The Bearing Capacity And Seismic Performance Of High Strength Steel Reinforced Concrete Column

To meet the requirements of rapidly-growing high-rise buildings and long-span structures, the high-strength steel is combined with composite structures to make full use of the mechanical properties of high-strength steel and the superior behaviors of composite structures. Compared to the United States, Japan and other countries, however, steel with the yield strength of 235MPa and 345MPa is still mainly used in China due to the lack of research on high-strength steel reinforced concrete structures.In order to promote the application of high strength steel in the field of civil construction, the 460MPa high-strength steel was applied in the super high-rise building in Henan, instead of 345MPa ordinary steel. The existing design specification of composite structure would be not applicable to the bearing capacity calculation of high-strength steel reinforced concrete columns (referred to as HSSRC columns). To address this issue, experimental investigation is conducted to study the bearing capacity of Q460GJ HSSRC columns under axial loading with or without small eccentricity, and also its seismic performance. Based on the test results, parametric study is carried out to evaluate the effects of important parameters. A simple method is proposed for calculating the compression capacity of HSSRC columns, and a threshold value of the axial load ratio is suggested. This study mainly includes the following sections:(1) A total of six small-scale HSSRC columns embedded with cross-shaped steel members were tested under axial loading with or without small eccentricity and also cyclic loading. These test specimens were designed according to practical engineering. Focus was put on the deformation process, failure mode, ultimate deformation capacity, hysteretic performance, ductility and capacity of energy dissipation. It was found that HSSRC columns enjoy better ductility, capacity of energy dissipation and ultimate deformation, all of which can satisfy the requirements of the seismic design code.(2) A finite element model was developed with ABAQUS to simulate the performance of HSSRC columns. The finite element model was first validated against experimental results and then used to conduct a parametric study. The results reveal that the high-strength steel greatly improve the bearing capacity, ductility and capacity of ultimate deformation of composite columns. Therefore, the cross-section of composite columns can be reduced.(3) The theoretical methods proposed by different specifications of China, Japan, Europe and the United States were used to predict the ultimate bearing capacity of HSSRC columns. Predictions were compared with experimental and numerical results to evaluate these different methods. The proposed method from the design code of China was modified to consider the beneficial effect of circumferential steel reinforcements. A good agreement with the experimental results is achieved with the modified method, which can serve as a reference for practical design of HSSRC columns with regards to the compression capacity.(4) The OpenSees software was adopted to analyze the seismic performance of HSSRC columns. It showed that the seismic performance (energy dissipation, number of load cycles sustained and ultimate deformation capacity) of HSSRC columns improves with the increase of the shear span ratio, the steel reinforcement ratio or the stirrup ratio, and with the decease of the axial load ratio. Under the same axial load ratio, the ductility of HSSRC members is inferior to that of composite columns with low-strength steel.(5) To ensure satisfactory seismic performance, the average limit value of axial load ratio for HSSRC columns was deduced, based on the theory of balanced failure between compression failure and tension failure in combination with the numerical results and the general requirements of ductility for frame columns. According to the experimental and numerical results, the limit values of axial load ratio for HSSRC columns were proposed for practical design, considering the effects of shear span ratio, stirrup ratio and concrete strength.