Experimental Study on Elasto-Plastic Behavior of R/C Exterior Beam-Column Joints With Parameters of Varying Axial Forces and Lateral Reinforcements

Abstract eng:
In the Japanese seismic design criteria for beam-column joint of reinforced concrete frame structures with beam yielding, it is restricted that the shear force at the joint panel does not exceed the shear strength of joint on basis of past experimental data. However, in recent research (Dr. Shiohara’s studies), it was shown that the maximum strength of frame structures with the beam yielding total collapse mechanism does not achieve the expected design strength (beam bending strength) due to joint panels eventually collapse; this may occur even when frame structures satisfy the current seismic design standards if column-to-beam bending strength margin of the frame structure is less than 2.0. On the other hand, it was found, through an experimental study that it is possible to reduce the damage to the joint panels and achieve the design strength of the structural frame when increasing confinement of joint panel by lateral reinforcements and applying low level constant compressive axial loading to the columns, for the exterior beam-column joint in a frame structure with column-to-beam bending strength margin of approximately 1.5. The objective of this study is to clarify seismic performance of exterior beam-column joint structures with column-to-beam bending strength margin of less than 1.5 when the structure is subjected to high level varying axial forces (an axial force ratio of 0.6 in tension to 0.5 in compression). In addition, the purpose of this study is to establish stiffening effects of lateral reinforcements in the joint panel. Six identical 1/2-scale models of exterior beam-column joint specimens with two levels of column-to-beam bending strength ratios (approximately 1.2 or 1.5) were prepared. Experimental parameters of six test specimens were column-tobeam bending strength ratio, axial stress level and lateral reinforcements of joint panel. In terms of loading method that assumed seismic forces, the test specimen was subjected to static horizontal cyclic loading at the top of the column. Simultaneously, a varying axial load proportional to the beam shear forces was applied. From the experimental results, it is revealed how varying axial forces affect structural performances in terms of damage on joint panel, strength, deformation capacities, and failure mechanisms of structures; it was also possible to verify whether using lateral reinforcements improved the performance of structures.

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