Modeling the fire response of reinforced concrete columns under biaxial bending

Reinforced concrete (RC) columns, under fire conditions, are often subjected to biaxial bending arising from eccentricity in loading, 1-, 2-, 3- side fire exposure or due to non-uniform spalling. Effect of such biaxial bending is often not taken into consideration in evaluating fire resistance of RC columns. Also, current fire provisions in codes and standards do not provide clear and specific guidelines for fire resistance evaluation under biaxial bending. An approach is presented for modeling the fire response of RC columns under biaxial bending. This approach accounts for high temperature material properties, geometric and material nonlinearity, fire induced spalling, and restraint effects and can be applied under realistic fire and loading scenarios. The validity of the approach is established by comparing the predictions from the model with results from full-scale fire resistance tests. The model is applied to study the effect of fire exposure on fire response of RC columns. Also, fire resistance predictions from the numerical model are compared with those from code provisions. These comparisons indicate that the current codes and standards neglect the effect of uniaxial/biaxial bending and thus may not yield reliable fire resistance predictions.