Improving testing procedures to obtain more reliable strength data for structural glass design

Dr. Matthias Haldimann, Emch+Berger AG Bern – Engineering and Consulting & Michel Crisinel, Ecole polytechnique fédérale de Lausanne (EPFL), Steel Structures Laboratory (ICOM)

Laboratory testing is an integral part of the design process of many innovative glass structures. Since these experiments are performed at ambient conditions, the measured fracture strength is dependent on the flaws on a specimen’s surface and on the subcritical growth of these flaws during the tests. This paper shows that the relationship between stress intensity and crack velocity varies widely and depends strongly on the environmental conditions, on the residual stress in the glass and on the stress rate at which a specimen is loaded. This prevents accurate estimation of the growth of surface flaws during experiments. Inaccurate estimation, however, can result in unsafe design parameters. An innovative testing procedure that solves this problem by preventing crack growth is presented.

An additional problem with design based on strength data from experiments is that specimens with as-received surfaces or with artificially induced homogenous surface damage are normally used. Such surface conditions are often unrepresentative of in-service conditions, especially in the case of glass building components that may be exposed to severe surface damage, e.g. because of accidental impact or vandalism. It is shown how this problem can be addressed by creating reproducible deep close-toreality flaws on glass surfaces. The mechanical behaviour of such flaws is discussed based on experimental data.

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The Authors

Dr. Matthias Haldimann Chief of Staff Emch+Berger AG Bern - Engineering and Consulting Matthias Haldimann is Research Engineer and Doctoral Candidate at the Steel Structures Laboratory (ICOM) of the Swiss Federal Institute of Technology Lausanne (EPFL). He has been working on composite ... Read more