297Failure Test of InService Glass

The strengths of new glass and in-service glass differ considerably. While the design of glass panels is mostly based on new glass, the actual failure load of in-service glass is of greater interest when one considers safety during the service life of a building.

In this example, the testing results obtained by the IRC of the National Research Council of Canada for 47 in-service window glasses removed from the University of Ottawa's Thompson Residence in 1986 were compared.

The breaking stress of glass is determined by Equations 29.4 and 29.5 with the characteristic strength equal to 32.1 MPa, probability of failure equal to 0.008, reference area, A0, equal to 1 m2, and the Weibull parameter, m, equal to 7 as recommended by the Canadian Code. It is generally believed that in-service time reduces the breakage stress of a glass panel due to the increased density

TABLE 29.2 Test Results of In-Service Glass (Mean = 2.51, Standard Deviation = 0.62)

No.

P60 (kPa)

Thickness (mm)

X (mm)

Y (mm)

NAShell

Ratio

0 0

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