Research On Effect Of Structural Measures On Frame Beam End For "Strong Column And Weak Beam" Failure Mode

The earthquake damage shows that the frame structure which is designed based on the 2001 edition seismic code was shown the column-hinging failure mechanism, which belied the objective of seismic code. Numerous tests and analysis show that one of the predominant reasons is the lack of consideration of the influence of slab reinforcement paralleled to the frame beam. With a difference from the method of reinforcing the flexural capacity at column ends given in the code, this paper ―artificially sets‖ the weak position at beam ends by taking three different slotting methods, in order to achieve the designing objective(that is ―strong column-weak beam‖), so as to ensure the seismic performance under rare earthquakes.Based on the previous research, this paper makes elastic-plastic static analyses of three various slotting methods and general two-story(2×2) frame structures, and studies the seismic performance of each model via mechanical analysis and numerical analysis method by ABAQUS. Results indicate that compared with general frame, when adopting the three slotting methods proposed in this paper: little changes in the bearing capacity reserves of the structure, deformation capacity reserve increases, and the seismic performance improves; under the impact of seismic waves, the degree of damage of concrete at beam ends increases, that at column ends and joint decreases, plastic hinging appears earlier at beam ends than column ends, a higher degree of plastic hinging development appears at beam ends than column ends, which is more consistent with the ―strong column-weak beam‖ failure mode in the code. In order to study the seismic performance of slotting structure models under different fortification level, this paper makes dynamic time history analysis for three various slotting methods and general six-story(3×2) frame structures under frequent, intermediate, rare and large earthquakes. Results indicate that compared with general frame, when adopting the three slotting methods :the location of maximum inter-story displacement angle does not change; the degree of participation of slab reinforcement decrease in earthquakes, the method with right angle is more satisfied;the three slotting methods are conducive to increase the seismic performance of structure, plastic hinge distribution of frame are more consistent to the ―strong column-weak beam‖ failure mode under rare and large earthquakes. Meanwhile, practical realization of slotting method with right angle and filling program of slot are also proposed in this paper.In summary, through static and dynamic elastic analysis, this paper indicates that the method that ―artificially sets‖ the weak position by slotting on slab at beam ends is more conducive to realize beam-hinge-dominated beam-column hinge mixed failure mode under earthquakes compared with the method of reinforcing the flexural capacity at column ends given in the code.