Moment capacity of cast iron beams in jack arched construction exposed to fire

Cast iron girders were used in many 19th century structures, especially in fireproof flooring systems (such as jack arch). Many such structures are still in use today and it is important that they fulfill the current requirements on fire resistance when there is a change of use. This paper presents the development of a simplified method to calculate the bending moment capacity of unprotected cast iron beams in jack arched system exposed to the standard ISO 834 fire. Cast iron has limited ductility so it is not possible for a cast iron beam to achieve total plasticity as in modern steel beams. Therefore, for cast iron beams, a simplified method is developed, based on strain distribution in the cross-section. The method deals with non-uniform temperature distribution in the cast iron beam section and uses different mechanical properties of cast iron in tension and compression. A comparison between calculation results using the simplified method and those using the fiber method, validated by ABAQUS simulation results, indicates that the proposed simplified method is sufficiently accurate as the basis of a design method.