## 3 Experimental Results
### Analysis of the Test Results
#### 3.2.4 Out-Of-Plane Deflections  
Figure 17 shows the out-of-plane (vertical) deflections of each measuring point. During the heating stage, the deflections in the concrete slab increase rapidly in the initial 10  min, and the maximum midspan deflections of the CS1 and CS2 slabs (V7) reach 63 mm (6.3 mm/min) and 57 mm (5.7 mm/min), respectively. After 60 min, the deflections of V7 reach 141.9 mm (1.6 mm/min) and 193.7 mm (2.7 mm/min), and the growth rate tends to be stable. At 180 min, the deflections of V7 were 244.5 mm (0.86 mm/min) and 251.3 m (0.48 mm/min), respectively. After the fire test is stopped, the deflections of CS1 and CS2 were 244.5 mm and 261.4 mm, respectively. During the cooling stage, the deflections exhibited a rebound trend, which was faster in the initial stage and smoother in the later stage. When data collection stopped, the deflections of V7 were 166.8 mm and 180.6 mm, respectively. The trends of the other deflection measuring points in the plate were similar to that of V7 during the heating and cooling stages. At all out-of-plane measuring points, V7 was the largest in the middle of the span, and V8, V3, and V4 decreased in turn near the 1/4 span of the simply supported edge; V11 and V12 were the smallest near the 1/4 span of the clamped supported edge.  
According to the deflection or deflection rate failure criteria [45; 46], which involve the deflection or deflection rate of the slab exceeding span/20 (or span/30) at any time, the fire resistance of each slab can be calculated as shown in Table 3.  
Figure 18 shows the curve of the vertical out-of-plane deflections versus the furnace temperature. The curve shows that the growth rate of the out-of-plane deflections in the slab is low before the furnace temperature reaches 600 \({}^{\circ}\)C and increases when the furnace temperature is higher than 600 \({}^{\circ}\)C. When the furnace temperature is lower than 600 \({}^{\circ}\)C, the deflections increase, and the rebound rate accelerates. This phenomenon is due to the thermal inertia of the concrete materials. After the fire exposure stops, the temperature at the bottom of the slab decreases rapidly, but the temperature inside the slab continues to  
Figure 16: Curves of the temperature of the steel bars versus the furnace temperature.  
transmit heat to the top of the slab. The temperature of the concrete in the slab is relatively stable, and the deflections do not change greatly.  
Figure 19 shows the curves for the vertical out-of-plane deflection of the middle slab edge versus time. The results show that the edge of the concrete slab experiences a downward trend in the early stage of combustion, which is caused by the expansion of the concrete, the obvious warping of the slab corner, and the downward trend in the middle of the slab edge; however, with the increase in time of fire exposure, the deflections in the slab become larger, and the deflections of the slab edge move up relatively. When fire test stopped, the deflections of slabs CS1 and CS2 with a long simply supported side span (V1) reached 21.75 mm and 23.56 mm, the deflections of the span supported on the short side (V9) reached \(-0.95\) mm and 1.47 mm, and V13 reached \(-0.53\) mm and 2.67 mm, respectively. The difference in the values at the edge of the slab shows that the restraint effect of the bending moment at the clamped end on the deflections at the edge of the slab is very obvious.  
Figure 17: Curves of the vertical out-of-plane deflections versus time.  
Figure 18: Curves of the vertical out-of-plane deflection versus furnace temperature.