Dapeng Town Industrial Park, Tongshan District, Xuzhou City, Jiangsu Province, China
In 2024, there is a feeling that there will be a significant increase in the number of fires, such as the recent fire at a lithium battery factory in South Korea and a chemical factory fire in Tianjin, which caused a lot of casualties.
(South Korean lithium battery factory after a fire, photo credit: CCTV News)
However, the fire data released by the Fire and Rescue Service shows that the total number of fires up to now is 450,000, down 4% year-on-year, and the number of fatalities has risen by 19%. There is the illusion of an increase, in fact, because of the individual major fires of heightened concern, was magnified. Steel buildings are becoming more and more common, especially all types of factories and warehouses, to assess the impact of fire on the steel structure, will also be more and more encountered, today to talk about this topic.
Possible effects of fire
Loss of structural strength High temperatures reduce the yield strength and modulus of elasticity of steel, making it weaker and more susceptible to deformation under load. Uneven heating and cooling during a fire can lead to warping, twisting or buckling of steel members.
Residual stresses Rapid cooling (e.g., firefighting) can create residual stresses within steel members that may lead to rupture or further deformation. Connection Damage High temperatures can weaken or destroy bolts, welds and other connections, thus compromising the overall stability of the structure.
Post-fire assessment
Common sense basic judgment For the steel structure after the fire, in fact, from the common sense intuitively, there can be some basic judgment: for example, steel is also refined in the fire, as long as the deformation is not deformed, although subjected to high temperatures, certainly still good. If the member is deformed, is it corrected or replaced? It mainly depends on which costs less. Regarding the connection nodes, if the bolts are loose, then replace them, high-strength bolts are not recommended for reuse. Anti-corrosion and fire protection paint is damaged, it is to be repaired and repainted.
Technical professional judgment
From the engineering point of view, there will be some complicated issues to consider: for example, there may be more residual stresses; after experiencing different high temperatures, there will be some changes in the material properties of the steel; damage to the weld; loss of pre-tensioning force of the high-strength bolts, and so on. These work, there are already a lot of research results. And a standard has been formed (quoted from the Standard for Appraisal of Engineering Structures after Fire T/CECS 252-2019):
The occurrence of the following conditions can be initially rated as Ⅳ class:
1.1. severe scorch damage, excessive overall deformation, severe residual deformation, cracking or fracture, localized buckling, twisting or partial tearing of welds resulting in loss of load carrying capacity or a large part of it.
2.2. extensive damage to steel connections after fire, severe cracking of welds, burned or broken off bolts.
Summary
How to assess and reinforce a steel building after a fire is actually very complex, with many empirical and technical components accounting for it. These can become even more complicated especially when the design still has the requirement of reviewing the drawings.
