比较大,密砂的特征状态应力比较小的特性;3通过引入临界状态参数来建立砂土的水滴形屈服面,模型可以合理描述临界状态线(CSL)在e–lnp空间内的位置。相对于UH模型,本文所提的砂土模型只增加了3个材料参数,且3个参数都可通过室内常规试验确定。最后,利用该模型对砂土排水和不排水试验进行预测,预测结果与试验结果吻合很好。     

全桥气弹模型颤振导数识别

将节段模型颤振导数识别方法用于全桥气弹模型,对其可行性和便利性进行详细论述;给出气弹模型模态质量的确定方法;采用随机子空间方法和随机搜索方法识别均匀流场和紊流场中苏通大桥气弹模型的18颤振导数,并和特征系统实现算法识别结果进行对比分析。研究结果表明:节段模型颤振导数识别方法是识别气弹模型颤振导数的有效和实用方法;模型模态质量可以方便地根据几何缩尺比由实桥对应值直接推算得到,且比通过模型试验实测精度更高;不同方法识别得到的均匀流场中苏通大桥气弹模型大部分颤振导数基本吻合;相对于紊流场中的气弹模型而言,均匀流场中的节段模型颤振导数识别精度更高。     

岩石裂隙非饱和水力模型及其模拟计算

基于单裂隙非饱和渗流入侵概念模型,考虑裂隙排水起始毛细压力及排水过程开度范围等因素,推导了单裂隙非饱和渗透的饱和度与毛细压力及相对渗透系数的本构关系,根据有关试验资料进行了模型的验证分析。研究表明:推导的单裂隙饱和度与毛细压力关系与试验结果吻合较好,饱和度与相对渗透系数关系与经典模型具有良好可比性。考虑裂隙空隙存在非连通情况及起始毛细压力机制,引入压力修正项,同时考虑最小及最大排水概率开度能使入侵概念模型更符合实际。最后采用离散元软件UDEC应用本模型进行了单裂隙非饱和排水过程模拟,计算结果与Van Genchten模型结果接近反映模型合理。     

A simplified model for analysis of high‐rise buildings equipped with hysteresis damped outriggers

A simplified model is developed to estimate the seismic response of high‐rise buildings equipped with hysteresis damped outriggers. In the simplified model, the core tube is considered as a cantilever beam, and the effects of outriggers on the core tube are considered as concentrated moments. Modal decomposition method is adopted to obtain the seismic response of the simplified model. To investigate the accuracy and effectiveness of the simplified model, a high‐rise building with a height of 160 m was adopted as the example structure, and its response subjected to a ground motion was analyzed using the simplified model. A corresponding finite element model was built and analyzed by a finite element program called SAP2000 (Computers and Structures, Inc. Berkeley, California, United States). The analysis results obtained from the two models were compared. To consider the randomness of the ground motion, comparisons between the two models were further conducted using another 22 ground motions. It is found that the analysis results obtained from the simplified model agree well with those obtained from the finite element model, and the computation time used for the simplified model is almost negligible compared to that used for the finite element model. Such observations demonstrate that the simplified model is accurate and effective. Copyright © 2013 John Wiley & Sons, Ltd.     

Impact of turbulence anisotropy near walls in room airflow

The influence of different turbulence models used in computational fluid dynamics predictions is studied in connection with room air movement. The turbulence models used are the high Re-number kappa-epsilon model and the high Re-number Reynolds stress model (RSM). The three-dimensional wall jet is selected for the work. The growth rate parallel to the wall in a three-dimensional wall jet is large compared with the growth rate perpendicular to the wall, and it is large compared with the growth rate in a free circular jet. It is shown that it is not possible to predict the high growth rate parallel with a surface in a three-dimensional wall jet by the kappa-epsilon turbulence model. Furthermore, it is shown that the growth rate can be predicted to a certain extent by the RSM with wall reflection terms. The flow in a deep room can be strongly influenced by details as the growth rate of a three-dimensional wall jet. Predictions by a kappa-epsilon model and RSM show large deviations in the occupied zone. Measurements and observations of streamline patterns in model experiments indicate that a reasonable solution is obtained by the RSM compared with the solution obtained by the kappa-epsilon model. PRACTICAL IMPLICATIONS: Computational fluid dynamics (CFD) is often used for the prediction of air distribution in rooms and for the evaluation of thermal comfort and indoor air quality. The most used turbulence model in CFD is the kappa-epsilon model. This model often produces good results; however, some cases require more sophisticated models. The prediction of a three-dimensional wall jet is improved if it is made by a Reynolds stress model (RSM). This model improves the prediction of the velocity level in the jet and in some special cases it may influence the entire flow in the occupied zone.