Longitudinal vibration characteristics of a tapered pipe pile considering the vertical support of surrounding soil and construction disturbance

This research is concentrated on the longitudinal vibration of a tapered pipe pile considering the vertical support of the surrounding soil and construction disturbance.First,the pile-soil system is partitioned into finite segments in the vertical direction and the Voigt model is applied to simulate the vertical support of the surrounding soil acting on the pile segment.The surrounding soil is divided into finite ring-shaped zones in the radial direction to consider the construction disturbance.Then,the shear complex stiffness at the pile-soil interface is derived by solving the dynamic equilibrium equation for the soil from the outermost to innermost zone.The displacement impedance at the top of an arbitrary pile segment is obtained by solving the dynamic equilibrium equation for the pile and is combined with the vertical support of the surrounding soil to derive the displacement impedance at the bottom of the upper adjacent segment.Further,the displacement impedance at the pile head is obtained based on the impedance function transfer technique.Finally,the reliability of the proposed solution is verified,followed by a sensitivity analysis concerning the coupling effect of the pile parameters,construction disturbance and the vertical support of the surrounding soil on the displacement impedance of the pile.

Investigation on seismic response of a three-stage soil slope supported by anchor frame structure

Based on a typical prototype of a soil slope in engineering practice, a numerical model of a three-stage soil slope supported by the anchor frame structure was established by means of FLAC3D code. The dynamic responses of three-stage soil slope and frame structure were studied by performing a series of bidirectional Wenchuan motions in terms of the failure mode of three-stage structure, the acceleration of soil slope, the displacement of frame structure, and the anchor stress of frame structure. The response accelerations in both horizontal and vertical directions are the most largely amplified at the slope top of each stage subjected to different shaking cases. The platforms among the stages reduce the amplification effect of response acceleration. The residual displacement of frame structure increases significantly as the intensity of shaking case increases. The frame structure at each stage presents a combined displacement mode consisting of a translation and a rotation around the vertex. The anchor stress of frame structure is mainly increased by the first intense pulse of Wenchuan seismic wave, and it is sensitive to the intensity of shaking case. The anchor stress of frame structure at the first stage is the most considerably enlarged by earthquake loading.

Sensor monitoring of a newly designed foundation pit supporting structure

A new type of pit supporting structure, which was tested and verified using the sensor monitoring technology, was presented. The new supporting structure is assembled by prefabricated steel structural units. The adjacent steel structural units are jointed with fasteners, and each steel structural unit has a certain radian and is welded by two steel tubes and one piece of steel disc. In order to test and verify the reliability of the new supporting structure, the field tests are designed. The main monitoring programs include the hoop stress of supporting structure, lateral earth pressure, and soil deformation. The monitoring data of the field tests show that the new supporting structure is convenient, reliable and safe.

Effects of foundation rocking and uplifting on displacement amplification factor

Prediction of displacement demand to assess seismic performance of structures is a necessary step where nonlinear static procedures are followed.While such predictions have been well established in literature for fixed-base structures,fewer bodies of researches have been carried out on the effect of rocking and uplifting of shallow foundations supported by soil,on such prediction.This paper aimed to investigate the effect of soil structure interaction on displacement amplification factor C1 using the beam on nonlinear Winkler foundation concept.A practical range of natural period,force reduction factors,and wide range of anticipated behavior from rocking,uplifting and hinging are considered and using thousands nonlinear time history analysis,displacement amplification factors are evaluated.The results indicate that the suggested equations in current rehabilitation documents underestimate displacement demands in the presence of foundation rocking and uplift.Finally,using regression analyses,new equations are proposed to estimate mean values of C1.

Multiple Tuned Mass Damper Based Vibration Mitigation of Offshore Wind Turbine Considering Soil–Structure Interaction

The dynamics of jacket supported offshore wind turbine （OWT） in earthquake environment is one of the progressing focuses in the renewable energy field. Soil-structure interaction （SSI） is a fundamental principle to analyze stability and safety of the structure. This study focuses on the performance of the multiple tuned mass damper （MTMD） in minimizing the dynamic responses of the structures objected to seismic loads combined with static wind and wave loads. Response surface methodology （RSM） has been applied to design the MTMD parameters. The analyses have been performed under two different boundary conditions： fixed base （without SSI） and flexible base （with SSI）. Two vibration modes of the structure have been suppressed by multi-mode vibration control principle in both cases. The effectiveness of the MTMD in reducing the dynamic response of the structure is presented. The dynamic SSI plays an important role in the seismic behavior of the jacket supported OWT, especially resting on the soft soil deposit. Finally, it shows that excluding the SSI effect could be the reason of overestimating the MTMD performance.

On time-step in structural seismic response analysis under ground displacement/acceleration

There are two models in use today to analyze structural responses when subjected to earthquake ground motions, the Displacement Input Model （DIM） and the Acceleration Input Model （AIM）. The time steps used in direct integration methods for these models are analyzed to examine the suitability of DIM. Numerical results are presented and show that the time-step for DIM is about the same as for AIM, and achieves the same accuracy. This is contrary to previous research that reported that there are several sources of numerical errors associated with the direct application of earthquake displacement loading, and a very small time step is required to define the displacement record and to integrate the dynamic equilibrium equation. It is shown in this paper that DIM is as accurate and suitable as, if not more than, AIM for analyzing the response of a structure to uniformly distributed and spatially varying ground motions.

盾构机始发井深基坑力学和变形特性离心模型试验研究

为探究盾构机始发井深基坑开挖过程中周边土体的应力、变形和土压力分布规律,通过对工程原型进行概化,在典型土层条件下,采用停机-开挖-支护的模拟方式开展了方形基坑和圆形基坑两种方案共2组离心模型试验,从地连墙的弯矩和其后土体的水平位移、基坑外侧土压力分布以及地表沉降等角度,对比分析了两种盾构机始发井深基坑开挖过程的工程特性。结果表明:地面沉降随基坑开挖深度增大逐渐增加,形成沉降槽状;地连墙土压力变化呈非线性,随着基坑开挖不断深入的,离地表较近处的土压力逐渐变大,而深处的土压力则逐渐减小;在第5步开挖时2组模型地下连续墙水平位移均达到最大值,圆形基坑是方形基坑的1.4倍,同时地连墙的弯矩也达到最大值,圆形基坑比方形基坑小320 kN·m。研究成果可为深埋隧道深基坑的优化设计和开挖提供指导。

深基坑支护理念演进和设计方法改进剖析

基于我国30多年建设实践,分析现有深基坑支护临时性理念、与主体结构相结合理念实施的优点和不足,提出促进基坑支护工程高质量发展的永久化理念。结合济南某基坑工程,阐释三个理念的逐次提升和相应支护结构的计算内容,定义适应与主体结构相结合理念、永久化理念的结构岩土化、岩土结构化设计方法;重点分析土钉墙与抗浮锚杆相结合的复合土钉墙的设计,以及抗浮锚杆与外伸支撑、水平楼板永久支护结构中抗浮锚杆的力学性状与耐久性,分析了永久支护对于地下室外墙受力机制的影响,阐释深基坑支护理念演化方向和与之适应的设计改进内容。对于反思我国岩土与结构设计管理体制,促进基坑与基础设计理论和方法进步,推动“新发展理念”在基坑工程的实践具有导向价值。

Interaction of Building Frame with Pile Foundation

The study deals with physical modeling of a typical building frame resting on a pile group embedded in cohesive soil mass using complete three-dimensional finite element analysis. The elements of the superstructure frame and that of the pile foundation are discretized using twenty node isoparametric continuum elements. The interface between the pile and pile cap is idealized using sixteen node isoparametric surface elements. The more improved finite element mesh is used for modeling soil element as compared to the one used in the study reported in the literature. The soil elements are discretized using eight node, nine node and twelve node continuum elements. Both the elements of superstructure and substructure (i.e., foundation) including soil are assumed to remain in elastic state at all the time. The interaction analysis is carried out using sub-structure approach to attempt a parametric study. The effect of the parameter such as spacing between the piles in a group and diameter of pile is evaluated on the response of superstructure. The response includes the displacement at the top of the frame. The effect of the soil-structure interaction is observed to be significant for the type of foundation and soil considered in the present study.

17m超高坐地式玻璃肋幕墙系统结构性能和试验研究

文章以泰康大厦工程为背景,针对超高坐地式玻璃肋幕墙系统进行了大风压作用下的结构性能和位移能力试验研究,通过有限元、试验、理论三者进行对比分析。研究表明,该幕墙系统不仅满足1.75kPa风压作用下的结构性能要求和2.63kPa大风压下结构的安全性能要求,而且满足三个方向位移能力的要求。充分说明17m超高坐地式玻璃肋幕墙系统的设计方案安全可行,设计方案和试验结果可为今后超高坐地式玻璃肋幕墙系统的设计提供支持。

顶置磁力搅拌器磁悬浮支承结构设计与仿真分析

针对顶置磁力搅拌器陶瓷轴承内部结构复杂,存在接触摩擦和润滑,且不利于在位清洗和在位灭菌的问题,对磁力搅拌器的载荷组成及搅拌轴支承布局进行分析,采用磁悬浮支承技术,增大主动磁轴承转子的轴向长度,确保转子在产生轴向位移时能被稳定支承;不考虑被动磁轴承与磁力联轴器因不对中产生的径向力,建立搅拌器转子的四自由度支承刚性转子模型,研究不同外部载荷对搅拌器转子的动态响应和线圈控制电流的影响,结果表明:外部载荷越大,外部载荷在长悬臂结构上的力矩作用效果越明显,主动磁轴承需提供的电磁力越大,对磁轴承功率放大器的要求越高。

考虑桩-土相互作用的超大型单桩式海上风机结构地震响应

为了解决桩-土相互作用对超大型单桩式海上风机结构地震响应影响的问题,基于IEA 15 MW的固定式单桩海上风机原型,使用Abaqus建立考虑桩-土相互作用与泥面固定2种风机结构模型,桩-土相互作用通过一组非线性弹簧模拟。考虑风-波浪与地震联合作用,分析桩-土相互作用对超大型固定式单桩海上风机结构动力响应的影响。结果表明:针对超大型海上风机,桩-土相互作用效应使风机支撑结构的特征频率降低3%~6%;考虑桩-土相互作用的大兆瓦风机动力响应远大于泥面固定风机模型的动力响应;海上风机尺寸越大,桩-土相互作用引起的海上风机结构动力响应偏差越显著。

排桩复合土钉支护结构水平位移简化计算方法

针对排桩复合土钉支护结构,基于其受力变形机理,引入了土钉钉头与排桩在相应位置处变形协调的基本假定,考虑了分步开挖施工工况,采用增量法建立了考虑施工过程影响的排桩复合土钉支护结构水平位移简化计算方法。算例及工程实例计算的对比分析表明,所建立的排桩复合土钉支护结构水平位移简化计算方法具有工程适用性。

考虑土性参数空间变异性的珠三角软土地区土钉支护结构可靠度分析

如何定量定性描述软土土性参数空间变异性对准确确定软土土性参数和合理评价软土地区土钉支护结构稳定性至关重要。采用既有统计分析方法定量描述空间变异性通常需要大量数据,难以满足。本文基于随机场理论模拟软土土性参数空间变异性,建立了一套考虑土性空间变异性的软土地区土钉支护结构可靠度设计方法,最后以MATLAB软件包为平台进行计算程序的开发与工程实例研究。分析结果表明,本文采用随机场方法模拟软土土体固有空间变异性及其在土钉支护结构可靠度分析中的应用具有合理性与普适性。

气承式膜结构煤棚调整内压下的实测位移响应分析

随着气承式膜结构煤棚跨度和单体面积的增加,内压分布特征的变化复杂。目前缺乏针对大型项目的内压升降与位移响应变化关系的实测验证,以确定结构位移响应理论计算值与实测数据是否吻合。基于布设在浙江乐清电厂115m×317m的气承式膜结构煤棚的健康监测系统,在台风来临前对结构进行了升降压-保压测试。实测了结构7个不同测点的位移响应,分析了调整内压时结构的位移响应特征。同时,将实测结果与数值模拟结果进行对比分析,验证了对于大跨度气承式膜结构基于压力等效分析方法的可靠性。

星载迈克尔逊干涉仪直线动镜的柔性支撑结构研究

针对传统迈克尔逊干涉仪动镜支撑结构存在成本高、寿命低、维护难度大、大行程大负载下导向精度差的问题,设计了一种高精度迈克尔逊干涉仪角镜柔性支撑结构,具有低成本、高精度、大负荷的优点。提出以柔性支撑结构的承载能力、行程和导向精度为优化目标的结构刚度模型,选择材料和尺寸参数,开展运动结构设计。有限元分析结果表明该支撑结构在1.5 kg的负载(角镜)下,当行程达到4.5 mm时,柔性结构的最大拉应力约为169 MPa,结构安全裕量为1.98,角镜竖直方向的寄生位移小于4.1μm。专项测试结果显示,支撑结构承载1.5 kg负载(角镜)在4.5 mm行程内,竖直方向的寄生位移小于4.7μm,直线度的均方根误差为1.5μm,与设计结果较吻合,可以满足星载迈克尔逊干涉仪对高精度直线动镜的支撑要求。

深基坑工程不同施工阶段对其围护结构及临近在役铁路路基稳定性影响分析

为研究基坑工程不同施工阶段对基坑围护结构及临近在役铁路稳定性的影响,针对盐城市铁路综合客运枢纽能源中心深基坑工程,首先分析不同施工阶段对基坑围护结构变形量的影响;然后基于临近铁路路基沉降变形监测数据,分析各施工阶段对铁路路基稳定性的影响。研究结果表明:土方开挖过程中基坑圈梁水平和竖向位移、支撑轴力、格构柱竖向位移均呈逐步增大的变化规律,支撑施工及底板浇筑过程中基坑各结构的位移量及支撑轴力逐步减小;随着施工进程的不断推进,铁路路基的竖向位移逐渐增大,直至拆撑结束后逐渐趋于稳定。最后通过收集若干基坑开挖对临近铁路路基影响的工程实例,发现铁路路基最大沉降值S_(max)与mH_(e)/L_(t)(m为基坑靠近路堤一侧的宽度、L_(t)为基坑坑壁至路基坡脚线的水平净距、H_(e)为基坑开挖深度)存在良好的对数关系。

橡胶支座-地铁车站减震结构的动力响应及关键设计参数研究

基于地下结构布设隔震支座可有效控制结构地震反应,以某实际两层两跨地铁车站为研究对象,建立了橡胶支座布设于地铁车站结构的三维全时程动力分析模型,探讨了橡胶支座关键设计参数-水平刚度比对多层地铁车站减震结构地震响应的影响,并进一步分析了在最佳水平刚度比条件下减震结构的动力响应。研究结果表明:(1)中柱布设橡胶支座后,中柱内力及位移均有不同程度的减小,表现出良好的减震效果;(2)水平刚度比的变化对减震结构中柱的动力响应结果影响显著,对结构侧墙的动力响应结果影响较小,且水平刚度比会对中板的变形模式产生影响,综合考量,建议最佳水平刚度比的范围为0.06~0.08;(3)在最优水平刚度比条件下,结构中柱位移减震率最高可达85%,且中柱及侧墙始终处于安全工作状态,达到了破坏模式可控的效果。

高层建筑深基坑支护结构位移动态监测方法

针对高层建筑深基坑支护结构位移监测时,位移轨迹、位移速率以及位移时间变化监测准确性较差问题,本文研究了高层建筑深基坑支护结构位移动态监测方法。对支护结构位移影响因素进行具体分析,生成了影响指标;再对基坑数据进行采集,建立数据集并进行降维处理;计算获取目标函数,结合影响指标建立时间序列模型,依据对模型的计算建立动态变量矩阵;通过对矩阵的计算获取动态监测数据的统计量,完成支护结构的动态监测。研究结果表明:运用该方法进行监测时,位移移动轨迹监测误差为0.1,位移速率保持在0.9 mm/d以下,且与实际位移速率基本一致,纵向位移量达到202 mm,且与实际沉降量一致。本文方法能够有效应用于高层建筑深基坑支护结构的位移动态监测,为保障高层建筑的稳定性和安全性提供重要的技术支持。

弹性支撑条件下声子晶体角梁结构振动特性分析研究

为了进一步探究一维声子晶体结构的振动特性,本文开展了弹性支撑条件下一维声子晶体角梁结构弯曲位移的振动特性研究。通过采用有限元分析法,分别对L型和T型声子晶体角梁结构进行模型建立,并对频率范围内的弯曲位移响应曲线进行绘制。同时,对弹性支撑条件、晶格长度、组分比、连接角度以及弹性支撑刚度对不同类型声子晶体角梁结构的带隙影响规律进行了研究。结果表明,弹性支撑刚度对声子晶体角梁结构的第一带隙有着明显的影响。