Study on Control of Crack Width in Reinforced Concrete Members under Sustained Loading

本研究通过对静载和持续荷载作用下的钢筋混凝土梁进行试验，探讨混凝土力学性能对受弯裂缝行为的影响。从这些试验结果来看，在静荷载作用下，高强混凝土的使用对裂缝宽度没有显著影响，但会使裂缝间距增大。而在持续荷载作用下，高强混凝土的干缩率低，抗拉强度高，对裂缝宽度的控制是有效的。为了评估混凝土的干燥收缩、徐变以及钢筋与混凝土粘结的时间效应等材料性能的影响，对试件进行了持续加载的有限元分析。分析结果表明，在持续荷载作用下，虽然混凝土体积变化对裂缝宽度的影响最大，但裂缝表面附近的粘结特性对裂缝宽度的影响也相当。为了改进裂缝宽度的估计，进行了拉拔试验，并采用有限元法对混凝土表面附近的锥破坏进行了分析。从分析结果来看，混凝土表面的粘结退化可以用示踪的圆锥裂纹扩展来表示。为了研究持续加载下的粘结滑移关系，采用拉拔试件进行了粘结试验。根据试验结果，评价了变形形状对配筋的影响，推导了广义粘结滑移关系。

In this study, experiments were performed on reinforce concrete beams under static loading and sustained loading, to investigate the influence of mechanical properties of concrete on flexural crack behavior. From the results of these experiments, use of high-strength concrete does not influence significantly on crack width under static loading, though it makes crack spacing larger. However, under sustained loading, it is efficient for control of crack width, because of low drying shrinkage and high tensile strength of high-strength concrete. To evaluate the influence of material properties such as drying shrinkage, creep of concrete and time effect of bond between reinforcements and concrete, finite element analysis was applied to the specimens under sustained loading. Analytical results showed that though volume change of concrete most influences on increase of crack width under sustained loading, bond characteristics near the crack surface have comparable effect.To improve the estimation of crack width, pull out test were carried out and cone-failure near the concrete surface was analyzed by finite element method. From the analytical results, bond degradation near the concrete surface was represented by tracing conic crack growth.To investigate the bond-slip relationship under sustained loading, bond tests using pull-out specimen were carried out. From the test results, the effects of deformed shape on reinforcement were evaluated and generalized bond-slip relationship were derived.