Effect of boundary conditions on tensile bending strength of glass under four-point bending

Tensile bending strength is the most crucial property of structural glass. An evaluation procedure of tensile bending strength is specified in EN 1288-3 using the four-point bending (4PB) tests. However, the effects of boundary conditions of the supporting and bending rollers on tensile bending strength have not been well documented. The purpose of this paper is to provide a modified procedure for evaluating tensile bending strength considering the combined effects of boundary conditions and friction. The 4PB test method was re-evaluated by performing a comprehensive experimental, analytical and numerical study on ultra-white annealed glass (ANG) and fully tempered glass (FTG) subjected to large deflection. The results demonstrate that different boundary conditions can lead to a deviation between the EN 1288-3 standard method and the newly proposed evaluation procedure, which is strongly dependent on boundary conditions and friction effects. If laboratory conditions permit, it is highly recommended to ensure that the supporting and bending rollers can rotate freely during the 4PB test to avoid overestimating the tensile bending strength of structural flat glass. Otherwise, it is necessary to employ the newly proposed evaluation procedure to obtain the tensile bending strength accurately.