Designing structural elements requires accurate glass edge strength values. However, these values are poorly documented in the existing standards. In several cases, the only possibility is to perform design assisted by testing according to EN 1990 annex D. In the existing testing standard EN 1288-1, the required number of specimens in order to estimate mean or characteristic values of glass strength is not specified. This standard only mentions that a low crack probability can require large numbers of specimens to estimate a characteristic strength value. In this project, 4 mm glass specimens with simple cut edges are subjected to in-plane four-point bending tests (100 test specimens) and the results from this large test program are used in order to estimate the influence of the number of test specimens on the estimates of glass strength values.@en

The edge strength of glass is affected by the load history. To quantify this effect, 12 series of glass specimens were subjected to either linearly increased (reference value), constant or cyclic loading. For constant loading the experimental values could be accurately predicted by linear elastic fracture mechanics (LEFM). However, for cyclic loading the LEFM prediction was 4-8% more conservative than the test results. Furthermore, a comparison of the experimental results with the prediction method provided in the standards shows that for cyclic loading the number of cycles should be taken into account in the rules of the standards.@en

During their lifetime, glass panels are repetitively exposed to thermal stresses. These thermal stresses result from temperature differences within the panel, which most notably cause the edges of the panels to be stressed in tension. When these thermal stresses exceed the glass edge strength, failure will occur. In this study, the thermal stresses are calculated by finite element software on the basis of real climate data during a twenty year period. By means of these finite element analyses it is investigated whether or not the stresses in the glass exceed the edge strength of the glass, thereby causing its failure. For this purpose, the yearly maximum stresses are derived from the model. In addition, the entire thermal stress history has been taken into account to incorporate the effects of stress corrosion on the edge strength of the glass. From the study it is observed that the latter criterion may be more stringent than the former.@en

A precise estimation of the edge strength becomes an important issue when designing structural glass beams or façade mullions. However, in literature, the glass edge strength is poorly documented compared to the surface strength. In particular, the experimental validation of an edge strength model is lacking. Therefore, in this project, a ratio is assessed between the flaw depth and the mirror zone depth to determine more easily the geometry factor used in the edge strength model. Glass specimens with arrised and ground edges were tested at a high stress rate (50 MPa/s) with an in-plane four-point bending test setup. After failure, the critical flaw and the corresponding mirror zone was examined by means of an optical microscope. As the ratio of these values could be determined rather accurately, in future the geometry factor can be determined only by measuring the mirror zone depth instead of the flaw depth.

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The influence of stress corrosion on the edge strength becomes important when designing structural glass elements. As the load duration of the design wind load (600 s) or the design temperature load is larger than the common load duration during testing the glass edge, a strength model must be used to take into account the load duration properly. In such a model, both short term parameters (i.e. the flaw geometry and depth) and stress corrosion parameters are involved. The stress corrosion parameters strongly depend upon the environment, especially the temperature and the humidity. In this study, the latter two are kept constant, for the testing at high stress rate (50 MPa/s), to determine the short term parameters as well as for the testing at low stress rate (2 MPa/s), to determine the stress corrosion parameters. The geometry factor and the stress corrosion parameters were determined for arrised and ground edges.

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In literature, the experimental validation of a glass edge strength model is lacking. Therefore, in this study, an edge strength model was established and validated. The short-term parameters of the edge strength model, i.e. the flaw geometry and depth, were determined by means of testing at a high stress rate. This was done for polished and cut edges. Next, the strength model, including subcritical crack growth, was established. Finally, the edge strength model was validated by the test results at a low stress rate. The assessed model was found to be slightly conservative, compared to the test results.

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The edge strength of glass is affected by the load history: i.e. the load duration and the loading type, e.g. constant loading, cyclic loading or linearly increasing loading. In standards, these influences are expressed by the factor k_mod, which reduces the strength depending on the load type, e.g. wind load, temperature load. In this study, five series of glass specimens with a cut edge finishing were subjected to in-plane four-point bending tests. First, the specimens were subjected to a linearly increasing loading. Then identical specimens were subjected to either a constant loading or a cyclic loading or both. These test results were compared to the theoretical prediction, based on the theory of fracture mechanics, as well as to the guidelines of the standards.

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For the past three decades, glass has become more frequently used for secondary construction elements in façade glazing, as well as for structural elements. In the latter case, the edge strength becomes an important issue when designing a structural glass beam or a façade fin. Different parameters affect the edge strength of glass, such as 1) the type of edge finishing and the supplier, 2) the size of the element and 3) the load duration. The first parameter affects the number and the shape of the edge flaws caused by cutting or polishing the edge. Secondly, the size effect is important because larger elements tend to have a greater probability of larger flaws. Finally, the load duration has an impact on the time-dependent strength. In this study, 16 series of glass specimens with different edge finishings and sizes were subjected to in-plane four-point bending tests at several loading rates. The environmental effect (i.e. humidity) was not examined, as all the tests were carried out under constant laboratory conditions. After comparing different distributions, the most appropriate distribution, i.e. Weibull, was used. The results of the series were compared statistically relative to the parameters mentioned above. The results indicate large variations in the edge strength, which are assumed to be related to the edge finishing and the glass supplier. A detailed manufacturing protocol is needed for a more accurate comparison of the results. Furthermore, unlike the size effect, the load duration effect was found to comply with earlier results given in literature.@en