Structural Design of Domestic Low-Mo Fire-Resistant Steel in Fire-Resistant Design of Tall Space Buildings Canopy

Fire is one of the critical safety threats to steel structures. The main conventional fire-resistant measures include painting fireresistant coating, forming composite structures by combining steel with concrete and setting fire-resistant plates, among which the fireresistant coating is the most widely used. However, the fire-resistant coating painted outdoors performs poor durability, owning the hidden danger that the coating may fall and hurt people. In addition, the extremely thick coating is required for steel structures with strict demand on fire resistance, which will especially affect the architectural rending of landmark buildings. In recent years, fireresistant steel has been paid more attention for its ability to effectively avoid the above drawbacks, as a novel fire-resistant approach. However, the cost usually becomes higher due to the massively added high-price alloy Mo. As a result, the novel fire-resistant steel proposed by the Institute of Nanjing Iron & Steel Co. Ltd gained widespread attention owing to the much lower cost by reducing the additive quantity of alloy Mo while maintaining excellent fire-resistant properties. This paper investigates the feasibility of applying low-Mo fire-resistant steel in the fire-resistant design, based on the carrying capacity method and relying on a large steel canopy with a tall space. The large canopy should meet the 3 h fire-resistant requirement as a landmarking building. First of all, the material properties of domestic fire-resistant steel are investigated under high temperatures. It is found that the novel fire-resistant steel meets the requirements of general fire-resistant steel by comparing with the current specification and the reduction of material properties can be accurately predicted according to corresponding equations in the specification. Subsequently, a total of 11 fire scenes located at the side-span and the middle-span are identified according to the structural design criterion, which is thought to include all the possible fire scenes of the large canopy during service. Furthermore, it is analyzed that the heating laws of the large canopy under various fire scenes. The results show that the highest temperatures of air and steel beam are close to 750 ℃ and 730 ℃, respectively, when the canopy is in the side-span fire scene, and those for the canopy in the mid-span fire scene are 600 ℃ and 570 ℃, respectively. All of them are much lower than the temperature in a standard fire specified in ISO 834, which demonstrates that the tall space structure could be the main application scene of fire-resistant steel. Finally, the bearing capacity and stability of the structural members are analyzed and validated using the general structural steel Q355 and the domestic fire-resistant steel Q345FR. It is indicated that the steel beams GL3, GL3a and GL4 fail to meet the load-carrying requirements when using the general structural steel Q355, while the strength and overall stability requirements can be achieved when applying the fire-resistant steel Q345FR.