# Numerical Analysis of a Moderate Fire inside a Segment of a Subway Station
## 1 Introduction  
Structural engineers are interested in the load-carrying behavior of reinforced concrete (RC) structures exposed to fires. Research on the high-temperature performance of RC structures involves the entire field of engineering sciences, dealing with the thermal degradation of concrete [1; 2; 3], the underlying hygro-thermo-chemo-mechanical couplings [4; 5], transport of heat and moisture [6; 7; 8], the transient thermal strain of concrete [9; 10; 11], also referred to as load-induced thermal strains [12], spalling of concrete [13; 14; 15], the interaction between concrete and steel rebars [16; 17; 18] and the interaction between different RC elements that are connected to form RC structures. These interactions were studied by means of experiments and/or numerical analyses. As for structural elements, related studies have been devoted to normal-strength concrete columns with circular cross-sections [19], high-strength concrete columns with quadratic cross-sections [20; 21; 22], RC beams, either unprotected [23] or protected by fiber-reinforced polymer laminates [24], high-performance self-compacting concrete slabs with superabsorbent polymers and polypropylene fibers [25], T-shaped beams, made of high-strength reinforced concrete [26] and prefabricated RC segments for linings of shield tunnels [27]. As for entire RC structures, testing and/or simulations were carried out for RC slabs resting on steel frames [28], slab-column connections, made ofreinforced concrete [29], composite slabs with, as well as without a supporting secondary beam [30], RC frame structures [31; 32; 33], the Channel Tunnel between France and the United Kingdom [2; 13], other monolithic tunnel linings with cross-sections in the form of a segment of a circle [34; 35], of an ellipse [36] and in the form of a double box [37], a segmental tunnel ring of a metro tunnel [38] and the twin-tube cross-section of the immersed tunnel of the Hong Kong-Zhuhai-Macao-Bridge [39]. The present study refers to another interesting structure: a segment of a subway station. It represents a statically indeterminate RC structure, consisting of a top slab, a bottom slab, two lateral walls and two columns connecting the top and bottom slabs. A 1:4-scale model of this structure was tested by [PERSON] et al. [40]. Before the fire test, the structure was subjected to mechanical loads, simulating a combination of in situ ground pressure, water pressure, as well as dead and live loads that occur in the tunnel under service conditions. These loads were kept constant throughout the subsequent fire test. During this test, the temperature of the air in the interior of the tested structure was increased according to a prespecified temperature history. The performance of the structure was monitored during the test by means of temperature sensors (\"thermocouples\") and strain gauges. The aforementioned studies refer to catastrophic fire scenarios with maximum temperatures typically larger than 1000 \({}^{\circ}\)C. Such disasters are fortunately rare events, whereas moderate fires happen much more frequently [41]. Thereby, the expression \"moderate fire\" refers to a scenario that develops initially like a catastrophic fire disaster, but is stopped by fire fighters early enough so that the structure is not damaged severely. Consequently, moderate fires are, at least from the structural viewpoint, non-catastrophic events. Because of their frequency, however, they deserve more attention from structural engineers. This is setting the scene for the present study. Here, the first 30 min of the fire test by [PERSON] et al. [40] are analyzed, based on three-dimensional Finite Element simulations using the commercial software Abaqus FEA 2016 [42]. This period of time is chosen since it is representative of a moderate fire. Heat transfer in the analyzed reinforced concrete structure is simulated first.