高强混凝土双向板在短期及长期荷载作用下的非线性行为研究

With the tremendous use of high-strength concrete (HSC) in engineering structures, the HSC wall panel has received increasing number of attentions. Vertical HSC wall panels are generally subjected to in-plane compression forces and out-of-plane transverse loads and/or bending moments. They are more prone to buckling failures than panels made of normal-strength concrete (NSC) because of their higher slenderness ratio. Moreover, the HSC panel undergoes excessive out-of-plane deflection and crack with time when subjected to sustained loads, due to the long-term effects of concrete creep and shrinkage. This time-dependent behavior may consequently cause the panel to loss stability over time. Obviously, there is a lack of studies on the instantaneous and time-dependent behavior of HSC panels, in particular, of the ones in two-way actions. Therefore, this research proposal will firstly investigate the nonlinear repose of two-way HSC panels under instantaneous loads by means of experimentation and theoretical analysis and computation. It will develop a theoretical model that considers large deformation of the structure and material nonlinearities of concrete and steel reinforcement. Furthermore, this project will study the nonlinear time-dependent behavior of HSC two-way panels by way of theoretical analysis and computation. A theoretical model that accounts for concrete creep, shrinkage, cracking and aging, as well as geometric nonlinearity will be developed, based on which the influence of creep and shrinkage on the load-carrying capacity of the HSC panel will be examined. Meanwhile, this study will also investigate the mechanism and rule of creep buckling failure for two-way panels, which will provide valuable theoretical foundation for the stability design of high-strength concrete panels.

随着高强混凝土在工程中的大量应用，混凝土板构件也得到越来越多的关注。混凝土墙板做为承重构件主要受面内压力和面外侧向力及/或弯矩的作用，因其比普通强度混凝土板长细比更大，所以也更容易发生屈曲破坏。除此以外，在长期荷载的作用下，因受徐变与收缩等因素的影响，混凝土板随时间会出现过大的侧向位移和开裂，甚至最终导致结构失稳。当前关于高强混凝土板特别是双向板短期和长期的性能的研究明显不足。本项目通过静力试验结合理论分析和数值计算的方法，首先考察高强混凝土双向板在短期荷载作用下的力学行为和非线性结构响应，建立考虑大变形和材料非线性的理论计算模型。其次，基于理论分析和计算，研究高强混凝土双向板的非线性时变行为，建立考虑混凝土徐变、收缩、开裂、老化和几何非线性等因素的理论模型，分析徐变和收缩等因素对板承载力的影响规律，阐明高强混凝土板发生徐变屈曲的规律和机理，为板结构的稳定设计提供理论依据。

随着高强混凝土在工程中的大量应用，混凝土板构件也得到越来越多的关注。混凝土墙做为承重构件主要受面内压力和面外侧向力及/或弯矩的作用，因其比普通强度混凝土板长细比更大，所以也更容易发生屈曲破坏。除此以外，在长期荷载的作用下，因受徐变与收缩等因素的影响，混凝土板随时间会出现过大的侧向位移和开裂，甚至最终导致结构失稳。..本项目首先针对高强混凝土板时变行为进行了试验研究，并且根据试验结果对之前建立的理论计算模型进行了验证。该模型考虑了混凝土材料开裂与拉伸硬化效应，能更真实地反应高强混凝土板在长期荷载作用下的结构响应，同时也更能准确的模拟和预测高强混凝土单向板的时变行为。实测与理论结果比对显示理论模型能准确的预测结构在不同时间点的各项性能参数的变化。研究显示，由于徐变和收缩的影响，混凝土板随着时间的变化有可能发生开裂，并且开裂的范围会逐渐地变大，同时，由于混凝土材料徐变、收缩以及开裂的耦合作用，导致结构失稳的长期荷载远远小于弹性结构的失稳荷载。..本课题第二个主要任务，是研究了高强混凝土双向板在长期面内和面外荷载作用下的时变响应。根据薄板理论以及平面应力，利用时步分析法，成功地建立了混凝土双向板的长期结构响应模型。该模型建立在混凝土粘弹性材料特性的基础上，并且考虑了双向混凝土墙的几何非线性与混凝土材料徐变的耦合影响。该模型适用于在任何形式的荷载作用及边界约束条件，包括面内受压以及面外横向荷载。通过数值分析和参数分析，该模型可以有效的跟踪和预测双向高强混凝土墙面外挠度变形、内力以及应变随时间的演化规律。明确了混凝土材料徐变和材料几何非线性耦合作用对墙体正常使用状态和极限承载力状态下的结构性能有至关重要的影响。阐明了目前国内外混凝土结构规范中，墙体设计公式的缺陷，指出混凝土墙体的设计中必须考虑结构长期性能的影响。