| CRB550 grade steel is formed by HPB235 grade steel through cold-working, which strength is greatly improved, but the ductility doesn't change much. While, if widely used to replace a Low-strength grade of steel, it can greatly save the amount of steel, in promoting conservation and low carbon today, which has important practical significance. The steel is mainly applied in ligament and distribution reinforcement of shear wall, but still relatively rare used in the beam or column. The main reason is that stirrup configurated mainly according to detailing requirements in general seismic design of building, while the Seismic code made specific provisions for the diameter and spacing of stirrups .It is not economical if selecting CRB550 grade steel according to the specification limits. Since the "Code for Seismic Design of Buildings" GBJ11-89 was enacted, specification requirements on the beam stirrups structure have not changed. For 20 years, development and application of high strength reinforcements are rapid, but that provision only make demands to the diameter of the steel, without considering the impact of steel strength, therefore, it is necessary to study the limit diameter of stirrups in the frame beam end encrypted area.This paper includes the following content:(1).According to " Code for Seismic Design of Buildings" (GB50011-2001 2008 edition) on the length of beam end encryption area, the maximum stirrup spacing and the minimum diameter requirements, 18 reinforced concrete beam spicemens which constitute from different intensity levels and diameter of stirrups are designed and carried out quasi-static experiment under low cyclic loading.(2). Detail description and analysis are made for crack extension mechanism, specimen failure patterns, Steel strain distribution and development law, hysteresis curve of the form and other aspects in the process of the experiment. Concrete beam spicemens configurated smaller diameter CRB550 stirrups have the similar seismic performance compared with specimens which stirrups are configurated by HPB235 grade steel,according to the principles of equal strength, is verified preliminarily.(3).The skeleton curve, displacement ductility, strength degradation, stiffness degradation, energy dissipation and other aspects of the 18 spicemens are compared, and strength grade and size of the stirrup on the seismic performance of the specimen are deeply investigated .(4). According to the experiment results, applicable proposal for the CRB550 grade steel, for the length of beam end encrypted area , the maximum stirrup spacing and the minimum diameter requirements on "Seismic Design of Buildings" (GB50011-2001 2008 version) are made.
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