【作者】 徐炳伟；

【导师】 姜忻良；

【作者基本信息】 天津大学 ， 结构工程， 2010， 博士

【摘要】 天津站交通枢纽工程作为北京奥运的配套项目,天津市“十一五”规划重点工程,需要对工程结构的各方面进行深入研究。作为生命线工程的重要组成部分,交通枢纽抗震问题已经成为城市工程抗震和防灾减灾研究的重要课题,因此以天津站交通枢纽工程为背景,选取天津站整体结构有代表性的一部分按照比尺缩小制作成模型,考虑其与土相互作用,首次开展了大型复杂结构-桩-土体系振动台模型试验研究,与国内外已有的土-结构相互作用振动台模型试验相比,该试验模型由土、群桩、地下结构、地上结构多个部分组成,具有尺寸大、体系复杂的特点,更具有代表性,其主要工作和结论如下:1.通过推导动力模型试验的相似关系,着重指出结构-桩-土体系模型与原型各物理量难以做到完全相似,于是本文提出了用土的卓越周期相似比来设计模型土,使结构-桩-土体系模型与原型之间做到部分相似,振动台试验结果证明这种方法是合理的。2.给出求解土卓越周期的有限元数值模型,指出波动理论公式( T = 4H/v_s)求卓越周期的适用范围及存在偏差,通过模型土模态分析研究了模型土卓越周期随土体性质、土域范围及边界条件的变化规律,得出通过适当提高模型土的宽高比和合理选择边界条件及模型土材料配合比均可以减小边界对模型土的影响。利用动三轴试验数据拟合,求出模型土的动剪切模量和阻尼比计算公式中需要的参数,提出用数值拟合来求模型土的最大动剪切模量的方法;求出模型土的动C、φ值并与其静C、φ值相比较,结果表明:动力加载中,土的C值明显降低,φ值有所增长,有限元数值计算动力模型中,推荐使用动C、φ值。3.完成模型制作,主要采用以下做法:结构分两部分制作、后组装;桩做成空心内部填充铁砂作为配重;用铜管微粒混凝土模拟钢管混凝土;为减小刚度影响,采用泡沫塑料对地下结构开口两端封口;用玻璃板替代原屋面钢网架。试验表明这些措施行之有效。制作土箱并通过试验数据和数值分析对其进行检验,研究表明:在土箱底部,通过设置分割条嵌入模型土中做成的摩擦边界效果较好;在土箱垂直于地震动两侧壁上,聚苯乙烯泡沫塑料做成的柔性边界对Taft波和人工波加载的效果较好,而对天津波加载效果略差;在土箱平行于地震动两侧壁上,通过侧壁内表面贴聚氯乙烯薄膜并涂抹润滑油做成的滑动边界起到一定的效果。4.完成测点布置、模型土装填、模型组装及确定试验加载制度等试验准备工作,提出一些有效的新做法,如加速度计的埋设采用挖埋而不是填埋的方法,现场材料含水率的测定中采用双锅加热法烘干土和锯末。5.试验结果整理从分析大型复杂结构-桩-土振动台模型试验数据入手,用加速度、变形、正应变、动土压力等指标全面分析结构的地震响应,并比较桩、地下结构、地上结构的不同响应。研究发现:1)结构不同部分最大地震响应发生的频率不尽相同,且受地震波频谱特性及自身频率影响,天津波加载时结构的地震响应较大;2)地震波向上传播过程中,土与结构对地震波均有过滤作用,地表以下,当震级较小时,土-结构对地震波起放大作用,随着震级的增加,对地震波放大作用减缓甚至减小;3)最大变形随结构高度增加逐渐增大,在桩与地下结构交界处和地表处,位移改变较大;4)地下结构柱、桩最大正应变呈中间大、两头小分布,残余正应变对结构正应变影响比较大,影响呈桩、地下结构、地上结构递减;5)残余动土压力对动土压力分布有一定影响,土越深,影响越大,最大动土压力随着深度增加呈两头大、中间小分布,且地表处最大,总的土压力受最大动土压力影响较大,随深度增加有先降低后增大的趋势。6.加载过程中,结构最大层间位移角基本满足规范限值,并且从正应变看,只是部分结构达到极限应变,从动土压力看,只有部分土进入塑性,直至试验加载结束,结构整体并未倒塌,表明结构满足抗震设计的要求。更多还原

【Abstract】 As a supporting project of the Beijing Olympics and key project of Tianjin Eleventh Five-Year Plan, the engineering and construction of Tianjin Station transportation junction requires deep study on all aspects of the structures. As an important component of the lifeline engineering, the seismic performance of the transportation junction has become an important issue of the city earthquake disaster prevention and mitigation engineering. And therefore, a shaking table test studying large-scale complex structure -pile- soil interaction is carried out on the transportation hub of Tianjin station. In the test the scaled down model was established based on a typical section of Tianjin Station. The model is large and multiplex which is made of piles, underground structure and groung structure. The major work and conclusions are as follows.1. In developing the similarity ratio of the dynamic model test, it is found that it is hard to make the model’s physical parameters completely similar to the prototype’s of the complex structure -pile- soil interaction system. Hence, the similarity ratio based on soil’s predominant period is adopted in the shaking table test to design the model soil, which enables partial similarity between the physical model and the prototype of soli-pile-structure interaction system. It is proven that the method is reasonable by the test resutls.2. The finite element numerical model to get the soil’s predominant period is established, through which it is found that the traditional fluctuation theory formula ( T = 4H/v_s) solving soil’s predominant period shows a certain amount of error with its scope of applicability. The effects of the soil property, size of soil domain and boundary conditions on the model soil’s predominant period are studied though a series of soil modal analyses. It is found that the soil would be affected less by increasing model soil’s ratio of the width and height, selecting reasonable boundary conditions and model soil’s mixing proportion.The parameters needed in the formulas solving model soil’s dynamic shear modulus and damping are obtained through data fitting of the model soil’s dynamic triaxial tests. The method solving model soil’s maximum dynamic shear modulus by data fitting is proposed. At the same time, by comparing dynamic C &φwith static C &φ, it shows that the model soil’s value of C reduces obviously and value ofφ increases a little during dynamic loading. Thus, it is recommended that parameters of dynamic C &φbe used in the finite element numerical model.3. The following measures are adopted in setting up the model, which include the model being divided into two parts, fabricated separately and assembled together finally; the piles being made of hollow pipes filled with iron ore to balance the weight; the micro concrete-filled brass tubes being used to simulate the concrete-filled steel tubes; using foam plastic to seal both opening ends of underground structure to reduce the stiffness effect; replacing the original steel truss roof with glass plate, etc. It is proven by the test results that these measures are effective.The soil box is fabricated and verified though both test data and numerical analysis. Research shows that the frictional boundary applied at the bottom of the soil chamber using dividing strip embedded inside of the model soil works very well. It is also proven that the flexible boundary made of foamed polystyrene applied at the side walls perpendicular to the seismic direction works well to Taft seismic wave and artificial seismic wave but doesn’t work so well to Tianjin seismic wave. The sliding boundary using oil lubricated polyvinyl chloride film attached onto the longitudinal inner side surface of the soil chamber works to a certain extent although with relatively large deviation.4. The other test preparation work includes the measuring points arrangement, the model soil filling, model assembling and loading steps determining etc. Some new practices are adopted. For examples, accelerometers in the soil are buried after digging a little well inside the filled soil rather than being buried when filling the soil and double oven heating is used to dry the soil and sawdust in their moisture measurement.5. During the data analysis of the shaking table test studying complex structure-pile-soil interaction, the structure’s earthquake response is fully studied based on the acceleration, maximum deformation, maximum normal strain and maximum dynamic soil pressure etc. The findings are summarized as follows:1) It is found that the frequencies inducing the maximum earthquake response on different parts of the structure are different. The response is also influenced by spectral characteristics of seismic waves and its vibration frequency. The earthquake response is drastic when the Tianjin seismic wave is applied.2) The seismic waves are filtered a bit when spreading upward. The amplification for the seismic waves by soil-structure is big when the magnitude is small, while it slows down and even reduces when the magnitude increases underground.3) The maximum deformation becomes bigger while the structure’s height increases, and it changes obviously at the interface between the pile and the underground structure and at the soil’s surface.4) The maximum normal strain of the underground structure’s column is big in the middle but is small at both the ends. Structure’s normal strain is affected a lot by the residual normal strain, and this effect attenuates from piles, underground structure to ground structure.5) Also, the soil’s dynamic pressure is affected by soil’s residual dynamic pressure and the effect increases with the soil depth. The profile of the maximum dynamic soil pressure indicates bigger value at both the ends but smaller in the middle when the soil’s depth increases. The maximum dynamic soil pressure occurs at the soil surface. The total soil pressure is affected obviously by the maximum dynamic pressure and it reduces first and then increases when the depth goes down.During the process of loading, the maximum story drift angles on the ground structure meet the Code requirement on the whole. Only a part of the whole structure’s normal strains go beyond the limit strain and only part of the foundation soil enters plasticity. Besides, even at the end of test, the structure doesn’t collapse. It shows that the structure design is in accordance with the principle of seismic structure design.更多还原