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.

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.

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.

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.

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.

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.