Experimental study on seismic behavior of reinforced concrete frame joints with consideration of strain rate effect.

A series of experimental studies on the seismic behavior of reinforced concrete frame beam-column joints were carried out in order to well understand the effect of loading speed on the bearing capacity and failure pattern of the joint assembly. The results show that the orders of magnitude of the strain rate in the joint core area are 10-5 , 104 , and 102, in response to the loading speed at beam ends of 0. 4 mm/s, 4 mm/s and 40 mm/s, respectively. It is observed that with the increase of loading speed, the extent of damage of the frame joint assembly becomes greater and the cracking distribution becomes more concentrated. The energy dissipation of the joint assembly under higher loading speed is larger than that under quasi-static loading before the final failure. Besides, the yielding bearing capacity of the joint assembly has no significant change as the loading speed increases, while there is a marginal increase of the ultimate bearing capacity. However, the bearing capacity and stiffness of the post-peak branch at higher loading speed drops more rapidly. Under rapid loading, the axial compression ratio, within the range of current studies, has little effect on the shear bearing capacity of the joint assembly, while the crack width of the joint core concrete decreases with the increase of the axial compression ratio. If the dynamic strengths of both concrete and reinforcement bars are directly substituted into the quasi-static design formulas, the shear carrying capacity of the beam-column joint is overestimated, i. e. higher than that observed in the test, indicating the unsafe result of this direct approach. [ABSTRACT FROM AUTHOR]