【作者】 王震；

【导师】 王景全； 赵国堂；

【作者基本信息】 东南大学 ， 桥梁与隧道工程， 2018， 博士

【摘要】 预应力预制拼装桥墩具有快速施工优势,可以为新材料、新技术的引入与推广提供实践平台,但因抗震性能不明确及抗震设计方法不完善、针对自复位特性的研究不足、耗能能力需要专门设计、预应力损失对脚趾压碎敏感等原因,制约了其在中高烈度区桥梁中的应用。超高性能混凝土(Ultra-high performance concrete,UHPC)具有高强度、高延性、高耐久性的材料特点,用于土木工程,可以实现结构在严酷条件下的高可靠性、多灾变作用下的高工恢复性能、长期使用的高耐久性、全寿命周期内的高环保性,用于制作预制拼装桥墩,一方面,可以直接利用材料本身优异的力学特性降低桥墩脚趾处在地震中的损伤以及提高耗能能力;另一方面,可以将韧性抗震理念融入预制拼装桥墩中进行结构形式创新,通过合理的构造措施实现震后桥墩功能的快速恢复。因此,本文以预制拼装UHPC空心墩作为研究对象,通过试验、有限元和理论研究等手段研究其抗震性能特别是自复位能力;基于试验、有限元及理论研究结果,建立设计参数与抗震性能目标之间的关系,并基于预期性能目标,在设计过程中确定出合理的设计参数取值,实现性能化抗震设计。具体研究内容和成果如下:(1)自复位预制拼装UHPC空心桥墩大比例尺拟静力试验研究利用UHPC制作预制拼装空心墩,节段之间采用无粘结后张预应力筋拼装成整体,利用底接缝设置有无粘结段的耗能钢筋增加耗能能力,研究参数包括后张预应力大小及耗能钢筋用量。提出一种新型的震损可恢复功能预制UHPC空心墩结构形式,通过试验检验可更换UHPC板与桥墩底节段之间的连接以及可更换耗能钢棒与螺纹接头之间的连接是否能实现预期功能,研究参数包括后张预应力大小及可更换耗能钢棒用量;通过对修复后桥墩的重新加载,研究修复后桥墩的抗震性能。(2)基于等效塑性铰模型的预制拼装UHPC空心墩抗震变形能力研究通过理论推导建立耗能钢筋和后张预应力筋的等效材料本构关系,建立满足平截面假定的纤维截面模型进行截面分析,然后基于等效塑性铰模型,计算出预制拼装UHPC空心墩的水平力-位移曲线,并与试验结果进行比较。利用建议模型进行参数分析,研究设计参数对预制拼装UHPC空心墩抗震变形能力的影响。基于参数分析结果,通过回归分析得到了关于有效刚度的简化计算公式。(3)基于纤维单元的预制拼装UHPC空心墩耗能与自复位能力研究基于OpenSees计算平台,利用耗能钢筋和无粘结后张预应力筋等效应力-应变关系,建立满足平截面假定的等效纤维截面用于模拟底接缝,利用等效塑性铰长度考虑钢筋和混凝土之间的粘结滑移,并在有效刚度的计算中计入剪切变形的影响。利用拟静力试验结果对有限元模型进行验证。基于有限元模型,研究设计参数对预制拼装UHPC空心墩耗能与自复位能力的影响。(4)预制拼装UHPC空心墩自复位能力设计准则首先通过机理分析,确定出残余位移与水平位移最大值和自复位系数两个影响因素的定性关系,然后基于拟静力结果,得到残余位移角关于自复位系数和水平位移角最大值的定量计算公式,并利用非线性动力时程分析结果,验证了残余位移角定量计算公式在控制地震动激励下残余位移角的有效性,最后利用残余位移角的定量计算公式,得到了预制拼装UHPC空心墩在不同抗震设防水准下自复位系数的限值,用于指导自复位能力设计。(5)基于理想旗帜型模型的预制拼装UHPC空心墩滞回性能研究通过理论分析和参数讨论,建立了理想旗帜型模型关键参数与水平力-位移骨架曲线中屈服点和峰值点之间的联系,通过建立关于屈服点和峰值点的解析计算方法,得到理想旗帜型模型关键参数。利用拟静力试验结果,对关键参数的解析方法进行试验验证。分别基于有限元模型和由解析方法确定出关键参数的理想旗帜型模型进行动力时程分析,比较得到的水平位移最大值和累积耗散能量最大值两个指标,评价由解析方法确定出关键参数的理想旗帜型模型在对预制拼装UHPC空心墩进行动力时程分析时的适用性。(6)基于性能的预制拼装UHPC空心墩后张预应力可行域研究首先介绍基于“残余位移可控”、“接缝抗剪需求”和“大震不倒”三个方面的性能需求确定出后张预应力上下限取值的基本思路,然后基于极限状态解析计算结果,建立后张预应力上下限的解析计算方法,确定出后张预应力的可行域。基于后张预应力上下限的解析计算方法,研究设计参数对后张预应力可行域的影响。通过讨论极限状态对应的底接缝处截面受压区高度的取值对后张预应力可行域的影响,给出了后张预应力可行域的无迭代简化计算方法。(7)考虑变形与自复位能力的预制拼装UHPC空心墩地震易损性研究从实际工程中选择出现浇钢筋混凝土桥墩,通过5个等效原则设计出预制拼装UHPC空心墩。根据既有研究建议方法,分别确定出基于位移延性系数和残余位移角的损伤状态量化标准。据此量化标准处理现浇钢筋混凝土桥墩和预制拼装UHPC空心墩在远场、近场无脉冲和近场脉冲三种不同类型地震动下的增量动力分析结果,建立不同类型地震动下两种结构形式桥墩的概率地震需求模型,得到相应的易损性曲线,完成对现浇钢筋混凝土桥墩和预制拼装UHPC空心墩抗震性能的评估。更多还原

【Abstract】 Precast segmental bridge piers have fast construction speed and provide a practice platform for introduction and promotion of new material and technology.Due to uncertainty of seismic performance and imperfection of seismic design,insufficient research on self-centering,required additional design of energy dissipation capacity,and prestressing loss sensitive to toe crushing,the bridge piers are limited to bridges in moderate and high seismicity areas.Due to its high strength,superior ductility and enhanced durability,ultra-high performance concrete(UHPC)is applied in civil engineering to ensure structures with high reliability in limit state,high resilience under the disaster action,high durability within long service time,and high environmental friendliness over the life cycle.Specially,when UHPC is used to fabricate precast segmental bridge piers,on one hand,the material is used to fabricate precast segmental hollow bridge piers to reduce damage at column toe and improve energy dissipation in earthquake shock;on the other hand,UHPC is used to develop a novel structural type of precast segmental bridge piers,which can rapidly recover their function after earthquake by adopting reasonable details considering a new concept of earthquake resilience.Therefore,precast segmental UHPC hollow bridge piers are selected as research objective,and experimental,numerical and theoretical researches are conducted to study their seismic performance.The relationship between design parameters and seismic performance objective is established based on the results of those researches.The design parameters can be determined in design process according to the expected seismic performance objective,which can realize performance-based seismic design.The detailed research contents and results are listed as follows:(1)Large-scale cyclic loading experimental research on self-centering precast segmental UHPC hollow bridge piersUHPC is used to fabricate precast segments.Separated segments are connected to a whole by using unbonded post-tensioning tendons.Energy dissipation capacity is enhanced by using energy dissipation(ED)bars with unbonded length at the base joint.Trial parameters include post-tensioning force level and amount of ED bars.A new earthquake resilient UHPC bridge pier is proposed and fabricated with precast segmental construction.The experimental research is used to examine the connection between replaceable UHPC plates and base segment and the connection between replaceable ED steel rods and the corresponding threaded ends.Experimental parameters include post-tensioning force level and amount of replaceable ED steel rods.Cyclic loading were conducted on repaired bridge piers to study their seismic performance.(2)Seismic deformation capacity of precast segmental UHPC hollow bridge piers based on the equivalent plastic hinge modelThe equivalent constitutive relationships of the post-tensioning tendons and the ED bars are analytically derived to meet the plane section assumption for sectional analysis.Based on the equivalent plastic hinge model,the lateral force-displacement curve is calculated and compared with experimental results.Using the proposed model,a parametric study is conducted to investigate the effects of nine main design parameters on the seismic deformation capacity of the bridge pier.Based on the results of the parametric study,a simplified formula for the effective stiffness is developed through regressive analysis.(3)Energy dissipation and self-centering capacities of precast segmental UHPC hollow bridge piers based on fiber elementBased on OpenSees calculation platform,the equivalent fiber section,meeting the plane section assumption,is established to simulate the base joint by using the equivalent constitutive relationships of the post-tensioning tendons and the ED bars.The equivalent plastic hinge length is used to consider the bond-slip between rebar and concrete,and the effective stiffness is calculated to take the effect of shear deformation into account.The finite element model is verified by the results of cyclic loading test.The effects of design parameters on energy dissipation and self-centering capacities are studies based on the finite element model.(4)Design criterion for self-centering capacity of precast segmental UHPC bridge piersAt first,the qualitative relationship,between the residual displacement and two influencing factors including lateral displacement maximum value and self-centering coefficient,is determined by mechanism analysis.Then,the quantitative calculation formula of residual drift is obtained and composed of the maximum of lateral displacement and the self-centering coefficient based on the results of pseudo-static loading test The results of nonlinear dynamic time history analysis are used to verify the quantitative calculation formula of residual drift under seismic excitation.Eventually,using the quantitative calculation formula of residual drift,limit values of self-centering coefficient are obtained at different seismic design levels.The limit values can be used to guild the design of self-centering capacity for precast segmental UHPC hollow pier.(5)Hysteretic behavior of precast segmental UHPC bridge piers based on the idealized flag-shaped modelThrough theoretical and parametric analysis,the idealized flag-shaped hysteretic model parameters are deemed to be dependent on the yield point and the peak point of the lateral force-displacement skeleton curve.Key parameters of the idealized flag-shaped hysteretic model are obtained by establishment of the analytic calculation method about the yield point and the peak point.The analytical calculation method of those key parameters is verified by the pseudo-static test results.Dynamic time history analysis is conducted respectively based on the finite element model and the idealized flag-shaped hysteretic model with parameters determined by the proposed method.Based on the two models,the two indicators including lateral displacement maximum value and cumulative energy dissipation maximum value are calculated compared to evaluate the applicability of the idealized flag-shaped hysteretic model with parameters determined by the proposed method in the dynamic time history analysis.(6)Feasible region of post-tensioning force for precast segmental UHPC hollow bridge piers based on performanceFirstly,the basic idea is introduced that the upper and lower limit values of post-tensioning force is determined by three performance requirements including "residual displacement controlled","joint shear demand" and "no collapsing with strong earthquake".Then,the analytical calculation method for the upper and lower limit values of post-tensioning force is established based on the analytical calculation results of the limit state to determine the feasible region of post-tensioning force.The influence of design parameters on the feasible region of post-tensioning force is studied based on the proposed analytical calculation method for post-tensioned prestressed upper and lower limits.Through discussion about the influence of the compressive zone height of the bottom section at the limit state on the feasible region,a non-iteration simplified calculation is proposed for the feasible region of post-tensioning force.(7)Seismic fragility of precast segmental UHPC hollow bridge piers considering deformation and self-centering capacitesA reinforced concrete bridge pier is selected from practical projects and regarded as a reference to design a precast segmental UHPC hollow bridge pier through five equivalent design principles.Due to the proposed method by existing research,a quantitative standard,expressed by displacement ductility factor and residual drift,respectively,is determined for bridge piers at damage states.According to the quantitative standard,the results of increment dynamic analysis are dealt with for the two bridge piers with different structural types subjected to three different types of ground motions including far field,near field with no pulse and pulse.For the two bridge piers with different structural types under different types of ground motions,the probability seismic demand models are established,and the fragility curves are obtained to evaluate the seismic performance of the two bridge piers.更多还原