SEISMIC PERFORMANCE OF NEW RC EXTERIOR BEAM-COLUMN JOINT MADE OF HIGHLY-FLOWABLE STRAIN HARDENING FIBER REINFORCED CONCRETE
Journal
World Conference on Earthquake Engineering Proceedings
Journal Volume
2021
Start Page
2c-0016
ISSN
30065933
Date Issued
2021
Author(s)
Abstract
The New RC Project conducted by Japan in 1988 mainly used high strength materials to reduce the section sizes of members and to save the consumption of materials. However, the brittle nature of high strength concrete should be considered compared to ductile response of normal strength concrete. Therefore, ACI 318-14 requires denser transverse reinforcement while using high strength concrete (fc'≥70MPa) in column members to assure its toughness. For special moment frames, beam-column joint is a key element to transfer shear and moment forces. Nevertheless, beam-column is an intersection of longitudinal reinforcement of beams and columns along with transverse reinforcement of columns. The heavy reinforcement arrangement may result in construction difficulty and poor construction quality. This issue could be severer in New RC members since their section sizes are smaller. Highly flowable strain hardening fiber reinforced concrete (HF-SHFRC) has excellent workability in the fresh state and exhibits the strain-hardening and multiple cracking characteristics of high performance fiber reinforced cementitious composites (HPFRCC) in their hardened state. Application of HF-SHFRC to beam column joints may be an alternative to transverse reinforcement since its validity has been verified in columns. This study investigates the seismic performances of high strength fiber reinforced exterior beam-column joints. Estimation of shear strengths and quantification of confinement efficiency are also discussed. Five full scale New RC exterior beam-column joints, including three made of HF-SHFRC with 1.5% volume fraction steel fibers, were subjected cyclic loading under low and high axial loading levels. The high axial load specimen was designed to verify the fiber confinement efficiency in terms of toughness ratio. The test results show not only toughness ratio can properly quantify fiber confinement efficiency, but 75% of transverse reinforcement can be eliminated owing to steel fibers under high axial loading. One specimen was designed to obtain its shear capacity under low axial loading level by joint shear failure. The test results show that its shear strength is 1.91 times of that suggested in ACI 318, even there is no any transverse reinforcement in the joint. Additionally, the specimen ends up with shear failure, but it still can keep the good shape and satisfy all the criterions of a qualified beam-column joints required in ACI 374. In summary, application of high strength fiber reinforced concrete in New RC beam-column joints offers opportunities to significantly simplify the design and construction work, while ensuring adequate ductility and damage tolerance.
Subjects
beam-column joint
fiber reinforced concrete
high strength concrete
shear strength
strain hardening
Publisher
International Association for Earthquake Engineering
Type
conference paper