The influence of the design methodology in the response of transmission towers to wind loading

From a theoretical approach, the design procedure for the establishment of wind loading on transmission towers was reviewed and current procedures, such as Davenport's gust response factor (GRF), were compared with the statistical method using influence lines (SIL), which is considered more realistic. This latter approach can account for unbalanced loading effects, shear and axial loads and the effects of higher modes of vibration in the calculation of the response factors. Several responses due to certain assumed transverse wind characteristics were calculated for some typical transmission towers. The main findings were: (a) Peak loads calculated using SIL were larger than peak loads given by the GRF. (b) The dynamic response of transmission structures is strongly dependent on the turbulence intensity level and its spectrum. (c) For members in which there is reversal in the forces on the load position, the resonant response in the second mode of vibration was bigger, even by four to five times, than the corresponding one in the first mode. Although this effect is not as severe in terms of resulting stresses when all the components are computed in the peak responses, it can lead to fatigue problems. From the current results it can be concluded that the incorporation of the dynamic properties of transmission structures in the design methodologies is needed and that the statistical method using influence lines is a more correct approach since it allows for the inclusion of a larger number of factors in the design methodology.     

Simulation of simply cross correlated random fields by series expansion methods

A practical framework for generating cross correlated random fields with a specified marginal distribution function, an autocorrelation function and cross correlation coefficients is presented in the paper. The approach relies on well-known series expansion methods for simulation of a Gaussian random field. The proposed method requires all cross correlated fields over the domain to share an identical autocorrelation function and the cross correlation structure between each pair of simulated fields to be simply defined by a cross correlation coefficient. Such relations result in specific properties of eigenvectors of covariance matrices of discretized field over the domain. These properties are used to decompose the eigenproblem, which must normally be solved in computing the series expansion, into two smaller eigenproblems. Such a decomposition represents a significant reduction of computational effort.

Non-Gaussian components of a multivariate random field are proposed to be simulated via memoryless transformation of underlying Gaussian random fields for which the Nataf model is employed to modify the correlation structure. In this method, the autocorrelation structure of each field is fulfilled exactly while the cross correlation is only approximated. The associated errors can be computed before performing simulations and it is shown that the errors happen only in the cross correlation between distant points and that they are negligibly small in practical situations.

Some comments on available techniques for simulation of underlying random variables in connection with the accuracy of basic fields’ statistics at a given sample size are made. For this purpose a simple error assessment procedure is presented.

Simulated random fields can be used both for representation of spatially correlated properties of structure or random load in the stochastic finite element method (SFEM). An example of this application is related to size effect studies in the nonlinear fracture mechanics of concrete, and is used to illustrate the method.     

高层建筑不规则结构多维地震效应组合研究

首先建立了不规则偏心结构在三维平动地震动作用下的振型分解方法，探讨了振型的组合方法，并建议了各分量的地震效应组合的SRSS方法。通过多维地震作用下的时程分析与单维地震作用下的时程分析，得出了多维地震的结构内力效应相对于单维地震结构内力效应的增值情况。统计了双向水平地震动同时作用下地震效应值与两正交水平地震动分别单独作用按SRSS方法的组合值之间的比值，根据统计结果对SRSS方法进行系数修正，从而可以用反应谱方法进行双向地震动作用下的抗震分析。     

带有双塔楼高层建筑结构动力特性分析

本文通过对带有双塔楼的高层建筑结构动力特性的分析研究，证明在地震作用下这类结构存在五种基本的振动形式，当按现行建筑抗震设计规范理论计算地震作用时，其中有三类振型对结构的内力与位移没有贡献，因而在实际工程中此类结构可以用简单的力学模型进行计算分析。本文算例给出的结果与理论推导完全一致。     

大跨度屋盖结构等效静风荷载研究

有关等效静风荷载理论的研究，以往多针对高层、高耸结构展开。大跨度屋盖结构与高层、高耸结构形式相比，最大的不同在于要考虑多阶振型的影响。由此带来的问题有：对于结构的不同构件和不同响应类型，其等效原则不是惟一的；结构振动模式与荷载分布形态密切相关；如何考虑多阶振动模态的组合。针对以上3个问题，分别探讨了相应的解决思路，并初步给出了关于结构等效背景分量和等效共振分量的确定方法。研究表明：该方法在保证控制点等效的同时，还能使结构其他部位的等效响应更接近于实际可能出现的最不利响应，因而能够更加准确地反映出大跨度屋盖结构风振响应的本质特征。     

单层折面空间网格结构风荷载特性及等效静风荷载研究

对单层折面空间网格结构的表面风压分布和风振响应特性进行研究,采用荷载 响应相关法(LRC)与惯性力法计算结构的等效静风荷载,并分析了其计算精度,结果表明：在迎风面的体育场屋盖部分,气流在经过迎风面屋盖檐口后发生明显分离,形成漩涡,此处的平均负风压和脉动风压最大;整个屋面的绝大部分表面风压都表现为负压。增加肩谷环后,结构横向刚度提高较大,结构的1阶和2阶振型由原来的结构整体水平振动变为罩棚前端内环端部的局部竖向振动;在单层折面空间网格结构的风振响应中,参与结构振动振型较多,需要考虑多阶振型影响,且参与结构振动的主要为低阶振型;在脉动风荷载作用下各振型耦合作用较小;用LRC与惯性力法得到的单层折面空间网格结构等效静风荷载,计算精度可满足工程要求。     

Hierarchical modeling method and dynamic characteristics of cutter head driving system in tunneling boring machine

Traditional modeling method is difficult to establish the fully coupled model of the cutter head driving system in tunneling boring machine (TBM) owing to the structural complexity. In this paper, a generalized hierarchical modeling method is proposed to establish the entirely dynamic model of the TBM cutter head driving system. The components are equivalent to beam element with the same mass and stiffness characteristics, and the nonlinear coupling factors such as time-varying mesh stiffness, transmission error and gear backlash of both the multiple pinions driving and planetary gearbox are considered. The overall dynamic equation is formed by assembling the unit matrixes of basic finite elements according to the coupling relationships. Based on the proposed model, the vibration modes of driving system are classified into axial modes, rotational modes and lateral modes with distinct characteristics. The effects of coupling parameters on the natural frequency of driving system are investigated as well. The dynamic model is also simulated to analyze the dynamic response of driving system under two load conditions, cyclic external loads and simulated external loads. The main response frequency components and the effect of damping coefficients on vibration amplitudes are investigated. The proposed modeling method can be generalized to other complex driving system, and the obtained results provide data support for the dynamic design of driving system in TBM.     

大跨空间网格结构风振响应主要贡献模态的识别及选取

首先简单介绍静荷载参与比例的概念和基于虚拟激励法的风振响应分析原理。考虑脉动风荷载的空间相关性,推导出脉动风作用下系统背景响应总应变能的计算公式,以及模态对背景响应总应变能的贡献,从而定义了各阶模态的模态贡献系数及模态组合的累积模态贡献系数计算公式,其中模态贡献系数可以准确地识别出所有能被脉动风激振的模态,而累积模态贡献系数可以作为模态组合合理性判别的量化标准。然后介绍了一种简单的补偿模态构造方法,并提出了模态组合的选取方法和步骤。算例分析验证了模态贡献系数和累积模态贡献系数的有效性,以及低阶主要贡献模态和高阶主要贡献模态的重要性,进而指出目前通过比较前若干阶模态的相对误差或仅考虑补偿模态的模态组合选取方法并不合理。合理的模态组合应包含绝大部分主要贡献模态,以满足累积模态贡献系数大于0.9的要求。     

Inverse analysis of deformation moduli for high arch dams using the displacement reconstruction technique and multi-objective optimization

The inverse analysis of the deformation moduli of high arch dams based on displacement monitoring data is essential for structural safety assessment. In traditional inverse analysis methods, the deformation moduli are identified based on the single-objective optimization and the hydrostatic component derived from the statistical model. This type of method has two main shortcomings: First, it treats the essential multi-objective optimization problem as a single-objective problem; second, the extracted hydrostatic component may be biased due to the multicollinearity of variables in the statistical model. This paper presents a methodology for the inverse analysis of the deformation moduli of high arch dams under a multi-objective optimization strategy. The methodology employs empirical mode decomposition to extract the aging component from displacement monitoring data. Then, thermomechanical analysis is used to reconstruct the remaining hydrostatic and temperature components, thereby avoiding the biases encountered in solving the statistical model. The adaptive polynomial chaos expansion method is embedded in the NSGA-III algorithm to establish and solve multi-objective functions in the inverse analysis. Additionally, a composite decision index considering errors and test information is proposed to determine acceptable deformation moduli from the Pareto solution set. A high arch dam is selected to illustrate this methodology with static and dynamic monitoring data. The results show that the identified deformation moduli have errors of 3.8% and 7.2% in displacement and acceleration, respectively. The proposed methodology can yield deformation modulus values that are more consistent with the physical implications than those of the single-objective optimization method.     

浅埋地下结构底板在竖向地震作用下动力响应

本文研究了地下结构底板在地震竖向分量作用下的动力响应。利用结构动力学和弹性力学的理论,得到底板的运动微分方程,根据边界条件确定底板在的特征频率和振型。针对输入的地震竖向分量的形式,采用分离变量法求解了强迫振动方程.计算时取前三阶振型,采用振型叠加法得到底板的相对位移和绝对位移,并进而求得底板的弯矩,利用求得的弯矩,可以求解底板的受力情况。通过底板的受力情况,可以直观地对地下结构底板进行评价分析,并且推进了地下结构底板抗震理论的研究和发展。     

Estimation models for heating energy and electricity costs

Heating energy and electricity represent a significant proportion of the overall financial expenditures over the life cycle of buildings and play a decisive role in the assessment of ecological quality. To ensure ecological and economical sustainability, the planning and construction of energy efficient buildings have become increasingly important. The present study introduces statistical models for the estimation of energy costs during the planning process as well as for the purpose of monitoring and controlling costs during operation including a wide range of facility types. Based on a data sample of 206 occupied facilities located in Germany, regression models are presented in detail including significant predictor variables. The provision of correctly specified models as well as a consistent and unbiased estimation beyond the employed data is verified by validation tests. The practical significance of the determined variables is presented by the calculation of various scenarios. The best estimation accuracy is indicated for regression models with transformed response and predictor variables achieving mean absolute percentage errors of 20.5% (heating energy) and 20.7% (electricity), respectively. An extension of the data sample, a consideration of further facility types, and an implementation of additional statistical methods may be considered by future approaches to improve the estimation accuracy.     

Efficient solution of modal equations with arbitrary loadings

Commonly time-varying loadings such as wind, waves and earthquakes which act on engineering structures are specified in the form of discrete time-series. The dynamic response of a linear structural system when subjected to such inputs may be computed by modal analysis techniques. These methods require the solution of a set of uncoupled second-order linear ordinary differential equations with constant coefficients. Implicit to any solution used, however, is the requirement that the original loading be matched exactly or approximated closely by a continuous time-function. Frequently a piecewise linear interpolation of the discrete input data is adopted. This paper presents superior local interpolations which have been derived and optimised by considerations in the frequency domain. These local interpolations of the input are then subsequently used in conjunction with an exact solution to the modal equations. This implies that errors are due solely to the limitations of the interpolating process, a feature absent from numerical integration methods. By the use of discrete time-systems theory and the $\text{z}$ transform some simple recursive algorithms are derived for the solution of the modal equations. These algorithms, which operate linearly on the loading data, can be made very accurate, are unconditionally stable and are suitable for use with a hand calculator.The paper concludes with sections on methods of processing the discrete time-series loading data so as to increase or decrease the sample time step length. Increasing the step length can economise analysis when only low frequency components are of interest. Reducing the step length by inserting intermediate values is advantageous when high frequency components in the solution are of importance and in the direct solution of the matrix equations of motion. Simple but effective digital filters are specified for these operations, and in the case of sample rate increase (digital interpolation) the filters are much superior to linear interpolation.     

Recording duration of ambient vibration monitoring for system identification of tall telecommunication towers

It is necessary to have reliable field measurement records for estimation of dynamic characteristics. Increasing duration of the record is one of the common methods for reduction of such errors in the results. Dynamic characteristics of telecommunication towers in higher modes are important for designers, but these parameters could be obtained from ambient vibration monitoring during typhoons in which duration of vibration is not long enough for reducing measurement errors. This paper suggests a procedure for obtaining the duration of recording time for more reliable determination of structural characteristics of telecommunication towers. It is suggested to record the vibration of towers in the form of a set of long‐term and short‐term duration recordings for lower and higher modes, respectively. This procedure was verified with field measurement of Milad telecommunication tower. The results show that natural frequencies determined by this procedure are in good agreement with finite element model analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

框架式结构自振特性基本规律的研究

本文用动力有限单元法对框架式结构自振特性基本规律进行了一定的研究。结果表明,空间框架作为平面框架进行自振特性分析,不仅自振频率有出入,而且自振振型的变化规律也不一致。本文认为,空间框架式结构无论是低层还是多层或高层作为平面框架问题进行自振特性分析是值得商榷的。     

高层建筑结构三维抗震设计

本文参照我国现行《工业与民用建筑抗震设计规范》,讨论了三维坐标系下高层建筑结构地震设计荷载的选取。采用地震惯性力逐层传递求得结构各楼层地震剪力和扭矩,由振子广义位移幅值和备振型的乘积直接给出地震荷载下各振型结构楼层的相对位移。本文方法不仅节省机时、概念清楚,而且为高阶振型对结构各楼层影响的研究提供了有效的依据。此外,还提出按振子能量比选取振型及振型组合所需振型个数和选择合适振型组合法的方法,并在几个算例中均取得较为满意的结果。     

The influence of train properties on railway ground vibrations

This paper uses a sensitivity analysis to quantify the dominant train properties (mass and spacing of wheels and bogies) that contribute to ground-borne vibration generation, with the aim of reducing the complexity of train–track numerical models. This research is significant because ground-borne vibration from railways is a growing problem, particularly in urban areas. Despite this fact, attempting to predict vibration levels is complex because there are many variables that contribute to the overall dynamic response. Therefore, a deterministic approach is commonly used, that ignores many of these variables. Thus, this paper identifies the variables that can be ignored, while highlighting those that are highly influential on vibration generation. For this purpose, a previously validated 2.5D finite elements-boundary elements approach is used to simulate dynamic train–track interaction. It is computed many times for a variety of modelling variables to investigate the effect of each on the ground-borne vibration levels in the far field. It is found that increases in unsprung mass of the train causes a large increase in vibration levels. Furthermore, changes in wheel/bogie spacing and semi-sprung mass are found to have a minimal effect on vibration generation.     

Einsatz von multiplen Schwingungstilger‐Systemen an schlanken Fußgängerbrücken

The Application of Multiple Tuned Mass Damper Systems at slender footbridges. While for standard footbridge only a few vibration modes are within the critical footfall frequency range and hove to be considered for the dynamic design, lightweight structures dis‐play multiple modes in that frequency range. Furthermore the modal masses are very little so also the smaller load components for the excitation of higher harmonic vibration modes can become significant to assess the vibration susceptibility. Various observations have been made during experimental tests of these structures and will be introduced in this contribution using the example of a canopy walk structure and a stress ribbon bridge. To understand the observed effects at such continuous dynamic systems for pedestrian loading, numerical calculations have been performed for which a similar lightweight structure has been modelled and pedestrian loading was simulated with several footfall frequencies. Similar to the experimentally investigated structures it was found that the multimodal dynamic response of the bridges strongly depends on the pedestrian loading (footfall frequency). Experimental tests have shown, that the application of a Tuned Mass Damper System to dampen only the critical mode that is within the footfall frequency range is not sufficient to reduce the multi‐modal dynamic response of the lightweight bridge structures under pedestrian so the occurring accelerations remain below certain comfort levels. Therefore the concept of Multiple Tuned Mass Dampers was introduced to the bridge structure and its practicability was investigated.     

雕塑类大型复杂组合结构抗震性能研究

泉州郑成功雕塑为复杂组合空间结构,其动力性能复杂.本文对其抗震性能进行详细研究,包括:结构自振特性分析、反应谱分析、时程分析、非一致激励分析等.研究结果表明,郑成功雕塑结构振型复杂,以水平振型为主,高阶振型间存在耦合效应.扭转耦连效应在复杂异形结构中比较重要,进行地震作用的反应谱分析时,建议采用CQC算法,并应考虑双向地震波输入和高阶振型影响.对于复杂组合空间结构,时程分析与反应谱分析结果的差异分布具有不确定性,在结构采用反应谱法设计完成后,应进行时程分析校核.郑成功雕塑的抗震性能良好,非一致激励影响可以忽略.本文研究方法和结果可对同类大型复杂组合结构的抗震性能研究提供参考.     

巨型框架多功能减振结构脉动风振的时程分析

本文以一种结构方案为算例 ,建立了巨型框架多功能减振结构及抗振结构的分析模型 ,并随机模拟了脉动风的速度时程 ,由此研究了巨型框架多功能减振结构脉动风振的位移及加速度时程反应 ,结果表明巨型框架多功能减振结构能够显著降低结构的风振反应 ,是一种较有前途的结构形式。