低应变瞬态荷载作用下基桩动力响应解析解

目前广泛采用的基桩低应变检测问题的理论基础是基于平截面假定的一维应力波理论。而实际上,锤击产生的应力波是三维应力波,不仅沿桩身纵向传播,还沿径向传播,对于基桩低应变检测问题平截面假定实际上是不成立的。此时,一维纵波传播问题转换为应力波沿三维柱体传播问题。文章从基桩三维理论出发,忽略桩土径向位移,考虑桩体中应力波沿纵向和径向传播与桩土的相互作用,建立三维条件下桩土系统瞬态振动计算模型,推导得到低应变瞬态荷载作用下基桩三维动力响应的解析解,以期为基桩低应变检测提供新的理论指导。     

An analytical model for dynamic response analysis of tubular tall buildings

In this paper, on the basis of the D'Alembert's principle, approximate formulas for dynamic response of tubular tall building structures are presented. Using D'Alembert's principle and applying the compatibility conditions on deformation of the tubes, the governing dynamic equation of the tubular structure's motion is derived. Then, natural boundary conditions of the parallel cantilevered flexural–shear beams are derived, and by using Rayleigh–Ritz method, value problem is solved, and trivial and nontrivial solutions are derived, which can be used for calculating natural frequencies and mode shapes of tubular structures. By solving numerically the frequency equation, a design chart and graph are given for the first five nondimensional natural frequencies of tubular tall buildings. The proposed mathematical model gives dynamic characteristics and provides a simple, efficient and reasonably accurate algorithm for free vibration studies that are needed to be quick at the preliminary design stages of tall buildings with tubular systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Application of linear regressions to the comparison of analytical procedures for the determination of SO2 in ambient air

Three commonly used analytical methods for the determination of SO2 in ambient air were compared during 10 months at six different sites. The acidimetric method, used in the Sulfur-Black Smoke network, and the FPD method, used in the Belgian Automatic Network for Air Pollution, were compared with the TCM reference method. Several regression methods were used to calculate the relationships between the daily averages obtained by the three measuring techniques. Knowledge of the relative importance of the errors on the different sets of data was a determining factor for the selection of the most suitable regression method. The results show good agreement between the three methods during the field-test period.     

A generalized analytical approach to the buckling of simply-supported rectangular plates under arbitrary loads

An analytical approach for the elastic stability of simply-supported rectangular plates under arbitrary external loads is presented which, for the first time, may be described as ‘exact’. This is achieved through the use of exact solutions for the in-plane stresses and the adoption of double Fourier series for the buckled profiles which, together, ensure that accurate results are obtained in the Ritz energy technique. Several cases of plate buckling under direct, shear and bending loads (or their combinations) are studied to show the generality of the proposed approach, with the ensuing results compared with existing data (if available) and with numerical FE results.     

The dynamic response of coupled frame—wall systems to earthquake excitations

This paper presents a method for the analysis of the response of periodic frame—wall systems to earthquake excitations modelled as stationary random or evolutionary random processes. The transfer matrix required by the analysis, together with its powers is provided directly, thus avoiding calculation of the left and right-hand eigenvectors of the transfer matrix and eliminating computations for the evaluation of all its powers. It is shown how the method can be applied to structures that are only piecewise periodic and how results can be obtained for the static case. Finally, it is shown how the method may be used for both deterministic and probabilistic analyses.     

Mode shape corrections for dynamic response to wind

A correction factor, for nonlinear mode shapes, to the generalized force spectra in the first mode of vibration produced by wind action on tall structures, is proposed. This lies between theoretical limits for low and high correlation of the wind forces with height and agrees well with experimental data.     

基于线性方程组右端向量修改的拓扑图同构判别

为了提高拓扑图同构判别速度,借助邻接矩阵动态修改法的拓扑图同构判别思想,即利用素数对拓扑图顶点动态赋值以获得线性方程组解向量的改变,从而找到拓扑图同构的映射关系。为进一步减少计算量,简化判别过程,提出保持邻接矩阵不变,仅修改线性方程组右端向量以获得解向量的改变的方法,给出了该方法的初步理论依据。与邻接矩阵动态修改法相比,该方法无须重新形成邻接矩阵,在每次右端向量修改中省去了形成邻接矩阵的运算量,且判别算法变得更为简单。拓扑图同构判别实例表明,该方法有效、可靠。     

Quantification of fecal coliform inputs to aquatic systems through soil leaching

In order to assess the fecal contamination of rivers in the Seine watershed through soil leaching, 78 small streams located in rural areas were sampled upstream from any wastewater outfall. Culturable fecal coliforms (FC) and beta-D-glucuronidase activity (specific of Escherichia coli) were measured in the samples. Data showed a significant correlation between both estimates of fecal contamination. In the two different areas of the Seine river watershed investigated, most of the small streams were significantly contaminated by fecal bacteria. In general, the streams flowing through areas partly or fully covered with pastures were more contaminated than those flowing through forest and cultivated areas. Rainfall increased the suspended solid content of small streams as well as their fecal contamination, as an important fraction of FC was adsorbed on particles. Calculations showed that, at a large watershed scale, the input of FC in rivers through soil leaching was very low when compared to the input through the discharge of treated domestic wastewater but this could not be true at local scale.     

初始几何缺陷对网壳结构线性动力反应的影响初探

自振频率的密集分布和不可避免的初始几何缺陷,将导致网壳结构出现模态局部化现象,而模态局部化将导致结构振动呈现局部化。通过矩阵摄动理论分析并给出了模态局部化现象发生的诱因,讨论并确定了初始几何缺陷的大小和分布模式。以一个单层球面网壳为例,进行了同一地面运动激励下,50个包含不同初始几何缺陷网壳结构的线性动力反应分析,结果表明,初始几何缺陷对网壳结构线性动力反应的影响是不可忽略的,建议在网壳结构的抗震计算中予以重视。     

地震与锚固系统的抗震分析及各种类型锚索对动荷载反应

本文提出了两种锚圈系统抗震分析方法，介绍了不同类型锚索对动荷载的反应。笔者认为：重大岩土锚固工程或强震区岩土锚固工程，设计时必须考虑动荷载作用；从抗错动和避免产生较大的应力集中角度考虑问题，压力型锚索优越于拉力型锚索。     

水平动荷载作用下海洋大直径管桩动力响应解析解

考虑桩–土–流体耦合振动,研究了谐和激振水平动荷载作用下的海洋大直径管桩振动响应问题.将桩周和桩芯海水考虑为无黏性不可压缩流体建立其控制方程求得海水速度势解析表达式,继而得到作用于桩身动水压力表达式.将土体看作黏弹性介质建立桩周土和桩芯土控制方程,对土体方程直接解耦求解,得到桩周土和桩芯土位移和抗力表达式.利用桩–土体...     

A phenomenological model for the dynamic response of wind turbines to turbulent wind

To predict the average power output of a wind turbine, a response model is proposed which takes into account: (i) the delayed response to the longitudinal wind speed fluctuations; (ii) a response function of the turbine with arbitrary frequency dependence; (iii) wind fields of arbitrary turbulence intensity. In the limit of low turbulence intensity, the dynamical ansatz as proposed in 1992 by Rosen and Sheinman is reproduced. It is shown, how the response function of the turbine can be obtained from simulation experiments of a specific wind turbine. For two idealized situations the dynamic effect of fluctuating wind is estimated at turbulence intensities 0?I_u?0.5. At the special mean wind speed , the turbine response function is determined from simulation data published by Sheinman and Rosen in 1992 and 1994.     

模拟路基动力响应的原位激振试验研究

动荷载下路基动力响应规律是研究路基长期动力稳定性的基础。采用自行研制的分离式变频激振器,开展铁路路基动力响应的模型试验,研究不同激振频率、动载水平下铁路路基本体的动力响应规律,掌握石灰改良土+粉质黏土填筑的铁路路基本体的共振频率约为25 Hz,路基表层的振动加速度、动应力随着激振频率的增加而显著增大;弄清了振动加速度、动应力沿深度和水平方向的变化规律,两者在主要影响深度1.5 m处已衰减90%,表明其沿深度方向的衰减速度较无砟轨道路基情况下快,而两者沿水平方向的变化受到应力扩散效应的影响,在浅层水平面会迅速衰减,而一定深度(0.7 m)处反而比较稳定,反映了路基动力响应的空间变化特征。     

非比例滞变阻尼线性体系的反应谱CCQC法

基于比例阻尼体系建立的振型分解反应谱法应用广泛,是各国规范常用的结构地震作用效应计算方法,直接将其用于非比例阻尼体系(如设置耗能阻尼器的结构)是不合理的.为拓展规范反应谱法的适用范围,在基于复阻尼模型的滞变阻尼模型复模态叠加法基础上,该文结合虚拟激励法和平稳随机理论,推导基于滞变阻尼模型的反应谱CCQC (comple...     

A new analytical method for determination of discharge duration in tunnels subjected to groundwater inrush

Bulletin of Engineering Geology and the Environment - Unexpected water inrush to tunnels is one of the most hazardous events, especially in karst terrains that could take place during mechanized...     

An analytical study of the across-wind response of cylinders due to vortex shedding

The across-wind response of tapering cylinder-like structures, such as chimneys, due to periodic shedding of vortices is obtained under lock-in conditions. The method of analysis incorporates aerodynamic effects and describes the lift forces by a linear model monoharmonic in nature. Under lock-in conditions, the critical wind speed and the lift and aerodynamic coefficients are assumed to be uniform throughout the height of the chimney, although its outside diameter varies. The aerodynamic and lift coefficients are derived from a lift oscillator model which adequately describes the experimental results of the vortex-induced oscillation (at lock-in) of an elastically-supported cylinder. With the help of an example problem, the paper shows how the response of the chimney is sensitive to the choice of the critical diameter used for the determination of critical wind velocity and the lift and aerodynamic coefficients. It also emphasizes the importance of the lock-in condition in the second mode in relation to bending stresses.