Experimental Research On Seismic Behavior Of Reinforced Concrete Column With Cross- Shaped Section

At present, HRB500 steel bar will be widely used, however, there are few studies on seismic behavior of specially-shaped column reinforced with 500MPa high strength steel bar at home and abroad, which causes inconvenience in revising the item on HRB500 steel bar of the code JGJ 149-2006 as well as in application of HRB500 steel bar in projects. As an important part of revising the code JGJ 149-2006, studies of seismic behavior of cross-shaped section column reinforced with HRB500 steel bar, which provides theoretical foundation and experimental basis for the code revising and high strength bars'application.Experiments of 7 specially-shaped columns with HRB500 steel bars under constant axial loads and low cyclic lateral reversed loads are presented in this paper. Some factors are analyzed on the influence of seismic behaviors of the columns, such as compression ratio and stirrups ratio. The development of the cracks and test phenomenon are described. Meanwhile, the characters of the strain curves of the steel bars, hysteretic loops, skeleton curves, stiffness degradation and permanent deformation are studied as well as the displacement ductility coefficient.Based on the analysis of test results, the main conclusions are as follows: the ultimate failure modes for all of the specimens are flexural failure. The longitudinal reinforcements at the end of the webs of large eccentric compression specimens reach its tensile yield strength and compression yield strength before reaching the ultimate load. However, for the small eccentric compression specimens, the longitudinal reinforcements only reach its compression yield strength. The stirrups of all specimens are in tension state, only a small amount of pressure at early stage of loading, and the stirrups don't reach its tensile yield strength. With axial compression ratio increases, the ultimate bearing capacity of the specimen is increased, but its ductility and energy dissipation capacity is reduced. The ultimate bearing capacity and ductility are improved by reducing stirrup spacing. The ultimate bearing capacity under the low cyclic loading is 80% of the ultimate bearing capacity under the monotonic loading. All of the specimens have good ductility in the test, so, we can draw a conclusion that HRB500 steel bar can be applied in seismic design.Based on design method for normal section bearing capacity of flexural member with rectangular section, the calculation formula for normal section bearing capacity of cross-shaped section column has discussed. The difference between calculated value and test value of the bending capacity on six specimens are analyzed. The result shows that the bending capacity using the diagrams of big eccentric compressive members is relatively small. But for members with small eccentricity, the calculating results agree well with experimental ones.