Fatigue Resistance of Sealant at the Linear Section of Sealed Joints
Test Specimen—The test specimen simulating the linear sections of sealed joints in actual buildings is shown in Fig. 3. Table 4 shows the three types of two-part building sealants—two-part polysulfide PS-2,
TABLE 4—Sealants studied
two-part silicon-modified polyether MS-2, and two-part silicone SR-2, and their evaluation and performance. Sealants were injected into the space between two aluminum bars, which were fixed to provide a joint with a cross section of 20 mm width and 13 mm depth. A polyethylene film was installed at the bottom of the test joint as a bond breaker; the film was removed just prior to fatigue testing. The specimens were cured for two weeks at room temperature, and then stored for two weeks more in a chamber controlled at a temperature of 50±2°C and relative humidity of 50±5 %.
Fatigue Test—The specimens were attached to the fatigue test equipment as shown in Fig. 4. In the sealed joint design method, when the story drift (R) is 1/300, a relative story displacement (shear movement) with amplitude of ±60 % of the joint width is allowed according to JASS 8 . By the relationship between the story drift of the curtain wall panel and the size of the movement occurring in the sealed joint in this study, a story drift of R= 1/200 can be calculated to an amplitude of ±90 % and a story drift of R= 1/100 to ±180 %. By placing the joints at two locations in the apparatus, they were subjected to repeated relative story displacement in the form of a sine curve with amplitudes of ±60 % = ±12 mm, ±90 % = ±18 mm, and ±180 % = ±36 mm of 20 mm width and a period of 10 s. The surfaces of the specimens were periodically inspected, by visual examination of the top surface, and by using a glass-fiber scope for the bottom surface. The number of movement repetitions to crack initiation and the patterns of cracking were recorded. The fatigue tests were carried out at a temperature of 20±2°C and were stopped at one million cycles unless any defects were observed in the sealant beads.
Test Results and Discussion—Cracking pattern due to shear movement was observed, and the crack at the sealed joint started near the substrate bars. The number of cycles to crack initiation for the linear section of the sealed joint and the range between minimum and maximum values of the number of cyclic movements on sealed joints for the last 75 years in Japan are shown in Fig. 5. The larger the story drift (relative story displacement), the earlier the crack initiation of the sealed joint. Then, the number of cycles to crack initiation obtained through the fatigue test is higher than the number of maximum cycles to relative story displacement that occurred at the sealed joint during the last 75 years.