Performance of reinforced,DMM column-supported embankment considering reinforcement viscosity and subsoil’s decreasing hydraulic conductivity

It has been widely accepted that reinforcement made of polyethylene and polypropylene is susceptible to creep and soil’s hydraulic conductivity varies with its void ratio. However, unfortunately there is no available sensitivity analysis on time-dependent embankment behaviour taking either reinforcement viscosity or time varying hydraulic conductivity of subsoil into consideration. The influence of geosynthetic reinforcement viscosity and decreasing hydraulic conductivity with consolidation on the time-dependent performance of embankments with floating columns is investigated using a fully 3D coupled model. For an embankment at the working height corresponding to a post-consolidation polypropylene geotextile strain of about 5%, it is shown that the assumption of constant hydraulic conductivity and the failure to consider the viscous behaviour of geosynthetic reinforcement can underestimate time-dependent embankment deformations (including differential crest settlement and horizontal toe movement). The effects of factors including the foundation soil, reinforcement stiffness, column stiffness, column spacing, column type (floating and fully penetrating), and construction rate, on the time-dependent behaviour of column supported embankments are explored.     

单层柱面网壳的粘滞阻尼器减振分析

采用粘滞阻尼器减振系统对单层柱面网壳的减振效果进行了较为系统的分析，分别考虑了阻尼系数C0、结构自身阻尼比ζ、屋面质量和结构自身刚度对结构减振系数δ的影响，同时考察了设置阻尼器的数目以及阻尼器的位置的影响。通过较大规模参数化分析，基本了解了粘滞阻尼器减振系统在单层柱面网壳中的减振规律。     

新型形状记忆合金阻尼器的试验研究

本文在对形状记忆合金(SMA)的力学性能研究的基础上，设计和制造出一种性能良好的SMA阻尼器，介绍了其工作原理及有关试验结果，将该阻尼器安装在斜拉桥模型上，进行了斜拉桥模型振动试验。试验结果表明该阻尼器的耗能效果明显，在工程结构振动控制方面具有比较好的应用前景。     

Dynamic response characterization and simplified analysis methods for viscoelastic dampers considering heat transfer

Viscoelastic (VE) dampers are sensitive to temperature, excitation frequency, and strain level. As they dissipate the kinetic energy from earthquake or wind-induced structural vibrations, their temperature increases from the heat generated, consequently softening their VE materials and lowering their dynamic mechanical properties. Temperature increase can be significant for long-duration loading, but can be limited by heat conduction and convection which depend on damper configuration. The writers analytically explored such effect on the six different dampers by using their previously proposed three-dimensional finite-element analysis method. Results provided better understanding of how heat is generated within the VE material, conducted and stored in different damper parts, and dispersed to the surrounding air. These results also led to characterization of both local (e.g., temperatures, properties, and strain energy density) and global (e.g., hysteresis loops, and stiffness) behavior of VE dampers, and provided a framework for a new simplified one-dimensional (1D) modeling approach for time-history analysis. This new proposed 1D method greatly improves the computation time of the previously proposed long-duration method coupling fractional time-derivatives VE constitutive rule with 1D heat transfer analysis. Unlike the previous method, it idealizes uniform shear strain and VE material property distributions for computational efficiency, but still simulating non-uniform temperature distribution along the thickness direction of the VE material. Despite the approximations, it accurately predicts VE damper global responses.     

Experimental verification of seismic vibration control using a semi‐active friction tuned mass damper

A tuned mass damper (TMD) system consists of an added mass with properly functioning spring and damping elements for providing frequency‐dependent damping in a primary structure. The advantage of a friction‐type TMD, that is, a nonlinear TMD, is its energy dissipation via a friction mechanism. In contrast, the disadvantages of a passive friction TMD (PF‐TMD) are its fixed and predetermined slip load and loss of tuning and energy dissipation capabilities when it is in a stick state. A semi‐active friction TMD (SAF‐TMD) is used to overcome these disadvantages. The SAF‐TMD can adjust its slip force in response to structure motion. To verify its feasibility, a prototype SAF‐TMD was fabricated and tested dynamically using a shaking table test. A nonsticking friction control law was used to keep the SAF‐TMD activated and in a slip state in earthquakes at varying intensities. The shaking table test results demonstrated that: (i) the experimental results are consistent with the theoretical results; (ii) the SAF‐TMD is more effective than the PF‐TMD given a similar peak TMD stroke; and (iii) the SAF‐TMD can also prevent a residual TMD stroke in a PF‐TMD system. Copyright © 2011 John Wiley & Sons, Ltd.     

摆,油阻尼器减振的试验研究

高柔结构在地震或风荷载作用下会产生很大的振动，本文提出一种控制高柔结构振动的新方法－－摆、油阻尼器体系，并在振动台进行了模拟试验，结果表明：该方法可使结构振动位移幅值减小５０％，在试验中变换了体系的各有关参数，研究了摆长，质量比，碰击间隙对减振效果的影响，文中详细研究了油阻尼器的工作过程及减振机理，从理论上初步分析了摆，油阻尼器体系减振原因，提出了可供实际设计参考的方法和原则。     

Semigeostrophic Frontal Boundary Layer

The viscous semigeostrophic solutions obtained for the baroclinic Eady wave fronts are analyzed for the generation of the cross-frontal temperature gradient in the boundary layer. In the case of free-slip boundaries, the cross-frontal gradient is maximally generated at the surface by meridional temperature advection. In the case of no-slip boundaries, surface friction reduces the meridional temperature advection in the boundary layer: The maximum generation occurs above the surface layer and the temperature gradient at the surface is maintained by vertical diffusion. The no-slip solution is compared with the Ekman-layer model solution. Errors are quantified for the use of the Ekman-layer model in the mature state of frontogenesis.The surface frontogenesis is found to be affected by diffusivity both directly and indirectly. The direct effect of diffusivity is represented explicitly by the diffusion term in the potential temperature equation. The indirect effect of diffusivity is related implicitly to the temperature advection caused by the viscous part of the ageostrophic motion whose horizontal velocity component is defined by the frictional wind deflection (away from the geostrophy). The direct effect of diffusivity is frontolytical, whilst theindirect effect of diffusivity is frontogenetic in the mesoscale vicinity of the front. The indirect effect of diffusivity contributes dominantly to the mesoscale surface frontogenesis for the free-slip case, but it is offset by the divergence of the dynamic part of the ageostrophic motion at the surface level for the non-slip case.     

新型自复位连梁阻尼器设计及其力学性能数值模拟研究

为改善高层建筑联肢剪力墙抗震性能,消除传统连梁阻尼器残余位移较大或等效阻尼比较小等问题,设计了一种兼具耗能和自复位功能的形状记忆合金粘弹性连梁阻尼器（Shape Memory Alloy Viscoelastic Coupling Beam Damper,SVCBD）,给出了新型连梁阻尼器的构造形式和工作原理。利用拉普拉斯变换得到的粘弹性材料粘性系数以及超弹性形状记忆合金（Shape Memory Alloy,SMA）本构模型,基于ABAQUS仿真平台建立了SVCBD精细有限元模型;对SVCBD滞回特性进行了模拟分析,并与普通粘弹性阻尼器进行了对比。考虑了SMA丝束初始预应力度、横截面总面积和粘弹性材料层剪切面积等参数对SVCBD滞回特性的影响。分析结果表明:与普通粘弹性连梁阻尼器（Viscoelastic Coupling Beam Damper,VCBD）相比,SVCBD滞回曲线更加饱满,耗能能力更强,残余位移减小,初始刚度也大大提高,具有很好的耗能和复位效果;SMA丝束初始预应力大小、横截面面积（即配置数量）和粘弹性材料层剪切面积均对SVCBD的耗能和复位能力具有明显的影响。     

磁流变阻尼器的两种力学模型和试验验证

本文根据我们设计制作出的磁流变阻尼器的阻尼特性试验结果，提出了描述阻尼器动态特性的两种新的力学模型。一种称之为修正的Bingham模型，它由Bingham单元（库仑摩擦单元与粘滞单元并联）与弹簧单元串联组成。该弹簧单元与磁流变液屈服前区的初始剪切模量和蓄能器的刚度等有关。另一种称为修正的Dahl模型，它采用Dahl模型来模拟库仑摩擦力，克服了常用的Bouc-Wen模型需要确定的参数过多的缺点。为了使模型在阻尼器的电流强度（磁场强度）改变的情况下仍然有效，引入一个内变量描述模型参数与电流强度（磁场强度）的关系。最后，通过理论分析与试验结果的比较，证明本文提出的两种力学模型能够较为精确地描述大多数的磁流变阻尼器在改变电流强度（磁场强度）情况下的动态特性。     

Studies on structural vibration control with MR dampers using μGA

A new approach to reducing the seismic response of spatial structures with magneto-theological （MR） dampers is presented in this paper. The Genetic Algorithm with small populations （μGA） is used to optimize the control for the MR dampers to reduce structural vibration, which is difficult to achieve using classical optimal control. The advantages of μGA are the use of global properties and that fewer conditions are required to obtain the optimal function. Numerical results demonstrate the effectiveness of the proposed method in reducing the seismic response of structures.