Abstract
This work aims to investigate the seismic behavior and shear bearing capacity of Ultra-High Performance, Fiber-Reinforced Concrete (UHPFRC) beam-column joints. Quasi-static tests were conducted on five exterior and four interior reinforced UHPFRC beam-column joints; the behavior of specimens was examined in terms of failure processes, shear deformation angle, load transfer, and loadbearing capacity. The influences of the joint types, axial compression load level, and stirrup ratio in joint cores on the failure modes and shear carrying capacity of joints were analyzed. The shear resistance mechanism of a reinforced UHPFRC beam-column joint consists of the diagonal strut and truss mechanisms. The role of steel fiber through cracks is similar to reinforcement bars in the truss mechanism; based on these mechanisms and the test results, a formula was proposed to predict the shear carrying capacity of reinforced UHPFRC joints. The formula can reflect the effects of axial compression load level, steel fiber content, and stirrup ratio in the joint core on the shear carrying capacity of the beam-column joint, which can be used not only for UHPFRC beam-column joint design, but also steel fiber high-strength concrete joints.
Highlights
The beam-column joint is the important element in the reinforced concrete (RC) frame structure, which carries large horizontal and vertical shear forces as the internal forces of beam and column transfers through joints
The Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) strains in the joint core were 282 × 10−6 ~396 × 10−6 at the initial crack moment
The results indicate that the UHPFRC exhibited a higher deformation capacity under tensile stress owing to the use of steel fiber, which can enhance ductility and improve the deformation capacity of beam-column joints
Summary
The beam-column joint is the important element in the reinforced concrete (RC) frame structure, which carries large horizontal and vertical shear forces as the internal forces of beam and column transfers through joints. Earthquake damage demonstrates that beam-column joints are susceptible to shear failure. In order avoid shear failure, a high percentage of transverse stirrups are required in the joint core [1], which may lead to reinforcement congestion and, construction difficulties in casting concrete in the joint regions [2,3]. The main objective of this research is to provide experimental evidence of the behavior of beam-column joints with UHPFRC under earthquake loads and with various design parameters, and determine the effect of UHPFRC on the shear bearing capacity of beam-column joints. Since the mid-1960s, numerous researchers have conducted a series of studies on the calculation of the shear carrying capacity of beam-column joints, and proposed certain analytical models; for instance, the diagonal strut mechanism, truss mechanism [6], softened strut-and-tie model, simplified softened strut-and-tie model [7,8], general analytical model [9], and two diagonal axial springs model [10]
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