利用Himawari-8高频次监测太湖蓝藻水华动态

新一代静止气象卫星Himawari-8以其10 min/次的高观测频次,为连续动态监测蓝藻水华提供了有力的数据支持.基于太湖实地光谱测量资料,提出Himawari-8卫星资料太湖蓝藻水华动态监测方法.以2015年10月2日蓝藻水华发生过程为例,利用连续、多时次Himawari-8资料,动态监测了太湖蓝藻水华的发展变化,分析蓝藻水华的出现、发展和消失,计算蓝藻水华强度的动态变化,认识蓝藻水华程度及变化特征,估算蓝藻水华的动态变化速度.上述分析为研究蓝藻水华的生长消亡过程提供了支持.进一步探讨蓝藻水华动态变化与气象要素的关系,发现在相同的温湿条件下,风场对蓝藻水华的形成、运动和消失有直接的驱动作用.     

Liquefaction mitigation in silty soils using composite stone columns and dynamic compaction

The objective of this study is to develop an analytical methodology to evaluate the effectiveness ofvibro stone column (S. C.) and dynamic compaction (D.C.) techniques supplemented with wick drains to densify and mitigate liquethctionin saturated sands and non-plastic silty soils. It includes the following: (i) develop numerical models to simulate and analyze soil densification during S.C. installation and D.C. process, and (ii) identify parameters controlling post-improvement soil density in both cases, and (iii) develop design guidelines for densification of silty soils using the above techniques. An analytical procedure was developed and used to simulate soil response during S.C. and D.C. installations, and the results were compared with available case history data. Important construction design parameters and soil properties that affect the effectiveness of these techniques, and construction design choices suitable for sands and non-plastic silty soils were identified. The methodology is expected to advance the use of S.C. and DC. in silty soils reducing the reliance on expensive field trials as a design tool. The ultimate outcome of this research will be design charts and design guidelines for using composite stone columns and composite dynamic compaction techniques in liquefaction mitigation of saturated silty soils.     

柔性承台板与群桩的竖向动力作用

采用动力文克尔地基模型模拟均质粘弹性土层,推导出了均质土中单桩动阻抗;引用桩-桩动力相互作用因子,得到了刚性承台下群桩的动阻抗;而且建立了柔性承台与桩基础的竖向振动模型,该模型考虑了筏板自身的变形,并导出了其共同作用的运动方程。最后对柔性承台与刚性承台的计算结果作了对比分析。     

Testing a proposed new chronology for the Jasmund Glacitectonic Complex (SW Baltic Sea): No indication of incipient deformation during MIS 3

Weichselian advances of the Scandinavian Ice Sheet have generated several glacitectonically deformed structures in the southwestern Baltic Sea area. One example is the 100 km² large Jasmund Glacitectonic Complex (JGC), which was formed proglacially and consists of two subparallel-orientated sets of composite ridges that represent a northern and southern structural complex. The two-part morphological structure of the JGC suggests a formation by two ice advances, one approaching from NE and one from SE direction. So far, this divided structure has been assumed to have been formed by short-time ice-front oscillations during an MIS 2 ice advance. However, based on their recently published ice dynamic model for MIS 3 and the available age data from Jasmund, lüthgens et al. (2020) propose a chronological reinterpretation of the JGC development, according to which two distinct ice advances during early and late MIS 3 formed the JGC. In order to test this novel stratigraphical model for the JGC formation, five OSL samples were taken from fluvial and lacustrine deposits at a key section near Glowe (NW Jasmund). The investigated succession is divided into pre-kinematic sediments, deposited before the glacitectonic deformation, and post-kinematic sediments, deposited after the deformation. Our results show that the youngest dated pre-tectonic sediment has a burial age between ∼40 and 34 ka, which rules out a glacitectonic deformation during an early MIS 3 ice advance (∼60–50 ka). In addition, by reviewing the existing age data set, a development of the JGC during an early and late MIS 3 advance of the SIS must be rejected. Instead, our data confirm the genesis of the JGC during MIS 2.     

钢管混凝土框架-混凝土核心筒减震结构振动台试验研究

某超高层钢管混凝土框架-混凝土核心筒结构因指标超限在设计中采用了耗能减震技术,为了检验该减震结构的抗震性能,制作了1/35的缩尺模型,通过在钢管混凝土框架设置阻尼器或不设置阻尼器,进行模拟地震振动台对比试验,研究了模型结构的动力特性和不同烈度地震作用下的加速度、位移和应变响应。研究结果表明:地震作用下,该钢管混凝土框架-混凝土核心筒减震结构与钢管混凝土框架-混凝土核心筒结构相比,位移、加速度和应变响应均有一定程度的降低;罕遇地震作用下,通过设置耗能减震构件,层间位移角最大值从超过规范要求的1/84减低至满足规范要求的1/130,表明该减震结构具有更优良的抗震性能。     

大型岩体洞室采用柔性垫层减震的可行性研究

采用无限元作为岩体地下洞室静动力分析的边界条件,建立了岩体地下洞室的静动力有限元一无限元(FE-IE)计算模型,分析了柔性垫层对水电站厂房这类大型岩体洞室结构的减震效果.研究结果表明:柔性垫层虽未能从根本上改变岩体洞室结构的地震响应,但是设置一定厚度的柔性垫层后不仅能充分发挥岩体洞室围岩的自承能力,而且还能明显地减小混...     

竖向质量分布对框架结构动力特性影响的研究

在框架结构动力分析中,往往是把填充墙质量集中在楼层处进行求解.文中考虑填充墙实际分布对结构自振特性的影响,通过传递矩阵法求解结构自振频率和振型,并进一步分析了高阶频率的分布规律.结果表明,与采用集中质量模型的振型叠加法相比,填充墙的竖向质量分布会对框架结构高阶频率产生很大影响;框架结构的高阶模态具有局部性和密集分组的特...     

Dynamic performance analysis of a seismically isolated bridge under braking force

In order to study the dynamic performance of seismically isolated bridges under the most unfavorable loads in the longitudinal direction,a dynamic equation for vehicle braking in the longitudinal direction is established.A four or fiveorder Runge-Kutta method is adopted to obtain the time-history response of a wheel set under braking force.The quadratic discretization method is then used to transform this time-history into a braking and bending force time-history of a structural fixed node,and a dynamic response analysis of the seismically isolated bridge under the vehicle’s braking force is carried out using ANSYS,a universal finite element analysis software.According to the results,seismic isolation design results in a more rational distribution of braking force among piers;the influence of the initial braking velocity on the vehicle braking force is negligible;the location where the first wheel set leaves the bridge is the most unfavorable parking location;a seismic isolation bridge bearing constructed according to typical design methods enters into a yield stage under the braking force, while the shearing force at the bottom of the pier declines as the isolation period is extended;the design requirements can be met when the yield displacement of the seismic isolation bearing is less than 5 mm and the yield strength is greater than the braking force.     

Evaluation of force-based and displacement-based out-of-plane seismic assessment methods for unreinforced masonry walls through refined model simulations

The performance of force-based and displacement-based seismic assessment methods for the life-safety limit state check of out-of-plane loaded unreinforced masonry walls is evaluated on the basis of refined numerical simulations. For this purpose, a discrete element model of a vertically spanning wall is built and validated against experimental results from static and dynamic test conditions. The model is then analysed for a large range of wall configurations. For each configuration, a static pushover analysis and a series of incremental dynamic analyses are run, the latter permitting to determine the capacity of the wall under dynamic loading. The accuracy of the assessment methods in predicting the acceleration at which the walls collapse is evaluated. It is found that the displacement-based method is more accurate, robust, and safe than the force-based method. The comparison also shows that for walls characterised by a relatively high ratio of axial load to Euler's critical load, both assessment methods lead to an overestimation of the wall capacity. As a remedy, a modification to the methods based on a recently developed mechanical model is put forward and tested. For the force-based method, it is additionally suggested to set for walls with relatively high overburden ratios the behaviour factor equal to 1. To ensure reproducibility of this study, all input and output files of the numerical simulations are made publicly available.     

Seismic performance of buildings retrofitted with nonlinear viscous dampers and adjacent reaction towers

An effective strategy of seismic retrofitting consists of installing nonlinear viscous dampers between the existing building, with insufficient lateral resistance, and some auxiliary towers, specially designed and erected as reaction structures. This allows improving the seismic performance of the existing building without any major alteration to its structural and nonstructural elements, which makes this approach particularly appealing for buildings with heritage value. In this paper, the nonlinear governing equations of the coupled lateral‐torsional seismic motion are derived from first principles for the general case of a multistory building connected at various locations in plan and in elevation to an arbitrary number of multistory towers. This formulation is then used to assess the performance of the proposed retrofitting strategy for a real case study, namely, a 5‐story student hall of residence in the city of Messina, Italy. The results of extensive time‐history analyses highlight the key design considerations associated with the stiffness of the reaction towers and the mechanical parameters of the nonlinear viscous dampers, confirming the validity of this approach.