# Fatigue Resistance at the Intersection of Sealed Joints

Test Specimen—The test specimen simulating the intersection of sealed joints is shown in Fig. 6. The cross section of the sealed joints, types of sealants, and curing method is the same as for the linear section of the sealed joint.

Fatigue Test—For the sliding type of curtain wall panel fixing system, the specimen is deformed by repeated shear movement, as shown in Fig. 7. For the rocking type of curtain wall panel system, the movement occurs not only in the vertical direction, but also in the horizontal direction, as shown in Fig. 8. The movement in vertical direction is affected by the width (Wp) of the curtain wall panel. In contrast, movement in the horizontal direction is affected by the fixing position (F) of the curtain wall panel and is calculated by the following Eq 2.

8h = RXF (2)

where:

8h = movement in the horizontal direction (mm),

 n Sealant Substrate ( £ V /
 i 210 У ft5? 210 і
 FIG. 8—Behavior of the intersection of the sealed joints to rocking motion in actual building.

R = story drift,

F = distance between the upper and lower floor fixation of curtain wall panels (mm).

For sealed joints, under the condition of F/Wp=0, movement occurs only in the vertical direction, with F/Wp= 1, the movement occurs in both vertical and horizontal directions. In our study, the fatigue test was carried out under the condition of F/Wp=l, which is the most severe condition for sealants.

The fatigue test was carried out with the same conditions as for the linear section of sealed joint test. Namely, the fatigue test used the fatigue apparatus [10] to perform the same movements in the vertical and horizontal directions, as shown in Fig. 7. The fatigue tests were carried out at three amplitudes, i. e., ±60 %; ±90 %; and, ±180 %. A 10 s (6 cycle/min.) period was adopted for the fatigue test. All tests were carried out at a temperature of 20±2°C and were continued up to one million cycles, unless any defects were observed in the sealed joint.

Test Results and Discussion of Sliding-Туре Curtain Wall Panel Fixing System—The comparison of the number of cycles to crack initiation at the intersection of sealed joints under sliding motion with the range between minimum and maximum values of the number of cyclic movements at sealed joints in Japan for the last 75 years is shown in Fig. 9. The cracks at the intersection of sealed joints occurred at an earlier stage when compared with the linear section of joints on the surface of all specimens. For R = 1 /300, R= 1 /200, and R= 1 /100 with SR-2 and MS-2, the number of cycles to crack initiation obtained by the fatigue test is higher than the maximum values of the number of cyclic movements at sealed joints for the last 75 years. However, for R= 1 /100 with PS-2, the number of cycles to crack initiation is lower than the maximum value.

 X Crack initiation at sealed joint I I Range between minimum and maximum values of the number of cyclic movements al sealed joints in Japan for the past 75 years
 FIG. 10—Number of cycles to crack initiation under rocking motion at intersection of sealed joints.

Test Results and Discussion of Rocking-Туре Curtain Wall Panel Fixing System—The number of cycles to crack initiation at the intersection of sealed joints under rocking motion is shown in Fig. 10. For all story drift with MS-2 and PS-2, the number of cycles to crack initiation is lower than the maximum values of the number of cyclic movements at sealed joints in Japan for the last 75 years. In contrast, fatigue resistance of SR-2 is higher than with other sealants, however, crack initiation occurred at tens of cycles for amplitude of ± 180 % (R= 1 /100). The fatigue test with F/ Wp= 1 is very severe for the sealants, thus fatigue resistance of sealants is higher when F/Wp is smaller.