【作者】 邢帆；

【导师】 祝兵；

【作者基本信息】 西南交通大学 ， 桥梁与隧道工程， 2011， 博士

【摘要】 当前全球地震活动明显进入多发期,更加需要深化有关抗震基本理论的研究。地震动是强非平稳过程,钢管混凝土拱桥受输入地震频谱特性的影响,非线性响应结果差别巨大。同时,结构动力失稳问题也要从地震响应角度出发进行研究,所以地震频谱特性的差异也会对动力稳定分析产生不容忽视的影响。而关于地震频谱特性对结构非线性响应的影响研究是当前结构抗震分析中的前沿课题,需要涉及数字信号处理及非线性动力学的多学科知识,目前难以使用准确的数学解析模型来描述地震的非平稳性。尽管地震频谱特性对结构反应影响复杂,但还是可以通过地震时变谱估计大致建立起地震能量的时频分布特征与结构非线性响应之间的联系。论文以有关地震频谱特性的研究作为主线,同时也关注了包括材料非线性、几何非线性、初始几何缺陷等因素对钢管混凝土拱桥的地震响应及动力稳定的影响问题。由于近断层地震(近场地震)更易对长周期大跨桥梁结构造成严重破坏,因此论文不但对近断层地震的频谱特性及其反应特点加以总结,还通过小波分析数值方法建立了能够反映近断层地震作用大小的指标,并就近断层地震作用下的动力稳定问题展开深入讨论,研究了钢管混凝土拱桥的动力失稳形态特点。论文主要进行了以下几个方面的研究：(1)介绍了现代非平稳信号时-频分析技术及各种时变谱估计方法,发现在它们在一定程度上均可描述地震信号的非平稳特性。由于改进L-P小波具有快速算法,并且计算数据量小,所得到的局部谱密度具有重要工程应用价值。提出利用改进L-P小波变换的二进正交特性对地震信号进行快速时-能密度分析,能够准确描述地震信号能量沿时域的分布特征。(2)以主跨132米的下承式钢管混凝土拱梁组合桥为实例建立了有限元模型并进行相应的非线性地震响应分析,考虑了初应力效应对模态分析的影响。研究发现,从整体上说结构的几何非线性效应不明显,更主要的是材料非线性的影响。随输入地震作用的增强,材料塑性的发展会改变内力的分布规律,并有利于结构受力。在研究地震非平稳性影响时,通过小波变换对地震信号进行分解与重构,阐明了反应谱无法充分表达地震频谱特性与结构反应之间的联系,而小波方法在确定地震信号时频分布特征及其频率成分对结构作用方面的优势明显。(3)就发生在我国台湾地区的集集地震(CHI-CHI,09/20/99)展开了各类场地近断层地震频谱特性研究。结果表明,随着近断层地震效应的增强,更易产生持续密集的低频能量脉冲,加速度反应谱峰值可能出现在中长周期段。结合近断层地震低频脉冲效应对长周期钢管混凝土拱桥的作用特点,提出可以通过二进离散小波分解方法将地震加速度信号进行频域分解并得到了能够描述结构非线性反应的地震作用指标WAPA (Weighted Average Peak Acceleration),体现了基于性能的结构抗震设计思想。(4)论文使用了IDA (Incremental Dynamic Analysis)动态增量分析方法并结合B-R (Budiansky-Roth)系统响应准则来确定钢管混凝土拱桥的动力失稳临界荷载。发现材料非线性的影响对动力失稳占主导作用,单纯考虑几何非线性的影响对动力稳定极限承载力分析仅具有理论意义。而钢管混凝土拱桥对初始几何缺陷的敏感性较低,其影响可不予考虑。在研究了近断层地震作用下的动力稳定问题后,指出脉冲型近震的破坏力巨大,有可能造成非线性极值动力失稳,结构的失稳临界荷载会明显降低。使用指标WAPA作为新的IDA分析强度指标IM (Intensity Measure),可显著改善IDA曲线簇的离散性,利于研究近断层脉冲运动对钢管混凝土拱桥结构所造成的动力失稳破坏特点。更多还原

【Abstract】 In recent years, global seismic activity is more and more frequent, thus it needs more strengthened research in seismic design theory. The ground motion is a strong non-stationary process, and the nonlinear response results of CFST arch bridge vary enormously because of the influence of earthquake spectrum characteristics. Meanwhile, the research of structure dynamic instability needs to proceed from seismic response, the influence of the earthquake spectrum characteristics can not be ignored in dynamic stability analysis also. To research the relationship with the nonlinear response and the earthquake spectrum characteristics is an advanced subject yet, and it will involve with digital signal processing and nonlinear dynamics interdisciplinary knowledge. At present, there is no appropriate mathematical analytical model to describe non-stationary of the earthquake yet, but time-varying spectral estimation of the earthquake can make connections roughly between time-frequency distribution characteristics of the earthquake energy and the corresponding structure nonlinear responses.This paper is mainly concerned with the influence of earthquake spectrum characteristics to seismic response and dynamic stability of the CFST arch bridge, and the other influencing factors such as material nonlinearity, geometrical nonlinearity and initial geometric imperfection are given an intensive study also. Large-span arch bridge with long period is liable to meet with a serious damage by the action of strong near-fault earthquakes. In view of this fact, the spectrum characteristics of the near-fault earthquakes and the reaction characteristics are summarized, and a novel assessment indicator is proposed consequently through wavelet analysis method to identify seismic action effect of the near-fault earthquake. An intensive study on the problem of the CFST arch bridge dynamic stability under the action of near-fault ground motion is carried out also, and the characteristics of dynamic instability forms are investigated thoroughly. The main content of the paper includes the following aspects:(1) Several modern time-frequency distribution estimate methods are studied, and they are able to describe the non-stationary characteristics of the seismic signal in a certain extent. With the advantages of fast algorithm and small calculated data, local spectral density through improved L-P wavelet analysis is proved to be of great engineering application value. A novel time-energy density analysis method through dyadic orthogonal wavelet transform is proposed, and it can be beneficial to describe seismic energy distribution characteristics along time domain.(2) Nolinear seismic response analysis is conducted through an example of CFST arch bridge with132m main span, and the bridge type is a box girder and CFST arch combination bridge. The influence of initial stress effect about modal analysis is considered also. In general, research results suggest that geometry nonlinear effect is not obvious to the seismic response, and material nonlinearity influence appears to be more importantly. With the increasing earthquake effect, the development of yielding plastic materials can change the laws of internal force distributing, and improve the structure seismic performances to some extent. The earthquake signals are taken decomposition or reconstruction process by wavelet transform to research the influence of earthquake non-stationary. It is demonstrated that response spectrum can not sufficiently show the connection between earthquake spectrum characteristics and structure response, but the wavelet method has distinctive advantages in revealing earthquake time-frequency distribution characteristics and seismic effects of certain frequency components.(3) Near-fault ground motion spectrum characteristics are studied in-depth by the records of Taiwan chi-chi earthquake (CHI CHI,09/20/99) at three sites. The results show that with the enhancing near-fault seismic effects, low-frequency energy pulses become intensively and sustainable, and the peak value of acceleration response spectrum may also appears in long cycle section. Since long-span CFST arch bridge is liable to suffer a great destruction by near-fault ground motion with low-frequency impulsive effect, the near-fault earthquake acceleration signal is decomposed by dyadic discrete wavelet analysis in frequency domain then. Combined with the characteristics of low earthquake frequency pulses, a new assessment indicator WAPA (Weighted Average Peak Acceleration) of the seismic action is presented, representing the ideology of performance-based seismic design.(4) Dynamic stability research about the CFST arch bridge is carried through, and the instability critical load is determined by the dynamic incremental analysis (IDA) method and Budiansky-Roth system response criterion. It is indicated that material nonlinearity played a dominant role in the dynamic buckling development, and there is merely theoretical meaning only if the influence of geometric nonlinear is taken into account. At the same time, the influence of initial geometric imperfection can be ignored because of low sensitivity to the structure. Near-fault pulse-like ground motions are likely to resulting extremal dynamic instability, and the corresponding critical load will be significantly dropped. If the assessment indicator WAPA is chosen as the intensity measure (IM) in IDA analysis, the discrete level of the IDA curve cluster can be alleviated observably, and the performance features of dynamic instability about CFST arch bridge caused by near-fault pulsed movements will be more apt to be represented also.更多还原