آزمایشی برای بررسی مقاومت آتش زیر ساخت های RC زیرزمینی
Abstract
1- Introduction
2- A typical underground station and typical fire scenarios
3- Test setup
4- Experimental results and discussion
5- Conclusions
References
Abstract
Fire disasters occurring in underground structures generally result in severe damage. In order to investigate the fire performance of typical underground structures, a large-scale fire test on a three-span frame structure was carried out. The tested model was loaded both by vertical and horizontal earth pressures. The applied temperature history, representing the time-dependent fire load, was determined by simulations of fire scenarios in the underground structure with the help of the software FDS. The paper contains test results of the temperature of the air in the furnace, the concrete and the steel bars in the structural model, and the state of deformation of the model. Apparent phenomena, such as cracking and spalling, were observed throughout the whole testing process. The results show that a very dangerous situation of the underground structure exposed to fire may occur during the cooling process. Curling of the top slab was observed during the heating process. More attention in fire-resistance design must be paid to the columns. The fire test results are useful for validation of numerical models and for further fire-resistance research of underground structures.
Introduction
Fire disasters in underground structures have generally resulted in severe damage of structures [17,5,10,30]. As indicated by performancebased fire resistance design, research results for ground structures cannot directly be used for underground structures, because of different fire scenarios and of different restraint conditions and loads [4,9,7,2]. During the last decades, a large number of simulations of structures subjected to fire, using the Finite Element Method (FEM), were reported in the literature [13,18]. In particular, fire scenarios, i.e. temperature fields to which the underground structures were assumed to be subjected and their performance under the resulting temperature loads, were thoroughly investigated. Savov et al. [22] have studied the behavior of shallow tunnels, subjected to fire loads, by simulating the structure with the “beam-spring” model. Concrete spalling of the tunnel lining was simulated and its influence on the collapse of the structure was analyzed, considering the failure mechanism of beams, modeled by the FEM. This permitted prediction of the failure mode of the tunnel structure. Ring et al. [19] have simulated the behavior of underground tunnels subjected to various fire scenarios, considering different material parameters and structural models. They have performed research of the spalling problem and on the effect of load-induced thermal strains (LITS). Amouzandeh [1] has carried out a series of FE simulations, including treatment of the burning process of fire in tunnels by means of CFD (Computational Fluid Dynamics) and analyses of the structural performance. Their calculations and analyses revealed that the fire resistance of the tunnel with a circular cross-section is greater than the one of tunnels with a rectangular cross-section. Zeiml et al. [29] have investigated the safety of an underground frame structure subjected to fire, with the help of the FEM.