Issue 53

D. Wang et alii, Frattura ed Integrità Strutturale, 53 (2020) 236-251; DOI: 10.3221/IGF-ESIS.53.20 239 Fire test furnace The tests were performed in a combined horizontal fire furnace in the structural laboratory of Huaqiao University. The net size of the furnace is 5.95m in length, 4.31 m in width and 1.5 m in height. Three burners were installed on the long side of the furnace, and two on the short side. To correctly install and position specimens, a movable partition wall was added in the fire furnace. Two burners were arranged in the middle of the wall, with a spacing of 2.8 m. Fig. 3(a) shows the jet flame of the burners. On the unexposed surface of the wall, a 0.3 m-wide steel platform was set up for applying the fireproof cotton (Fig. 3(b)). After the wall is fixed, the net distance from the edge of the exposed surface to the inner edge of the short side of the furnace is 3.7m. (a): Jet flame of burners. (b): Movable partition wall. (c): Lifting and installation of specimen Figure 3: Fire furnace reconstruction and lifting and installation of specimen Loading plan and fire plan Before the test, the column and its foundation were covered by aluminum silicate fireproof cotton. As shown in Fig. 3(c), each specimen was lifted into the horizontal fire furnace by the lifting equipment in the lab. Once the specimen was in place, the plate surface is about 0.3 m taller than the movable partition wall. According to the provisions of reference [32], the punching bearing capacity of slab without stirrup under local load or concentrated reaction is F l ≤ 0.7  h f t  u m h 0 (1)  h : the influence coefficient of section height h, when h ≤ 800mm,  h = 1.0, when h ≥ 2000mm,  h = 0.9, and the middle is taken as linear interpolation method; f t : design value of concrete tensile strength;  shall be calculated according to the following two Equations, and the minimum value shall be taken: 1 1.2 =0.4+ s   (2a) 0 2 =0.5+ 4 s m h u   (2b)  s : the ratio of the long side to the short side of the rectangular time in the local load or concentrated reaction area, and  s should not be greater than 4. When  s is less than 2, it is taken as 2; for the circular cutting surface, it is taken as 2.  s is the influence coefficient of column position: middle column  s = 40; side column  s = 30; corner column  s = 20. u m : critical section perimeter, take the perimeter of the plate section at 0.5 h 0 away from the column edge; h 0 : effective height of the plate. For the members in this paper, f cu can be used to calculate the average f t = 1.95N/mm2, h 0 =165 mm. After calculation, F l =509kN at room temperature. In the design of loading target value, the ratio of punching force and F l on the column is about 60-70%.The dead weight of the test piece plate is about 100kN, and the dead weight of the first level distribution beam (only one) and the second level distribution beams (there were two beams) in the loading device is about 25 kN. During the test, the target loading value is rounded and the final target loading value is determined to be 200 kN.