加筋土整体式桥台地震响应数值分析

发布时间：2018-07-20 16:18

【摘要】：传统简支桥梁的支座和伸缩缝要经常维修和更换,全生命周期成本高,且抗震性能差。整体式桥的桥身与桥台刚性连结,取消了支座和伸缩缝,具有很好的抗震性能。但是目前对全高整体式桥动力响应的研究较少,还没有关于整体式桥台后动土压力计算的规范。针对整体式桥台后的回填土会产生过大土压力和沉降变形问题,学者提出加筋土整体式桥的概念,但对其地震响应还很不清楚。本文在FLAC2D上开发能反映土体循环荷载下滞回性的非线性滞回模型。对单跨全高整体式桥的动力响应进行数值计算及参数分析。然后对加筋土整体式桥的动力响应进行模拟计算与参数分析。具体内容如下:(1)应用FISH语言二次开发出反映土体动力滞回性、压硬性和非线性的本构模型,用土柱单元对该模型进行数值验证。利用该模型对基坑的存在对场地地震响应的影响这一具有工程意义的问题进行数值模拟。(2)对单跨全高整体式桥的动力响应进行数值模拟,结果表明,桥身和桥台的刚性连结会显著影响桥台的动力响应。现有桥台抗震设计规范中所采用M-O方法不能正确反映整体式桥台后水平土压力的分布形式与合力作用点位置,偏不安全。参数分析表明:地震峰值加速度增大和桥梁跨度增加使桥身惯性力增加,导致水平土压力、顶部弯矩、顶部水平位移等增大;桥台高度增加,桥台的变形模式由转动变为弯曲;设置可压缩材料后,水平土压力分布变均匀,最大土压力显著减小,但是桥台产生更大的弯矩。(3)对加筋土整体式桥台进行数值模拟,结果表明:传统支座桥台、加筋土传统支座桥台、整体式桥台、加筋土整体式桥台等四种桥台的抗震性能依次提高。0.4m厚的加筋土整体式桥台相较于1m厚的整体式桥台,位移不增加、自振频率不变、弯矩显著降低,且所需钢筋明显减少。桥台厚度较小或高度较大时,加筋土整体式桥台具有显著优势。(4)对加筋土整体式桥台的参数分析表明:桥台高度较大时,加筋土能显著减小桥台的弯矩和位移;筋材的刚度和长度超出一定数值后,对桥台抗震性能的提高帮助不大;筋材的层间距对桥台的地震反应几乎没有影响。(5)针对地表残余沉降突变问题进行了优化设计,结果表明:上部长度大而下部长度小的筋材布置能够很好地解决桥台后地表的沉降突变问题。
[Abstract]:The support and expansion joints of traditional simply supported bridges should be maintained and replaced frequently, the whole life cycle cost is high, and the seismic performance is poor. The rigid connection between the body and abutment of the monolithic bridge eliminates the support and expansion joint and has good seismic performance. However, there are few researches on the dynamic response of the full-height monolithic bridge, and there is no code for calculating the dynamic earth pressure behind the monolithic abutment. In view of the problem that the backfill behind the integral abutment will cause excessive earth pressure and settlement deformation, the concept of reinforced earth integral bridge is put forward, but the seismic response of the bridge is not clear. In this paper, a nonlinear hysteretic model is developed on FLAC2D to reflect the hysteresis behavior of soil under cyclic loading. The dynamic response of a single-span full-height integral bridge is numerically calculated and its parameters are analyzed. Then the dynamic response of reinforced earth integral bridge is simulated and analyzed. The main contents are as follows: (1) the constitutive model which reflects the dynamic hysteresis, compression and nonlinearity of soil is developed by using fish language, and the model is verified numerically by soil column element. The model is used to simulate the influence of the foundation pit on the seismic response of the site. (2) the dynamic response of the single-span full-height integral bridge is numerically simulated, and the results show that, Rigid connections between the abutment and the abutment will significantly affect the dynamic response of the abutment. The M-O method used in the existing seismic design code of abutment can not correctly reflect the distribution form of horizontal earth pressure behind integral abutment and the position of working point of resultant force, which is not safe. The parameter analysis shows that the increase of seismic peak acceleration and the increase of bridge span increase the inertia force of bridge body, resulting in the increase of horizontal earth pressure, bending moment at the top and horizontal displacement at the top, and the deformation mode of abutment changes from rotation to bending when the height of abutment increases. With compressible materials, the horizontal earth pressure distribution becomes uniform, the maximum earth pressure decreases significantly, but the abutment produces greater bending moment. (3) numerical simulation of the reinforced earth integral abutment shows that: traditional abutment, The seismic behavior of the four abutments, traditional supported abutment, monolithic abutment and monolithic abutment with reinforced earth, are improved in turn. Compared with the monolithic abutment with a thickness of 1m m, the displacement of the abutment is not increased, and the natural vibration frequency is not changed. The bending moment is significantly reduced and the reinforcement required is obviously reduced. When the abutment thickness is small or the height is larger, the reinforced earth integral abutment has significant advantages. (4) the parameter analysis of the reinforced earth integral abutment shows that the reinforced soil can significantly reduce the bending moment and displacement of abutment when the abutment height is higher; When the stiffness and length of steel bar exceed a certain value, the improvement of abutment seismic performance is not helpful, and the interval between layers of reinforcement material has little effect on the seismic response of abutment. (5) the optimization design is carried out to solve the catastrophe problem of surface residual settlement. The results show that the arrangement of steel bars with large upper length and small lower length can solve the problem of ground subsidence catastrophe behind abutment.
【学位授予单位】：清华大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U442.55

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