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

本文通过钢筋混凝土梁的静载和恒载试验，研究了混凝土力学性能对钢筋混凝土梁抗弯开裂性能的影响。从试验结果来看，高强混凝土的使用虽然使裂缝间距增大，但对静载下裂缝宽度的影响并不显著。但在长期荷载作用下，由于高强混凝土干燥收缩小、抗拉强度高，对裂缝宽度的控制是有效的。为了评估材料性能，如干燥收缩，混凝土徐变和钢筋与混凝土之间的粘结的时间效应的影响，有限元分析施加到持续荷载下的标本。分析结果表明，在持续荷载作用下，混凝土的体积变化对裂缝宽度的增加影响最大，但裂缝表面附近的粘结特性对裂缝宽度的增加也有类似的影响，为了改进裂缝宽度的估算，进行了拔出试验，并对混凝土表面附近的锥形破坏进行了有限元分析。为了研究在持续荷载作用下的粘结-滑移关系，进行了拉拔试件的粘结试验。根据试验结果，分析了变形形状对加固效果的影响，并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.