Effects of Axial Restraints on Beam Flexural and Joint Shear Behaviors in Reinforced Concrete Frames under Seismic Loading

The elongation of beams in reinforced concrete frames due to flexural cracking and yielding is restrained by the surrounding structural components, thereby leading to axial force in the beams. To study the effects of beam axial restraint on the beam flexural and joint shear behaviors, cyclic lateral loading experiments were conducted on four beam-column substructures, two of which were restrained from beam elongation. The experiments indicated that the passively developed axial force significantly increases the beam flexural capacity. Moreover, the beam axial restraint increased shear demand on beam-column joints; as a result, joint shear failure occurred in one test specimen.