【作者】 郑明燕；

【导师】 鄢泰宁；

【作者基本信息】 中国地质大学 ， 地质工程， 2014， 博士

【摘要】 对于建筑抗震体系,在理论分析和设计中通常忽略土-结构相互作用(SSI)。即采用刚性基础的假定,认为地震时基础的运动与邻近的自由场一致。也就是说,上部结构的惯性力传给地基,使之产生的变形,比地震波引起的地基变形应当小很多。否则假定不合理,基础会产生相对于地基的变形,从而导致上部结构的实际运动与按照刚性基础的假定得到的响应有较大的差别。因此,对柔性基础上的建筑物,在计算地震响应时有必要考虑土-结构的相互作用目前,隔震技术已经基本成熟,土-结构相互作用(SSI)研究正在深入,而二者的耦合研究则刚刚起步,研究文献不多,得出的结论有时还互相矛盾,因此关于隔震技术与SSI的耦合有待进一步研究。现今,关于考虑SSI影响的隔震研究还限于简单模型,结构简化为单质点或多质点剪切结构,地基假定为弹性半空间。研究主要集中在刚性浅基础对隔震的影响,对柔性基础对隔震的影响研究较少,但实际桥梁和渡槽很多采用具有一定柔性的桩基。本课题对柔性地基中简支桥梁(或渡槽)的减隔震进行研究,能够更真实地揭示土-结构相互作用对该类桥梁减隔震系统的影响。课题针对某试验隔震渡槽(即过水的桥梁)结构和常见的三跨桩基隔震桥梁结构,研究SSI对其减隔震效果的影响。研究内容如下：第一章绪论,综述了考虑土-结构动力相互作用问题的隔震结构研究与发展以及桥梁脆弱性曲线的研究与发展。第二章,论文对某简支渡槽进行了比较精细的有限元分析,桩采用梁单元建模,土和桩的相互作用采用弹簧单元,槽墩、槽身及槽中的水体,采用实体建模。这样可以得到工程上比较关注的上部结构不同部位的具体响应。通过该模型分析了实际的隔震支座对系统响应的的影响。第三章,对前面的模型桩基部分,采用了不同的建模方式,并进行了动力分析比较。即桩土之间的相互作用分别采用Mindlin方法和规范推荐的m法两种方法进行分析比较。改进的Penzien模型采用一组带阻尼的弹簧单元来模拟自由场土层在不同深度对桩的刚度效应和阻尼效应,弹簧的一端与桩连接,另一端和一足够大的质量单元连接,以模拟自由场地土对结构的质量效应；桩周土质量间增加了土的剪切弹簧和阻尼器；自由场地质量间也增加了土的剪切弹簧和阻尼器。第四章,采用Mindlin方法对某渡槽拟动力试验的结果进行了分析,说明该法有一定的可信性。实验位于大型土槽内,设计制作了缩尺的渡槽试验模型。模型由四根钢管桩支撑,上部槽体模拟单跨槽体和水体的作用,采用等效质量块代替,承台、槽墩及槽体均采用钢筋混凝土材料,槽墩与等效质量块之间布有四个抗震支座。实验主要了解桩土相互作用。本章采用三维有限元模型对实验进行了模拟。第五章,对不同场地土对智能隔震渡槽的影响进行了分析。智能隔震支座由隔震支座和磁流变阻尼器构成,位于渡槽墩顶,智能隔震系统的控制策略为半主动控制。对此智能隔震渡槽,分析了地震作用下,不同的场地土对结构体系的影响,智能隔震装置的有效性。第六章,对典型的三跨简支梁进行了隔震分析,特别考虑了桥面板之间、桥面板与桥台之间碰撞对隔震桥梁的的影响。前面的渡槽是简支结构,属于简支桥梁类型,与普通简支桥梁比,只是荷载不同罢了。前面的渡槽三维有限元模型比较复杂,自由度也较多。而第五章,考虑SSI的智能隔震渡槽的地震响应,其模型相对简单,自由度也较少。事实上,模型的复杂程度变化是很大的,可以从简单的,仅包括几个自由度的杆件模型(如第五章),到很精细的模型,即包括各个不同杆件的非线性行为的模型。合理的模型应该与桥梁的配置、桥梁的类型、期望的地震需求和地震响应相关。本章对典型的三跨简支桥梁进行了建模,比较全面地考虑了地震动力分析时的需要的一些重要因素,包括材料非线性、支座非线性、土-结构相互作用以及桥面板的碰撞等,对桥面板采用梁单元建模,对关键的桥墩柱采用纤维单元建模,对桥面板的碰撞采用碰撞单元建模。所建三维模型,既能较好反映该类桥梁的地震动力分析的响应特点,又不至于太复杂,导致后面脆弱性分析的计算成本过高。本章重点采用此模型,对桥面板的碰撞进行了研究,分析了碰撞对结构地震动力响应的影响,对隔震简支桥梁的减震效果的影响。第七章,对典型三跨简支梁进行了脆弱性分析,比较了隔震前后的桥梁构件和桥梁系统的脆弱性的变化。脆弱性是在给定地震动强度情况下,结构或结构达到或超过某个设定的损伤程度的条件概率。本章采用地震峰值加速度(PGA)作为地震动强度度量,挑选了五种地震类型中共10条地震波,每条地震以O.1g作为PGA增量来分析,共100个计算工况。通过对各个地震波的增量时程分析,共获得100个时程分析结果。从各时程分析中提取关注的响应变量,包括柱子曲率,固定支座位移,滑动支座位移等。这便是桥梁部件的地震需求。对这些量值进行回归分析,可以得到响应LN (Sd)和地震峰值LN (PGA)之间的关系。再根据桥梁损失极限状态比较,得出桥梁部件的脆弱性曲线,由此,进一步得到桥梁系统的脆弱性曲线。根据支座脆弱的特点,进行坚固处理时,优先考虑支座的替换。替换为隔震支座后,再按同样的方法进行各地震波的增量时程分析,得出隔震桥梁的需求响应。最后,可计算出隔震桥梁部件和桥梁系统的脆弱性曲线。并对隔震前后的脆弱性进行比较。第八章,给出了主要的研究结果和结论。论文的主要成果如下：1)渡槽结构采用减震支座后的动力响应安装减震支座后渡槽结构的最大动应力和内力得到了不同程度的抑制,支座在横槽向和顺槽向滞回曲线的滞回环明显、饱满,表明减震支座具有明显耗能效果。2)不同桩土作用模型在三维渡槽地震动力响应分析中,采用m法和Mindlin方法分别建立桩。土相互作用模型,其余相同,Mindlin方法计算的桩顶剪力和弯矩比m法略小,而桩顶位移略大,这说明两种考虑桩-土作用的方法差别不大。而且,两种方法对上部结构,特别是槽体影响不大,渡槽的前三阶振型均为槽体的运动振型,且频率保持不变,槽身的位移也不变,这也说明对此类结构,桩-土作用的影响对上部结构影响较小。3)计算分析与实验验证通过多种工况的计算,包括不同的地震波及不同地震波峰值,渡槽非线性有限元动力分析成果,无论是位移时程响应特征,在槽墩中部点位移响应的极值,还是桩体水平位响应值,与渡槽拟动力试验结果都比较接近,这在一定程度上验证了拟动力试验的合理性和正确性,也表明采用的计算模型在中、小震条件下,能够比较准确的模拟地震作用下的土-桩-结构-水体系统的地震响应。4)对不同土体类型,SSI对减震效果的影响有隔震支座时,考虑SSI后,槽身和墩顶的水平横向位移略大。土越软,横向位移越大,但最大基底剪力,无论是软基还是刚基,差别不大有智能隔震系统时,考虑SSI后,槽身和墩顶的水平横向位移急剧减小。这种效果可以避免位移过大,损坏水封。有智能隔震系统时,考虑SSI后,最大基底剪力减小了。土越硬,基底剪力越小。考虑SSI后的减隔震控制系统,其控制效果不如不考虑SSI的情况。土越软,控制效果越差。硬土和刚性基础的控制效果相接近。故,对硬土上的基础,可以当作刚性基础处理,对中、软土上的基础,要考虑SSI效果,否者会高估减震的效果。小阻尼隔震支座,对横向漂移、横向速度和最大基底剪力的减小,均比大阻尼隔震支座要好。5)考虑SSI的典型简支桥梁结构隔震(1)碰撞对响应的影响：由于地震波的不同,碰撞可能导致柱子的响应或呈增加趋势,或者呈减小趋势。(2)减震效果：从减震效果看,纵向减震效果良好,柱子的响应减小,减震支座的力-位移滞回曲线明显,但同时明显放大了支座以上梁的纵向瞬时加速度和梁的纵向位移。而横向减震,不仅没有效果,反而响应有所放大。(3)碰撞对减震效果的影响：考虑碰撞,对隔震支座以下部位柱子的纵向隔震影响比不考虑碰撞更有效或接近。但都放大了支座以上梁的纵向位移和加速度。对横向,隔振支座不仅不能减震,反而增加了横向响应,考虑碰撞产生的放大作用更明显。(4)隔震桥梁对基频更接近的地震波,减震效果更好。(5)对同样的隔震支座,不同场地土情况下,土变硬后,隔震桥梁纵向地震力逐渐变大,而墩顶的位移以及中跨面板梁的位移变化不大。6)通过对简支桥梁的脆弱性分析,明确了薄弱环节确实首先在于固定支座,其次是滑动支座和柱子。通过采用隔震支座,可以明显改善桥梁系统的脆弱性。论文的创新点：考虑土-结构相互作用对隔震桥梁的影响,以前的研究模型往往只考虑一个方向,并忽略碰撞的影响。本文采用合理的模型,可考虑两个方向的隔震效果,同时也考虑桥面板碰撞效果的影响。论文的章节安排如下：第一章,绪论。对考虑SSI的减隔震研究及桥梁结构脆弱性分析进行综述。第二章,简支渡槽动力数值模拟建模及减震模拟分析。包括建模及减震分析。第三章,考虑不同桩土作用模型的简支渡槽减震动力分析。包括两种桩土作用的模型建模,和对模型的动力时程分析和反应谱分析比较。第四章,对某渡槽拟动力试验的数值模拟分析。第五章,对不同场地土对智能隔震渡槽的影响进行了分析。第六章,考虑碰撞的简支桥梁在不同场地土中的隔震分析。对典型的三跨简支梁进行了隔震分析,特别考虑了桥面板之间、桥面板与桥台之间碰撞对桥梁隔震的影响。第七章,简支桥梁脆弱性分析,对典型三跨简支梁进行了脆弱性分析,比较了隔震前后的桥梁构件和桥梁系统的脆弱性的变化。第八章,结论与建议更多还原

【Abstract】 Soil-Structural Interaction (SSI) is often ignored in practice on aseismic analysis. This leads to discrepancy between computed result and reality response when rigid foundation is assumed. This assumption is more common for isolated structures because of concept that SSI can be advantageous to structures. In fact, because of flexibility of foundation, SSI may be advantageous or detrimental to isolated structures or controlled structures. The effect of SSI on isolated structures is complex.Present isolated techniques and structural control techniques are getting more and more attractive in civil engineering. In practice, many stuctures are designed or retrofitted by the techniques, especially in bridge engineering. The research on SSI effect is getting deeper. Unfortunately, the research on combination of SSI and structural control is scarce.There is very limited literiture on the topic, in which controvesal conclusions sometimes got drawn. Therefore, further investigation on combination of SSI and structural control is needed. The present research on the combination focuses on rigid shallow foundation, seldom on flexible foundation, with simple mass point model under assumption that earth is elastic half space. In fact, most of bridges are built on pile foundation, one type of flexible foundations.The focus in this paper is on the isolated or hybrid isolated bridge (including aqueduct, a kind of bridge transporting water) with simply support considering SSI subjected to earthquake load.The reseach content is as follow.Chapter1introduces the development of seismic isolated stuctures considering SSI, and development of fragility analysis of bridge.Chapter2focuses on a simply supported aqueduct with isolated bearings. A refined finite element model is established in order to get data which is useful to designer. In the model, beam element is employed to represent pile, spring element is employed to represent SSI, relevant solid elements are used for pier, acqueduct body and water. By this model, dynamic analysis is accomplished. The effect of isolated bearings on structural response under earthquake is investigated.Chapter3uses the same model as in Chapter2. In the analytic model, keeping the superstructure unchanged, two kinds of methods of modeling foundation are applied. One is improved Penzien model, using Mindlin method to determinate spring and dashpot coeffecients. The orther one is m method recommended by the code. The comparison of these two methods is maked.Chapter4simulates the response of a scaled aqueduct model, which undergoed a quasi dynamic test in a large soil box. The analytic model employs the improved Penzien model to model pile-soil interaction.Chapter5studys a hybrid isolated aqueduct or intelligent control aqueduct subjected to earthquake load in different soil profiles. The hybrid isolated device is comprised of ordinary isolated bearing and MR damper, loacated on the top of pier. The control strategy is semi-active control. The influence of different soil profiles on the hybrid isolated aqueduct system is obtained.Chaper6takes a classic three-span simply supported isolated bridge as an example. Dynamic analysis is taken from the model, which considers the pounding between the decks or deck and abutment.The aqueduct aforementioned is also a simply supported bridge, just with different load. The analytic model complexity of bridge is varied according to analysis purposes. The models in Chapter2amd3are complex, but the model in Chapter5is simple. How to develop a reasonable model depends on types of bridge, layout of bridge, what you expect, analysis category et al.In this chapter, in order to perform full nonlinear dynamic time history analysis, a refined model is modeled, which includes some significant factors, such as materal nolinearity, bearing nonlinearity, soil-structure interaction and pounding between decks and deck and abutment. The column is modeled in fiber elements, pounding is modeled in pounding element and deck is modeled in beam elements, which is expected to be elastic. The whole model is not too complex, ortherwise it is unacceptable in fragility analysis in Chapter7.This model here is used to investigate the pounging effect on classic three-span isolated simply supported bridge.Chapter7takes fragility analysis to the aforementioned model in Chapter6. Furthermore, comparison of fragility before-isolated and after-isolated bridge is taken.Fragility is a conditional probability of structure reaching or exceeding a limit state damage under given earthquake intensity (such as PGA or Sa). In this Chapter,10earthquake waves are chosen from five earthquake wave bins,2waves per bin. Then incremental dynamic analysis is performed with0.1g incerement from0.1g to1g. Thus100time history analysis for non-isolated and isolated bridge are gathered respectively. The interested responses, such as column ductility, fixed bearing displacement, expansion bearing displacement et al, can be extracted. The extracted responses are earthquake demand. The relationship between demand and PGA can obtained through regression. Finally, based on limit state damage, fragility curve can be drawn. The system’s fragility can be got based on components fragility curves according reliability theory.The fragilitie of isolated and non-isolated bridge are compared in order to understand the isolation effect.The main conclusions are drawn as follows.For the dynamic response of aqueduct mounted seismic isolated bearingsThe peak dynamic stress and acceleration are mitigated after employing seismic isolated bearings. The effectness of mitigation depends on frequency of the input earthquake wave.For different pile-soil interaction modelsImproved Penzien model method and m method lead to similar analysis result. But m method has more flexible to obtain spring coefficient, which is hard to master. Therefore, improved Penzien method is better.For simulation and testThe responses, including displacement time history, peak displacement of pier, and pile displacement, are close between simulation and test under minor earthquake.For different soil profiles’ effect on the hybrid isolated aqueductThe control effect of hybrid isolation device is less when considering SSI, especially in soft foundation.For classic simply supported bridgeThe displacement, shear force and moment of column are increased or decreased depending on the earthquake wave in horizontal direction when considering pounding. The effectiveness in longitudal direction is good, but is bad in transverse direction. The responses in transverse direction are amplified when isolated device employed considering pounding.For fragility analysisThrough fragility analysis, fixed tranditional bearing is the weaket part, which needs to replace together with expansion bearing. After replacing tranditional bearings with isolated bearings, the fragility of components and system are improved.The highlight of the paper is to investigate pounding, between decks or deck and abutment, effect on the isolated simply supported bridge considering SSI through full nonlinear dynamic analysis.更多还原