桩筏基础相互作用下土中应力场的变化规律

在以往文献的基础上,通过计算分析,研究了不同桩数和桩长对土中应力场的影响以及桩基工作性状的变化规律,从应力角度探讨了桩基对沉降的控制作用。     

控制超高层建筑桩筏基础筏板弯矩的方法

为保证超高层建筑桩筏基础的筏板弯矩设计能够控制在安全范围内,采用相对弯曲计算筏板弯矩法(简称反算弯矩法)与共同作用理论的解析-数值解混合法(简称共同作用混合法)分别对金茂大厦、上海环球金融中心两个实例进行分析。根据共同作用混合法计算上海中心大厦的地基变形,用以计算相对弯曲,求得相应弯矩,同时,分别采用共同作用混合法和共同作用数值解-迭代法(简称共同作用迭代法)计算上海中心大厦筏板弯矩并进行比较。利用上述计算的结果,分析上海中心大厦的筏板弯矩,确定控制其筏板弯矩的安全范围。     

121‐story Shanghai Center Tower foundation re‐analysis using a compensated pile foundation theory

This paper attempts to re‐analyze the piled raft foundation in the Shanghai Center Tower as a fully compensated foundation using a hybrid method of superstructure–foundation interaction and other methods. Some cases were used to the applicability of the methods. The deformation analysis is divided into four parts: (a) Part 1: heave due to the weight of the excavated soil, (b) Part 2 : recompression due to the dead load of the structure, (c) Part 3 : recompression due to the live load of the structure and (d) Part 4 : settlement due to the constant load. Load acting on the top of the pile group and load sharing between the raft and the piles are also considered. The results are also compared in detail with the measured ones. In addition, research based on earth pressure theory was conducted to determine how to reduce or control the overturning moment caused by wind. Finally, this paper suggests that the Shanghai Center Tower, which is currently under construction, can have more than 121 stories by improving the design, which will also result in great investment savings. Copyright © 2013 John Wiley & Sons, Ltd.     

分层地基模型|桩筏基础|沉降|非线性|离心模型试验

基于改进的分层地基模型,考虑桩–土–筏的共同作用,提出了刚性桩筏基础非线性分析方法。地基附加应力计算考虑土层参数的变化,采用层状弹性体系的Burmister应力解;地基变形采用分层总和法,所采用的计算参数压缩模量和一维回弹模量试验确定方便。通过简单的室内一维加卸载试验确定其随加卸载次数的变化,进一步得到桩筏基础在重复加卸载下的沉降规律。对单桩和桩筏基础进行离心模型试验,并将计算结果和试验结果进行对比分析,验证了本文方法的正确性,可应用于实际工程问题的分析。     

高层建筑应用长-短桩复合地基的现场试验研究

对采用带垫层的长-短桩复合地基的1幢14层小高层建筑,在建造和使用过程中观测了长桩、短桩和地基土的受力状况以及基础沉降的变化,并由此分析了长-短桩复合地基中的桩-土荷载分担特性、桩-土共同作用机理和荷载-沉降特性,所得结论可为进一步的理论研究及工程设计提供有益的参考依据。     

黄土地基超高层桩筏基础变刚度调平设计

西安飞机公司运营及研发设计中心为黄土地基上的大底盘超高层建筑,塔楼、裙房和地下室连为一体不设缝。针对工程土质地基、摩擦桩型、超高层带裙房等特点,桩筏基础设计时采用以控制沉降变形为目的、以共同工作分析为手段的变刚度调平设计方法,使反力与荷载分布相协调,有效地减小基础沉降差、降低筏板内力及上部结构次应力、减小筏板厚度及配筋;采用合理的基床刚度系数,使变形计算结果接近工程实际;钻孔灌注桩采用后注浆工艺,有利于提高单桩承载力及控制沉降。     

Comparative study of load distribution ratio of various piled raft foundations based on coupled stiffness matrix

Load distribution ratio of piled raft foundation was investigated based on an interactive foundation analytical method that considers the coupling effect between the stiffness of the superstructure, the piled raft, and the soil. Series of numerical analysis was performed to verify the proposed analytical routine in comparison with various methods and field measurements. Through the comparative studies between various piled rafts with different aspects, it was found that the proposed analytical method derived accurate results in structural response compared with actual field data, in settlement, load distribution ratio, and raft bending moment. And it was also found that the proposed analytical method was capable of considering interaction between superstructure and foundation in predicting the behavior of building structures. As a result, it was found that in most cases, the pile in the piled raft foundation supports a majority portion of the structural load. However, for cases where the length of the pile was short and acts as a short column, the load distribution ratio between raft and pile may be overturned and shows significantly different behavior and load distribution ratio.     

Response in piled raft foundation of tall chimneys under along-wind load incorporating flexibility of soil

The present paper deals with the numerical analysis of tall reinforced concrete chimneys with piled raft foundation subjected to along-wind loads considering the flexibility of soil. The analysis was carried out using finite element method on the basis of direct method of soil-structure interaction (SSI). The linear elastic material behavior was assumed for chimney, piled raft and soil. Four different material properties of soil stratum were selected in order to study the effect of SSI. The chimney elevation and the thickness of raft of piled raft foundation were also varied for the parametric study. The chimneys were assumed to be located in terrain category 2 and subjected to a maximum wind speed of 50 m/s as per IS:875 (Part 3)-1987. The along-wind loads were computed according to IS:4998 (Part 1)-1992. The base moments of chimney evaluated from the SSI analysis were compared with those obtained as per IS:4998 (Part 1)-1992. The tangential and radial bending moments of raft of piled raft foundation were evaluated through SSI analysis and compared with those obtained from conventional analysis as per IS:11089-1984, assuming rigidity at the base of the raft foundation. The settlements of raft of piled raft foundation, deflection of pile and moments of the pile due to interaction with different soil stratum were also evaluated. From the analysis, considerable reduction in the base moment of chimney due to the effect of SSI is observed. Higher radial moments and lower tangential moments were obtained for lower elevation chimneys with piled raft resting on loose sand when compared with conventional analysis results. The effect of SSI in the response of the pile is more significant when the structure-foundation system interacts with loose sand.     

不同桩长、桩径桩筏基础的分析方法

针对具有不同桩长、桩径群桩的桩筏基础进行研究,采用筏基无单元方法对筏板进行模拟,基于共同作用原理,以桩与桩、桩与土相互作用的解析模型为基础,建立了层状地基上不同桩长、桩径、桩体材料情况下,桩筏基础与地基共同作用的一种分析方法。旨在解决具有特殊桩群,或通过桩长、桩径、桩体材料的变化、优化桩土刚度分布、调平设计时的桩筏基础计算问题。该方法可方便地用于非均匀布桩、非规则平面形状桩筏基础的计算和优化分析。与基于实际工程的大型模型试验结果的比较表明,该方法是合理可行的,并具有较好的实用性。     

高层建筑厚筏反力及变形特征试验研究

根据大型模型试验证明 ,高层框架及厚筏的刚度近似于箱型基础 ,当筏板厚度超过 1/ 6柱跨时 ,用倒梁法计算与整体分析法效果相近。利用局部荷载作用下计算筏板反力和沉降的方法按叠加原理 ,可近似求出多个塔楼作用下大面积厚筏基础的沉降     

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。     

设置变形调节装置桩筏基础设计方法及工程实践

设置变形调节装置桩筏基础通过调节装置实现对桩土支承刚度的调整与优化,使其可应用于端承型桩基桩土共同作用、变刚度调平设计、老桩的再生利用以及土岩结合地基等支承刚度严重不均匀的情况。作为一种新的桩筏基础形式,工程实践表明设置变形调节装置桩筏基础可取得显著的经济效益和社会效益。为推动其进一步应用与发展,形成成套设计理论与方法,本文详细介绍了变形调节装置桩筏基础的设计过程,并通过一工程实例对其设计方法进一步进行了分析,供广大工程技术人员参考。     

穿越软土层嵌岩桩筏基础沉降特征与计算方法

结合某双塔高层建筑核心区桩筏基础和核心区外独立承台桩基础沉降变形监测资料,分析了嵌岩桩筏基础的沉降特征。结果表明,双塔核心区嵌岩桩筏基础沉降变形的整体性较好,沉降随施工加载过程增长较为稳定,而核心区外嵌岩桩基础的沉降对主楼施工和环境条件(如地下水)较为敏感,施工中出现了桩体上浮现象。根据桩顶荷载计算的嵌岩桩桩身压缩量与实测沉降相比,实测值远大于计算值。考虑嵌岩桩施工和桩筏基础工作特点,提出了穿越软土层的嵌岩桩筏基础沉降的两个主要影响因素:沉渣效应和桩侧负摩阻。在此基础上,提出了考虑沉渣和桩侧阻影响的桩筏基础沉降估算方法,并通过本工程及文献中的工程实测对提出公式的适用性进行了检验。     

高层建筑中箱基和上部结构共同作用下的计算和调整沉降方案

笔者2次指出国内外技术规程中建议的箱基与上部结构共同作用下的计算是错误的,并建议新的计算。为了从理论上解决箱基渗漏问题,曾提出“反盆式沉降方案”,现改为“调整沉降方案”,并介绍了工程实例。     

Nonlinear time history analysis of a super‐tall building with setbacks in elevation

Standing 260 m above the ground, the super‐tall building employs steel reinforced concrete frame and reinforced concrete core wall system strengthened by a belt truss story to resist lateral and vertical loads. It has two setbacks in elevation. One is structurally designed by direct termination of vertical members, and the other is realized by inclining columns. Because of these characteristics, the building is classified as an irregular and complex structure. To investigate the seismic behavior of the structure under rare earthquake action, a refined finite element model was developed by using ABAQUS (Dassault Systèmes Simulia Corp., Providence, RI, USA). Nonlinear time history analyses were conducted using explicit integration method. The results show that the structural system has sufficient seismic capacity and ductility to resist rare earthquake. The plastic deformation capacity of this building can meet the requirement of Chinese code, and seismic performance objective of no collapse under rare earthquake can be reached. However, deformations were found concentrated in members within and adjacent to setback stories, at the bottom strengthening portion of core walls and its upper story where lateral stiffness suddenly changed. It was suggested that transfer stories should be placed above or below these stories to improve the concentration of strain and deformation. Copyright © 2011 John Wiley & Sons, Ltd.     

Coupled‐two‐beam discrete model for dynamic analysis of tall buildings with tuned mass dampers including soil–structure interaction

An equivalent coupled‐two‐beam discrete model is developed for time‐domain dynamic analysis of high‐rise buildings with flexible base and carrying any number of tuned mass dampers (TMDs). The equivalent model consists of a flexural cantilever beam and a shear cantilever beam connected in parallel by a finite number of axially rigid members that allows the consideration of intermediate modes of lateral deformation. The equivalent model is applied to a shear wall–frame building located in the Valley of Mexico, where the effects of soil–structure interaction (SSI) are important. The effects of SSI and TMDs on the dynamic properties of the shear wall–frame building are shown considering four types of soil (hard rock, dense soil, stiff soil, and soft soil) and two passive damping systems: a single TMD on its top (1‐TMD) and five uniformly distributed TMDs (5‐TMD). The results showed a great effectiveness of the TMDs to reduce the lateral seismic response and along‐wind response of the shear wall–frame building for all types of soils. Generally speaking, the dynamic response increases as the flexibility of the foundation increases.     

Behavior of coupled shear walls with buckling‐restrained steel plates in high‐rise buildings under lateral actions

Traditional coupling beams in coupled shear walls (CSWs) may be lack of required ductility or inconvenient to be fully repaired or replaceable after earthquake damage. To improve the CSW seismic performance, a type of new structural system, which is referred to as coupled shear walls with buckling‐restrained steel plates (CSW–BRSP), is proposed and thoroughly studied. In the system, a pair of individual concrete wall is coupled through buckling‐restrained steel plates instead of traditional concrete coupling beams. Based on the continuous medium method (CMM), stiffness and strength design formulas are developed for the seismic design of this system. Intensive investigations have been conducted to assess the undesirable axial forces in the buckling‐restrained steel plates induced by lateral loads. In order to facilitate the application of this system, a detailed design procedure is also explicitly stated. Finally, an example of typical high‐rise building is presented to illustrate the design procedure as well as demonstrate the excellent seismic performance of the proposed system by means of nonlinear time‐history analysis. Copyright © 2015 John Wiley & Sons, Ltd.     

Rectification of jacking method for brick‐wooden buildings in deformation analysis with CFST reinforcement

The tilting of buildings not only leads to inconvenience but also causes serious building collapses with heavy casualties and serious social impacts. However, rectification and reinforcement construction method started late in China. Now, this construction pattern mainly depends on sophisticated design techniques, without systematic techniques to reference. Based on the in‐depth analysis on tilt reason of a brick‐wooden building in Yunnan Province in China and combined with jacking rectification method, the impact pile project, artificial inserting shield engineering for steel box girder project, unbonded prestressed engineering project and concrete filled steel tube reinforcement example. Analyzing the multipoint synchronous lifting process by 3‐dimensional numerical simulation in ANSYS finite software. The actual monitoring results showed that the maximum inclination rate was reduced to less than 2.95‰ in the end, and the architectural distortion was stabilized in the process of rectification and reinforcement, which guarantees building safety and efficiency in the process of rectification.