混凝土桥梁后张锚固区的力流传递及空间拉压杆模型

The strut-and-tie model (STM) has been adopted as a preferred methodology for the design of discontinuity regions (D-regions) in American and European concrete bridge design specifications. However, this method can be hampered by uncertainties in the proportioning of appropriate STMs, especially in the design of post-tensioned anchorage zones with complex configurations. So that, alternative approaches are needed. Upon following up the frontier researches in this respect, a study is to be carried out for tracing a force-flow path which contains a constant quantity of load, referred as isoplethic load paths. To this end, a comprehensive study is therefore proposed. First, quantitative criteria for defining an isoplethic load path need to be established. After that, the shape of the load paths will be described through two ways. One way is to derive analytical models for determining the load paths in anchorage zones with some specific occasions. The other way is to develop a computer-based design tool for the automatic generation of the load paths in anchorage zones with more general cases, accounting for elasto-plastic characteristics of concrete material. Furthermore, for the end anchorage zones of Tee or box sections, the spatial stress field of the region will be converted to an isoplethic load path featuring in simplicity, and then quantitative spatial strut-and-tie models will be finally developed. In addition to the above analytical studies, experimental tests including reinforced concrete and photoelastic specimens will be conducted to validate the proposed theoretical models. In a word, this study is important to revealing the load transfer mechanisms in post-tensioned anchorage zones, and will greatly facilitate the advancement of design theories for all types of D-regions in structural concrete.

拉压杆模型(STM)是欧美混凝土桥梁规范中推荐的应力扰动区(D区)设计方法，然而现有构形方法均存在一定经验性和不确定性。后张锚固区因受力复杂，需更加理性的构形方法。本课题在跟踪D区前沿研究基础上，探索一种表达力流传递的新模型:"等值力流线"模型。主要研究内容为：(1)等值力流线的定量化准则；(2)针对几种典型受力情形的平板锚固区，给出等值力流线的数学解析表达；(3)针对一般受力情形的锚固区，通过数值算法实现力流线的计算机自动生成；(4)针对T形、箱形类带有翼缘的后张锚固区，研究将空间应力场转换成由"等值力流线"表达的简约化的空间传力路径，实现空间拉压杆模型的定量化构建；(5) 考虑混凝土的弹塑性发展，研究基于力流线的锚固区抗裂设计方法。研究手段包括理论解析、数值分析和混凝土及光弹模型试验。研究成果有助于深入揭示混凝土桥梁后张锚固区的传力机理，促进一般D区拉压杆模型设计理论和方法的完善。

拉压杆模型(STM)是欧美混凝土桥梁规范中推荐的应力扰动区(D区)设计方法，然而，现有构形方法均存在一定经验性和随意性，对于受力复杂的后张锚固区则需更加理性的构形方法。基于结构内部力流传力机制，本项目系统建立了混凝土结构D区的 “力流模型设计理论和方法”。取得的主要研究进展为：（1）系统建立了典型D区力流模型理论，一方面针对后张预应力锚固区等典型D区，推导得到力流线的数学解析表达式，美国科技媒体以“东南大学为土木工程领域增加了一项新发现”为题进行报道；另一方面，针对一般力学边界条件，建立了力流线自动搜索算法，并从平面受力问题拓展至空间受力问题，实现空间拉压杆模型的定量化构建。（2）系统开展了平板锚固区的混凝土模型及光弹模型试验，验证了所提出的力流模型理论。（3）基于力流模型理论，建立了后张预应力锚固区、桥墩盖梁、支座盖梁等典型D区的实用设计方法，相关成果纳入了我国《钢筋混凝土及预应力混凝土桥梁设计规范》（2016年总校稿）之中，对于提高我国桥梁结构关键部位的安全性和抗裂性，具有重要的工程价值。