Development of the cyclic p–y curve for a single pile in sandy soil

Pile foundations that support transmission towers or offshore structures are dominantly subjected to cyclic lateral load induced by wind and waves. For a successful design, it is crucial to investigate the effect of cyclic lateral loads on the pile behavior that is loaded laterally. Although the p–y curve method is generally utilized to design the cyclic laterally loaded pile foundations, the effect of cyclic lateral loads on the pile has not been properly implemented with the p–y curve. This reflects a lack of consideration of the overall stiffness change in soil–pile interaction. To address this, a series of model pile tests were conducted in this study on a preinstalled aluminum flexible pile under various sandy soil conditions. The test results were used to investigate the effect of cyclic lateral loads on the p–y behavior. The cyclic p–y curve, which properly takes into account this effect, was developed as a hyperbolic function. Pseudo-static analysis was also conducted with the proposed cyclic p–y curve, which showed that it was able to properly simulate cyclic laterally loaded pile behavior in sandy soil.     

Lateral cyclic response of an aluminum model pile in sand

Lateral cyclic load tests were performed on an aluminum model pile in dry sand. Two levels of loading were adopted to represent different service load conditions. The maximum number of loading cycles was 1,000. From the test results, it was found that the even though in the service load condition, the pile response was still affected by cyclic effects and a larger load level would produce more significant influence. In a global point of view, the lateral displacement and maximum moment increased with loading cycles, while the secant stiffness within a cycle decreased with cycles. The cyclic effect was more significant on the lateral displacement than on the moment. In a local point of view, cyclic loading would degrade the equivalent subgrade stiffness for the soil shallower than about seven times diameter. In addition, the secant subgrade stiffness within a cycle increased with loading cycles. Some experimental relationships of lateral pile response and loading cycles were built and compared with those in the literature.     

屈曲约束支撑滞回曲线模型和刚度方程的建立

针对屈曲约束支撑,本文根据其反复荷载作用下的滞回特征,提出了一种滞回模型,并建立了屈曲约束支撑的弹塑性刚度方程。根据这种模型编制程序模拟绘制了屈曲约束支撑的滞回曲线,将模拟计算曲线与试验所得曲线进行对比,对比结果表明本文所提模型是准确、有效的。     

高层隔震建筑设计中隔震支座受拉问题分析

高层建筑由于高宽比相对较大,倾覆效应明显,当采用隔震技术时,有可能使隔震支座出现拉应力,而通常使用的叠层橡胶隔震支座抗拉能力不强。因此,隔震支座受拉问题成为隔震技术在高层建筑中推广应用的主要障碍之一。本文提出了避免隔震支座受拉的上部结构布置原则及隔震层优化设计方法,并对目前隔震支座拉应力计算方法提出了改进建议。本文的研究工作可为工程设计提供借鉴,为隔震设计相关规范的修订提供依据。     

主动变刚度-阻尼系统预测最优控制的理论与试验研究

介绍了一种具有自主知识产权的新型开关控制型半主动控制系统——主动变刚度.阻尼(AVS.D)系统的减振控制机理,建立了AVS.D结构振动控制体系的运动方程。为了合理补偿AVS.D系统实时控制过程中不可避免地存在着的控制时滞,本文提出一种预测最优控制算法,推导了其开关控制律。为了检验AVS.D系统的减震控制效果及预测最优控制算法的有效性,我们设计研制出AVS.D装置,编制了AVS.D系统预测最优控制的实时控制软件,在某单层钢框架模型上进行了AVS.D系统的模拟地震振动台试验,比较了不同控制方式时的减震效果。研究结果表明,本文所提出的预测最优控制算法是非常有效的,可推广应用于所有开关控制型半主动控制系统。AVS.D系统具有反应放大功能,经济可靠、安全有效,可望有较好的工程应用前景。     

Drained cavity expansions in soils of finite radial extent subjected to two boundary conditions

The problem of drained cavity expansion in soils of finite radial extent is investigated. Cylindrical and spherical cavities expanded from zero radius subjected to either constant stress or zero displacement at the finite boundary are considered. The generalised analytical solution procedure presented enables more advanced constitutive models to be implemented than have been possible in previous studies. Results generated for Sydney quartz sand highlight substantial differences between cavity limit pressures for the two boundary conditions and for boundaries of finite and infinite radial extent. This is of significance in accounting for boundary effects when interpreting cone penetration tests conducted in calibration chambers. Copyright © 2011 John Wiley & Sons, Ltd.     

Study of bond stress–slip relationship and radial dilation in prestressed concrete

This paper presents two test procedures for evaluating the bond stress–slip and the slip–radial dilation relationships when the prestressing force is transmitted by releasing the steel (wire or strand) in precast prestressed elements. The bond stress–slip relationship is obtained with short length specimens, to guarantee uniform bond stress, for three depths of the wire indentation (shallow, medium and deep). An analytical model for bond stress–slip relationship is proposed and compared with the experimental results. The model is also compared with the experimental results of other researchers. Since numerical models for studying bond‐splitting problems in prestressed concrete require experimental data about dilatancy angle (radial dilation), a test procedure is proposed to evaluate these parameters. The obtained values of the radial dilation are compared with the prior estimated by numerical modelling and good agreement is reached. Copyright © 2012 John Wiley & Sons, Ltd.     

An example of slip instability resulting from displacement-varying strength

A rock cylinder, containing a clay-filled sawcut making an angle of 30° to the sample axis, was deformed at constant confining and pore pressures and constant remote shortening rate. The sawcut surfaces contained a series of regularly spaced ridges and grooves oriented perpendicular to the direction of shear. The interaction of these grooved surfaces resulted in a sliding strength which varied periodically with displacement. By varying the effective machine stiffness through the use of an electronic feedback circuit, a range of stable and unstable slip behavior was achieved. In this way, we examined fault slip behavior which was dominated by displacement-dependent strength.     

用于生成DTM的改进的最小二乘匹配(LSM)算法

本文提供了一种用于生成DTM的LSM算法的数学模型。其特点是,引入了辐射线条件和共面条件的几何约束,以及辐射偏差和几何变形参数的虚拟观测方程。试验表明.改善了LSM算法的收敛性、稳定性和可靠性,因而提高了图像配准的质量。     

多卜勒雷达经向速度资料的预处理方法

利用变分法原理提出了对雷达速度资料进行预处理的一种方法，数值试验表明该法能有效地消除雷达速度资料中的小尺度运动径向速度分量及“噪声”。