دانلود رایگان مقاله انگلیسی ارزیابی های بعد از آتش سوزی و بازگرداندن سازه های فولادی - امرالد 2017

1. Introduction

The last decades, the post-fire performance of structural steel elements has attracted many researchers. Although the fire safety of a structure is of paramount importance, the reinstatement of fire damaged structures is in the center of interest nowadays. Since 1960's, the research is focused on the mechanical properties of the material as well as the holistic behavior of the structure, taking into consideration both low strength [1-7] and high strength steels [8-11], while cold-formed [12] and stainless steel [13] have gained considerable attention as well. In particular for cold-formed steel, distinguish from hot-rolled sections is deemed mandatory, taking into consideration the manufacturing process and the sensitivity to stability phenomena. Despite the recent interest in the post-fire performance of steel structures, an important study published by Kirby et al. [4] in 1986 contributed to the onset of several specifications. Apart from steel features, elevated temperature properties of wrought iron have been documented therein; furthermore, an extensive investigation of the residual properties of cast iron was conducted recently by Maraveas et al. [14].

5. Conclusions

This paper investigates the assessment of the post-fire properties for a large range of structural steel and high strength bolts as well as their subsequent reuse after a fire event. A review of the reinstatement of structural use is unfolded. The engineer is advised to investigate the fire-damaged steel structure via a flow chart while several issues are highlighted for the suitable restoration guidance, the lack of which is noticeable in the existing specifications.

The analysis of the influencing factors indicates the complexity of the problem; for this purpose the micro-structural alterations during elevated temperatures as well as following the cooling down period are thoroughly illustrated. Subsequently, the post-fire properties of the material can be developed using the suggested equations for each type of steel. An extended collection of experimental results is taken into account for various cases of structural steel and bolts that can be encountered in steel building and structures.

In conclusion, it is verified that the residual capacity is not strongly affected until the steel is exposed to certain fire temperatures and then cooled down. In particular, mild, high-strength and stainless steels are able to regain at least 75% of their mechanical properties, for temperatures above 600oC, whereas the yield strength for heat-treated or cold-worked steels reduces to 40% for temperatures up to 1000oC. Regarding high strength bolts, the capacity reduces only when the temperature exceeds 400oC, before cooling to ambient temperature while the influence of the cooling method is obvious for all cases. The last observation also regards cast iron steel; a brief review of the mechanical behavior is illustrated in a graphical form for the ease of understanding. The reuse of distorted members is documented, in some cases by using repairing methods, provided that the material strength is not deteriorated. The results and recommendations are presented in both graphical and tabular forms, aiming to a better insight of steel behavior after the fire event.