| Because of its prominent property of high ratio strength to weight, ease installation and excellent corrosion resistance, Fiber-Reinforced polymer(FRP) has been widely used in the field of structural strengthening and retrofitting. RC(Reinforced Concrete) rectangular column as one of the most common type of structural column in frame structure, its seismic strengthening research with FRP started relatively later compared with circular and square column. The existing researches have showed that FRP confined RC rectangular column can obviously improve its seismic performance, which has laid a good foundation for further research.When earthquake occurs, earthquake action comes from random directions, which means the structures actually suffer from multi-dimension earthquake action. But the existing researches about the seismic performance of FRP confined RC rectangular column are mainly conducted by quasi-static tests under unidirectional horizontal load. Studies have shown that: the seismic performance of RC rectangular column showed obviously biaxial coupling effect, which means that the cumulative damage in one direction can adversely affect the perpendicular direction. This phenomenon is particularly prominent when the cross-sectional aspect of rectangular column is large. However, the research is blank about FRP confined full-scale RC rectangular column under unidirectional horizontal load. Related experiments showed that the seismic performance in two-way horizontal earthquake can use a range of different angles quasi-static tests under oblique horizontal load to inspect.Therefore, for the lack of research on the above-mentioned, this paper firstly studied bidirectional seismic performance and law on RC rectangular column through the multi-angle pseudo-static tests. Then based on finite element softwares Open Sees, the numerical simulation of multi-parameter expansion analysis was carried out. Qualitative analysis of the seismic performance was taken on the impact of longitudinal reinforcement layout, cross-sectional aspect ratio and other parameters. Then Proposed the best reinforcement height of the CFRP reinforced rectangular columns. Finally, the bidirectional shear bearing capacity of relevant norms is verified by test results. At last, proposed the reduction coefficient and suggestion on design of after CFRP Strengthened. The main contents are as follows:1. Ten full-scale quasi-static experiments whose section is 300mm×450mm are carried out under oblique horizontal loads. The results showed that:1) The impact of changes in loading angles of RC rectangular column on the bearing capacity and initial stiffness is obvious, but less impact on ductility and energy dissipation capacity. After CFRP reinforcement the changes of loading angles have a significant influence on initial stiffness, bearing capacity and energy dissipation capacity, in which the ductility and energy dissipation influence more. 2) Under same loading angles, after CFRP strengthened there is little effect on the initial stiffness and peak capacities, but the ductility and energy dissipation capacity have a significant improvement.When loading angle are 0 degrees and 30 degrees, ductility and energy dissipation capacity increase most significantly.2. Compared with the experimental results, the numerical simulation results show good agreement. A large number of load cases on multi-parameter expansion analysis are studied based on Open Sees system. Parametric analysis results showed that: 1) Whether or not the use of FRP wraps, the horizontal bearing capacity follows elliptical law. When cross-sectional aspect ratio is greater than 2, only FRP reinforcement is not recommended. 2) When the coefficient a greater than 1, the weakest angle of horizontal bearing capacity is not appear at 90 degrees, with the increase of the sectional aspect ratio the weakest angle transfer from 45 degrees to 90 degrees direction. 3) When the cross-sectional aspect ratio is less than 2 and short side is less than 400 mm, the effective reinforcement height correlated with the length of short side, and the effective height of common rectangular columns is about B~1.25 B.3. The suggestion of norms: when loading the angle between load degrees and strong axis angle is greater than 45 degrees, the bearing capacity is unsafe. This paper suggested reduction factor less than 0.85 on weak axis. CFRP reinforcement had little effect on the bidirectional shear bearing capacity, so the paper suggested using unstrengthened bearing capacity to guide design. |
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