Analysis on reinforced measures of steel frame in connection regions with unbonded steel brace encased in panel

Abstract:

To ensure that steel frames with unbonded steel plate brace encased in panel, which is also called as panel buckling restrained brace (panel BRB), can use yielding of panel BRBs to dissipate energy under large drifts while keeping regions of the frames connected with panel BRBs in elastic state, finite element analysis was conducted to investigate effects of factors, such as the type and connection location of panel BRBs, on force transfer mechanics of connection regions and corresponding reinforced measures. The analysis reveals that reinforced plates fixed on beam let yielding of beam occur near the ends of unreinforced segments. The distance between the plastic hinge of unreinforced segment and the end of reinforced plate was about half of the height of the beam, and the maximum bending moment at the plastic hinge, with small local buckling or without buckling for flange plates, was close to the plastic moment of beam within drifts of 1/50. Based on the conditions above, together with connection locations and axial forces of panel BRB, the internal forces at the ends of beam can be acquired, hence the shear resistance of panel zone of column can be checked. The analysis also shows that bending moments at ends of beam transferred to the panel zone according to the proportion of flexural rigidity for flange and wed of beam rather than according to only two flanges required by design codes. The shear deformation of panel zone greatly increased after shear yielding, inducing the increase of inter-story drifts. Based on the analysis results, design suggestions on the determination of the thickness of reinforced plates on flange and web of beam and panel zone of column were provided.