دانلود رایگان مقاله انگلیسی مدل سازی اسلب های بتنی تقویت شده در آتش - الزویر 2018

Abstract

A numerical procedure for the thermal analysis of RC slabs at elevated temperatures is the subject of this study, where the moisture increase due to the so-called moisture clog occurring in the cooler parts of reinforced concrete (RC) slabs is introduced as well. Starting from a systematic investigation on the existing concrete constitutive laws available in the literature and in the codes, improved concrete constitutive laws are proposed to describe concrete thermal and mechanical properties at elevated temperatures. The proposed laws – called also models - are validated against well-documented full- and small-scale tests on simply-supported RC slabs. Parametric analyses on the behaviour of RC slabs in fire are carried out as well, to clarify the role that the different constitutive laws may have in the numerical prediction of RC slabs behaviour under fire conditions.

Conclusions

In this paper a numerical procedure for thermal analysis of RC slabs at elevated temperatures has been proposed. In this model the moisture increase due to the moisture clog within the cooler part of the cross-section of a RC member is considered. Based on a systematic investigation of the existing concrete constitutive laws available from current design codes and literature, the concrete constitutive laws at elevated temperatures are proposed. The proposed thermal and constitutive laws of concrete are compared with the laws of the current design codes and the laws proposed in the previous literature. The new models are also validated against the well-documented full-scale and small-scale fire tests on simply supported RC slabs. A series of parametric studies on the behaviour of RC slabs under fire conditions are conducted to investigate the effect of moisture content, transient strain, different concrete material laws and size effect on the analyses of the RC slabs under fire conditions. Based on the results generated in this research the following conclusions can be drawn:

• The thermal analysis model developed in this paper can be used to predict the temperatures of RC slabs under fire conditions. The moisture content within the RC slabs has a considerable influence on the temperature distributions of the slabs in fire. The structural behaviour of the slabs is also affected by the moisture content of the concrete. Hence, the moisture content of RC slabs needs to be accurately accounted for in calculating the fire resistance of RC slabs.

• There are considerable variations of the predicted temperatures for RC slabs in using the existing concrete thermal models. The EC2 [11] and ASCE [13] laws cannot predict the temperature plateau (about 100°C) within RC slabs.