Optimal experimental design in stochastic structural dynamics

This paper provides a methodology for optimal prediction of the response of randomly vibrating structures using information from a limited number of measurements. The objective is to optimize the locations of sensors for the purpose of making the most accurate predictions of the response at unmeasured locations in structural systems. The kriging method is used to find the response predictions and the corresponding mean-square errors at unmeasured locations. The mean-square errors in the predictions depend on the locations of sensors and the correlation characteristics of the response evaluated from the model of dynamics and the characteristics of the excitation. The response predictions depend also on the information contained in measurements. The optimal sensor locations are selected to minimize the total mean-square error of the response predictions at unmeasured points. This leads to a complicated non-convex optimization problem in which multiple local and global optima may exist. A hybrid optimization method based on evolution strategies is used to determine a global minimum. The optimal experimental design method presented in the paper is illustrated by designing the optimal sensor locations for an elastic beam and a plate subjected to a class of random stationary loads.     

软土地基深基坑工程不同围护结构的实测变形研究

由于城市建设用地稀缺,为了建设地铁、地下车库、地下商场等,经常在人口稠密、建筑林立、道路纵横交叉的城市中心区开挖深大基坑。基坑施工过程中,为了减小对周边环境的不利影响,必须控制基坑围护结构的侧向变形。总结了软土地基深基坑常用的围护型式和变形监测项目,结合实测数据分析了不同围护型式的变形规律,指出了不同围护型式的适用范围,对基坑设计及施工单位具有一定的借鉴意义。     

Diagrid structures for tall buildings: case studies and design considerations

The originality of form is one of the new trends that can be identified in the current design of tall buildings. In this design trend, the so‐called diagrid structures, which represent the latest mutation of tubular structures, play a major role due to their inherent esthetic quality, structural efficiency and geometrical versatility. In this paper, an overview on application of such typology to high‐rise buildings is carried out; in particular, in the first part of the paper, the peculiarities of diagrid systems are described: starting from the analysis of the internal forces arising in the single diagrid module due to vertical and horizontal loads, the resisting mechanism of diagrid buildings under gravity and wind loads is described, and recent researches and studies dealing with the effect of geometry on the structural behavior are discussed. In the second part of the paper, a comparative analysis of the structural performance of some recent diagrid tall buildings, characterized by different number of stories and different geometries, namely the Swiss Re building in London, the Hearst Headquarters in New York and the West Tower in Guangzhou, is carried out, and some general design remarks are derived. Copyright © 2012 John Wiley & Sons, Ltd.     

Smart Power Line and photonic de-icer concepts for transmission-line capacity and reliability improvement

This paper introduces the Smart Power Line (SPL) concept. This novel approach can be implemented on existing transmission lines comprising of single- or multiple-conductor bundles. It can also be applied to new, advanced line schemes. The SPL addresses three important needs: line de-icing, line impedance modulation and line monitoring.Line de-icing (LDI) can be activated prior to or during any severe climatic event, for concentrating the total power line current into one subconductor at a time and therefore de-icing by the Joule effect. Line impedance modulation (LIM) is another feature of the SPL by which line power flow and stability are also controlled by individually switching in and out subconductors of bundled-conductor lines, thereby modifying the net line impedance directly and dynamically. Line monitoring (LMO) provides real-time data related to electrical, mechanical or climatic events needed for line de-icing, power flow or stability control. By combining these three functions together, the SPL concept is expected to improve transmission-line reliability and transmission-line capacity. The power line reliability and life expectancy are increased by avoiding line and tower collapse due to ice deposits, hard rime or wet snow, reducing metal fatigue and avoiding failure due to galloping. The SPL concept can be applied to bundled-conductor transmission lines at any voltage level (HV and UHV).In addition to the SPL concept, new de-icing equipment, the so-called photonic de-icer, is also introduced in this paper. In order to ensure the mechanical robustness of the transmission line in the event of severe ice storms, past experience has shown that the switchgear must be maintained operational at all times. The photonic de-icer is operated at ground level and at ground potential to melt ice on substation apparatus or to keep the latter warm during icing events.     

长江航道模型120m跨试验大厅结构设计

该工程为120m跨的单层建筑,采用张弦桁架结构.针对常规张弦桁架室内观感效果较差的缺点,提出了一种上部为变截面桁架的张弦桁架结构形式.该文详细介绍了屋盖结构选型、张拉力选择、稳定分析和节点设计等,对同类工程有重要的参考价值.     

Performance of composite girders strengthened using carbon fibre reinforced polymer laminates

This paper highlights the structural performance of steel–concrete composite girders strengthened using advanced composite laminates. Nonlinear 3-D finite element models have been developed to investigate the flexural behaviour and load carrying capacity of the girders. The composite laminates comprised carbon fibre reinforced polymer (CFRP) plates and sheets as well as steel reinforced polymer (SRP) sheets. The elastic modulus and ultimate tensile strength of the laminates varied from low to high 60–300 GPa and 700–3100 MPa, respectively. The nonlinear material properties of the strengthened composite girder components comprising concrete, structural steel beam, reinforcement bars, adhesive and composite laminates were incorporated in the finite element model. The interfaces between the composite girder components were also considered allowing the contact and bond behaviour to be modelled and the different components to retain its profile during the deformation of the strengthened composite girder. Furthermore, the load-slip characteristic of headed stud shear connectors was incorporated in the finite element models based on previous experimental and numerical investigations conducted by the author. The finite element models have been validated against published tests on composite girders strengthened using different advanced composite laminates and having different cross-section geometries, lengths, layers of laminates with different elastic moduli and ultimate tensile strengths, concrete strengths and structural steel strengths. The load carrying capacity of strengthened composite girders, load–vertical displacement behaviour and failure modes were predicted from the finite element analyses and compared against test results. Parametric studies were conducted to study the effects on the load carrying capacity and structural behaviour of strengthened composite girders owing to the change in the composite laminate elastic modulus, number of laminate layers, concrete strengths and structural steel strengths. The study has shown that the increase in the load carrying capacity and ductility of strengthened composite girders due to the increase in steel beam strength is significant with high strength concrete slab. Also, it has been shown that the increase in concrete strength offers a considerable increase in the initial stiffness of strengthened composite girders, while the increase in structural steel strength offers a considerable increase in the stiffness of strengthened composite girder in the post-yielding stage.     

LNG储罐有限元静动力分析方法的探讨

目前,国内自主设计和建造LNG全容罐还存在很大的困难,有限元软件的发展给储罐的研究提供了有效的途径,但是,大型LNG储罐的有限元静动力分析在国内还相对较少,如何建立与实际工程相一致的有限元模型是一个关键问题.本文总结了部分前人对储罐构筑物结构的有限元静动力分析方法,并针对大型LNG全容罐自身的特点,对其有限元静动力分析方法做了探讨,最后提出了在模型建立中需要深入考虑的几个问题,给相关工程设计研究人员提供参考.     

Zwitterionic ammonium and neutral amino molecules as cathode interlayer for inverted polymer solar cells

Cathode interlayer is essential to inverted bulk heterojunction polymer solar cells (PSCs). A series of zwitterionic ammonium and neutral amino organic molecules are introduced into inverted PSCs as cathode interlayer and power conversion efficiency (PCE) as high as 8.07% is demonstrated. Compared to the devices without interlayer, all the devices exhibit significant improvements of the device parameters by reducing the work function of indium tin oxide (ITO) cathode. It is striking that the devices with neutral amino molecules as interlayer exhibit remarkably higher PCEs than the devices with zwitterionic ammonium molecules as interlayer. We attribute the improved performance to the better photoactive morphology induced by the hydrophobic properties of the neutral amino derivatives through research of ultraviolet photoelectron spectroscopy, atomic force microscopy, and contact angle measurements. Interestingly, the PCEs of the inverted PSCs with cathode interlayer are positively correlated with the hydrophobic properties of the interlayer materials, since devices with neutral amino molecules or molecules with a more hydrophobic alkyl pendant (piperidine) as interlayer exhibit higher PCEs. These results pave the way to the design of effective cathode interlayer materials.