Application of Pushover Method to Seismic Performance Evaluation of Tall Piers for Bridge

For bridge with tall piers, the influence of higher modes on structural responses becomes more evident. Modified MPA method(MMPA) which is based on MPA theory and the concept of “equivalent mode height” is presented. To verify the effectiveness and the degree of accuracy of this method, several Pushover methods including MPA and MMPA methods were adopted to analyze tall piers for bridge, and then compares the results with that in dynamic time-history analysis. It is shown that MPA and MMPA methods can improve computational accuracy comparing with other normal Pushover methods when seismic intensity is lower, whereas the computational accuracy for MMPA methods is superior to that in MPA analysis with the seismic intensity becoming larger.     

根—土复合体强度及其非线性特性试验研究

[目的]研究根—土复合体的非线性破坏准则,并结合不同含根量(G=0.12%,0.24%,0.36%)、不同含水率(w=13.22%,16.22%,19.22%)条件下根—土复合体强度,开展根—土复合体非线性特性研究,为生态水土防治工作提供科学参考。[方法]采用GDS三轴仪开展了根—土复合体的固结不排水三轴试验,获得根—土复合体应力—应变曲线及抗剪强度指标。[结果]素土与根—土复合体应力—应变关系曲线为硬化型。含根量与根—土复合体峰值强度成正比关系,但含水率对其峰值强度的影响表现出反比关系。当G=0.36%时,根—土复合体峰值强度的最大增幅为70.1%;当w=13.22%时,根—土复合体峰值强度最大增幅为86.7%。根—土复合体非线性破坏准则在正应力低于临界应力时呈非线性,在正应力高于临界应力时呈线性。c,k为根—土复合体非线性破坏准则中描述根系作用的关键参数,其中c与含根量和含水率均成正比关系,c越大,根系对根—土复合体强度的贡献程度越大;k与含根量成反比,与含水率成正比,k越小,根—土复合体强度包线的非线性化特征越明显。[结论]含根量(G)和含水率(w)对根—土复合体强度有显著影响。...     

Seismic Response Analysis of Transmission Tower-line System under Multi-component Ground Motion Excitations

Seismic responses of power transmission tower-line system under multi-component excitations were analyzed by numerical simulation. A three-dimensional finite element model of transmission tower-line coupled system considering the geometric nonlinearity of transmission line was established. Twelve seismic records of different soil types were selected based on Code for Design of Seismic of Electrical Installations. Seismic responses of power transmission tower-line system under single component, two horizontal component and multi-component excitations were investigated using nonlinear time history analysis method, respectively. The results show that the responses of transmission tower-line system under multi-component excitations are significantly larger than those under single component excitation only, especially for considering vertical ground motion excitation only, and neglecting multiple nature of ground motion in analysis will underestimate the responses of the structure. To obtain an accurate seismic response and a better seismic design of transmission tower-line system, multi-component ground motion inputs need to be considered. The results provide reference for seismic design of transmission line practical engineering.     

Modeling and Its Application of Reinforced Concrete Columns Considering Nonlinear Shear Effects

A fiber beam-column element in conjunction with zero-length elements attached to its ends was proposed to simulate the flexural and shear mechanism respectively. Based on the Limit State Material model and the Shear Limit Curve model provided by OpenSees, the nonlinear shear effect of reinforced concrete column and its coupling with the flexural effect were defined. The reliability of the proposed model was validated by means of comparisons with existing test results. Finally, a plane frame from in-situ pushover test was simulated. It is shown that the proposed method, by taking the nonlinear shear effect into account, produces satisfactory results for frame columns with shear strength and stiffness degradation, while the conventional fiber beam-column element can hardly simulate actual flexure-shear failure mechanism for columns characterized by insufficient transverse reinforcement. The proposed method is applicable for nonlinear analysis of reinforced concrete frame structures with shear deficiencies.     

我国杉木通用性立木生物量模型研究

以我国南方地区的最重要针叶树种杉木为研究对象,综合利用非线性混合模型、哑变量模型和误差变量联立方程组方法,建立了适合杉木不同生长区域（总体）应用的一体化一元和二元地上生物量方程及根茎比函数.结果表明：不同总体的地上生物量模型之间存在显著差异,总体（一）的估计值要大于总体（二）,而地下生物量则差异不明显;地上和地下生物量方程的平均预估误差分别在5％和10％以内,可应用于不同区域的杉木林生物量估计.     

基于SVM的RBF网络在农机总动力预测中的应用

径向基神经网络是一种单隐层的三层前向网络,具有结构简洁、学习速度快等优点。为此,分析了径向基神经网络采用传统聚类方法确定基函数中心存在的问题,提出了一种基于支持向量机聚类确定径向基网络基函数中心的方法。该方法以最大间隔原理和结构风险最小化原则为前提,利用核方法把输入空间的样本映射到高维特征空间完成聚类工作来确定基函数的数量。采用改进的方法训练的径向基神经网络对黑龙江省农机总动力进行非线性时间序列预测,结果表明:改进的网络在确定网络结构、学习速度和提高网络预测精度方面都有较好的效果。     

A Method for Solving Strong Nonlinear Vibration

A method,stroboscopic harmonicbalance method which is used to solve strong nonlinear system, is proposed. The method is used to find the solution of strong nonlinear system. In investigation,the existence conditions of primary resonance solution and subharmonic resonance solutions are obtained. The results which are obtained by the stroboscopic harmonicbalance method are compared with those by computer numerical simulation. The results show that the stroboscopic harmonicbalance method is correct in qualitative analysis and it can meet the demands in engineering.     

Study on the Iterative Methods in the Nonlinear Full_RangeAnalysis of Concrete Structures

Based on the extensive study of various iterative methods, a simple but practical way of the iterative route search and acceleration is introduced into the normal displacement and arc-length methods to fit the nonlinear full-range analysis of concrete structures, by which the convergence of iteration is much improved.     

计算潜水蒸发系数的反Logistic公式

根据新疆叶尔羌河流域地下水均衡场裸地潜水蒸发的试验观测资料,提出了进行潜水蒸发系数计算的反Ｌｏｇｉｓｔｉｃ公式,同时采用可变多面体法对公式进行了非线性拟合。该公式较全面地反映了潜水蒸发系数的变化规律,简单实用,适于当地潜水蒸发量的估算     

多自由度强非线性系统的一种近似解法

地单自由度的频闪法推广到多自由度系统、建立了多自由度强非线性系统的频闪方法,求出了系统的周期解的近似表达式,分析了近似周期解的存在性和稳定性。