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

为了准确地模拟建筑结构体系在地震荷载作用下的性能，结构构件的模型必须足够精确，特别是在动力和循环荷载作用下。为此，对三分之一比例尺钢筋混凝土悬臂梁试件进行了失效试验，比较了其在动态和准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、剪切配筋量、剪切跨深比、剪应力水平、横向配筋强度和加载历史。结论如下：1。动加载下试件的抗弯屈服强度始终大于准静态加载下相同参数试件的抗弯屈服强度。通过考虑纵向钢屈服点强度的增加和弯曲理论，可以以可承受的精度定量估计强度的增加。就本研究的试验而言，加载速度对循环加载后产生显著强度衰减的最大挠度的延性能力影响不大。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，试件的强度衰减明显延迟。提出了一种测量纵杆拉伸屈服后应力的特殊方法，并应用于试验。在弯曲屈服前，受弯理论可以很好地估计纵向钢筋的拉应力，而铰区受拉钢筋的拉应力大于理论，受压钢筋的压应力随着循环加载逐渐增大。

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.