摘要
近年来,随着地下结构建设规模的不断扩大,地下结构的抗震设计及其安全性越来越成为工程界所关心的重要课题。土-地下结构动力相互作用问题是成为地下结构抗震设计研究的重要内容。本文根据土-结构动力相互作用的基本理论,利用ANSYS软件建立了土-地下结构相互作用的有限元模型,取得的主要成果如下：
1、分别对自由场地和土-地下结构动力相互作用体系进行了水平地震、竖向地震和水平-竖向地震耦合作用下的时程反应分析,对不同工况的计算结果进行了对比研究。
2、根据现行规范对上海某地铁车站在各项荷载进行基本组合的条件下进行静力分析,得出在静力条件下,地铁车站的中柱受到的弯矩和剪力很小,主要承受轴力,弯矩和剪力的最大值发生在车站底板与侧墙的结合处。并与结构在地震过程中产生的结构内力做对比。
3、对该车站所处地质环境进行地震的自由场分析,得出EI-Centro波、迁安波、阪神波在基岩水平方向输入时,虽然引起的地表加速度峰值相同,但在基底输入的加速度峰值和引起的地表位移峰值并不相同。证明了位移反应不仅与输入地震波的峰值有关,还与其频率组成有关。
4、对地铁车站分别进行了水平地震波和水平-竖直耦合地震波反应分析,得出耦合作用增加了体系的最大反应。因此,在进行地震反应分析时,只考虑水平剪切破坏的做法,对工程抗震是不够安全的,应充分考虑耦合地震的作用。
5、在地下结构的动力反应分析中,顶板中部的变形和受力较大,两侧壁角隅处的应力高度集中,变形也较大。因此在设计和施工过程中,应对上述部位予以重视。
6、增大车站主体结构的密度和刚度对土-结构体系的自振频率改变很小,对抵抗地震作用下结构的位移效果也很小,反而结构应力增加很多。土-结构体系的自振频率主要受结构周围土体控制,土体弹性模量较大时,结构在地震作用下的位移和应力会明显减小。
Recently, with the expanding of underground structure construction, anti-seismic design of the underground structure as well as its security assessment become an topic that is attracting more and more concern, thus making soil and underground structure dynamic interaction an important part of such a design. Under the framework of soil-underground structure dynamic interaction theories, this paper has established a finite element model of soil-underground structure interaction with the help of ANSYS software, and has made the following achievements:
1 Time-history response analysis has been conducted on free field and soil-underground structure dynamic interaction respectively under the effect of horizontal seism, vertical seism and the coupling of horizontal-vertical seism.
2 According to current specifications, a static analysis has been carried out on the basic combinations of various loads for a subway station in Shanghai. And the analysis shows that under static condition, the central pillar of the subway station is bearing mainly the axial force, and is under small bending moment and shearing force, the maximal force of the latter occurs at the joint of the station floor and the flank walls. The result is compared with internal force that the structure produces during seismic process.
3 Analysis on the seismic free field for the geological environment of the subway station shows that, when EI-Centro wave, Qian'an region wave and kobe wave are input along the horizontal direction of bed rocks, though the peak values of surface acceleration are the same, the acceleration peak values of the base and the surface displacement peak values are different. This proves that displacement response is not only related with the peak value of seismic wave that is input, but also with the combination of frequencies.
4 Horizontal seismic wave response analysis and horizontal-vertical coupling seismic wave response analysis on the subway station are conducted respectively, and the result shows that coupling has increased the maximum response of the system. Therefore, when doing seismic response analysis, considering only horizontal shear failure will not ensure anti-seismic security of project, and coupling seismic function shall be taken into full consideration.
5 In the underground structure dynamic response analysis, central part of the roof is under great force and has a large degree of distortion, so do the corners of the flank walls for the high concentration of forces. Therefore, aforementioned parts shall be given special attention to in design and construction.
6 Increasing density and rigidity of station body structure has little influence on changes of natural frequency of vibration of the soil-structure system as well as structure displacement under anti-seismic effect, but structure stress grows a lot. Natural frequency of vibration of the soil-structure system is mainly determined by structure surrounding soils, and displacement and stress of the structure under seismic effect dwindle markedly with the increase of the elastic modulus of the soils.
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