Web infilled columns

60 minutes fire resistance is obtained when normal weight, poured concrete is fixed between column flanges by shear connectors attached to the web. The concrete is retained by a web stiffener fixed at the bottom of the connection zone. 

The load carrying capacity of the concrete is ignored in the design of the column but in fire, as the exposed steel weakens at high temperatures, the load carried by the flanges is progressively transferred to the concrete. This provides stability in fire for periods of up to 60 minutes. The connection zone at the top of the column is protected along with the beam.