Strain Rate Effect on Reinforced Concrete Members under Cyclic and Dynamic Loading

为了准确模拟建筑结构体系在地震荷载作用下的行为，结构构件的模型必须具有足够的精度，特别是在动力和循环荷载条件下。为此，进行了1/3比例的9根钢筋混凝土悬臂梁试件的破坏试验，以比较它们在动、静态加载条件下的性能。试验参数包括加载速度、纵向配筋量、剪力配筋、剪跨比、剪应力水平、横向配筋强度和加载历史。主要结论如下：1.动荷载作用下试件的弯曲屈服强度始终大于同参数试件在准静态荷载作用下的弯曲屈服强度。通过考虑纵筋屈服点强度的增加和弯曲理论，可以用可承受的精度定量估计强度增加。2.就本研究中的试验而言，加载速度对延性能力的影响不大，因为循环加载后最大挠度开始显著的强度衰减。对延性影响最大的参数之一不是加载速度，而是加载历史，即在单向循环加载历史下，试件的强度衰减显著延迟。3.发明了一种测量拉伸屈服后纵筋应力的特殊技术，并将其应用于试验。在弯曲屈服前，纵向钢筋的实测拉应力用弯曲理论进行了较好的估算，但在铰链区的拉应力和压筋的压应力都比理论计算的要大，并随着循环荷载的作用逐渐增大。

To simulate accurately the behavior of building structural systems under earthquake loading, the model for the structural members should be accurate enough in particular under dynamic and cyclic loading condition. Hence, one-third scale nine-teen reinforced concrete cantilever beam specimens were tested to failure to compare their behavior under dynamic and quasi-static loading condition. The parameters for the test include loading speed as well as amount of longitudinal reinforcement, shear reinforcement, shear-span to depth ratio, shear stress level, strength of transverse reinforcement and loading history. The list of conclusions are as follow,1.The specimens under dynamic loading showed always larger flexural yielding strength than its pair with same parameter tested under quasi-static loading. It is possible to estimate the strength increase quantitatively with affordable presision, by considering the increase in yield point strength of the longitudinal steel and flexural theory.2.As far as the tests in this research concerns, loading speed has little effect on the ductility capacity in terms of the largest deflection at which significant strength decay initiates after cyclic loading. One of the most influential parameter on the ductility is not loading speed, but loading history, i.e. strength decay was delayed significantly in the specimen tested under one directional cyclic loading history.3.A special technique was invented to measure stress in longitudinal bar after tensile yielding and applied to the tests. The observed tensile stress in longitudinal bar were well estimated by flexural theory before flexural yielding, whereas, larger tensile stress is obtained than the theory for tensile reinforcing bars in hinge zone and larger compressive stress in compressive reinforcing bars which gradually increased due to cyclic loading.