Upgrading seismic performance of beam-column joints using steel-polypropylene hybrid fiber: Experiment and numerical simulation

Abstract

Due to the exceptional resistance to concrete cracking, appropriate incorporation of steel-polypropylene hybrid fiber is anticipated to enhance the mechanical properties of beam-column joints that are crucial for ensuring the integrity of frame structures under earthquake excitations. In this study, twenty-eight steel-polypropylene hybrid fiber reinforced concrete beam-column joints (HFRC-BCJs) were tested under cyclic loading to investigate their seismic performance, in which the effects of fiber types, concrete strength, axial compression ratio, and characteristic parameters of hybrid fiber are taken into account. The results indicated that the incorporation of steel-polypropylene hybrid fiber can exert a beneficial synergetic effect on improving the seismic responses of beam-column joints in multiple aspects. Specifically, hybrid fiber not only alleviated the concrete damage within the core region significantly, but also augmented the initial cracking load, displacement ductility coefficient, and energy dissipation coefficient of the beam-column joints by an average of 40.5 %, 31.4 %, and 37.3 %, respectively. Moreover, with the purpose of enabling a reasonable prediction of the seismic responses of HFRC-BCJs, a modified super degree-of-freedom (DOF) element was adopted for the numerical simulation, in which a user-defined UMAT subroutine was developed to more accurately reflect the enhancements of fiber inclusion on the tensile and compressive stress-strain behaviors of HFRC, as well as the associated damage evolution.