For high-rise reinforced concrete buildings, it is generally recognized that beam-column joints, under earthquake-type loading, may become more critical structural components than other elements. Therefore, the behavior of reinforced high-strength concrete beam-column subassemblies must be accurately assessed in order to use new structural material such as high-strength concrete with confidence in reinforced concrete frame structures.
In this dissertation, experimental research was carried out to study the hysteretic behavior of reinforced high-strength concrete beam-column joints, and to develop new approaches for the design of such joint in high-rise reinforced concrete buildings.
First, it was undertaken to study the hysteretic behavior of reinforced high-strength concrete beam-column subassemblies subjected to reversed repeated loadings. The effects of the primary variables, such as concrete strength, loading rate, and ratio of the column to beam flexural capacity etc., on the behavior of reinforced high-strength beam-column connections were investigated. Based on the test results reported in this study, the reinforced high-strength concrete beam-column joint, which was designed by ACI Building Code and ACI-ASCE Recommendation based on normal concrete test results, was satisfactory behavior under displacement ductility of 6. However, the hysteretic behavior of reinforced concrete members subjected to repeated reversed loading depends on the concrete strength. Such joints represented also stable hysteretic behavior for the displacement ductility of 6 or lower, but sudden degradation in stiffness and strength, and unstable hysteretic behavior was observed owing to the brittleness of high-strength concrete beyond its range. Therefore, research is needed to modify the current design recommendation, to improve the earthquake-resistant performance of reinforced high-strength concrete members and joints before high-strength concrete, in severe seismic areas, can be used with confidence in reinforced concrete frame structures.
Secondly, new approaches were developed to improve the structural performance of reinforced high-strength concrete beam-column joints for the design of such joints in high-rise reinforced concrete buildings. New design details were proposed to move the location of the beam plastic hinging zone away from the column face, and to improve the seismic resistance performance by adding supplemental intermediate longitudinal reinforcement with or without closed stirrup over a specific length of the beam adjacent to the joint. Techniques of diagonal anchorage bars within the joint also are proposed to prevent the diagonal crack in the joint region. For the reinforced high-strength concrete beam-column joint, which was designed with relocating the beam plastic hinge and added the supplemental intermediate longitudinal reinforcement with or without closed stirrup to improve energy dissipation capacity, a greatly satisfactory behavior and significant increase of energy dissipation capacity, especially after displacement ductilities of 7 or higher, was apparent by comparison with the test results of standard specimen. Developing the diagonal anchorage method in the joint region, reinforced high-strength concrete beam-column joints would attain a basic objective of preventing the diagonal cracking in the joint region under large load reversals. However, the hysteretic behavior for such joints, represented the pinching effects due to the sliding shear failure in the beam to column face. Therefore, the diagonal anchorage method in the joint would be corrected. A new modified design, which combines the moving of the beam plastic hinge with the preventing of diagonal cracks in the joint region, is expected to be more effective in improving the seismic resistance performance in the reinforced concrete frame structures.
