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Earthquakes and Structures
  Volume 8, Number 3, March 2015, pages 665-679

Effect of loading velocity on the seismic behavior of RC joints
Licheng Wang, Guoxi Fan and Yupu Song

    The strain rate of reinforced concrete (RC) structures stimulated by earthquake action has been generally recognized as in the range from 10-4/s to 10-1/s. Because both concrete and steel reinforcement are rate-sensitive materials, the RC beam-column joints are bound to behave differently under different strain rates. This paper describes an investigation of seismic behavior of RC beam-column joints which are subjected to large cyclic displacements on the beam ends with three loading velocities, i.e., 0.4 mm/s, 4 mm/s and 40 mm/s respectively. The levels of strain rate on the joint core region are correspondingly estimated to be 10-5/s, 10-4/s, and 10-2/s. It is aimed to better understand the effect of strain rates on seismic behavior of beam-column joints, such as the carrying capacity and failure modes as well as the energy dissipation. From the experiments, it is observed that with the increase of loading velocity or strain rate, damage in the joint core region decreases but damage in the plastic hinge regions of adjacent beams increases. The energy absorbed in the hysteresis loops under higher loading velocity is larger than that under quasi-static loading. It is also found that the yielding load of the joint is almost independent of the loading velocity, and there is a marginal increase of the ultimate carrying capacity when the loading velocity is increased for the ranges studied in this work. However, under higher loading velocity the residual carrying capacity after peak load drops more rapidly. Additionally, the axial compression ratio has little effect on the shear carrying capacity of the beam-column joints, but with the increase of loading velocity, the crack width of concrete in the joint zone becomes narrower. The shear carrying capacity of the joint at higher loading velocity is higher than that calculated with the quasi-static method proposed by the design code. When the dynamic strengths of materials, i.e., concrete and reinforcement, are directly substituted into the design model of current code, it tends to be insufficiently safe.
Key Words
    reinforced concrete (RC) beam-column joints; seismic behavior; loading velocity; shear carrying capacity; failure mode
Licheng Wang, Guoxi Fan and Yupu Song: State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, China

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