Aquaria and Glass with Water
There are numerous uses for glass in contact with water. Unlike most other architectural applications the load applied by water to glass is constant but not uniform. The greater the height of the water in relation to the glass the greater the pressure. The ability of glass to withstand a constant force is lower than that for transitory stresses. The design stress is adjusted accordingly to allow for the different conditions that the glass must endure.
There are several factors that need to be considered when selecting the glass. Not all liquids have the same density but the most common designs involve fresh water and marine. We calculate the glass thickness based on the load applied by the liquid but additional allowances may need to be made for dynamic loads of swimmers or marine life. In some designs the glass is only partially submerged or exposed only when the tank is emptied. Glass that is partially submerged may become subject to thermal stress if the sun can heat the top half while the bottom half is kept cold. Toughened glass laminated together may be the technical solution here. The support system for the glass is critical and apart from small domestic tanks we would expect all three of the glass edges to be fully supported.
The consequences of glass failing when holding back water are easily imagined. For small volumes monolithic annealed glass can be used but, for larger scale projects, laminated annealed and laminated toughened glass may need to be used. When using laminates the ability of the glass to share the load is considered and this is not just a case of summing the individual glass thicknesses. Under constant pressure even PVB interlayers will allow a small amount of creep between the panes. With toughened laminated glass we allow for one pane to break whilst the remaining glass has sufficient strength to maintain its integrity. A broken toughened pane in a construction adds no support to the remaining glass.