ALC Panel Joint Movement

As already mentioned, deformation on the exterior wall of panel joints can be divided into deformation due to expansion and contraction of the joint and that due to shear deformation. In this section, the amount of deformation due to

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Specimen number

expansion and contraction of ALC panel joints was measured from actual ALC panel joints used in a building; the amount of deformation in shear was deter­mined via the calculation of joint displacement based on existing knowledge.

Measurement of Expansion and Contraction Movement between ALC Panel Joints—Measurement Method. Tables 3 and 4 provide information on a building having ALC panels of which measurements were made. Figure 6 shows the loca­tion on the facade of the actual building at which displacement measurements were recorded. It is a steel-frame building with deep ALC panels that were affixed to the building frame via the “rocking" method. The rocking method is a means of fixing a wall panel to a frame by restraining the rotation (rocking) of the panel when the building frame responds to the effects of and deforms dur­ing an earthquake event as depicted in Fig. 7. The joints were sealed using a two-component polyurethane sealant and applied with the two-sided adhesion method. The measurements were taken in both summer and winter and included recording the ambient local temperature at the building location and the ALC surface temperature, as well as the joint displacement. The measure­ment of the joint displacement was determined on four panel surfaces, each having a different orientation, namely, east, west, south, or north, but limited to

TABLE 3—Summary information for building on which displacement measurements were recorded.

Wall Type

Main Structure

ALC Panel Fixing Method

Joint Type

Joint Width

ALC panel

Steel frame

Rocking type

2 fixed joint

8 mm

TABLE 4—Information on displacement measurements.

ALC Length

Direction

Thickness

ALC

Width

Upper

Floor

Lower

Floor

Measurement

Date

Weather

East-south-west

North

100 mm

600 mm

3100 mm 2900 mm

3100 mm 3700 mm

August 23-24, 2001

Good

the shorter joints of selected ALC panels that, in fact, had a greater degree of expansion and contraction. A contact type digital thermometer (resolution of 0.1°C) was used for measurement of the ambient local and ALC panel surface temperatures. Movement at selected panel joints were measured by mounting screws on panels on either side of the joint, as shown in Fig. 8; joint

FIG. 6—Location of displacement measurements on external wall.

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FIG. 7—Rotation (rocking) of the panel.

displacement was determined by measuring the displacement of the screws ev­ery two hours using a digital caliper (resolution of 0.01 mm).

Measurement Results. Table 5 shows the results for joint displacement. A large difference in the surface temperature was observed on the west and south sides of the building, and sealed joint movement was largest on the west side of the building. The movement per unit temperature change was also calcu­lated, and the results indicated a thermal expansion coefficient for ALC exterior wall panels of 6 to 7 x 10~6/°C, which is close to the standard value for ALC pan­els of 7 x 10~6/°C. On the other hand, when the external wall panel deforms in

FIG. 8—Example of method for measuring displacement.

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TABLE 5—Test results for the surface temperature and joint movement of ALC panels in summer.

Contents

East Side

South Side

West Side

North Side

Surface temperature high/low, °C

40.0/24.6

42.2/25.0

43.1/24.8

34.0/24.7

Temperature difference, °C

15.4

17.2

18.3

9.3

Joint movement, mm

0.31 0.31

0.37

0.37

0.47

0.48

0.2

0.25

mm/m

0.1 0.1

0.12

0.12

0.15

0.15

0.06

0.08

Coefficient of thermal expansion (x 10~6), mm/°C

6.49 6.49

6.94

6.94

8.28 8.46

6.52 8.15

relation to the expected rocking response of the panel, the degree of joint dis­placement decreases by a fixed ratio [2]. The displacement reduction ratio for the deep ALC panels affixed to the steel frame building could not, however, be confirmed within the measurement range recorded in this study. Figure 9 shows the results for the amount of displacement in the expansion and contraction of sealed joints of a panel located on the exterior of the building of which meas­urements were taken every two hours, starting at noon, over a 24 h period in the summer (August 6-7, 2001) and in the winter (January 28-29, 2001). Tem­perature differences between summer and winter on the east side had a maxi­mum of 38.0°C. As for movement, the amount of displacement measured was 0.76 mm on the south side of the building. On the east, west, and north sides of the building, the joint width in the winter was smaller than that in the summer. It is believed that this was caused by certain factors such as the effect of the de­formation behavior of the steel building frame and the effect of panel expansion and contraction due to temperature changes on the panel surface. Based on the above measurement results, the movement between ALC panels was small, with measurements of less than 1 mm, and within the measurement range of this study.

Calculation of Shear Movement between ALC Panel Joints—The movement of sealed joints due to shear (i. e., relative story displacement) is mainly caused by the interstory deformation of exterior wall panels due to displacements that occur after earthquake events. Such a shear movement is specified in Ref 2, in which it is stated that “the relative story displacement performance required to ensure water tightness must be considered so that joint design can allow joints to follow relative story displacement at an inter-storey deflection ratio of 1 /300 without causing any damage on the joint." In addition, it must also be consid­ered that the shear deformation of ALC panels is greater along the vertical joint, whereas the amount of deformation is determined by the length of the short side of the joint. The length of the short side of an ALC panel is different from that of other exterior panels and is typically fixed at 600 mm. Therefore, the shear movement can readily be calculated, even without considering the reduc­tion in the ratio with the panel fixation method, as 2 mm, given that the inter­story deflection ratio is 1 /300. This is illustrated in Fig. 10.

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FIG. 9—ALCpanel surface temperature andjoint movement in summer and winter.

Structural flame

inside a chamber in which the temperature can be maintained and tests can be conducted at specified levels. One side of the substrate is fixed, and the other side of the substrate is exposed to a relative movement. A brass fixing plate is placed onto the base to hold the test specimen. Table 6 provides a description of the test specimens and test conditions.

For the tensile fatigue test method, elongation movement was created by applying a tensile force to the specimen. The amount of joint extension on an actual building was considered to behave in a series of five steps, with the entire set forming a fatigue test series; the initial step ranged from 0 mm to + 1 mm in tension, and the fifth and final step ranged from 0 mm to + 5 mm. The test for shear fatigue was set in relation to a panel’s interstory deflection ratio, again with five steps ranging from 0 mm to a shear deformation of ±1 mm in the ini­tial step (interstory deflection ratio of 1 /600) to a final step of 0 mm to a shear deformation of ±5 mm (interstory deflection ratio of 1/120). The number of cycles for each fatigue test series was a maximum of 5000; this took into consid­eration both the fatigue due to temperature fluctuations and that due to move­ment during earthquake events. Three test specimens were used for each test condition; these were also monitored visually every 1000 cycles in order to determine whether there existed the initiation of fatigue cracks.

Fatigue Test Results—Figure 12 shows the test results from the fatigue tests. For both the elongation fatigue test and the shear fatigue test, two-sided adhe­sion test specimens showed higher fatigue resistance than the three-sided adhe­sion test specimens. Test specimens subjected to two-sided adhesion passed the elongation fatigue limit of 0 to +2 mm and the shear fatigue limit of 0 to ±4 mm (R = 1/150); for all specimens, the fracture mode for the sealant product was CF. In contrast, some of three-sided adhesion test specimens did not pass the tensile fatigue limit of 0 to +1 mm or the shear fatigue limit of 0 to ±1 mm (R = 1/600). It was also observed that three-sided adhesion test specimens had ALC AF. Such results indicate that test specimens installed with three-sided ad­hesion are not likely to reach a service life of 10 years.

TABLE 6—Fatigue test conditions.

Items

Contents

Test type

Elongation fatigue test

5 steps: 0 to + 1.0 mm ! 0 to + 2.0 mm! 0 to + 3.0 mm! 0 to + 4.0 mm! 0 to + 5.0 mm

Shear fatigue test

5 steps: 0 to ±1.0 mm (1/600) ! 0 to ±2.0 mm (1 /300) ! 0 to ±4.0 mm (1/150) ! 0 to ±6.0 mm (1/100) ! 0 to ±12 mm (1/50)

Test condition

Movement cycle

10 s (6 cycle/min)

Number of cycles

Maximum: 5000 cycles

Test temperature

20° C

Number of specimens

Three specimens in each test

FIG. 12—Fatigue test results.

Conclusions

The results of this research study can be summarized as follows:

(1) The results of tensile tests and shear tests indicated that the sealed joint fracture location differs with the maximum tensile stress and maxi­mum shear stress of 0.6 to 0.7 N/mm2, or 50 % modulus at around approximately 0.2 N/mm2. The results of 50 % modulus at 0.2 N/mm2 comply with the exterior wall watertightness design to avoid ALC frac­ture, and anything below that value led to sealant failure, whereas any­thing above that value caused ALC panel failure. The performance of the sealed joint in accommodating movement was greater for test speci­mens configured with a two-sided adhesion joint than for specimens having three-sided adhesion. However, a sealant with a two-sided adhe­sion joint specimen and a high tensile modulus (i. e., given value of modulus) showed a significant reduction in movement capacity.

(2) The results of actual measurements of expansion and contraction movement on ALC panel joints of an actual building showed that the thermal expansion coefficient of ALC exterior wall panels ranged from 6 to 7 x 10~6/°C, and the joint movement per year of the ALC panel was very small (less than 1 mm). Shear movement was also calculated based

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on Ref 2, and the results indicated that the relative story movement of around 1 /300 interstory deflection ratio should be set at 2 mm, given that this is the relative story performance movement requirement in order to ensure watertightness.

(3) The results of tensile fatigue and shear fatigue tests showed that suffi­cient fatigue resistance was achieved for test specimens of two-sided adhesion joints. However, some of the three-sided adhesion test speci­mens did not pass the tensile fatigue limit of 0 to +1 mm or the shear fatigue limit of 0 to ±1 mm (i. e., R = 1/600); in addition, in these instances ALC material failure was also observed. Such results indicate that test specimens configured as three-sided adhesion joints might not fulfill the service life of 10 years.

Therefore, on the basis of the results derived from all the studies, it was determined that a suitable sealant for use on ALC substrates is a sealant having a low modulus that is applied in the normal fashion as a two-sided joint.

Acknowledgments

This work was performed as part of the research activities of the working group for the “Research of Sealants for Sealed ALC panel Joints" conducted by the To­kyo Institute of Technology, Autoclave Lightweight aerated Concrete panels and the Japan Sealant Industry Association. This work was also supported by the Basic Science Research Program of the National Research Foundation of Korea (NRF), funded by the Ministry of Education, Science and Technology, Korea (2009-0069919). Some researchers were funded by the Korean Government and supported by the 2nd Korea Brain (BK21) foundation. The writers are grateful to all these parties for their support.