Dynamic response of floating structures

The analysis techniques for offshore floating structures have, until recently, been borrowed from the study of ship motions. These structures, however, differ in many ways from surface ships and simplified procedures developed for the latter are, therefore, not applicable. In this paper these dissimilarities are discussed and an overview of the techniques suited to the analysis of these structures is presented.     

超高压变电构架钢管混凝土Y型相贯节点平面内受弯性能研究

以国内首例采用钢管混凝土的750kV超高压变电构架工程为背景,设计了3个1:2缩尺、主管灌注混凝土的Y型相贯节点试件,其中包括2个采用不同加强方式(即瓦形板、外套筒加强)和1个作为对比的无加强节点试件,并对其进行了平面内受弯性能试验。试验结果表明：相比无加强节点,采用的2种加强节点的最终破坏形态均为支管失效破坏,均符合“强柱弱梁”的设计原则;节点的转动刚度和受弯承载力均显著提高,平面内转动刚度均可达到欧洲规范规定的刚性节点要求,且平面内受弯承载力基本可以达到支管全截面塑性时的弯矩值。此外,对节点的有限元分析表明：主管轴压比、瓦形板长度和宽度对节点刚度和承载力影响较小,而瓦形板厚度对此影响较为显著。     

张拉薄膜结构动力特性研究

分析了张拉薄膜结构动力特性的基本特点,研究了膜面预应力、矢跨比、跨度、边索预应力、膜面索以及支承体系对结构动力特性的影响.结果表明,薄膜结构频率密集,连续成丛分布并且有多个频率重迭;刚性边界跨度较小的薄膜结构的频率较高;跨度较大且比较平坦的大面积薄膜曲面的频率较低,并且分布非常密集;考虑支承体系的张拉索膜结构的频率比未考虑的偏低,振型发生改变;膜面索对自振频率影响不显著,但会使结构的振型发生较大的变化.     

Risk-based decision support for seismic rehabilitation of structures

This study presents a risk-based decision support framework for seismic retrofit of building structures where the decision criterion is to minimize the sum of the cost required for the rehabilitation and the expected seismic loss over a specified time period. Probabilistic seismic hazard model (PSHM) and probabilistic seismic demand model (PSDM) are utilized for manipulation of the uncertainty propagation from the seismic hazard to the structural damage. A mathematical formula is then developed for probabilistic estimation of the seismic damage and losses over a specified time period. The analysis procedure is developed such that the effect of the different configurations of the decision inputs can be promptly observed. The proposed procedure is demonstrated by performing a decision analysis for a hypothetical RC building structure for determination of the optimal level of seismic rehabilitation using steel bracings.     

在役钢筋混凝土变电构架耐久性调查与分析

为了解在役混凝土变电构架结构耐久性问题,对1970年以来山东省和山西省共38例在役变电构架外观现状、构件节点拼接、保护层厚度、混凝土强度、钢筋锈蚀情况等进行了调查,基本得到了不同地域、不同使用年限混凝土结构耐久性问题的分布情况。结果表明:变电构架主要耐久性问题是混凝土碳化、混凝土构件裂缝、钢板圈/钢筋锈蚀等;混凝土表观强度普遍高于原有强度设计值,但构件脆性严重;混凝土保护层厚度沿构件环向分布不均匀现象明显;得到了混凝土变电构架的合理应用范围和维护加固建议。     

Dynamic control of structures subjected to constraints

This study presents a dynamic equation of constrained motion and illustrates its validity through a dynamic analysis on the structural control by a constraint. Minimizing a function of the variation in kinetic energy at constrained and unconstrained states with respect to the velocity variation, the dynamic equation is derived and it is shown that the result compares with the generalized inverse method proposed by Udwadia and Kalaba. It is investigated that the responses of a 10‐story building are controlled by a constraint due to the installation of a two‐bar structure. The structural responses are affected by various factors like the length of each bar, damping, stiffness of the bar structure, and the boundary positions between two structures. Under an assumption that the bars have the same mass density, this study determines the optimal boundary positions to minimize the total responses of the structure, and compares the responses and control forces by optimal feedback control with the results. Copyright © 2007 John Wiley & Sons, Ltd.     

大跨度结构工程高支撑木模板的应用

通过对结构工程分析,采用大跨度高支撑木模板体系进行施工,分析、计算了这一技术的可行性和可操作性并组织施工,并得到了良好的效果。     

Dynamic analysis of partially prismatic thin-walled structures

A mixed-mode method is investigated for the dynamic analysis of partially prismatic structures, such as box girders with intermediate diaphragms and supports, or with variable-depth webs. Thus the prismatic ‘main structure’ is discretised by finite strips, and the non-prismatic ‘sub-structure’ by finite elements. After dynamic reduction of the finite element degrees of freedom, advantage may be taken of the finite strip harmonic expansions in determining mode shapes. The method is tested by a variety of examples. Thus for structures with transverse substructures (e.g. diaphragms), the method is shown to be successful, being up to an order of magnitude faster than finite elements. However, for structures with longitudinal substructures (e.g. variable-depth webs) the method is shown to be unreliable. This is because for such structures, approximations in the dynamic reduction procedure are found to be significant.     

Dynamic alongwind fatigue of slender vertical structures

The wind-excited vibrations of structures induce fluctuating stresses around mean deformation states that lead to fatigue damage accumulation and can determine structural failure without exceeding design wind actions. This paper proposes a mathematical model aimed at deriving a histogram of the stress cycles, the accumulated damage and the fatigue life of slender vertical structures (e.g. towers, chimneys, poles and masts) in alongwind vibrations. The formulation, integrally in closed form, is based on a probabilistic counting cycle method inspired by narrow-band processes. An example illustrates the proposed procedure and shows, through the comparison with Monte Carlo simulations, the entity of the approximations involved by treating the response as narrow-banded instead of broad-banded.     

Dynamic analysis of reinforced concrete frame-wall structures

The nonlinear response and failure mechanism of reinforced concrete frame-wall systems is investigated through the employment of a mathematical model. The mathematical model is composed of two mechanical models: a concentrated spring model used for the flexural behaviour of beam and column type members and a multiple spring model used for the response of the wall system. Both account for inelastic behaviour of reinforced concrete.The mathematical model is applied to a ten-storey frame-wall system. The constituent members are replaced by one of the mechanical models whose stiffness characteristics reflect the inelastic properties and hysteresis tendencies of the member. The resulting equations are solved by a step by step time integration procedure. Computed results are compared with experimental results obtained from a structure tested on the Illinois earthquake simulator. The correlated results are then used to define the significant response characteristics.     

某综合楼基坑围护设计

杭州上塘镇人民政府办公综合楼位于沈半路闹市区,三面紧邻民房和变压器,周围环境复杂,对基坑开挖相当不利。根据工程的特点,综合考虑围护结构的安全、对环境的影响、施工工期、围护费用等因素,对办公综合楼基坑围护结构进行了精心设计。采用规范推荐的m法计算了围护桩内力和变形,用通用的边坡稳定分析REAME程序进行了基坑整体稳定分析。监测结果表明:所采用的基坑围护设计实现了安全、经济、便于施工的要求,且经受了冬季暴雨的考验,为同类工程提供了参考。     

基底隔震框-剪结构的动力模型

在结构连续化假定的基础上，提出了基底隔震结构的剪-弯梁隔震模型，导出了问题的控制微分方程，求出了相应矩阵形式的初参数解，给出了该模型下的频率方程及振型函数的解析表达式。     

Dynamic torsional coupling in asymmetric building structures

An approximate method is proposed for the dynamic analysis of torsionally coupled tall building structures by utilizing the properties of their uncoupled counterparts. An exact solution is first given for the particular case in which the lateral and torsional stiffness matrices are uncoupled by same transformation. The method is then applied to a wider class of structures where this condition is only approximately satisfied by reducing the dynamic coupling problem to an approximate two-degrees-of-freedom system. Simple formulae and graphical representations of dynamic magnification of static eccentricity are given. Two numerical examples illustrate the use of the proposed method, checking on its accuracy and comparing its results with seismic code provisions.     

地下结构动土压力简化计算方法研究

基于波动力学理论,考虑土–结构动力相互作用、土介质特性及地震波的传播特性,提出了地震作用下地下结构的动土压力简化抗震设计方法。首先,将土–地下结构体系简化为单自由度的质量–弹簧–阻尼体系。其次,通过建立该体系的波动方程,并进行求解,将自由场响应换算为作用在结构上一点的动土压力,并结合结构周围土体的自由场响应分布特征,可得整个结构上的动土压力分布。最后,以振动台试验结果为基础进行了简化方法的验证,得出本文提出方法能够与试验结果吻合很好。该方法具有概念明确、计算简便、计算效率和精度高等特点,能够求解各类地下结构的地震反应,为地下结构的抗震设计提供了一种简单、实用的工具。     

钢结构管架设计探讨

以某工程项目为例,针对施工场区风荷载较大且竖向荷载较小的情况,探讨了钢结构管架设计要点,并通过计算分析调整支撑体系,使其形成更为合理的结构形式,可为类似工程提供参考借鉴。     

A computer-based design support system for steel frame structures

This paper describes the development and utilization of a computer-based support system for the conceptual design of moment resisting steel frame structures. This design support system, ‘Building Engineering and Reasoning Tool’ (BERT), incorporates a behavior-based methodology for designing structural members that satisfy strength and interstory drift requirements due to gravity and lateral (earthquake) loads. Given the loading conditions and building configuration, BERT has the capability of selecting efficient member sizes through reasoning about the behavior of the structure. Different configurations can be evaluated by means of a cost estimating scheme that incorporates steel material, fabrication, and erection costs. This paper focuses on a discussion of the design methodology implemented in BERT. Illustrative examples are presented to demonstrate the range of applications of this design support system.     

玻璃建筑柔性支承体系的动力特性分析

柔性支承体系是玻璃建筑的常用支承结构形式，工程应用日益广泛．目前，国内对玻璃建筑柔性支承体系的动力性能研究尚属空白，本研究了其动力特性，分析了矢高、杆件截面、质量等不同参数对其动力特性的影响，希望能为进一步的研究提供参考。     

Metamirror channel structures: Optical properties

A new kind of metamaterial based on hierarchically organized mirror channels with partially reflecting walls, metamirror structures (MMS), is proposed. Properties of MMS are close to those exhibited by left-handed materials, despite the difference in underlying physical mechanisms. Transmission and reflection of rays are considered for different MMS geometries and types. It is shown that a one-step reflective 2D MMS based on rectangular elementary unit cells, being properly curved, possess the properties of a lens, and a generalized law describing MMS-based lenses is presented. If the MMS have relatively small sizes of unit cells (from one to tens of micrometers), then they may be treated as solid materials with anomalous optical properties in a wide range from visible and near-infrared up to UV wavelengths. It is concluded that MMS features may be observed in metamaterials of other kinds.     

半刚性连接球面网壳结构的动力分析

通过半刚性节点模型,利用有限元方法对球面网壳结构进行动力分析.建立了半刚性情形下单元刚度矩阵.通过求解特征值问题,得到半刚性球面网壳结构自振特性规律,并与理想刚接及理想铰接情形进行了对比.采用时程分析法对球面网壳进行了水平地震作用下的分析计算,比较了半刚性节点模型所得结果与理想刚接及理想铰情形的异同,说明使用半刚性模型进行结构计算分析的合理性.论文结论对网壳结构的工程设计及施工有一定的参考价值.     

冲击地压巷道围岩支护作用动力学分析

建立了冲击地压巷道围岩支护作用动力学模型,模型将上覆岩层简化为由多个质量块组成的块系,岩块简化为刚体,岩块间的连接简化为Kelvin-Voigt模型,把支护系统简化为弹簧和耗能阻尼器,初始岩块受冲击载荷作用。支护系统中阻尼为零时,为常规支护系统;支护系统中阻尼大于零时,为吸能防冲支护系统。分析得出:加强支护,提高支护强度,可以大幅度减少巷道冲击载荷作用下围岩加速度和位移幅值;支护系统中加入阻尼构件有利于快速平息围岩震动,增强支护抗冲击载荷能力,提高巷道围岩稳定性。提出了高强度吸能支护防治巷道冲击地压,为冲击地压巷道安全防冲支护设计提供理论依据。