预制装配式桥墩在地震作用下存在墩身损伤集中、整体耗能不足和抗震机理不明确等问题，阻碍了其在中高地震区的推广。为提高预制装配桥墩在中高地震区的服役能力，减少桥墩结构地震损伤及修复成本，本文以装配式钢管混凝土Y型（CFST-Y）桥墩及其自复位桥墩（含耗能装置）为研究对象。利用OpenSees软件建立了两种装配式钢管混凝土Y型桥墩纤维模型，对两种桥墩的抗震性能及其多级抗震机理进行了研究，并对两种桥墩的结构形式和设计参数进行优化分析。主要研究内容如下：

（1）采用非线性静力推覆分析法，研究了装配式CFST-Y型桥墩在常遇地震、罕遇地震和极罕遇地震作用下的抗震性能。本文通过理论推导的桥墩抗侧刚度公式，开展了固结、支撑铰接和自由铰接三种类型CFST-Y型桥墩的有限元分析，研究了桥墩-主梁连接形式、结构几何尺寸和支座剪切刚度对桥墩抗震性能的影响。结果表明：桥墩-主梁连接形式是影响桥墩侧向刚度和结构延性的主要因素。桥墩的肢高、柱高决定了其塑性铰的发展，通过肢底、柱底的多塑性铰可实现不同地震作用下的多级耗能目标。

（2）基于三种类型CFST-Y型桥墩的结构形式，提出一种有效利用桥墩构件局部延性的多级耗能抗震设计方法。采用拟静力分析法对三种类型桥墩的滞回性能进行评价，对比分析了桥墩-主梁连接形式、结构几何尺寸对桥墩耗能的影响。基于自由铰接桥墩耗能的形式，提出了以CFST-Y型桥墩的肢部构件为“结构保险丝”的耗能理念，建议在桥墩上采用多塑性铰的多级耗能机制。

（3）采用拟静力分析法，研究了装配式CFST-Y型自复位桥墩（含内置、外置耗能装置）的抗震性能。本文选取内置耗能钢筋数量、初始预应力水平、恒载轴压比以及外置耗能钢筋的布置角度、截面贡献率等关键设计参数，研究了耗能装置的主要控制参数对桥墩抗震性能的影响，并给出合理的取值建议。在此基础上对装配式CFST-Y型自复位桥墩（含外置耗能钢筋）进行非线性时程分析，发现含外置耗能钢筋的装配式CFST-Y型自复位桥墩在不同地震等级下可以很好的实现分级耗能。

The prefabricated assembled piers have problems of concentrated pier damage, insufficient overall energy consumption and unclear seismic mechanisms under earthquake action, which hinder their promotion in medium and high seismic zones. In order to improve the serviceability of prefabricated assembled piers in medium and high seismic zones and to reduce the seismic damage and repair costs of bridge pier structures, this paper takes assembled steel pipe concrete Y-type (CFST-Y) piers and their self-resetting piers (including energy-consuming devices) as the object of study. Two fibre models of assembled tubular concrete Y-shaped bridge piers were established using OpenSees software, the seismic performance of the two piers and their multi-stage seismic mechanism were investigated, and the structural forms and design parameters of the two piers were optimised and analysed. The main research contents are as follows:

(1) The seismic performance of assembled CFST-Y piers under normal, rare and very rare earthquakes was investigated using non-linear static pushover analysis. In this paper, finite element analysis of three types of CFST-Y piers, namely solid, braced hinged and free hinged, is carried out by means of theoretically derived lateral stiffness equations for bridge piers, and the effects of pier-deck connection form, structural geometry and support shear stiffness on the seismic performance of the piers are investigated. The results show that the pier-deck connection is the main factor affecting the lateral stiffness and structural ductility of the bridge pier. The limb height and column height of the piers determine the development of their plastic hinges. The objective of energy dissipation under different seismic effects can be achieved by means of multiple plastic hinges at the bottom of the limbs and the bottom of the columns.

(2) Based on the structural forms of three types of CFST-Y piers, a multi-stage energy dissipation seismic design method that effectively utilises the local ductility of the bridge pier members is proposed. The hysteresis performance of three types of bridge piers is evaluated

using the proposed static analysis method, and the effects of pier-deck connection form and structural geometry on the energy dissipation of bridge piers are compared and analysed. Based on the form of energy dissipation in freely articulated piers, a multi-stage energy dissipation concept with CFST-Y pier limbs as the "structural fuse" is proposed, and a multi-stage energy dissipation mechanism with multiple plastic hinges is suggested for the piers.

(3) The seismic performance of the assembled CFST-Y type (with built-in and external energy dissipation devices) self-resetting piers was studied using the proposed static analysis method. In this paper, key design parameters such as the number of built-in energy dissipating bars, initial prestressing level, gravity axial compression ratio and the arrangement angle and section contribution rate of external energy dissipating bars are selected to study the influence of the main control parameters of energy dissipating devices on the seismic performance of bridge piers, and reasonable recommendations are given. On this basis, a non-linear time analysis of the assembled CFST-Y (with external energy dissipating reinforcement) self-reversible piers was carried out and it was found that the assembled CFST-Y self-reversible piers with external energy dissipating reinforcement could achieve good graded energy dissipation under different seismic levels.

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