混合配束节段预制梁密齿配筋胶接缝的抗剪性能试验研究

Epoxy joints of the precast segmental girders are the key location under load. Two new trendy designs using hybrid tendons with internal bonded tendons and external unbonded tendons and multiple reinforced shear keys become increasing popular. However, up to now, the studies on the shear performance of the precast segmental girders are very scare when both design techniques described above are adopted. The purpose of this project is to learn the shear performances through experimental investigation, numerical simulation and theories analyzes. The main study contents include three aspects: the first focuses on the study on behaviors of epoxy resin joints under pure shear or shear-bending load. The entire process of structural behaviors such as cracks appearance, development, and eventually failure will be given in details. Final failure modes and characteres will also be presented considering the combination of different effect factors. The second concentrates on the numerical simulation calculation method based on the tension, compression and adhesive constitutive model of the concrete-epoxy-concrete joint. An element with a test attribution will be developed. And a step by step failure analyze will be built to reveal the transfer mechanism of epoxy joints. The third is to obtain the fracture mechanics character of the concrete - epoxy - concrete joints and determine the stress intensity factors ( K ) and the fracture energy ( G ) based on the existing test. And then, according to the macroscopic mechanics characters observed in the pure shear and bending-shear test, several different fracture mechanics analysis models are developed. Furthermore, the practical formulations are proposed for the shear capacity calculation of epoxy joint. The experimental and theoretical results developed in this project would have important effect on designing epoxy joints with reinforced shear keys and hybrid tendons and improving the process of accelerated bridge construction.

胶接缝是节段预制梁的关键受力部位，体内体外混合配束和密齿配筋是节段预制梁设计方法的新趋势，但针对同时采用这两种设计方法后节段预制梁胶接缝的抗剪性能研究非常少。本项目将通过试验研究、数值模拟和理论分析三种手段，研究节段预制梁采用体内体外混合配束和密齿配筋两种设计形式后，胶接缝在直剪和弯剪荷载作用下裂缝出现、发展直至破坏的全过程结构行为，明确各种因素组合下胶接缝的破坏模式和特征；然后基于胶接缝的拉、压及粘结本构模型，开发新的单元特性，建立反映胶接缝渐进破坏全过程的数值模拟方法，揭示胶接缝的传力机理；研究胶接缝断裂力学特性，确定应力强度因子K和能量释放率G，并依据胶接缝在直剪和弯剪荷载作用下的宏观力学特征，建立不同阶段断裂力学分析模型，提出胶接缝抗剪承载力实用计算公式。研究成果对节段预制梁胶接缝的设计与推进桥梁快速化施工具有重要科学意义。

胶接缝是节段预制梁的关键受力部位，体内体外混合配束和密齿配筋是节段预制梁设计方法的新趋势，但针对同时采用这两种设计方法后节段预制梁胶接缝的抗剪性能研究非常少。本项目围绕体内体外预应力混合配束加密齿配筋的抗剪性能展开硏究,取得了以下研究成果:(1)开展了混合配束节段预制梁密齿配筋胶接缝直剪荷载作用下的结构行为研究,探明了齿深、齿目、齿距、配筋、体内预应力及究键齿的角度等关键参数对键齿胶接缝抗剪性能的影响规律,并根据胶接缝的传力机制，依据莫尔－库仑摩擦破坏准则，并结合 AASHTO 规范与Buyukozturk 的试验研究成果，提出了预测胶接缝配筋剪力键直剪承载力的抗剪承载力计算公式；(2)开展了混合配束节段预制梁密齿配筋胶接缝弯剪荷载作用下的结构行为研究，通过节段预制拼装箱梁进行极限承载力试验得到了体内体外不同配束比下与不同加载模式下，节段预制箱梁的变形特点、裂缝分布特征及破坏模式。其次，基于截面法计算理论理论，提出适用于不同配束比的节段预制箱梁的抗剪承载力计算建议公式；(3)开展了混合配束节段预制梁密齿配筋胶接缝传力机理数值模拟研究，结合之前所做试验结果，收集混凝土—环氧树脂—混凝土胶接缝的数值模拟资料和文献，选择合适的单元、构造形函数，采用混凝土塑性损伤模型，为单元定义本构关系和破坏准则。依据试验模型尺寸建立有限元模型，胶接缝选择开发的单元模拟，进行从弹性-开裂-破坏的全过程模拟，并将试验数据和数据模拟数据进行比较分析，揭示胶接缝在直剪和弯剪作用下的渐进破坏过程和传力机理。（4）开展混合配束节段预制梁密齿配筋胶接缝抗剪承载力实用计算公式探索，通过实验与有限元结合的方法，通过数值仿真模拟，建立节段箱梁纯弯段标准节段的有限元模型，并根据有限元模型弹性应力分析和拓扑优化分析结果，建立节段箱梁纯弯段标准节段的拉压杆模型并进行验证，定量确定了节段边缘的竖向拉力和腹板中部水平拉力的大小，提出了节段箱梁胶接缝边缘竖向配筋以及腹板水平配筋的计算方法和公式。在此基础上，将该方法推广到弯剪区段，建立了弯剪区段的节段梁边缘配筋的拉压杆模型。最后利用本文推荐的拉压杆模型，对标准节段胶接缝接缝边缘竖向配筋及腹板水平配筋进行校核，并给出相应的配筋建议。