# Numerical Analysis of a Moderate Fire inside a Segment of a Subway Station
## 2 Experimental Results from a Scaled Fire Test
### Production of the Tested Structure  
Inspired by the structure illustrated in Figure 1, a model of the upper floor was tested at a scale of 1:4; see Figure 2 and [40]. The width of the tested structure was \(5260\,\mathrm{mm}\); its height was \(1880\,\mathrm{mm}\); and its axial length was \(1200\,\mathrm{mm}\); see Figure 3.  
Figure 1: Cross-sectional view (vertical cut through the structure, normal to the axis of the tunnel) of a three-span two-floor reinforced concrete frame, providing the inspiration for fire testing in [40]. Figure 3: Geometric dimensions of the tested structure (mm): (**a**) cross-section and (**b**) perspective representation; adapted from [40]. Figure 2: Setup of the large-scale fire test, taken from [40]. The specimen was placed sidelong on top of the furnace and closed with a fire-resistant cover. The dimensions of the top slab and the lateral walls amounted to one fourth of the real dimensions. The total length of the inner span of the structure amounted to \(20.7\,\mathrm{m}/4=5.175\,\mathrm{m}\). However, it had to be slightly adjusted to fit the dimensions of the furnace. Thus, the inner span of the model is \(4.91\,\mathrm{m}\), which is equal to that of the furnace. The design of the columns was the result of the following considerations: The scaled distance of neighboring columns in the axial direction of the tunnel amounted to \(7.5\,\mathrm{m}/4=1.875\,\mathrm{m}\). This is by a factor of \(1.5652\) larger than the axial length of the tested structure. Thus, the 1:4 scaled cross-sectional area of the columns, amounting to \(300\,\mathrm{mm}\times 200\,\mathrm{mm}\), had to be divided by a factor of \(1.5652\); see [40] for details. In order to obtain a geometrically similar cross-section, both scaled dimensions were divided by \(\sqrt{1.5652}=1.25\). Therefore, the cross-sectional area of the columns of the tested structure amounted to \(240\,\mathrm{mm}\times 160\,\mathrm{mm}\). Finally, the thickness of the bottom slab was set equal to \(190\,\mathrm{mm}\), in order to account for the influence of the lower floor on the stiffness of the modeled upper floor; see [40] for details. The reinforcement ratio of the top slab, the bottom slab, the columns and the walls amounted, by analogy to the real structure, to \(1.22\%\), \(1.19\%\), \(2.95\%\) and \(1.76\%\), respectively. The reinforcement bars had diameters of \(10\,\mathrm{mm}\), \(12\,\mathrm{mm}\) and \(14\,\mathrm{mm}\), respectively; see Figure 4.  
Temperature and strain sensors were put in place already before casting of the concrete. In this way, the sensors were finally embedded inside the tested structure. As to be expected in fire testing [45], some of the sensors failed during the experiment. Therefore, the following description is limited to measurement equipment, the readings of which are considered in the present work. Thermocouples were placed at six positions within the tested structure (Figure 5): three in the top slab (one at the midspan of each one of the three cells), one in the right column, one in the right wall and one in the middle cell of the bottom slab. At the selected positions, several sensors were placed at different distances from the heated inner surface, in order to monitor the ingress of heat into the structure; see Figure 5. The minimum cover depth of the thermocouples amounted to \(2\,\mathrm{mm}\). Strain gauges were mounted to steel bars of the inner and the outer reinforcement layer. Measurement positions were located at the top slab, at the midspan of the left cell and at the center of the right wall; see Figure 5.  
Normal concrete \"C40\", with a mass density of \(2373\,\mathrm{kg}/\mathrm{m}^{3}\), was used for the production of the tested structure; see Table 1 for the composition of the material. The stiffness and the strength of both concrete and steel were quantified before the test, following protocols from the Chinese Standard for  
Figure 4: Reinforcement drawing of the tested structure (mm), taken from [40].