Modeling of composite beam-column flexible endplate joints at elevated temperature

The paper presents a numerical study on two composite cruciform beam-column joints with flexible endplates subjected to elevated temperature. A two 356 × 171 × 51 UB connected to a 254 × 254 × 89 UC labeled Joint-A and two 610 × 229 × 101 UB connected to 305 × 305 × 137 UC labeled Joint-B. Numerical experiments were performed to estimate moment capacity of the joints at ambient temperature. Four fire tests for Joint-A and two for Joint-B were investigated with applied moment varying between 30%-70% of the joint capacity. Heating was applied linearly at a rate of 10 °C/min. Utilizing biaxial symmetry, only one fourth of joint configuration was modeled in ABAQUS. The bare steel and concrete slab components of the joints were modeled using a four-noded tetrahedral element capable of coupled thermal displacement analysis. EC3 recommendations for degradation in strength and stiffness were employed to model steel behavior. The concrete slab was modeled using damaged plasticity. Based on temperature-rotation relationship, the predicted results showed good agreement with experiment data in the elastic range while slight overestimates were observed in the plastic region. The results indicated high stress concentration in the top end of the endplate, top bolts and lower portion of the beam web close to bottom of the endplate. It was also observed that base of the embedded shear studs were heavily stressed. The failure modes of both joints in all loading cases were well predicted in simulation.