Assessment Of Fire Impacts Upon Strength Of Concrete And Reinforced Steel Bars In Concrete Structures

Public constructions such as large shopping malls, hotels, etc. that are closely linked to people's life all mainly have concrete structures. They are areas that are very likely to suffer from fire disasters, and they are usually filled with people's mass activities, so fire prevention is naturally the most important. Once fires flare up, they will induce heavy losses, so it is especially important to appraise and repair the buildings after fires so that they can be put to use again as soon as possible.Concrete structures are usually reinforced concrete structures made of reinforced steel bars and concrete, so it is natural that our major subject for study focuses on reinforced steel bars and concrete, with emphasis on the variation regularities of strength.Through analytical results from various data collected from labs, the paper shows that the strength of concrete and reinforced steel bars demonstrate good linear attenuation regularities under varied impacts of fires and temperatures, and it has established theoretical regression models, which has opened the gate for further research and furnished a theoretical platform for structure checking computations and rehabilitation consolidations in actual work.Through analyses of several project cases and summarized results, this paper has revealed the basically linear variation regularities on the yield strength, which is very similar to the lab results. However, there exist many abnormal data and quite a lot of flexibilities, which are related to the fact that the raw materials used in the projects varied quite a lot. It is the feature of actual fact.When lab data and screened engineering data were compared and sorted out, it was found out that engineering data were usually rather high. It provides very useful values to actual work, showing that using actual engineering data to caliber experimental data is closer to realities. It also shows that in actual projects, structures are usually longer in age, so they can raise the protection functions to concrete and reinforced steel bars to varied extents.The verification and modification of Linear regression equation in the lab can use a direct and more practical model to show fire impacts upon reinforced concrete strength and upon the yield strength of reinforced steel bars respectively to provide a reference for the calculation of the reinforcement theory in post-disaster restorations. All the analyses and assessments of the structures after fires are to provide scientific basis to save constructions, and, with theoretical references, we can make theoretical bearing capacity check to the remainder. But different repair methods and the use of different materials will bring different impacts to the repairs and consolidations, and their economic costs are quite different, too. Therefore, the state has adopted reinforced concrete structure design specifications, providing a wide range of reinforcement methods. The purpose is very clear to use more economical single method or an integrated approach as much as possible on condition that the structure safety is guaranteed.This paper recommends several reinforcement ways, and they are in the national norms. The reason of the recommendation mainly lies in the fact that their integrated values are rather high from practical experience, and they are more appropriate to the requirements for the short-term, fast and fine development in the construction market in cold regions like northeast China.