混凝土桥梁结构D区的弹塑性拉压杆模型理论研究

The strut-and-tie model (STM) has been adopted as a preferred methodology for the design of disturbed regions (D-regions) in American and European concrete bridge design specifications. However, the existing “Elastic Strut-and-Tie Model” is not sufficient in cracking prediction and capacity assessment of D-regions. This project is devoted to develop an advanced “Elasto-Plastic Strut-and-Tie Model”, for the purpose of capturing the full elastic and inelastic response of the structural concrete D-regions. First, a new criterion by minimizing complementary energy will be developed for the adaptive generation of the STMs, which is intended to overcome the problem of non-uniqueness of the model. After that, the elasto-plastic strut-and-tie modelling technique will be extended for the nonlinear analysis of structural concrete D-regions, allowing a consistent study of the load-transfer mechanisms throughout the loading process. At the same time, an appropriate bond stress-slip relation under complex stress status will be incorporated realistically to derive a method for crack width analysis in reinforced concrete D-regions. Furthermore, experimental tests including reinforced concrete panels and pier caps will be conducted, for realistically studying the load-carrying mechanisms in these structural members and validating the proposed theoretical models. In a word, this study will greatly facilitate the limit state design of various D-regions, and will provide effective techniques for controlling structural cracking in concrete bridge D-regions, such as post-tensioned anchorage zones and bridge pier caps.

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，现有的“弹性拉压杆模型”方法还不能较好回答D区裂缝预测和承载能力计算问题。本课题致力于探索一种新的“弹塑性拉压杆模型”方法，以期准确分析混凝土结构D区的弹塑性受力行为。首先，拟提出基于“余能驻值条件”的拉压杆模型自适应构形新准则，可望攻克拉压杆模型“构形不唯一性”难题。接着，拟将弹塑性拉压杆模型拓展至D区非线性分析，以期完整揭示D区内部传力机制的全过程演变规律。同时，拟引入复杂应力状态下钢筋与混凝土的黏结本构关系，探讨基于黏结-滑移理论的D区裂缝宽度计算方法。最后，还将开展薄板劈裂试验和桥墩盖梁模型试验，研究锚固区集中力扩散机制和小剪跨区桁-拱受力机制的演变规律，并验证所提出的理论模型。研究成果有助于混凝土桥梁结构D区极限状态设计理论框架的建立，并可望解决预应力锚固区、桥墩盖梁等D区频发的结构性裂缝病害。

当前，重大工程结构高安全性与高耐久性的需求，对混凝土桥梁的结构分析理论提出了新的发展要求，亟待进行精细化分析模型方面的基础理论研究。在混凝土桥梁的应力扰动区（D区，截面应变不符合平截面假定的区域），普遍面临着裂缝病害频发而设计依据不足的技术挑战。现有的“弹性拉压杆模型”方法还不能较好地回答D区裂缝预测和承载能力计算问题，本项目致力于探索一种新的“弹塑性拉压杆模型”方法。本项目取得的主要成果为：（1）发展了钢筋混凝土结构受剪分析的修正变角桁架模型理论；（2）通过引入拉压杆模型材料非线性和余能驻值原理，建立了基于自适应构形方法的弹塑性拉压杆模型理论（EPSTM），实现了模型构形参数随着结构“弹性-开裂-塑性-破坏”全过程受力状态的自适应演变；（3）在EPSTM的基础上，引入复杂应力状态下钢筋与混凝土的黏结本构关系，建立了基于黏结-滑移理论的典型D区裂缝宽度计算方法。研究工作为解决混凝土桥梁应力扰动区频发的结构性裂缝病害提供了设计理论支撑，部分成果纳入了新修编的我国混凝土桥梁设计规范。