斜桩承台桩基沉降影响有限元分析

马来西亚槟城二桥部分基础采用斜桩双承台,由于其采用斜桩基础,且桩基间距小于规范要求,沉降不方便计算。为控制其变形,需预估沉降值,通过有限元软件建立其中两个最具代表性的斜桩承台的空间模型,分为单承台和双承台两种情况,分析两种情况的沉降情况以及两承台间的相互影响,得出单承台和双承台两种情况下的沉降计算值以及变形情况,进而确定出双承台间的影响系数。同时比较桩身压缩量与总沉降的关系,结果表明沉降主要是由桩身压缩量引起,且总沉降满足要求。     

In-situ horizontal cyclic loading tests on composite foundation composed of soilbags and piles

The authors have been developing a new composite foundation composed of piles and soilbags. The foundation is characterized by the laying of soilbags between the pile heads and the footing on which a superstructure stands. The expected effect of the foundation is to cut off the fixed connection between the piles and the footing in order to reduce the bending moment of the piles and the response acceleration of the structure. In this study, in-situ horizontal cyclic loading tests were conducted on the proposed composite foundation with two piles to investigate the seismic response characteristics of the foundation at real scale. It was found from the tests that the horizontal force reached its peak due to the uplift of the footing during horizontal loading, and that larger hysteresis damping was obtained than that of spread foundations due to the hysteresis effect in the shear deformation of the soilbags. As for the sectional force of the piles and the vertical stress inside the soilbags, it was found that the axial force and bending moment of the piles concentrated on the pile on the front side in the loading direction, and that the vertical stresses inside the soilbags concentrated just above the pile head on the front side in the loading direction. Although residual horizontal displacement and settlement occurred due to the cyclic load, little damage to the soilbags was observed.     

条形承台梁与桩基的有限元分析

针对工程设计中通常按弹性支承计算的桩基条形承台梁,将桩与条形梁视为刚性连接的整体结构进行了有限元分析,求得梁、桩内力,可供工程设计时参考。     

Finite element reliability analysis of bridge girders considering moment–shear interaction

Reliability analysis is necessary in bridge design to determine which parameters have the most significant influence on the structural response to applied loadings. To support finite element reliability applications, analytical response sensitivities are derived with respect to uncertain material properties, girder dimensions, reinforcing details, and moving loads by the direct differentiation method (DDM). The resulting expressions have been implemented in the general finite element framework OpenSees which is well suited to the moving load analysis of bridges. Numerical examples verify the DDM response sensitivity equations are correct, then a first-order reliability analysis shows the effect uncertain parameters have on the interaction of negative moment and shear force near the supports of a continuous reinforced concrete bridge girder. A unique contribution is the treatment of moment–shear interaction using Lamé curves with foci calculated from MCFT equations. In addition, the analysis demonstrates non-seismic bridge engineering applications that have been developed in the OpenSees framework.     

Alternative solution for kinematic interaction problem of soil–structure systems with embedded foundation

An effective procedure to incorporate kinematic interaction (KI) aspects in seismic analysis of soil–structures systems was presented. In this regard, first, the effect of KI on the structural response was investigated with special focus on the role of rocking component of foundation input motion (FIM). This was performed parametrically for a wide range of selected nondimensional parameters, which well define the introduced simplified soil–structure model. It was observed that ignoring the effect of rocking input motion may introduce errors, which can be on the unsafe side especially for slender structures with large embedment ratios. On the other hand, it was known that introducing the rocking input motion makes the problem too complicated to be addressed by simplified guidelines suitable for seismic codes or practicing engineers. As an alternative solution, a modified translational input motion was introduced, which can replace both translational and rotational components of FIM. This modified input motion, which was referred to as the net horizontal (NH) FIM in this article, was generated such that the roof displacement of the soil–structure system to this motion is identical to that of the same model subject to the multicomponent FIM resulted by KI. The applicability of the proposed procedure was then examined for a wide range of soil–structure systems subjected to a couple of real ground motions. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

Seismic performance of reinforced concrete shear wall frames considering soil–foundation–structure interaction

A practical application of ‘beam on nonlinear Winkler foundation’ approach has been utilized in this paper for a case study on seismic performance of concrete shear wall frames to assess the soil–foundation–structure interaction effects. A set of 3‐, 6‐, 10‐ and 15‐story concrete shear wall frames located on hypothetically soft, medium and hard soils were designed and modeled using the OpenSees platform. The numerical model of each frame was constructed employing the distributed and lumped plasticity elements as well as the flexure–shear interaction displacement‐based beam–column elements incorporating the soil–footing interface. Pushover analysis was performed, and the results were studied through two code‐based viewpoints: (a) force‐based design and (b) performance‐based design. A comparison was made afterwards between the frame behaviors in the fixed‐/flexible‐base conditions. The results indicate some degree of inaccuracy in the fixed‐base assumption, which is regularly applied in analysis and design practice. The study emphasizes on how the fixed‐base assumption overestimates the design of the wall element and underestimates the design of the connected moment frame. Copyright © 2012 John Wiley & Sons, Ltd.     

钢管桩复合土钉墙支护的有限元分析

结合北京三峡大厦工程概况,提出基坑主要采用钢管桩复合土钉墙的支护方案,建立了FLAC3D数值模型,并对位移试算值与现场监测值进行了对比分析,通过对整个基坑开挖过程的检测,指出钢管桩复合土钉墙对增强整体稳定性,保证边坡开挖中不发生局部坍塌等具有重要作用。     

Evaluation of ground motion scaling methods in soil–structure interaction analysis

Dynamic analysis of structures deals with scaling of ground motions, which is vital for estimation of seismic responses. A major source of variability in seismic responses of structures arises from scaling of ground motions. In this paper, the accuracy of six conventional scaling methods on estimation of engineering demand parameters of soil–structure interacting systems is investigated. Two‐dimensional structural models of 5, 10, and 20 stories shear buildings are studied by using stick models, whereas the underlying soil is modeled using the cone model concept. This research attempts to elucidate the accuracy of considered methods for the evaluation of responses. The results show that a suitable scaling method for a response may differ from one to another in terms of accuracy and efficiency. Copyright © 2012 John Wiley & Sons, Ltd.     

基坑开挖对临近桩基性状影响的有限元模拟

采用二维弹塑性有限元法进行了基坑开挖对临近桩基性状影响的数值模拟,分析了基坑开挖所引起的临近桩基周围土体变形场的特性,讨论了不同开挖深度对桩身水平位移和弯矩的变化特性,得出了一些对工程实践有理论指导意义的结论。     

台后路基填土对桥台桩基础影响的有限元分析

针对在湿陷性黄土地区一座高填方路段上的桥梁，建立了桥台桩基础三维弹塑性有限元分析模型，采用ANSYS软件进行模拟，分析了路堤在填方高度不同、基础在不同桩长、不同桩径的条件下，桥台基础沉降的变化情况，探索了路基的填方高度、基础的桩长、桩径的变化对桥台桩基沉降的影响规律，得到关于桥台基础设计有益的结论。     

深大基坑桩锚支护体系的有限元分析

结合桩锚支护的工程实例,选用合适的土体模型和接触面,运用预应力锚索施工过程的简化模拟方法,对预应力锚索和围护桩与土体的相互作用进行了模拟,得到该基坑施工过程的地表位移,沉降,围护桩位移,受力和锚索轴力,并根据计算结果分析了该基坑支护方案的可行性。     

地基加固控制开挖对附近桩基影响有限元分析

采用有限元手段分析开挖施工对临近建筑物桩基影响规律,侧重于评估坑外地基加固控制开挖影响的有效性。对基坑开挖、地基加固以及邻近建筑桩基进行整体建模,以临近桩基承台水平位移为控制指标,对6种不同地基加固方案进行对比分析,研究复杂施工环境下地基加固控制开挖对已建和拟建建筑物影响的不同机理。研究表明,地基加固控制开挖对临近桩基的影响很大程度上取决于二者施工的前后性,开挖在临近桩基承载之后,则选择靠近临近桩基侧地基区段进行重点加固,反之,若开挖在临近桩承载之前,则选择近基坑侧地基区段进行重点加固。     

考虑粘弹性的中挤土桩沉降时效性分析

在研究沉桩过程中超静孔隙水压力的形成及消散规律的基础上,研究了桩周地基土再固结沉降的变化规律;从桩土相互作用的原理出发,建立了均质地基土粘弹性中单桩弹性微分方程,由此求得单桩弹性微分方程的解析解。     

西部红层软岩地区某桥梁扩大基础有限元分析

以西部红层软岩地区渝邻高速公路Ⅰ合同段林家湾大桥的1号桥墩扩大基础为例,通过有限元数值计算,分析了实际工程中桥梁扩大基础下红层软岩地基受基础传来的竖向力、水平力和弯矩复合荷载作用下的强度变形受力特性.分析结果表明,红层软岩地基沉降值较小,故一般均能满足JTJ024-85<公路桥涵地基与基础设计规范>要求,而桥梁扩大基础受基顶水平力及弯矩荷载影响较大,在基础底面尺寸设计的时候应充分考虑这一影响,使基底最大反力满足红层软岩地基承载力的要求.     

Shaking table test and theoretical analysis of the pile–soil–structure interaction at a liquefiable site

Pile foundations are widely used to support high‐rise buildings, in which piles transmit foundation loads to soil strata with higher bearing capacity and stiffness. This process alters the dynamic characteristics of the pile–soil–structure system in seismically active areas, especially at a liquefiable site. A series of shaking table tests on liquefiable soils in pile group foundations of tall buildings were performed to evaluate the liquefaction process and dynamic responses of the pile, soil, and structure. The soil was composed of two layers: the upper layer was a clay layer and the lower layer was saturated sand. These layers were placed in a flexible container that was excited by El Centro earthquake events and Shanghai Bedrock waves at different levels. The test results indicate that the pore pressure ratio is gradually enhanced as the amplitude of the input acceleration increases. The liquefied sand has a filtering effect on the vibration with a high frequency and an amplified effect on the vibration with a low frequency. With increased excitation, contact pressure and strain amplitudes of the pile increase, whereas the peak acceleration magnification coefficient decreases. The seismic responses of a structure with pile–soil–structure interaction are generally smaller than those on a rigid foundation.     

Influence zones for 2D pile–soil-tunnelling interaction based on model test and numerical analysis

In the congested urban areas, tunnelling close to existing structures or services often occurs due to the lack of surface space. Consequently, tunnelling-induced ground movements may cause a serious damage to the adjacent structures. This study focussed on two-dimensional laboratory model test for the pile–soil-tunnelling interaction using a close range photogrammetric technique and numerical analysis. Model testing equipments and procedures were introduced, particularly the use of aluminium rods regarded as the frictional granular material. The normalised pile tip movements were identified by both the model test and finite element analysis. The model test results found to be in good agreement with the finite element analysis. Based on the normalised pile tip settlements due to tunnelling adjacent to a line of loaded piles, influence zones were proposed in this study. The proposed influence zones are relatively wider and deeper than those proposed in previous studies. The authors believe that it will be useful to decide the reasonable location of tunnel construction in the planning stage.     

An empirical relationship to determine lateral seismic response of mid‐rise building frames under influence of soil–structure interaction

In this study, to determine the elastic and inelastic structural responses of mid‐rise building frames under the influence of soil–structure interaction, three types of mid‐rise moment‐resisting building frames, including 5‐storey, 10‐storey and 15‐storey buildings are selected. In addition, three soil types with the shear wave velocities less than 600 m/s, representing soil classes C_e, D_e and E_e according to AS 1170.4–2007 (Earthquake action in Australia, Australian Standards), having three bedrock depths of 10 m, 20 m and 30 m are adopted. The structural sections are designed after conducting nonlinear time history analysis, on the basis of both elastic method and inelastic procedure considering elastic‐perfectly plastic behaviour of structural elements. The frame sections are modelled and analysed, employing finite difference method adopting FLAC2D software under two different boundary conditions: (a) fixed base (no soil–structure interaction) and (b) considering soil–structure interaction. Fully nonlinear dynamic analyses under the influence of different earthquake records are conducted, and the results in terms of the maximum lateral displacements and base shears for the above mentioned boundary conditions for both elastic and inelastic behaviours of the structural models are obtained, compared and discussed. With the results, a comprehensive empirical relationship is proposed to determine the lateral displacements of the mid‐rise moment‐resisting building frames under earthquake and the influence of soil–structure interaction. Copyright © 2012 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.     

地基土震陷的有限元分析

采用弹塑性模型编制了二维问题的动力有限元分析程序，对地基土在8度地震烈度下的震陷值作了数值估计，并结合具体工程的算例分析进行了阐述。