钢筋混凝土动态粘结-滑移关系及其结构抗连续倒塌性能影响研究

Progressive collapse attracts more and more attentions from both academic and engineering communities after vicious collapses of a number of high-rise buildings (such as collapse of WTC twin towers in 911 event) caused by localised damage due to accidental loads. In the most of existing studies regarding reinforced concrete (RC) framed structures, dynamic effect, induced by damage propagation and internal force redistribution after initial localised damage, has not been investigated in detail when evaluating the progressive collapse resistance. As the start of this proposed project, the experimental study on resistance mechanisms and failure modes dominating the dynamic bond-slip relationship between steel reinforcement and concrete is to be performed, while a theoretical model is to be proposed to quantify the bond resistance against slip when analysing structural progressive collapse resistance. Subsequently, based on in-house nonlinear finite element programs and energy equivalence theory, the effect of dynamic bond-slip relationship to ductility, stiffness and load-bearing capacity of different structural scales, i.e. the whole RC frame, beam-column sub-assemblages and beam-column joints, will be explored to find out the dominant resistance mechanisms, failure modes and dynamic deformation characteristics under the scenario of progressive collapse. Finally, a generalised DIF (dynamic increase factor) model for the bond-slip relationship is to be proposed to illustrate the evolution of structural dynamic resistance at different structural scales during such collapses with severe deformation and damage dominated by various resistance mechanisms. To better evaluate the dynamic resistance of RC framed structures against progressive collapse, this project will provide theoretical basis to improve the practical design and analysis approach of the design code of building structures in our country.

因偶然载荷作用造成建筑结构局部破坏，导致诸多恶性倒塌事件（如“911”世贸大厦倒塌），连续倒塌成为国内外科研人员和工程师亟待解决的重要难题。但已有钢筋混凝土框架结构研究多未充分考虑连续倒塌中破坏扩展和内力重分布所引起的动态效应，本项目拟从最基本的钢筋混凝土界面入手，开展其动态粘结-滑移关系受力机制和破坏模式的实验研究，建立适于抗连续倒塌分析的钢筋混凝土界面动态粘结性能理论模型。利用已有非线性有限元程序，结合能量等效原理，揭示动态粘结-滑移关系对连续倒塌下不同结构尺度（框架整体、梁柱组合件和梁柱节点）延性、刚度和承载力的影响规律，明确主导抗连续倒塌性能的受力机制、破坏类型和动态变形特征。通过建立统一的粘结-滑移关系动力放大系数，阐明极端变形和破坏倒塌过程中各种受力机制作用下不同尺度结构抗连续倒塌动力性能的衍化规律。本项目可为推进我国建筑结构规范抗连续倒塌性能分析设计方法的发展提供理论依据。

钢筋混凝土界面粘结-滑移性能是保证钢筋和混凝土共同抵抗外力的重要基础，对钢筋混凝土框架结构整体变形过程中的延性、刚度以及承载能力有着极其重要的意义。但国内外关于钢筋与混凝土间动态荷载作用下粘结性能研究较少。本项目试验过程中实时记录了加载过程中荷载、钢筋的滑移、钢筋沿锚固长度应变分布与变化规律，重点研究了短锚固和长锚固试件不同拔出速率情况下钢筋混凝土界面动态粘结应力的作用机制。首先通过在不同加载速率下对约束良好短锚固试件开展轴心拔出试验，探究钢筋在拔出试验中加载速率对粘结性能的影响，试验中最高加载速率达100mm/s。通过分析钢筋应变值计算得到的粘结应力，发现加载速率的提高会增大短锚固钢筋与混凝土间的粘结应力，该结论对评估钢筋混凝土动态粘结性能有重要意义。其次，针对实际工程中钢筋埋置与混凝土中的长度相对较长的真实情况，本项目深入研究了长锚固长度钢筋在不同锚固长度、混凝凝土强度下高加载速率对变形钢筋与混凝土动态粘结性能的影响。通过系统的研究发现如下变形和承载机制：钢筋应变由加载端向自由端线性减小；未达到静态屈服应变时，随着外荷载的持续增加，钢筋应变也不断增大，相应产生变形的范围也逐渐向自由端延伸；钢筋屈服后，屈服点应变快速增加，而未屈服测点应变增量非常小；随着加载速率越高，钢筋产生应变的长度越短，混凝土强度的提高会减少试件中钢筋为抵抗外荷载产生变形的长度。当加载速率为0.1mm/s和100mm/s时，钢筋埋置长度试件承载能力影响较小，加载速率的影响更加显著。当加载速率逐渐增大时，钢筋埋置长度越长，混凝土强度越高，试件承载能力随加载速率增加的反应就越加迟钝。加载速率较低时，混凝土强度的增加有助于提高试件承载能力；当加载速率提高时，长锚固试件中混凝土强度对提高承载能力起积极作用，但同时使承载能力对加载速率变得迟钝而起到消极作用，钢筋与混凝土间动态粘结性能是两者共同影响的结果。