Minimum Column Dimension for Interior Joints of Reinforced Concrete Special Moment Frames

• Main Authors: CHEN, HSI-CHING, 陳錫慶
• Other Authors: LEE, HUNG-JEN
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/9c5v9g

博士 === 國立雲林科技大學 === 工程科技研究所 === 105 === Taiwan is on the Pacific Fire Ring and has high seismic hazard. Most buildings here are made with reinforced concrete special moment-resisting frames because of the advantages of ductility, economic, and space flexibility. More recently, it is a strong demand on the high-rise buildings due to urban renew and social housing. Designers and contractors are looking forward to using high-strength reinforcement for concrete structures, especially for the frame joints with steel congestion. However, it is well-known that the higher yield strength, the longer bond development length required. The limited joint depth for anchorage of beam bars becomes a critical issue for the use of high-strength reinforcement. Special moment frame beams are expected to develop plastic hinges at joint faces which generate high bond stress along the beam bars in the joint. If the joint depth is not capable of anchoring the beam bars, which may slip under reverse cyclic loading reversals and result in poor hysteresis behavior. Where beam bars extend through a beam column joint, current ACI 318 codes requires a minimum 20-bar-diameters column dimension for bar fy of 420 MPa. This provision should be revised for higher yield strength reinforcement, such as bar f_y of 550 MPa and 690 MPa. This study is aim to figure out the minimum column dimension for special moment frames with high-strength reinforcement. A comprehensive literature review and database investigation were completed. For each beam-column joint specimen, the hysteresis behavior at the limiting drift ratio of 4% was evaluated using specific acceptance criteria, rated in scales, and used for assessment of existing design equations. To conclude, this study recommends a simple equation for modifying ACI 318 code. The minimum joint depth for special moment frames shall be the larger of 20db and (dbfy)⁄((3.2(fc')^0.5)) where the fy and fc' are in MPa. Database investigation shows that the hysteresis performance of tested beam-column joints could satisfy the ACI standards, provided the joint depth exceed the minimum joint depth. The bond failure can be prevented for the drift level of design earthquakes.