Comparative Study On Different Structural Fire Design For Large Space Steel Structures

It is necessary to carry out refractory check and fire protection design for large space steel structures,which have poor resistance for fire.According to the current Code for fire safety of steel structures in buildings,for long-span steel structures with spans of 60m-120 m,it is advisable to adopt a method based on the whole structure.And it also point out that the component fire resistance analysis method can be used instead of the whole structure when the surrounding structure has little effect on the stress of the local substructures.For the differences between different methods,the results obtained by different refractory checking methods are different even the same steel structure is checked.Based on the above problems,combined with the large space steel structure examples,the differences of refractory calculations and the applicable scope of refractory checking methods for steel structures with different spans are studied.The specific research work includes the following aspects:(1)This paper briefly introduces the fire characteristics of large space steel structure,fire-heating model,physical and mechanical properties of steel in high temperature state,failure criterion of steel structural components and refractory calculation method of large space steel structure.(2)Combined with engineering examples,the bearing capacity method based on the whole structure,the critical temperature method and the simplified critical temperature method,the bearing capacity method and the critical temperature method based on different specifications(Code for fire safety of steel structures in buildings,Eurocode3:Design of steel structures-Part1-2)are respectively used for refractory verification.Then a series of comparative analysis of results are carried out.The results show that the different refractory check calculations of large space steel structures have some differences.Based on the overall structure refractory checking method,the thermal expansion effect of the structure and the mutual influence between the components are considered.The obtained results are safer.The results based on the component check are more conservative than the overall structure check.(3)The large space grid models with different spans are established,which have the same initial flexural ratio or initial stress.The critical temperature method based on the whole structure and components is used to perform refractory check on these structures to study the scope of application of different methods.Through the above research,the following suggestions can be given: the component-based refractory verification method can be adopted when the span is shorter than 68 m,because the results based on the component is more conservative;It is recommended to use refractory verification method based on the overall structure when the span is longer than 88 m,because the component-based verification results are dangerous in this case.