Analysis of Fire-Resistance Performance of Fire Doors Depending on Gap Size Using a Thermomechanical Model

A fire door is a critical building component installed within compartments to prevent the spread of fire to adjacent areas. During a fire event, these doors experience bending deformation due to temperature differences between exposed and unexposed surfaces. The maximum deflection typically occurs at the top corner on the lock side, causing the door leaf to bend away from the supporting frame. Such out-of-plane deformation compromises the integrity of the door, reducing its fire-resistance performance. While previous research, including a simplified thermomechanical model proposed by Italian researchers in 2017, investigated the thermomechanical behavior of fire doors, this study advances the understanding further. Specifically, (1) an enhanced thermomechanical model is developed by incorporating three previously neglected factors: door width, temperature-dependent elastic modulus, and the gap size between the door leaf and the frame; (2) the developed model demonstrates high accuracy, correlating strongly (\(r^{2} = 0.9\)) with deformations measured in fire-resistance tests; and (3) a robust design approach for fire doors is presented, ensuring sustained fire-resistance irrespective of gap variations. Experimental validation confirmed that the robustly designed fire doors exhibited approximately 5 mm less deformation compared to standard fire doors.