高强钢筋功能梯度混凝土梁的受弯性能及其设计方法研究

With the present-day tendency toward the use of higher strength reinforcing steel, the problem of controlling crack width for reinforced concrete beams under service loads is assuming greater importance. The normal concrete has the charactristic of low tensile strength and poor ultimate elongation rate. This program attempts to introduce the design thought of gradient function to the design of reinforced concrete beams and design a kind of functionally-graded concrete (FGM) beams reinforced with high-strength steel bars, which has some practical advantages such as improving bearing capacity and durability of reinforced concrete beams. The flexural behavior and design method of the FGM beams reinforced with high-strength steel bars will be investigated. Firstly, a high-ductility concrete will be developed which can be used to control crack width and its mechanical property will be systematically studied. And then, a new material named functionally-graded concerete will be designed and its mecroscopic interface property and interface microstructure will be investigated and, a numerical model of interface concrete will be built to study the effect of microscopic structural parameters and physical parameters on the mecroscopic interface property. Third, some functionally-graded concrete beams reinforced with high-strength longitudinal steel bars will be cast and tested under two-point symmetrical concentrated static loading to investigate their flexural behavior.A milti-scale finite element model will be built for the FGM beams reinforced with high-strength steel bars, and calculation results will be compared with experimental ones achieved in this investigation. Based on the experimental results and numerical ones, the mechanism for the control of crack in the FGM beams reinforced with high-strength steel bars will be thoroughly understood, and analysis and calculation method for mechanical performance of the FGM beams reinforced with high-strength steel bars will be developed. The results of the program will provide theoretical and experimental evidence for the design of the functionally-graded concrete beams reinforced with high-strength steel bars.

针对高强钢筋推广过程中遇到的裂缝宽度控制问题，以及普通混凝土存在的抗裂能力差、极限延伸率小等缺点，本项目拟在钢筋混凝土梁的设计中引入功能梯度材料，设计一种由高强钢筋、普通混凝土以及大变形混凝土构成的新型高强钢筋功能梯度混凝土梁，其特点是承载能力强和耐久性能更高。本项目将针对高强钢筋功能梯度混凝土梁的设计，研发一种能控制裂缝宽度的大变形混凝土，研究其力学性能；基于功能层界面区混凝土的宏观力学性能及微观结构特征研究，建立功能梯度混凝土的层间界面性能表征方法；建立针对该新型混凝土梁受弯性能的宏细观数值分析模型，研究梁结构整体的受弯力学性能。并把数值计算结果与高强钢筋功能梯度混凝土梁的试验结果作对比，验证分析计算模型的正确性。通过理论分析和数值计算揭示该新型混凝土梁的开裂机理，为最终实现设计一种新型高强钢筋功能梯度混凝土梁提供理论基础、参考数据和有效的分析计算方法。

本课题借鉴已有的大变形混凝土研究成果，采用国产PVA纤维试配ECC。通过直接拉伸试验、单轴压缩试验、抗压和四点弯曲试验，研究静载作用下ECC的力学性能，分析水胶比、砂胶比、粉煤灰掺量及PVA纤维品质对其力学性能的影响，确定了制备国产PVA-ECC的最佳配合比，并建立了该材料的拉、压本构关系模型。. 基于试验确定的国产PVA-ECC的最佳配合比，通过拉拔试验研究了钢筋的锚固长度、钢筋直径、ECC保护层厚度等因素对该材料与高强钢筋粘结性能的影响，分析了该材料与高强钢筋的粘结滑移机理，提出了该材料与500MPa钢筋的受拉极限粘结强度计算公式，并建立了两种材料的粘结滑移本构关系模型。. 通过双面剪切试验和劈裂抗拉试验分别研究了混凝土强度等级、界面增强工艺以及ECC厚度三种参数对功能梯度混凝土层间界面粘结强度和劈裂抗拉强度的影响。试验研究了功能梯度混凝土的静力抗压弹性模量，基于普通混凝土的弹性模量计算公式，建立了功能梯度混凝土的弹性模量计算式，并按照复合材料理论计算了功能梯度混凝土的弹性模量。采用扫描电子显微镜和电子探针X射线能谱仪对功能梯度混凝土层间界面进行微观测试。. 试验研究高强钢筋功能梯度混凝土梁在静载作用下的正截面受力过程和变形特征；分析截面配筋率、控裂功能层厚度、纤维品种及类型、受拉钢筋及普通混凝土的强度等级等参数对其抗裂性能、破坏模式、极限承载力和荷载－挠度关系等受力性能的影响。基于一些假定，采用弹塑性理论对ECC-RC功能梯度混凝土适筋梁的正截面受力全过程进行分析，并给出了受弯各阶段承载能力的计算方法。基于试验结果，建立构件的数值分析模型，对其在整个加载过程中的内力变化、裂缝及挠度开展进行模拟计算，分析了截面配筋率和控裂功能层厚度对功能梯度混凝土梁受弯性能的影响。. 课题研究成果对设计高强钢筋功能梯度混凝土梁提供理论基础、参考数据和有效的分析计算方法。