Issue 53

D. Wang et alii, Frattura ed Integrità Strutturale, 53 (2020) 236-251; DOI: 10.3221/IGF-ESIS.53.20 240 To reach the target load of 200 kN, the load was applied by a jack with a measuring range of 1,000 kN, and transmitted to four loading points through two stages of distribution beams. There is one primary distribution beam and two secondary distribution beams. The total dead weight of these beams stood at 25 kN. The primary distribution beam, connected to the jack via a ball hinge, was placed right between the two secondary distribution beams. A steel roller (diameter: 45 mm) was added between the two stages of beams and cushioned with a 200 mm×350 mm baseplate. Each secondary distribution beam was deployed close to the edge of the short side of plate surface. A steel roller (diameter: 45 mm) was added between the beam and the edge and cushioned with a 300 mm×300 mm baseplate. Before the beam was in place, the outer edge of the baseplate was fixed at 0.4 m from the edge of the short side of plate surface. To prevent rollers from falling off under load, two 15 mm-diameter steel rods were welded to each baseplate. Fig. 4(a) provides the details on the steel rollers and baseplates. Fig. 4(b) shows both the specimen and the testing arrangement. (a) Details of the roller. (b) Relative position between test device and specimen. Figure 4: Details of the roller and relative position between test device and specimen. Before the fire test, each specimen was loaded preliminarily in five stages at room temperature. The target loads of the five stages were 50, 100, 150, 175 and 200 kN, respectively. From the first to fourth stages, each target load was held for 10 min. On the fifth stage, the aluminum silicate fireproof cotton was applied after reaching the target load. Specifically, the fireproof cotton was folded into L-shape: one side on the side of the reinforced concrete plate of the specimen, and the other side on the furnace wall or the upper edge of the partition wall, extending to the fixed steel beam outside the furnace wall or to the steel platform outside the wall. The fireproof cotton was kept in place by fire bricks (Fig. 5). The pre-loading lasted 47 min for S1, 32 min for S2 and 65 min for S3. The duration of each fire test was 3 h. Figure 5: Application of fireproof cotton. Infrared observation In the event of a fire, the crack development on plate surfaces can be recorded in real-time by infrared detection technology [35]. In our tests, the temperature field and crack development on the plate surface were observed by a fully digital dynamic infrared thermal monitoring device (Fig. 6).