基于细观断裂判据的钢管柱与钢梁连接节点超低周疲劳破坏机理与全程滞回模型研究

Severe earthquake usually induces extremely low cycle fatigue (ELCF) and fracture in steel connections with large-scale plasticity, that is prone to cause structural collapse. Considering the limitations of traditional fracture mechanics for dealing with ELCF and fracture prediction, a ductile fracture criterion will be proposed based on micromechanics-based ductile failure theory of metals, which can capture plastic damage mechanism and is applicable to Chinese common used structural steel. The related parameter calibrations will be also conducted. This project plans to study steel beam to tube column connections, and to focus on their component-based ELCF mechanism under severe earthquake. In order to achieve this goal, numerical methodologies introducing micromechanics-based fracture criterion will be developed to be capable of modeling non-continuum deformation, and the connections and components will be tested under monotonic and cyclic loadings. Some design concept and method will then be proposed to delay ductile fracture of the connections. At last, the full-range hysteresis model of the joint will be built comprising ductile fracture as well as post-fracture behavior through experiments and numerical modeling. The following two achievements are expected by the research including development of a new research methodology for earthquake-induced fracture of steel connections, and supply of the scientific proof and technical support in ensuring structural safety of modern steel buildings under severe earthquake.

强震作用极易导致钢结构节点发生具有大尺度塑性特征的超低周疲劳断裂，从而诱发结构体系的倒塌破坏。考虑到传统断裂力学方法在预测超低周疲劳断裂时存在的局限性，本项目以金属延性破坏的细观力学理论为基础，通过宏、细观试验与高精度有限元模拟相结合的手段，建立基于材料塑性损伤机制且适用于国产常用结构钢材的延性断裂判据，并进行参数校准；以钢管柱与钢梁连接节点为研究对象，开发集成细观断裂判据并可模拟裂后非连续变形效应的有限元数值算法，结合节点及其组件的单调与往复加载试验，研究强震下基于组件相关的节点超低周疲劳失效机理；提出增强节点超低周疲劳断裂韧性的设计概念与方法；在大尺度节点试验全程性态观测与数值模拟的基础上构建考虑超低周疲劳断裂及其裂后行为的节点滞回模型。本项目成果不仅能为地震导致的钢结构节点断裂研究提供新的思路，而且还能为保障现代钢结构体系在强震下的安全性提供科学依据和技术支撑。

强震作用极易导致钢结构节点发生具有大尺度塑性特征的超低周疲劳断裂，从而诱发结构体系的倒塌破坏。考虑到传统断裂力学方法在预测超低周疲劳断裂时存在的局限性，本项目以金属延性破坏的细观力学理论为基础，通过宏、细观试验与高精度有限元模拟相结合的手段，建立了基于材料塑性损伤机制且适用于国产常用结构钢材的延性断裂判据，并进行了参数校准；以典型钢结构连接节点为研究对象，开发了集成细观断裂判据并可模拟裂后非连续变形效应的有限元数值算法，结合节点及其组件的单调与往复加载试验，研究了强震下基于组件相关的节点延性断裂和超低周疲劳失效机理；提出了增强节点断裂韧性的设计概念与方法；在大尺度节点试验全程性态观测与数值模拟的基础上构建了考虑延性断裂及其裂后行为的节点滞回模型。本项目成果不仅为地震导致的钢结构节点断裂研究提供了新的思路，而且还为保障现代钢结构体系在强震下的安全性提供了科学依据和技术支撑。